{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

407 Class Notes 5, 2010 [Compatibility Mode]

# 407 Class Notes 5, 2010 [Compatibility Mode] - Thermal...

This preview shows pages 1–5. Sign up to view the full content.

Thermal Properties A. Heat capacity Heat capacity, C, is a measure of a material’s ability to absorb heat from the external surroundings, or C = dQ/dT where dQ is the energy required to produce a dT temperature change Normally specified as heat capacity per mole (e g cal/mol K) Normally specified as heat capacity per mole (e.g. cal/mol-K) -- specific heat is also used; represents the heat capacity per unit mass (cal/g-K) -- measured either by maintaining a constant specific volume, C V , or by maintaining a constant external pressure, C P In most solids, thermal energy absorption occurs primarily by imparting In most solids, thermal energy absorption occurs by imparting vibrational energy to the atoms -- due to atomic bonding, vibrations are coordinated in such a way that travelling lattice waves (sound waves) are generated, which have very high frequencies -- quantum mechanics allows certain energy values, called phonons.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
The heat capacity at constant volume, C V , is zero at 0º K but rises rapidly with temperature. At low temperatures C V = AT 3 AT where A is a temperature-independent constant Above the Debye temperature θ D , C V becomes relatively independent of Above the Debye temperature becomes relatively independent of temperature and attains a value of about 3R. In other words, the quantity of energy required to produce one-degree temperature change is constant. Fig. X - Temperature dependence of the heat capacity at constant volume; θ D is the Debye temperature.
B. Thermal expansion Thermal expansion is a measure of the extent to which a material expands upon heating or contracts upon cooling, or Δ / 0 = α Δ T where α is called the linear coefficient of thermal expansion The expression for the volumetric expansion, α v , is similar -- in many materials, the value of α v is anisotropic, i.e. it depends on crystallographic direction -- when thermal expansion is isotropic, then α v is about 3 α The stronger the bonding the deeper and narrower the energy trough, resulting in a lower value of α , as is the case for many ceramics

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Fig. X - Temperature dependence of the potential
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 9

407 Class Notes 5, 2010 [Compatibility Mode] - Thermal...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online