ch19-shin

ch19-shin - Introduction to Materials Science and...

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UNIST 2011 Spring AME20201 Introduction to Materials Science and Engineering Hyung-Joon Shin School of Mechanical and Advanced Materials Engineering Ulsan National Institute of Science and Technology (UNIST) Chapter 19: Thermal Properties

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UNIST 2011 Spring AME20201 Energy Storage Atomic vibrations are in the form of lattice waves or phonons How is the energy stored? Phonon = Vibrational Modes = Thermal Waves
UNIST 2011 Spring AME20201 Phonon Atoms in solids are constantly vibrating at very high frequencies with relative small amplitudes In most solids , thermal energy = vibrational energy of atoms . Phonon : single quantum of vibrational energy (waves) Phonon is one of the major causes of electron scattering during the electric conduction Phonon + electron participate in the transport of energy during thermal conduction

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UNIST 2011 Spring AME20201 Quantitatively: The energy required to produce a unit rise in temperature for one mole of a 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 usually > C v • Specific Heat : Heat capacity per unit mass (J/kg-K) dT dQ C = The ability of a material to absorb heat from external surroundings.
UNIST 2011 Spring AME20201 Heat capacity... - increases with temperature - For solids, it reaches a limiting value of 3 R From atomic perspective: -- Energy is stored as atomic vibrations. -- As temperature increases, the average energy of atomic vibrations increases. Dependence of Heat Capacity on Temperature R = gas constant 3 R = 8.31 J/mol-K C v = constant Debye temperature (usually less than T room ) T (K) D 0 0 C v

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UNIST 2011 Spring AME20201 increasing c p Why is c p significantly larger for polymers?
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