Weight change and oxygen consumption measurements were used to study the oxidation of molybdenum from 550 ~ to 1704~ for pressures of 5 to 76 Torr. For temperatures of 550~176 two processes occurred simultaneously, oxide scale formation and molybdenum trioxide volatility. Above 800~ at pressures up to 76 Tort molybdenum trioxide volatilized as fast as it formed. At 900~ and 76 Torr using 1.2 cm 2 samples the primary chemical reaction gave a rate of about 10 is at. molybdenum/cm2/sec. Above this temperature for 1.2 cm 2 specimens the reaction was limited by gaseous diffusion of oxygen. Little change was found in the rate of oxidation to 1615~ Pressure had only a small effect on the rate of reaction for these reaction conditions. However, in the chemically controlled region pressure had an important effect on the rate of oxidation. To extend the temperature region where the primary chemical reaction was rate controlling, samples of small area were used. A sample having a total area of 0.12 cm 2 gave a reaction rate of 8 x 10 is at./cm2/sec at 1410~ For these very fast reactions, appreciable temperature rises occurred, and the actual sample temperature had to be estimated. A log K vs. 1/T plot of the primary chemical

A kinetic study was made of the oxidation of high-purity silicon carbide using a dynamic-type reaction system. Two types of oxidation behavior were found. Passive oxidation occurred for conditions where silica films were formed on the surface. Active oxidation occurred for conditions where volatile silicon monoxide was formed. The transition conditions between the two types of oxidation were studied as a function of oxygen pressure and temperature. The transition temperatures and pressures were related to thermochemical conditions for the reaction of silicon carbide with silica to form silicon monoxide and carbon monoxide.

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Weight change and oxygen consumption measurements were used to study the kinetics of oxidation of tungsten from 1150° to 1615°C at oxygen pressures of 2–100 Torr. The data were collected in a static type reaction system. Volatilization of tungsten trioxide above 1100°C changed the nature of the oxidation reaction for temperatures between 1100° and 1250°C. At 1150°C and 76 Torr oxygen pressure, oxide scale formed and some tungsten trioxide volatilized, while at 1250 °C and 76 Torr oxygen pressure, all of the oxygen reacted to form volatile tungsten trioxide.Initial oxidation rates were used to evaluate the effect of temperature and pressure on the kinetics of oxidation. Between 1100° and 1250°C, the initial rates of oxidation were nearly independent of temperature. A rapid increase in the rates of oxidation occurred between 1250° and 1350°C for oxygen pressures above 5 Torr. Above 1350 °C the rate data also increased with temperature but to a smaller extent. Due to oxide volatility, oxygen pressure had a major influence on the formation of oxide scale for temperatures between 1000° and 1250 °C. Low oxygen pressures favored volatilization of the oxide for a given temperature. Above 1300 °C, where oxide scales were absent, the effect of oxygen pressure on the rate of reaction followed the equation normaldn/normaldt=KP1.1 Here normaldn/normaldt is the rate of oxidation, P is the pressure, and K is a constant. Above 1300°C, the rate‐controlling process was probably the diffusion of oxygen gas through a barrier layer of tungsten trioxide vapor. Comparison of the rates of oxidation with those for carbon and molybdenum obtained under similar reaction conditions showed tungsten to have the fastest rate of oxidation. This may be related to the nature of the barrier layer of reaction product surrounding the specimen undergoing reaction.

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