Abstract
In the usual determination of micro amount of oxygen less than 10 ppm in nickel and cobalt, more than 2 grams of the sample is necessary because of the sensitivity of the usual method and of the influence of the blank values from the graphite crucible. However, such a large amount of the sample often gives inaccurate results and incomplete extraction when it is analysed by the conventional method of iron bath and dry crucible. In this paper, a new method using the carbon chips is proposed. The apparatus used in this study was Rigo analyzer for gases in metals S. H. O. II (sensitivity : 0.0055 mg/ mm Oil). The surface of sample was electropolished.
The recommended procedure is as follows : Carbon chips{(1620)mesh}, 2grams, is previously placed in the crucible and degassed for 5 hours at 2300°C. After degassing, the crucible temperature is lowered to the gas extraction temperature, 1750°C for nickel and 1700°C for cobalt, respectively, and then the sample is added to the crucible and gases are extracted and collected for 5 minutes. Before next sample is added to the crucible, carbon chips, 0.5 gram, is added to the crucible and degassed for a few minutes at 2000°C. Coefficient of deviation of this method was 5.6 (%) for electrolytic nickel (0 : 7.6 ppm), 18.6(%) for zone melted nickel (0 : 2.2 ppm) and 9.2(%) for zone melted cobalt (0 : 7.5 ppm).
