Finite strain isotherm and velocities for single‐crystal and polycrystalline NaCl at high pressures and 300°K

Abstract

Ultrasonic, pressure‐volume, and shock wave measurements of NaCl are reviewed, with the purpose of representing as much as possible within a single theoretical framework, A large portion of the data is consistent, to within reasonable uncertainties, with the Eulerian formulation of finite strain, in the BE 2 form. This contains three parameters, of which two, K 0 and K 0 ′, are obtainable from single‐crystal ultrasonic measurements, while the third, K 0 ″, may be found with the aid of shock wave data. The combination of the values of Spetzler et al. (1972 a ) with the isotherm of Fritz et al. (1971) gives an equation of state consistent with the pressure‐volume measurements to 300 kbar, to within a kilobar or two. There remain small but possibly significant discrepancies with the high‐precision measurements of linear change at low pressures. Various two‐parameter isotherms are also examined and found to fail either at low or at high compressions: While other three‐parameter forms may be fitted to the data, they do not afford a satisfactory general treatment of wave propagation. Finite strain theory is applied to project the effective elastic coefficients of single‐crystal NaCl to 270 kbar. The anisotropy index, 2 B 44 ( B 11 – B 12 ), falls from 0.7 at P = 0 to 0.12 at 270 kbar, and the usual methods of averaging to find the properties of a quasi‐isotropic aggregate diverge increasingly as pressure increases. The methods of Kröner and of Peresada give fair agreement with recent measurements of velocities in NaCl aggregates to 270 kbar.