The Preferred Orientation of the Ferrous Sulfide Scale on Pure Iron at 700°C

The preferred orientation and its variation with sulfur pressure were observed in the course of the study on the sulfurization of pure iron at 700°C. Further, SEM observations revealed the characteristic variation of the surface morphology of the scale with sulfur pressure.The preferred orientation of the grown scale changed with sulfur pressure and the orientation differences were quantitatively determined by means of X-ray pole figures.By using the diffusion theory as well as the present observations the effect of the preferred orientation of the scale on the overall corrosion rates was disclosed.The calculated value of 1/n as a measure of the pressure dependence of the corrosion rates is about 1/5.7. This value suggests that there is no interaction between vacancies and positive holes in the ferrous sulfide at 700°C. The similar conclusion was obtained from the relationships between vacancy concentration and sulfur activity determined previously by several authors.