Brief introduction to the related knowledge of metal bismuth

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Bismuth is a kind of rare metal being used early and discovered later. Under normal temperature, it appears to be silver white or reddish, has metallic luster, crisp property and poor electrical and thermal conductivity. Its volume will be increased under solidification conditions, of which the expansion rate is 3.3 percents. The bismuth selenide and telluride both have semiconductor property.

Bismuth will not react with oxygen or water at indoor temperature. It is stable in the air and will burn when heated above its melting point, in which it will generate light blue flame and bismuth trioxide. It will also have chemical combination with sulphur and halogen under red heat conditions. Bismuth powder can fire in the chlorine condition. Besides, bismuth is insoluble in water and non oxidizing acid. It will have only a little reaction with concentrated sulfuric acid and concentrated hydrochloric acid when they are commonly heated. However, it is soluble in auqa regia and nitric acid.

Due to the low melting point of bismuth, it can be reduced from its natural ore by using carbon. Therefore, it was obtained early by the ancient people. However, as it has crisp and hard properties and also lack of durability, it was kept in the alloy after the ancient people obtained it and did not find its applications.

Bismuth reserves are very few. According to the data of U.S. Geological Survey, the global bismuth reserves are 330,000 tons which are a little lower than white silver that has 400,000 tons of reserves and 680,000 reserve base. Bismuth resources are mainly distributed in China, Australia, Peru, Mexico, Bolivia, the United States, Canada and Japan. Bismuth is existed in the forms of free metals and minerals in nature. It has not very much content in the Earth’s crust. It is generally obtained by mixing heating and reducing bismuth oxide generated by roasting the minerals with carbon, while the bismuth ingots can be produced in the method of pyro-refining and electrorefining. The annual output of bismuth is relatively little which is about 16,000 tons per year and is less than the white silver that has 20,000 tons of output per year. Although bismuth belongs to the small metal species, its usages are relatively wide.

Bismuth, mainly used in producing fusible alloy, has the melting point from 47 degrees Celsius to 262 degrees Celsius. The alloys composed by bismuth together with lead, tin, antimony and indium are most commonly used, which can be used as the safety plug of fire protecting arrangement, automatic sprinkler and boiler. When the fire is occurring, some pistons of the water pipe will “automatically” melt and gush out water. In the fire protection and electric industry, it can be used for automatic fire extinguishing systems, electrical fuses and tin soldering. In addition, bismuth alloys will not shrink under solidification condition and can be used in casting printing type and high precision mould.

Bismuth is most widely used in the electron industry in which it is mainly applied in the voltage dependent resistor, thermistor, zinc oxide arrester, kinescope and other fields. If it is distinguished by material, bismuth oxide is mainly used in the electronic ceramic powder materials, electrolyte materials, photoelectric materials, high-temperature superconducting materials, temperature difference semiconductor materials and so on, among which the electronic ceramics powder materials have the widest application area.

In the chemical industry, bismuth is mainly used as the pigments, catalysts, fire retardants, etc. Among them, bismuth oxychloride is a kind of excellent pearlescent pigment that has been used for a long time while bismuth oxide is also a kind of yellow pigment with high performance. Bismuth yellow, served as the non-toxic and non-polluting senior pigment, has gradually replaced the cadmium yellow, chrome yellow, lead yellow and other pigments that contain toxic elements; in the catalyst aspect, bismuth is mainly used as the molybdenum bismuth catalysts, yittrium bismuth catalysts and combustion catalysts; in the fire-retardant additives, the effects of bismuth trioxide are better than antimony trioxide, besides, it is safe and non-toxic.

In the future, with the further development of energy, electron and other high-technology industries, bismuth will become irreplaceable in the application on superconducting material alloy of new energy and new material fields, the carrier of nuclear fuel and coolant. In addition, as many of the bismuth performances are similar with lead and as it is called “green metal” that is harmless to human body, it has become the preferred material for replacing lead. Because bismuth is regarded as the safe “green metal”, it is widely applied in the semiconductors, superconductors, fire retardants, pigments, cosmetics, chemical reagents, electronic ceramics and other fields except for its applications on the pharmaceuticals industry, which will threaten to replace lead, antimony, cadmium, mercury and other toxic elements. With the implement of “Instructions about the Prohibiting Use of Some Hazardous Substance in Electrical and Electronic Equipment” issued by EU, the new consumer channel of bismuth will be opened. Meanwhile, bismuth will speed up its pace of replacing lead and the requirement space of bismuth will be further opened in the future.