Nickel Critical Point Parameters from Shock Experiments with Porous Samples

Results of experiments on expansion of shock‐compressed nickel samples into helium is presented. The brightness temperature of nickel sample and shock velocity in helium were measured by an optical pyrometer, other parameters (particle velocity, pressure, helium temperature) were calculated. To increase the shock entropy up to near‐critical value, shock compression of porous (m=1.91) samples were used. Isoentrope with initial pressure 170 GPa was studied, with final states below 1.4 GPa, determined by initial helium pressures. The peculiarities of isentrope slope in pressure‐particle velocity graph allowed to estimate a point of it’s entrance into two‐phase region. The isobaric overheat of expanded nickel by hot shocked helium allowed to get an additional information about phase diagram and to estimate of critical temperature and pressure of nickel, using the van‐der‐Waals model of liquid nickel spinodal.