Synthetic Oil

any of the synthetically produced liquids used mainly as lubricants, coolants, or hydraulic fluids. Synthetic oils are often used in the preparation of greases. These oils include synthetic hydrocarbons, esters (in particular, esters of phosphoric acid), polysilicones, carbon halides, and poly-alkylene glycols.

Synthetic hydrocarbons are obtained by the polymerization of olefins (ethylene, propylene) or the alkylation of aromatic hydrocarbons (benzene, xylene). Their uses are similar to those of petroleum oils.

Esters are obtained mainly by the reaction of monobasic and dibasic acids with monohydroxy and polyhydroxy alcohols. Complex esters of the dioctyl sebacate type and pentaerythritol esters of monobasic acids are the most often used. They have good viscosity characteristics, low volatility, and better thermal and chemical stability than petroleum oils. Esters are used in aircraft engines as transmission lubricants and hydraulic fluids. Polyphenyl esters and esters of α-dihydroperfluoroalcohols are especially stable at high temperatures (up to 300°–400°C) and high levels of radiation. Esters of phosphoric acid are used as incombustible hydraulic fluids. All esters have good antiwear properties.

Polysilicones are a variety of organosilicon polymer and are distinguished by low volatility and a sufficiently high thermal stability. They are superior in viscosity characteristics to all other synthetic oils but are less effective as lubricants. Phenyl polysiloxanes are the most thermally stable of this group and withstand heating above 250°C. Methyl polysiloxanes do not congeal at temperatures of - 100°C and lower. Polysilicones are used for lubricating low-load friction points in mechanisms and instruments operating over a broad range of temperatures. Their high compressibility makes them suitable for use in shock absorbers, brakes and damping devices.

Carbon halides are hydrocarbons in which hydrogen atoms have been replaced by either fluorine or fluorine and chlorine. They are distinguished by an especially high resistance to O₂, HNO₃, H₂ O₂, and other chemically reactive compounds. These oils have poor viscosity characteristics and high volatility. Perfluoroalkyl polyesters (stabilized polymers of the oxide of perfluoropropylene) have the most valuable characteristics of this group. Carbon halides are used in nuclear and rocket technology and in the chemical industry when processes involve high temperatures or contact with corrosive media.

Polyalkylene glycols are products of the reaction of ethylene oxide or propylene oxide (or a mixture of the two) with water, alcohol, and ethylene glycol. They have good viscosity characteristics and do not leave deposits on machine parts after decomposition from heating. These oils are used as high-temperature lubricants and coolants in, for example, the paper, ceramic, and glass industries. Because of their scarcity, rather high cost, and specialized properties, the demand for synthetic oils is only a fraction of that for petroleum oils. However, with the advance of technology and the complex lubricating conditions of certain processes, the use of synthetic oils is increasing.