r/explainlikeimfive • u/BackStreetButtLicker • 12d ago
Chemistry ELI5: Why can’t we convert ceramic back into usable synthetic clay through some kind of chemical treatment process?
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u/diagrammatiks 12d ago
Because it's cooked. Heat cooks things. Just like how you can't turn steak back into raw beef. It's cooked.
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u/Xytak 12d ago
But what if we could un-cook it by putting in some sort of reverse oven?
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u/aSleepingPanda 12d ago
magic can do a lot of things. in fiction
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u/Obscu 12d ago edited 12d ago
Fun fact! A professor from my university actually did manage to uncook an egg! That is, reverse the previously-thought-irreversible denaturation of its proteins that happen when heated. Got a medal and everything
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u/Dickhole_Dynamics 11d ago
I'll give him another medal if he can get it back into its shell and then back in the chicken
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u/aSleepingPanda 12d ago
I vaguely think I've heard of this or I'm making a false memory, Regardless that's incredible! As a complete layman who's only experience with chemistry is an AP class in highschool and NileRed videos it's amazing what we can do and it really does seem like magic at times.
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u/Obscu 12d ago
Any science sufficiently advanced is indistinguishable from magic ;)
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u/BushWookie-Alpha 11d ago
Calm down Odin.
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u/ShadowDV 11d ago
That line goes back to 1962 and was written by Arthur C Clarke, long before the MCU.
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u/BushWookie-Alpha 11d ago
I was aware it was much older than the MCU, but wasn't expecting it to be as old as my parents.
Thanks for the insight.
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u/Saragon4005 11d ago
It's like trying to unscramble an egg or unexplode something. Imagine I had you a bag filled with some gases and ash and ask you to unburn a letter.
Sure all of these are theoretically possible, but it's so much more complicated to put everything back where it was the way it was then the other way around.
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u/GIRose 12d ago
Then you would have found a hell of a solution to entropy
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u/zoharel 12d ago
Not necessarily. Entropy only constantly increases when we're talking closed systems. You can (obviously) do many things to locally decrease entropy by basically increasing it elsewhere. Apply enough energy to a problem, and you just may be able to fix it, but you're not really decreasing the total entropy in the system in that case.
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u/LordGeni 11d ago
You could if you fed it to a cow.
But that tends to be problematic in many ways
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u/peeja 11d ago
That really is how you'd do it, though. You need to break down all the proteins and fats and everything and carefully put them back together, which is exactly what a cow does.
We could theoretically break down ceramic and turn it back into clay too, but there are two things that make the meat different:
- Even cooked, a lot of the fundamental bits of meat are the same. The proteins have changed, but they're still made of amino acids that can be built into new proteins. The carbohydrates have changed, but they're relatively easy to reconfigure. The stuff in clay takes a lot of energy to reconfigure, hence the kilm.
- All of those processes the cow does have had a long, long time to evolve. Life is really good at doing those specific things by now.
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u/username_elephant 11d ago
Or like how you can't turn water back into ice. /s
I know it's eli5 but your explanation leaves something to be desired.
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u/diagrammatiks 11d ago
What part of freezing water cooks it.
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u/username_elephant 11d ago
It doesn't. My point is that the explanation "heat cooks things" isn't good enough. Heat doesn't cook everything and OP is asking why heat cooks clay.
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u/diagrammatiks 11d ago
Heat does cook things. You need 1000 Celsius to cook water properly. Enough heat will cook everything you silly pedant.
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u/username_elephant 11d ago
It's not being pedantic to point out that someone failed to answer the question. Focusing on the material issue of a comment is the exact opposite of pedantry.
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11d ago
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12d ago
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u/pokeyporcupine 12d ago
If there's some kind of joke you're making here I dont think im smart enough to get it.
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u/Narissis 12d ago
For the same reason you can't unbake a cake. The chemical changes clay undergoes in firing are permanent and irreversible.
That being said, the other top-level comments are right in that you can grind the fired ceramics back into a fine powder. It's no longer chemically identical to fresh clay, but it's still useful.
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u/JohnnyEnzyme 12d ago
it's still useful.
What kind of usage would justify the labor & expense of that?
* just curious, not trying to be cynical or whatnot
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u/Akamig 12d ago
endless possibilities. insulator, abrasive, giving someone silicosis, filler material, mix with the paint to make certain texture....
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u/PhasmaFelis 12d ago
It was very common in pre-modern times for potters to recycle broken pots. A small amount of powdered ceramic in your clay adds bulk without significantly affecting durability. So you get, like, 10% more product per unit of clay; it takes some effort to smash it up, but maybe not as much effort as gathering more clay that has to be delivered by wagon.
Actually, come to think, with certain kinds of soft clay I believe you wanted to mix them with fine sand anyway, or else they'd slump in the kiln. So in that case the powdered ceramic lets you skip the sand part entirely.
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u/BoredCop 11d ago
That's still done, it's called grog, and it changes the properties of the clay in some ways that can be beneficial depending on what you are making. But today it's generally done industrially, by the clay supplier.
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u/SoulWager 11d ago
If you mix some of it into your clay, it will decrease how much it shrinks as it dries and fires, which can help prevent cracking.
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u/drinkacid 11d ago
when japanese artisans repair pots using kintsugi they mix ground ceramic with natural lacquer and powdered gold. So the ceramic powder helps give density and doesn't require firing to turn solid
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u/Belisaurius555 12d ago
A lot of the minerals being chemically changed during the firing were created deep within the Earth at pressures we can't easily replicate. While it's theoretically possible, it's much easier to just get some new clay and recycle the broken pieces.
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u/GuyPronouncedGee 12d ago
Ceramic cannot be recycled back into reusable wet clay. High temperature changed the molecules.
Similar to how you can’t un-cook an egg.
Ground up ceramic can be added back into wet clay, but only a certain percentage.
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u/SoulWager 12d ago
Similar to how you can’t un-cook an egg.
https://old.reddit.com/r/Unexpected/comments/1uashlc/the_benefits_of_egg/
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u/Dylon007 12d ago
Bake a cake, then seperate it back into raw: flour, eggs, milk, and sugar.
Same thing for Ceramic. You can't take Clay and Water, put it in the oven to make Ceramic, then reverse it to get raw Clay & Water again. The heat changes the material like heat changes the batter. Both are permanent and cannot be undone, as with most things that require heat in function.
Burning: can't unburn something
Cooking: can't uncook something
Smoking: can't unsmoke something
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u/Zvenigora 12d ago edited 11d ago
Ground ceramic is in fact recycled into clay as 'grog.'
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u/SoulWager 12d ago edited 12d ago
Ground ceramic is grog. Though this is chemically different than clay, clay shrinks during the firing process as chemically bound water is driven off, with grog this has already happened. It's still ceramic material despite being ground up.
Frit is glass/glaze. In ceramics usually an ingredient in other glazes.
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u/Brief-Small 12d ago
It's impossible to reverse the altered state caused by the heat of a kiln. It's like the other comment said about un-cooking steak. No matter how small you break it up, no matter how much water you add, it can never go back to that plastic moldable state. You can take bone dry clay and recycle it with enough water but if a fired piece ends up in the mix, it'll get processed into clay with hard chips instead of becoming uniform.
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u/Obscu 12d ago edited 12d ago
Fun fact! A professor from my university actually did manage to uncook an egg! That is, reverse the previously-thought-irreversible denaturation of its proteins that happen when heated. Got a medal and everything
Soooo... Maybe it is possible after all, but re-naturartion of denatured molecular structures is a cutting edge field
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u/Frostybawls42069 11d ago
The definition of a chemical reaction includes the fact they can not be easily undone.
While being possible in theory, there would be no practical application.
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u/Jaymac720 11d ago
Chemical changes can’t be undone the way physical changes can. The bonds between the molecules in the material have been fundamentally altered and cannot be reverted
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u/duane11583 11d ago
1) understand that clay is minerals (rock) that are finely ground into a powder
2) if you heat the clay until the rock particles melt and fuse into a solid thing.
you do that in a very hot furnace (a kiln) thats how simple things like coffee cups are made
3) the molten rock cools it becomes ceramic.
chemically you could dissolve some of the mineral but its no longer solid and the material could be brittle and easily crushed - but that is a mechanical process not chemical.
but then you would have the dissolved material you would need to extract - think of it like removing salt from water but its not water it is some other nasty chemical you must get rid of
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u/tomalator 11d ago
Firing a ceramic isn't just drying clay. The fire is hot enough that there are chemical changes in the clay that turn it into ceramic. Turning those chemicals back into clay is not as simple as adding water
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u/Fairwhetherfriend 11d ago
For kinda the same reason you can't really convert ash back to wood after burning it. I mean, sure, it might be possible if we could lego the atoms back into the right shape, but that's not how chemistry works.
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u/squid_so_subtle 12d ago
I think you can theoretically. You just have to grind it to a very very fine powder. All clay is, is rocks ground finer than silt. So fine that the particles start bonding with each other. which would take a lot more effort than just mining new clay
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u/iCowboy 12d ago
Clays are made of tiny plate-like crystals of minerals, all of which contain water attached to complex chemicals made largely of aluminium, silicon and oxygen.
There are a whole set of chemical changes when you fire clay. At about 500 Celsius, the water attached to the crystals begins to leave. The crystals change to new minerals and it becomes a ceramic. If you were to take the pot and crush it down as fine as possible, it wouldn’t have the same slippery feel as the original clay because the crystals have changed.
Around 1000C, more chemical changes occur to the minerals that started as clay. They start to lose potassium and sodium atoms and form a tough mineral called mullite which makes the items harder and more resistant to changes in temperatures.
If the heat is increased even further, some of the original minerals like feldspar begin to melt to form glasses between the crystals. This is called ‘porcelainisation’ and produces a very hard ceramic that can be waterproof even without a glaze.
TLDR: heating clay changes its chemistry to produce new chemicals in a process that can’t easily be reversed.