Noble metals and noble metal alloys

Abstract

The properties of metallic materials depend sensitively not only on their chemical composition and on the electronic and crystal structure of the phases formed, but also to a large degree on their microstructure, including the kinds and distribution of lattice defects. The phase composition and microstructure of metallic materials are strongly dependent, in turn, on the thermal and mechanical treatments, which are applied under well-controlled conditions to achieve the desired properties. The noble metals are characterized by their high densities, high melting temperatures, high vapor pressures, high electrical and thermal conductivities, optical reflectivities and catalytic properties. They are comparatively soft and ductile, and their hardness increases in the order Rh < Ir < Ru < Os. Solid solution and dispersion hardening strengthen the alloys, while corrosion resistance against various agents decreases in the order Ir > Ru > Rh > Os > Au > Pt > Pd > Ag. Being key materials in electronics and electrical engineering, the pure elements and their alloys serve as materials to manufacture high-strength, corrosion-resistant, high-temperature, and highly oxidation-resistant structural parts. The platinum group metals silver and gold are effective heterogeneous or homogeneous catalysts for a wide variety of chemical reactions. Traditional applications of noble metals and their alloys are in dentistry and jewelry, as well as in coins and medals.