Measurements of Ultrasonic Absorption and Velocity in Silicones

Abstract

Measurements of the ultrasonic absorption and velocity in Dow Corning 200 Fluids of various viscosity grades were made at a temperature of 20°C for different frequencies from 10 to 90 Mc, using a pulse technique employing transmitting and receiving crystals. Relaxation is indicated both by falling α/ν2 curves and values of α/ν2 which are very small compared to the Stokes low-frequency value. As an indication, the theoretical low-frequency value for 1000 Stokes Silicone Fluid is 26 000 × 10−15 cm−1 sec2, where the present measurements give 15.5 × 10−16 cm−1 sec2 at 10 Mc, falling to 6.6 × 10−15 cm−1 sec2 at 90 Mc. The curves give no accurate indication of the relaxation frequencies, other than that they are apparently much lower than the region of measurement. No dispersion was detected. (This work was supported in part by the office of Naval Research.)