Selective, low-temperature synthesis of niobium carbide and a mixed (niobium/tungsten) carbide from metal oxide-polyacrylonitrile composites by carbothermal reduction

B. F. Dal, S. G. Hardin, D. G. Hay, T. W. Turney

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Composites of polyacrylonitrile (PAN) with the layered oxides (C6H13NH3)Nb3O8, (C8H17NH3)Nb3O8 and α-(C6H13NH3)NbWO6 undergo carbothermal reduction in an argon atmosphere at 1000 °C to give the cubic carbides NbCx and (Nb, W)Cx, respectively. Reduction of the Nb3O8/PAN composites to NbCx proceeds via the formation of tetragonal NbO2, with no other intermediates being detected. Formation of NbCx begins at 800 °C but is not complete until 1000 °C. The resultant carbide appears in a highly porous form in admixture with approximately 50% wt/wt amorphous carbon. The carbide content, x, of cubic NbCx increases with heating time (at 1000 °C) as expected. Values of x ranging from 0.69-0.95 have been observed. The cubic mixed carbide, (Nb, W) Cx, is formed similarly from the α-NbWO6 system via an alkylammonium form in the presence of PAN, although progressive separation into cubic NbCx and hexagonal WCx occurs at temperatures above 1000 °C. The β-NbWO6 system does not form a well-defined alkylammonium salt; instead a mixture of β-HNbWO6 with PAN gives rise to a very poorly crystalline (Nb, W) carbide on reduction. In all cases, both a layered oxide and PAN are necessary to form the pure carbides at 1000 °C. The oxide/PAN composites appear to be intimate physical mixtures rather than ordered layered nanocomposites.

Original languageEnglish
Pages (from-to)6657-6664
Number of pages8
JournalJournal of Materials Science
Issue number24
Publication statusPublished - 1 Jan 1993
Externally publishedYes

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