Hemispherical total emissivity and specific heat capacity measurementsby electrical pulse-heating method with a brief steady state

Abstract

A new method for specific heat capacity and hemispherical totalemissivity of electrically conducting materials at high temperatures using afeedback-controlled pulse-heating technique has been developed. This techniqueis based on a quick resistive self-heating of a ribbon-shaped sample up to apreset high temperature, and then keeping the sample at that temperature in abrief steady state (about 500 ms). A computer-controlled feedback system wasemployed to control the heating current. The true temperature of the samplewas determined using a high-speed radiation thermometer and an ellipsometer.Hemispherical total emissivity and specific heat capacity of the sample werecalculated from measured quantities using a heat balance equation based on theStefan-Boltzmann law.Using this method, the hemispherical total emissivity and specific heatcapacity of the four refractory metals (niobium, molybdenum, tantalum andtungsten) were measured in the temperature range from about 1500 K to a highertemperature close to the melting point of each metal. In addition, an estimateof uncertainties including numerical thermal analysis shows that theuncertainties in the measured hemispherical total emissivity and specific heatcapacity are about 3 and 2%, respectively at 2200 K and at a standarddeviation.