Characterization of Oxidation Kinetics of Mo-Si-B-Based Materials

Characterization of oxidation kinetics of composites based on refractory metals like Mo by means of thermogravimetry is often very complex, because of the simultaneous formation of both volatile and stable oxides. Specifically, thermogravimetrically measured specific mass changes represent the sum of opposite mass change processes: (i) mass loss due to the formation of volatile oxide species and (ii) mass gain as a result of oxygen uptake due to the growth of solid, adherent oxide layers. In order to unambiguously assess the oxidation resistance of such alloys, a separation of these two opposing processes and their quantitative description are needed. In this study, a novel approach is proposed that enables determination of the amount of the material affected during oxidation using the measured oxide layer thickness. This approach also permits a quantitative separation of thermogravimetric data into mass loss (oxide evaporation) and mass gain (oxygen uptake). The advantage of splitting of the thermogravimetric curve into mass gain and mass loss is discussed on the basis of the multiphase material Mo-9Si-8B.