The elastic moduli of fused quartz have been determined by ultrasonic measurements under high hydrostatic compressive stress and showed a nonlinear decrease to a minimum value at 2.1–2.5 GPa, and thereafter an increase with increasing pressure. Changes in the Debye temperature and the Grüneisen constant are determined using the present results. Assuming a contribution of the fourth-order elastic constants to the nonlinear dependence, C1111, C1112, C1122, and C1123 have been tentatively evaluated to be 11.0±1.0, 10.8±3.6, 22.7±11.1, and 8.6±2.0 TPa, respectively. However, the possibilities of a complicated potential curve or a higher-order phase transition are also discussed.

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synopsisA convenient pressure apparatus was designed for crystallization of high polymers under hydrostatic pressure up to 5OOO atm. Melt crystallization as well as heat treatment under various temperatures and pressures was carried out on several polymers, and the effects of pressure on the molecular and crystal structures of the samples are discussed. Heat treatment of syndiotactic polypropylene under high pressure yields a new crystal modification rather than the previously known helii and planar zigzag modifications. Of the three modifications of poly(viny1idene fluoride), modification I11 was found as a high-pressure phase for specimens in the unoriented state, while modification I was obtained as the most stable one on heat treatment of oriented specimens under high pressure. Heat treatment under high pressure converts ordinary isotactic poly-4-methylpentene-1 with a lower density than the noncrystalline value, to a new crystal modification with higher density. As is reasonable, the dense modification is stable in a highpressure range. For these three cases, the orientation of specimens was found to remain unchanged during the transitions, which must therefore occur in the solid state.

A shock wave investigation on fused quartz was performed in the permanent densification region, using a double stage light-gas gun with dc x-ray velocity meter and the electromagnetic particle velocity measurement technique. The elastic limit obtained in this work [(8.81±0.11) GPa] was somewhat lower than the published value. The compression curve obtained was quite different from the published curve and indicated that a rapid volume contraction occured just above the elastic limit. The tetrahedral coordinations seemed to remain at least up to 22 GPa, but above 16 GPa, they would be distorted or in some parts destroyed. The pressure of 16 GPa was considered as the limit of the permanent densification process, and the specific volume at atmospheric pressure interpolated along a hypothetical release adiabat was about 0.32 cm3/g.