What are the characteristics of synthetic lubricants

Synthetic oil has a working environment that cannot be met by mineral lubricants. As a base oil for lubricants, it can be used to produce lubricating oil products that are resistant to harsh conditions such as high and low temperatures, high loads, high speeds, high vacuum, high radiation, and strong oxidation corrosion. The shortcomings of this type of base oil include limited sources, high costs, and prices that are several to tens of times higher than ordinary mineral lubricants, with some even reaching hundreds of times higher. Synthetic lubricating oil has a series of advantages compared to mineral oil, which can compensate for the shortcomings of mineral oil.

(1) High temperature performance, low temperature performance, and viscosity temperature performance

Synthetic oil generally has good thermal stability, high thermal decomposition temperature, high flash point and self ignition point. Synthetic oil has better high-temperature performance than mineral oil, allowing it to be used at higher temperatures. Table 1-2-1 lists the thermal decomposition temperature and overall limit operating temperature range of various synthetic oils. From the table, it can be seen that synthetic oil has a higher operating temperature than mineral oil for oils with similar viscosity.

The viscosity index of most synthetic lubricants is higher than that of mineral oils, and the viscosity changes less with temperature. When the high-temperature viscosity is the same, most synthetic oils have lower low-temperature viscosity and pour point (or pour point) than mineral oils, which allows synthetic oils to be used at lower temperatures. Table 1-2-2 lists the viscosity index and pour point ranges of various synthetic lubricants. Category viscosity index pour point/Category viscosity index pour point/T Mineral oil 50-130-45--6 Silicone oil 100-500<-90+10

Polyolefin oil 80-150-60-20 silicate ester 110-300<-60 diester 110-190<-80--40 polyphenylene ether 100-10-15?+20 polyol ester 60~190<-80--15 all #; carbon compound -240-+10<-60-+16 polyether 90-280-65-5 perfluoroalkyl ether 23-355-77-40 phosphoric acid rubbing 30~60<-50~-15

(2) Oxidative stability

Compared with mineral oil, synthetic oil has better oxidation stability, and after adding additives, it can be used at higher temperatures. The viscosity changes of various synthetic oils after oxidation are lower than those of mineral oils, and the precipitation is much less than that of mineral oils, indicating that the antioxidant capacity of synthetic oils is much stronger than that of mineral oils. Due to the higher flash point, self ignition point, and thermal decomposition temperature of synthetic oil compared to mineral oil, and the better thermal oxidation stability after adding antioxidants, synthetic oil is used at a higher temperature than mineral oil.

(3) Volatilization*

The volatility of oil products is a key performance during use. Volatile oil products not only have high fuel consumption, but also become viscous due to the volatilization loss of light components, resulting in changes in basic performance and thus affecting the service life of the oil products. Compared to mineral oils of the same viscosity, synthetic oils have lower volatility. This is because synthetic oil is generally a pure compound with a narrow boiling range, while mineral oil is a fraction of oil that contains both small and large molecules. At a certain temperature, its light saturated fraction (small molecules) is easily volatile.

⑷ Flame resistance

Mineral lubricating oil will burn when exposed to fire. In many areas close to heat sources, major accidents often occur due to the leakage and ignition of mineral oil. At present, there is no way to improve the ignition performance of mineral oil by adding additives. However, some blended oils have excellent flame retardancy. For example, although phosphate esters do not have a high flash point themselves, they do not cause continued combustion due to the absence of flammable and combustible decomposition products. Aryl phosphate esters will ignite when exposed to open flames above 700 ^, but they do not spread flames. Once the source of fire is cut off, combustion will immediately stop. So phosphate esters themselves have flame retardancy. Polyether is an important component of water ethylene glycol flame retardant liquid, mainly used to increase viscosity. Polyether and ethylene glycol can both burn, but water ethylene glycol flame retardant liquid contains 40% to 60% water. In the event of ignition, due to the large evaporation of water, the water vapor isolates the air, thereby achieving the purpose of preventing combustion. Perfluorocarbon lubricating oil does not burn in air, and perfluoroalkyl ether oil cannot even burn in oxygen. Table 1-2-3 lists the flame retardancy of synthetic oils.

(5) High density

The relative density of mineral oil is less than 1. Some synthetic lubricants have a relatively high relative density and can meet the requirements of certain special applications, such as gyro fluid for navigation, instrument isolation fluid, etc. The relative density of synthetic lubricating oil is shown in Table 1-2-4.

⑹ Other special properties

Fluorinated lubricating oils include perfluorocarbons, fluoro chlorinated oils, fluoro brominated oils, and perfluoroalkyl ethers, all of which have excellent chemical stability that mineral oils and other synthetic oils cannot match. Below loot, perfluorocarbon oil, fluorochlorocarbon oil, and perfluoropolyether oil do not work with fluorine gas, chlorine gas, 68% nitric acid, 98% sulfuric acid, concentrated hydrochloric acid, aqua regia, chromic acid wash solution, potassium permanganate, and 30% hydrogen peroxide solution, respectively.

Polyphenylene ether has excellent radiation resistance. Mineral oil can withstand a dosage of 108-109 rad/year. The radiation resistance of ester oil, poly (alpha olefin) oil, and mineral oil is similar, while silicone oil and phosphate ester are lower than mineral oil, and can only withstand a dose of 107 rad/year. If lubricating oil with an absorption capacity of 109 rad/year is required, synthetic oils containing phenyl groups, such as alkylated aromatic hydrocarbons, polystyrene, or polyphenylene ether, are needed. Polyphenylene ether has the best radiation resistance and can withstand an absorbed dose of 1011 rad/year.

Mineral lubricants are non biodegradable and therefore cause serious pollution to the environment. Esters and polyether synthetic oils have biodegradable properties.