The NaCl pressure standard

A revised pressure scale for NaCl is proposed as an update for the 30-year-old work of Decker. An alternative approach to the analysis is utilized in conjunction with more recent data. The zero-Kelvin compression curve is parameterized using local basis functions (splines) and constrained by accurate pressure-volume-temperature data. Thermal pressures are estimated within a quasiharmonic framework using a volume-dependent Gruneisen parameter and the Debye thermal energy. In the pressure regime extending to 5 GPa uncertainties in pressure (based on measured volumes) are estimated to be less than 1%. Uncertainty increases to 1.5% at 10 GPa and 3% at 25 GPa. The largest contribution to systematic uncertainty at the highest pressures is the lack of knowledge of the volume dependence of the Gruneisen parameter. Misfit of other calculated thermodynamic properties with respect to data is relatively small. On the basis of the current analysis, pressures determined using the older Decker calibration are low. Along the 300 K isotherm, apparent errors in the Decker scale are as large as -3% (-0.3 GPa at 10 GPa, -0.47 GPa near 18 GPa, and -0.37 GPa at 25 GPa). At higher temperatures the apparent errors are smaller. At 1100 K and 20 GPa the error is -0.2 GPa. (C) 1999 American Institute of Physics. [S0021-8979(99)01922-2].