Netsu Bussei

SiC refractories are attracted as the material which is good against corrosion. But their thermal conductivity is too high to be measured by the thermal conductivity measuring apparatus using the Guarded Hot Plate(GHP) method. So we have tried to measure it by the cyclic heat method which we have used to measure thermal conductivities of fibrous insulations for several years. We pay attention to a time lag method in the cyclic heat method, because the thermal diffusivities are able to be measured without taking care of the heat loss from specimen's edge in this way. We have designed a new apparatus with the high cooling system by the cyclic heat method. We have determined thermal conductivity values by multiplying thermal diffusivity, specific heat, and bulk density. We show the relation between the thermal conductivity values of SiC refractories and the particle size consisting of them in this report.

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The present paper describes a new method for measuring thermal conductivity of a single fine fiber with its radius around several microns. The method is based on the heat transfer from the test fiber as a pin fin attached to a short hot wire with a uniform heat generation. The average temperature of the hot wire depends on the heat conducted away through the test fiber. Based on the dependency obtained by analytical solutions for given geometric sizes of the hot wire and test fiber, the thermal conductivity of the test fiber is evaluated from the measured average temperature and heat rate of the hot wire. The measurements for standard materials, that is, platinum fiber with 10μm dia. and copper with 22μm dia. proved that the present method can measure the thermal conductivities of fibers within estimated errors. Then, the thermal conductivities of four kinds of carbon fibers with diameters of about 7μm are measured and compared to those measured with the existing methods.

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