ISSN:
1573-4889
Schlagwort(e):
Chromium
;
sulfidation kinetics
;
chromium sulfides
;
multilayer structure
;
H2S-H2 gas mixtures
Quelle:
Springer Online Journal Archives 1860-2000
Thema:
Maschinenbau
Notizen:
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.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1007/BF00667060
Permalink
