01 Properties and Classification of Silicone Oil 
△ Physical and Chemical Properties
Silicone oil, a linear polysiloxane product that remains liquid at room temperature, is characterized by being colorless (or pale yellow), odorless, non-toxic and having low volatility. It is insoluble in water, methanol and ethylene glycol, but is miscible with substances such as benzene, dimethyl ether, carbon tetrachloride and kerosene. It also slightly dissolves in acetone, dioxane, ethanol and butanol. 
△ Chemical Classification and Applications
Silicone oil has various classifications in terms of chemical structure, including methyl silicone oil, ethyl silicone oil, etc. Meanwhile, based on different applications, silicone oil is further categorized into damping silicone oil, diffusion pump silicone oil, hydraulic oil, etc. Additionally, from the perspective of processing status, silicone oil can be divided into primary products and secondary products. The former mainly refers to silicone oil products before processing, while the latter are lipid-like substances, emulsions, and solutions processed from silicone oil through specific techniques. 
02 Applications of Silicone Oil 
△ Application Forms
In terms of application, silicone oil is usually not used alone but combined with other components through special formulations to achieve specific effects. Common forms of silicone oil on the market include pure silicone oil, solutions, and emulsions, etc. 100% pure silicone oil is renowned for its excellent stability, heat resistance, frost resistance, and good storability. It has a high flash point and ignition point, making storage and transportation relatively simple. However, in practical applications, pure silicone oil often needs to be diluted, and at this point, users may find it somewhat difficult to prepare the solution themselves. To meet different needs, aliphatic, aromatic, or chlorinated hydrocarbons can be used as solvents. It is worth noting that the concentration of high-molecular-weight polysiloxane solutions is usually no more than 35% to avoid excessively high viscosity. 
Silicone oil or silicone-containing products in emulsion form have advantages such as low cost, non-flammability, and no harm to health. Compared with solvent-based silicone oil, these emulsions usually present as "oil-in-water" (O/W) type heterogeneous systems, where silicone oil is dispersed in the aqueous phase in the form of fine droplets and can be easily diluted with water to the desired concentration. The stability of this emulsion can be further enhanced by reducing the droplet size and utilizing the stabilizing effect of emulsifiers. 
△ Unique Properties
In addition, silicone oil possesses a variety of unique properties, including excellent heat resistance, stability, electrical insulation, hydrophobicity, and a small viscosity-temperature coefficient. These characteristics make silicone oil widely applicable in many fields. High compressibility resistance: The unique helical structure of silicone oil molecules and the large distance between them endow it with outstanding compressibility resistance. As a result, silicone oil can be ingeniously used as a liquid spring, significantly reducing the volume compared to traditional mechanical springs. Low surface tension: Silicone oil has a remarkable low surface tension property, which stems from the high surface activity of its molecular structure. Therefore, silicone oil demonstrates excellent defoaming and anti-foaming performance, as well as effective isolation and lubrication capabilities with other substances. Non-toxic, odorless and physiologically inert: From a physiological perspective, siloxane polymers are regarded as one of the least active compounds. Dimethyl silicone oil is inert to the body and does not cause rejection reactions in animals, thus being widely used in surgery, internal medicine, medicine, food, and cosmetics, among other fields. Excellent lubrication performance: As a lubricant, silicone oil has many outstanding properties, such as a high flash point, low freezing point, thermal stability, and stable viscosity. Moreover, its low surface tension and good spreading ability on metal surfaces further enhance its lubrication effect. To improve the lubrication of silicon steel on steel, lubricating additives that are miscible with silicone oil can be added. By introducing chlorophenyl or trifluoropropyl methyl groups to replace dimethyl groups on the siloxane chain, the lubricity of silicone oil can be significantly improved. Chemical properties: Although silicone oil is generally inert, its Si-C bond is quite stable. However, in high-temperature environments, strong oxidants can easily react with it. Particularly when reacting with chlorine, methyl silicone oil may undergo violent or even explosive reactions. At the same time, the Si-O bond is sensitive to strong bases or acids and is prone to chain-breaking reactions. At low temperatures, concentrated sulfuric acid can rapidly react with the siloxane chain and cause the phenyl-silicon bond to break. 
03 Regeneration and Recycling of Silicone Oil 
Regeneration of silicone oil: After long-term use, silicone oil may deteriorate due to oxidation and the invasion of impurities. As silicone oil is expensive, it needs to be recycled and regenerated separately. Waste silicone oil is usually regenerated by adsorption refining, which involves contact with adsorbents such as silica gel and activated alumina to remove impurities. Subsequently, vacuum degassing or nitrogen stripping at an appropriate temperature can yield purified regenerated silicone oil. Another method for treating waste silicone oil is solvent vapor treatment of liquid waste silicone oil. In this process, the dissolution effect during solvent condensation is utilized to dissolve and extract impurities from the waste silicone oil, thereby forming a liquid phase that is immiscible with silicone oil. This method is particularly effective in dissolving and removing polychlorinated biphenyls (PCBs) from waste silicone oil. Finally, vacuum drying is used to remove trace amounts of solvent remaining in the treated silicone oil. Commonly used solvents in this process include hydrocarbon solvents and chlorinated hydrocarbon solvents.