A noncontact measurement technique for the specific heat and total hemispherical emissivity of undercooled refractory materials

Abstract

A noncontact measurement technique for the constant pressure specific heat (c(pl)) and the total hemispherical emissivity (epsilon(T1)) of undercooled refractory materials is presented. In purely radiative cooling, a simple formula which relates the post-recalescence isotherm duration and the undercooling level to c(pl) is derived. This technique also allows us to measure epsilon(Tl) once C(pl) is known. The experiments were performed using the high-temperature high-vacuum electrostatic levitator at JPL in which 2-3 mm diameter metallic samples can be levitated, melted, and radiatively cooled in vacuum. The averaged specific heats and total hemispherical emissivities of Zr and Ni over the undercooled regions agree well with the results obtained by drop calorimetry: C(pl,av(Zr)=40.8+/-0.9 J/mol K, epsilon(Tl,av) (Zr)=0.28+/-0.01, c(pl,av)(Ni)=42.6+/-0.8 J/mol K, and epsilon(Tl,av)(Ni)=0.16+/-0.01.

Additional Information

Copyright © 1994 American Institute of Physics. Received 20 September 1993; accepted 13 December 1993. We gratefully acknowledge Professor R. Hauge of Rice University for providing us with a preprint of his extensive survey on liquid metal property data. We thank Dr. Eugene Trinh and Dr. K. Ohsaka of the Jet Propulsion Laboratory for valuable discussions and critical comments on the manuscript, Professor F. G. Shi of the University of California, Irvine, for bringing an important paper by Barth et al., to our attention, Mr. Craig Morton of Vanderbilt University for providing the zirconium samples, Mr. Kelly Perry for developing the data analysis software, and Dr. Kin Fung Man, Mr. Daniel Barber, and Mr. Robert McMillan for their generous help throughout the experiments. This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Files

Additional details