Self-diffusion in compressed liquid heavy water

Abstract

The self-diffusion coefficients D in liquid heavy water have been measured by the NMR spin-echo method over the temperature range 10–200°C and the pressure range 1 bar to 9 kbar. A good agreement with tracer diffusion studies by Woolf performed over a more limited range of temperatures and pressures has been obtained. As in other studies, we find an anomalous initial increase in the diffusion coefficients with pressure at temperatures below approximately 30°C. At high temperatures compression leads to a monotonic decrease of the self-diffusion. The fact that the activation energies at constant density decrease both with increasing temperature and increasing density indicates that both high temperature and high compression significantly affect the hydrogen bond network and produce a more ’’normal’’ liquid. We find that the Stokes–Einstein equation is accurate to within 10% over the range of experimental conditions studied. Phenomenological interpretation of plots of D/T vs molar volume supports the view that at high compression and high temperature the dynamic behavior of heavy water resembles that of a hard sphere liquid. All experimental results are in agreement with our conclusions obtained in our earlier study of NMR relaxation in compressed liquid water and heavy water.