Determination of traces of carbon in silicon, tantalum and titanium alloy by combustion-nonaqueous coulometric photometric titration

• Published in: BUNSEKI KAGAKU Vol. 38; no. 4; pp. T45 - T48
• Main Authors: TANAKA, Tatsuhiko, KUTSUMI, Hiroyuki, HATANO, Hiroshi, YOSHIMORI, Takayoshi
• Format: Journal Article
• Language: Japanese; English
• Published: Tokyo The Japan Society for Analytical Chemistry 1989; Japan Science and Technology Agency
• Subjects: combustion of silicon with flux by resistance furnace; microdetermination of carbon in silicon, tantalum and titanium alloy; nonaqueous coulometric photometric titration of carbon
• ISSN: 0525-1931
• DOI: 10.2116/bunsekikagaku.38.4_T45

Optimum combustion conditions were achieved for metals whose complete combustions were difficult. The carbon dioxide formed was determined after absorption in N, N-dimethylformamide containing 3.5% 2-aminoethanol, 3.5% water and 3.5% potassium iodide by coulometric neutralization titration. The end point of the titration was located photometrically using thymolphthalein indicator. The maximum sensitivity of the endpoint detection was obtained with a concentration of 7 × 10-4w/v% thymolphthalein. By using this concentration of indicator, as little as 0.03 μg of carbon in sucrose could be determined with a standard deviation of 0.01 μg. The mixed flux iron-tin was appropriate to assist the complete combustion of a high-purity silicon in a purified oxygen flow at nearly 1400°C. In the bottom of the boat, first iron was placed, then the silicon, and both were covered by tin. To achieve complete combustions of tantalum powders and titanium alloy tin and copper fluxes are recommended. Trace amounts of carbon (454 ppm) in these metallic samples could be determined with standard deviations of a few ppm.