Carbon Determination in Hyperpure Elemental Boron Using Gas Chromatography

Abstract

A convenient, rapid, extremely sensitive, and highly precise method for the determination of carbon in boron has been developed. Powdered boron mixed with tin powder, which serves as an accelerator, is burned under controlled conditions in an induction-heated furnace. The gaseous products are passed through a molecular sieve column at an initial temperature of 100°C. The carbon dioxide remains trapped in the molecular sieve, while the oxygen is swept out by helium after the combustion is completed. The carbon dioxide is then driven off the column by means of a rapid temperature increase. The amount of carbon dioxide is determined by the electroconductometric method or by gas chromatography. (The latter is more sensitive.) National Bureau of Standards steel and iron samples with carbon contents of 0. 011–3. 28% were used to establish a standard curve. The method permits detection of 0. 0005% C under ideal conditions. The time required for a single run is approximately 25 min. The boron samples used in this study contained only a few parts per million of spectrographically detectable impurities. They were prepared by the hydrogen reduction of high-purity BBr3 or by the thermal decomposition of BI3 and deposition on a boron substrate.