GROWTH ISOTHERMS OF LIQUID-PHASE SINTERED SILICON-NITRIDE

Grain-growth data, collected after isothermal treatment of four Si3N4 materials, which contained different metal oxides as densification age nts, are revisited. Diffusion-controlled Ostwald ripening mechanism is generally recognized to be mainly responsible for grain coarsening up on post-densification anneal. Emphasis is placed on rationalizing the grain-growth rate in terms of viscosity of the residual intergranular glass. A simple phenomenological equation is given that allows to pred ict the size of the Si3N4 grains upon annealing process. The pre-expon ential coefficient and the exponent of the equation were determined us ing both grain-growth and intergranular viscosity data of a model Si3N 4 system, which contained only pure SiO2 glass at grain boundaries. Th is general formulation allows to estimate the effective glass viscosit y of Si3N4-based materials.