Brief introduction to pure metal and its development

• Posted by Samantha James April 21, 2020 Filed in Arts & Culture 202 views
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  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 cannot 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

   

  Introduction to Terminology

  People usually refer to materials or substances that consist essentially of a metal as pure metals.

  Pure metals can only be produced and used in large quantities on the basis of modern science and technology. The so-called pure also has a relative meaning, and absolute pure is not. Pure metals can be divided into industrial pure metals and chemical pure metals according to their purity. Most of the industrially used and produced industrial pure metals. Chemically pure metals need special methods and equipment to be produced, and the output is also limited. They are mostly used in scientific research, cutting-edge technology or some special production fields.

  Now science and technology can produce pure metals with a purity of over 99. 999%, and the purity of some semiconductor materials can even be reached.

  However, no matter how high the purity is, it always contains trace amounts of other elements.

  The mechanical properties of pure metals are not high. Taking strength as an example, the strength of pure metals is generally low. The tensile strength of iron is about 200MPa, and the tensile strength of pure aluminum is about 100MPa, which is obviously not suitable for various structures in engineering. Materials. In addition, the types of pure metals are limited, the production is difficult, and the price is relatively high, so it is rarely used in various industries. In fact, the metal materials used in the project are all alloys, such as carbon steel, alloy steel, cast iron, copper alloy, and tin alloy, especially alloys with iron and carbon as the main components.

   

  Classification

  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. For example, the impurity content generally refers to the sum of certain specified impurities is one millionth, which is called 6 "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 substitutions or gaps. 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 residual resistivity (ρ4.2K / ρ300K), industrial pure metals are usually expressed as a percentage of the main metal.

   

  Preparation method

  The production process of pure metals can be summarized into two types.

  One is to obtain pure metal compounds through precipitation, solvent extraction, ion exchange, etc., and then reduce them to pure metals. Such as pure metal titanium, TiCl4 is often purified by rectification and then reduced to pure sponge titanium.

  The second is to obtain crude metals and then purify them into pure metals. There are two types of purification methods: chemical purification and physical purification.

  The chemical purification methods mainly include electrolytic refining, oxidation refining, chlorination refining, and disproportionated metallurgy.

  Physical purification methods mainly include regional purification, distillation, rectification and refining, drawing single crystal, vacuum refining, etc.

  Pulling single crystals is a method of pulling single crystals out of the melt by using seed crystals or self-generated seed crystals to purify the metal. The physical purification method has simple equipment, convenient operation, and little reagent pollution, and can be used as the final purification method. The chemical purification method has great flexibility and strong selectivity, but it often has the disadvantage of reagent contamination, and is widely used in pre-purification and intermediate purification. But in production, the two methods are often used in conjunction with each other. At present, ultra-high purity germanium with a purity of 12 "9" can be prepared, and high-purity silicon, arsenic, gallium, indium, etc. with more than 7 "9" can also be prepared. These high-purity metals are used as materials for the semiconductor industry.

   

  Detection method

  The detection methods of pure metals include activation analysis, atomic absorption spectrometry, fluorescence spectrophotometry, mass spectrometry, chemical spectrometry and gas analysis.

  The ionization concentration in semiconductors can be determined by measuring the Hall coefficient, and the purity of ultrapure gallium can be determined by measuring the residual resistivity.

   

  Development status

  At present, there are 26 varieties of high-purity metals (elements). Compounds, related alloys and high-purity metal sheets, grains, rods, etc. can also be produced or trial-produced. High-purity metals are important basic materials for cutting-edge industries such as electronics industry, defense industry, aerospace, communications and high science and technology, and have broad development prospects.

  New technologies should be adopted to further improve product quality. Only by expanding production capacity and reducing costs can we take the initiative in market competition.

   

  About us

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