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Coke formation during metal dusting of iron in CO‐H 2 ‐H 2 O gas with high CO content
Author(s) -
Zhang J.,
Schneider A.,
Inden G.
Publication year - 2003
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/maco.200303741
Subject(s) - graphite , coke , materials science , cementite , layer (electronics) , petroleum coke , carbon fibers , metal , metallurgy , composite material , chemical engineering , microstructure , austenite , engineering , composite number
Iron carburisation and coke formation during metal dusting of iron have been investigated in the gas mixture of 75%CO‐24.8%H 2 ‐0.2%H 2 O at 600°C and 700°C. In all cases, cementite is formed at the surface, together with a coke layer on the top. In the coke layer, two morphologies of graphite are identified: compact bulk graphite with a uniform thickness and a columnar structure, and filamentous carbon with iron‐containing phases at the tip or along its length. The examination of coke formation in different stages of reaction at 700°C reveals that the coke contains two layers. The inner layer is composed of filaments, while the outer layer consists of the compact columnar graphite. After 2 h reaction the top compact graphite layer has suffered a serious deformation and has formed fractures because of the growth of catalytic filamentous carbon underneath. These filaments grow outside from these fractures and finally cover the whole surface after 4 h reaction. At 600°C, however, the coke contains a thick bulk graphite layer and non‐uniformly distributed filaments on the top. The bulk graphite layer is composed of many graphite columns which are loosely piled and are vertical to the surface. Each graphite column consists of many fine graphite fibres in parallel with the columnar axis. Filaments grow outside preferably from the gaps among these graphite columns and along the grinding scratches. TEM analysis of the coke detects very convoluted filaments with iron‐containing particles at the tip or along their length. XRD and TEM analyses show that these particles are Fe 3 C rather than metallic iron.