DETERMINATION OF IMPURITIES IN SILICON-NI TRIDE AND SILICON-CARBIDE BY MICROWAVE DIGESTION

Microwave digestion techniques were examined to determine impurities i n silicon nitride and silicon carbide powders. Each sample was decompo sed within two hours by the following procedures. A 0.5 g sample of si licon 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 polyprop ylene jacket, and then decomposed by heating in a microwave oven. Simi larly an approximately 0.5 g sample of silicon carbide (beta-SIC) powd er 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 wer e determined by ICP-AES and AAS. Analytical results were compared with the results of conventional acid pressure decomposition method.