Dear Serdar,

First of all, it would be interesting to know how you are making the thermal treatment. If you are doing under air, probably it will degrade by CO2 formation. It could be interesting to use a sealed quartz tube keeping the approximate relation between CO2 and O2 in the atmosphere, you should like to have in the sample. If you have performed the thermal treatment under controlled conditions, probably decreasing the cooling rate could help. In any case, it is going to depend on many factors, then it would be very helpful to know how the total thermal process has been made.

Sincerely,

Dear Serdar,

First of all, it would be interesting to know how you are making the thermal treatment. If you are doing under air, probably it will degrade by CO2 formation. It could be interesting to use a sealed quartz tube keeping the approximate relation between CO2 and O2 in the atmosphere, you should like to have in the sample. If you have performed the thermal treatment under controlled conditions, probably decreasing the cooling rate could help. In any case, it is going to depend on many factors, then it would be very helpful to know how the total thermal process has been made.

Sincerely,

Dear Prof Sotello 

Thank you so much for your advise

We are doing under air at 900 C for 24 h by 10C/min heating and cooling rate

As you and Dr Pınar said, we will try lower heating and cooling rate under oxygen atmosphere, the other important parameter can be heat treatment temperature, mat be I should decrease the heating temperature, what is your suggestion? 

Sincerely yours

Dear Serdar,

After these data, I do not think 10C per minute is too high cooling rate. My other question could be about how do you prepare the samples. Are you using carbides and oxides as starting materials or just oxides and you add grafite or some similar C source?. If this is the case, small amounts probably do not have significant effect on the mechanical properties but for high content they can have a great influence, mostly if it is not reacting with the oxides due to its chemical stability (if we do not consider its degradation at high temperature under air). It should be interesting to know the approximate volume proportion in these cracked samples.

Best regards,

We are using carbonates and oxides, after mixing to powder we are calcined for evaporation of the carbonates above 800 C, and then again grounding in agate mortar and we performing final heat treatments.  After then we observe a lot of cracks for example when you touch with twisters they divide like a broken glass

Thank you

Sincerely yours

Serdar

Dear Serdar,

Then, probably it would be interesting to know the decomposition temperature of these carbonates, as they can be decomposing in the thermal treatment, making negligible the compaction made previously.

Sincerely,