Copper greater strength than monocrystalline forms. The softness of copper partly explains its high electrical conductivity (59.6×10 S/m) and high thermal conductivity, second highest (second only to silver) among pure metals at room temperature. This is because the resistivity to electron transport in metals at room temperature originates primarily from scattering of electrons on thermal vibrations of the lattice, which are relatively weak in a soft metal. The maximum permissible current density of copper in open air is approximately 3.1×10 A/m of cross-sectional area, above which it begins to heat excessively. Copper is one of a few metallic elements with 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