Determination of impurities in silicon nitride and silicon carbide by microwave digestion

Microwave digestion techniques were examined to determine impurities in silicon nitride and silicon carbide powders. Each sample was decomposed within two hours by the following procedures. A 0.5 g sample of silicon nitride powder and mixture of 9 ml of hydrofluoric acid and 3 ml of nitric acid were put into a Teflon pressure vessel with a polypropylene jacket, and then decomposed by heating in a microwave oven. Similarly an approximately 0.5 g sample of silicon carbide (beta-SIC) powder was decomposed with a mixture of 3 ml of hydrofluoric acid, 3 ml of nitric acid and 6 ml of sulfuric acid by heating in a microwave oven. alpha-SiC powder, however did not dissolve, while beta-SiC powder did. The proposed methods were applied to JCRM-R-005 and some commercial powders of silicon nitride and silicon carbide, and the impurities were determined by ICP-AES and AAS. Analytical results were compared with the results of conventional acid pressure decomposition method.