The Si-C System

Silicon carbide (SiC) is the only solid compound known in this system. It occurs with two modifications, cubic jS-SiC (referred to as low temperature modification) and hexagonal a-SiC with numerous polytypes where 4H, 6H and 15R are the most common ones. The a-/) -SiC transformation temperature is not well known. Kistler-de Coppi (1985) [77] studied in detail the transformation kinetics at temperatures between 1973 K and 2573 K. According to these results (metastable) ) -SiC transforms at temperatures above 2273 K to a-SiC. SiC melts incongruently forming a sihcon-rich liquid phase and graphite. 

An overview of experimental phase diagram data is given in Table 6 [78-87]. A first assessment of the Si-C system was provided by Olesinski and Abbaschian (1984) [88] mainly recommending the experimental phase diagram work of DoUoflf (1960) [80]. 

The peritectic melting temperature of SiC was set to 2818 K and the eutectic temperature between (Si) and SiC to 1677 K. However, these data were significantly corrected later by Kleykamp and Schumacher (1993) [85] due to literature assessment and their own experimental results for temperatures between 1700 and 3300 K. The peritectic temperature for SiC was measured to occur at 3103 K 40 K. This temperature confirms the data given by Scace and Slack (1959) [79] and Kieffer et al. (1969) [89]. The (degenerated) eutectic point between (Si) and SiC was set to 1686 K 1 K (melting point Si 1687 K) and 0.02 at.%. Additionally, the liquidus on the Si-rich side of the system was measured. Data provided by DoUoff (1960) [80] scatter significantly from data 

Type of experiment, Type of Temp. Cone. Literature 

Thermal analysis, metallography, X-ray diffraction Liquidus, complete phase diagram 1675-2950 0-1 Dolloff (1960) [80] 

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A single carbide, SiC, exists in the Si-C system and this compound decomposes near 2830 C. While it can exist in two different structures, which are a form (diamond... 

The new assessment for the Si-C system was primarily based on experimental SiC solubility data in liquid solution given by Scace and Slack [34], Hall [35], Iguchi [36], Kleykamp and Schumacher [37], Oden and McCune [38], and Ottem [14], Solid solubility data given by Nozaki et al. [39], Bean [40], and Newman [41] were used to determine the properties of solid solution. The eutectic composition reported by Nozaki et al. [39] and Hall [35] and peritec-tic transformation temperature determined by Scace [34] and Kleykamp [37] were also used in the thermodynamic optimization. Thermodynamic description of the SiC compound was taken from an early assessment [42]. The... 

Calculations of the Si-C system were presented by Kaufinan (1979) [113] and Olesinski and Abbaschian (1984) [88]. Lim and Lukas (1996) [36] published a thermodynamically optimized dataset which was refined by Grobner (1996) [35]. This dataset is accepted by the present evaluators. The accompanying calculated phase diagram is shown in Fig. 3. SiC decomposes to graphite and carbon-rich liquid silicon at a temperature of 3095 K. 

But if, in this reaction, organolithium derivatives are applied with groups R which, when introduced to the silene silicon atom of 3a-c, provide sufficient stabilization to the Si=C system by... 

Most SiC deposition systems involve the Si-C-H-Cl chemical combination. Avery commonly used reaction is the decomposition of methyl trichlorosilane (MTS) P CP" ]... 

These multicomponent calculations are now computerized, and complicated systems, such as the Si-C-H-Cl quaternary, may be solved by the use of commercially available software, e. g. the IVTAN database. The solution to this multicomponent system which is obtained by this means is somewhat subjective, since, at the time of writing for example, data are available for 72 gaseous species in the quaternary system Si-C-H-Cl. Choosing 19 of the most probable of these, and using the IVTAN software to solve this multicomponent equilibrium, yields the following results for the most probable species (see Table 3.2). 

In the Si-C bond system the silicon is the more positive partner (Sise-Cse). 

The preparation of silyl derivatives with a Si—C bond between the silicon atom and the drug is not so easy to realize as compared with Si—O and Si—N systems. In most cases the Si-C bond must be constructed at the beginning of synthesis. This is shown for the triethylsilyl derivative (4) of phenethylamine (3) in Scheme 1 ... 

A recent investigation has involved a system in which the vacant p orbital of the carbocation has an orthogonal relationship with the Si—C bond (equation 17)44. 

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