The oxidation resistance and constitution of Y₉Co₇ and nearly-relatedcompounds

Abstract

The ratio of the thermal oxidation parameter to the decomposition point (T _p/T _m) is of the order of 0 85 for Y₉Co₇, indicating a high degree of chemical binding. The persistence of high values of this ratio has been investigated with respect to (a) other compounds in the Y-Co system, (b) replacement of cobalt in Y₉Co₇ by other d-e!ements, and (c) replacement of yttrium by other rare-earth elements. High ratios are found for (a) Y-Co compounds where Y/Co > 0.5, (b) Y-3d compounds with cobalt and niche! only, end (c) RE-Co compounds generally. However, there are differences in level of the ratio amongst the rare-earth compounds, from which it is inferred that the highest values coincide with full electron shells, that is, without participation of 4f electrons. Additional work is described on an effect of preparation arc-melting current 0n theT _p value for Y₉Co₇, and on compounds of the same pattern where both components are changed.