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For the first time this name appeared in the scientific literature at the beginning of the 20-ies of the last century. But especially urgent need in the rare metals occurring in the middle of the twentieth century with the advent of electrical engineering, electronics, stratospheric aviation, rocketry, nuclear power. It is natural that with the development of new industries and the increasing consumption of these metals, the term «rare metals» loses its original meaning. Abroad rare metals are sometimes referred to as «less common metals» (Less Common Metals).
To the class of refractory metals are those that melt at a temperature — not less than 1650−1700°C. the refractory metals Group it is impossible to imagine without tungsten and molybdenum. They differ in the densely Packed atomic structure. High melting point, high hardness, electric resistance and strength occurs due to the close interatomic electronic links.
Mining and processing of tungsten and molybdenum is associated with a number of difficulties that increase the cost of these metals. Prices in Russia and Ukraine is formed taking into account the rate on the London stock exchange of nonferrous metals, rare metals today there are more than 50 items. These are metals that are relatively new and still unfamiliar with modern industry. Their production continues to grow, expands the application. Group of these metals are not widespread, their deposits scattered in the earth’s crust; extracting from ores and obtaining in pure form due to a number of difficulties. This seriously complicates the study and technical development of rare metals.
Trace metals are in the form of isomorphic impurities of the ore and can be extracted from the waste of metallurgical or chemical means. So gallium can be extracted from alumina, indium — waste from the production of lead or zinc. Rare earth metals have similar chemical properties. In deposits they coincide with each other and separate them — a difficult task.
Typically, rare metals are not smelted from ore concentrates, and recover from chemical compounds. Widely used a variety of methods: recovery of oxides gases, e.g., carbon or more active metals, oxidized, take oxygen. The pyro uses thermal dissociation, vacuum, or electron-beam zone melting. Electrochemistry — electrolysis of aqueous solutions and melts. For making alloys of refractory metals, the greater the relevance of the received methods of powder metallurgy.
To date, there is no single generally accepted classification of rare metals. The similarity of the physico-chemical characteristics, location, production technology and a number of other properties is composed of technical classification. It is quite conditional, since the same elements are in different groups. So, cesium and rubidium at the same time scattered and light elements. Classic trace element rhenium — refractory metal simultaneously. Refractory metals such as hafnium and vanadium are trace elements. And titanium — refractory and one of the light metals.
lungs and rare refractory metals
The first are characterized by a minimum density (from 0.54 g/cm3 for lithium to 1.87 g/cm3 for cesium). It is chemically active elements. The properties and production methods they are similar to light nonferrous metals such as sodium and magnesium. Refractory rare metals are located in the transition groups IV to VII group of the periodic table. They have an unfinished e-d-level. Have a high melting point (1668 °C for titanium up to 3410 °C for tungsten). With a number of nonmetals form more refractory compounds (carbides, silicides, borides).
There are natural, or natural radioactive elements — France, radium, polonium, uranium and artificial, such as technetium. The greatest technical importance for nuclear energy are plutonium and uranium-235. In ore raw materials, such metals are typically present in minimal quantity. Therefore, great value in technology of extraction of these metals acquires processing of metals and technology of isolation, separation and purification.
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