HEAT CAPACITY OF A LIQUID INDIUM-TIN ALLOY. Third Technical Report

Abstract

The heat capacity of a liquid indium-tin alloy containing 47.22 atomic percent tin has been measured as a function of temperature in an isothermal calorimeter. The data extend from 394 deg K, slightly above the alloy eutectic temperature, to 758 deg K. The measured Cp values decrease with temperature, the rate of decrease becoming smaller as the temperature increases, resembling the behavior shown by pure liquid metals for which precise data are available. The magnitude of the decrease in Cp for the alloy above its eutectic temperature has been found to be considerably greater than those found in previous investigations on the pure liquid components. Above the melting temperature of Sn, the alloy Cp data are compared with values calculated from Kopp's Law using previously reported data for the pure liquid components. It is found that, well within the over-all accuracy of the data, DELTA Cp = 0 for the formation of the liquid alloy from the liquid elements at temperatures where it can be evaluated. This is consistent with the results of reported heat of formation and activity data for the liquid solution which indicate it to approach closely the properties of an ideal solution and suggest the absencemore » of strong unlike atom interactions. The rapid change of Cp with T for the liquid alloy above its eutectic temperature is interpreted as being due primarily to the same mechanisms responsible for similar behavior in pure metals and not to an increase in DELTA Cp with decreasing temperature. Assuming DELTA Cp = 0 for the liquid alloy at temperatures below the melting point of Sn, Cp values for supercooled liquid In and supercooled liquid Sn have been calculated. The postulated Cp curves so derived join smoothly with those for the liquid metals above their melting temperatures. (auth)« less