What Is Silicon Tetrachloride?
Silicon tetrachloride is an inorganic compound consisting of silicon (Si) bonded with four chlorines.
It is also known as silicon chloride, silicon tetrachloride, tetrachlorosilane, and silicon tetrachloride. Although silicon tetrachloride exists as a liquid at room temperature, it quickly volatilizes upon heating due to its low boiling point of 57.6°C.
Uses of Silicon Tetrachloride
Silicon tetrachloride is rarely used in its raw state. It is basically used as a raw material for other silicon compounds.
1. High-Purity Silicon Tetrachloride
It is used as a raw material for silicon single crystals, for epitaxial growth of silicon wafers, for etching gas and other semiconductor fields, for synthetic quartz, and for synthetic quartz glass. Synthetic quartz glass has high purity and low metallic impurities. Besides, it allows light to pass through well and is resistant to heat, so it is used in photomasks for optical fibers and semiconductors.
2. General-Purity Silicon Tetrachloride
It is used as a raw material for silicon oxide (silica), which is used as a reinforcing filler for resins, CMP slurry for semiconductor polishing, adhesives, and viscosity adjusters for paints. It is also used as a raw material for various organic silicones (silane coupling agents, silicone resins, etc.).
Characteristics of Silicon Tetrachloride
The molecular formula of silicon tetrachloride is SiCl4, and its molecular weight is 169.89. It has a specific gravity of 1.52, a melting point of -70°C, and a boiling point of 57.6°C. At room temperature and pressure, it is a colorless, viscous liquid. It also has a pungent odor that can be suffocating. It is soluble in ether, benzene, chloroform, and carbon tetrachloride.
It reacts violently with water, strong oxidizers, strong acids, alcohols, bases, ketones, and aldehydes to form toxic and corrosive hydrogen chloride (HCl). In humid air, it hydrolyzes instantly to produce white smoke containing chlorine gas.
In the presence of water, the hydrochloric acid produced by hydrolysis corrodes many metals. For this reason, the metals that can be used are limited to nickel steel and copper-nickel alloys. Polyethylene, polyvinyl chloride, and Teflon can be used as resins.
Other Information on Silicon Tetrachloride
1. How Silicon Tetrachloride Is Produced
It is produced by heating silicon metal and chlorine or hydrogen chloride, or by chlorinating calcium silicide or other materials. Raw materials of a purity corresponding to the product purity required must be used.
Chlorination of metallic silicon: Si + 4HCl → SiCl4 + 2H2
Chlorination of calcium silicide: CaSi2 + 5Cl2 → 2SiCl4 + CaCl2
Research has also been reported on the production of Silicon Tetrachloride from silicate biomass such as rice chaff and rice straw.
2. Safety of Silicon Tetrachloride
Handling
Silicon tetrachloride is a severe irritant when adhered to skin and mucous membranes, and may cause erythema, edema, severe conjunctivitis, and coughing. When handling, wear a protective mask, impervious protective gloves, protective glasses with side plates, and long-sleeved work clothes.
In the event of a fire, heat, flames, and water used to extinguish the fire will generate hydrogen chloride gas, which is corrosive and highly toxic, and will emit very thick smoke, so care should be taken. If there is no danger, it is recommended to take measures such as moving the container away from the fire location.