Determination of oxygen and Hydrogen in tungsten and other metals by a vacuum-fusion gas-chromatographic method

Abstract

A gas-chromatographic method has been developed for the analysis of gas evolved from tungsten and tungsten-base alloys in the vacuum-fusion process. The method is suitable for determining 5–3,000 p.p.m. of oxygen and 0.2–300 p.p.m. of hydrogen, and can be applied to other metals. Above 50 p.p.m. of oxygen and 3 p.p.m. of hydrogen, the values found compare favourably with those obtained by alternative methods; below these levels, no reliable alternative procedures are readily available. In the proposed method, the sample is submitted to vacuum fusion in a molten platinum bath in a graphite crucible, and an aliquot of the evolved gas is transferred by means of a specially modified Drallim valve, to a stream of high-purity helium. The components are separated on a column of molecular-sieve 5A at 100° and detected with a radioactive-type ionization detector. Calibration and operation of the system are described in detail, and the effects of variables are discussed. Evidence was obtained that hydrogen recoveries by the conventional vacuum-fusion method are sometimes slightly low, because of methane formation. An important advantage of the method is that the evolved gases are positively identified by their retention volumes.