タングステンの炭化速度におよぼすコバルトの効果

Abstract

Pure tungsten powder and tungsten-cobalt mixed powder were carburized by H2-10%CH4 mixed gas at temperatures from 1073 to 1473 K. In order to examine the carburizing process, tungsten plates were also carburized under similar conditions.Methan was decomposed by either of tungsten and cobalt, and the larger fraction of methan was decomposed by the tungsten-cobalt mixed powder of a given composition than the total fraction of methan which was decomposed by each powder of tungsten and cobalt equivalent to that in the mixed powder. In carburization of pure tungsten, the deposition amount of carbon corresponded to the amount of carbon diffused into tungsten, and the least amount of free carbon was observed. The amount of free carbon in the mixed powder was higher than that of carbon combined with tungsten at 1073 K, but it decreased as the temperature rose and approached to zero at temperature above 1273 K.Coexisting with cobalt, the carbide formation rate of tungsten was approximately 2 to 7 times as large as that of pure tungsten, and the effect of cobalt enhance with increase in carburizing temperature. The relation between formation amount of carbide h and carburizing time t was expressed in the form of h=qtp. The value of p was 1⁄2 for pure tungsten. While coexisting with cobalt, the value of p varied from 2⁄3 to 1 where the shift from the parabolic law increased with rising temperature, and the activation energy for formation of tungsten carbide also increased.