Reaction of Nb-19 at%Al Alloy in a Technical-grade Nitrogen Gas and in an Artificial Air During a Slow Constant Rate Heating up to 1000°C

Abstract

A Nb-19 at%Al alloy, which composed of Nb₃Al-phase and a small amount of Nb-phase, was heated in a technical-grade nitrogen and in an artificial air at a rate of 2°C/min up to 1000°C. The reactions were compared with those in pure nitrogen, on which a paper has already been published.
In both gases weight increase started at ca. 800°C, as did in pure oxygen. The weight increases at 1000°C were, however, ca. 10% in the nitrogen and ca. 40% in the artificial air respectively of that in the oxygen.
In the case of the nitrogen, major components of the scale were oxides, although nitrogen compounds were detected in the X-ray diffraction pattern (XRDP). The major reaction was considered to be the oxidation caused by oxygen and moisture in the nitrogen, whose process was identical with that in the oxygen.
In the cases of the air, no nitrogen compound was detected in XRDP, although the surface was in a color specific to reactions in nitrogen. The reaction was considered to be akin to that in the oxygen. A comparison with the reaction in Ar-20 vol%O₂ revealed nitrogen retarding the reaction.