Silicon tetrachloride, oxidation

Both the Toth and Alcoa processes provide aluminum chloride for subsequent reduction to aluminum. Pilot-plant tests of these processes have shown difficulties exist in producing aluminum chloride of the purity needed. In the Toth process for the production of aluminum chloride, kaolin [1332-58-7] clay is used as the source of alumina (5). The clay is mixed with sulfur and carbon, and the mixture is ground together, pelletized, and calcined at 700°C. The calcined mixture is chlorinated at 800°C and gaseous aluminum chloride is evolved. The clay used contains considerable amounts of silica, titania, and iron oxides, which chlorinate and must be separated. Silicon tetrachloride and titanium tetrachloride are separated by distillation. Resublimation of aluminum chloride is requited to reduce contamination from iron chloride. 

Chlor-siure, /. chloric acid. -sMureanhydrid, n. chloric anhydride, chlorine(V) oxide, -schwefel, n. sulfur chloride (esp. the monochloride). -silber, n. silver chloride, -sili-cium, n. silicon tetrachloride, -soda, /. = Chlornatron. -stickstoff, m. nitrogen chloride. -Strom, m. stream of chlorine, -strontium, n. strontium chloride, -suifonsaure, /. chlorosulfonic acid, chlorosulfuric acid, -toluol, n. chlorotoluene. -fibertrager, m. chlorine carrier. 

The reinforcing fibers are usually CVD SiC or modified aluminum oxide. A common matrix material is SiC deposited by chemical-vapor infiltration (CVI) (see Ch. 5). The CVD reaction is based on the decomposition of methyl-trichlorosilane at 1200°C. Densities approaching 90% are reported.b l Another common matrix material is Si3N4 which is deposited by isothermal CVI using the reaction of ammonia and silicon tetrachloride in hydrogen at 1100-1300°C and a total pressure of 5 torr.l" " ] The energy of fracture of such a composite is considerably higher than that of unreinforced hot-pressed silicon nitride. 

An extension of the reduction-chlorination technique described so far, wherein reduction and chlorination occur simultaneously, is a process in which the oxide is first reduced and then chlorinated. This technique is particularly useful for chlorinating minerals which contain silica. The chlorination of silica (Si02) by chlorine, in the presence of carbon, occurs above about 1200 °C. However, the silica present in the silicate minerals readily undergoes chlorination at 800 °C. This reaction is undesirable because large amounts of chlorine are wasted to remove silica as silicon tetrachloride. Silica is, therefore, removed by other methods, as described below, before chlorination. Zircon, a typical silicate mineral, is heated with carbon in an electric furnace to form crude zirconium carbide or carbonitride. During this treatment, the silicon in the mineral escapes as the volatile oxide, silicon monoxide. This vapor, on contact with air, oxidizes to silica, which collects as a fine powder in the furnace off-gas handling system ... 

Titanium tetrachloride is produced on an industrial scale by the chlorination of titanium dioxide-carbon mixtures in reactors lined with silica. During the reactor operation, the lining comes into contact not only with chlorine but also with titanium tetrachloride. There appears to be no attack on silica by either of these as the lining remains intact. However, the use of such a reactor for chlorinating beryllium oxide by the carbon-chlorine reduction chlorination procedure is not possible because the silica lining is attacked in this case. This corrosion of silica can be traced to the attack of beryllium chloride on silica. The interaction of beryllium chloride with silica results in the formation of silicon tetrachloride in accordance with the reaction... 

Aminolysis of the corresponding halides is the preferred method for the synthesis of dialkylamino derivatives of boron,1 silicon,2 germanium,3 phosphorus,4 arsenic,5 and sulfur.6 (Dialkylamino) chlorosilanes are prepared stepwise by the reaction of silicon tetrachloride with dialkylamines. This method may be utilized equally well for the conversion of alkyl- or aryl-substituted halides [e.g., (CH3) SiCl4. ] or of oxide and sulfide halides (e.g., POCl3 or PSC13) to the corresponding dialkylamino compounds. 

Reduction of the diazaphospholines (151) by trichlorosilane yields a mixture of cis- (Ra = H, R3 = Ph) and trans- (R2 = Ph, R3 = H) phosphines, the lack of stereospecificity being attributed to changes in a pentaco-ordinate intermediate. Stereomutation of the starting oxide is brought about by hexachlorodisilane or silicon tetrachloride.118... 

Liquid perchloryl fluoride is a typical nonpolar solvent. Most inorganic and organic salts are insoluble in it. Conversely, most covalent, essentially nonpolar substances, boiling within about 50°G of perchloryl fluoride, are completely miscible, e.g., chlorine, boron trifluoride, sulfur hexafluoride, silicon tetrafluoride, phosgene, nitrous oxide, chlorine trifluoride, chlorofluorocarbons, silicon tetrachloride, sulfuryl chloride, dinitrogen tetroxide, and thionyl chloride 106). 

Silicochloroform Silicolluoric Acid Silicon Chloride Silicone Fluids Silicon Tetrachloride Silver Acetate Silver Carbonate Silver Fluoride Silver Iodate Silver Monofluoride Silver Nitrate Silver Oxide Silver Sulfate Silvisar 510 Slaked Lime Slow-Curing Asphalt Sodamide Sodium... 

J. L. Gay Lussac and L. J. Thenard 5 showed in 1811 that if many of the metallic oxides be intimately mixed with carbon the reaction with chlorine proceeds more readily than with the oxide alone the metal chloride and carbon monoxide or dioxide are the products of the reaction. M. le Quesneville and F. Wohler used this process for aluminium chloride, chromic chloride, silicon tetrachloride, etc., and C. Baskerville for thorium tetrachloride. 

The products of the reaction between silicon(IV) oxide and powdered magnesium can also be used to prepare silicon tetrachloride without the separation of free silicon. 

Silicon carbide is comparatively stable. The only violent reaction occurs when SiC is heated with a mixture of potassium dichromate and lead chromate. Chemical reactions do, however, take place between silicon carbide and a variety of compounds at relatively high temperatures. Sodium silicate attacks SiC above 1300°C, and SiC reacts with calcium and magnesium oxides above 1000°C and with copper oxide at 800°C to form the metal silicide. Silicon carbide decomposes in fused alkalies such as potassium chromate or sodium chromate and in fused borax or cryolite, and reacts with carbon dioxide, hydrogen, air, and steam. Silicon carbide, resistant to chlorine below 700°C, reacts to form carbon and silicon tetrachloride at high temperature. SiC dissociates in molten iron and the silicon reacts with oxides present in the melt, a reaction of use in the metallurgy of iron and steel (qv). The dense, self-bonded type of SiC has good resistance to aluminum up to about 800°C, to bismuth and zinc at 600°C, and to tin up to 400°C a new silicon nitride-bonded type exhibits improved resistance to cryolite. 

Pyrosulphuryl Chloride, S205C12.—Rose first prepared this substance in 1838 by the interaction of sulphur trioxide and sulphur monochloride.4 It is formed by the action of many chlorides on sulphur trioxide sulphur monochloride,4 thionyl chloride,5 silicon tetrachloride,6 phosphorus pentachloride,7 phosphorus oxychloride,8 sodium chloride 9 and carbon tetrachloride 10 all yield the desired product when treated with sulphur trioxide at a suitable temperature. With sodium chloride a mixture of pyrosulphufyl chloride and sodium pyrosulphate is obtained, whilst with the exception of carbon tetrachloride and phosphorus pentachloride, which are converted into oxychlorides, all the remaining chlorides are changed into oxides ... 

Carbon brings about reduction of arsenious oxide at a temperature below red heat,11 while in carbon monoxide reduction begins at 60° C.12 The numerous reactions of arsenious oxide with organic compounds are described in Vol. XI, Part II, of this Series. Silicon tetrachloride heated for 30 hours at 270° to 280° C. with the oxide yields arsenic trichloride,13 whilst silicochloroform when heated with the oxide in the presence of aqueous sodium hydroxide-or sodium hydrogen carbonate... 

A number of other metallic halide salts have been found to condense with ethylene oxide, propylene oxide, or epichlorohydrin in a similar fashion (Eq. 662). Among them are phosphorus trichloride/ 7- a 17 bismuth trichloride,1SM arsenic trichloride,1000 silicon tetrachloride/7 1 titanium tetrachloride/ 09 16,7 beryllium chlorido/189 and Won trifluoride.401 Depending on their reactivity, on the reactant ratio, and... 

The most widespread technique, however, is the chlorination of titanium dioxide with chlorine or chlorine-containing substances (carbon tetrachloride, chloroform, sulftuyl chloride, phosphorus oxychloride, silicon tetrachloride). These reactions give high yield at high temperatures (800 °C and more) the chlorination with free chlorine occurs at noticeable speed only in the presence of reducing agents (e.g., coal). If there is a lack of coal, the reaction forms carbon dioxide if there is an excess of coal, it releases carbon oxide ... 

AMIDES N-Ethoxycarbonyl-2-ethoxy-l,2-dihydroquinoline (EEDQ). Silicon tetrachloride. Sodium hydride-Dimethylsulf-oxide. Triphenyl phosphite. 

Molybdenum Sesquisilicide, MOjSi, is said to result when crv stallised silicon is heated in a carbon crucible in the electric furnace with the oxides of molybdenum obtained by calcining ammonium molybdate. The mass is disintegrated by electrolysis in hydrochloric acid, and the residue successively treated with aqua regia, caustic alkali, and hydrofluoric acid. The silicide burns in chlorine at 800° C., with formation of silicon tetrachloride and molybdenum pentachioride. 

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