Surface analytical studies of metal dusting of iron in CH4-H2-H2S mixtures

Schneider, A.; Viefhaus, H.; Inden, Gerhard

doi:10.1002/(sici)1521-4176(200005)51:5<338::aid-maco338>3.0.co;2-k

Cited by 26 publications

(16 citation statements)

References 8 publications

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“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Despite of these many studies, the details of the reaction mechanism of Fe3C formation and its physical properties have not yet been established well. The reason for the lack in knowledge mainly comes from the metastability of the carbide causing experimental difficulties.…”

Section: Introductionmentioning

confidence: 95%

Cementite Formation from Magnetite under High Pressure Conditions

2013

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Measurements have been made of the rate of Fe3C formation from Fe3O4 powder and Fe3O4 single crystals at 773 K and 1 023 K under the high pressure of 0.5 and 1.0 MPa by using thermo-gravimetric method. Along with the kinetic study of Fe3C formation, high resolution TEM observation around the interface between Fe3O4 matrix and the formed Fe3C have been carried out to confirm the thermodynamically possible direct Fe3C formation from Fe3O4 without the formation of intermediate metallic Fe. Analysis of the rate results suggests that the reaction mechanism of Fe3C formation was possibly described by the sequential reactions of the conversion of Fe3O4 to Fe3C via intermediate metallic Fe although the metallic Fe existence was not confirmed by TEM observation. This inconsistency was explained by considering the relative reaction rates of Fe3C formation from Fe and Fe formation from Fe3O4. It was also found that not only the carbon activity of more than unity but also the low oxygen potential enough for metallic Fe existence might be required for the Fe3C formation.

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Section: Introductionmentioning

confidence: 95%

Cementite Formation from Magnetite under High Pressure Conditions

2013

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“…The information about sulfur adsorption on cementite, however, is poor. It has been shown that sulfur can be adsorbed [37] or segregated to cementite surfaces [38], but more quantitative data are missing.…”

Section: Introductionmentioning

confidence: 78%

Carburization and Metal Dusting on Iron

2001

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Fundamentalstudies have been conducted on the kinetics and mechanisms of reactions of iron in CH4-H2and CO-H2-H20 mixtures, also in the presence of H2S, to understand earburization, iron oarbide formation, metal dusting and carbon deposition. Therate equations and mechanisms of the surface reaction in oarburization of iron are presented, the carburization in CH4-H2 is muchslower than in CO-H2. Both reactions are retarded by adsorbed sulfVr, the carburization rate becomesinversely proportional to the sulfur activity as~PH2S/pH2 with increasing as. At carbon activities ac ) I cementite growth oan be started in both gas mixtures on iron, however, the decomposition of this unstable oarbide gives rise to a corrosion process 'metal dusting', i.e. the material disintegrates to a dust of metal particles and graphitic carbon. This disintegration ean be prevented by adsorbed sulfur which hinders the nucleation of graphite. The stabilizing effect of sulfur on cementite and higher carbides such as Hagg carbide, allows fundamental studies about their thermodynamics, non-stoichiometry and diffusional growih mechanisms, on the other hand the presenoe of sulfur will allow iron oarbide production in the reduction of iron ores in carburizing gas mixtures.

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“…1 can also be applied for the complex processes during metal dusting of iron, surface analytical studies on sulphur segregation on Fe 3 C surfaces have been performed in an in situ experiment with a hot stage in an Auger apparatus [15]. At first an iron foil was carburised at 700 8C for 340 h in a CH 4 -H 2 -H 2 S gas mixture with a C ¼ 100 and 1 ppm H 2 S to obtain Fe 3 C on the surface.…”

Section: Effect Of H S On Carburisation Kinetics and Graphite Formationmentioning

confidence: 99%

“…Consequently, without H 2 S addition cementite starts to decompose before Hägg carbide nucleation sets on. The presence of segregated sulphur is observed [15] The effect of sulphur on metal dusting was also studied using CH 4 -H 2 -H 2 S gas mixtures [15]. The TGA curves in Fig.…”

Section: Effect Of H S On Carburisation Kinetics and Graphite Formationmentioning

confidence: 99%

Effect of H₂S on metal dusting of iron

Schneider¹,

Grabke

2003

Materials & Corrosion

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A review is given on the effect of H 2 S on metal dusting of iron which has been studied by gas carburisation in CO-H 2 -H 2 O-H 2 S and CH 4 -H 2 -H 2 S mixtures at 500 and 700 8C.The presence of H 2 S in carburising gas atmospheres leads to sulphur adsorption on the iron surface, which retards carbon transfer. Segregation experiments and surface analyses have shown that sulphur segregates (and thus adsorbs) on cementite surfaces as well as on iron surfaces. The adsorbed sulphur also suppresses graphite nucleation and thus can stop the reaction sequence of metal dusting.Experiments by thermogravimetric analysis (TGA) have shown that the extent of retardation of metal dusting depends on temperature, carbon activity and H 2 S content. The higher the carbon activity, the higher is the H 2 S content required for suppression of metal dusting.At carbon activities a C > a C (Fe/Fe 3 C) the metastable iron carbide, cementite (Fe 3 C), occurs as an intermediate phase during metal dusting. Carburisation experiments in CO-H 2 -H 2 O-H 2 S mixtures at 500 8C and X-ray diffraction analysis (XRD) of carburised samples have revealed that at very high carbon activities a second iron carbide, Hägg carbide (Fe 5 C 2 ), forms on the cementite surface. Microstructural investigations have shown that both metastable carbides decompose during metal dusting.Metal dusting experiments on iron at 700 8C have been performed in CH 4 -H 2 -H 2 S gas mixtures. By adding 15 ppm H 2 S to the CH 4 -H 2 atmosphere the onset of metal dusting can be retarded for more than 350 hours. By means of Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) it was shown that coke contains graphite, cementite and iron particles with adsorbed sulphur.

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Surface analytical studies of metal dusting of iron in CH4-H2-H2S mixtures

Cited by 26 publications

References 8 publications

Cementite Formation from Magnetite under High Pressure Conditions

Cementite Formation from Magnetite under High Pressure Conditions

Carburization and Metal Dusting on Iron

Effect of H₂S on metal dusting of iron

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Surface analytical studies of metal dusting of iron in CH4-H2-H2S mixtures

Cited by 26 publications

References 8 publications

Cementite Formation from Magnetite under High Pressure Conditions

Cementite Formation from Magnetite under High Pressure Conditions

Carburization and Metal Dusting on Iron

Effect of H2S on metal dusting of iron

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Effect of H₂S on metal dusting of iron