On the critical point of tungsten

Full Text: For tungsten the liquid-vapor critical point lies in the region of extraordinarily high temperatures and pressures which are far beyond the current limits of static experiments. The critical point was evaluated by many authors using the corresponding states law or some semi-empirical rules. These evaluations give a large scatter in the critical constants and their accuracy is very uncertain. For instance, the critical temperature estimated in this way falls in the range 12x103 K - 23x103 K and the critical pressure is between 3 kbar and 16 kbar. The data obtained by dynamic methods are used for this purpose too. Unfortunately the results of the shock wave experiments give thermodynamic information in a region far from the critical point. In our opinion, the exploding wires data used for such estimates are interpreted in a rather questionable way. In the present work a self-consistent model describing vaporization dynamics and transition to the plasma state in exploding wires is developed. Using the model, the temporal dependencies of the typical quantities measured are analyzed to recognize the effects of vaporization and passing of the critical region. These dependencies are compared with those from the measurements for a variety of regimes, e.g. wires in water at different ambient static pressures, wires in plastic shells and wires in sapphire capillaries. For these regimes the pressures up to 20 kbar and the temperatures up to 30x103 K are achieved. As a result of the work, some essential information on equation of state and electrical conductivity of tungsten at so high temperatures and pressures is obtained and used for evaluation of the critical point. (author)