Carbon reaction + silica

Production. Silicon is typically produced in a three-electrode, a-c submerged electric arc furnace by the carbothermic reduction of silicon dioxide (quartz) with carbonaceous reducing agents. The reductants consist of a mixture of coal (qv), charcoal, petroleum coke, and wood chips. Petroleum coke, if used, accounts for less than 10% of the total carbon requirements. Low ash bituminous coal, having a fixed carbon content of 55—70% and ash content of <4%, provides a majority of the required carbon. Typical carbon contribution is 65%. Charcoal, as a reductant, is highly reactive and varies in fixed carbon from 70—92%. Wood chips are added to the reductant mix to increase the raw material mix porosity, which improves the SiO (g) to solid carbon reaction. Silica is added to the furnace in the form of quartz, quartzite, or gravel. The key quartz requirements are friability and thermal stability. Depending on the desired silicon quality, the total oxide impurities in quartz may vary from 0.5—1%. 

Salt-inclusion solids described herein were synthesized at high temperature (>500°C) in the presence of reactive alkali and alkaline-earth metal halide salt media. For single crystal growth, an extra amount of molten salt is used, typically 3 5 times by weight of oxides. The reaction mixtures were placed in a carbon-coated silica ampoule, which was then sealed under vacuum. The reaction temperature was typically set at 100-150 °C above the melting point of employed salt. As shown in the schematic drawing in Fig. 16.2, the corresponding metal oxides were first dissolved conceivably via decomposition because of cor-... 

An example for a non-structure-sensitive reaction is provided by Davis et al. [102], who investigated the liquid-phase hydrogenation of glucose over carbon and silica based ruthenium catalysts with particle sizes between 1.1 and 2.4 run. Depending on catalyst loading which was between 0.56 wt.% and 5 wt.%, dispersion decreased from 91% to 43%. At the same time, TOFs varied only insignificantly in a range between 0.21 1/s and 0.32 1/s. 

Membranes with extremely small pores ( < 2.5 nm diameter) can be made by pyrolysis of polymeric precursors or by modification methods listed above. Molecular sieve carbon or silica membranes with pore diameters of 1 nm have been made by controlled pyrolysis of certain thermoset polymers (e.g. Koresh, Jacob and Soffer 1983) or silicone rubbers (Lee and Khang 1986), respectively. There is, however, very little information in the published literature. Molecular sieve dimensions can also be obtained by modifying the pore system of an already formed membrane structure. It has been claimed that zeolitic membranes can be prepared by reaction of alumina membranes with silica and alkali followed by hydrothermal treatment (Suzuki 1987). Very small pores are also obtained by hydrolysis of organometallic silicium compounds in alumina membranes followed by heat treatment (Uhlhom, Keizer and Burggraaf 1989). Finally, oxides or metals can be precipitated or adsorbed from solutions or by gas phase deposition within the pores of an already formed membrane to modify the chemical nature of the membrane or to decrease the effective pore size. In the last case a high concentration of the precipitated material in the pore system is necessary. The above-mentioned methods have been reported very recently (1987-1989) and the results are not yet substantiated very well. 

The different types of admixtures, known to reduce alkali-aggregate reactions, can be divided into two groups those that are effective in reducing the expansion due to the alkali-silica reaction, and those that lower expansions resulting from the alkali-carbonate reaction. For the alkali-silica reaction, reductions in the expansion of mortar specimens have been obtained with soluble salts of lithium, barium and sodium, proteinaceous air-entraining agents, aluminum powder, CUSO4, sodium silicofluoride, alkyl alkoxy silane,... 

Ultramarine blues are prepared by a high temperature reaction of intimate mixtures of china day, sodium carbonate, sulfur, silica, sodium sulfate, and a carbonaceous reducing agent, eg, charcoal, pitch, or rosin. 

Nonetheless, the general understanding of magnesium and calcium carbonation reactions has improved significantly (see also the studies by Hanchen et al. [107-110] on the relative importance of process parameters such as temperature, C02 pressure and particle size distribution). Studies involving a three-step process of olivine carbonation, involving (i) dissolution of olivine (ii) precipitation of magnesite and (iii) precipitation of silica in an aqueous solution, were recently reported from Norway [69], where the process proceeds without chemical additives at 10-15 MPa and 403-523 K. No reaction rates were reported, however. 

A wide variety of catalytic materials are used as slurry-phase catalysts, most being metals supported on high surface area alumina, carbon, and silica (Fig. 2, label 3). Physical properties such as density are important since these catalysts must be suspended in the reaction mix. Since rapid agitation could lead to abrasion and attrition of the catalyst particles, strength is important. 

The most important sources of phosphorus are phosphate rocks containing either apatite, (a mixed fluoride-phosphate of calcium, Ca2FP04 Ca3(P04)2), or calcium phosphate itself. These yield elemental phosphorus when heated with a mixture of carbon and silica the latter forms a fusible slag with the CaO formed during the reaction, and the phosphorus formed from reduction by the carbon is distilled away from the mixture. 

The initial reaction step involves the deposition of carbon and silica, as shown experimentally by Lin et al.14 In their work, they examined the reaction front separating the reaction product from the unreacted composite using transmission electron microscopy (TEM). During the initial stages of reaction, graphitic carbon and silica glass were formed at the SiC-alumina interface, as... 

Of particular interest in the present chapter is the effect of test atmosphere on creep and creep damage mechanisms. While there are undoubtedly several factors that can promote creep cavitation and contribute to the observed changes in stress exponent and activation energy, the fact remains that the strain rates are substantially higher in air than in inert atmospheres, as shown in Fig. 8.12. This phenomenon is a direct consequence of the topotactic oxidation reaction of SiC whiskers exposed at the surface. As described by Porter and Chokshi,38 and subsequently by others,21,22 at high temperatures in air, a carbon-condensed oxidation displacement reaction occurs in which graphitic carbon and silica are formed at the whisker interface via... 

Isomer 2, isocyanogen,54 and isomer 3, diisocyanogen,55 have been detected by nmr and other spectroscopies isocyanogen is extremely unstable and polymerizes above -80°C. Isomer 1, cyanogen, is a flammable gas (Table 7-3) which is stable even though it is unusually endothermic (AHf% = 297 kJ mol"1). It can be prepared by oxidation of HCN using (a) 02 with a silver catalyst, (b) Cl2 over activated carbon or silica, or (c) N02 over calcium oxide-glass the last reaction allows the NO produced to be recycled ... 

Fig. 8.30. SEM images of the fi-S C nanowires obtained by, (a) heating the gel containing the activated carbon and silica at 1360 °C in NH3 for 4 h and (b) heating the gel prepared by the reaction of ethylene glycol with citric acid in the presence of TEOS at 1360 °C in NH3 for...

---