Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Silicon carbide defined

Toropov and Leszczynski [67] also predicted the Young s modulus for metal oxides, nitrides, mullite, and silicon carbide by using a DCW descriptor defined as follows ... [Pg.211]

PZCs/IEPs of sparingly soluble salts (other than combination of two or more sparingly soluble oxides) are presented in Tables 3.1568 through 3.1910. PZCs/IEPs of silicon carbide and nitride are also presented in this section. Salt-type compounds composed entirely of sparingly soluble oxides are discussed in Section 3.3. In the studies devoted to the effect of water-soluble salts with an anion or cation in common with the sparingly soluble salt of interest, the IEP has been defined in terms of concentration of these salts (ions) in addition to (or rather than) pH. [Pg.665]

Infiltration combines a melt with a porous free-standing solid (the preform ). In the main and defining step of the process, the melt flows into open pores of the preform after solidification a new material results. Composites of all classes (polymer, ceramic and metal) are produced by this process, as are compounds such as reaction bonded silicon carbide. The process can also be adapted to make open-pored foams of carbon, ceramic, polymer or metal. [Pg.380]

From an optical viewpoint, on the other hand, the difference between semiconductors and insulators lies in the value of Eg. The admitted boundary is usually set at 3 eV (see Appendix A for the energy units) and materials with Eg below this value are categorized as semiconductors, but crystals considered as semiconductors like the wurtzite forms of silicon carbide and gallium nitride have band gaps larger than 3 eV, and this value is somewhat arbitrary. The translation into the electrical resistivity domain depends on the value of Eg, and also on the effective mass of the electrons and holes, and on their mobilities. The solution is not unique moreover, the boundary is not clearly defined. Semi-insulating silicon carbide 4H polytype samples with reported room temperature resistivities of the order of 1010flcm could constitute the... [Pg.1]

Silicon carbide net-shaped ceramics are candidate materials for high-temperature applications as engine and turbine parts and as cutting tools. They are also important for the construction of reactors which show a high chemical resistance. SiC material that reveals a well defined organization of its microstructure is also a goal in the development of microelectronic devices. [Pg.60]

After the current is switched of, the furnace is allowed to cool for several days. Then the side walls are removed, and the excess reaction mixture is carried off. The roll of silicon carbide contains not only the original resistance core, but also graphite formed by decomposition of silicon carbide. The boundary between the graphite and the SiC is very sharply defined. The innermost SiC zone is of the highest quality, as the purest and largest crystals can form in this region. Moving... [Pg.688]

Silicon carbide is nontoxic, and is therefore a nonhazardous material as defined by GefStoffV [252]. [Pg.736]

The coated preform is densified with a silicon carbide matrix via CVl. The gaseous precursor is methyl chi orosilane (MTS). When the CVl process is carried out isothermally (I-CVl), surface pores tend to close, restricting the gas flow to the interior of the preform. This phenomenon requires an intermediate operation of surface machining to obtain an adequate density. The CVl parameters (i.e. total pressure, temperature and gas flow rate) have to be selected according to the preform geometry defined by the pore spectmm and the thickness, the number of preforms present in the chamber and the size of the chamber. Finally several coating systems can be applied to these composites via CVD to provide environmental and oxidation protection. [Pg.60]

Large numbers of experiments have been conducted by various researchers in an attempt to define stability regions for the basic silicon carbide polytypes. Work by both Knippenberg [5] and Inomata et al. [6] resulted in stability diagrams. In both studies, the stability was shown to increase with temperature moving from 3C to 2H to 4H to 15R to 6H. Specifically, the work by Inomata et al. indicates that 3C polytype will convert to a hexagonal polytype above about 1600°C and that near eomplete eonversion, to the 6H polytype, will occur alx>ve approximately 2200°C. Thus, at high process temperatures, the formation of the 6H polytype is predieted. [Pg.116]

The 400°C NMR and the DRIFTS data do not support the formation of hydrogenated silicon carbide. However, at 600°C, the corresponding spectra are quite different All evidence of well-defined molecular stmcture disappears. In the DRIFT spectmm, the only clear features consist of vC-H ( 2900 cm ) and vSi-H (- 2100 cm ) which now suggest hydrogenated SiC. By 800°C, the DRIFT spectmm indicates that most of the C-H and Si-H bonds have disappeared. Absorptions in the 400-1000 cm region suggest the formation of p-SiC. At 1000°C these absorptions are all that remain. [Pg.141]

A study of Vickers hardness of polycrystalline ceramics revealed that cracking may cause critical transition points in the Vickers ISE trends. The transition point was associated with extensive cracking in and around the indentation and a shift in the energy balance during indentation. Different ratios of the indentation work are expended on volumetric deformation and surface fracture processes above and below the transition point. The transition point was very distinct for brittle materials such as silicon carbide. The Vickers hardness transition point was related to a new index of ceramic brittleness defined as ... [Pg.277]

The arrangements of atoms in the first and second coordination spheres are identical in all polytypes of silicon carbide and other diamond-like semiconductors. Each atom is tetrahedrally surrounded by four nearest atoms of another type. The second coordinational sphere consists of 12 atoms of the initial type. For most polytypes, surroundings of atoms of the same type in the lattice can differ e.g., nonequivalent atom states are probable. It is possible to define them in the (1120) plane by use of the difference of the distances between atoms in the C-axis direction (vertical lines in Fig. 2). In cubic SiC and in the 2H polytype the distances between two atoms of the same type along the C-axis are the same and equal to heights of three and two layers, respectively. There are two such nonequivalent positions in the 4H polytype (h, k), three of them (hi, ki, k2) in 6H, five (h, ki, k2, h2, kj) in 15R, etc. (Fig. 2). [Pg.411]

Similar equations for vapor pressures over other silicon carbide polytypes can be defined with the help of Table 3. The ratio of silicon and carbon concentrations in the gas phase, NsJ Nc, for most temperature values is greater than unity and can be estimated using the equation... [Pg.414]


See other pages where Silicon carbide defined is mentioned: [Pg.437]    [Pg.5]    [Pg.528]    [Pg.144]    [Pg.247]    [Pg.94]    [Pg.932]    [Pg.115]    [Pg.319]    [Pg.44]    [Pg.319]    [Pg.240]    [Pg.93]    [Pg.75]    [Pg.78]    [Pg.90]    [Pg.58]    [Pg.214]    [Pg.14]    [Pg.2]    [Pg.648]    [Pg.3]    [Pg.668]    [Pg.775]    [Pg.763]    [Pg.79]    [Pg.138]    [Pg.278]    [Pg.6]    [Pg.577]    [Pg.579]    [Pg.43]    [Pg.103]    [Pg.30]    [Pg.409]   


SEARCH



CARBIDES SILICON CARBIDE

Silicon carbide

Silicone carbide

© 2024 chempedia.info