Near-critical point thermodynamics from shock experiments with porous Ni samples

Full Text: Results of experiments on expansion of shock-compressed nickel samples into helium is presented. Brightness temperature of nickel sample and velocity of shock wave, generated in helium were measured by a fast multichannel optical pyrometer, other parameters (particle velocity and pressure on He-Ni interface and helium temperature) were calculated using He EOS (chemical plasma model). To increase the shock entropy up to near-critical value and to intensify the process of heat- and mass-exchange, shock compression of porous (m=1.93) samples was made. Isoentrope with initial pressure 170 GPa was studied. Final states with pressures below 1.4 GPa, determined by initial helium pressure, were generated. The following overheat of nickel by hot shocked helium allowed to get an additional information about nickel spinodal. The peculiarities of isentrope path in P-U plane allowed to estimate parameters of it's entrance in two-phase region. The estimate of critical temperature and pressure of nickel was made from peculiarities of P-T path, using the Van-Der-Vaals model of nickel spinodal. (author)