Properties Molybdenum: silver metal, hard and tough, is one of a refractory metal element as a Group VIB element in the periodic table, the atomic number 42, atomic weight 95.94, density 10.2 g / cm 3, a melting point of 2610. deg.] C, a boiling point 5560 ° C. The valence price is +2, +4 and +6, and the stable price is +6. The first ionization energy is 7.099 eV. It is not eroded by air at normal temperature. Does not react with hydrochloric acid or hydrofluoric acid. Molybdenum never appears as a natural element, but always combines with other elements. Molybdenum is a pro sulfur, so molybdenite (MoS 2) is the major mode of occurrence of molybdenum, of molybdenum and tungsten followed, copper, vanadium, rhenium, niobium and other elements symbiotic oxide ores. There are about 20 kinds of molybdenum minerals known at present, but only four of them have industrial application value: molybdenite (MoS 2 ), calcium molybdate (CaMoO 4 ), molybdenum [Fe 2 (MoO 4 ) ) 3 · 71 / 2H 2 O ] and lead molybdate ore (PbMoO 4). in addition to primary molybdenite minerals molybdenum, the other are associated secondary mineral or molybdenum (symbiosis) molybdenum minerals. Molybdenum is stable in air or water at normal temperature, but starts to slightly oxidize when the temperature reaches 400 ° C. When it reaches 600 ° C, it undergoes intense oxidation to form MoO 3 . Hydrochloric acid, hydrofluoric acid, dilute nitric acid and an alkaline solution have no effect on molybdenum. Molybdenum is soluble in nitric acid, aqua regia or hot sulfuric acid solutions. At very high temperatures, molybdenum does not react with hydrogen, but reacts with nitrogen at 1500 ° C to form a nitride of molybdenum. The carbon, carbon monoxide and hydrocarbon are reacted at a temperature of 1100 to 1200 ° C or more to form a carbide such as MoSi 2 . This MoSi 2 is relatively stable even in an oxidizing atmosphere of 1500 to 1700 ° C and is not oxidatively decomposed.
Molybdenum Applications: steel, stainless steel, tool steel and cast iron is the main application field of molybdenum, which determines the demand for production of molybdenum, molybdenum role in the above steel are as follows:
Decreasing the cooling rate to an appropriate value to obtain a hard martensite structure, thereby increasing the strength, hardness and toughness of the large-section member;
â— reduce temper brittleness;
â—Anti-hydrogen embrittlement;
â— Stress cracking caused by sulfide resistance;
â— Improve high temperature strength;
â— Improve the corrosion resistance of stainless steel, especially against chloride pitting;
â— Improve the welding performance of high strength low alloy steel.
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