Silicone oil usually refers to a linear polysiloxane product that maintains a liquid state at room temperature. It is generally a colorless (or light yellow), odorless, non-toxic, and non-volatile liquid. It is insoluble in water, methanol, and ethylene glycol. It can be mixed with benzene , dimethyl ether, carbon tetrachloride or kerosene, etc. miscible, slightly soluble in acetone, dioxane, ethanol and butanol.
Classification of silicone oil
Silicone oil is divided according to chemical structure, including methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil, methyl chlorophenyl silicone oil, methyl ethoxy silicone oil, methyl trifluoro Propyl silicone oil, methyl vinyl silicone oil, methyl hydroxy silicone oil, ethyl hydrogen silicone oil, hydroxyl hydrogen silicone oil, cyano silicone oil, etc.
In terms of usage, there are damping silicone oil, diffusion pump silicone oil, hydraulic oil, insulating oil, heat transfer oil, brake oil, etc.
According to the processing status, it can be divided into primary products and secondary products. The former refers to silicone oil products before processing, including four categories: hydroxyl silicone oil, silicon-functional silicone oil, carbon-functional silicone oil and inactive modified silicone oil. Customarily, the first two types are called linear silicone oils, and the latter two types are called modified silicone oils; the latter is made of silicone oil, mixed with thickeners, surfactants, solvents and additives, etc., and processed by specific processes. Products such as grease, emulsion and solution, such as silicone grease, silicone paste, defoamer, release agent and release agent, etc.
Silicone oil is often not used alone, but is made into an effective application through a special formula; it is not used as a raw material, but as an auxiliary material to produce a certain effect. Generally speaking, there are three basic forms of silicone oil on the market: pure silicone oil, solution, and emulsion.
○ 100% pure silicone oil
Pure silicone oil is very stable, heat-resistant, freeze-resistant, good storage, has high flash point and high fire point, and has few storage and transportation problems. the
○ solution
In fact, it is often necessary to dilute the silicone oil solution, and it is not convenient for users to configure the solution by themselves. During use, it is sometimes desirable to add active auxiliary agents (catalysts, cross-linking agents, etc.) to the solution for easy storage and use. Aliphatic, aromatic or chlorinated hydrocarbons can be used as solvents as desired. Other types of solvents are used only in special cases. Polymer polysiloxane solution, the concentration can only reach 35%, otherwise the viscosity is too large.
○ Lotion
A large part of silicone oil or silicone oil-containing products are made into emulsion form. Compared with solvent silicone oil, it has the advantages of cheap, non-flammable, and harmless to health. Different from solvent type, all silicone emulsions are "oil-in-water" type (O/W type) heterogeneous phase system, its external closed phase is water phase, silicone oil is dispersed in the water phase with very fine droplets, it is easy to Dilute with water to desired concentration for application. The stability of this emulsion can be achieved by making the droplets as thin as possible and the stabilizing effect of the emulsifier.
Properties of silicone oil
Silicone oil has many special properties:
○ Good heat resistance
Since the main chain of polysiloxane molecules is composed of -Si-O-Si-bonds, it has a structure similar to that of inorganic polymers, and its bond energy is very high, so it has excellent heat resistance.
○ Good oxidation stability and weather resistance
○ Good electrical insulation
Silicone oil has good dielectric properties, and its electrical characteristics change little with the change of temperature and cycle number. The dielectric constant decreases with increasing temperature, but only slightly. The power factor of silicone oil is low and increases with temperature, but it does not change regularly with frequency. Volume resistivity decreases with increasing temperature.
○ Good hydrophobicity
Although the main chain of silicone oil is composed of polar bonds Si-O, the non-polar alkyl groups on the side chains are oriented outwards, preventing water molecules from entering the interior and acting as hydrophobic. The interfacial tension of silicone oil to water is about 42 dynes/cm. When it spreads on the glass, due to the water repellency of silicone oil, it forms a contact angle of about 103oC, which is comparable to paraffin wax.
○ Small viscosity-temperature coefficient
The viscosity of silicone oil is low and changes little with temperature, which is related to the helical structure of silicone oil molecules. Silicone oil is a type of oil with the best viscosity-temperature characteristics among various liquid lubricants. This characteristic of silicone oil is very meaningful for damping equipment.
○ High compression resistance
Due to the helical structure of silicone oil molecules and the large distance between molecules, it has high compression resistance. Utilizing this characteristic of silicone oil, it can be used as a liquid spring, and compared with a mechanical spring, the volume can be greatly reduced.
○ low surface tension
Low surface tension is a characteristic of silicone oils. Low surface tension means high surface activity. Therefore, silicone oil has excellent defoaming and anti-foaming properties, isolation properties from other substances and lubricating properties.
○ Non-toxic, odorless and physiologically inert
From a physiological point of view, silicone polymers are among the most inactive compounds known. Simethicone is inert to organisms and has no rejection reaction with animal organisms. Therefore, they have been widely used in departments such as surgery and internal medicine, medicine, food and cosmetics.
○ Good lubricity
Silicone oil has many excellent properties as a lubricant, such as high flash point, low freezing point, thermal stability, small change in viscosity with temperature, no corrosion of metals, no adverse effects on rubber, plastics, paints, organic paint films, and low surface tension. Easy to spread on the metal surface and other characteristics. In order to improve the steel-to-steel lubricity of silicone oil, lubricity additives that are miscible in silicone oil can be added. Introducing chlorophenyl into the siloxane chain or replacing dimethyl with trifluoropropylmethyl can greatly improve the lubricating properties of silicone oil.
○ Chemical properties
Silicone oil is relatively inert because the Si-C bond is very stable. But strong oxidizing agents are easy to interact with, especially at high temperatures. Silicone oil reacts violently with chlorine gas, especially methyl silicone oil. Sometimes there are explosive reactions. Si-O bonds are easily broken by strong bases or acids. Concentrated sulfuric acid reacts quickly at low temperatures, breaking and attaching siloxane chains. In this regard, silicone oils with higher alkane groups and phenyl groups are relatively stable, but concentrated sulfuric acid will break the benzene-silicon bond of the phenyl group and release benzene.
Regeneration of silicone oil
The chemical properties of silicone oil are relatively warm, but after long-term use, it will also deteriorate due to oxidation and the intrusion of foreign impurities. Due to the high price of silicone oil, it should be recovered and regenerated separately.
Waste silicone oil is usually regenerated in two ways. Waste silicon oil in electrical equipment is mainly treated by adsorption and refining, and waste silicon oil can be contacted and refined with adsorbents such as silica gel, activated alumina, activated clay, and activated carbon. After filtering out the waste adsorbent, vacuum degas the silicone oil at 50-110°C (such as vacuum degassing at 95°C) or strip it with nitrogen blowing at 20-80°C to obtain purified regenerated silicone oil.
Another method is to treat the liquid waste silicon oil with solvent vapor, and use the dissolution effect of the solvent to dissolve and extract the impurities in the waste silicon oil to form another liquid phase immiscible with the silicone oil. This method can dissolve and remove polychlorinated polycyclic aromatic hydrocarbons (PCBs) in waste silicone oil. The treated silicone oil also contains traces of solvent, which can be removed by vacuum drying. Commonly used are hydrocarbon solvents and chlorinated hydrocarbon solvents.
About vinyl silicone oil, please check the details:
https://www.siliconefoam.net/product-side-chain-vinyl-silicone-oil-iota-272-.html
