Liquid silicon carbides

More recently, Stanicioiu, Chinta Hartner (1959) attempted to reinforce the cement with glass fibres, but this was not successful. The most serious study on the reinforcement of dental silicate cement was made by J. Aveston (in Wilson et al., 1972). Silicon carbide whiskers, carbon fibres and alumina powder were introduced into the cement mix. Unfortunately, the glass powder/liquid ratio had to be reduced, and the strength gained by reinforcement was thereby lost. It is clear that dental silicate cement cannot be strengthened by fibre or particulate reinforcement. 

Phosphoric acid fuel cells (PAFC) use liquid phosphoric acid as an electrolyte - the acid is contained in a Teflon-bonded silicon carbide matrix - and porous carbon electrodes containing a platinum catalyst. The PAFC is considered the "first generation" of modern fuel cells. It is one of the most mature cell types, the first to be used commercially, and features the most proven track record in terms of commercial applications with over 200 units currently in use. This type of fuel cell is typically used for stationary power generation, but some PAFCs have been used to power large vehicles such as city buses. 

The electric infrared incineration technology is a mobile thermal processing system that is suitable for soils or sediments contaminated with organic compounds, polychlorinated biphenyls (PCBs), and metals. Liquid organic wastes can be treated after mixing with sand or soil. Electrically powered silicon carbide rods heat organic wastes to combustion temperature while any remaining combustibles are incinerated in an afterburner. 

Muffle Furnaces or Retorts of Graphite or Silicon Carbide. The metal is fed into the furnace either batchwise as a solid or continuously as a liquid. The heat of vaporization is supplied by heating the outside of the retort with a burner. The nonvolatile residues (iron and lead in the case of dross from smelting) accumulate in the retort and must be removed at intervals. This is facilitated by tipping the retorts. 

Fig. 5. Radioactivity after shutdown per watt of thermal power for A, a liquid-metal fast breeder reactor, and for a D—T fusion reactor made of various structural materials B, HT-9 ferritic steel C, V-15Cr-5Ti vanadium—chromium—titanium alloy and D, silicon carbide, SiC, showing the million-fold advantage of SiC over steel a day after shutdown. The radioactivity level after shutdown is also given for E, a SiC fusion reactor using the neutron reduced...

This reaction is endothermic and additional energy must be provided to sustain it, usually by induction heating, or by adding silicon carbide grain which chlorinates exothermically. The product gases are cooled below 200°C to condense and collect the zirconium—hafnium tetrachloride as a powder. The offgas stream then is refrigerated to obtain by-product silicon tetrachloride liquid. 

Russell, L.M., Donaldson, K.Y., Hasselman, D.P.H., Corbin, N.D. Petrovic, J.J. and Rhodes, J.F. Effect of vapor-liquid-solid and vapor-solid silicon carbide whiskers on the effective thermal diffusivity/conductivity of silicon nitride matrix composites , J. Am. Ceram. Soc., 74[4] (1991) 874-877. 

Wang, C.M., Mitomo, M., and Emoto, H., Microstructure of liquid phase sintered superplastic silicon carbide ceramics , J. Mater. Res. 1997, 12, 3266-70. 

Nagano, T., Gu, H., Shinoda, Y., Zhan, D., Mitomo, M., and Wakai, F., Tensile ductility of liquid-phase sintered (3-silicon carbide at elevated temperatures , Mater. Sci. Forum, 1999, 304-6, 507-12. 

Silicon carbides are generally synthesized by the pyrolysis of precursors, prepared by liquid phase methods. One possible way for precursor synthesis is the addition of carbon black or sucrose, to a gelling silica.8 In this method, the carbon is introduced from an external source. A more intimate contact between the carbon and silicon in the precursor is assured with the use of organometallic polymer precursors. The use of silane polymers for silicon carbide production was initiated by Yajima.9,10 Polymers having a -[Si-C]- backbone are crosslinked and pyrolysed to yield SiC." In the initial work, dimethyldichlorosilane was used as a starting monomer, which was subjected to a sodium catalyzed polymerization (reaction (C)). 

Thin silicon (oxy)carbide coatings can be formed using the liquid phase CSC method. This involves the liquid phase modification of the silica substrate with APTS, followed by a thermal treatment under inert atmosphere. At temperatures of 1873 K the material is a mixture of graphite and partially crystalline silica, coated with a molecular layer of silicon carbide. 

The catalysts and electrode materials used in PAFCs are also similar to those in acidic H2/air fuel cells. Carbon-supported Pt is used as the catalyst at both anode and cathode, porous carbon paper serves as the electrode substrate, and graphite carbon forms the bipolar plates. Since a liquid electrolyte is used, an efficient water removal system is extremely important. Otherwise, the liquid electrolyte is easily lost with the removed water. An electrolyte matrix is needed to support the liquid phosphoric acid. In general, a Teflon -bonded silicon carbide is used as the matrix. 

Less-conventional processing techniques are also used to make ceramic matrix composites. Siliconized silicon carbide, for example, is made by liquid infiltration.16,17 A compact of SiC particles is formed and then presintered, or reaction bonded. Liquid silicon is then infiltrated into the structure. Many different microstructures of siliconized silicon carbide can be made in this manner. The volume fraction of SiC particles can be as high as 90vol.%. Bimodal structures have also been made by this technique. These materials are used for radiant heaters and heat exchangers.17,19... 

Properties of Dense Silicon Carbide. Properties of the SiC structural ceramics are shown in Table 1. These properties are for representative materials. Variations can exist within a given form depending on the manufacturer. Figure 2 shows the flexure strength of the SiC as a function of temperature. Sintered or sinter/HIP SiC is the preferred material for applications at temperatures over 1400°C and the liquid-phase densified materials show best performance at low temperatures. The reaction-bonded form is utilized primarily for its ease of manufacture and not for superior mechanical properties. 

A vapor-liquid-solid (VLS) technique (Petrovic et al, 1985 Milewski et al, 1985) can be used to grow exceptionally strong and stiff silicon carbide whiskers. The name VLS comes from the fact that the process uses vapor feed gases, a liquid catalyst, and solid crystalline whiskers are the end product. Figure... 

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