Chromium forms a massive disseminated ores in ultrabasic rocks, the chemical element more common in the Earth's mantle.This metal deep zones of the planet, they are also enriched stony meteorites.
are more than 20 minerals chromium, but the commercial value have only Cr-spinels.In addition, the chromium contained in a number of minerals that accompany chromium ores, but they do not represent practical value.
chromium is found in plant and animal tissues, it is present in the leaves of a low molecular weight complex in the organism of animals and participates in the metabolism of proteins, lipids and carbohydrates.The reduced content of chromium in the diet leads to a decrease in growth rate and reduction of sensitivity of p
eripheral tissues.
Chrome crystallizes in a body-centered lattice.At a temperature of around 1830 ° C possible its transformation into a modification of a face-centered lattice.This element chemically maloaktiven, chromium is stable to oxygen and moisture under ambient conditions.
interaction of chromium with oxygen initially proceeds actively, then abruptly slowed down due to the formation of the oxide film on the metal surface.The film breaks at 1200 ° C, after which the oxidation begins to flow quickly.At temperatures around 2000 ° C chromium lights, forming a dark green oxide.
Chromium reacts readily with dilute solutions of sulfuric and hydrochloric acids, so obtained sulphate and chromium chloride, and the hydrogen is released.This metal forms a variety of salts with oxygen-containing acids.Chromic acid and its salts are potent oxidants.
raw material for chromium are Cr-spinels, they are subjected to enrichment, and then fused with potassium carbonate in the presence of oxygen.Thereby forming a chromate, potassium leached with hot water under the action of sulfuric acid, turning it into a dichromate.Under the action of a concentrated sulfuric acid solution of chromic anhydride, dichromate prepared.
In industrial environments clean chrome produced by electrolysis of chromium sulfate and concentrated aqueous solutions of its oxide.Chromium thus released at the cathode of aluminum or stainless steel.Then the metal was purified from impurities by treatment with pure hydrogen at a temperature of 1500-1700 ° C.Small amounts of chromium can be prepared by reduction of chromium oxide with silicon or aluminum.
Use of chromium based on its resistance to corrosion and heat resistance.His considerable amount goes to the decorative coatings, powder chromium is used for the production of metal products and materials for welding electrodes.