"The transport of heat in solids is attributed to the combined effect of the quantized vibrations of lattice points, or phonons, and the flow of valence electrons. In dielectric solids, the thermal conductivity is due almost entirely to phonons, while in metals the latter method preponderates. Scattering processes in dielectric solids, giving rise to thermal resistance, also serve to limit the thermal conductivity. Scattering results from vacancies, dislocations, interstitial atoms and phonon interaction. Crystal boundaries also function as scattering points and in crystals of small dimensions, this process is the most pronounced conductivity-limiting factor. At low temperatures the thermal resistance of an ideal crystal is due almost entirely to boundary scattering while at high temperatures anharmonic coupling is the primary limiting factor. As the temperature increases, boundary scattering becomes less pronounced but anharmonic coupling increases. At some median temperature the conductivity is a maximum….
Considerable experimental work has been done in the past to determine the thermal conductivity of various alkali halides below the boiling point of water. Values determined by early experimenters differed widely, but these discrepancies are attributed to various major defects in the samples used. Measurements at the Missouri School of Mines and Metallurgy of the conductivity of sodium chloride above this temperature and to approximately 600°K indicate a relationship proportional to l/T1.3. Therefore, it appears that if theory is to be substantiated by experimental determinations, the conductivity of a single specimen must be examined to the maximum attainable temperature, i.e. the melting point of the substance.
Equipment built by Weisbrod and improved by Brown and Ohlsen was available at the beginning of the investigation. Its design utilizes an absolute steady state method of measurement. Two nearly perfect cylindrical crystals of potassium chloride were used in the experiment, one approximately half the thickness of the other. The purpose of this investigation was to improve the operation of existing equipment and to extend the experimental data available on the conductivity of potassium chloride"--Introduction, pages 1-3.
Bessey, William H.
M.S. in Physics
Missouri School of Mines and Metallurgy
v, 33 pages
© 1956 Wendell D. Miller, All rights reserved.
Thesis - Open Access
Potassium chloride -- Thermal conductivity
Materials at high temperatures
Scientific apparatus and instruments -- Testing
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Miller, Wendell D., "The thermal conductivity of potassium chloride at elevated temperatures" (1956). Masters Theses. 2574.