Tetrachlorosilane

Description

Chlorosilanes (general formula RnHmSiCl4-n-m, where R is an alkyl, aryl, or olefin group) are compounds in which silicon is bound to between one and four chlorine atoms, bonds with hydrogen and/or organic groups making its total number of bonds up to four. Chlorosilanes react with water, moist air, and steam, producing heat and toxic, corrosive hydrogen chloride fumes. Contact between gaseous hydrogen chloride and metals may release gaseous hydrogen, which is inflammable and explosive. Chlorosilanes react vigorously with oxidizing agents, alcohols, strong acids, strong bases, ketones, and aldehydes.

Chemical properties

Clear colorless liquid

The Uses of Tetrachlorosilane

. Silicon tetrachloride (SiCl4) may be used as an intermediate in the manufacture of high purity silicon. High purity silicon derived from silicon tetrachloride may find major applications in the semiconductors industry and photovoltaic cells. . High purity SiCl4 may be used to manufacture of optical fibers.

The Uses of Tetrachlorosilane

Silicon tetrachloride (SiCl4), produced when both silicon and chlorine are combined at high temperatures, is used by the military to produce smoke screens.

The Uses of Tetrachlorosilane

Chlorosilanes are chemical intermediates used in the production of silicon and silicon-containing materials, and in the semiconductor industry; they are also protecting agents for intermediates in pharmaceutical syntheses. The most important industrially utilized silicon halides are trichlorosilane and silicon tetrachloride.
Silicon tetrachloride (SiCl4) can be manufactured by chlorination of silicon compounds such as ferrosilicon or silicon carbide, or by heating silicon dioxide and carbon in a stream of chlorine. It can also be obtained as a by-product in the production of zirconium tetrachloride, and in the past substantial quantities were produced by this route, which in recent decades has lost importance owing to the reduced demand for zirconium in nuclear facilities. Nowadays, industrial silicon tetrachloride is produced either by direct reaction of hydrogen chloride with silicon – this product mainly being employed as an intermediate in fumed silica production – or as the by-product of the production of silane for the microelectronics industry by disproportionation of trichlorosilane.

The Uses of Tetrachlorosilane

Tetrachlorosilane, can be used as a coupling agent for the synthesis of amine from carboxylic acid and an amide. It can also be used in preparation of high purity silicon, used in photovoltaic cells, and in the semiconductors industry.

Production Methods

Manufactured directly by the reaction of chlorine on silicon metal or ferrosilicon at 500C or silicon carbide.

General Description

Tetrachlorosilane is a colorless, fuming liquid with a pungent odor. Tetrachlorosilane is decomposed by water to hydrochloric acid with evolution of heat. Tetrachlorosilane is corrosive to metals and tissue in the presence of moisture. Tetrachlorosilane is used in smoke screens, to make various silicon containing chemicals, and in chemical analysis.

Reactivity Profile

Chlorosilanes, such as Tetrachlorosilane, are compounds in which silicon is bonded to from one to four chlorine atoms with other bonds to hydrogen and/or alkyl groups. Chlorosilanes react with water, moist air, or steam to produce heat and toxic, corrosive fumes of hydrogen chloride. They may also produce flammable gaseous H2. They can serve as chlorination agents. Chlorosilanes react vigorously with both organic and inorganic acids and with bases to generate toxic or flammable gases. Tetrachlorosilane is incompatible with alkali metals and dimethyl sulfoxide.

Hazard

Toxic by ingestion and inhalation, strong irritant to tissue.

Health Hazard

Inhalation causes severe irritation of upper respiratory tract resulting in coughing, choking, and a feeling of suffocation; continued inhalation may produce ulceration of the nose, throat, and larynx; if inhaled deeply, edema of the lungs may occur. Contact of liquid with eyes causes severe irritation and painful burns; may cause permanent visual impairment. Liquid may cause severe burns of skin. Repeated skin contact with dilute solutions or exposure to concentrated vapors may cause dermatitis. Ingestion causes severe internal injury with pain in the throat and stomach, intense thirst, difficulty in swallowing, nausea, vomiting, and diarrhea; in severe cases, collapse and unconsciousness may result.

Fire Hazard

Behavior in Fire: Contact with water in foam applied to adjacent fires will produce irritating fumes of hydrogen chloride.

Flammability and Explosibility

Not classified

Safety Profile

Mildly toxic by inhalation. A corrosive irritant to eyes, skin, and mucous membranes. Reacts with water to form HCl. Violent reaction with Na, K. When heated to decomposition it emits toxic fumes of Cl-. See also CHLOROSILANES.

Environmental Fate

Studies of rats subjected to acute inhalation of 10 structurally similar chlorosilanes, including tetrachlorosilane, suggest that the acute toxicity of chlorosilanes is largely due to the hydrogen chloride hydrolysis product. The observed effects were similar to those of HCl inhalation both qualitatively (clinical signs) and quantitatively (molar equivalents of hydrogen chloride at the atmospheric LC50).

Purification Methods

Distil it under vacuum and store it in sealed ampoules under N2. It fumes in moist air and is very sensitive to moisture. It is soluble in organic solvents. It is a strong irritant. [Schenk in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I pp 682-683 1963.]

Toxicity evaluation

Silicon tetrachloride is a colorless, noninflammable, volatile liquid with a pungent, suffocating odor. It fumes in air and is corrosive to metals and tissues in the presence of moisture. In experiments at Argonne National Laboratory in which it was mixed with water and stirred under room conditions, about 35% of the theoretical yield of HCl evolved as a gas in the first minute. It also reacts very rapidly with alcohols, primary and secondary amines, ammonia, and other compounds containing active hydrogen atoms. Thermal decomposition or burning may produce dense white clouds of silicon oxide particles and hydrogen chloride.
Silicon tetrachloride is a by-product in the production of polysilicon, the key component of sunlight-capturing wafers in solar energy panels, and for each ton of polysilicon produced, at least four tons of silicon tetrachloride liquid waste are generated. Pollution by silicon tetrachloride has been reported in China, associated with the increased demand for photovoltaic cells that has been stimulated by subsidy programs.