Accession Number : AD0278826

Title :   KINETICS OF OXIDATION IN THE MO-SI SYSTEM

Corporate Author : LITTLE (ARTHUR D) INC CAMBRIDGE MASS

Personal Author(s) : BERKOWITZ,JOAN

Report Date : MAY 1962

Pagination or Media Count : 1

Abstract : The oxidation behavior of Mo, Mo3Si, Mo5Si3, and MoSi2 was studied at temperatures between 1000 and 1725 C at oxygen partial pressures less than 20 mm. Pure Mo metal oxidizes linearly in this range, with a ratio constant k=k(sub o)l(-22,000/RT)p(0.87), where p is oxygen partial pressure, the gas constant R is in cal/mole, T is in K, and k(sub o) is a constant independent of temperature and pressure. To a good approximation, oxidation of the Mo silicides follows a logarithmic rate law, Q=Q(sub o)(1-l(-alpha t), where Q is the total oxygen consumed between time zero and time t, while Q(sub o) and alpha are constants, dependent upon composition, pressure and temperature. At any fixed temperature, the most oxidation resistant material is MoSi2; Mo5Si3 is oxidized to a larger extent before a protective coating is established, and Mo3Si is oxidized still more extensively. The rates of oxidation of all 3 compounds eventually reaches a low-limiting value. Metallographic examinations established that oxidation proceeds at least in part by diffusion of oxygen inward. An apparatus utilizing a thermal conductivity bridge is described for continuous measurement of the rate of oxidation of metallic materials at temperatures between 900 and 2100 C. (Author)

Descriptors :   ANTIOXIDANTS, CHEMICAL REACTIONS, FILMS, GROWTH(PHYSIOLOGY), INTERMETALLIC COMPOUNDS, OXIDES, PHASE STUDIES, SILICON, SILICON COMPOUNDS, TEST EQUIPMENT, THERMAL CONDUCTIVITY, VAPORIZATION

Distribution Statement : APPROVED FOR PUBLIC RELEASE