Niobium—Al2O3 Reactions Yielding Condensed and Volatile Products

A mass‐spectrometric and thermogravimetric study of the equilibrium interaction between Al₂O₃ and Nb between 1800° and 2200°K has been conducted. The reaction proceeds principally as ${\mathrm{Al}}_2{\mathrm{O}}_3\text{+3}\mathrm{Nb}\text{=2}\mathrm{Al}(\mathrm{g}\text{)+3}\mathrm{NbO}(\mathrm{s})$ ; two secondary reactions of about equal importance under neutral conditions are ${\mathrm{Al}}_2{\mathrm{O}}_3+\mathrm{Nb}={\mathrm{Al}}_2\mathrm{O}(\mathrm{g}\mathrm{)+}{\mathrm{NbO}}_2(\mathrm{g})$ and ${\mathrm{Al}}_2{\mathrm{O}}_3\text{+2}\mathrm{Nb}+\frac{1}{2}{\mathrm{O}}_2={\mathrm{Al}}_2\mathrm{O}(\mathrm{g}\mathrm{)+}{\mathrm{NbO}}_2(\mathrm{g}\mathrm{)+}\mathrm{NbO}(\mathrm{s})$ . The latter reaction can dominate under oxidizing conditions. The weight loss caused by the gaseous reaction products is about one hundred times the weight loss caused by the evaporation of alumina under neutral conditions. Calculations show that yttria and some other oxides can be used with Nb at high temperatures with no significant reaction.