Thermal conductivity the list of thermal conductivities. These should be considered approximate due to the uncertainties related to material definitions. High energy generation rates within electronics or turbines require the use of materials with high thermal conductivity such as copper "(see: Copper in heat exchangers)", aluminium, and silver. On the other hand, materials with low thermal conductance, such as polystyrene foam and fire brick, are used in building construction or in furnaces in an effort to slow the flow of heat, i.e. for insulation purposes. The reciprocal of thermal conductivity is "thermal resistivity", usually expressed in kelvin-meters per watt (K⋅m⋅W). For a
Thermal conductivity the molar volume. More rigorously, the mean free path of a molecule in a gas is given by formula_77 where "σ" is the collision cross section. So The heat capacity per particle "c" and the cross section "σ" both are temperature independent so the temperature dependence of "k" is determined by the "T" dependence of "v". For a monatomic gas, with atomic mass "M", "v" is given by formula_79 So This expression also shows why gases with a low mass (hydrogen, helium) have a high thermal conductivity. For metals at low temperatures the heat is carried mainly by the free