The oxidation number is 6, 5, 4, 3, 2, 1, 1, ? 2, ? 4. It is the hardest metal.
Chromium is a silvery white shiny metal. Pure chromium is malleable, and chromium containing impurities is hard and brittle. The density is 7.20g/cm3. Soluble in strong alkali solution.
Chromium has high corrosion resistance and is slowly oxidized in air, even in a red-hot environment. Insoluble in water. Electroplating on metal can play a protective role.
The sword excavated by China archaeologists in the Qin Mausoleum is extremely sharp, because the blade is covered with chromium. It doesn't sound magical, but it can prove that we discovered and used chromium thousands of years ago.
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Use of chromium
Chromium is used to make stainless steel, automobile parts, tools, magnetic tapes and video tapes. Chromium plating on metal can prevent rust, also called keduomi, which is strong and beautiful.
Chromium is one of the essential trace elements for human body and plays a key role in maintaining human health. Chromium is a trace element that is very beneficial to human body and can not be ignored. It is an important element for normal growth and development and regulating blood sugar.
Chromium is an essential element to maintain human life activities, which can help insulin promote the efficiency of glucose entering cells, and is an important blood sugar regulator and a function of promoting growth and development. In addition, chromium is the "nemesis" of diabetes, and you can eat more foods rich in chromium in your daily life.
Ferrochrome and silicon-chromium alloy widely used in iron and steel industry are melted by electric furnace. Metal chromium production adopts metal thermal reduction (aluminothermic) method and electrolysis method.
The aluminothermic production includes two processes: preparing chromium oxide from chromium ore and preparing metallic chromium by reducing chromium oxide with aluminum.
The thermite reduction requires that the content of Cr2O3 in raw materials is more than 99%, the content of sulfur is less than 0.02%, and the contents of lead, arsenic, tin and antimony are less than 0.00 1% respectively. The particle size of aluminum particles should be less than 0.5 mm, and the amount of aluminum should not exceed 98% of the theoretical amount. Nitrite, magnesium chips and aluminum particles are used as kindling materials.
Electrolytic production generally takes ferrochromium as raw material and adopts chromium ammonium alum electrolysis process. Crushing ferrochrome, dissolving it in the mixed solution of electrolytic anode return liquid, crystallization mother liquid and sulfuric acid, filtering to remove silicate and other residues, and treating the filtrate with ammonium sulfate to remove iron.
References:
Baidu encyclopedia-chromium