L26ThermProps145s09r

L26ThermProps145s09r - Lecture 25, spring 2009 ENGR 145,...

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Unformatted text preview: Lecture 25, spring 2009 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 Lecture 25: Thermal Properties 1 Lecture 25, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Overview of Thermal Properties [C&R Ch. 17] Some ways that materials store heat 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 Phonons present in all solids Conduction electrons significant in metals Photons significant in transparent materials Thermal expansion: temperature changes dimensional changes Origin in the interatomic potential 2 Lecture 20, spring 2009 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., relative size of atomic displacements is too small to be seen here Each atom is coupled to its neighbors, so vibrations travel Traveling wave of vibration C&R Fig. 17.1 3 Lecture 25, spring 2009 ENGR 145, Chemistry of Materials Case Western Reserve University Thermal Expansion [C&R 17.3] The interatomic potential is asymmetric C&R Fig. 17.3 Asymmetric potential: average interatomic distance as T 4 Lecture 25, spring 2009...
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L26ThermProps145s09r - Lecture 25, spring 2009 ENGR 145,...

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