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Simultaneous reduction nitridation for the synthesis of tungsten nitrides from Ni–W–O precursors
Central Metallurgical Research and Development Institute (CMRDI), Helwan, Cairo.
Royal Institute of Technology, Stockholm.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
Royal Institute of Technology, Stockholm.
2013 (English)In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 56, no 5, 411-419 p.Article in journal (Refereed) Published
Abstract [en]

Tungsten nitrides were synthesised from NiO–WO3 and NiWO4 precursors at 973–1273 K in a flow of H2–N2 gas mixture. The reduction–nitridation reactions were carried out isothermally in fluidised bed reactor, and the off-gas from the reactions was continuously analysed by gas chromatography. The effect of reaction temperature and precursor composition on the rate of formation of Ni–W nitrides was studied. The different phases developed during the reduction– nitridation reactions were identified by X-ray diffraction analysis technique. The morphology and the grain structure of the precursors were examined by SEM, and the elemental composition in the structure was analysed by electron dispersive spectrometry. The results showed that the reduction of Ni–W–O precursors proceeded in a stepwise manner (NiWO4RNi–WO3RNi– WO2RNi–W). Tungsten nitrides (WN and WN2) were formed from the reaction of the freshly reduced W metal with N2 gas and WN was the predominant phase detected at higher temperatures. The reaction mechanisms were elucidated from the apparent activation energy values and the application of different formulations derived from the gas–solid reaction model at early and later stages of reactions. It was concluded that the interfacial chemical reaction is the rate determining step at initial stages, while a combined effect of gaseous diffusion and interfacial chemical reaction controlled the reaction at later stages. At final stages, the nitridation reactions contributed to the reaction mechanism leading to produce tungsten nitrides.

Place, publisher, year, edition, pages
2013. Vol. 56, no 5, 411-419 p.
National Category
Metallurgy and Metallic Materials
Research subject
Process Metallurgy
Identifiers
URN: urn:nbn:se:ltu:diva-38594DOI: 10.1179/1743290113Y.0000000061Local ID: d0a19faf-18bc-469a-b0af-3d44d2810857OAI: oai:DiVA.org:ltu-38594DiVA: diva2:1012094
Conference
Conference on Euro PM : 16/09/2012 - 19/09/2012
Note
Validerad; 2014; 20131206 (hesahm); Konferensartikel i tidskriftAvailable from: 2016-10-03 Created: 2016-10-03Bibliographically approved

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