Internal Friction of Quartz

The internal friction of quartz was studied by measuring the logarithmic decrement of a bar vibrating in resonance at its fundamental mode at 21 kilocycles per second and at its second harmonic mode at 42 kilo-cycles per second as a function of temperature from 200°C to 440°C. The logarithmic decrement was found to rise rapidly to a maximum of 16×10−5 at about 240°C, then fall slowly to a minimum of about 8×10−5 at about 350°C, and then rise rapidly up to and beyond 460°C. The high temperature portion shows a temperature hysteresis in which the cooling curve is lower than the heating curve. Furthermore the magnitude and, to a certain extent, the position of the peak may depend upon previous history but heating in a vacuum can reduce the logarithmic decrement curve to a reproducible one, independent of room temperature handling and thermal gradients (up to 1.5°C/cm) or stress amplitudes (up to 10 g/mm2) applied at higher temperatures. The measured curve can be considered as the sum of two relaxation peaks and an exponential curve. One peak has an activation energy of 27.2×103 calories per mole, and the other, 12.6×103 calories per mole. The exponential curve appears to be characterized by an activation energy of about 22×103 calories per mole but may vary with heat treatment.