"Tungsten / wolfram (W), also known as tungsten or wólfram, is the chemical element with atomic number 74 of group 6 of the periodic table of elements. It is a rare metal in the earth's crust and is found in certain minerals in the form of oxide or salts. It is gray in its pure state. It is a very hard and dense metal. Its melting occurs at 3,422 ° C making it the metal with the highest melting point. It also has the highest boiling point (5930 ° C). High of the known elements. It is the metal that most withstands friction. It has an acceptable chemical resistance and cannot be easily attacked by acids. When exposed to ultraviolet light it has a very bright bluish shine. Its density is 19600 kg / m3. Tungsten in its natural form is brittle and difficult to work with, but alloyed can be worked more easily. It is difficult to alloy. Tungsten alloys (heavy alloys) are typically 90-97% tungsten. Tungsten + Nickel + Iron: It is the most common alloy. In magnetic. This alloy is perfect for radiation shielding due to its high density combined with radiation resistance. Tungsten + nickel + copper: they have less ductility than the previous one. Its biggest advantage is that it is not magnetic. It is used for example in oncology tools. Tungsten Carbide (Tungsten + Carbon): It is not an alloy, but is a ceramic-like compound made by the sintering process in which adding black carbon to the tungsten powder produces an extremely hard and brittle cement when it is cools down. It is the most important compound of tungsten. It is used in industrial machinery, wear resistant tools ... Tungsten, not found free in nature, is extracted from several wolframic minerals: wolframite, scheelite, ferberite, cuproscheelite, hübnerite and stolzite. The largest producers are China, Bolivia and Russia. Mining occurs in several stages: it is converted to tungsten trioxide, heated with carbon and hydrogen, and powdered tungsten is produced. To obtain tungsten in its pure state, metallurgy is easy, but as it has a very high melting point, the treatment of the final product is difficult. To obtain it, the minerals are fused with sodium carbonate and you acquire a soluble salt that comprises tungsten. Then it is treated with hydrochloric acid and tungsten oxide is obtained. Finally, the oxide is reduced with a stream of hydrogen. This is how tungsten powder is obtained. Tungsten is used to make carbide inserts and tools. The recycling of these products is very important to preserve the environment and to be able to satisfy the demand for this precious and scarce material. About 30% of tungsten scrap is recycled. Many of the waste materials are richer in tungsten than mineral concentrations, which is why recycling these materials is so valuable. The demand for the products of this metal is increasing and consequently the demand for this resource. "
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