Pure metals refer to metals that do not contain other impurities or other metal components. Pure metal has the advantages of high electrical conductivity, thermal conductivity and good plasticity, but due to the limitations of its performance, it can not meet the requirements of various occasions. In fact, due to smelting reasons, the purity of pure metals is less than 100%, but only as close to 100% as possible, which always contains a very small amount of impurities. Pure metal smelting is difficult and expensive, and various alloys are mainly used in production
According to the impurity content, it can be divided into industrial pure metal and ultra pure metal. In the production practice, the percentage purity of some non-ferrous metals commonly used in industrial purity are: zinc 99.995, lead 99.994, tin 99.95, nickel 99.99, aluminum 99.7 and so on. The impurity content of ultra-pure metals is in the order of parts per million or the content of main metals is above 99.9999%, while the impurity content in ultra-pure semiconductor materials is in the order of parts per billion.
The method of expressing purity is used in practice. It is used to express the main metal content of a few nines (N). For example, the impurity content generally refers to the sum of certain specified impurities is one millionth, which is called 6 “9 “Or 6N.
Impurities in a broad sense refer to chemical impurities and physical impurities (crystal defects), the latter refers to dislocations and vacancies, etc .; chemical impurities refer to the incorporation of atoms other than the matrix in the form of substitution or interstitial filling. But only when the purity of the metal reaches a very high standard (such as a metal with a purity of 9N or more), the concept of physical impurities is meaningful.
Therefore, the metal currently produced in industry is still based on the content of chemical impurities. There are two ways to express it: one is based on the use of materials, such as “spectral grade purity”, “electronic grade purity”, etc .; Expressed by a certain characteristic, for example, the semiconductor material is represented by the carrier concentration, that is, the number of impurities (atoms / cm) that play a role in the basic element of a cubic centimeter, and the metal can be used for the residual resistivity (ρ4.2K / ρ300K), industrial pure metals are usually expressed as a percentage of the main metal.