The temperature dependence of the elastic constants of a machinable glass-ceramic

The velocities of longitudinal and transverse ultrasound at a frequency of 10 MHz have been measured in a machinable glass ceramic (Corning Macor 9658) over the temperature range from 4.2 to 300 K using a pulse-echo overlap technique. The glass ceramic is a glassy matrix containing randomly oriented mica crystallites which are approximately 2 μ thick and 5–20 μ square, and which comprise approximately 50% of the volume. The room-temperature elastic constants calculated from the sound velocities are in good agreement with values calculated from the technical specifications given for Macor by Corning Glass Works. The longitudinal elastic constant at 4.2 K is 8.145×1010 N/m2 and the shear elastic constant at 4.2 K is 2.729×1010 N/m2. The general temperature dependence of the elastic constants is characteristic of a glassy material. The Debye heat capacity is shown to be less than the measured heat capacity at low temperatures as is typical of glassy materials.