Synthesis of metal carbides

Most forms of carbon, except diamond, which are renowned as supports for precious metal catalysts in certain applications [3], interact strongly with MW [4]. Amorphous carbon and graphite, in their powdered form, irradiated at 2.45 GHz, rapidly (within 1 min) reach very high temperatures (>1300 K). This property has been used to explain MW-assisted syntheses of inorganic solids [5], In these syntheses carbon is either a secondary susceptor which assists the initial heating but does not react with other reactants, or is one of the reactants, e. g. in the synthesis of metal carbides. MW-carbon coupling has also been widely developed ... 

A synthesis of metal carbides in plasma can be provided by heating dispersed or bricked mixture of the metal oxide and carbon in the form of graphite or soot and using thermal discharges in inert gases. The synthesis of metal carbides takes place in such systems in the solid phase and proceeds as follows ... 

Synthesis of Metal Carbides by Reaction of Solid Metal Oxides with Gaseous Hydrocarbons in Thermal Plasma... 

Temperature-programmed reactions (TPR), developed by Volpe and co-workers, are efficiently used for the synthesis of metal carbides [45]. This method is prominent for the synthesis of metal carbides and other inorganic nanomaterials of desired shape and properties. Metal oxides are essentially heated at high temperature in the presence of hydrocarbon. In this synthesis method, the reactant gases of optimized ratio of CH4/H2 or are passed over the metal oxides. After the... 

The synthesis of metal carbide nanoparticles has been demonstrated by carrying out laser vaporization in the presence of a convenient source of carbon such as methane, ethylene or isobutene. Thus, silicon carbide nanoparticles were prepared by laser vaporization of Si in a He/isobutene mixture (54). Surface analysis using FT-IR has indicated that the nanoparticles consist of SiC cores covered with pure silica layers. 

Duncan M A 1997 Synthesis and characterization of metal-carbide clusters in the gas phase J. duster Soi. 8 239... 

Advani, A. H., Thadhani, N. N Grebe, H. A., Heaps, R., Coffin, C., and Kottke, T., Dynamic modeling of self propagating high temperature synthesis of titanium carbide ceramics. Scripta Metall. Mater., 25, 1447(1991). 

In Chapter 8 we described how metal carbides (first mentioned in Section 6-1-4) could serve as precursors to carbyne complexes by way of electrophilic addition. Scheme 10.8 revisits a portion of Scheme 8.12, showing Os-carbide complex 72—with its nucleophilic Ccarbide atom—reacting with methyl triflate or tropylium ion to give alkylidynes 73 and 74, respectively. Comparable reactions occur with the corresponding Ru-carbide complex.87 This method may become more general after the synthesis of additional carbide complexes occurs. 

A large number of binary ceramics such as carbides, nitrides, and oxides have been obtained by the decomposition of metal-organic precursors. The following text presents some selected examples to demonstrate the promises and limitations of molecular precursor approach. A complementary account of the synthesis of metal oxide nanoparticles from solution-based methods is given in Chapter 12.03. 

Production of Metal Carbides by Solid-Phase Synthesis in Thermal Plasma of Inert Gases... 

The advantage of metal carbide synthesis via reaction of solid metal oxides with gaseons hydrocarbons is because one reactant is in the gas phase. In contrast to (7-92), a solid oxide reacts in this method with a gas-phase hydrocarbon. Consider, as an example, the synthesis of titanium carbide from titanium oxide (Hancock, 1973 Walder Hancock, 1973) ... 

Moshtaghioun BM, Monshi A, Abbasi MH, Karimzadeh F (2011) A study on the effects of silica particle size and milling time on synthesis of silicon carbide nanoparticles by carbothermic reduction. Int J Refract Metal Hard Mater 29 645-650... 

Hara Y, Minami N, Matsumoto H, Itagaki H (2007) New synthesis of tungsten carbide particles and the synergistic effect with Pt metal as a hydrogen oxidation catalyst for fuel cell applications. Appl Catal A 332(2) 289-296... 

Hydrogenation of Carbon Monoxide or Carbon Dioxide. There are two important aspects of metal carbides in CO-H2 reactions including methana-tion, Fischer-Tropsch synthesis, alcohol synthesis, and water gas shift reaction. First, metal carbides, by themselves or together with other phases, are considered as active phases in these reactions catalyzed by Fe, Co, and Ni. These carbide phases are formed in situ from the respective metals or oxides during the reaction. This aspect is not discussed here. Instead, catalysis by early transition metals intentionally prepared in a stable carbide form is the subject of this section. Molybdenum and tungsten carbides are by far the most extensively studied. 

THE SYNTHESIS OF BORIDES, CARBIDES AND SBLICIDES OF REFRACTORY METALS IN IONIC-ELECTRONIC MELTS... 

The X-ray phase analysis confirmed that the synthesis products are TiC, ZrC, NbC and TaC carbides, which do not contain free carbon. Fineness of the carbides is determined by the grain size of the metal powder. The synthesis time depends on the diffusion rate of carbon into the volume of the grain or the crystallite. We used oxides of refractory metals as the starting materials for production of fine (1-5 pm) carbides. In this case the mass of the metallic calcium was increased taking into account its consumption for the calcium thermal reduction of the oxides. The presence of a higher amount of the calcium oxide in the salt melt did not incur large difficulties in the synthesis of the carbides and their washing with water to remove salts, because the calcium oxide easily dissolves in acidified water. This method of the carbide synthesis has been covered by a Russian Federation patent [6]. 

Moreover, some elements as sulfur, added to the precursors during the synthesis, can suppress the formation of metal carbides during the pyrolyzation. Metal carbides, in fact, lead to the disintegration of Fe-N4 active ensembles, thus decreasing the number of ORR active ensembles on the final catalyst [77]. 

FIGURE 11.1 Schematic of the apparatus used in the synthesis of CDC through the halogen treatment of metal carbides. 

Estimates of the metallic vacancy formation energy ( ) in the systems under discussion show that > EP-. This gives a qualitative explanation for the known difficulties in the synthesis of metal-defect carbides and nitrides and confirms the conclusions on this question drawn from cluster calculations. 

Xiang, J. Y, Liu, S. C., Hu, W. T., Zhang, Y, Chen, C. K., Wang, P. et al. (2011). Mechano-chemically activated synthesis of zirconium carbide nano-particles at room temperature A simple route to prepare nano-particles of transition metal... 

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