Fifteen lubricating oils which include mineral oils, a synthetic hydrocarbon oil, ester lubricants, a polyether oil, a silicone oil and fluoro-lubricants were irradiated with
60Co γ-rays at room temperature in vacuo, in air and under bubbling oxygen. The irradiation was carried out at a dose rate of 1×10
6 rad/h up to 1, 000Mrad.
Viscosity, total acid number, flash point, specific gravity and color were measured for the irradiated oils. All these properties were altered by the irradiation. The type and amount of the change were dependent on the irradiation conditions. Irradiation under bubbling oxygen was the most severe condition for the degradation of the oil. Particularly, the total acid number increased rapidly with dose under this condition and reached the limit for use of oil. For use of oil in vacuo, viscosity change mainly reached the limit.
Among the oils tested here, mineral oils and a synthetic hydrocarbon oil exceeded in radiation resistance. Silicone oil was affected at the lowest irradiation dose.
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