The wolfram

The wolfram is a chemical element with atomic number 74 in the periodic table of chemical elements, denoted by W. Wolfram is the most refractory metal. Higher melting temperature has only a non-metallic element - carbon. Under normal conditions, chemically resistant.

The wolfram is a chemical element with atomic number 74 in the periodic table of chemical elements, denoted by W

Wolframium name passed to the element with the mineral wolframite, known as early as the 16th century. called "wolf's froth" - in Latin, or "Wolf Rahm" in German. The name was due to the fact that wolfram, accompanying tin ore, tin smelting interfered, transforming it into a slag foam.

The wolfram is found in nature mostly as oxidized complex compounds formed of tungsten trioxide WO3 with oxides of iron and manganese or calcium and sometimes lead, copper, thorium and rare earths.

The process of obtaining the wolfram passes through the sub-step selection trioxide WO3 of ore concentrates and subsequent reduction to metal powder with hydrogen at a temperature of about 7000 C.

The wolfram in chemical reactions has a valence of from 2 to 6. The most stable 6-valent. 3- and 2-valent compounds are unstable and do not have practical significance. W has high corrosion resistance: at room temperature in air is not changed; at red heat slowly oxidized to wolfram oxide (6). The voltage range W is immediately after hydrogen and hydrochloric acid, dilute sulfuric and hydrofluoric acids, almost insoluble. The nitric acid and aqua regia oxidized surface. Easily soluble in a mixture of nitric and hydrofluoric acid reacts with molten alkali in the presence of oxidants.

The wolfram can be some interesting transport reactions that sometimes occur in the bulb light bulb filament. When water penetrates, tungsten spiral bulb reacts with water vapor in the tube-bottom flask:

W + 3H2O = WO3 + 3H2.

The wolfram trioxide is a volatile compound, sublimating, it flies in the colder part of the light bulb and is reduced by hydrogen. In this case, the lamp bulb is allocated to a superfine W black powder:

WO3 + 3H2 = W + 3H2O.

Water molecules to fly again incandescent spirals which wolfram reacts, and the process is repeated with them. Therefore, the electric lamp darkens with time, as with steam W is gradually transferred from the helix to the lamp bulb wall.

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