Silicon carbide crystalline

Properties For silicon carbide, crystalline form ranges from small to massive crystals in the hexagonal system, the crystals varying from transparent to opaque, with colors from pale green to deep blue or... 

The atomic and crystalline structure of the two non-metallic carbides, boron and silicon carbides, is less complex than that of the... 

When Acheson found the hexagonal crystals in the voids, he sent some to B.W. Frazier, a professor at Lehigh University. Professor Frazier found that although the crystals were all silicon carbide, they differed in their crystalline structure. He had discovered the polytypism of SiC [18]. Polytypism will be explained in Section 1.3.2. 

The structure of presolar silicon carbide grains can provide information about the conditions of formation. Crystalline silicon carbide is known to form about 100 different polytypes, including cubic, hexagonal, and rhombohedral structures. Presolar silicon carbide exists in only two of these, a cubic (fi-SiC) polytype and a hexagonal (a-SiC) polytype (Daulton et al.,... 

Twenty-five years later, Burhard reported the preparation of permethylated. polysilane (2). These materials were, however, highly crystalline, insoluble white solids which evoked little scientific interest until recently when it was discovered that silane polymers could be used as thermal precursors to / -silicon carbide fibers (3-5). In this regard, Yajima and co-workers reported that poly (dimethyl) silane could be converted by the two-step process shown below to / -silicon carbide, a structural material of considerable industrial importance. 

ELECTROLUMINESCENCE. Luminescence generated in crystals by electric fields or currents in the absence of bombardment or other means of excitation. It is a solid-state phenomenon involving />- and n-type semiconductors, and is observed in many crystalline substances, especially silicon carbide, zinc sulfide, and gallium arsenide, as well as in silicon, germanium, and diamond. 

Benzene, ethylene and acetylene were the predominate observed volatiles at 550 °C whilst methane was evolved from 650 °C to 875 °C. An amorphous SiCO material was obtained at 1200 °C and bond redistribution and carbothermic reduction occurred up to 1800 °C to give a ceramic material composed of substantial amounts of crystalline fi-silicon carbide. The preparation of bulk ceramic components from materials in the system... 

The product is a partially crystalline, partially amorphous mixture of SiC, C and Si02. The silicon carbide content was shown to be highest for gels with the lowest relative oxygen content.19... 

A -C-Si-C- network is formed on the (partially crystalline) oxide surface. This coating can therefore be treated as a silicon carbide coating. 

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. 

Gogotsi, Y., Weltz, S., Ersoy, D.A., and McNallan, M.J. Conversion of silicon carbide to crystalline diamond-structured carbon at ambient pressure. Nature 411, 2001 283-287. 

Schnabel, C., Womer, M., Gonzalez, B., Del Olmo, I. and Braun, A.M., (2001) Photoelectrochem-ical characterization of p- and n-doped single crystalline silicon carbide and photoinduced reductive dehalogenation of organic pollutants at p-doped silicon carbide. Electrochim. Acta... 

Some of the chondritic meteorites contain grains (including crystalline and amorphous silicates, diamonds, silicon carbide, graphite, metal oxides, and metal nitrides) that have been identified as presolar based on non-solar isotopic ratios (Zinner 1988 Anders Zinner 1993 Bematowicz et al. 2006), particularly for... 

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... 

The preparation, manufacture, and reactions of SiC have been discussed in detail in Gmelin, as have the electrical, mechanical, and other properties of both crystalline and amorphous of SiC. Silicon carbide results from the pyrolysis of a wide range of materials containing both silicon and carbon but it is manufactured on a large scale by the reduction of quartz in the presence of an excess of carbon (in the form of anthracite or coke), (Scheme 60), and more recently by the pyrolysis of polysilanes or polycarbosUanes (for a review, see Reference 291). Although it has a simple empirical formula, silicon carbide exists in at least 70 different crystalline forms based on either the hexagonal wurtzite (ZnS) structme a-SiC, or the cubic diamond (zinc blende) structme /3-SiC. The structmes differ in the way that the layers of atoms are stacked, with Si being fom-coordinate in all cases. 

Salinger (44) reported the successful conversion of methyltrichloro-silanes to silicon carbide in a 50-kW RF plasma torch. The liquid methyltrichlorosilanes were fed to the tail flame of various plasmas and the solid products were recovered in an acid-resistant bag filter. Up to 85% recovery of theoretical solid product was reported, which was subsequently heated at 500°C to remove elemental carbon. Under the best condition (20-25% vol. hydrogen in argon plasma at 36 kW), up to 70%o conversion to j3-SiC was obtained with ca. 10% conversion to amorphous SiC. Salinger suggested that the good crystallinity of the )3-SiC so obtained meant that the reaction occurred in a gas temperature range in which )3-SiC was the stable crystalline form (i.e., < 2300°C). 

Pyrolysis of one of the products whose NMR spectrum and elemental analysis indicated a constitution of [(CH3SiH)o.73(CH3Si)o.i[(CH3)-SiCH2CH2Si(CH3)NH] 117] indicated a formal composition of 1 SiC + 0.033 Si3N4 + 0.04 C. Thus the stoichiometry and reaction conditions in this experiment gave a high yield of a ceramic product that was silicon carbide contaminated with only minor amounts of silicon nitride and free carbon. When such a pyrolysis was effected to 1500 C, the ceramic product was at least partly crystalline. X-ray diffraction showed lines due to P-SiC only. 

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