The conversion of chromium oxide to chromium carbide

Chu, W. F.; Rahmel, A.

doi:10.1007/bf01058833

Cited by 41 publications

(14 citation statements)

References 5 publications

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“…Table 1. Variation of the Gibbs energy during the formation of the different phases in the Fe-C-O system This transformation is well known [24] for chromium oxide Cr 2 O 3 and occurs when the alloys is covered with a graphite layer and heated to temperatures > 1050 8C. The atmosphere at the oxide/metal interface has a carbon activity a c ¼ 1 (equilibrium with graphite) and its oxygen activity decreases because of the reducing gas mixture.…”

Section: Thermodynamic Calculationsmentioning

confidence: 99%

Filamentous carbon formation caused by catalytic metal particles from iron oxide

Bonnet

Ropital²,

Berthier

et al. 2003

Materials & Corrosion

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The thermodynamic equilibrium between metallic iron, iron oxides, iron carbides and an hydrocarbon/hydrogen mixture was calculated at 600 8C. On the basis of the metastable Fe-C-O phase diagram, both metallic iron and iron oxides can be directly converted into carbides in reducing and carburizing atmosphere. Thermogravimetric (ATG) measurements have been performed in iC 4 H 10 -H 2 -Ar atmosphere at 600 8C on reduced and pre-oxidised iron samples. The kinetic of coke formation was studied on both surface states by sequential exposure experiments. The initial stages of the transformation were characterised by scanning electron microscopy (SEM) observations and X-ray diffraction (XRD) analysis. On a reduced surface, the results are consistent with the mechanism currently proposed to explain catalytic coke formation. Cementite (Fe 3 C) is formed on the iron surface after carbon supersaturation (a c > 1).The graphite deposition on its surface (a c ¼ 1) induces its decomposition. Iron atoms from cementite diffuse through the graphite and agglomerate to small particles that act as catalysts for further carbon deposition. A new mechanism of catalytic particle formation is proposed when an oxide scale initially covers the iron surface. In the carburizing and reducing atmosphere, magnetite (Fe 3 O 4 ) can be directly converted into cementite (Fe 3 C). XPS analysis confirm that, in this process, metallic iron is not an intermediary specie of the oxide/carbide reaction. At the same time, graphite deposition occurs at the metal/oxide interface through the cracks present in the oxide scale. Iron carbide in contact with graphite is partially decomposed and acts as catalyst for graphitic filaments growth.

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Section: Thermodynamic Calculationsmentioning

confidence: 99%

Filamentous carbon formation caused by catalytic metal particles from iron oxide

Bonnet

Ropital²,

Berthier

et al. 2003

Materials & Corrosion

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“…3) and the conversion will start. The rate of the reaction is slow in CO À CO 2 mixtures [17] but fast in the presence of carbon deposits and when H 2 À H 2 O are present. Cracking tubes are endangered especially during de-coking, by the exothermic burning of the carbon layer with H 2 O-air mixtures.…”

Section: Failures Due To Carburization 21 Conversion Of the Chromiummentioning

confidence: 99%

Carburization - introductory survey

Rahmel¹,

Grabke

Steinkusch³

1998

Materials and Corrosion

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“…In our previous study , Cr 3 C 2 peaks are easy to be found in the XRD patterns as compacts prepared by HP densification in which the vacuum maintained at about 10 -5 torr, however in this SPS process that is about 6 pa (~10 -2 torr). According to the report of Chu & Rahmel, 1981, carbon would be consumed by oxygen in a higher oxygen pressure in SPS process and inhibits the formation of Cr 3 C 2 . This result is consistent with the apparent density shown in Fig.…”

Section: Effect Of Sps Sintering Temperature On the Color Changes Of mentioning

confidence: 99%

Processing and Characterization of Alumina/ Chromium Carbide Ceramic Nanocomposite

Huang¹,

Nayak²

2011

Advances in Nanocomposite Technology

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The conversion of chromium oxide to chromium carbide

Cited by 41 publications

References 5 publications

Filamentous carbon formation caused by catalytic metal particles from iron oxide

Filamentous carbon formation caused by catalytic metal particles from iron oxide

Carburization - introductory survey

Processing and Characterization of Alumina/ Chromium Carbide Ceramic Nanocomposite

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