ELECTRON-PROBE MICROANALYSIS OF CHEMICAL GRADIENTS IN GAS-PRESSURE SINTERED SILICON-NITRIDE

During gas pressure sintering of silicon nitride (Si3N4) - which normally contains oxide additives such as SiO2, Al2O3 and Y2O3 - in a resistance heated graphite furnace, a reduction of the Si3N4, sample takes place. At high temperatures (> 1800-degrees-C) this effect is accompanied by decomposition reactions of Si3N4. Both lead to chemical gradients in larger components which influence the strength of the sintered article. Electron probe microanalysis (EPMA) has been carried out in order to study the influence of the crucible material [graphite (C), boron nitride (BN)] and the quantity of filling on the gradient formation.