Transport Phenomena in the Scale Formed on Cr in SO_2 at 3X10~4 Pa and 10~5 Pa

摘要

The kinetics, phase composition and morphology of the scales growing on chromium in SO_2 atmospheres were studied at 1073 K/1273 K and SO_2 pressures of 3X10~4 Pa and 10~5 Pa. The scales consisted mainly of Cr_2O_3, while a small amount of sulfur (probably CrS) was detected only on the surface of metallic core and in the scale next to metallic core. Oxidation proceeds according to the linear rate law at 10~5 Pa of sulfur dioxide, whereas at 1173 K and 1273 K under 3X10~4 Pa of SO_2 it proceeds according to the parabolic rate law. The transport phenomena were studied by radiotracer as well as marker techniques. The oxide-sulfide scales grew by outward diffusion of the metal. Inward transport of S_2 or SO_2 molecules probably through the discontinuities in the scale was observed. The mechanisms of sulfide an oxide formation are discussed on the basis of the experimental results.