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Molybdenum and oxygen can produce a variety of oxides. The relationship between oxidation process and temperature can be divided into four stages: (1) The adhesion oxide film formed by molybdenum and oxygen below 475 °C is a thin layer of MoO2, and the outer layer is MoO3. (2) At the same time as the formation of an oxide film at 475 ° C to 700 ° C, MoO 3 evaporation occurs, and the oxidation rate depends on the metal surface adsorption, chemical reaction, and desorption process. X-ray structural analysis showed that the oxide film was divided into two layers, and the inner layer was MoO2 and the outer layer was MoO3. (3) In the range of 700-800 ° C, the inner layer reaches a critical thickness and then ruptures, causing the oxidation rate to suddenly increase. Above 725 ° C, the oxidation of steel quickly forms no molybdenum oxide layer on the surface of molybdenum, only the sublimation of yellow oxide (MoO3) appears, and "destructive oxidation" occurs. This is due to the appearance of volatile MoO3 and liquefied molybdenum, and the oxidation rate is so fast that the heat released during the oxidation reaction is too late to diffuse, and the self-heating causes the temperature to exceed the melting point of MoO3. This autocatalytic action results in devastating destruction of the material. This exothermic reaction should be used to recover waste molybdenum during production. (4) Above 850 ° C, the vapor of MoO3 forms a dense shielding layer on the surface of molybdenum, preventing oxygen from reaching the surface of molybdenum, and the oxidation rate is somewhat reduced. The rate of oxidation at this time is determined by the rate of diffusion of oxygen through the shield. Molybdenum absorbs ammonia NH3 at temperatures above 900 ° C and at a pressure of one. The solubility (atomic fraction) of ammonia in molybdenum increases from about 0.01% to about 0.1% with increasing temperature between 900 °C and 2600 °C. Molybdenum nitride is formed at about 1500 ° C. The molybdenum material will become brittle after inhaling nitrogen during processing. When the dense molybdenum material is heated to 1100 ° C - 1500 ° C in ammonia, nitride formation occurs. In the ammonia decomposition medium (ammonia decomposition to N2 and H2), the nitriding rate is faster than in pure ammonia. Nitride stability is high. The nitride alloy can be dispersed and strengthened with a nitride at an operating temperature of 1000 ° C to 1400 ° C. Therefore, ammonia decomposition cannot be used as a reducing gas for molybdenum powder. 3. Molybdenum is used in the superhard material industry. In the production of diamond and cubic boron nitride composite sheets, it utilizes its high melting point, high strength, high elastic modulus and improved oxidation resistance. It is applied to 1000°C--2000°C. The high temperature heat resistant alloy or strong alloy has high strength when applied under high load under high load without plastic deformation and fracture. Therefore, high temperature creep resistance is one of the main indicators of superalloys. Molybdenum is the highest temperature metal material currently used. Molybdenum in the superhard material industry, the production of composite sheets, the molybdenum is sintered, smelted, rolled into molybdenum foil 0.03-0.05 mm, made of different specifications of molybdenum strip, molybdenum rod, molybdenum plate molybdenum seal cover, molybdenum ball , molybdenum trapezoidal cup, molybdenum cone and so on. (see picture 1). According to the different requirements of users, the shaped molybdenum cup has a high melting point, high modulus of elasticity, high temperature strength, metal barrier layer, which is a powder product made of molybdenum crucible. In the super-hard materials industry, composite sheets are one of the indispensable molybdenum cup base materials. Therefore, in the super-hard materials industry, high-temperature sintering furnaces, degassing furnaces, vacuum annealing furnaces and high-temperature electric furnace heating bodies and reflective screen materials use molybdenum. Operating temperature up to 1700 °C long service life and low cost. The molybdenum foil is heat-treated before rolling, because the finished semi-finished products of molybdenum and its alloy mainly adopt stress relief annealing, incomplete recrystallization annealing and complete recrystallization annealing, high temperature annealing and deformation heat treatment. Thereby, the metal working temperature and the use temperature are increased, and the molybdenum foil in a crystalline state exhibits a different mechanical behavior from the face-centered cubic metal material at room temperature. The recrystallized annealing treatment of the back core-cube structure metal material forms an equiaxed restructured structure, has excellent room temperature plasticity, and can be processed at room temperature. IV. Summary Due to the excellent high melting point, high temperature strength, high modulus of elasticity and good electrical and thermal conductivity of molybdenum, it has not only become the sheath material and core structure material of military industry, atomic energy industry and gas cooling reactor. Especially in the ultra-hard materials industry, the application market is extensive. The molybdenum wire, rods, foils and various shaped parts produced by Baoji Sanli Nonferrous Metals Co., Ltd. for more than ten years have been exported to Japan, Italy and South Korea. (Author: Li Lu Fen)
Analysis of the application of molybdenum in the superhard material industry
I. Introduction Molybdenum is listed as a rare high melting point metal material. Both tungsten and molybdenum are elements of group VIB in the same periodic table. They are typical high melting point metals. They have similar basic properties, but they also have their own characteristics. The surface has a silver-gray luster and the powder is dark gray. Their commonality is: high melting point, High strength, high modulus of elasticity, small expansion coefficient, low vapor pressure, excellent electrical and thermal conductivity, and good corrosion resistance, but all have the common shortcomings of high temperature oxidation and low temperature brittleness. Therefore, molybdenum has become a major additive element for various structural steels and corrosion-resistant steels. Molybdenum has good elongation and superior thermal conductivity in electrical and electrical electrical fields. Molybdenum was discovered in 1778, and ten years later, molybdenum was reduced with carbon to obtain metal molybdenum. At the beginning of the 19th century, purer molybdenum was obtained by hydrogen reduction. It was discovered in about 1910 that molybdenum can significantly improve the properties of steel, and molybdenum has become a major addition to various structural steels and corrosion resistant steels. Molybdenum has good extensibility and is used in both the electronics and electrical industries. In the past ten years, the production of composite sheets in the super-hard materials industry was firstly applied by Baoji Sanli Co., Ltd. to molybdenum and its alloys in various plates, foils, rods, wires, various molybdenum cups, molybdenum trapezoidal cups, and molybdenum cones. It is widely used in the production of composite sheets (see Table 1 below). The main use of molybdenum is as an additive for various steels such as stainless steel, tool steel, low alloy steel, and titanium molybdenum alloy. The addition of molybdenum in the steel can refine the grains, increase the grain coarsening temperature, and significantly improve the hardenability, toughness, high temperature strength and creep properties of the steel. Because molybdenum has a high melting point and good electrical and thermal conductivity, it can be used as a heating element and a reflective screen material for high-temperature furnaces. The electric furnace with molybdenum as a heating element can reach a working temperature of 1900 degrees, and has a long service life and low cost, which makes it A wider range of applications. Second, the physical properties and characteristics of molybdenum metal materials. Molybdenum is a group VIB element of the periodic table and is a typical high melting point metal. Molybdenum has high melting point, high strength, high modulus of elasticity, small expansion coefficient, low vapor pressure, and excellent electrical and thermal conductivity. The important physical properties and high temperature mechanical properties of molybdenum are shown in Table 1 for the chemical properties of molybdenum. Molybdenum is a group VIB element of the periodic table, and the valence is 2.3.4.5.6. It is alkaline at low valence and acidic when it is high in valence. The hexavalent molybdenum compound is the most stable. Molybdenum does not react with hydrogen until the melting point. Hydrogen is the main reducing agent for molybdenum powder, and it is also a good protective gas for high-temperature processing of molybdenum.