Effect of Aging Time on the Stability of Aqueous Y-α-SiAlON Precursor Powder Suspensions

A temporarily stable aqueous slip of Y-α-SiAlON precursors powders (Si3N4, Al2O3, Y2O3, and AlN powders) was successfully prepared using an AlN powder thermo-chemically treated against hydrolysis (AlN-TC). Aqueous suspensions of AlN-TC and an Si3N4-based powders' mixture (Si3N4/Y2O3/Al2O3) proved to have long-term stability under separate deagglomeration by ball milling. However, the kinetic stability decreased when the two suspensions were mixed in the required proportion to obtain a precursor Y-α-SiAlON composition. This work aims at understanding better the aging phenomena and evaluating the feasibility of using aqueous processing to fabricate Y-α-SiAlON ceramics. The pH and rheological behavior of the suspensions were monitored along the time. The effects of drying conditions (room temperature or humidity-controlled chamber) of slip-cast samples on the crystalline phases and oxygen contents before and after sintering were evaluated. Drying under a moisture-rich atmosphere favored hydrolysis of AlN and the appearance of β-SiAlON as the main phase after sintering. The results allowed concluding that there is a time frame within which Y-α-SiAlON ceramics can be fabricated from aqueous suspensions.

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