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
Conductivity near the percolation threshold critical exponents we have the "correlation length", formula_10 formula_11 and the "percolation probability", P: formula_12 For the description of the electrical percolation, we identify the occupied bonds of the bond-percolation model with the metallic component having a conductivity formula_13. And the dielectric component with conductivity formula_14 corresponds to non-occupied bonds. We consider the two following well-known cases of a "conductor-insulator mixture" and a "superconductor–conductor mixture". In the case of a conductor-insulator mixture we have formula_15. This case describes the behaviour, if the percolation threshold is approached from above: formula_16 for formula_6 Below the percolation threshold we have no conductivity, because