Carbothermal synthesis

Carbothermal synthesis of nano-sized tungsten carbide catalyst... 

Carbothermal synthesis has been used to prepare yttrium a-sialon from mixtures of halloysite clay and Y2O3 with either Si02 or elemental Si. The reaction mechanism, particularly the role played by intermediate SiC phases, was monitored by Si NMR (Ekstrom et al. 1998). The preparation of fine-grained Ca a-sialon has also been studied by 2 Si NMR (Hewitt et al. 1994). 

Carbothermal synthesis and its variant, silicothermal synthesis, have proved attractive routes for preparing sialons from readily available clay mineral raw materials. The clay is mixed with fine carbon and/or silicon powder and reacted in a stream of purified nitrogen at > 1400°C. The 3-sialon product carbothermally synthesised from kaolinite has the composition Si3Al303N5 (z = 3), controlled by the Si02 Al203 ratio of the clay... 

UTC Fuel Cells Dr. Shari Bugaj Carbothermal synthesis of ternary Pt alloys [Pt-Ir-X and Pt-Rh-X, [X=Ni, Co and V]]... 

UTCFC has modified the carbothermal synthesis process (U.S. Patent 4,677,092, US 4,806,515, US 5,013,618, US 4,880,711, US 4,373,014, etc.) to prepare 40 wt% ternary Pt alloy catalysts. Various high-concentration Pt catalyst systems were synthesized and the electrochemical surface area (EGA) and electrochemical activity values compared to commercially available catalysts (see Table 3). The UTCFC catalysts showed EGA and activity values comparable to the commercial catalysts. A rotating disk electrode technique for catalyst activity measurements has been developed and is currently being debugged at UTCFC. 

Dasa M, Basua AK, Ghataka S, Joshib AG (2009) Carbothermal synthesis of boron nitride coating on PAN carbon fiber. J Eur Ceram Soc 29(10) 2129-2134... 

Makarenko, G.N. and Mahajan, Y.R. (2002) Features of carbothermal synthesis of aluminum nitride under nitrogen pressure. Powder Metall. Met. Ceram., 41 (5-6), 1068-1302. 

Chen, L.L., Ye, H.H., Gogotsi, Y, and McNallan, M.J. Carbothermal synthesis of boron nitride coatings on silicon carbide. Journal of the American Ceramic Society 86, 1830-1837, 2003. 

The solid solution obtained consisted of two phases. The nonuniformity of the Pu distribution was less than 5%. Fabrication techniques for synthesis of solid solutions of UN+ZrN from initial oxides, and fabrication of fuel columns with different density, sh e and size, were also investigated. As mentioned above a method of synthesising PuC+ZrC solid solution from oxides was developed. Its properties are close to those of PuN+ZrN solid solution. This fact and existing experience of UN+ZrN fabrication proved the feasibility of carbothermal synthesis of PuN +ZrN from initial oxides. The feasibility of fabricating UN+ZrN and PuN+ZrN solid solutions from initial metals was also demonstrated. A subassembly with 19 fuel pins was irradiated in BOR-60. 7 of the fuel pins contained 55%PuC+45%ZrC fuel, and 12 contained 56%UC+44%ZrC. The irradiation parameters are shown in Table 7.9. 

A method for producing submicrometer (0.1 im), low-oxygen-content nonagglomerated TiC powders involved the carbothermal reduction of carbon-coated titanium diboride (TiOa) (27), where carbothermal synthesis proceeded via the purification of titanium oxycarbide toward pure titanium carbide. The carbon coating process provided a high contact area of the reactants to produce a TiC powder with uniform shape by synthesis at 1550 C for 4 h. 

R Koc, JS Fohner. Carbothermal synthesis of titanium carbide using ultrafine titania powders. J Mater Sci 32 3101, 1997. 

Vapor—sohd reactions (13—17) are also commonly used ia the synthesis of specialty ceramic powders. Carbothermic reduction of oxides, ia which carbon (qv) black mixed with the appropriate reactant oxide is heated ia nitrogen or an iaert atmosphere, is a popular means of produciag commercial SiC, Si N, aluminum nitride [24304-00-3], AIN, and sialon, ie, siUcon aluminum oxynitride, powders. 

Cochran GA, Conner CL, Eismann GA, Weimer AW, Carroll DF, Dunmead SD, Hwang CJ (1994) The Synthesis of a High Quality, Low Cost Silicon Nitride Powder by the Carbothermal Reduction of Silica. In Hoffmann MJ, Becher PF, Petzow G (eds) Silicon Nitride 93. Key Eng Mater 89-91. Trans Tech Publications Ltd, Switzerland, p 3... 

There are several reports on the preparation of SiC nanowires in the literature but fewer on the preparation of SisKi nanowires.38-39 The methods employed for the synthesis of SiC nanowires have been varied. Since both SiC and Si3N, are products of the carbothermal reduction of SI02, it should be possible to establish conditions wherein one set of specific conditions favor one over the other. We have been able to prepare SijN nanowires,40 by reacting multiwalled carbon nanotubes produced by ferrocene pyrolysis with ammonia and silica gel at 1360... 

The first six reactions form mixed oxide ceramic powders. The last three reactions are carbothermal reductions to produce different metal carbides. The most famous is the Atcheson process for synthesis of SiC from Si02 and carbon, where the carbon in the mixture of reactant powders is used as a resistive electrical conductor to heat the mixture to the reaction temperature. This reaction is performed industrially in a 10-20 m long bunker fixed with two end caps that contain the source and sink for the cLc current. The reactant mixture is piled to a height of 2 m in the bunker and a current is applied. The temperature rises to the reaction temperatures, and some of the excess C reacts to CO, providing further heat. The 10-20 m bunker is covered with a blue flame for most of the reaction period. The resulting SiC is loaded into grinding mills to produce the ceramic powders and abrasives of desired size distributions. 

However, the synthesis process most extensively studied by solid-state NMR is that of carbothermal reduction of aluminosilicate minerals such as kaolinite, which are mixed with finely divided carbon and heated in nitrogen at > 1400°C (Neal et al. 1994, MacKenzie et al. 1994a). Under carbothermal conditions the clay decomposes to a mixture of mullite and amorphous silica (MacKenzie et al. 1996b), the latter forming SiC which reacts with the mullite to form P-sialon, in some cases via other sialon phases such as X-sialon (see below). The precise reaction sequence and the nature of the intermediates has been shown by the NMR studies to depend on various factors including the nature of the aluminosilicate starting mineral (MacKenzie er a/. 1994a). 

Figure 5.38. Effect of hot-pressing on the MAS NMR spectra of yttrium-a-sialon synthesised by carbothermal and silicothermal synthesis using Si02 as the silica source (top) and Si as the silica source (bottom). Asterisks denote spinning side bands. From Ekstrdm et al. (1998).

Other synthesis methods have also been developed but may not be practiced on a large commercial scale as compared to those indicated above. Examples of syntheses that begin from liquid phase precursors include the sol-gel, hydrothermal, and Pechini methods. In the course of these reaction schemes, polycondensation or precipitation occurs, and the volatile components are removed, often by thermal methods. Other synthesis routes to ceramic materials include the nitridation of metals to form metal nitrides and the carbothermal reduction of oxides to form carbides and borides. 

Synthesis and characterization of nanostructured M02C on carbon material by carbothermal hydrogen reduction... 

To understand the carbothermal hydrogen reduction process, the reactant and principal products were monitored with mass spectroscopy in real time. The sample was first dried at 150 °C in a stream of nitrogen for 2 h, then cooled to room temperature in order to avoid the desorption peak of water at about 100 C. Fig. 4 shows the synthesis traces of masses (M) 2, 16, 18, 28 and 44 with the increase of temperature. The signals at M=2 and 16... 

FI. Federer, J. I., and V. J. Tannery Synthesis of (U, Pu)C by Carbothermic Reduction of Mixed Oxides and Evaluation of Sintering Behavior, Report ORNL/TM-6089,1978. 

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