Trichlorosilane

Chemical Name Synonyms Chemical Formula CAS nmnber Molecular Weight Boiling point Melting point Vapor pressure (14.6°C) Latent heat of vaporization Solubility in water 

Flammable limits in air Autoignition temperature DOT classification DOT label 

No occupational exposure limits have been established by OSHA, NIOSH, or ACGIH 1000 ppm/4 HRS RAT LClq 

Trichlorosilane is a severe eye, skin and mucous membrane irritant. Poisoning may affect the blood. Acute exposure may cause coughing, choking headache, weakness, hypotension, pulmonary edema and cyanosis. Convalescence may be prolonged with frequent relapses. Chronic exposure may cause erosion of the teeth and jaw necrosis, bronchial pneumonia a gastrointestinal disturbances. 

Vapor air mixtures can be explosive. Reacts violently with water. Keep from oxidizers and combustible materials. 

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The silanization reaction has been used for some time to alter the wetting characteristics of glass, metal oxides, and metals [44]. While it is known that trichlorosilanes polymerize in solution, only very recent work has elucidated the mechanism for surface reaction. A novel FTIR approach allowed Tripp and Hair to prove that octadecyl trichlorosilane (OTS) does not react with dry silica. 

Organosilanes, such as trichlorosilanes or trimethylsilanes, can establish SA monolayers on hydroxylated surfaces. Apart from their (covalent) binding to the surface these molecules can also establish a covalent intennolecular network, resulting in an enlranced mechanical stability of the films (figure C2.4.11). In 1980, work was published on the fonnation of SAMs of octadecyltrichlorosilane (OTS) 11171. Subsequently, the use of this material was extended to the fonnation of multilayers 11341. 

The formation of silicon carbide, SiC (carborundum), is prevented by the addition of a little iron as much of the silicon is added to steel to increase its resistance to attack by acids, the presence of a trace of iron does not matter. (Addition of silicon to bronze is found to increase both the strength and the hardness of the bronze.) Silicon is also manufactured by the reaction between silicon tetrachloride and zinc at 1300 K and by the reduction of trichlorosilane with hydrogen. 

Silicon is prepared commercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be prepared as a brown powder, which can be easily melted or vaporized. The Gzochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Hyperpure silicon can be prepared by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone process. 

The reaction of hydrosilanes with butadiene is different from other reactions. Different products are obtained depending on the structurelof the hydrosilanes and the reaction conditions. Trimethylsiiane and other trialkylsilanes react to give the I 2 adduct, namely the l-trialkylsilyl-2,6-octadiene 74, in high yields[67-69]. Unlike other telomers which have the 2,7-octadienyl chain, the 2,6-octadienyl chain is formed by hydrosilylation. On the other hand, the 1 I adduct 75 (l-trichlorosilyl-2-butene)is formed selectively with trichlorosilane, which is more reactive than trialkylsilanes[69]. The Reaction gives the Z form stereoselectively[70]. A mixture of the I 1 and I 2 adducts (83.5 and 5.2%) is... 

At 165°C and in the presence of chloroplatinic acid as catalyst, isoprene reacts with trichlorosilane, metbyldicblorosilane, ethyldichlorosilane, ben2yldichlorosilane, and diben2ylchlorosilane (72). The addition is 1,4- with the substituted silane group attaching to the first carbon atom. 

UsuaHy, trichlorosilane, trialkoxysilane, methyl dichlorosHane, and methyl dialkoxysHane are used. For example, the reaction of trichlorosilane with aHyl methacrylate is as foHows ... 

Silicon reacts at elevated temperatures with the halogens, forming SiCl, Sil, SiBr, and SiF. There is also a series of halogen-substituted silanes such as trichlorosilane, SiH Cl, and dichlorosilane, S1H2CI2. Both SiCl and SiH Cl are relatively easy to make, purify, and reduce to silicon. These are the silicon compounds most often used as feedstocks in the manufacture of high purity silicon. 

The electronics market uses sihcon as trichlorosilane, which is decomposed with hydrogen at high temperatures to produce semiconductor-grade sihcon (see Silicon compounds). 

The physical properties of siUcon tetrahaUdes are Hsted in Table 1 those of the halohydrides are Hsted in Table 2. A more complex review of the physical properties of these chemicals is available (2). Detailed Hsts of properties of the colorless fuming Hquids, siUcon tetrachloride and trichlorosilane, are given in Table 3. A review of the physical and thermodynamic properties of siUcon tetrachloride is given in Reference 3. 

Table 3. Physical Properties of Silicon Tetrachloride and Trichlorosilane ...

At equihbrium the vapors are predominantly hydrogen and sihcon tetrachlorides. However, these can be easily removed from the trichlorosilane and recycled. A once-common commercial manufacturing procedure for sihcon tetrachloride was the reaction of chlorine gas with sihcon carbide. 

Silicon Tetrachloride. Most commercially available sihcon tetrachloride is made as a by-product of the production of alkylchlorosilanes and trichlorosilane and from the production of semiconductor-grade sihcon by thermal reduction of trichlorosilane. 

Trichlorosilane. The primary production process for trichlorosilane is the direct reaction of hydrogen chloride gas and sihcon metal in a fluid-bed reactor. Although this process produces both trichlorosilane and sihcon tetrachloride, production of the latter can be minimi2ed by proper control of the reaction temperature (22). A significant amount of trichlorosilane is also produced by thermal rearrangement of sihcon tetrachloride in the presence of hydrogen gas and sihcon. 

The two largest global producers of trichlorosilane are Wacher in Europe and Dow Coming in the United States. In addition, there are three primary producers in Japan Tokuyama Soda, Mitsubishi Materials, and Osaka Titanium. 

At atmospheric pressure, the conversion to trichlorosilane is limited to about 16%. The conversion of SiCl to HSiCl was found to be at equiUbrium. If contact time was greater than 45 s and the mole ratio of hydrogen to siUcon tetrachloride 1 1, then at 14 kPa (2 psi) and 550°C, the HSiCl mole fraction reached 0.7 but substantial formation of H2SiCl2 occurred (62). Enhancements in yield have been reported through preactivating the siUcon mass by removal of oxides (73) and the rapid thermal quench of the effluent gas stream (74). The reduction of siUcon tetrachloride in a plasma has also been reported (75). 

The most common catalysts in order of decreasing reactivity are haUdes of aluminum, boron, zinc, and kon (76). Alkali metals and thek alcoholates, amines, nitriles, and tetraalkylureas have been used (77—80). The largest commercial processes use a resin—catalyst system (81). Trichlorosilane refluxes in a bed of anion-exchange resin containing tertiary amino or quaternary ammonium groups. Contact time can be used to control disproportionation to dichlorosilane, monochlorosilane, or silane. 

Dkect synthesis is the preparative method that ultimately accounts for most of the commercial siUcon hydride production. This is the synthesis of halosilanes by the dkect reaction of a halogen or haUde with siUcon metal, siUcon dioxide, siUcon carbide, or metal sihcide without an intervening chemical step or reagent. Trichlorosilane is produced by the reaction of hydrogen chloride and siUcon, ferrosiUcon, or calcium sihcide with or without a copper catalyst (82,83). Standard purity is produced in a static bed at 400—900°C. 

Only three inorganic halosilanes are produced on a large iadustrial scale, ie, tetrachlorosilane [10026-04-7] tetrafluorosilane [7783-61-17, and trichlorosilane. 

The production of sihcon tetrachloride by these methods was abandoned worldwide in the early 1980s. Industrial tetrachlorosilane derives from two processes associated with trichlorosilane, the direct reaction of hydrogen chloride on sihcon primarily produced as an intermediate for fumed sihca production, and as a by-product in the disproportionation reaction of trichlorosilane to silane utilized in microelectronics. Substantial quantities of tetrachlorosilane are produced as a by-product in the production of zirconium tetrachloride, but this source has decreased in the 1990s owing to reduction in demand for zirconium in nuclear facihties (see Nuclearreactors). The price of tetrachlorosilane varies between l/kg and 25/kg, depending on grade and container. 

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