A method is described that can be used for the determination of the heat capacity of a metal (or a semiconductor) as a function of pressure and temperature. The method involves use of a DC electric pulse. If a constant current I is passed through a wire sample of resistance R, the heat capacity C is related to the increase in temperap ture by the expression% where R' is the temperature derivative of the resistance, and (dE/dt)t=O is the limiting value of the time rate of change of the EMF across the sample. Data are given for iron to 100 kbars in the temperature interval from 77°F to 300°K. The results obtained are in accord with earlier theoretical estimates. The Curie temperature, T , of gadolinium has c also been determined from heat capacity measurements; its rate of change with pressure was found to be dT /dP = -1.3°K/kb. For the equipment c that is available at the present time, the measurements can be made as long as the specific resistance is 5~-cm or greater.(,i -1- UCRL-18497 INfRODUCfIONThe heat capacity of a subs tance is an important thennodynamic . parameter characterizing the internal energy state of that substance.It is therefore of great interest to examine th~ variation of the heat capacity with temperature and pressure •. Numerous investigationS involving temperature as the independent variable have been carried out, leading to a generally good understanding of the temperature variation of the heat capacity; however, very little work has been done at high pressures since conventional calorimetric techniques face the difficulty of gross heat leakage when used in high pressure apparatus.Some success has been dbtained in those cases where pressures were low \ .. , . . I enough that flow techn1quescould be used, or in those cases where temperatures were sufficiently low so the heat capacity of the pressure vessel was a detenninable, and reasonably small, fraction of the entire 2 3 system. ' .In this paper we describe the development of a general method of measuring the heat capacities of metals (and semiconductors) under:high pressures.· The technique is based on electrical pulse heating of the metal sample , and has been successfully applied in measurements up to 100 kilobars over a temperature interval between 77°K and 300 o K. The precision appears to be + 5% or better.As the discussion and description of the technique is developed in this paper, it will be evident that the heat capacities obtained ar~ relative, rather than absolute, due to the fact that the geometryof the system is such that only' relatively short wire samples can be used. There is a large uncertainty of how much of'the sample at the ends is actually involved in the measurement. In the discussion that follows, it is assumed that the end effects remain constant as the external conditions are changed. TIffiORYConsider a metal wire sample of resistance, R, and heat capacity, . C p ' through which a constant current, I, is pulsed; if ohmic heating I is the only source of heat, the power balance equation, is:HeredH/dt is th...
.The Subterrene is a rock-melting earth-penetration system representing a significant advancement in excavation technology.
The chemical dissolution of molybdenum, tungsten, and soma of their alloys in liquid basalt, tuff, and granite has been investigated over the temperature range 1700 to 2100 K. Static compatibility tests and a limited number of fluid-motion experiments were conducted. Wet chemical, neutron-activation, and electronmicroprobe analyses were used to determine compositional changes in the rock melt and on the surfaces of the metals. This study determined that tungsten was more reactive than molybdenum over a wide range of complex silicate compositions. The enhanced solubility of tungsten is discussed in terms of some simplified thermodynamically possible reactions. The detailed mechanism of dissolution, however, cannot be totally explained although correlations with, e.g., the initial rock ferric-ferrous ratio, have been obtained. A simplified geometric model has been developed for the determination of surface recession rates on Subterrene penetrators. Experimental data were used in applying the model. The limitations of experimental solubility data for performance predictions under field operating conditions of Subterrene penetrators are discussed.The results of qualitative compatibility tests made with selected high temperature-high strength metals and alloys, intermetallics, and ceramics are summarized.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.