Change of the dynamic modulus of elasticity as criterion of the state of oxidation of boron fibers

Conclusions At 723 K, which obviously is the melting point of the oxide B₂O₃, the mechanism of growth of the oxide on BF changes. Below 723 K the activation energy of growth of oxide is equal to 1.0; above 723 K it is equal to 1.7 eV.The suggested method of investigating the oxidation of solids is based on the measurement of the normalized dynamic modulus of elasticity of the specimen in the process of oxidation. This method can be used for studying oxidation from the surface, not only of cylindrical specimens but also of specimens with other cross-sectional profile. It is also applicable in the investigation of intracrystalline corrosion because expression (9), determining the thickness of the oxide film, was obtained on the basis of the ratio of the volume fractions of the phases coexisting in the specimen, independently of the place in the specimen at which the new phase grows and what profile it has. Formula (9) describes some effective thickness of the phase which would grow from the surface if the specimen had cylindrical shape. The change of the effective thickness of the phase in annealing in dependence on time makes it possible to determine the true kinetic parameters of the process because this change corresponds to the change of the volume fraction of the growing phase.Translated from Poroshkovaya Metallurgiya, No. 11, pp. 91–95, November, 1990.