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Microprocesses of coke formation in metal dusting
Author(s) -
Wei Q.,
Pippel E.,
Woltersdorf J.,
Grabke H.J.
Publication year - 1999
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/(sici)1521-4176(199911)50:11<628::aid-maco628>3.0.co;2-3
Subject(s) - carbide , carburizing , coke , graphite , metallurgy , metal , carbon fibers , nucleation , materials science , chemical engineering , chemistry , composite material , organic chemistry , composite number , engineering
The microprocess of coke formation during metal dusting on iron in a carburizing atmosphere with medium and extremely high carbon activities as well as the influence of sulphur have been studied down to the nanometer scale using high resolution electron microscopy (HREM) and analytical electron microscopic techniques (AEM). While for medium carbon activities the metal dusting proceeds via a formation, disintegration and further decomposition of a metastable carbide Fe 3 C into Fe and C, the additional formation of the carbide Fe 5 C 2 and the stabilization of carbides in the coke region have been observed for extremely high carbon activities. If sulphur is present in the atmosphere metal dusting takes place solely in the S‐free surface areas. Furthermore, sulphur deposited from the atmosphere will suppress the nucleation of graphite in the coke. In addition, the results reveal that, irrespective of the degree of the carbon activity, there is a fundamental initial reaction micromechanism of metal dusting characterized by a vertically oriented deposition of graphite lattice planes with respect to the original surface of the substrate and with free ends affecting the decomposition of the carbides and thus forming a coke of carbon and iron, or of carbide particles, depending on the carbon activity.