Kinetics of Oxidation of Fe–6Si

Abstract

Surface oxidation of Fe-6Si during annealing in low-pressure air (*10 4 Pa) in the temperature range 500-550°C was investigated using resistivity measurements, Mössbauer spectroscopy, X-ray diffraction and scanning-electron microscopy (SEM). The time dependence of the resistivity exhibits an increase in two steps, which indicates changes in the structure and/or phase composition of the alloy. Structure and phase investigations show that the first step can be explained as formation of hematite (a-Fe 2 O 3 ) and the second step is due to transformation of the hematite to magnetite (Fe 3 O 4 ). The kinetics of the transformations were derived from the resistivity data. The activation energies (estimated from Arrhenius plots) of 194 kJ/mol and 165 kJ/mol were obtained for the formation of hematite and transformation of hematite to magnetite, respectively.

High temperature corrosion of Fe‐6 wt% Si steel in various atmospheres

“…. Lashin also used resistivity measurements together with other methods for an explanation of hematite (α‐Fe 2 O 3 ) to magnetite (Fe 3 O 4 ) transformation in the temperature range 500–550 °C and low‐pressure air (∼10 4 Pa). Adachi and Meier studied isothermal and cyclic oxidation in air and in argon at 900, 1000, and 1100 °C for 1 week.…”