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Oxidation of Metals

, Volume 27, Issue 3–4, pp 221–237 | Cite as

Sulfidation kinetics and scale structures of chromium at temperatures of 973–1173 K and 104–10−6 Pa sulfur pressures

  • Toshio Narita
  • Tatsuo Ishikawa
  • Keizo Nishida
Article

Abstract

The sulfidation behavior of chromium was investigated over a temperature range of 973–1173 K in H2S-H2 gas mixtures of 104–10−6 Pa sulfur partial pressures using thermogravimetry, X-ray diffractometry, optical and scanning electron microscopy, and electron-probe microanalysis. Sulfidation kinetics are rapid for short periods and obey a linear rate law at low sulfur pressures, whereas at high sulfur pressures sulfidation tends to be parabolic. The surface morphologies can be divided into four types: at high sulfur pressures a petal-like crystal of Cr2S3(rho. and tri.) (type 1), at intermediate sulfur pressures a twinlike structure of Cr3S4 (type 2), at low sulfur pressures a flat surface with numerous hexagonal pits of Cr1−xS (type 3), and a fine twinlike structure of ordered Cr1−xS (type 4). At 973 K, the sulfur pressure ranges are type 1 at\(p_{S_2 } \) > 10−4, type 2 at\(p_{S_2 } = 10^{ - 5} \), and type 3 at\(p_{S_2 }< 10^{ - 6} Pa\). The critical sulfur pressure where type 2 was formed, 10−5 Pa at 973 K, shifts toward higherressures at higher temperatures and becomes 10−3 Pa at 1073 K and 10−1 Pa at 1173K. Type 4 is observed at 1173K and 10−6 Pa sulfur pressure. Thesulfide scale is composed of two distinct layers: an external layer, which is dense with a fine columnar structure, and an inner layer, which is porous with a layered structure of sulfides and voids. The external scale is composed offour layers at high sulfur pressures: at the scale-gas interface Cr2S3(rho.), next Cr2S3(tri.), third Cr3S4, and innermost Cr1−xS. With decreasing sulfur pressures,the number of layers in the external scale was reduced. Pt markers were positioned between the external and inner scales.

Key words

Chromium sulfidation kinetics chromium sulfides multilayer structure H2S-H2 gas mixtures 

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Copyright information

© Plenum Publishing Corporation 1987

Authors and Affiliations

  • Toshio Narita
    • 1
  • Tatsuo Ishikawa
    • 1
  • Keizo Nishida
  1. 1.Department of Metallurgical Engineering, Faculty of EngineeringHokkaido UniversitySapporoJapan

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