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R. J. Abraitis A. K. Dargis A. A. Rusyatskas É. J. Sakalauskas 《Refractories and Industrial Ceramics》1999,40(7-8):351-358
At the present time, experiment is a reliable method for studying the thermal conductivity of new ceramic materials and especially
refractories. However, the range and possibilities of existing devices do not meet the requirements for measuring thermal
conductivity, especially at a high temperature. At very high thermal loads under the conditions of formation of surface columnar
crystal structures, thermoelastic stresses, disturbances in vibration of the elementary lattice, and other phenomena, the
thermal conductivity can be a function of the temperature drop. The present paper concerns the physical fundamentals of heat
conduction in current ceramic materials and refractories based on MgO, A12O3, and Si3N4. The classical stationary and nonstationary methods for determining thermal conductivity are considered. Special attention
is devoted high-temperature processes and the difficulties arising in this case. It is recommended to solve high-temperature
problems by using methods based on solving inverse problems of heat conduction 相似文献
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R. I. Abraitis A. K. Dargis A. A. Rusyatskas é. I. Sakalauskas 《Refractories and Industrial Ceramics》2000,41(3-4):140-143
The process of heat propagation in a specimen is considered in an approximation of a one-dimensional heat flow with side leakages
of heat. They are modelled as a function of the heat sources (sinks). The chosen stationary heating and the temperature field
in the specimen are described by a nonlinear one-dimensional differential equation. The boundary conditions and the source
function are determined from experimental data. The nonlinear one-dimensional differential equation is used in an implicit
identification method and solved numerically; a minimum of the quality criterion is determined at each iteration step in the
search procedure. The identification procedure is performed by explicit and implicit methods of solution of inverse problems
of heat conduction. A numerical simulation has shown that the method of component-wise minimization is the most efficient.
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 4, pp. 39–42, April, 2000.
Part I appeared in No. 8, 1999, and Part II in No. 2, 2000. 相似文献
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R. I. Abraitis A. K. Dargis A. A. Rusyatskas é. I. Sakalauskas 《Refractories and Industrial Ceramics》2000,41(2):60-70
The process of energy transfer in refractory materials is studied under conditions of intense high-temperature heating. The
coefficients of inverse problems of heat conduction (IPHC) are analyzed. The extremum coefficients of IPHC are determined
and classified as explicit and implicit in accordance with the methods used for their estimation. Coefficient-type IPHC make
it possible to bring the processing of results as close as possible to the measuring cell and to diminish the effect of errors
of measurement on the solution of the problems and to increase simultaneously the efficiency of the experiments. A method
for performing physical experiments, high-temperature heating sources, and measuring cells are described. The boundaries of
the confidence interval of the instrumental error are shown. Results of single measurements of the thermal conductivity of
MgO-base ceramics in an optical furnace are presented. Computation of the errors shows that the total relative instrumental
error of measurement of the thermal conductivity is quite acceptable for high-temperature studies.
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 2, pp. 33–43, February, 2000.
For the beginning of the series see No. 8 of 1999, p. 22. 相似文献
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Abraitis R. I. Dargis A. K. Rusyatskas A. A. Sakalauskas É. I. 《Refractories and Industrial Ceramics》2001,42(9-10):331-334
The heat conductivity of an Si3N4-based ceramic is studied. A sintered silicon carbide, prepared from ultrafine (0.5 μm) powder Si3N4 with aluminum and yttrium oxides added to form a liquid phase and thus to activate the sintering process, is used for the study. The Si3N4-based ceramic has a heat conductivity higher than that of an oxide-based ceramic. The approximation function for heat conductivity at temperatures below 1400 K has a negative slope, that is, the effective heat conductivity tends to decrease with temperature. Above 1400 K, the effective heat conductivity tends to increase. 相似文献
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