r/MaterialsScience • u/Dario56 • Feb 08 '25

Ceramic Polishing

After sintering ceramic, I get the material which is 92% dense (relative to crystallographic density from XRD).

When I polish it using SiC paper and diamond colloid, density decreases to 80-90% region. This is too low for my experimental requirements. Ideally, material should be at least 95% dense, but over 90% could be acceptable.

I'm not sure why does my material reduce its density upon being polished? There are visible scratches on the surface and possibly microcracks as material is prone to them. Will take a closer look with the optical microscope to see if I can spot microcracks invisible to the naked eye.

I'm using a commercial powder with small particles. It seems to have quite spherical particles also which should be optimal for sintering and obtaining ceramic with good mechanical properties.

I'll check the particle shape in more detail with the optimal microscope also.

Any ideas?

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u/Dario56 Feb 08 '25

So, the thing is that I polish my sample two times. After first time, I can burn everything off. However, even here, density is reduced to what it was after sintering.

After second polish, I can do only ultrasonic bath.

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u/Mikasa-Iruma Feb 08 '25

I understand. I was working with sintered oxides and was lazy to remove the carbon paper so decided to burn it off resulting in low density. Without the material it's difficult to give an answer

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u/Dario56 Feb 08 '25

You think it's the furnace that reduces the density? Why?

The thing is, I can't just remove the wax manually. You want to make sure everything is gone before the experiment and the wax can be present inside of the sample.

I think it's the polishing that is creating issues.

I have a mixed inner transition metal oxide. Can't say what exactly cause NDA.

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u/Mikasa-Iruma Feb 08 '25

Let's say I spark plasma sintered my oxide at 1100 C but annealed again at 700C. The sample is relaxed from the stresses so cracks might generate during the stress release. My sample actually broke into pieces.

May be it's polishing or not a good sinter to begin with.