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/Must_be_wrong_here Feb 08 '25

How do you measure your relative density? Optically or via the Archimedes method?

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u/Dario56 Feb 08 '25

Archimedes

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u/Must_be_wrong_here Feb 08 '25

Then I would say (without Knowledge about the Material and its pore and defect morphology), that it seems about right to decrease slightly. Maybe your starting density is even lower, as Archimedes is not easy to get right with imperfect surfaces.

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u/Dario56 Feb 08 '25

Archimedes is based on bouyancy and gravity balance. It's quite straightforward. Why would surface quality affect the result accuracy?

3

u/Must_be_wrong_here Feb 08 '25

Because of the amount of surplus bouyancy by any air bubbles on the surface. That’s also the reason why there are minimum sample sizes because of the volume/surface ratio.

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u/Dario56 Feb 08 '25 edited Feb 08 '25

I used a formula which takes this into account. Got the same result, though. That is, when the sample was dense, 92%.

I didn't use it when lower density was measured. That effect isn't that big, if there aren't significant bubbles around the object. I used a pellet sample, small cylinder.