make hot ice experiment

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Make Hot Ice From Baking Soda and Vinegar

Hot ice is another name for sodium acetate (CH 3 COONa or NaOAc). It is the sodium salt of acetic acid, which is the key component of vinegar. Hot ice gets its name from the way it solidifies. A solution of sodium acetate supercooled below its melting point suddenly crystallizes. Heat is released and the crystal resemble ice so… “hot ice.” All you need to make sodium acetate and crystallize it into hot ice is baking soda and vinegar. It’s a great chemistry demonstration because it illustrates chemical reactions, supercooling, crystallization, and exothermic processes . From start to finish, the project takes less than an hour. Once you have the sodium acetate, you can melt and crystallize it over and over again.

You only need two ingredients, plus a pan and stove:

• 1 liter Vinegar (weak acetic acid)
• 4 tablespoons Baking soda (sodium bicarbonate)

The quantities of baking soda and vinegar are not critical so long as all of the baking soda dissolves. If measuring the ingredients isn’t an option, just dissolve baking soda in vinegar until no more dissolves, filter off the liquid using a coffee filter or paper towel to remove any solids, and proceed from there.

Be sure to use plain white (clear) vinegar and not cider, red wine, or some other colored vinegar. You can substitute sodium carbonate (washing soda) or sodium hydroxide (caustic soda or lye) for the baking soda. If you have access to pure sodium acetate (inexpensive online), you can skip the procedure to make it and go directly to the step for re-using it.

• The first step is reacting the baking soda and vinegar . Stir baking soda into vinegar a little at a time. If you add it all at once, you’ll basically get the classic baking soda and vinegar volcano and could overflow your pan! The reaction between baking soda and vinegar produces sodium acetate, water, and carbon dioxide gas: Na + [HCO 3 ] –  + CH 3 –COOH → CH 3 –COO –  Na +  + H 2 O + CO 2 However, at this point there’s too much water for the sodium acetate to crystallize.
• Next, concentrate the solution by boiling it. It took me about an hour at medium heat to reduce the volume from a liter to about 100-150 milliliters. Don’t use high heat because you may get discoloration (golden or brown). The discoloration doesn’t ruin the sodium acetate, but the hot ice will look a bit like you made it from yellow snow. You’ll know you’ve boiled off enough water when a crystalline skin starts to form on the surface of the liquid.
• Once you see a skin, immediately remove the pan from the heat. Carefully pour the liquid into a clean container and cover the new container with plastic wrap or a lid to prevent further evaporation. You should get crystals in the pan, which you can use as seed crystals for activities, but the liquid in the new container should not contain any crystals. If you do have crystals, stir in a very small volume of water or vinegar to dissolve the crystals. If the entire solution crystallizes, add more water and go back to the stove to boil it down again.
• Place the covered container of sodium acetate solution in the refrigerator to chill it. It’s also fine to let the solution cool to room temperature on its own, but this takes longer. Either way, reducing the temperature produces a supercooled liquid. That is, the sodium acetate remains liquid below its freezing point.

Hot Ice Activities

Solidification of sodium acetate is the basis for one type of hot pack , but it’s also great for crystallization demonstrations. Three popular activities are the “sea urchin,” “flower,” and “tower.”

• Sea Urchin : Pour the cooled liquid into a clear container. Use a toothpick or bamboo skewer to scrape a few sodium acetate crystals from the pan used to make the solution. Dip the toothpick into the liquid so the tip with crystals are in the middle of the container. Needle-like crystals immediately grow out from the center. Also, crystallization releases heat as chemical bonds form to make the solid. The final structure resembles a spiny sea urchin.
• Flower : Pour the cooled sodium acetate liquid into a flat dish (preferably a dark-colored one). Scrape one or more crystals from the pan and drop them onto the liquid. The crystals act as seeds . The hot ice crystals spread out radially and form structures that resemble flowers.
• Tower : Place a few crystals onto a surface. Slowly pour the liquid onto the crystals. The hot ice solidifies as you pour the liquid, forming a tower (or whatever shape you can manage).

Re-Using Hot Ice

Save the solid sodium acetate so you can use it again without going through the whole baking soda-and-vinegar process. Simply dissolve the hot ice in water and boil off the smaller amount of excess water.

Safety Information

Sodium acetate is a safe, non-toxic chemical, so it’s perfect for chemistry demonstrations. It is used as a food additive to enhance flavor and is a key ingredient in some chemical hot packs. The heat released by hot ice crystallization of a refrigerated solution doesn’t present a burn hazard. However, making hot ice from baking soda and vinegar does involve boiling liquid on a stove, so adult supervision is required. If you use sodium hydroxide in place of baking soda, heed the cautions on the product label.

• ChemEd Xchange (2019). “ Crystallization of Supersaturated Sodium Acetate – Demonstration .”
• Clayden, Jonathan; Greeves, Nick; Warren, Stuart; Wothers, Peter (2001). Organic Chemistry (1st ed.). Oxford University Press. ISBN 978-0-19-850346-0.
• Seidell, Atherton; Linke, William F. (1952). Solubilities of Inorganic and Organic Compounds . Van Nostrand.

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How to Make Hot Ice

Last Updated: January 15, 2023 Fact Checked

This article was reviewed by Anne Schmidt . Anne Schmidt is a Chemistry Instructor in Wisconsin. Anne has been teaching high school chemistry for over 20 years and is passionate about providing accessible and educational chemistry content. She has over 9,000 subscribers to her educational chemistry YouTube channel. She has presented at the American Association of Chemistry Teachers (AATC) and was an Adjunct General Chemistry Instructor at Northeast Wisconsin Technical College. Anne was published in the Journal of Chemical Education as a Co-Author, has an article in ChemEdX, and has presented twice and was published with the AACT. Anne has a BS in Chemistry from the University of Wisconsin, Oshkosh, and an MA in Secondary Education and Teaching from Viterbo University. There are 8 references cited in this article, which can be found at the bottom of the page. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 877,569 times.

How can ice be hot? When it's not ordinary ice. Using the same ingredients as a baking soda volcano, [1] X Research source you can create sodium acetate. By cooling this below its freezing point, you get a liquid that's ready to freeze at the slightest trigger. In the process of forming a solid crystal, it releases a burst of heat. And that's how you get "hot ice."

Making Sodium Acetate At Home

• Do not use a copper pot.

• You cannot use baking powder, which contains other chemicals that interfere with the process.

• This measurement assumes you're using 5% acetic acid, which is a common concentration for commercial vinegar. This doesn't need to be a precise measurement, though.

• If it does get very brown and cloudy, add a bit more vinegar and boil again.
• The sodium acetate starts out as "sodium acetate trihydrate," meaning it contains water. Once all the water around it is gone, those water molecules start to evaporate and the sodium acetate becomes "sodium acetate anhydrous," meaning "without water."

• It's a good idea to add 1 or 2 tablespoons (15–30 mL) of vinegar. The vinegar will help keep the solution in its aqueous state, instead of forming that crust again.

• If the liquid freezes during this stage, there might be a solid piece of crystal in it, or some other impurity. Add more vinegar, return to the stovetop, and try again. This is a difficult process, so it's rare that you'll get it on your first try.

• If this does not happen, there is a problem with your solution. Add more vinegar and boil again — or try the more reliable store-bought method below.

Using Store-Bought Sodium Acetate

• Sodium acetate is also sold as "sodium acetate anhydrous," and some vendors do not specify which form they mean. The instructions below cover both forms.

• If the sodium acetate does not melt, you've bought sodium acetate anhydrous. To turn it into sodium acetate trihydrate, add hot water while it's still in the boiling water bath. It will take about 2 mL water for every 3 grams of sodium acetate to fully dissolve the substance.
• Don't use all of your sodium acetate. You'll need a little for later.

• Other impurities can trigger the freezing if they happen to be the right shape. This means you can sometimes trigger it by touching it with a toothpick or your finger, but solid sodium acetate is the only reliable way.

Expert Q&A

• You can melt the solid "hot ice" and repeat the show by cooling it again. You can melt it easily in the microwave, since you no longer need to boil away any water. Thanks Helpful 4 Not Helpful 1
• You can make ice sculptures if you pour the solution onto a pinch of the solid crystals. The solution will turn into a solid when it comes in contact with the crystals, and will continue to solidify while you pour. The ice will soon tower up! Thanks Helpful 1 Not Helpful 1
• The home-made hot ice is more difficult to use and gives less impressive results than the store-bought method. If you have any problems with it, your best bet is to add more vinegar, boil away the water, and try again. Thanks Helpful 0 Not Helpful 0

• Do not touch the solution until it's cooled! Thanks Helpful 45 Not Helpful 13

Things You'll Need

• Sodium acetate trihydrate (or white vinegar and baking soda)
• Medium to large pot (steel or Pyrex)
• Clean container
• Ice bath (or refrigerator)

You Might Also Like

• ↑ http://www.rsc.org/learn-chemistry/resource/res00002026/bubble-volcanoes?cmpid=CMP00006775
• ↑ http://smile.cosi.org/cooking-with-chemistry-teacher-packet-and-classroom-activities.pdf#page=10
• ↑ https://youtu.be/g584hrAIMKc?t=40
• ↑ https://youtu.be/AedL_NCv1Pw?t=82
• ↑ https://www.raisingmemories.com/2014/05/homemade-hot-ice-sodium-acetate.html
• ↑ https://youtu.be/pzHiVGeevZE?t=60
• ↑ https://www.fleet.org.au/blog/hot-ice/
• https://www.raisingmemories.com/2014/05/homemade-hot-ice-sodium-acetate.html

About This Article

To make hot ice, combine baking soda and white vinegar in a large steel pot. When the mixture stops fizzing, put the pot on a stovetop and bring the mixture to a boil. Right when a crusty film starts to form on top of the mixture, turn the stovetop off. Scrape off the powdery crystals on the side of the pot with a spoon and put them in a separate container. Then, transfer the liquid mixture into a heat-resistant container, seal it shut, and chill it in an ice bath for 15 minutes. Finally, sprinkle some of the powdery crystals into the mixture to create hot ice! If you want to learn how to use store-bought sodium acetate for hot ice from our Biochemistry Ph.D. co-author, keep reading! Did this summary help you? Yes No

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Awesome Science Experiment: Make Hot Ice with Baking Soda and Vinegar

January 20, 2018, 23 comments, join the conversation, categories/tags:, ages 5-7 ages 8-10 ages 11+ science, want these great ideas sent right to your inbox sign up for the newsletter..

Here’s a fun science experiment that will definitely get a “wow” from the kids. Combine baking soda and vinegar to make sodium acetate, or hot ice! It crystalizes instantly when you pour it, allowing you to create a tower of crystals. Since the process of crystallization is exothermic, the “ice” that forms will be hot to the touch. Science is so cool!

Making hot ice is a simple process, and you probably have everything you need on hand. You’ll need a couple of hours, though, so keep that in mind.

Step 1: Combine 4 cups of vinegar and 4 tablespoons of baking soda in a pot. Before we did this experiment, I read instructions for hot ice on a few different websites. I decided to use the amounts given on Playdough to Plato . Add the baking soda a little at a time so that when it fizzes it won’t overflow over the edges of your pot!

Janie and Jonathan were quite impressed with this step.

Step 2: You have now made sodium acetate! (As well as carbon dioxide – it was given off in the reaction, which created all that fizzing.) You’ll need to boil the solution, though, to reduce the amount of water so that it is concentrated enough to form crystals.

Cook your solution over low to medium heat for about an hour. You want to reduce it down to 1 cup or less.

Now, the stuff I read online said that crystals would start to form around the edge of the pan. This is important because you’ll need a few crystals as “seeds” to start the crystallization process. Well, our solution never formed crystals while it was cooking. When it was down to 3/4 cup, I finally stopped boiling it.

Step 3: Pour your sodium acetate into a glass container and put it in the refrigerator for 30 to 45 minutes.

We did this, and while it was in the refrigerator, I scraped some of the dried solution off the sides of the pot, hoping that it would work as the crystals needed to start the reaction.

It didn’t work. Boo. We poured the solution over the pan scrapings, and nothing happened.

We tried putting it in the refrigerator for awhile longer. Still nothing.

But, this experiment is very forgiving! I left the solution on the counter and came back to it the next day. I decided to boil it a little more – maybe it wasn’t concentrated enough. And we had never seen any crystals form in the pan. After about 10 more minutes of boiling, there still weren’t any crystals on the edges of the pan, but I decided that the solution was reduced down so far that we just had to stop.

As soon as I poured the solution out of the pan and into a glass jar, the remaining liquid in the bottom of the pan crystallized instantly! So I knew we were getting somewhere!

This time, I put the solution in the freezer for about 20 minutes. Much faster.

Step 4: Pour the cooled solution onto a few crystals that you scraped from the pan.

I scraped off some crystals from the bottom of the pan and put them in a plastic tray.

Then Aidan poured the solution very slowly onto the crystals.

The first little bit took a few seconds to crystallize… but it DID!

He kept pouring, a little at a time…

If you pour too quickly, the crystals will spread out horizontally. So we went nice and slow.

It was so fun to watch! By the end, Aidan was pouring just a drop at a time, and we could actually watch each drop piling up on top of the tower of hot ice.

We didn’t get a chance to measure our final tower, but it was impressive!

Why does this work?

The sodium acetate solution contains water. We reduced the amount of water in the solution by boiling it, but there is still water in there. The water molecules keep the sodium acetate from forming crystals. Well, crystals may start to form, but as a few molecules join together, the water molecules pull them apart again.

When we cooled the solution, we were able to bring the sodium acetate down to a temperature lower than the point at which it would normally become a solid. This word for this is supercooled.

By the way, we think of melting and freezing points mainly in reference to water, but all substances have a melting/freezing point. For example, copper remains a solid until it reaches 1,984 degrees Fahrenheit!

Back to the sodium acetate… The crystals in the tray provided a starting point for crystals to grow in the solution, called a nucleation site. This gave the sodium acetate the push it needed to crystallize!

The directions on Instructables said to filter the solution to get rid of any impurities that might inhibit the crystallization process. We didn’t do that step, and it turned out fine.

The crystallization process gives off heat, so the hot ice is hot to the touch! Not hot enough to burn, though. We all had fun touching it!

Our tower was pretty flimsy and broke quickly, but we had a great time with this science experiment. If you want to repeat the process, you can melt the crystals down into a liquid again, cool it again, and make another tower!

Also, I was a little worried about our pot, but it was super easy to clean. The sodium acetate dissolves easily and rinses right off.

Have fun with science!

23 Comments

Anne-line feb 1, 2018.

How strong (%) was your vinegar?

william Oct 30, 2018

this is so cool i wated to try sence i was 5

islam Feb 7, 2018

what is he adding on it water or vinegar ?

Sarah Feb 7, 2018

He is pouring sodium acetate, which we made by combining baking soda and vinegar. We boiled it down to make it more concentrated.

Bobbie Feb 7, 2018

I absolutely loved science & chemistry in school & this experiment is one I've never seen. I enjoyed your post so much that I thoroughly read the entire thing (I'll admit I skim through a lot of other sites posts) & am super excited to try this with my grandkids. Thank-you for detailing everything, even the difficulties. I feel very confident going into this experiment. And since I just found your site I look forward to perusing the rest of your site.

Mohamed Borhami Feb 8, 2018

Hi Sara , you are amazing , wonderfull , i have a chemistry graduate , but you can simplify science to kids its perfect i 'm following your site ,and pass what you did to my grandson , my daughter follow the homeschooling with the kids and i know how the effort and responsibility , but she was happy as she add one day a week for free activities, go on and good luck .

Marlene Manning Feb 9, 2018

Hi Sara, I am a science relief teacher from Australia and was wondering if you can make the solution at home, carry it to school in a cooler bag, pop it in the fridge at school to use with different classes?

Sarah Feb 11, 2018

Hmmm, now that's a good question! You can definitely make the solution ahead of time. What I don't know is whether you would need to heat it at school for a few minutes, then cool it to get it to the supercooled state. You might want to test it out first!

Shana Fordahl Mar 20, 2018

I want to try this with my STEAM club at school but I too would need to cool it at home and bring it later. Did you try it. Did it work?

SuperDan Sep 7, 2018

You'll have to refreeze in. If that doesn't work, Reboil it back onto liquid, 5hen refreeze. That should do it.

Linda Feb 2, 2021

Heat it at(before) school and let it come to room temperature. It will work that way. A microwave or hotplate will work to heat it.

Lorraine Feb 19, 2018

Thank you for sharing! I plan to make this with my grandson today, would you happen to know if any type of vinegar can be used? Seems all I have on hand is red wine vinegar ?

It is all 5 percent acetic acid.

Amanda Feb 24, 2018

Ahhh, what do I keep doing wrong? We have had 3 goes at this and the coolest thing I can do is make it freeze in the bowl as soon as I "disturb" it. Which is actually quite cool and my boys love it but we can't get it to the state of being able to pour it and watch it freeze!

Add a little more water if it does this and it should become a solution. You may have to heat it a little.

Pamela Apr 21, 2018

This was so awesome, I love watching kids get involved in things like this, great kids and I love seeing parents that are spending time with there kids to teach them things like this. Keep learning kids science is so awesome. This was very impressive. Thanks, Pamela

Carolyn Apr 26, 2018

Thanks for sharing this and the science behind it! It really helped explain the process. My 5th grader would like to try to do the boil-ahead idea and bring it to school after - I'd also love to hear if that worked for anyone. :)

By the way, I've assumed that this is the same process as what's in those "heat packs" sold for health needs and such - but they activate with a click of a metal disk. Any idea what that disk is??

Kelly Jun 12, 2018

It took me 5 attempts to get this right but once I did, WOW! It is so exciting to see those crystals form :)

Sam Mar 16, 2020

Hi Kelly, I’m trying to get this to work, but each batch I make fails. What did you change to make yours work? Thx Sam

Hena Jose Jun 29, 2018

Really good one. well explained. surely will try

Lisa Jul 18, 2018

I wasn't able to get this to work. Our solution turned slightly brownish as it simmered and we were not able to get it to freeze to the crystals we got off the bottom of the pan.

Should the solution be cool when you pour it?, cold? slightly warm?.....

We are trying again!

Looks so cool...my boys are excited to see if we can get it to work this time.

Tara Aug 7, 2018

Did the vinegar and baking soda dissolve together? We tried it and it was a bunch of mush and didn't even pour. Are we supposed to stir as it cooks?

Jo Sep 21, 2018

My son is doing this for school so do you think you can leave the liquid overnight?

Sarah Sep 24, 2018

Yes, but... he may need to heat the liquid again and then cool it rapidly in order to get the crystals to form. The supercooled state of the liquid seems to be important for forming the crystals. I would definitely test it first before taking it to school!

gdgkufgdiyv Nov 12, 2018

Barb jan 24, 2019.

Very interesting! I am wondering how much of the 'crystals' that recipe of 4 cups/4tbsp made? Approximately? I'm hoping to use it in the 'still solution state' for the making of a mordant for fabric (long story)

Crystal Apr 26, 2020

My Boys and I tried this today. We had to boil a second time to get Crystals. After cooling the liquid when we went to pour crystals formed instantly in the jar, then all of The solution crystallized before we could add it to the plate! Still cool!

Mariska Bishop May 6, 2020

This experiment is cool

Meredith Wagoner Jul 7, 2020

This one didn't work for us. The solution turned into a sludgy consistency when we put it into the fridge. Any idea where we might have gone wrong? I'd love to try it again. And thank you for including your process- super helpful!

Elliot Driver Dec 7, 2020

I am making this for class can i cool it and un cool it to bring it to school or does it need to stay cooled .

Tammie Niffenegger Feb 21, 2021

You are making a supersaturated solution. The water is holding more sodium acetate than normal. This is because the solution was made at a high temperature which holds holds alot of sodium acetate, but when cooled the molecules slow and cannot hold the sodium acetate. So ANY disturbance will cause it to crystallize. When you heat it back up you are redissolving it. This is the same reaction as whats in the REUSABLE clear handwarmers that you boil to used again.

Kiki Apr 27, 2021

What happens if there are no crystals at the bottom of the pan?

LaVerne Apr 3, 2022

My grandson found this experiment on tou tube but it lack the depth of instruction and we did not get the required outcome. I told my grandson I think it has to be hot and after reading your post we realized the video skipped the boiling processed. It went drom disaolving the baking soda to pouring it in the glass and wait for the crystallization to happen. Thank goodness we didn't throw the concoction away so we can see if it still works

Post a Comment

How to Make Hot Ice From Vinegar and Baking Soda

Categories STEM Activities

Kids will love this wacky edition of winter science experiments ! Hot ice is a novelty any time of year. Learn the no-fail way for how to make hot ice here!

We watch a lot of science-themed YouTube videos, so of course, when we saw this video, we knew we had to try and make our own hot ice.

We thought the hot ice science experiment would be easy, but it turns out, there is a trick to it!

How to Make Hot Ice

Making hot ice isn’t difficult, but if you don’t follow the steps correctly, your project will be messed up and you will have to start over.

You want to get it right the first time because this experiment takes MASSIVE amounts of vinegar.

Add this experiment to your list of classic science fair projects to try.

Hot Ice Materials

You’ll need these materials to make hot ice!

• Baking soda
• Aluminum foil
• Rubbing alcohol
• Safety goggles
• Latex gloves

What You Need for a Science Fair

You’ll want to have these supplies on hand before doing your science fair project. Shop the included Amazon storefronts to make things easier and don’t forget to download the free science fair planning checklist before getting started!

Science Fair Project Planning

When you’re planning your project, you want to keep everything organized. Click the image below to get my free science fair project checklist so you can start organizing your project from the start.

You may also want to check out this list of science fair project research supplies.

Supplies for a Science Fair Project

There are so many supplies for science fair projects that are individual to each project, but if you want a general list of possible supplies and inspiration for your project, check out my selection of science fair experiment supplies on Amazon.

Supplies for a Science Fair Presentation

Your science fair presentation is important! It should look presentable and eye-catching. Check out this list of my favorite science fair presentation supplies.

How to do the Hot Ice Experiment With Baking Soda and Vinegar

Wear gloves and eye protection when doing this experiment to keep safe.

To make hot ice, you must boil vinegar and baking soda.

Mix 6 cups of vinegar and 6 tablespoons of baking soda in a pot. Add the baking soda slowly, because you don’t want too big of a reaction. This will create sodium acetate, which can eventually form crystals.

Your experiment might not work the first time (ours didn’t) so keep trying!

We used about a gallon of vinegar before we finally got the experiment to work. We felt like real scientists having to work so hard to make something happen!

Now, boil your sodium acetate mixture down until there is only about 1-2 cups left. Keep the heat as low as you can, otherwise it will turn yellow.

We boiled our vinegar too hot, so our ice turned a bit yellow. That doesn’t affect results, but it does make it look less like ice.

Our crystals finally formed after boiling our fifth batch.

Put your reduced mixture in the refrigerator for about 45 minutes to encourage crystals to form. You may not be able to see them until you pour off the liquid.

Save the liquid for later!

Rinsing the crystals with rubbing alcohol will get rid of some of the yellow color (but not all).

Can you believe this started as six cups of vinegar?

You’ll want to be careful when moving the mixture from the refrigerator to where you plan to pour it out, because if you bump it too much, it could harden in the cup.

Place a few of the crystals on a plate to “seed” your hot ice structures.

Let the kids pour out the vinegar mixture and watch it harden right before your eyes! Pour very carefully to stack the crystals.

After pouring it out, the kids can shape it and play in it safely ( wear latex gloves for maximum protection).

Next time, we’ll try making a giant batch for even more hot ice fun!

More Winter Science Experiments

Burning Ice Science Experiment

How to Make a Magnifying Glass from Ice

How to Make Frost

Galaxy Snow Experiment

Share this project with a friend!

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The illusion of Hot Ice

March 20, 2012 By Emma Vanstone 9 Comments

We love a science experiment that seems like a magic trick , and this activity is one of the best. We’re going to find out how to make hot ice .

Imagine saying to people, ‘I can make hot ice!’ They wouldn’t believe you would they?

As far as science theory goes, they shouldn’t, we know that in order for ice to exist, it has to be at 0 o C and that when heated it melts.

Note – this activity does not make ice, just something that resembles ice. It is NOT edible, so please discard the solution when you have finished experimenting.

How to make hot ice

To make hot ice, you will need

1 litre of acetic acid (white vinegar)

4 tablespoons of bicarbonate of soda ( baking soda )

Hob to heat the mixture

Pour the white vinegar into the pan.

Carefully add the bicarbonate of soda, half a tablespoon at a time and stir the mixture until it has all dissolved.

The baking soda and vinegar will fizz as they react together, which is why you need to add the baking soda slowly. You have now made a solution called sodium acetate . Carbon dioxide gas is also given off.

Simmer the solution on the hob until it has reduced to about 100ml. This should take about one hour. The solution is now supersaturated!

Once the mixture has reduced down, pour it into a jug, cover it and place it in a fridge to cool for 1 hour.

Once cooled, you can pretend the liquid is water to your friends and pour it out onto a surface. It should begin to crystallise straight away, forming towers of ‘ice’. It looks and feels hot because the reaction gives off heat. It is exothermic .

The great thing is you can remelt the ‘icicles’  to reuse when you want to perform the trick again! We put the jug in the microwave for 40 seconds to dissolve the crystals and then placed it back in the fridge for an hour.

If pouring isn’t working, try warming up your finger and gently touching the surface of the liquid. It should start to crystallise from your finger and spread outwards.

How does hot ice work ?

S odium acetate exists as a supercool liquid in the fridge, meaning that it is in liquid form below its usual freezing point . As soon as it is disturbed, it starts to crystallise. The crystallisation is an exothermic reaction which is why we call it hot ice!

Sodium acetate usually freezes at 54 o C, but as you have seen can exist in the supercool form below that temperature.

Uses of sodium acetate

• Sodium acetate is used in heat packs and hand warmers. Heating pads usually have a metal disc in them, which, when clicked, starts the crystallisation process, releasing heat. Hand warmers can usually be reused by boiling the pouch to melt the contents.
• As a flavouring in food.

Last Updated on March 15, 2023 by Emma Vanstone

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Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

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Reader Interactions

March 30, 2012 at 12:08 pm

Very cool kitchen chemistry!

April 01, 2012 at 10:02 pm

This is neat – I bet my kids would get a kick out of it! Thanks for the idea!

April 02, 2012 at 1:25 pm

That really is cool. Congrats on being nominated in the Schooldays category of the Mads. *bows out gracefully* 😉

April 04, 2012 at 12:50 pm

Thank you, stiff competition! 🙂

April 05, 2012 at 8:49 pm

Thank you…I’m sure there is no need to bow out though. xx

May 15, 2017 at 12:53 pm

April 06, 2012 at 1:57 am

What a fun “trick”! Thank you for sharing at Sharing Saturday!! I hope you will share with us again this week!

March 20, 2013 at 2:56 pm

That is so cool…. 😀

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Hot Ice Crystal Towers

  Secondary | Materials | Views: 69178

Did you Know?

• Sodium acetate or hot ice is an amazing chemical you can prepare yourself from baking soda and vinegar. You can cool a solution of sodium acetate below its melting point and then cause the liquid to crystallize.
• The crystallization is an exothermic process, so the resulting ice is hot.
• Solidification occurs so quickly you can form sculptures as you pour the hot ice.

Health and Safety: This experiment involves boiling solutions. Please take care when doing so and ensure you have adult supervision.

You will Need:

• 4 tablespoons of baking soda
• 1 litre clear vinegar

The concepts it illustrates are:

• Supercooling
• Crystallisation
• Exothermic Chemical Reactions

What to Do:

• In a saucepan, add baking soda to the vinegar, a little at a time and stirring between additions. The baking soda and vinegar react to form sodium acetate and carbon dioxide gas. If you don’t add the baking soda slowly, you’ll essentially get a baking soda and vinegar volcano, which would overflow your container.
• You’ve made the sodium acetate, but it is too dilute to be very useful, so you need to remove most of the water. Here is the reaction between the baking soda and vinegar to produce the sodium acetate: Na + [HCO 3 ] – + CH 3 –COOH → CH 3 –COO – Na + + H 2 O + CO 2
• Boil the solution to concentrate the sodium acetate. You could just remove the solution from heat once you have 100-150 ml of solution remaining, but the easiest way to get good results is to simply boil the solution until a crystal skin or film starts to form on the surface. This should take about an hour on the stove over medium heat. If you use lower heat you are less likely to get yellow or brown liquid, but it will take longer. Some discolouration is normal.
• Once you remove the sodium acetate solution from heat, immediately cover it to prevent any further evaporation. Pour the solution into a separate container and cover with plastic wrap. You should not have any crystals in your solution. If you do have crystals, stir a very small amount of water or vinegar into the solution, just sufficient to dissolve the crystals.
• Place the covered container of sodium acetate solution in the refrigerator to chill and await the amazing results!

« Back

How To : Make Hot Ice (Sodium Acetate) Using Baking Soda & Vinegar

Watch this science video tutorial from Nurd Rage on how to make hot ice with Dr. Lithium. This is the complete guide to making hot ice, more correctly called sodium acetate. See how to create it, fix it, and use it. All methods from baking soda and vinegar to laboratory synthesis are shown.

The basis for hot ice is sodium acetate trihydrate, which is heated above its melting point and then cooled below its melting point so it's supercooled. It's still liquid and quickly solidifies when a seed crystal is introduced.

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Hot Ice Science Experiment

You won’t believe how easy it is to whip up this hot ice science experiment! Just like all of our favorite science projects for kids , you just need a few simple supplies from your pantry: vinegar, baking soda and water.

The prep is quick and simple but the results are pure magic! Your kids are going to want to repeat this science experiment over and over again.

Grab 30 easy-to-follow science experiments kids will beg to repeat (plus a no prep science journal to keep track of their results!) in our shop !

Getting Ready

To prep the science experiment, I gathered a few common supplies:

• 4 cups of white vinegar (acetic acid)
• 4 tablespoons of baking soda (sodium bicarbonate)
• A glass measuring cup or mason jar (make sure it’s heat safe glass)

Making Hot Ice

After I collected the supplies, my kids measured 4 cups of vinegar and poured it into a medium-sized pot.

Then they took turns adding 4 tablespoons of baking soda (one tablespoon at a time) to the pot.

The sodium bicarbonate (baking soda) and acetic acid (vinegar) fizzed like crazy forming sodium acetate.

NOTE: The key is to add the baking soda slowly so it doesn’t erupt over the edges of your pot.

Next, we stirred the mixture until all the baking soda dissolved and stopped fizzing.

Then we slowly boiled the solution over medium-low heat for a little over an hour to remove the extra water.

The solution reduced by about 75% so there was just 3/4 cup remaining. I could see white powdery crystals forming on the sides of the pot near the top of the solution when the solution.

NOTE: If you boil your solution at a higher temperature it may turn yellow-brownish but don’t worry, the experiment will still work!

Next, I poured the concentrated sodium acetate into a glass pyrex measuring cup and placed it in the fridge to cool and scraped a little bit of the dried sodium acetate powder off the inside of the pot to use later.

After about 30-45 minutes, the solution was cool enough to turn into ice.

I grabbed my glass dish and placed a small pile of the sodium acetate powder from the pot in the center.  This would act as a seed for the crystals to start forming.

I very carefully took the cooled solution out of the fridge because any bump could start the crystallizing process.

I began pouring the solution very slowly into the pan and crystals began instantly forming.

We all gasped, it was like magic!

As soon as the clear liquid hit the plate white crystals would form like tiny fireworks.  I continued to pour and the liquid crystallized forming a solid as soon as it touched the growing “ice”.

The kids wanted a really tall crystal tower so I poured as slowly as I could.

It kept growing…

and growing.

In the end it was over 6 inches tall!

Of course we all just had to touch it. It was hard like ice but was hot!

NOTE: This form of sodium acetate while non-hazardous can irritate skin and eyes  just like vinegar can.  So be careful when handling the crystal.  Both of my kiddos ended up crumbling the crystal and didn’t have any reaction but I imagine it wouldn’t feel too good if your kiddo had a cut on his/her hands.

Once you are done creating and exploring the crystallized salt you can remelt it to use again and again.

We ended up repeating the experiment a few more times and every time the cooled solution was ready, the kids came running with excitement!

• After explaining nucleation, ask your students if they can think of any other processes that begin with nucleation. (Hint: rock candy, borax crystals, clouds and carbon dioxide bubbles in soda.)
• Ask students if they can think of other reactions that release heat like hand warmers and burning candles.
• Try adding a drop of food coloring to see if you can make colored crystals.

The Science Behind Hot Ice

The sodium acetate solution in the refrigerator is what is called a supercooled liquid .  That means the sodium acetate is in liquid form below its usual melting point.

Once you touch, bump, or add a small crystal that is not liquid, crystallization will begin and the liquid will change to a solid.

When the molecules in the solute (sodium acetate) are in a solution, they normally are surrounded by a solvent (in this case water molecules).

Occasionally, a few solute molecules will bump into each other and stick together for a little while but they will eventually break apart.

If enough solute molecules stick together, they can overcome the forces in the solvent that would normally break the solute molecules apart.

When that happens, the clump of solute molecules serves as a seed (or nucleation site) for other solute molecules to cling to so the crystallization process can take off again.

The sodium acetate powder we placed on the plate acted as a nucleation site for the dissolved sodium acetate in the solutions.

The crystallizing sodium acetate releases energy in the form of heat and is an example of an exothermic process. Sodium acetate is often used in hand warmers as it release heat when crystallizing!

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• DIY videos /

Make Hot Ice in 5 Steps

Materials you’ll need.

• 4 cups of vinegar
• 4 TBSP baking soda
• liquid measuring cup

Step-by-step tutorial

Step 2: When the solution starts to fizz, keep stirring until it stops producing bubbles and all of the baking soda has dissolved.

Step 3: Boil the solution over medium-low heat for 30 minutes to 3 hours until you can see crystals on the side of the pot (this depends on how well your stove or hot plate works). Then, pour the concentrated solution into a liquid measuring cup and let it sit in the fridge to cool.

Step 4: Scrape some of the solid sodium acetate off the bottom of the pot and put it on a plate.

Step 5: Slowly pour the solution on top of the solid, and watch crystals form!

A supercooled solution will begin to crystalize with the slightest movement or addition of crystals, which is exactly what you saw in this experiment. All the extra sodium acetate in the solution crystallized very quickly and became solid, which is what created the pillar of “ice” on the plate. This crystallization process releases heat, which is what makes the crystals warm to the touch.

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• Chemical Reactions
• Home Science Videos

How to make Hot Ice at home – Amazing Science Experiment

Sodium acetate or hot ice is an amazing chemical you can prepare yourself from vinegar and baking soda. You can cool a solution of sodium acetate below its melting point and then cause the liquid to crystallize. The crystallization is an exothermic process, so the resulting ice is hot. Solidification occurs so quickly you can form sculptures as you pour the hot ice.

Here is the reaction between the baking soda and vinegar to produce the sodium acetate:

Na+[HCO3]– + CH3–COOH → CH3–COO– Na+ + H2O + CO2

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Hot Ice For Summer

Creating Hot Ice: A Great STEM Experiment For Summer

There’s a Dad joke waiting in this project.  Make sure to grab it while you can!

“Son, it’s been so hot this summer that even the ICE is hot!”  

You can buy ice in the supermarket but hot ice you’ll have to make yourself.  Making hot ice is an easy fun experiment three to eight-year-old  kids can try with ingredients you have at home.  It takes about  1-2 hours  to conduct the experiment.    Your children will be amazed as the “ice” forms yet isn’t cold at all!

Hot ice is used in hand   warmers, heating pads, for a buffer in laboratory settings, and for pickling and tanning of food.  It’s chemical name is sodium acetate.

You also may be interested in:

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Supplies Needed

• A heat safe measuring jar or glass cup  
• 4 Cups of white vinegar which is  acetic acid
• 4 Tablespoons of baking soda which is  sodium  bicarbonate
• Hot plate  
• A spoon or spatula
• A pot or saucepan  (do not use a copper pot)

What Mystery Are We Solving?

Make hot ice and when you put your hand in the liquid the hot ice is formed around your fingers. It looks like your fingers are frozen, but it is hot to the touch.   

How does to everyday ingredients create ice that is hot to the  touch ? Isn’t ice supposed to be cold?

Safety Issues

Although young kids can create their own hot ice, adult supervision is recommended when the liquid is boiled.   

Hot ice isn’t the same as dry ice! Dry ice may cause severe burns when touched but hot ice is mostly harmless. For some people, hot ice may  irritate skin and eyes in the same manner vinegar would.  

How To Make Hot Ice

• Pour 4 cups of white vinegar into the saucepan or pot.
• Slowly add 4 tablespoons of baking soda a little at a time to the vinegar.  The liquid fizzes when the baking soda is added.  Stir with the spoon to mix the two ingredients as you add the baking soda.
• Wait for the fizzing to stop before you continue. 
• Place the pot on the hot plate  and boil at medium heat  until the fluid  evaporates  and you’re left with a dry sol vent .  It should take about 30 -60 minutes for all the liquid to disappear. 
• When the liquid starts forming a crusty film on the surface, turn the heat down immediately to prevent it forming a thick crust.  (Scrape some of the crystals off the side of the pot to use later)
• If the solution is brown and cloudy, add more vinegar. Boil again.  
• Break up the lumps in the powder solution.
• Place the powder in the glass container  with a lid  and add water until it dissolves into a liquid.  (66 g of water for every 100 g of powder) Cover with the lid to prevent more evaporation. 
• Place the glass jar in a container with ice water to cool down. It takes about 15 minutes. You may also cool it in the fridge , but it will take longer than the ice water. 
• When you put your hand in the glass jar, the hot ice forms crystals around your hand and it is frozen to the touch.   

What Just Happened Here?

The chemical reaction is also exothermically creating the hot feeling when touching the ice.   

The physical change is noticeable when the liquid mixture releases gas and changes into a solid form.  When water is added the powder dissolves.   

The solution  is a supercooled liquid that  stays liquid when cooled down below its freezing point in the ice water.    

The  unstable supersaturated  liquid will freeze forming crystals at the slightest trigger  when adding some of the crystals to the solution. For a cool effect dip your fingers  into  the liquid .   Crystallization  forms at the nucleation site whe n  solute molecules that bump into each other overcome the power of the sol vent that keeps molecules apart .   

More Resources

https://www.wikihow.com/Make-Hot-Ice  

https://www.youtube.com/watch?v=XiAv9GE_2o4  

https://www.playdoughtoplato.com/kids-science-experiment-hot-ice/  

https://www.thoughtco.com/hot-ice-or-sodium-acetate-607822  

Retha Groenewald is a professional writer working for FractusLearning. When not working with Fractus, she is web copywriter for the Christian market. Her writing is featured at Christian Web Copywriter and at Writing That Breathes Life.

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How to make “hot ice”

By Phillip Torrone

Phillip torrone.

current: @adafruit - previous: MAKE, popular science, hackaday, engadget, fallon, braincraft ... howtoons, 2600...

Hot Ice refers to a chemistry demonstration involving a supersaturated solution of Sodium Acetate which, when disturbed, will appear to freeze into “ice” as the cold solution turns from a liquid into a solid in a matter of seconds. This process is exothermic and the resulting “ice” is warm to the touch, contrary to what one would expect of ordinary ice. The picture to the left depicts pillars of Sodium Acetate Trihydrate which were created using Hot Ice solution. Supersaturated solutions of Sodium Acetate are used in certain types of hand-warmers.  When a metallic button is pressed inside a plastic pouch, the supersaturated solution begins to crystallize, in the process releasing heat. Sodium Acetate is one of the products of the reaction between baking soda (Sodium Bicarbonate, NaHCO3) and vinegar (Acetic acid, HC2H3O2). …In the video, a supersaturated solution of Sodium Acetate is carefully poured into an empty Petri dish and a small Sodium Acetate seed-crystal is dropped into the liquid. The seed-crystal triggers the “freezing” of the supersaturated solution and the liquid begins to crystallize. The crystallization expands outward from the seed crystal and quickly fills the entire Petri dish, converting all of the supersaturated Sodium Acetate solution into solid Sodium Acetate Trihydrate.

For students, DIY hobbyists, and science buffs, who can no longer get real chemistry sets, this one-of-a-kind guide explains how to set up and use a home chemistry lab, with step-by-step instructions for conducting experiments in basic chemistry. Learn how to smelt copper, purify alcohol, synthesize rayon, test for drugs and poisons, and much more. The book includes lessons on how to equip your home chemistry lab, master laboratory skills, and work safely in your lab, along with 17 hands-on chapters that include multiple laboratory sessions.

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British Science Week: Home science experiment – making hot ice

by How It Works Team · 14/03/2016

With this experiment, we will show that a substance could be created that was a liquid at room temperature but, when it was disturbed, would immediately crystallise and form what is known as hot ice.

Hot ice is an amazingly cool substance and the ingredients required are easy to obtain. However, it is difficult to make, and you probably won’t get it right on your first attempt, but don’t give up hope. You can either re-melt any failed hot ice or start again, making sure to follow the method carefully.

This is a great experiment to do at home and an even better one to do at school. You can directly see the effects of crystallisation and there’s plenty of science embedded into the fun of seeing hot ice in action. If you do replicate our experiment, make sure you send us some photos on Facebook  or Twitter  so we can see how it went!

You will need

1 litre of clear vinegar 4 tablespoons of baking soda Steel saucepan Container

Hot ice experiment – step 1

First, a litre of clear store-bought vinegar must be measured out. This must be clear, as brown vinegar contains impurities that will prevent the experiment from working. Next, you need to add about three to four tablespoons of baking soda (sodium bicarbonate) to the vinegar. This has to be done slowly, as the reaction can make the liquid explode over the side of the container. Stir this until all the baking soda is dissolved and then put the mixture on to the hob to boil.

Hot ice experiment – step 2

You need to get rid of about 90% of the liquid, so leave it to boil for over 30 minutes. You’ll start to notice a white substance on the side of the pan. This is sodium acetate, and a bit of this needs to be saved for later use. Eventually, a crust (sodium acetate anhydrous) will begin to form on the liquid. At this point, take it off the boil and transfer it into a container. This must be immediately covered to prevent the substance crystallising. You then need to cool it, so place it in an ice bath for 15 minutes or a fridge for a bit longer.

Hot ice experiment – step 3

The liquid needs to cool below room temperature. This makes it into a supercool liquid that will exhibit the characteristics of hot ice. Once it’s cooled, you can take the lid off and put some of the white sodium acetate collected earlier in the liquid.

Hot ice experiment – step 4

The points where sodium acetate is introduced will begin to crystallise. After a few seconds the entire liquid will appear to freeze. However, when touched, the substance is hot and not cold because the process of crystallisation here is exothermic, so heat is given off as the liquid solidifies. So, what’s happened in this experiment?

Hot ice experiment – conclusion

Almost every substance has a freezing point, but for something to solidify the molecules must rearrange from a liquid to a solid or crystal arrangement. However, hot ice, or sodium acetate trihydrate, is a supercool liquid where the molecules do not rearrange until they are disturbed, in this case by introducing sodium acetate. Hot ice melts at 58 degrees Celsius and is a crystalline solid at room temperature, allowing this effect to be produced as the baking soda and vinegar are heated. The unarranged molecular structure results in the occurrence of this crystallisation effect. You can re-use your hot ice by adding vinegar until the solid crystals are fully dissolved and repeating our method again.

Hot ice equation

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How to Make Hot Ice Using Homemade Sodium Acetate

Introduction: How to Make Hot Ice Using Homemade Sodium Acetate

Step 1: Making Homemade Sodium Acetate From Scratch

Step 2: Mixing Vinegar With Baking Soda

Step 3: Boiling It Down

Step 4: Filtration

Step 5: Last Boiling

Step 6: Testing Your Work

Step 7: It's That Simple!

Step 8: Hot Ice Preperation

Step 9: Dissolving

Step 10: Cooling

Step 11: Final Product

Attachments.

Get Hot Ice Help

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Several of you have written in asking for help with your homemade hot ice or sodium acetate. Here are the answers to the most common hot ice questions as well as advice on how to fix the usual problems making hot ice.

What Is hot ice?

Hot ice is a common name for sodium acetate trihydrate.

How Do I Make Hot Ice?

You can make hot ice yourself from baking soda and clear vinegar. I've got written instructions and a video tutorial to show you how to do it.

In the lab, you could make hot ice from sodium bicarbonate and weak acetic acid (1 L 6% acetic acid, 84 grams sodium bicarbonate) or from acetic acid and sodium hydroxide (dangerous! 60 ml water, 60 ml glacial acetic acid , 40 g sodium hydroxide ). The mixture is boiled down and prepared the same as the homemade version.

You can also buy sodium acetate (or sodium acetate anhydrous) and sodium acetate trihydrate. Sodium acetate trihydrate can be melted and used as-is. Convert sodium acetate anhydrous to sodium acetate trihydrate by dissolving it in water and cooking it down to remove the excess water.

Can I Substitute Baking Powder for the Baking Soda?

No. Baking powder contains other chemicals which would act as impurities in this procedure and prevent the hot ice from working.

Can I Use Another Type of Vinegar?

No. There are impurities in other types of vinegar which would prevent the hot ice from crystallizing. You could use dilute acetic acid instead of vinegar.

I Can't Get the Hot Ice to Solidify. What Can I Do?

You don't have to start from scratch! Take your failed hot ice solution (won't solidify or else is mushy) and add some vinegar to it. Heat the hot ice solution until the crystal skin forms, immediately remove it from heat, cool it at least down to room temperature , and initiate crystallization by adding a small quantity of the crystals that formed on the side of your pan (sodium acetate anhydrous). Another way to initiate crystallization is to add a small amount of baking soda , but if you do that you will contaminate your hot ice with sodium bicarbonate. It's still a handy way to cause crystallization if you don't have any sodium acetate crystals handy, plus you can remedy the contamination by adding a small volume of vinegar afterward.

Can I Re-Use the Hot Ice?

Yes, you can re-use hot ice. You can melt it on the stove to use it again or you can microwave the hot ice.

Can I Eat Hot Ice?

Technically you can, but I wouldn't recommend it. It is not toxic, but it is not edible.

You Show Glass and Metal Containers. Can I Use Plastic?

Yes, you can. I used metal and glass because I melted the hot ice on the stove. You could melt the hot ice in a microwave using a plastic container.

Are Containers Used to Make Hot Ice Safe to Use for Food?

Yes. Wash the containers and they will be perfectly safe to use for food.

My Hot Ice Is Yellow or Brown. How Do I Get Clear/White Hot Ice?

Yellow or brown hot ice works... it just doesn't look that much like ice. The discoloration has two causes. One is overheating your hot ice solution. You can prevent this type of discoloration by lowering the temperature when you heated the hot ice to remove the excess water. The other cause of discoloration is the presence of impurities. Improving the quality of your baking soda ( sodium bicarbonate ) and acetic acid (from the vinegar) will help prevent discoloration. I made my hot ice using the least expensive baking soda and vinegar I could buy and managed to get white hot ice, but only after I lowered my heating temperature, so it's possible to get decent purity with kitchen ingredients.

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Step by step how to make Instant Hot Ice with Sodium Acetate!

YOU NEED...

• 170g of Sodium Acetate Trihydrate .
• Water (tap is fine).
• Small sauce pot.
• 50ml or larger Graduated Cylinder .
• Medicine Dropper .
• Glass or 150ml Beaker (well cleaned).
• Scale (that can measure in grams).
• Refrigerator space.

PREPARING THE "HOT ICE"...

1) Measure out 30 mL of water (approximately 1 fluid ounce) and pour into a small stove-top pot. Weigh out 170 grams of Sodium Acetate Trihydrate and dump into the pot. Stir the water and sodium acetate trihydrate together to wet the dry flakes.

2) Put the sauce pot over medium heat on a stove and immediately begin to stir the mixture. Keep stirring constantly to avoid burning until the entire mixture turns into a liquid. This may take 10 to 15 minutes.

3) Once the mixture is all liquid with none, or almost none, of the dry sodium acetate still visible, pour the liquid into a clean glass or beaker large enough to hold all of the liquid. Leave any solids behind in the pot if there are any remaining.

4) Put the glass in the refrigerator to cool down. Do not shake or disturb the cooling solution. Check your solution after about five minutes of cooling.

NEXT, EVALUATE YOUR PROGRESS.. .

• If you see long thin crystals forming from the sides and bottom of the glass, or a thin layer of white crystals forming on the top of the liquid your ratio of sodium acetate is not quite right yet! (IF THIS IS NOT THE CASE SKIP TO PART C) .
• Take the glass out of your refrigerator and reheat in your pot while stirring to redissolve any solids. Add one to two drops of water. Pour the solution back into your clean glass and return it to the refrigerator to cool. Check again in five minutes and hopefully move on to part C.
• If you see a clear solution, with or without a thin transparent skin on the surface, your ratio of water to sodium acetate trihydrate is just about perfect. If you have a thin transparent skin on the surface, add a very small amount of water one drop at a time to the glass. Take note of how the skin disappears with just a drop or two of water. Once the skin has disappeared, continue letting the glass cool in the refrigerator.

FINAL PROCESS...

5) Continue checking on your cooling solution every five minutes and make adjustments as necessary according to step four. Wait about 15 to 20 minutes until the outside of the glass feels like it is about room temperature. If there are no signs of any solid material in the glass you are now ready to trigger the hot ice exothermic (release of heat) reaction!

6) Drop a small flake of dry sodium acetate trihydrate into the glass and observe the immediate crystallization that takes place! If nothing happens, or you get a slushy solid, your soultion does not contain enough sodium acetate. Add 10g of dry sodium acetate and remix over heat. Start over at step two.

Author - D. Bieniulis for The Science Company® Lakewood, Colorado

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• Published: 23 September 2024

Phase transition kinetics of superionic H 2 O ice phases revealed by Megahertz X-ray free-electron laser-heating experiments

• R. J. Husband   ORCID: orcid.org/0000-0002-7666-401X 1 ,
• H. P. Liermann   ORCID: orcid.org/0000-0001-5039-1183 1 ,
• J. D. McHardy   ORCID: orcid.org/0000-0002-2630-8092 2 ,
• R. S. McWilliams   ORCID: orcid.org/0000-0002-3730-8661 2 ,
• A. F. Goncharov   ORCID: orcid.org/0000-0002-6422-8819 3 ,
• V. B. Prakapenka   ORCID: orcid.org/0000-0001-9270-2330 4 ,
• E. Edmund   ORCID: orcid.org/0000-0003-4363-7434 3 ,
• S. Chariton 4 ,
• Z. Konôpková 5 ,
• C. Strohm 1 ,
• C. Sanchez-Valle   ORCID: orcid.org/0000-0001-5046-1612 6 ,
• M. Frost   ORCID: orcid.org/0000-0001-6879-0422 7 ,
• L. Andriambariarijaona 8 ,
• K. Appel   ORCID: orcid.org/0000-0002-2902-2102 5 ,
• C. Baehtz   ORCID: orcid.org/0000-0003-1480-511X 9 ,
• O. B. Ball   ORCID: orcid.org/0000-0002-5215-0153 2 ,
• R. Briggs 10 ,
• J. Buchen   ORCID: orcid.org/0000-0001-5671-5214 11   nAff15 ,
• V. Cerantola   ORCID: orcid.org/0000-0002-2808-2963 5   nAff16 ,
• J. Choi   ORCID: orcid.org/0000-0002-9143-4810 12 ,
• A. L. Coleman   ORCID: orcid.org/0000-0002-5692-4400 10 ,
• H. Cynn   ORCID: orcid.org/0000-0003-4658-5764 10 ,
• A. Dwivedi 5 ,
• H. Graafsma   ORCID: orcid.org/0000-0003-2304-667X 1 ,
• H. Hwang   ORCID: orcid.org/0000-0002-8498-3811 1   nAff17 ,
• E. Koemets 11   nAff18 ,
• T. Laurus   ORCID: orcid.org/0000-0002-2258-2123 1 ,
• Y. Lee   ORCID: orcid.org/0000-0002-2043-0804 12 ,
• X. Li 1   nAff19 ,
• H. Marquardt   ORCID: orcid.org/0000-0003-1784-6515 11 ,
• A. Mondal   ORCID: orcid.org/0000-0002-3424-5693 6 ,
• M. Nakatsutsumi   ORCID: orcid.org/0000-0003-0868-4745 5 ,
• S. Ninet 8 ,
• E. Pace   ORCID: orcid.org/0000-0002-7328-1099 2 ,
• C. Pepin   ORCID: orcid.org/0000-0002-9638-3303 13 ,
• C. Prescher 14 ,
• S. Stern 1   nAff20 ,
• J. Sztuk-Dambietz 5 ,
• U. Zastrau   ORCID: orcid.org/0000-0002-3575-4449 5 &
• M. I. McMahon 2  

Nature Communications volume  15 , Article number:  8256 ( 2024 ) Cite this article

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• Phase transitions and critical phenomena
• Planetary science

H 2 O transforms to two forms of superionic (SI) ice at high pressures and temperatures, which contain highly mobile protons within a solid oxygen sublattice. Yet the stability field of both phases remains debated. Here, we present the results of an ultrafast X-ray heating study utilizing MHz pulse trains produced by the European X-ray Free Electron Laser to create high temperature states of H 2 O, which were probed using X-ray diffraction during dynamic cooling. We confirm an isostructural transition during heating in the 26-69 GPa range, consistent with the formation of SI-bcc. In contrast to prior work, SI-fcc was observed exclusively above ~50 GPa, despite evidence of melting at lower pressures. The absence of SI-fcc in lower pressure runs is attributed to short heating timescales and the pressure-temperature path induced by the pump-probe heating scheme in which H 2 O was heated above its melting temperature before the observation of quenched crystalline states, based on the earlier theoretical prediction that SI-bcc nucleates more readily from the fluid than SI-fcc. Our results may have implications for the stability of SI phases in ice-rich planets, for example during dynamic freezing, where the preferential crystallization of SI-bcc may result in distinct physical properties across mantle ice layers.

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Introduction.

The high pressure ( P ) phase diagram of H 2 O is remarkably complex, containing numerous phases that differ in their crystal structures 1 , 2 , 3 , chemical bonding 4 , 5 , 6 , and degree of orientational 7 , 8 , 9 and dynamical disorder 6 , 10 . In recent years, particular interest has been given to the high temperature ( T ), superionic (SI) forms of solid H 2 O (ice) 11 , 12 , 13 , 14 , 15 , which are characterized by the fast diffusion of protons within a crystalline oxygen sublattice. In particular, studies of the stability fields, structural behavior, and protonic conductivity of SI ice are motivated by the theorized presence of vast quantities of these phases in the interiors of Uranus and Neptune 16 , 17 , where the unusual properties of these SI ice phases have been proposed to contribute to the non-dipolar and non-axisymmetric magnetic fields of these planets 18 . Since its initial prediction 19 , SI ice has been the focus of numerous theoretical studies which proposed that it adopts a body-centered cubic (SI-bcc) oxygen sublattice at low pressures 20 , 21 , 22 , transforming to a face-centered (SI-fcc) lattice above ~100 GPa 23 , 24 , 25 . The SI-bcc oxygen lattice is isostructural with that of cubic ice VII, which is stable at lower temperatures, but the boundary between the two phases is first order in nature 26 . Experimental studies, however, are comparably scarce due to the challenges associated with creating and probing SI states using both static and dynamic compression methods. The stability field of SI ice cannot be reached by single shock compression of the ambient liquid due to the steep rise in temperature along the principal Hugoniot at low pressures, and the first experimental verification of SI ice was achieved using shock compression of pre-compressed samples 11 and a reverberating shock compression scheme 14 , 27 , 28 based on its high (total) conductivity (>100 S/cm) 27 , 28 and low optical conductivity («100 S/cm) 11 above 100 GPa. The crystal structure in the SI region (at 160 GPa and 3200 K) was first identified as fcc using nanosecond X-ray diffraction (XRD) 14 , with the fcc phase remaining stable up to pressures >400 GPa; however, the subsequent observation of a bcc crystal structure at 3300 K and 5500 K at 205 GPa 29 suggests that the boundary between the bcc and fcc phases is strongly dependent on the time-dependent P-T path, and may lie at higher pressures than previously anticipated.

Static compression experiments using diamond anvil cells (DACs) and synchrotron XRD have mapped out the H 2 O phase diagram at lower pressures. However, experiments conducted above ~1300 K, which are performed either by direct heating of H 2 O using a CO 2 laser (wavelength λ  ~ 10.6 µm) or by indirect heating of an embedded laser absorber which interacts with near IR radiation ( λ  ~ 1 µm), can encounter additional complexities arising from temperature fluctuations (e.g. induced by changes in the optical properties of the sample during a phase transition 13 ) or the presence of temperature gradients within the sample chamber 30 . Indirect laser heating experiments using laser couplers are particularly susceptible to temperature gradients, resulting in a discernible signal originating from the colder regions of the sample in XRD patterns. Although CO 2 laser heating provides more spatially uniform heating as the laser is directly absorbed by the sample, CO 2 lasers typically exhibit large power fluctuations at microsecond timescales due to the use of pulse width modulation to control the average laser power 31 . In addition, direct CO 2 laser heating of H 2 O is not possible above ~60 GPa due to the reduced absorption of λ  ~ 10 µm radiation above this pressure 12 , 32 . Consequently, despite extensive experimental efforts, the location of the melting curve and the SI-bcc/fcc boundary remain controversial, with recent studies reporting melting temperatures which exhibit discrepancies of ~1000 K at 50 GPa 13 , 15 , 32 , 33 , 34 .

Ionic conductivity measurements performed using resistively-heated DACs initially identified the onset of superionic conduction at T  ~ 740 K at 56 GPa 35 ; however, the maximum reported conductivity (0.12 S/cm) was ~2 orders of magnitude lower than values determined in shock compression experiments at higher pressures 27 , 28 . A subsequent XRD study reported the observation of an isostructural phase transition on compression above 15.6(2) GPa at 905 K 15 , which was identified as the SI-bcc to ice VII transition based on the large entropy increase at the transition and agreement with results from ab initio molecular dynamics simulations. The same work also saw evidence of SI-bcc during laser heating in the 27–44 GPa pressure range, with the appearance of SI-bcc coinciding with the first observation of fluid diffraction 15 . In more comprehensive studies, the SI-bcc to SI-fcc transition was observed in two independent laser heating studies 12 , 13 , but with significant discrepancies in the reported phases diagrams. In particular, Prakapenka et al. 13 observed SI-fcc during heating at pressures as low as ~30 GPa, whereas Weck et al. 12 did not observe evidence of SI-fcc below 50 GPa. Instead, Weck et al. observed fluid/SI-bcc coexistence on heating in the 27–47 GPa range at temperatures below the SI-bcc to SI-fcc transition temperatures reported by Prakapenka et al. The SI-fcc phase boundaries reported by Prakapenka et al. consistently lie at higher temperatures than those reported by Weck et al., with reported SI-bcc/SI-fcc transition temperatures differing by ~600 K at 60 GPa.

In this work, the structural properties and phase stability region of SI ice were investigated using trains of MHz pulses produced by the European X-ray Free Electron Laser (European XFEL), which were utilized to create and probe high temperature states of statically-compressed H 2 O. This experiment used a femtosecond serial pump-probe X-ray heating scheme, where each pulse deposits energy into the sample and simultaneously captures a snapshot of the sample as it cools from the hot state created by the previous pulse 36 , 37 . The timescales associated with this dynamic heating approach are vastly different from those experienced in conventional laser heating DAC experiments; the near-instantaneous energy deposition in the sample during single pulse irradiation produces ultrafast (sub-ns) heating followed by rapid cooling and relaxation due to heat dissipation 38 . Due to the long X-ray absorption length of H 2 O (~4000 µm at 40 GPa and 18 keV), the necessarily thin (<30 µm) samples were heated using various inert couplers which were directly heated by the XFEL beam, many of which are not suitable for IR laser heating due to their high reflectivity in the IR spectrum. This ability of indirect XFEL heating to induce bulk heating of H 2 O was recently demonstrated at PAL XFEL 38 ; however, previous conclusions relied on indirect methods of melt detection due to the low repetition rate of the PAL source (30 Hz), which was insufficient to probe the hot state in situ. In our study, the structural evolution of H 2 O during the heating process was monitored using pulse-resolved, MHz XRD data collected using an Adaptive Gain Integrating Pixel Detector (AGIPD) 39 , which enabled the tracking of structural changes, including phase transformations and chemical reactivity, with sub-microsecond temporal resolution. The development of a data analysis methodology in which diffraction spots from individual crystallites were identified in XRD images allowed us to harness the extensive volume of XRD data collected from the hot sample, which significantly improved the diffracted signal of SI ice in comparison to time-integrating methods. H 2 O was observed to transform from ice VII to SI-bcc on heating in the 26–69 GPa pressure range, whereas SI-fcc was only observed at pressures ≥50 GPa. The absence of SI-fcc in the lower pressure runs, despite evidence of melting and SI-bcc/fluid coexistence, is in good agreement with previous CO 2 laser heating studies 12 , 15 but contrasts with results from IR laser heating experiments in which SI-fcc was observed at pressures as low as 30 GPa 13 . The discrepancies in the reported SI-fcc phase stability fields are discussed in terms of the timescales and P-T paths associated with different experimental approaches.

Results and discussion

X-ray heating.

High-pressure H 2 O samples were indirectly heated using a variety of mid- and high-Z couplers (see “Methods” section, Supplementary Table  1 , and Supplementary Fig.  1 ) which were irradiated with 300 XFEL pulses at a 2.2 MHz repetition rate. A number of different coupler geometries were employed, the majority of which were based on a doughnut-type crucible and two of which consisted of a dispersed nanopowder. One example of a doughnut-type design is shown in Fig.  1a-c , in which multiple couplers were embedded in a rhenium (Re) gasket and insulated from the diamonds by a thin self-insulating layer of H 2 O. Samples were subjected to multiple heating runs at different X-ray fluences by varying the beamline transport transmission to the target, starting from a low X-ray transmission (≤1%) and increasing in steps of 0.5–10%, where a run comprises a single train of X-ray pulses striking the sample. Data from doughnut-type crucibles were collected with the XFEL beam aligned to the center of the coupler hole so that heating of the coupler was primarily performed by the tails of the focused beam (outer region of the beam spot), whereas multiple spots were targeted on nanopowder couplers. Data were collected using three different X-ray focal spot sizes of <8 µm, 13 µm, and 26 µm (FWHM), which are specified in Supplementary Table  1 . For some samples, the temporal dependence of the coupler temperature was constrained by streaked optical pyrometry (SOP) measurements (Fig.  1d–f ).

a Photomicrograph showing the three doughnut-type couplers (Au, Cu, and Ag) in DAC 8, which were used to indirectly heat the H 2 O sample during XFEL irradiation. The couplers were imbedded in the Re gasket and insulated from the diamond anvils by a thin layer of H 2 O, as illustrated in ( b ) and ( c ). Data were collected with the XFEL beam (<8 µm FWHM) aligned to the center of the coupler hole so that the coupler was heated by the tails of the beam. d – f Data from run 533, which was collected from the Cu coupler using 70% X-ray transmission. d Pulse energy as a function of time for the 300 pulses in the train. e SOP spectrogram after fluorescence removal showing the thermal emission from the coupler during the run, where time 0 corresponds to the arrival of the first XFEL pulse. f Temporal evolution of the total SOP intensity and temperature determined from a Planck fit to the thermal emission in a 9.07 µs time window, where the horizontal error bars indicate the bin width and the vertical error bars correspond to one half of the standard deviation confidence from the Planck fit. The temporal resolution of the SOP is not sufficient to resolve temperature oscillations during the heating/cooling process (Fig.  2a ); instead, it is sensitive to the hottest part of the run where thermal emittance is the brightest. Source data for panels ( d )–( f ) are provided as a Source Data file.

Despite its weak scattering power, the use of intense XFEL pulses enabled the collection of high-quality XRD images from H 2 O using a single X-ray pulse even at the lowest X-ray transmission (0.3%). Due to the short duration of individual pulses ( < 50 fs), diffraction occurs before the thermal expansion of the lattice, providing an essentially instantaneous snapshot of the sample before it is heated by the XFEL beam. XRD from the first pulse in the train therefore probes the room temperature state, and was used for pressure determination and to confirm the integrity of the sample after the previous heating run. On longer timescales, energy transferred to the lattice via electron-phonon thermalization processes results in sub-ns heating followed by more gradual cooling via thermal conduction 38 , 40 , where cooling rates depend on material properties (i.e. thermal conductivity) and geometry of the sample/coupler assembly. Serial pulse irradiation produces incremental heating with a saw-tooth like temporal temperature profile until a limiting state of thermal balance is achieved 40 , with each XRD image providing a snapshot of the sample as it cools from the hot state created by the previous pulse. Finite Element Analysis (FEA) simulations (Fig.  2 ) suggest that indirectly heated materials experience reduced thermal oscillations due to the damping effect of heat diffusion; however, oscillations are still significant in the vicinity of the coupler. Overall, this dynamic heating approach reduces the total heating time to ~130 µs per run, which is ~10,000 times shorter than typical XRD exposure times at synchrotron sources 12 , 13 , 15 .

The model simulates X-ray irradiation of the Cu coupler in DAC 8 (run 533). a Temperature evolution at the coupler edge, in the crucible center, and 0.5 µm from the edge of the coupler. Although the coupler temperature undergoes continuous oscillations, these are strongly damped in the center of the crucible and the temperature stabilizes after ~20 pulses. However, temperature oscillations in the H 2 O are still significant in the vicinity of the Cu coupler (~500 K at 0.5 µm from the coupler edge). b Temperature distribution in the sample at the time of the 82nd XFEL pulse, showing conditions detected with XRD. Black lines show possible boundaries between ice VII and SI-ice, taken to be at 1500 K 12 or 2000 K 13 . The XFEL beam is incident from below. Temperatures in ( a ) are reported at the blue, green, and orange points. Source data for panel ( a ) are provided as a Source Data file.

Observation of body-centered cubic superionic ice

Evidence of SI-bcc was observed in data collected from 9 DACs between 26 and 69 GPa (Supplementary Table  1 ). The evolution of XRD patterns collected during irradiation was similar for all runs (Supplementary Figs.  2 and 3 ), illustrated here by a dataset collected from an Ag doughnut-type coupler at 69.3 GPa (Fig.  3 ). In the Ag run, heating resulted in a splitting of the ice VII and Ag reflections which increased during the first ~20 pulses, with both sets of reflections shifting to lower diffraction angles due to thermal expansion. At the same time, the growth of a new reflection at ~19.2° from pulse 3 onwards is consistent with the expected d -spacing of the (110) SI-bcc reflection at this pressure 12 , 13 . No other SI-bcc reflections could be observed due to the limited 2θ detector coverage, which prevented a definitive identification of the crystal structure. However, the possibility that this peak originated from SI-fcc was ruled out because of the absence of the (200) fcc reflection, which would fall within the angular range of our detector, and the fact that indexing this new peak as the (111) fcc reflection would imply an unphysical density almost identical to cold ice VII at the start of the run (Supplementary Table  2 ). The observation of SI-bcc alongside hot and cold ice VII is indicative of a significant spatial temperature gradient in the probed sample volume, which is typical in such X-ray heating experiments 41 . Although the SI-bcc (110) reflection overlaps with the weak signal from the (101) Re reflection, it is clearly identifiable in the 2D diffraction images due to the different texture of their Debye Scherrer rings. The possibility that the spots originated from the recrystallization of Re at high temperatures was ruled out because the texture of the (100) Re ring remained unchanged during the run, and because the spots identified as SI-bcc were absent in the first pulse pattern of the subsequent run.

Data were collected using an Ag doughnut coupler (DAC 8) and an X-ray beam diameter of <8 µm FWHM. a , b Integrated XRD patterns and ( c – h ) unwrapped (2θ-φ) XRD images collected during irradiation with 300 XFEL pulses at 29% transmission (run 505). In ( a ), darker shades correspond to higher intensity. In ( c – h ), lighter shades correspond to higher intensity. Heating results in a splitting of the ice (110), Ag (111), and Ag (200) reflections, which is indicative of two distinct temperatures in the probed volume, predominantly originating from the lack of thermal insulation between the H 2 O and the diamond anvils. Panel ( a ) illustrates how heating occurs during the first ~20 pulses, after which the diffracted signal from H 2 O remains essentially constant. In ( d ), the diameters of the orange circles are unrelated to individual spot sizes. Source data are provided as a Source Data file.

Following the disappearance of the hot ice VII reflection around pulse 20, no significant changes were observed for the remainder of the run (Fig.  3a and Supplementary Fig.  4 ), suggesting that the system reached a balance between X-ray heating and heat loss via thermal conduction 40 . Based on this observation, images from pulses 51-300 were summed and integrated to produce a 1D diffraction profile from the hot sample (Fig.  4a ) in which the (110) SI-bcc reflection is clearly visible alongside the broad, hot (110) ice VII reflection. Due to the spotty nature of the H 2 O signal, it was possible to analyze the unwrapped (2θ-φ) 2D diffraction images using a spot-finding algorithm (see Methods) to determine the 2θ position of H 2 O diffraction spots in each image, which was used to produce a histogram showing the total number of ice spots in images collected from pulses 51-300 (Fig.  4a and Supplementary Movie  1 ). The resultant histogram is in excellent agreement with the summed pattern after subtracting the Re signal, validating this approach. This analysis procedure was repeated for all runs from this sample in which SI ice was observed, and the datasets were combined to produce a single integrated profile and histogram (Fig.  4b ). Although these runs were collected with different X-ray transmissions (25.5–37%) which are expected to produce different temperatures, the SI-bcc reflection is clearly distinct from that of ice VII, confirming that the observed peak separation is not an artifact relating to the large temperature gradient within the heated area. The narrow width of the SI reflection is most likely due to the narrow temperature stability field of this phase at 69 GPa, which is above the upper pressure limit of the SI-bcc stability field reported in previous work 12 , 13 .

Data are shown for ( a ) run 505, and for ( b ) all runs collected from the Ag coupler in DAC 8 where SI was observed. The construction of the histogram for run 505 is illustrated in Supplementary Movie  1 . When the Re contribution (estimated from the first pulse pattern) is subtracted from integrated patterns, they are in good agreement with the histogram. Source data are provided as a Source Data file.

Observation of face-centered cubic superionic ice

The results from the Ag coupler in DAC 8 (Figs.  3 and 4 ) are compared to runs collected from Au and Cu couplers in the same DAC (Supplementary Fig. 5 ), which were analyzed using the summed and spot-finding methods described above (Fig.  5 ). The SI-bcc reflection is clearly visible in both the summed XRD pattern and histogram produced from the Au runs, and the lattice parameters determined using each approach are in excellent agreement with each other ( a  = 2.856 Å and 2.854 Å from the summed pattern and histogram, respectively), and with those determined from the Ag runs ( a  = 2.844 Å and 2.843 Å) where the pressure was 5.2 GPa higher. Although the summed pattern from the Cu runs is difficult to interpret due to the broad background originating from the detector behavior at high signal levels, the SI-bcc reflection is clearly visible in the histogram alongside a second, well separated, lower-angle reflection. Indexing this peak as the (111) SI-fcc reflection determines a density of 2.618 g/cm 3 , which is almost identical to the SI-bcc density of 2.619 g/cm 3 , in agreement with previous work which found that both SI phases can be described by the same equation of state (EoS) 13 . In addition to the observation of the (111) SI-fcc reflection in the 90 and 100% transmissions runs (Fig.  6 ), the (200) SI-fcc reflection is also present in the 80% and 100% runs (Supplementary Fig.  6 ), further confirming the nature of this phase. On subsequent re-examination of the Ag data, a small number of isolated SI-fcc diffraction spots were located in several XRD images from 2 different runs (Supplementary Fig.  7 ), confirming that the fcc reflections in the Cu runs originated from H 2 O rather than a chemical reaction between the sample and the coupler. However, no evidence of SI-fcc was located in any images from the Au runs from this DAC.

For each sample, histograms were compiled from XRD data collected from pulses 51-300 in runs where SI ice was observed. The width of each bin is 0.01 degrees. Histograms are compared with integrated XRD patterns produced from the summed Adaptive Gain Integrated Pixel Detector images of the hot (pulses 51–300) and cold (pulse 1) sample. The y -axis refers to the histogram plot, and the integrated patterns from the hot and cold sample were normalized to a single arbitrary scaling factor for the figure. The coupler material is specified in each case. The high-angle signal in the DAC 3 and 5 runs are from the hot coupler. With the exception of DAC 1 and DAC 2, in which the coupler was in the form of a dispersed nanopowder, all couplers were of a doughnut-type design. Source data are provided as a Source Data file.

Data were collected during irradiation of the embedded Cu doughnut coupler in DAC 8 using an X-ray beam size of <8 µm FWHM. Integrated XRD data are shown from runs ( a ) 532 and ( b ) 536, and single pulse, unwrapped (2θ-φ) XRD images from runs ( c ) 532 and ( d ) 536 are shown for a reduced 2θ range. In ( a – b ), darker shades correspond to higher intensity, whereas in ( c – d ), lighter shades correspond to higher intensity. The data shown in ( a ) and ( c ) were collected using 60% transmission, and the (110) SI-bcc reflection is observed from pulse ~5 onwards (see insert), The SI-bcc diffracted signal is predominantly from several intense spots, such as the one highlighted in ( c ). The data in ( b ) and ( d ) were collected at 100% transmission, and both SI phases (bcc and fcc) are observed. Source data are provided as a Source Data file.

The difficulty in forming SI-fcc in these runs is surprising when SI-bcc formed so readily. Although SI-bcc is stable at lower temperatures than SI-fcc (Fig.  7 ), these runs were performed at pressures of 64-69 GPa, which are close to (or above) the previously-reported upper limit of the SI-bcc pressure stability field. In particular, Weck et al. 12 did not observed SI-bcc above 57 GPa, and although Prakapenka et al. 13 reported a single SI-bcc data point at 67 GPa and ~2000 K, there is no evidence of SI-bcc in their 2500 K diffraction pattern at 67 GPa, despite clear evidence of SI-fcc and ice VII. Although the limited azimuthal coverage of the AGIPD may account for the absence of SI-fcc in certain runs, it is unlikely to be the only contributing factor given the consistently strong signal observed from SI-bcc. Instead, the difficulty in forming SI-fcc points to an intrinsic feature of the pump-probe X-ray heating scheme and the specific coupler materials and geometry used in these runs, combined with a large energy barrier to form SI-fcc. As XRD provides a snapshot of the sample during cooling, the sample temperature is heavily dependent on heat distribution to the surrounding media, and the high thermal conductivities of Au, Ag, and Cu (318, 429, and 401 W/mK at ambient conditions, respectively 42 ) limit heating of H 2 O by fast heat transfer away from the sample. Although the diffracted signal from hot Ag (Supplementary Fig.  8 ) suggests that a portion of the coupler remained close to its melting point after 443 ns, the coupler reflections in the Cu and Au runs remain essentially unchanged from the cold pattern (Supplementary Fig.  9 ) - despite SOP determining an average coupler temperature (Supplementary Table  3 ) which is well above the previously-reported lower temperature limit of SI-fcc 12 , 13 – suggesting that the coupler cooled significantly between subsequent XFEL pulses. These observations are supported by FEA simulations (Fig.  2a ) which suggest that the Cu becomes colder than the sample during the cooling process. Enhanced cooling in the real sample compared to the FEA is attributed to the significant reduction in the H 2 O insulation layer thickness at high pressure, potentially leading to direct contact between the coupler and the diamond anvil.

Data points correspond to the average SOP temperature during the run, and the error bars show the standard deviation. Source data are provided as a Source Data file. Thermal emission was not detectable for all samples, and data points are shown for runs in which thermal emission was observed. Due to the low emissivity of H 2 O, SOP measures thermal emission from the coupler surface, which does not necessarily correspond to the temperature in the H 2 O sample. Our data points are compared to the phase diagram of H 2 O reported in previous studies. The text labels indicate the phase stability regions reported in ref. 13 . For simplicity, we do not make any distinction between ice VII and VII’ in the main text. SI-bcc and SI-fcc data points from previous static 12 , 15 , 50 and shock compression 14 , 29 studies are included for comparison, as well as ice VII data points from shock compression work 14 , 29 and the H 2 O melting curves from ref. 15 , 32 . Ice VII data points from static compression studies are not included to avoid overcomplicating the figure. The data points from ref. 15 . indicate the SI-bcc/ice VII phase line determined on isothermal compression.

Optimal parameters for indirect X-ray heating

The summed XRD profiles and diffraction spot histograms are shown in Fig.  5 for DACs 1 - 8. The ice VII and SI-bcc peaks are very clearly separated at all pressures, particularly in the histogram plots, due to the lower photon energy (18 keV) compared to previous DAC experiments (>30 keV). Bulk heating is particularly pronounced in runs collected from the Rh doughnut-type coupler in DAC 9 (Supplementary Fig.  10 ), evidenced by the strong SI-bcc signal and almost complete disappearance of ice VII signal, most likely due to a combination of optimal geometrical parameters and coupler properties. In particular, the lower thermal conductivity of Rh (150 W/mK at ambient conditions) compared to Au, Ag, and Cu is expected to reduce heat dissipation in the unheated coupler, resulting in a more uniform temperature distribution in the sample. However, although Rh was the most promising coupler in terms of heating efficiency, the appearance of a number of unidentified diffraction spots after the first observation of SI-bcc in some runs suggests that Rh reacts with SI H 2 O. Data from DAC 9 were therefore not analyzed using the spot finding algorithm, but are presented to illustrate that uniform heating of low-Z samples using a high-Z coupler is possible by careful choice of X-ray parameters, sample geometry, and material parameters. Although chemical reactivity was a general problem for Rh couplers, one run from DAC 7 was included in the analysis because reaction products were not observed until the end of the run, after all traces of SI-bcc had disappeared.

Absence of face-centered cubic superionic ice at low pressures

Examination of individual XRD images from the lower pressure (<60 GPa) runs revealed a single (111) SI-fcc crystallite (Supplementary Fig.  11 ) at 49.9 GPa (DAC 6). Although this does not provide conclusive evidence for the existence of SI-fcc, it is consistent with the expected stability field of this phase reported by both ref. 13 , 12 and so was included in further analysis. No evidence of SI-fcc was observed in data collected from DACs 1-5 (26–38 GPa); however, the dramatic reduction in the H 2 O diffracted signal in the highest fluence runs collected from DAC 4 (~38 GPa) indicates that the bulk of the sample had melted. This is supported by SOP measurements, which determined the average coupler temperature to be above the ice melting temperature at this pressure. Melting is particularly striking in the 90% Ag run due to the strong signal from ice VII at the start of the run (Fig.  8 and Supplementary Movie  2 ), which almost completely disappears by pulse 30. Individual diffraction spots from both bcc phases reappear throughout the run, suggestive of solid-fluid coexistence. Although no evidence of diffuse scattering from the fluid was observed due to the weak scattering power of H 2 O and the limited azimuthal coverage of the detector, the possibility that the disappearance of the H 2 O solid signal originated from chemical reactivity or sample loss was ruled out by the strong ice VII signal and absence of chemical reaction products in the first pulse pattern of the subsequent run (Supplementary Fig.  12 ).

Data were collected using 90% X-ray transmission from the embedded Ag coupler in DAC 4 (36.7 GPa) using an X-ray beam size of <8 µm FWHM (run 917:17). Lighter shades correspond to higher intensity. Source data are provided as a Source Data file. The significant reduction in the intensity of the ice VII/SI-bcc diffracted signal during the run is attributed to melting of H 2 O. No evidence of the SI fcc (111) reflection was observed, which would be expected to be present at approximately 18.4°. Unwrapped images from the full run are shown in Supplementary Movie  2 .

The absence of SI-fcc in the 38–40 GPa runs is surprising due to the strong evidence for melting and fluid/SI-bcc coexistence, and the fact that previous work 13 observed SI-fcc at pressures as low as 29 GPa. Instead, our results are in agreement with previous CO 2 laser heating studies 12 , 15 which did not observe SI-fcc during heating at pressures up to 45 GPa, but instead observed SI-bcc to coexist with the fluid. In order to resolve the discrepancy between results obtained using different heating techniques (X-ray and CO 2 vs. IR laser heating), it is necessary to consider the differences and similarities between each experimental approach. The results do not appear to be correlated with the heating method (i.e. direct or indirect heating), as both Prakapenka et al. 13 and this work performed indirect heating using embedded absorbers and obtained different results. Heating durations of ≥5 s in the CO 2 and IR heating experiments are 4 orders of magnitude longer than XFEL heating (~130 µs), which seemingly suggests that timescale is not a factor. However, as the output power of CO 2 lasers is typically controlled by pulse width modulation which produces fluctuations in laser intensity 31 , the time that the sample lies within SI-fcc stability field could be reduced by the resultant thermal fluctuations which could potentially cause the sample to oscillate across the SI-fcc phase boundary. Although SI-fcc may be thermodynamically stable below the melting line, previous theoretical studies calculated a lower solid/fluid interfacial free energy for the SI-bcc lattice in comparison to SI-fcc 43 , suggesting that the fcc lattice may have a longer nucleation time than SI-bcc when crystallizing from the fluid. We therefore propose that the absence of SI-fcc in the 38–40 GPa XFEL heating runs is due to short heating timescales and the P-T path associated with XFEL pump-probe experiments, combined with kinetic hindrance associated with the formation of SI-fcc from the melt. This hypothesis is consistent with the results of IR laser heating experiments using the same approach as Prakapenka et al. (Supplementary Fig.  13 ), which were performed at the GSECARs beamline at the Advanced Photon Source using Au flakes as a laser absorber. After initially heating H 2 O above its melting temperature, molten ice was first observed to coexist with SI-bcc when the laser power was reduced, whereas the observation of SI-fcc on further decrease of the laser power coincided with the disappearance of the diffuse scattering signal. The observation of liquid/SI-bcc coexistence is attributed to localized heating and melting of the H 2 O in the vicinity of the Au flakes, which drives the movement of the Au particles and results in rapid melting and recrystallization of H 2 O. Consequently, the sample does not remain in the SI-fcc stability field long enough for SI-fcc to form. Similarly, thermal fluctuations in the vicinity of the coupler in the XFEL heating experiments (Fig.  2a ) due to the pulsed nature of the XFEL beam can account for fast recrystallization of SI-bcc from the fluid in the 90% transmission run collected from DAC 4 (Fig.  8 ), suggesting an approximate lower bound of 443 ns for the nucleation time. The observation of SI-fcc at higher pressures in the XFEL experiment is attributed to the higher melting temperature of H 2 O at this pressure and the fact that the average coupler temperature lies in the stability field of SI-fcc, which avoids transforming a portion of the sample into the fluid phase. This is consistent with the observation of large SI-fcc crystallites at the same azimuthal position for multiple frames in the 100% transmission run collected from DAC 8 (Fig.  6 ), rather than small, recrystallizing spots which are typically formed during fast quenching. The possibility of timescale- and path-dependent transitions in high-temperature H 2 O should therefore be taken into account when comparing results obtained using different experimental techniques; in particular, considering the conflicting results of recent shock compression experiments (Millot et al. observed SI-fcc near 160 GPa and 3200 K 14 , whereas Gleason et al. 29 saw SI-bcc as pressures as high as 207(10) GPa at 5500(500) K).

Density of superionic ice

The histograms in Fig.  5 were used to determine the densities of both SI phases, which are compared with the results of previous studies in Fig.  9 . Our SI-bcc points are in good agreement with the results previous studies 12 , 13 ; our highest-pressure data points lie closer to the Prakapenka et al. 13 EoS which includes a thermal pressure correction, despite the fact that such a correction was not included in our analysis, whereas our lower-pressure points lie closer to their uncorrected curve. The SI-fcc densities determined in this study are in excellent agreement with those of SI-bcc at the same pressure, in agreement with Prakapenka et al. 13 , but lie at lower densities than those reported by Weck et al. 12 at the SI-bcc/SI-fcc transition temperature. Weck et al. 12 reported the density of SI-fcc to be strongly temperature dependent, and our SI-fcc data are in better agreement with the density they report at 57 GPa and 1927 K, which is ~500 K above their reported SI-bcc/SI-fcc transition temperature. Although they report a corresponding SI-bcc density for the 57 GPa run which is significantly larger (~2.67 g/cm 3 ) 33 than our measured SI-bcc density at the same pressure (~2.55 g/cm 3 ), our data are in good agreement with the SI-bcc density determined from the 1927 K XRD pattern in Fig. S4 of their supplementary material (~2.55 g/cm 3 ), suggesting that the reported SI-bcc density actually corresponds to that of expanded ice VII. The possibility that SI-fcc was not observed in our XFEL experiments until ~500 K above the transition temperature is intriguing considering the difficulty in forming SI-fcc, and is consistent with a large energy barrier associated its formation. However, due to the lack of accurate temperature measurements in our XFEL experiments, it is not possible for us to resolve discrepancies between previous work. Overall, the large density difference between ice VII and SI-bcc reported in this work contrasts with the 108 GPa SI-bcc data point from the shock compression study of Gleason et al. 29 , which suggests that the two phases have similar densities. However, as their SI-bcc data point lies outside the SI stability field reported by ref. 13 , it is possible that that this sample was actually in the ice VII stability field.

The data points from this work show the SI-bcc and SI-fcc densities calculated from the histograms in Fig.  5 . Source data are provided as a Source Data file. The data point from DAC 9 (34.2 GPa) is included to illustrate the agreement with other data, despite weak evidence of chemical reactivity in this sample. Our results are compared with SI ice data from previous DAC experiments 12 , 13 , 15 , which are identified as using laser heating (LH-DAC) or resistive heating (RH-DAC) techniques. Ice VII data from ambient temperature 12 , 13 , 51 , 52 and high temperature 35 DAC experiments, shock compression experiments 14 , 29 , as well as data from the high temperature fluid 53 , are shown for comparison. In addition to the data points taken from the main paper of Weck et al. 12 , which indicate the SI-bcc and SI-fcc densities at the transition temperature, their SI-fcc data point at 57 GPa and 1927 K is also included to indicate the volume of thermally-expanded SI-fcc at higher temperature.

In conclusion, an indirect XFEL heating technique was used to investigate the structural properties of SI ice, demonstrating that stepwise XFEL heating is a viable method to study low-Z materials such as H 2 O at high pressures and temperatures. Evidence of SI-bcc was identified in a large number of runs performed at 27-69 GPa, illustrating that this approach is able to detect isostructural transitions, and SI-fcc was observed in runs ≥50 GPa. The large volume of XRD data collected using a pulse-resolved, MHz detector, combined with the highly textured nature of the SI-bcc diffraction signal, motivated the development of a new data analysis approach in which the identification of diffraction from individual crystallites in XRD images was used to enhance the signal from high-temperature SI phases and determine their density as a function of pressure. No evidence of SI-fcc was observed in lower pressure runs, despite clear evidence of melting and the simultaneous observation of SI-bcc and fluid at ~40 GPa. Based on previous theoretical studies which calculated a lower solid/fluid interfacial free energy for the SI-bcc lattice in comparison to SI-fcc 43 , and considering prior observations of SI-fcc forming at these P-T conditions upon heating 13 , we attribute the absence of SI-fcc in these experiments to the short heating timescale combined with the P-T path of the pump-probe approach in which SI ice is formed on cooling from the melt. The results may have important implications for the stability of SI phases in solar and extrasolar ice-rich planets during dynamical freezing such as in internal convection processes, where the preferential crystallization of SI-bcc from the fluid may result in different physical properties of the solid ice (e.g. electrical and thermal conductivity) across the same internal layer that in turn, may affect interior dynamics and magnetic fields.

Sample preparation

H 2 O samples were loaded into a total of 9 symmetric DACs (DACs 1–9) with standard design diamonds mounted on the upstream side and Boehler Almax diamonds facing downstream. Microscope images of the samples before the XFEL experiment are shown in Fig.  1a and Supplementary Fig.  1 , which were collected after the sample was compressed to the final pressure for data collection. A total of 5 different coupler materials were employed (Au, Ag, Cu, Rh, and Fe 3 O 4 ) in different coupler geometries (nanopowder, doughnut, and embedded doughnut) which were designed with the aim of minimizing the temperature gradient in the indirectly heated H 2 O samples (for preparation details see Supplementary Note  1 ). With the exception of DAC 7, all samples were loaded without a thermal insulation layer, relying instead on a self-insulating H 2 O layer close to the diamonds to act as a thermal barrier. This avoided the need for commonly-used insulation layers such as Al 2 O 3 , LiF etc., which can complicate the interpretation of diffraction patterns and/or result in unwanted chemical reaction products. After loading, samples were pre-compressed to the desired pressure for the XFEL experiment

Experimental details: sample screening at PETRA III

After compression to the desired pressure for the European XFEL experiment, samples were screened at the P02.2 beamline at the PETRA III synchrotron source to confirm the integrity of the sample loading using XRD. The screening was performed using 25.6 keV X-rays focused to 3(v) × 8(h) µm 2 (FWHM) using a series of compound refractive lenses (CRLs), and XRD data were collected using an XRD1621 area detector (PerkinElmer). After the XFEL experiment, a 2D diffraction map collected from DAC 8 found no evidence of chemical contamination. This was performed at the P02.2 beamline using 42.7 keV X-rays focused to 2(v) x 2(h) µm 2 (FWHM) using Kirkpatrick–Baez mirrors, and data were collected using an XRD1621 area detector.

Experimental details: European XFEL parameters

X-ray heating experiments were performed at the High Energy Density (HED) Instrument 44 at the European XFEL using the dedicated DAC platform in Interaction Chamber 2 36 . The experiment was performed using an X-ray photon energy of 18.047 keV and a 2.2 MHz intra-train repetition rate, which corresponds to a 443 ns spacing between consecutive pulses, where the photon energy was calibrated using the HIgh REsolution hard X-ray single-shot (HIREX) spectrometer 45 . X-rays were focused using a series of CRLs using three different configurations to achieve focal spot sizes of <8 µm, 13 µm, and 26 µm (FWHM), where the beam size was estimated from edge scans using a polished W rod. Accurate determination of the beam diameter for the smallest focal spot size was not possible based on the edge scan data due to erosion of the W rod.

Experimental details: X-ray diffraction at European XFEL

Pulse-resolved XRD data were collected using a 500k AGIPD detector positioned outside of the vacuum chamber at a sample-to-detector distance (SDD) of ~430 mm, which provided an angular coverage of ~7.5 to 27 degrees ( q  = 4.27-1.20 Å −1 ). The detector geometry (SDD, tilt, and rotation) was calibrated using a Cr 2 O 3 diffraction standard (NIST SRM 674b) using the Dioptas software 46 . Radial integration of diffraction images was performed using Dioptas and azimuthally unwrapped (2θ-φ) diffraction images were produced using FIT2D 47 . Prior to integration, the intensity of individual diffraction images was scaled using the pulse-resolved intensity and position monitor (IPM) 36 positioned upstream of the sample to account for fluctuations in the pulse energy across the pulse train, and all images within the run were normalized to the mean IPM value within the run to allow for comparison of runs collected at different levels of X-ray attenuation. The X-ray fluence incident on the sample during the run was controlled using a series of solid attenuators, which enabled the X-ray transmission to be varied from 0.3 to 100%. The pulse energy on target was determined using the IPM, which was calibrated using an X-ray gas monitor (XGM) 36 at the start of the experiment.

Alignment of the sample to the X-ray beam was performed based on visual observation using an optical imaging system. This alignment method resulted in an offset in the sample position along the X-ray beam direction with respect to the diffraction calibrant due to refraction from the downstream diamond anvil, which was corrected by changing the SDD used in the detector calibration based on the measured diamond thickness and refractive index. The X-ray position on the optical camera was determined by exposing an area on the gasket for several seconds at low fluence, which produced a small dark region resulting from X-ray damage. This approach was found to be sufficient to align the XFEL beam with small holes (6–22 µm diameter) in doughnut couplers, where the XFEL beam was positioned at the center of the hole to maximize the diffracted signal from the H 2 O sample. However, the positional jitter in the XFEL beam position (approximately equal to the X-ray focal spot size) meant that the beam position varied from run to run, which could potentially result in different degrees of X-ray heating in subsequent runs due to the large difference in absorption lengths of H 2 O and the mid/high-Z couplers.

Experimental details: streaked optical pyrometry

The temporal evolution of the temperature profile during the heating run was determined from streaked optical pyrometry (SOP) measurements performed using a streak camera (C13410-01A, Hamamatsu) coupled to an optical spectrometer (IsoPlane 160, Princeton Instruments), which collected thermal emission from a 50 µm diameter region on the upstream side of the sample. Full details of the SOP system are given in ref. 49 . In all cases, data were collected using a 200 µs streak window to cover the entire duration of the 132.9 µs long X-ray pulse train. SOP data collected using a low X-ray fluence were dominated by a fluorescence signal originating from the diamond anvils and/or H 2 O media, which was most prominent in the short wavelength (~500 nm) range. The presence of thermal emission at higher X-ray fluence was identified by a discontinuous increase in the total SOP intensity as a function of incident pulse energy when all runs from the same coupler were compared. For runs in which thermal emission was observed, the fluorescence signal was removed by subtracting the fluorescence-only spectrogram collected at the highest X-ray transmission. After the fluorescence correction was applied, the temperature was determined by fitting a Planck function to the 600–775 nm wavelength region of the thermal emission spectrum from each 9.1 µs temporal window assuming gray-body emission. The reliability of each temperature measurement was evaluated based on the criteria outlined in ref. 49 . Examples of SOP data treatment, including the fluorescence correction, are shown in Supplementary Fig.  14 . A summary of SOP temperatures from all runs are given in Supplementary Table  3 , and correspond to the average over the entire run. Due to the low emissivity of H 2 O in the temperature region investigated in this work, SOP provided a measurement of the coupler surface temperature at the hot spot, rather than a direct measurement of the sample temperature, which is expected to be lower than that of the coupler (Fig.  2a ). As the total radiated energy is proportional to T 4 , the strongest contribution to the thermal radiation spectrum is from the hottest region on the coupler surface. Thermal emission was not detectable for all samples, which we attribute to variations in the volume of heated coupler material due to a combination of factors such as X-ray focal spot size and coupler geometry.

Experimental details: IR laser heating at GSECARS

IR laser heating experiments were performed at the GSECARS undulator beamline (sector 13, APS, ANL). The experiment was performed using 37.07 keV X-rays focused to 3 ×4 µm 2 (FWHM), and XRD data were collected using a MAR-165 CCD (charge-coupled device). Doubled-sided, coaxial heating of samples was performed using a near-IR (1064 nm) laser with a 10 µm diameter flat-top focal spot 49 . The temperature was determined using spectroradiography measurements performed using a Princeton grating spectrometer (300 mm focal length) combined with PIXIS and PI-MAX3 CCD array detectors, and thermal emission was collected from both sides of the heated sample. For this experiment, the H 2 O sample was thermally insulated from the diamond by a layer of SiO 2 , and small flakes of Au were used as the laser absorber.

Data analysis: X-ray diffraction

Out of a total of 400 runs collected from H 2 O samples, evidence of SI-bcc was identified in 68 runs (Table SI) which were collected using a range of different coupler materials, geometries, and X-ray transmissions. In all cases, the (110) SI-bcc reflection was clearly distinct from the broad, hot ice VII reflection, consistent with the expected behavior for an isostructural transition. Two different approaches were used to evaluate the XRD patterns collected from the hot sample. In the first approach, images collected from pulse 51–300 from each run contained SI were summed to produce a single integrated XRD profile for each sample. For DACs in which multiple couplers were used (DACs 4 and 8), individual diffraction profiles were produced for each coupler type. For each sample, the cold pattern was produced by summing the first pulse XRD images from the runs used for data analysis, which determined the average pressure across all runs. In order to avoid systematic uncertainties introduced by the choice of EoS for different coupler types, the sample pressure was estimated based on the position of the (110) ice VII reflection in the cold pattern using the EoS of Prakapenka et al. 13 . The result of the summed approach is illustrated for DAC 1 in Supplementary Fig.  15 .

For construction of the histograms shown in Fig.  5 , a spot finding algorithm was used to identify the 2θ-φ positions of individual diffraction spots in the unwrapped (2θ-φ) diffraction images using a custom python code. First, a threshold of \({\bar{i}}_{{bk}}+n{\sigma }_{{i}_{{bk}}}\) was applied, where \({\bar{i}}_{{bk}}\) and \({\sigma }_{{i}_{{bk}}}\) are the mean and standard deviation, respectively, of the background intensity of a region on the detector in which no diffraction lines were observed. A value of n  = 6 was used in all cases except for the Cu coupler in DAC 8, where n  = 5 was used due to an increase in detector noise at the highest X-ray fluence due to issues related to gain switching. Individual reflections were identified as connected regions in the threshold image, and those with a pixel size of <2 were assumed to due to detector noise and discarded. The number of local maxima was computed for each of the identified regions. If multiple local maxima were present in a single identified region and separated by at least 3 pixels, the region was split into multiple reflections using a watershed algorithm. Finally, the angular coordinates (2θ-φ) of each reflection was determined from its center of mass, and the resultant list of 2θ positions was used to produce the histogram. The value of n was chosen by visual inspection of the number of spots located in the image (Supplementary Fig.  16 ). However, although the choice of n determined the number of spots which were identified, histograms produced using different values of n were found to be in good agreement with one another (Supplementary Fig.  17 ).

Finite Element Analysis

Finite Element Analysis (FEA) of sample heating, accounting for sample geometry, the materials used and their thermochemical parameters at relevant high pressure conditions, were performed using previously described techniques 38 , 40 , 41 , 48 . FEA was used primarily in planning experiments, to establish beam properties and sample designs to avoid coupler melting and damage, achieve sufficiently high temperature in the water sample, optimize heat transfer to the water, and minimize temperature gradients in the crucible. While major predictions of the models were confirmed by pyrometry measurements during experiments, including absolute temperatures reached and the achievement of a quasi-steady state at longer timescales, models predict a gradual rise in temperature at early times which contrasted with an observed decrease with time from elevated initial temperature. This effect could be related to beam misalignment with holes, coupler melting and movement as well as changes in sample optical properties at high temperature 41 . Due to the use of longer sweep windows with lower time resolution in SOP, the individual heating and cooling events seen in the models are not resolved 48 . For the model in Fig.  2 , representative high-pressure parameters of thermal conductivity k , heat capacity at constant pressure C P , density ρ , and absorptivity α were used for the H 2 O sample ( k  = 20 W m −1  K −1 , C P  = 3050 J kg −1  K −1 , ρ  = 2694 kg m −3 , α  = 201 m −1 ) and the Cu coupler ( k  = 450 W m −1  K −1 , C P  = 472 J kg −1  K −1 , ρ  = 9500 kg m −3 , α  = 4.41 × 10 4  m −1 ), along with standard parameters for the gasket and diamonds 40 .

Data availability

The DOI for the original European XFEL data is: https://doi.org/10.22003/XFEL.EU-DATA-002590-00 , and will be publicly available after the embargo period of 3 years. Source data are provided with this paper.

Code availability

The computer code used to generate the results reported in this study is available from the corresponding author upon request.

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Acknowledgements

We acknowledge European XFEL in Schenefeld, Germany, for provision of X-ray free-electron laser beam time at Scientific Instrument HED (High Energy Density Science) and would like to thank the staff for their assistance. These data were collected as part of a DAC community proposal (#2590, by McMahon and Husband: https://doi.org/10.22003/XFEL.EU-DATA-002590-00 ). The authors are indebted to the HIBEF user consortium for the provision of instrumentation and staff that enabled this experiment. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research were carried out at PETRA III (beamline P02.2). V.B.P. and S.C. acknowledge the support of GeoSoilEnviroCARS and National Science Foundation – Earth Sciences (EAR - 1634415). We acknowledge E. Shevchenko (CNM, ANL), who synthesized the nano-Fe 3 O 4 samples. J.D.M. acknowledges support from AWE CASE studentship P030463429. Support is acknowledged from the U.K. Engineering and Physical Sciences Research Council (EPSRC) Grant Nos. EP/R02927X/1 (E.J.P. and M.I.M.) and EP/P024513/1 (R.S.M). M.F. Acknowledges DOE FES funding FWP100182. Y.L. is grateful for support from the Leader Researcher programme (NRF-2018R1A3B1052042) of the Korean Ministry of Science and ICT (MSIT). This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344 (H.C.). This research was supported through the European Union’s Horizon 2020 research and innovation Programme (ERC grant 864877, H.M., and 101002868, R.S.M.) as well as UKRI STFC grant ST/V000527/1 (H.M.). A.F.G. and E.E. are grateful for the support of Carnegie Science and NSF EAR-2049127. A.F.G. is grateful for the support of NSF CHE- 2302437. S.N. and L.A. acknowledge financial support from Sorbonne University under grant Emergence HP-XFEL. We acknowledge support from the Deutsche Forschungsgemeinschaft (DFG) Research Unit FOR 2440 grants SA2585/5-1 (R.J.H, A.M., C.S.V., and H.P.L) and AP262/2-2 (K.A.).

Open Access funding enabled and organized by Projekt DEAL.

Author information

Present address: Bayerisches Geoinstitut, Universität Bayreuth, Universitätsstraße 30, Bayreuth, Germany

V. Cerantola

Present address: Department of Earth and Environmental Sciences (DISAT), University of Milano-Bicocca, Milan, Italy

Present address: School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea

Present address: Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot, Oxfordshire, UK

Present address: Synergetic Extreme Condition High-Pressure Science Center, State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun, China

Present address: X-Spectrum GmbH, Luruper Hauptstraße 1, Hamburg, Germany

Authors and Affiliations

Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany

R. J. Husband, H. P. Liermann, C. Strohm, H. Graafsma, H. Hwang, T. Laurus, X. Li & S. Stern

SUPA, School of Physics and Astronomy, and Centre for Science at Extreme Conditions, The University of Edinburgh, Edinburgh, UK

J. D. McHardy, R. S. McWilliams, O. B. Ball, E. Pace & M. I. McMahon

Carnegie Science, Earth and Planets Laboratory, Washington, DC, USA

A. F. Goncharov & E. Edmund

The University of Chicago, Center for Advanced Radiation Sources, Chicago, IL, USA

V. B. Prakapenka & S. Chariton

European XFEL, Schenefeld, Germany

Z. Konôpková, K. Appel, V. Cerantola, A. Dwivedi, M. Nakatsutsumi, J. Sztuk-Dambietz & U. Zastrau

Universität Münster, Institut für Mineralogie, Corrensstraße 24, Münster, Germany

C. Sanchez-Valle & A. Mondal

SLAC National Accelerator Laboratory, California, USA

Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Sorbonne Université, Paris, France

L. Andriambariarijaona & S. Ninet

Institute of Radiation Physics, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstraße 400, Dresden, Germany

Lawrence Livermore National Laboratory, Livermore, CA, USA

R. Briggs, A. L. Coleman & H. Cynn

Department of Earth Sciences, University of Oxford, Oxford, UK

J. Buchen, E. Koemets & H. Marquardt

Department of Earth System Sciences, Yonsei University, Seoul, Korea

J. Choi & Y. Lee

CEA, DAM, DIF, 91297 Arpajon, France; Université Paris-Saclay, CEA, Laboratoire Matière en Conditions Extrêmes, Bruyères-le-Châtel, France

Institute of Earth and Environmental Sciences, University of Freiburg, Freiburg, Germany

C. Prescher

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Contributions

R.J.H., M.I.M., H.P.L., J.D.M., R.S.M., A.F.G., V.B.P., Z.K., C.S., C.S.V., M.F., K.A., O.B.B., R.B., A.L.C., H.C., Y.L., H.M., S.N., E.P., C.Pe., C.Pr, and U.Z. were involved in the conception of the experiment and writing of the proposal. R.J.H., M.I.M., H.P.L., J.D.M., R.S.M., A.F.G., V.B.P., E.E., S.C., Z.K., C.S., C.S.V., M.F., L.A., K.A., O.B.B., R.B., J.B., V.C., J.C., A.L.C., H.C., H.H., E.K., Y.L., X.L., H.M., A.M., M.N., S.N., E.P., C.Pe., C.Pr, and U.Z. participated in discussions of the experimental approach and data analysis. R.J.H., J.D.M., V.P., S.C., E.E., and A.F.G. prepared the samples. R.J.H. performed the data analysis and wrote the manuscript with input from all authors. R.S.M. performed the FEA calculations. R.J.H, H.P.L., J.D.M, C.S.V., L.A., O.B.B. A.M., S.N., C.Pr., and M.I.M. performed the experiment at European XFEL, and R.S.M, A.F.G., V.B.P., E.E., S.C., R.B., J.B., J.C., A.L.C., H.C., H.H., E.K., Y.L., X.L., H.M., E.P., and C.Pe. provided remote data analysis support. Z.K., C.S., K.A., V.C., C.B., A.D., and M.N. provided support at the HED instrument (European XFEL). H.G., T.L., S.S., and J.S.-D. provided support for the AGIPD detector. R.J.H., J.D.M., and H.H. performed screening experiments P02.2 beamline (PETRA III), and H.P.L. provided support at P02.2.

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Husband, R.J., Liermann, H.P., McHardy, J.D. et al. Phase transition kinetics of superionic H 2 O ice phases revealed by Megahertz X-ray free-electron laser-heating experiments. Nat Commun 15 , 8256 (2024). https://doi.org/10.1038/s41467-024-52505-0

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DOI : https://doi.org/10.1038/s41467-024-52505-0

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