Preparation transition metal carbides/nitrides

This volume, which is unique in its coverage, provides a general introduction to the properties and nature of transition metal carbides and nitrides, and covers their latest applications in a wide variety of fields. It is directed at both experts and nonexperts in the fields of materials science, solid-state chemistry, physics, ceramics engineering and catalysis. The first chapter provides an overview, with other chapters covering theory of bonding, structure and composition, catalytic properties, physical properties, new methods of preparation, and spectroscopy and microscopy. 

Oyama ST (1992) Preparation and catalytic properties of transition-metal carbides and nitrides. Catal Today 15 179... 

Gas-Phase Reactions Gas-phase reactions are typically used for the preparation of thin films or nano-sized transition metal carbides and nitrides. High volatility of metal chloride precursors is useful and nitrides can be obtained by reaction with ammonia (M is the corresponding transition metal) ... 

Which solid precursors of carbon and nitrogen can be used for the preparation of nanoparticles of transition metal carbides and nitrides ... 

W. Lengauer, H. Wiesenberger, M. Joguet, D. Rafaja, and P. Ettmayer, in Transition Metal Carbides and Nitrides Preparation, Properties and Reactivity, S. T. Oyama (Ed.), Blackie, London, 1996, p. 91. 

Al alloys are frequently used to prepare composites with p- and y-BN [9 to 12]. This can be done by sintering the reaction mixture originating from preformed p-BN particles or from a-BN powder. The aluminium is often combined with transition metal carbides or nitrides (especially TiC and TiN) in order to form the binding phase [13 to 39]. However, TiC, TiN, and TiBg also form composites with the hard BN phases without the addition of aluminium [40 to 46] addition of TaN has also been reported [47]. 

Catalytic materials need high exposures or specific surface areas to be used economically. This has led to development of novel preparative methods, such as temperature programmed reaction (TPR) (d), laser pyrolysis (7), etc., to produce finely divided transition metal carbides and nitrides. Among these, TPR remains a practical method for making large batches with moderate to high surface area products. 

Silicon-containing ceramics include the oxide materials, silica and the silicates the binary compounds of silicon with non-metals, principally silicon carbide and silicon nitride silicon oxynitride and the sialons main group and transition metal silicides, and, finally, elemental silicon itself. There is a vigorous research activity throughout the world on the preparation of all of these classes of solid silicon compounds by the newer preparative techniques. In this report, we will focus on silicon carbide and silicon nitride. 

In the following sections some examples are given of the ways in which these principles have been utilized. The first example is the use of these techniques for the low temperature preparation of oxide ceramics such as silica. This process can also be used to produce alumina, titanium oxide, or other metal oxides. The second example describes the conversion of organic polymers to carbon fiber, a process that was probably the inspiration for the later development of routes to a range of non-oxide ceramics. Following this are brief reviews of processes that lead to the formation of silicon carbide, silicon nitride, boron nitride, and aluminum nitride, plus an introduction to the synthesis of other ceramics such as phosphorus nitride, nitrogen-phosphorus-boron materials, and an example of a transition metal-containing ceramic material. 

Ternary phases with structures different from those of the phases of the binary boundary systems are more the exception than the rule. Such phases have been reported in the systems Nb-Mo-N, Ta-Mo-N, Nb-Ta-N, Zr-V-N, Nb-Cr-N, and Ta-Cr-N. Information about ternary transition metal-nitrogen systems is often available for specific temperatmes only. This is even more the case for quaternary nitride systems, which play a role in the production of carbonitride cermets where quaternary compounds of the types (Ti,Mo)(C,N) and (Ti,W)(C,N) are of interest (see Carbides Transition Metal Solid-state Chemistry), as well as in layer technology where titanium nitride-based coatings of the type Ti(C,B,N) are prepared by magnetron sputtering. Layers consisting of ternary compounds of the type (Ti,Al)N and (Ti,V)N also have favorable properties with respect to abrasion resistance. 

Chen JG (1996) Carbide and nitride overlayers on early transition metal surfaces preparation, characterization, and reactivities. Chem Rev 96 1477... 

Iron and its compounds (carbide, nitride), as well as ruthenium, cobalt, rhodium, and molybdenum compounds (sulfide, carbide), are used most frequently to produce high-molecular-weight hydrocarbons. Iron can be prepared as a high-surface-area catalyst (==300 m /g) even without using a microporous oxide support. 7-AI2O3, Ti02, and silica are frequently used as supports of the dispersed transition-metal particles. Recently zeolites, as well as thorium oxide and lanthanum oxide, have... 

Different methods have been discussed for the preparation of transition metal nitride and carbide nanoparticles, including state-of-the-art procedures and more recently reported methods. 

The catalyst preparation procedure starting with the adsorption of a metal hydroxide followed by its reduction in a stream of H2 at 600 C and a further activation step in acetonitrile at 1,000°C was expanded to all transition metals of the first row. Catalysts for O2 reduction were obtained only with Cr, Fe, and Co. Cr203/C, Fe/C, and Co/C were detected after the reduction step in H2, while Co, Fe3C, and a chromium carbide-nitride (Cr6.2 C3 5 N0.3/C) were detected in the catalyst. The nominal loading of all metals was 10 wt%. Catalytic activity decreased as Cr > Fe > Co. Tests in fuel cells indicated that the Cr-based catalyst was not stable, while Fe and Co-based catalysts were stable (see Section 4 for details). 

Both early transition metal nitrides and carbides were prepared with MAFBS. Nitrides were prepared exclusively from reactions between metal powders and fluidizing Nj gas. Carbides were prepared either through fluidization of metal and carbon black powders with Ar gas or from reaction between metal powders and... 

This work clearly demonstrates that it is possible to produce carbide and nitride nanolayers on early transition metals with MAFBS. The extent of reaction, however, varied from metal to metal. CrjN was prepared more readily than MoN, but CrjN was less catalytically active. Using ethylene rather than carbon black as the carbon source was a more effective technique to prepare carbides. MojC and WC nanolayers were prepared with this method. Although none of the MAFBS-prepared catalysts were competitive with the commercial Cu-Zn-Al catalyst for the WGS reaction, M02C had the most promising catalytic properties of the compounds that were prepared. 

Kitaoka K., Koznka H., Yoke T. Preparation of lead lanthannm zirconate titanate (PLZT, (Pb,La)(Zr,Ti)03) fibers by sol-gel method. J. Am. Ceram. Soc. 1998 81 1189-1196 Koznka H., Knroki H., Sakka S. Flow characteristics and spinnability of sols prepared from silicon alkoxide solntion. J. Non-Cryst. Solids 1988 100 226-230 Kmger R., Glanbitt W., Lobmann P. Strnctnre evolntion in sol-gel-derived yttrium aluminum garnet-alumina precursor fibers. J. Am. Ceram. Soc. 2002 85 2827-2833 Kurokawa H., Ohta H., Sato T. Preparation of carbide fibres by thermal decomposition ofceUulose-metal (Ti, Zr) alkoxide gel fibres. J. Mater. Sci. Lett. 1994 13 516-518 Knrokawa Y., Ishizaki T., Suzuki M. Preparation of refractory nitride fibers by thermal decomposition of transition metal (Ti, Nb) alkoxide-cellnlose preenrsor gel fibres in NH3 atmosphere. J. Mater. Sci. 2001 36 301-306... 

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