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Oxidation of binary Hf-Nb alloys with 10-50wt%Nb and a few corresponding alloys with ternary additions of Cr, Ti, V, and W has been studied in the temperature range 800-1300 C. Most of the studies were carried out at 10 torr O2, but the oxidation of one binary alloy (Hf-34wt%Nb) was also studied as a function of oxygen pressure. The major reaction products are HfO2, Nb2O5, and Nb2O5 6HfO2. At and above 10 torr O2 the oxidation of the binary alloys increase with temperature up to 900-1000 C, where the oxidation goes through a maximum and then decreases up to about 1100 C. Above 1100 C the oxidation again increases with temperature. This maximum is interpreted as a result of an interplay between relative rates of formation of HfO2 and Nb2O5 and their subsequent reaction to form Nb2O5 6HfO2. The ternary alloy additions of Cr, Ti, and W did not significantly change the oxidation rates. Catastrophic oxidation was observed for Hf-25w/oNb-52/oV and Hf-20w/oNb-10w/oV alloys above 1000 and 900 C, respectively. The binary Hf-Nb alloys showed poor oxidation resistance, and at 900-1000 C the oxidation is as fast as for unalloyed niobium. (Author).
The vapor pressure of each of the niobium-zinc compounds was measured as a function of temperature. The kinetics of formation of the niobiumzinc compounds on pure niobium from zinc vapor were investigated, and oxidation tests were made on several coatings applied with zinc vapor. The mechanisms involved and the kinetics of the removal of interstitial impurities from niobium by the niobium-zinc compounds were also studied. Further studies of the effects of alloying elements added to the zinc bath used to coat niobium by the dip process confirmed that small amounts of nickel and aluminum in the proper combination are beneficial. (Author).