INTERACTION OF ALLOY NIOBIUM-25TITANIUM WITH AIR OXYGEN AND NITROGEN .2. REACTION OF NB-25TI IN AIR AND OXYGEN BETWEEN 650DEGREES AND 1000 DEGREES C

The oxidation behavior of Nb-25 wt.% Ti (39 at.% Ti) in air and oxygen between 650 ° and 1000 °C has been studied. Below 800 °C the alloy oxidizes in agreement with the parabolic rate law in either air or oxygen. The activation energy for the process, i.e., the dissolution of oxygen into the alloy, is 19.5 kcal mol-1. Between 650 ° and 800 °C little or no external oxide product is formed except after extended exposure. The nitrogen component of the air plays only a very minor role in the oxidation process. Above 800 °C, the oxidation behavior of the alloy is markedly different in air and oxygen. The kinetics are approximately linear in air and parabolic in oxygen. The activation energies for these processes are 38 and 76 kcal mol-1, respectively. In this temperature range an external oxide is formed and the internal structure observed at 1000 °C and described in Part I of this report1 is observed. Between 800 ° and 1000 °C the presence of nitrogen in the oxidizing atmosphere exerts a strong effect on the oxidation kinetics. © 1969.