After sintering pellets are very fragile although XRD show pure phase. what is the possible solution for this problem?How can we get dense ZrCeO2 pellets?
Dear Ghani,
Did you analyze the micro structure of the pellets? This problem could be related to the incomplete sintering.
Best Regards,
Fatih.
Dear Ghani,
if you already know that you have a pure phase, try to prepare the pellets by the highest pressure possible and use a very fine powder, the reduced voids will certainly produce a dense pellet.
regards,
Fernando
Dear Ghani,
I think you should use the hot isostaric press for the preperation of your specimen to avoid the problems of porosity and brittleness.
with all my best regards.
Baydaa.
The sintering ability of (Ce-TZP) depends on starting powder characteristics, which differs depending on the synthesis methods and conditions used. Characteristics include purity, homogeneity, particle shape and size, particle size distribution, presence of agglomerates, etc. Fine powders sinter better, i.e., faster and/or at lower temperatures than coarse ones. However, powders of very fine particles, usually synthesized by wet-chemical routes, do not always show good sinterability, because of the formation of agglomerates. Thus uncontrolled agglomeration or the presence of high-strength agglomerates (aggregates) can be detrimental to the properties of final products.
See refferences:
http://www.nanotecnologia.com.br/redecmdmc/lab/arquivos_publicacoes/642_Synthesis%20and%20sintering%20of%20ZrO2-CeO2%20powder.pdf
http://ul.qucosa.de/fileadmin/data/qucosa/documents/19291/diff_fund_8%282008%297.pdf
Cerium undergoes a change of oxidation state from +4 to +3 even in air, at sintering temperatures. In the +3 state Cerium is not a good stabilizer for the high-temperature tetragonal phase od zirconia. Hence, when you have ceria-zirconia mixture, and you want to sinter them, it is a good practice to use furnaces where you can keep a high partial pressure of oxygen, so that, on cooling, Ce ions can go back to the + 4 state.It also depends on the amount of ceria that you want to incorporate in the zirconia but, typically, the aforementioned change of oxidation state is at the base of the structural instability of ceria-zirconia solid solution.(You can easily check if you have Ce+3 ions: if the core of your sintered pellets are somewhat grey, than you can be sure that some ceria ions are in the reduced state. On the topic you can read my old papers. Also Anil Virkar from Utah university has worked a lot on the subject and, if I remember correctly, even I-Wei Chen).
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