The Close Relationship Between Radiation Resistance and Oxidation Stability of Silicone Oil
Nov 12, 2024
The radiation resistance of silicone oil is closely related to its oxidation stability. The radiation decomposition mechanism is the same as the oxidation decomposition mechanism in that methyl is more susceptible to attack than phenyl. The decomposition products of dimethyl silicone oil and methyl phenyl silicone oil are mainly methane, hydrogen, and residues of cross-linked polymers, in addition to a small amount of alkanes and aromatic hydrocarbons. The following reactions occur under irradiation:
These free radicals can combine with each other to form silicon methylene, silicon ethylene, and disilane bonds, as well as hydrogen, methane, and other hydrocarbon gases. In methyl silicone oil and methyl phenyl silicone oil, radiation does not produce acidic products.
The two important results caused by radiation are the increase in viscosity of silicone oil and the generation of gas. The increase in viscosity of silicone oil when irradiated with 60Co y-rays at room temperature: Methylphenyl silicone oil has better radiation resistance than dimethyl silicone oil.
After being irradiated with 7 rays, silicone oil not only increases in viscosity, but also slightly increases in density, refractive index, and dielectric constant, with the increase proportional to the irradiation dose. Although methylphenyl silicone oil is relatively stable under 7-ray irradiation, its electrical properties undergo significant changes and decrease.
Physiological safety of silicone oil
From a physiological perspective, polydimethylsiloxane is one of the least active polymers known. The toxicology research results indicate that dimethyl silicone oil, excluding low boiling point substances, is non-toxic and can be widely used in food, cosmetics, and pharmaceuticals. The animal lethal dose LD5 of dimethyl silicone oil. The value (50% lethal dose) is above 35 g/kg, which is equivalent to non-toxic according to the toxicity classification of the American Industrial Hygiene Association; There is no chronic poisoning problem and it will not be absorbed by the digestive system. No irritation to the membrane; Low viscosity dimethyl silicone oil has slight irritation to the cornea, but no harm.
It should be pointed out that the production method and production environment of silicone oil affect the purity of silicone oil (including low molecular weight siloxanes remaining in silicone oil, residues from catalyst decomposition and neutralization, and impurities brought by the production environment). When used in medicine, food, and cosmetics, specialized grade silicone oil should be selected.
Electrical properties and radiation resistance of silicone oil
Silicone oil has good electrical insulation properties and good heat resistance, which is of special significance to the electrical appliance industry.
Dimethyl silicone oil has good electrical strength, and there is almost no difference between silicone oils of different viscosities. The breakdown voltage (electrode diameter 25. 4 mm, gap 2. 54 mm, 60 Hz, 25°C) is 35~40 kV; once arc breakdown occurs, an electrical path is generated in the oil, and the electrical strength will be significantly reduced. , is its shortcoming. Measured with a needle or spherical electrode with a diameter of 12.7 mm (gap 1.27 mm), the pulse breakdown voltage is 260 kV; while the best petroleum-based transformer oil is only 90 kV.
Volume resistivity of dimethyl silicone oil at different temperatures: The volume resistivity of dimethyl silicone oil is 1015 fl • cm at room temperature, and can be maintained at 1014 Q • cm at 200°C. The effect of frequency on the dielectric constant and dielectric loss factor of dimethyl silicone oil The dielectric loss factor only tends to increase when the frequency increases to above 108 Hz, and is generally below 6X10-4.
Radiation resistance of silicone oil
The radiation resistance of silicone oil is closely related to its oxidation stability. In that methyl groups are more susceptible to attack than phenyl groups, the radiation decomposition mechanism is the same as the oxidation decomposition mechanism. The decomposition products of dimethyl silicone oil and methylphenyl silicone oil are mainly methane, hydrogen and cross-linked polymer residues, in addition to a small amount of alkanes and aromatics. The following reactions occur under irradiation:
These free radicals can combine with each other to form silylene, silylene and disilane bonds, as well as hydrogen, methane and other hydrocarbon gases. In methyl silicone oil and methylphenyl silicone oil, radiation does not produce acidic products.
Two important results caused by radiation are the increase in silicone oil viscosity and the generation of gas. When silicone oil is irradiated with 60Co y rays at room temperature, its viscosity increases: methylphenyl silicone oil has better radiation resistance than dimethyl silicone oil.
After silicone oil is irradiated with 7 rays, in addition to the increase in viscosity, the density, refractive index and dielectric constant also increase slightly, and the increase is proportional to the irradiation dose. Although methylphenyl silicone oil is relatively stable to 7-ray irradiation, its electrical properties change greatly and decrease.
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