I’m not a ceramics expert. Is the slaked lime somehow a replacement for kilning the clay? As far as I knew there was no process to get from clay to ceramic without a kiln
this post was submitted on 02 Mar 2025
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no, afaik kilning of clay is basically baking clay (I think that is why we have "brick kilns") that is basically drying of silica (or some secondary or tertiary silicate chains, or aluminate or borate chains) - removal of water, which is techinically a chemical reaction, but the boring kind. What I am thinking of baiscally making the silicate chain
I’m pretty sure it’s more than just drying and more akin to turning sand into glass. The glazing stage certainly is.
yes and no, turning sand to glass requires temperatures in ball park of 1600 C (close to glass transition temperature of Silica), even with mixing of stuff that will go to down to something like 1200, and the ones I found online were not going to that temperature. At lower temperatures, free silicates start to grow the existing silicate chains, knocking water out. Any glazing observed would be because now we are moving towards a more smoother surface (as in, due to solidification). There plenty other side reactions, but basically at low temperatures, we can only have chain growth or initiate (at this low temperature, initiation is also very slow, and growth is the dominiant mode).
Shrinkage while drying may be tricky. You can get all sorts of nasty stresses and irregularities depending on how much it shrinks while drying. Some metal 3d printing has mild shrinkage and gets around it somewhat with massive computations so it shrinks into the right shape, but I don't know how accurate that is.
ceramics kinda don't shrink. They do shrink, but CTE is very low (generally due to very deep potential wells). And assume we are at low temperature crystal growth range, we would see big crystals, with relatively low internal stresses.
Shapeways used to be offer ceramic prints. If I recall correctly, they stopped offering it because it required too much processing to be done profitably.
what kind of ceramic prints? the clay kind or the kind I am looking for?
I'm not sure. I never got any ceramic prints from shapeways. Anything useful would have been too expensive. And, as I said, they stopped offering that as an option.
I did come across this:
https://all3dp.com/2/ceramic-3d-printer-ceramic-3d-printing/
The water won't necessarily have the same surface tension depending on what is added to it.
You can look into inkjet technology regarding the uniform dispersal of the resulting fluid.
yes i did think of that, but that is (i think) a smaller overall effect. If tip has solidification, the edges will grow wider, and drop will get a much larger surface to form, and if i remeber correctly, for a drop to stable, it has to be basically be like a hemispherical dome, and base radii growing means a larger drop.
if you are talking about cement (like in mortar or concrete), we already have a process to turn powder into solid ceramics at room temperature. Otherwise :
Ca(OH)~2~ (powder) + CO~2~ → CaCO~3~ (powder)
I know about this, and this is the very source of my idea - basically thinking why dont we 3d print cement. Then realised cement or concrete are way too complex structures, lets just consider slaked lime to lime
... and i told you why it doesn't work. Alternatively, if you look at stalagmites, you are starting with dissolve salts with slow evaporation. Here you get a solid with good mechanical properties. But this process is very slow. Same idea applies to shells and bones.
that is also a problem i thought (last line of last issue). What I was thinking was that if some research group has already taken this, where for example the crystal structure has really high enthalpy (something like Al~2~O~3~) but also low enough activation energy, then at very low temps, the reaction will drive itself, and we can use fans to evaporate. I am sure there must be some goldy-locks zone somewhere
You are trying to put together some words that you think might make sense, but clearly, i am very sorry, but you do not master this domain.
Al2O3 : one process that exists to crystallize this at about room temperature is aluminium oxide purification :
https://en.m.wikipedia.org/wiki/Bayer_process
Bayer process
Sorry, but I do understand this stuff, my bachellors is in materials science, I do not master this domain, but I at least understand the thermodynamics and solidfication okay enough. I know of bayers process, and I know it can not be used for 3d printing. What I am saying is
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If something has very high enthalpy of formation, then end prouct is very stable - something I want for the end product (most ceramics have good enough stability for our needs).
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usually activation energy required is very high - one of the best way to give activation energy is raise temperature. Problem with very high temperature is now the nucleation rate is very high (nucleation rate is rouply proportional to temperature difference between equillibrium temperature and temperature of process). If nucleation rate is very high, we will form snow like crystals - fluffy (not dense), so we can not really use it to build layers above.
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If we find something with very low activiation energy (which the CaCO~3~ formation has (reasonably low compared to other ceramics, that is one of th ereasons why we use it as a primary test for verification) then we can perform reaction at very low temperature. And growth rate is exponential decaying with temperature (the mobility is exponential with temperature) so growth would be prefered and we will form large crystals.
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another thing to control is directionality - if we can have direcctional solidification (something like silicon manufacturing) then we can perform 3d printing, otherwise things will grow accordingly to minimise the surface energy (everything technically does, but what I mean is, if there is significant anisotropy in growth rate along particular direction we can use it))
I may be wrong here, I definitely have not given it much thought, but I don't think I am absolutely off the track. It doesn't also help that these days I am not pursuing Material processing at all, so I may have forgotten a few details, If I still have something wrong please correct me
You start with a powder ( then, maybe a chemical reaction or dissolution, whatever) and after that you don't want to end up with a powder.
To go from powder to one solid object, the only energy change is the decrease of surface energy. ... you must first see this.
there is also energy released in reaction, that can cover for decrease in surface energy and also the energy of dissolution (think of copper sulphate crystals forming). Energetically it is possible. Problem is find the particular system which checks all boxes
(...) there is also energy released in reaction, that can cover for decrease in surface energy (...)
Put this into equation or tell me how there is any meaning in this sentence.
A(dissolved) + B (gas) -> Delta (energy released) + C(precipitate)
since a was dissolved - there was some eenrgy of dissolution, now that there is a precipitate (and lets for simplicity assume K~sp~ = 0) then there is some energy required to create this surface.
for reaction to be energetically favorable (Gibs free energy, so entropy is also accounted)
abs(Delta) > abs(dissolution energy) + abs(surface creation)
this is going to maintained always. Now if Delta is very large reaction will almost run to completion (provided activation energy is given, lets say in form of temperature or mechanical agitation to increase the reaction probability of A and B)
You are getting to this :
A + B → C (metastable and insoluble)
https://en.m.wikipedia.org/wiki/Classical_nucleation_theory
Classical nucleation theory ...
Description ...
Homogeneous nucleation ...
C (metastable) → C(powder precipitate)
... unless you have heterogeneous nucleation
... first you have to eliminate all particle that can be nucleus on which powder can form, then,
... you need to stay away from homogeneous nucleation as described above.
... of course you have to provide a substrate on which C will nucleate, and grow,
... and this is why, in practice, (for large heterogeneous nucleated solids production) this process is very slow.