I am working on cement-based transparent ceramic. I synthesized the powder with 30%wt of CaO from starting materials. After synthesizing powder by sol-gel, I got the single mayenite phase at 1300oC. After shaping by CIP and annealing in air, I got Mayenite with lime resulting in opaque sample. How can I get dense material lower than 900oC?
there is a contradiction in your question. You know that opacifier is intended to opacify, that is, make something non-transparent. If you get transparent material, the filler cannot be called "opacifier" anymore.
To get the answer for your question, you could explain a little more on your material. What is the composition of your cement? Is there any evidence that cements can ever get sufficiently close to the non-porous state?
Dear Roman,
My material is 12CaO7Al2O3 it contain about 30% of CaO. However, I would like to make it transparent and afraid of facing the difficulty in CaO. So, I would like to ask about how can I sinter the sample to get transparency.
Sincerely yours,
Are you sure you meant cement-based, not zeolite-based ceramics?
I am sure you will get the trouble with CaO as it has a refractive index of 1.83 and the 12C7A - only 1.61. Even if you sinter your sample to their theoretical density, the mismatch of the refractive index is too high. I see the only possibility - to process your samples in some way, so that CaO crystallites (is it crystalline?) stay smaller than 50 nm, the smaller the better. If you succeed to suppress scattering, certain level of transparency can be achieved. I would give it a few tries of conventional sintering optimized for stoichiometric 12C7A. If it won't work, someting like microwave sintering could be attempted.
I guess that you have 12C7A and CaO in the mixture. Is that right? If yes you have to consider there are two components. It means you can get different sintering mechanisms from both. The CaO can be possible transparently sintered by using vacuum furnace, hot press,and long holding time or you can add CaF2 as sintering aid (if it dose not get involve in the solid state reaction and change your particular materials structure). I am sure that the basic idea is to physically remove porosity and get smaller grain(crystallizes) as much as possible. I am agree with Prof. Roman that MW, SPS, could be applicable.
Cheer !
Dear all,
I think my answer and question may mislead your understanding. I mentioned 30%CaO as the content of CaO with respect to %wt in binary system of CaO-Al2O3 in phase diagram not additional. I have already got the right single phase of C12A7 by sol gel synthesis process but I got very small amount of sample to make a bulk. So, I just need to get the most effective suggestion to continue working on because I have few experience working on transparent ceramic.
Thank you again for you kindness and patience.
Best regards,
If you can get access to an Spark Plasma Sintering (SPS) or Field Assisted Sintering Technique (Fast), it may be your best bet. The high current and heating rates allow for extremely fast sintering times, therefore hindering grain growth and keeping your crystallites small. (I guess your particle size really depends on the outcome of your sol gel synthesis, but at least there wont be much grain growth with FAST.) I have had much luck with sintering transparent MgO in a FAST.
I know this solution is a bit niche because not every institution has a FAST, but maybe asking around, you might find a place that would accommodate your needs.
Dear Micheal,
Thank you for your answer. I am not quite sure that we can discuss the detail in this forum or how can you give me more detail about SPS? In my department, we intensively use SPS for sintering. Anyway, my experience on this process need to be acquired.
Thank you,
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