TRANSMISSION ELECTRON-MICROSCOPY OF INTERGRANULAR REGIONS OF CORRODEDSILICON-NITRIDE

Two her-pressed, dense, silicon nitride materials have been exposed to the flue gases of an aluminium smelting furnace heavily contaminated with Al, Ca and K-containing dust and vapours. Transmission electron m icroscopy (TEM) has been used to examine microstructural changes occur ring in the silicon nitride at the interface between corroded and unco rroded material Extensive diffusion of contaminant metal into the inte rgranular glass of the silicon nitride occurs, associated with physica l and chemical changes in the intergranular regions, and a marked loss of mechanical strength.