Abstract
A layer of Y2O3–Al2O3, used as a sintering aid, was coated onto the surface of Si3N4 particles by the precipitation of inorganic salts from a water‐based solution containing Al(NO3)3, Y(NO3)3, and urea. The electrokinetic and colloidal characteristics of the Si3N4 powder were changed significantly by the coating layer. As a result, dispersion of the Y2O3–Al2O3‐coated Si3N4 powder was significantly greater than that of the original powder. Furthermore, the Y2O3–Al2O3 coating layer prevented the hydrogen‐gas‐discharging problem that occurred during gelcasting of the original Si3N4 powder because of reaction between the uncoated powder and the basic aqueous solution in suspension. Surface coating, as well as the gelcasting process, significantly improved the microstructure, room‐temperature bending strength, and Weibull modulus of the resulting ceramic bodies.
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