I have a reaction during the sintering of my ceramics accompanied by the formation of oxygen vacancies and I observed an important porosity in my materials. Is there any relation between the oxygen vacancies and the porosity? If yes, how can I calculate the pressure of oxygen generated by this reaction and responsible to the porosity formation?
when increasing vacancies the porosity is increasing
Dear Colleague,
In most cases there is no correlation between both, if you sinter alumina in hydrogen you form vacancies and still the material gets perfectly dense, the same is true for zirconia.In fact in many cases (oxides) the occurence of vacancies is the vehicle by which oxygen trapped in pores is transported out of the structure).
Read the works of R.L. Coble dating back to the early sixties. JACERS, 1962, vol. 45 (3) , pages 123 ff.
Insufficient density is typically encountered as a result of imprefect processing when the structure of the green body is not perfect enough (containing with a size of pores >> size grains) when the green bodies contain unbroken agglomerates. There are some materials where the cations may occur in different oxydation number such as in chromia (Cr2O3) here it is not possible to fully densify the material in air due to occurence of Cr4+ and volatile species CrO3. (but you can sinter it in hydrogen !!)
Check your microstructure (polished cross section) for defects and agglomeratesand look if you have different density in the inside and the outside this could indeed be an indication of decomposition.
Unfortunately you did not mention which ceramic you tried to sinter.
best regards
Frank
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