I had this effectively a shower thought idea - why don’t we have ceramic 3d printing?
Let me clarify - before posting, I looked it up, and I could not find exactly what I was looking for. There are already commercial offereings for Clay 3D printing, but that is not forming the ceramic in situ, we are depositing what is effectively ceramic in a solvent, and drying it. What I was thinking was making the ceramic on site.
Here is a example setup
-
Imagine a regular polymer 3D printing setup
-
imagine instead of filament, we have a tank of Ca(OH)2 (calcium hydroxide, or slaked lime) (not necessarily just this, but for example, consider this combination)
-
imagine we instead of droping a full thread like layer of semi-solid polymer, we form a trail of really tiny water drops
-
we sprinkle in Ca(OH)2 onto the drops (or this step can be skipped if we can pre mix it with water, and then somehow figure how to deposit really tiny drops of what is effectively a very strong base
-
now we let CO2 in, and form CaCO3
-
deposit a layer to fill voids in this layer (we dropped a non continous strings of drops earlier)
-
evaporate remainning water
-
repeat this step until this layer is complete.
-
repeat process for next layer
Now I can think of many problems here
-
how to handle very strong base - maybe a tip of refractory alloys, or something like Inconnel (or Ni Cr alloys in general), or ceramic (maybe alumina) coated metal (probably cheapest, but hard to make)
-
how to control solidification - we are effectively doing a solidification reaction, and growth of crystal would largely be dependant on the crystal facettes, and we would not be able to have any sharp angles. Also, we would not be able to have a very small width with this.
-
surface tension of water will not allow to easily create uniform small dots - only thing I can think of is using something mechanical to hit the water droplets at tips to effectively launch tiny droplets. (Imagine shuriken (stars or blades) breaking droplet, and water landing) - still we would not have control
-
how to control solidification rate in exothermic process - maybe easy, but we would need something like fans or coolant, otherwise we would form big drops at a spot due increased nucleation rate
-
how to introduce CO2 fast enough - we would have to have a very strong CO2 environment, somehow not let it solidify at tip. Also this reaction is very slow (maybe that is only the case at bulk solidification). Maybe the whole process would be very slow
Does this process already exist? If it does - any resources related to it would be helpful. If not, Why? Is it because we have not been able to solve the issues I listed, something I did not list? Would this be practical (economically)? I can definitely see both artistic and engineering use cases, and both of those can allow some big budgets.
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
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).
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.
If we find something with very low activiation energy (which the CaCO3 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.
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
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 Ksp = 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.