Noble metal alloy is an alloy based on a metal in a precious metal and composed of other elements. Precious metal alloy has the main characteristics of precious metal, for its specific use, it has better physical, chemical and mechanical comprehensive properties than single precious metal, as well as high reliability, stability and long life. Gold and platinum alloy was made in 1763. In 1802, hydrogen and oxygen blowpipe was invented, which provided a means of melting precious metal alloy at high temperature. By 1847, precious metals could be smelted with the exception of osmium and ruthenium. After 1892, electric arc furnace and induction furnace appeared one after another. These two furnaces are still the main smelting facilities for precious metals. By the end of 1930s, there were more than 50 platinum alloy systems available for application. This precious metal alloy is widely used in various industrial sectors. Since the 1970s, continuous ingot casting, extrusion, composite (including coating) and other technologies have been gradually applied in the precious metal alloy industry. The production of gold, silver and their alloys in China has a long history (see metallurgy); In 1964, platinum group metal alloy was produced in small batch. Since then, the scale and varieties of research and production gradually expanded. By the end of 1970s, there were about 200 kinds of precious metal alloys produced in China, and about 1000 kinds of profiles of various specifications.
Precious metal alloys are almost always used as functional materials. There are many classification methods for noble metal alloys: according to the base metal, they can be divided into silver base alloy, gold base alloy, platinum base alloy and palladium base alloy. According to the application can be divided into electric contact alloy, alloy, resistance alloy, resistance strain alloys, elastic alloys, magnetic alloys, catalyst, hydrogen through material, tube leakage cathode materials and glass fiber board, vessels and crucible materials, decoration materials, filler metals alloy, dental materials and metal COINS (see metal coin), etc. The application characteristics of precious metal alloys are: little (small batch and quantity), small (the volume of single articles and components is small), fine (high technical requirements, often used in key parts), wide (almost all modern science and technology fields and industrial production departments are required) and expensive (higher price).
The alloying elements used in noble metal alloys are mostly metals (mainly transition metals), and a few are semi-metals and non-metals. The total number is about 50. Generally speaking, lead, antimony, bismuth, silicon, phosphorus and iron are harmful impurity elements in noble metal alloys. Among the noble metal alloys, about 600 phase diagrams of alloy series have been studied, including the binary phase diagrams of the majority of gold and silver, and the binary phase diagrams of the majority of platinum group metals (the phase diagrams with alkali metals, alkali earth metals and rare earth metals as the other group elements are less studied). There are four main types of alloy systems (including binary systems, ternary systems and more and more multivariate systems) according to phase diagram: liquid and solid are mutually soluble indefinitely (such as ag-au, pt-rh, ir-rh, pd-ag-au, etc.); The liquid state is infinitely miscible, and the solid state is infinitely miscible at high temperature, but at low temperature there are insoluble regions (such as pt-ir, pd-ir, au-pt, au-ni, pd-ag-co, etc.) or orderly and disorderly transitions (such as au-cu, pt-co, pt-ni, pd-cu, etc.). Eutectic (Ag-Cu, Au-Sb, etc.); Peritectic crystals (such as pt-w, pd-w, pt-ag, au-cr, pt-ru series, etc.) In addition, there are a few alloys containing intermetallic compounds (such as au-ag-cu-mn-gd, au-ni-gd, au-ni-cr-gd).
