Study on the Improvement of Accuracy for the Measurement of Thermophysical Properties at High Temperature by a Singgle Rectangular Pulse Heating Method

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The information on thermophysical properties of new materials are required in vatious fields of industry. One of the authers presented a convenient measuring method of thermal conductivity and specific heat by a single rectanguar pulse heating. In this method, the thermal rdiation losses from all the surfaces of a finite disk specimen which is set in a vacuum high temperature furmace are taken into account. If the eemissivities are same on the all surfaces of the specimen, the rafiation heat loss increases with ambient temperature increase and decreases with thermal diffusivity and specific heat of the specimen increase. Therefore, if the measurement on a material having low thermal vonfuctivity as ceramics was carried out at high temerature tange, the rdiation loss will be large. So, the errors caused by uncertainty of the emissivity seem to be unavoidable. The obhjective of this study is to investigate the temperature dependence of the emissivity of the coatings on the specimen at high temperature up to 1600 k, and to improve the accuracy of the measurement.The technique of the emissivity measurement is based on comparing radiance from the specimen and a blackbody furnace keeping the same temperature. Four kinds of heat resisting coats were examined. It was found that no separation of coating from the specimen appeared and the temperature dependence was rather fiat in the 800-1600 k for SiC spray coating. Then, the thermal diffusivity and specific heat were measured on nickel and magnesia brick with SiC spray coating by the single rectangular pulse heating rechnigue. It was recognised that there were some differences between the present measuremeent recognized that there were some differences between the present measuremeent and the former one using carbon black coating, and improvement of the accuracy.