Organic silicon products have excellent resistance to high and low temperatures, and can generally work for a long time at a high temperature of 180 ℃. Silicone rubber can work for a long time at 250 ℃ and can withstand temperatures of over 1000 degrees Celsius instantly. Organic silicon materials have good low-temperature resistance and can generally work at -55 ℃. Some silicone rubber still has elasticity at -110 ℃. Organic silicon materials have excellent electrical insulation properties, and their dielectric properties do not change dramatically with temperature; The dielectric constant does not increase with frequency; And it is resistant to arc, corona, and leakage; Resistant to ozone, radiation, weather, and flame, therefore it has a wide range of applications. Below are several major categories of organic silicon products, briefly introducing their main uses:
1. Silane coupling agent is a type of low molecular weight compound, which is connected to one end of the silicon atom by a hydrolyzable chlorine or various alkoxy groups. After hydrolysis, it can be connected to inorganic substances; On the other end, there are various functional groups that can interact with organic compounds, such as amino groups, vinyl groups, thiol groups, etc. Therefore, silane coupling agents can bridge organic and inorganic compounds together. There are nearly a hundred commonly used silane coupling agents. Glass fibers used in fiberglass reinforced plastic need to be treated with ethylene based coupling agents to improve wet strength. The currently popular "green" tires extensively use silane coupling agents containing thiol groups; Polyethylene crosslinked with vinyltrialkoxysilane can work at a higher temperature than ordinary polyethylene and polyvinyl chloride, making it suitable for heating water pipes, cable sheaths, etc.
2. Silicone oil is a low molecular weight polysiloxane containing single or different organic groups, which can be made into various viscosities. Silicone oil has low surface tension and a large contact angle with water, making it a high-quality water repellent material. Silicone oil has a small change in viscosity temperature coefficient and does not solidify at low temperatures. It is a base oil for gyroscopes, antifreeze and heat-resistant lubricants, hydraulic oils, instrument oils, and high vacuum diffusion pump oils for aerospace vehicles that are both resistant to high and low temperatures. The application of organic silicone oil or its modified formulations in cosmetics has grown rapidly in recent years. Silicone oil applied to the skin is neither oily nor greasy, feels smooth and comfortable, and can be made into various skincare creams.
3. According to the vulcanization mechanism, silicone rubber can be divided into high-temperature vulcanized silicone rubber (HTV); Room temperature vulcanized silicone rubber (RTV) and additive liquid silicone rubber (LSR) have the characteristics of heat resistance, cold resistance, ozone resistance, ultraviolet resistance, atomic oxygen resistance, and cosmic ray resistance, as well as comprehensive properties such as waterproofing and shock resistance. LSR liquid silicone rubber (also known as silicon gel) is an excellent encapsulating and protecting material for semiconductor chips and electronic devices; Organic silicon gel with light transmittance up to 91% is the intermediate bonding layer of aircraft triple windshield glass that requires high temperature resistance, moisture resistance and no yellowing. LSR silicone rubber mold adhesive is used for precision casting of engine components.
The production of HTV and RTV accounts for a large share of organic silicon products (generally 40% to 50%), and HTV has a wider range of uses than RTV.
(1) RTV room temperature cured silicone rubber RTV is generally made of low molecular weight polydimethylsiloxane (107 glue) terminated with hydroxyl groups, combined with catalysts, fillers, etc. to form two-component or single component silicone rubber that is easy to use and can cure at room temperature. It has good adhesion to various materials such as glass, ceramics, metals, and concrete, and is widely used for bonding and sealing structural parts such as panoramic glass curtain walls, aluminum alloy doors and windows, as well as leak sealing and joint filling in households' bathrooms, toilets, etc. The RTV silicone rubber based erosion resistant thermal insulation coating has low thermal conductivity and is easy to apply. It is used as an insulation material for the tail nozzle of rockets and return space vehicles to prevent erosion, and is also an important material for making spacecraft components. RTV silicone rubber is also a flexible mold for various artistic decorative building materials.
(2) HTV high-temperature vulcanized silicone rubber is a high molecular weight (400000~800000) polydimethylsiloxane, which is added with reinforcing fillers and various other additives, vulcanized, formed and crosslinked into rubber. The composite insulators made of HTV silicone rubber for high-voltage transmission and transformation are not only 1/5 to 1/10 the weight of ceramic insulators, which is convenient to use, but also have good pollution flashover resistance and can operate safely in high-voltage transmission and transformation power grids. HTV silicone rubber, which uses carbon black as a conductive medium, is widely used as a key pad on keyboards such as mobile phones and computers; Silicone rubber is widely used in the production of shaft seals, gaskets, oil seals, industrial rubber rollers, shock-absorbing rubber, insulation products, medical products, etc. Silicone rubber insulated flame-retardant wires and cables are used in high reliability applications such as warships and aircraft. Silicone rubber has the characteristics of physiological inertness, non coagulation, and easy disinfection. It can be used to make silicone rubber parts that can be implanted into the human body, as well as various silicone rubber catheters, intubation tubes, hydrocephalus drainage tubes, peritoneal dialysis tubes, and artificial heart and lung machine transfusion pump tubes that can be used for a long time. In addition, silicone rubber has breathability and different permeability to different gases. The oxygen permeability is the highest in synthetic polymers and can be used as an oxygen rich membrane and gas separation membrane.
4. The insulation material made of silicone resin belongs to H level due to its good heat resistance and insulation performance. The electric motors made with it have small volume, light weight, and high reliability, and will not burn out under short-term overheating and overload conditions. Silicone resin can be used to prepare coatings that can withstand high temperatures up to 500 ℃; Organic silicon modified acrylic resin coating has good weather resistance, hydrophobicity, and stain resistance, making it a high-end exterior wall coating. Silicone plastic made of silicone resin can be used as micro switches for aircraft engines that are resistant to high voltage, high current, and arc. In short, organic silicon materials have a wide range of applications and significant effects.
