Über die Oxydation metallischer Hartstoffe

Abstract

AbstractThe oxidation of TiN, TiC and TiB2 has been investigated between 600 and 1100°C. In the case of TiN. the rate of oxidation can be described by a linear‐parabolic law. The only oxidation product is TiO2 (rutile which is formed at the inner phase boundary. The nitrogen escapes almost completely to the gas phase. The activation energy of the diffusion through the oxide layer as calculated from the isothermes agrees fairly well with the value obtained for the oxidation of titanium metal. It is concluded that the kinetics of the oxidation is not influenced to a considerable extent by the diffusion of the nitrogen.The oxidation of TiC is governed by a purely parabolic law yielding almost the same activation energie as obtained for Ti and TiN. The oxide layer is rutile containing 0,1–0,2 weight % of carbon. The rutile is formed at the inner phase boundary. Oxygen diffuses through the oxide layer to the inner phase boundary whereas carbon diffuses outwards, being oxidized to CO and CO2 at the outer surface.The oxidation of TiB2 follows a parabolic law below 850 and above 950°C. The activation energies are different in both cases. The 900°C isotherme can be described by a cubic law. At 700°C the oxide layer is a fine‐grained mixture of TiO2 and B2O3. At higher temperatures we have phase separation on the macroscopic scale. Three zones may be distinguished: Glassy B2O3, TiO2 and the fine‐grained mixture. Above 1000°C the B2O3 begins to evaporate more and more. At 1100°C it is not found by X‐ray diffraction. Both oxides are formed at the inner phase boundary.