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Reduction-Carburization of NiO-WO3 Under Isothermal Conditions Using H2-CH4 Gas Mixture
Department of Materials Science and Engineering, Royal Institute of Technology.
Kungliga tekniska högskolan, KTH.
2010 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 41, no 1, 173-181 p.Article in journal (Refereed) Published
Abstract [en]

Ni-W-C ternary carbides were synthesized by simultaneous reduction–carburization of NiO-WO3 oxide precursors using H2-CH4 gas mixtures in the temperature range of 973 to 1273 K. The kinetics of the gas–solid reaction were followed closely by monitoring the mass changes using the thermogravimetric method (TGA). As a thin bed of the precursors were used, each particle was in direct contact with the gas mixture. The results showed that the hydrogen reduction of the oxide mixture was complete before the carburization took place. The nascent particles of the metals formed by reduction could react with the gas mixture with well-defined carbon potential to form a uniform product of Ni-W-C. Consequently, the reaction rate could be conceived as being controlled by the chemical reaction. From the reaction rate, Arrhenius activation energies for reduction and carburization were evaluated. Characterization of the carbides produced was carried out using X-ray diffraction and a scanning electron microscope (SEM) combined with electron dispersion spectroscopy (SEM-EDS) analyses. The grain sizes also were determined. The process parameters, such as the temperature of the reduction–carburization reaction and the composition of the gas mixture, had a strong impact on the carbide composition as well as on the grain size. The results are discussed in light of the reduction kinetics of the oxides and the thermodynamic constraints.

Place, publisher, year, edition, pages
2010. Vol. 41, no 1, 173-181 p.
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
URN: urn:nbn:se:ltu:diva-5354DOI: 10.1007/s11663-009-9307-2Local ID: 370b7fb4-3bc5-43c2-b3d8-b27039c3f7e4OAI: oai:DiVA.org:ltu-5354DiVA: diva2:978228
Note
Upprättat; 2010; 20141022 (hesahm)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-10-19Bibliographically approved

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