Sep 15, 2018
According to the impurity content, it can be divided into industrial pure metals and ultra pure metals. In production practice, the percentage purity of some industrial pure nonferrous metals is zinc 99.995, lead 99.994, tin 99.95, nickel 99.99, aluminum 99.7 and so on.
The impurity content of ultrapure metals is in the order of several parts per million or more than 99.9999% of the main metals, while the impurity content of ultrapure semiconductor materials is in the order of several parts per billion.
 In practical use, it is customary to express the purity by several nines (N) of the main metal content, such as the impurity content is generally defined as the sum of certain impurities is one millionth, that is, 6 "9" or 6N.
Generally speaking, impurities refer to chemical impurities and physical impurities (crystalline defects), the latter refers to dislocations and vacancies, and chemical impurities refer to the addition of atoms outside the matrix in the form of substitution or filling gap. However, the concept of physical impurities is meaningful only if the metal purity reaches a high standard (e.g., metal purity above 9N).
Therefore, at present, the industrial production of metals is still based on the content of chemical impurities as the standard, there are two ways to express it: one is to use materials, such as "spectral purity", "electronic purity" and so on; the other is to express some characteristics, such as semiconductor materials with carrier concentration, that is, a cubic centimeter of the basic element. The number of impurities (atoms/cm) that act as conductive elements in the element is expressed, while the metal can be represented by the residual resistivity (p 4.2K/p 300K), and the industrial pure metal is usually expressed by the percentage of the main metal.