Determination of total carbon in silicon carbide by gravimetry of carbon dioxide after alkali fusion

An alkali fusion-gravimetric method has been applied to the determination of total carbon in silicon carbide which is used as abrasive materials and coated particle fuels. Carbon in silicon carbide was converted by sodium hydroxide-sodium peroxide fusion into sodium carbonate, and determined after dissolving the sodium carbonate in excess of sulfuric acid. The effects of fusion fluxes, extraction temperature and time on the recovery of total carbon from silicon carbide were examined. Recommended procedure is as follows: transfer an accurately weighed sample of approximately 0.1 g of silicon carbide to a nickel crucible. Add 2.0 g of sodium hydroxide and 1.0 g of sodium peroxide as fusion fluxes, and mix well by gentle shaking. Inductively heat the mixture to 4000C for 10 min, and then 8500C for 20 min in an oxygen stream. Cool, and dissolve the melt in 100 ml of sulfuric acid (1+5). Absorb the carbon dioxide in Natronasbestos, and weigh. Correct the result by blank determination for 2.0 g of sodium hydroxide and 1.0 g of sodium peroxide. Total carbon in NBS standard reference material (SRM 112, silicon carbide) was determined by the proposed method. The results were in good agreement with the certified value. The standard deviation was 0.3% for 29%-level of total carbon in silicon carbide samples. (auth.)