L26ThermProps145s10 - Lecture 25 Thermal Properties Reading...

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Lecture 26, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Reading assignment : C&R §17.1-17.4 Learning objectives: Qualitatively understand the origins of heat capacity, thermal expansion, and thermal conductivity in terms of atomic bonding Use thermal expansion data to compute dimensional changes from temperature changes Use thermal conductivity data to compute heat flux or temperature gradients Know how thermal conductivity varies among categories of materials, and with temperature and defect concentrations Lecture 25: Thermal Properties 1
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Lecture 26, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Overview of Thermal Properties [C&R Ch. 17] Some ways that materials store heat (mechanisms of heat capacity) Phonons: atomic vibrations present in all solids Conduction electrons small, even in metals Formation of intrinsic defects even smaller contribution Ways that materials conduct heat (mechanisms of thermal conductivity) Phonons present in all solids Conduction electrons significant in metals, graphite Photons significant in transparent materials Thermal expansion: temperature changes dimensional changes Origin in the interatomic potential 2
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Lecture 26, spring 2010 ENGR 145, Chemistry of Materials Case Western Reserve University Low-Frequency Phonons (schematic*) (i.e., at absolute zero) (i.e., at T > 0 Kelvin) * e.g., actual size of atomic displacements is too small to be depicted Each atom is coupled to its neighbors, so vibrations travel Traveling wave of vibration C&R Fig. 17.1 3
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Lecture 26, spring 2010
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