mse19 - Chapter 19: Thermal Properties ISSUES TO ADDRESS....

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1 Chapter 19 - 1 ISSUES TO ADDRESS. .. • How does a material respond to heat? • How do we define and measure. .. -- heat capacity -- coefficient of thermal expansion -- thermal conductivity -- thermal shock resistance • How do ceramics, metals, and polymers rank? Chapter 19: Thermal Properties Chapter 19 - 2 General: The ability of a material to absorb heat. • Quantitative: The energy required to increase the temperature of the material. heat capacity (J/mol-K) energy input (J/mol) temperature change (K) Heat Capacity Two ways to measure heat capacity: C p : Heat capacity at constant pressure. C v : Heat capacity at constant volume. C p > C v • Specific heat has typical units of K kg J dT dQ C =
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2 Chapter 19 - 3 Heat capacity. .. -- increases with temperature -- reaches a limiting value of 3 R • Atomic view: -- Energy is stored as atomic vibrations. -- As T goes up, so does the avg. energy of atomic vibr. Heat Capacity vs T Adapted from Fig. 19.2, Callister 7e . gas constant 3 R = 8.31 J/mol-K C v = constant Debye temperature (usually less than T room ) T (K) θ D 0 0 C v Chapter 19 - 4 Energy Storage How is the energy stored? Phonons – thermal waves - vibrational modes Adapted from Fig. 19.1, Callister 7e .
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3 Chapter 19 - 5 Energy Storage • Other small contributions to energy storage – Electron energy levels • Dominate for ceramics & plastics – Energy storage in vibrational modes Adapted from Fig. 19.3, Callister 7e . Chapter 19 - 6 increasing c p • Why is cp significantly larger for polymers?
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mse19 - Chapter 19: Thermal Properties ISSUES TO ADDRESS....

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