“…SiO 2 has one of the lowest diffusion coefficients of O 2 (Jacobson, 1993), and as a result, this passive oxidation process is a slow process. At very high temperatures, formation of gaseous SiO becomes possible, and the oxidation process moves into a phase of active oxidation, where because of absence of a protective scale, the rate of the reaction is very high (Wagner, 1958;Pareek and Shores, 1992;Zheng et al, 1992;Sickafoose and Readey, 1993;Nickel et al, 1993). This pattern of oxidation is qualitatively the same for all Si-based materials, but the location of the passive to active oxidation transition boundary on the [oxygen partial pressure, temperature] plane varies with each material (Jacobson, 1993).…”