Processing of Yttria-Alumina Coated Silicon Nitride Slips by Slip Casting |
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Authors: | María P. Albano Liliana B. Garrido |
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Affiliation: | (1) Centro de Tecnología de Recursos Minerales y Cerámica (CETMIC), C.C. 49 (1897) M. B. Gonnet, Provincia de Buenos Aires, Argentina |
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Abstract: | Si3N4powders coated with 6 wt% Y2O3and 4 wt% Al2O3were prepared by coprecipitation. The resulting powders were dispersed in water at different pH values and with addition of various amounts of ammonium polyacrylate (NH4PA) to produce 32 vol% slips. The influence of the amount of NH4PA solution added and pH on the rheological properties of 32 vol% coated Si3N4slips were studied. In addition, the sintered density of cast samples was determined and related to the degree of slip dispersion. The adsorption of the NH4PA on the coated particle surface was rather high and the surface became saturated near 0.86 mg/m2at pH 9.2. High NH4PA concentrations (1.7–3 wt%) were necessary to obtain well dispersed 32 vol% coated Si3N4slips at pH 9.2. The best stabilization was obtained with the addition of 2.3 wt% NH4PA; in this condition, the viscosity reached a minimum value of 35 mPa.s at 100 s–1. The slip viscosity increased with increasing pH from 9.2 to 10.2. Slips with low viscosities gave a more dense packing of cast samples and consequently higher sintered density values. |
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Keywords: | Silicon nitride coated with yttria and alumina ammonium polyacrylate adsorption slip dispersion slip casting sintering behavior |
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