Fast transient thermophysical measurements at Livermore

Abstract

The development of the Isobaric Expansion Experiment at Lawrence Livermore National Laboratory is described. Rod samples are self-heated by current from a capacitor bank while current and sample voltage, sample cross section, and temperature are measured continuously as functions of time. The system allows nearly complete thermodynamic characterization of a material along an isobar in a single shot. The pressure of the isobar is determined by containing the sample in argon gas at a predetermined ambient pressure. Correlation of the measured quantities allows elimination of time as a common parameter. Quantities corresponding to a given time are taken to refer to a single equilibrium state. Temperature stagnation and volume and resistivity changes during phase transitions may be seen and allow the heat of transformation and the slope of the phase line in theP, T plane to be determined. Other derived quantities are specific heatc _p, volume-corrected electrical resistivity, and bulk thermal expansion coefficient. A special advantage of the technique is that all quantities are measured on the same sample in a single experiment. The short time duration of the measurements allows access to a temperature range beyond that available to slower methods.