Application and development of molybdenum

Molybdenum and tungsten as a refractory rare metals. Since the discovery of molybdenum by Swedish scientist CWSCHEELE in 1778 , after more than ten years of efforts, M. MOISSAN has used electric furnaces to produce metal molybdenum, making it the first time for humans to obtain such metals with many excellent physical and chemical properties. The melting point of molybdenum is 2620 °C Because of the strong bonding between atoms, the strength is high at both normal temperature and high temperature. It has a small expansion coefficient, a large electrical conductivity, and good thermal conductivity. It does not react with hydrochloric acid, hydrofluoric acid and alkali solution at room temperature, and is only soluble in nitric acid, aqua regia or concentrated sulfuric acid. It is also quite stable to most liquid metals, non-metal slag and molten glass. Therefore, molybdenum and its alloys have extensive applications and good prospects in important sectors such as metallurgy, agriculture, electrical, chemical, environmental protection and aerospace, and have become an important raw material and an irreplaceable strategic substance in the national economy.

Molybdenum has a small amount of reserves on the earth, and its content is only 0.001% of the weight of the earth's crust. The total reserves of molybdenum ore are about 15 million tons, mainly distributed in the United States, China, Chile, Russia, Canada and other countries. China has proven reserves of molybdenum metal of 1.72 million tons and basic reserves of 3.43 million tons, ranking second in the world after the United States. Molybdenum ore is concentrated in four provinces including Shaanxi, Henan, Jilin and Liaoning. There are six large-scale molybdenum mines with a metal reserve of more than 500,000 tons in the world. China's three rivers of Luanchuan, Jilin Daheshan and Shaanxi Jinduicheng are famous. The abundant molybdenum resources provide extremely favorable conditions and solid foundation for the development of molybdenum smelting and processing in China and the promotion of molybdenum application.

In recent years, the mining, smelting and processing of molybdenum in China has developed rapidly. According to the data, in 2001 China's actual production of molybdenum concentrate 72,000 tons, 33,000 tons of molybdenum oxide, ferromolybdenum 7600 tons, 9500 tons of various types of ammonium, molybdenum 1183 tons, molybdenum slab 1,200 tons, 150 tons of molybdenum sheet, molybdenum More than 40 tons of wafers , about 50 tons of molybdenum heads and other special-shaped products , electric light source industry and mechanical processing of molybdenum wire 3.15 billion meters, as well as hundreds of tons of chemical products such as lubricants, catalysts and pigments. Not only that, China has a pivotal position in the world molybdenum market. According to customs statistics, in 2001 China exported more than 70,274 tons of molybdenum ore, molybdate, ferromolybdenum and other molybdenum products , with a foreign exchange of US$ 262 million.

The consumption form of molybdenum is mainly industrial molybdenum trioxide, accounting for about 70% , ferromolybdenum accounts for about 20% , and metal molybdenum and molybdenum chemicals each account for 5% . Its application area and distribution ratio are as follows: steel smelting consumption accounts for about 80% (including alloy steel is about 43% , stainless steel is about 23% , tool steel and high-speed steel is about 8% , cast iron and rolls are about 6% ), chemical industry Products account for about 10% , metal molybdenum products account for about 6% , high-temperature high-strength alloys and special alloys account for about 3% , and other molybdenum products are about 1% . It can be seen from the above that the development of the steel industry plays a decisive role in the consumption of molybdenum, but with the development of science and technology, the application of molybdenum in high-tech and other fields will continue to expand and develop.

iron industry

According to the statistics of molybdenum consumption in various countries around the world, the application of molybdenum in the steel industry still occupies the most important position. As an alloying element of steel, molybdenum can improve the strength of steel, especially high temperature strength and toughness; improve the corrosion resistance of steel in acid-base solution and liquid metal; improve the wear resistance of steel and improve hardenability and weldability And heat resistance. Molybdenum is a good carbide-forming element that does not oxidize during steelmaking and can be used alone or in combination with other alloying elements. The molybdenum consumption of special steel is increasing regularly. At present, the molybdenum consumption per ton of special steel has reached 0.201 kg.

Molybdenum and chromium , nickel , manganese and silicon can be used to make different types of stainless steel, tool steel, high speed steel and alloy steel. The stainless steel produced has good corrosion resistance and can be used for corrosion-resistant steel pipes for oil exploitation. A stainless steel with about 6% molybdenum can also replace titanium for seawater desalination plants, ocean-going vessels, offshore oil and natural gas production pipelines. This type of stainless steel can also be used in automotive housings, sewage treatment equipment, and the like. Molybdenum-containing tool steels are twice as efficient as tungsten tools, with excellent performance, low cost and light weight. Molybdenum series high speed steel has the advantages of carbide non-uniformity, wear resistance, good toughness, high temperature and plasticity, and is suitable for manufacturing forming tools. Molybdenum-containing alloy steels can be used in the manufacture of machine tool structural components, industrial vehicles and dozers. The molybdenum-containing alloy steel having a fine pearlite structure in a rolled state is an important steel material in the construction of rails and bridges.

As an alloying additive of iron, molybdenum helps to form a complete pearlite matrix, improves the strength and toughness of cast iron, improves the uniformity of large casting structures, and improves the hardenability of heat-treated castings. The molybdenum-containing gray cast iron has good wear resistance and can be used as a brake wheel and brake pad for heavy vehicles.

Agricultural fertilizer

Molybdenum is one of the necessary "trace elements" in plants, accounting for about 0.5ppm of plant dry matter , which is indispensable and irreplaceable. In recent years, ammonium molybdate has been widely used as a trace element fertilizer at home and abroad, which can significantly improve the quality and yield of legumes, pastures and other crops. This is mainly because molybdenum promotes the fixation of nitrogen in the air by Rhizobium and other nitrogen-fixing organisms, and further converts nitrogen into proteins required by plants. Molybdenum also promotes the uptake of phosphorus by plants and their role in plants. Molybdenum can also accelerate the formation and transformation of sugars in plants, increase the content and stability of chlorophyll, and increase the content of vitamin C. Not only that, molybdenum can also improve the drought and cold resistance of plants and disease resistance.

The application of molybdenum fertilizer is characterized by low dosage, high efficiency and low cost, which is an important measure to improve agricultural harvest, especially for soybean harvest. The wide application of molybdenum in agriculture has also opened up a new way for the comprehensive utilization of wastewater, waste residue and low-grade ore in China's molybdenum production plants.

Electronic and electrical

Molybdenum has good electrical and high temperature properties, especially similar to the thermal expansion coefficient of glass. It is widely used in the manufacture of core wires, lead wires, hooks, brackets, side bars and other components of spiral filaments in bulbs. Pole and anode support materials. In a very large integrated circuit, molybdenum is used as a metal oxide semiconductor gate, and mounting an integrated circuit on molybdenum eliminates the "bimetallic effect." Ultra-thin seamless tube of molybdenum (about 15 μ m) as an anode holder high definition television picture tube, the television image of the scan line 1125, a two-fold increase than the average television. The molybdenum wafer can also be used as a substrate and heat sink for power transistor heat shields and silicon rectifiers.

In the modern electronics industry, in addition to pure molybdenum, Mo-Re alloy can be used as a structural material for electronic tubes and special bulbs. Mo-50Re and TZM alloys can also be used as thermo-ion cathode structural components in high-power microwave tubes and millimeter-wave tubes. Its working temperature can reach 1200 °C The current density can reach 10 amps / cm 2 . The pure molybdenum wire as the lead wire has a low recrystallization temperature and is prone to embrittlement at high temperature, which affects the service life. In recent years, it has been developed to add elements such as Si , k and C to increase the recrystallization temperature and produce "high temperature". Molybdenum wire". Take the rare earth element yttrium, cerium, lanthanum molybdenum oxide production process, etc., more effective to raise the recrystallization temperature, to overcome the problem of high temperature embrittlement material. Containing 0.1 - 0.3% zirconium, 0.1% scandium molybdenum wire, in 1200 °C Nitriding treatment, so that the cerium is dispersed into the entire alloy. 20 °C The tensile strength can reach 1400 megapascals.

The rapid development of the mold industry has made EDM technology widely used. Molybdenum wire is an ideal electrode wire for EDM machine tools. It can cut all kinds of steel and hard alloy, and process extremely complex parts. Stable, can effectively improve the accuracy of the mold.

The above are the two most widely used uses of molybdenum wire. The development of the light bulb manufacturing industry and the rise of the mold manufacturing industry have made the production and consumption of molybdenum wire soar. According to the statistics of the China Lighting Association, in 2001 , the national production of molybdenum wire reached 3.15 billion meters, the actual production is estimated to reach 4 billion meters, and nearly 800 tons of molybdenum strips are consumed , which is quite impressive. Among them, the production of molybdenum wire for wire cutting exceeds 2 billion meters, accounting for more than half of the total amount of molybdenum wire, and its market development prospects are very optimistic.

Tungsten - copper pseudoalloys are widely used in EDM tools. However, in recent years, the use of molybdenum instead of tungsten as an electrode has shown that the corrosion resistance of tungsten-based and molybdenum-based electrodes with copper (≤ 50% by weight) is Different. In the presence of heating pulses and mechanical load pulses, this corrosion resistance mainly depends on the brittle fracture process. The ductile - brittle transition temperature of molybdenum is lower than that of tungsten, so the brittleness is small and the corrosion resistance is strong. Molybdenum - copper, molybdenum - silver pseudoalloys have ablation resistance and good electrical conductivity and can be used as contacts for air switches, high voltage switches and contactors. The molybdenum - copper composite film entrains a large amount of discrete molybdenum particles on a continuous copper body, has a uniform microstructure, good thermal conductivity and electrical conductivity, and can be used as a metal core in a multilayer circuit board.

  Recently, molybdenum trioxide has also been developed which can change color under strong light and can be easily reduced, and can be used for electronic computer optical storage elements and copying materials for multiple uses.

  Car spraying

Molybdenum has a high melting point 2620 °C With good high temperature performance and corrosion resistance, molybdenum and steel have strong bonding strength, so it is the main thermal spraying material in the production of automobile parts. Auto parts are generally sprayed with high-speed flame of molybdenum wire. The gas mixing jet of the spray gun produces high-temperature gas combustion. The specially designed combustion chamber and gas jet mixing chamber allow the molybdenum wire to be sprayed on the surface of the workpiece at a very high speed before it is completely melted. Above, the density of sprayed molybdenum can reach more than 99% , and the bonding strength is close to 10 kg / mm 2 . This process effectively improves the wear resistance of the surface to be polished and also provides a porous surface that can be impregnated with lubricating oil. It is widely used in the automotive industry to improve the performance of piston rings, timing rings, shift forks and other abrasive components, as well as to repair worn crankshafts, rolls, shafts and other mechanical components. According to information on spraying molybdenum wire in the European market sales of up to 1,000 tons, consumption is also up to the United States each year about 600 tons of molybdenum wire Japan consumes 30 per year - 40 tons of spray molybdenum wire market capacity is still less than 30 tons per year. However, with the development of China's automobile industry, thermal spraying of automobile gears and other components will be greatly developed, and the sales volume of sprayed molybdenum wire will increase substantially.

High temperature component

The high purity, high temperature resistance and low vapor pressure of molybdenum make it often used to manufacture heating elements and structural materials for high temperature furnaces. In the production process of tungsten-molybdenum and cemented carbide, the reduction furnace and the sintering furnace are mostly made by molybdenum wire heating. Some iron products are continuously sintered and heated by molybdenum rods for heating. The molybdenum rod heating row is suspended by molybdenum hooks. On both sides of the stove. Such furnaces are generally in a reducing atmosphere or a non-oxidizing atmosphere. In hydrogen and decomposing ammonia, molybdenum wire can be used to near the melting point, and can be used in nitrogen gas. 2000 °C . Above 1700 °C When used, a TZM alloy or a molybdenum- niobium alloy having a higher recrystallization temperature and a higher strength can be used as the heating element. Molybdenum has good ablation resistance in molten quartz and is used as an energized molten electrode in the glass industry. It only loses per ton of glass molybdenum electrode. 7.8 grams The service life can be as long as more than one year. In addition to electrodes, molybdenum is also used as a glass melting high-temperature structural material, such as channels, tubes, crucibles, orifices, and stir bars for rare earth smelting. The use of molybdenum platinum on the fiberglass drawing furnace has a good effect, which greatly reduces the production cost. The newly developed nuclear fuel sintering furnace is heated by molybdenum mesh, using ф 0.8mm The molybdenum wire is woven into a three-phase mesh heater with an operating temperature of up to 1800 — 2000 °C . In addition, molybdenum and its alloys can also be used as hot isostatically pressed hobs, heat shields, sintered and steamed boats, SmCo magnets and uranium dioxide sintered mats, thermocouples and protective casings. Wait.

Molybdenum silicide ( MoSi2 ) is a widely used electrothermal element material with high temperature oxidation resistance, excellent corrosion resistance and high melting point. Oxidation resistance due to the formation of the glass film in the heating surface of the gas-impermeable, so that from oxygen, destruction of nitrogen, carbon monoxide and sulfur dioxide, in 1700 - the 2000ºK temperature, molybdenum disilicide heating may work two, three years . However, the inferior mechanical properties affect the application of molybdenum silicide. If SiC is added to the molybdenum silicide to form a composite material, the material disperses silicon carbide into the matrix of molybdenum disilicide to form a bimetallic compound containing molybdenum atoms and silicon atoms. Its high temperature strength is 8 times higher than that of molybdenum silicide monomer , which makes its application prospects popular.

   Oil exploitation

When developing acid natural gas, oil fields and developing submarine oil and gas fields in low-lying areas, not only a large amount of H2S gas is produced, but also seawater erosion, which makes the drilling pipelines vulcanized and brittle and rapidly corroded. The use of molybdenum-containing high-strength stainless steel pipe can effectively resist the corrosion of H2S gas and seawater, greatly save steel and reduce the drilling cost of oil and gas wells.

Molybdenum can not only be used in oil and gas field drilling pipelines, but also often cooperates with drilling and nickel in petroleum refining pretreatment catalysts, mainly petroleum, petrochemical products and liquefied coal desulfurization. During the hydrogen treatment, the sulfide reacts with hydrogen on the surface of the catalyst, and the sulfur ions are removed in the form of hydrogen sulfide, while eliminating nitrogen and metal impurities in the crude oil to reduce the poisoning of these impurities to other catalysts during petroleum refining. Thereby improving the color, odor and stability of the product. Molybdenum catalyst deactivation residual layer of carbon on the surface thereof, if the burned carbon layer, the catalyst can resume its active state, can be life 1-- about 5 years. Molybdenum plays an important role in petroleum cracking and reforming and is an ideal electron donor and carrier.

Environmental protection

It is becoming more and more clear that molybdenum plays an important role in controlling environmental pollution. The large application of molybdenum-containing stainless steel greatly reduces the environmental impact caused by corrosion; in addition, molybdenum and its compounds are mostly non-toxic, utilizing The safer molybdenum replaces toxic metals and is also a major contribution of molybdenum to human environmental protection. In the paint and pigment industry can replace toxic chromium molybdenum, lead, titanium and other metals, and is highly effective colorant; may be substituted in the chemical industry and preservatives chromium flame retardants, smoke was antimony; molybdenum There is also potential in applications in the water treatment industry, mainly for the suppression of corrosion in the treatment of cooling water in open circuit and closed circuit cooling systems. In the open circuit cooling tower, the sodium dimolybdate content per liter of coolant is 10 mg, while closed circuit The cooling water air conditioning unit can reach 150 mg per liter , and the amount of sodium molybdate used as an antifreeze and cooling system for automobiles and preservatives in cutting fluids is also increasing. It has also been suggested that molybdenum can improve vitrified soils, simplify the treatment of highly polluted soils, and reduce soil pollution.

Aviation and nuclear industry

Due to its excellent heat resistance and high temperature mechanical properties, molybdenum alloys can be used as flame guides and combustion chambers for aircraft engines, hoses, nozzles and valves for spacecraft liquid rocket engines, returning to the ends of aircraft, satellites and spacecraft. The skin, the wing and the guide sheet and the protective coating material, the molybdenum has a low thermal expansion coefficient and good thermal conductivity, and the dimensional stability is particularly good under the strong action of the solar radiation. The metal molybdenum mesh is used as the satellite antenna to maintain its The shape of the complete parabola is lighter than the graphite composite antenna. Cruise missiles use molybdenum-coated materials as turbine rotors, 1300 °C High temperature, the speed per minute up to 4 - 6 million transfer, has shown good results.

Molybdenum has a small neutron absorption cross section, good strength, good stability to nuclear fuel, good corrosion resistance to liquid metal, and a protective sheet for converter armor components in nuclear fusion reactors. Mo-Re alloys can be used in thermal ion energy converter jacket materials, heaters, reflectors and other wire or sheet components for space nuclear reactors.

Molybdenum alloys and other molybdenum alloys are highly efficient and versatile alloying elements that not only add unique features to steel, but also produce alloys with excellent properties for a variety of non-ferrous metals.

An oxide or carbide of Ti , Zr , or C is added to molybdenum to form a dispersion strengthened alloy TZM . In addition to the aerospace and nuclear industries, TZM alloys can also be used as X -ray rotating anode parts, die-casting molds and extrusion dies. When squeezing copper-based alloys, the operating temperature can be 870 . 1200 °C . TZM alloy is also very suitable for stainless steel hot piercing head. The inner wall of perforated steel pipe has good quality and long service life. The TEM alloy with a small amount of rare earth element has a higher recrystallization temperature, and the ductility during recrystallization is 5 times higher than that of the ordinary molybdenum material , and has a good application prospect.

Molybdenum alloys containing titanium, zirconium and carbon (MT-104), a molybdenum alloy (HCM) and carbon and hafnium-containing molybdenum alloy (HMW) tungsten, hafnium and carbon have high strength, be processed into bars, Plates, forgings and other products are of great use. Mo-30w is a solid solution alloy with a melting point of 2800 °C In the above, in the zinc smelting, it is used as a molten metal pump valve and a shaft, a nuclear fuel purification and electroplating equipment pipeline, a stirring shaft, and an impeller pump. Adding a certain amount of molybdenum to the tungsten high specific gravity alloy ( 90W-7Ni-3Fe ), its strength and hardness are increased with the molybdenum content, and its ductility is continuously reduced, which can greatly improve the performance of the material as an armor-piercing weapon.

Molybdenum carbide ( Mo 2C Mixing with tungsten carbide, adding appropriate niobium powder, sintering into a hard material, adding a certain amount of nickel after coarse crushing, using the usual method of hard alloy production, the binder phase distribution is good, compact and refined. Molybdenum carbide based cemented carbide. The metal binder phase uses Co or Ni , and can also form complex molybdenum-tungsten carbide-based cemented carbide. Molybdenum carbide can also be added to the cermet to improve its performance.

Molybdenum chemical products

Molybdenum and chromium and aluminum salts can be co-deposited to form molybdenum chrome red pigment. Molybdate ions form insoluble Fe2(MoO4)3 with iron ions on the metal surface, thereby passivating the metal surface and achieving anti-rust effect. Its color change from light to light red, with strong coverage and bright colors, mainly used in coatings, plastics, rubber, ink, automotive and marine coatings. Zinc, calcium and sodium molybdates are used as anti-corrosive pigments and are generally receiving attention because they do not contain lead which affects the environment and human health.

Molybdenum disulfide ( MoS2 ) is a good solid lubricant that plays an important role in industrial applications. It has a very low coefficient of friction ( 0.03 - 0.06 ), a high yield strength ( 3.45MPa ), and can be used at high temperatures ( 350 °C ) and use in a variety of ultra-low temperature conditions, even under vacuum conditions 1200 °C Normal operation, especially in high-speed mechanical parts, has very good lubrication. It is therefore widely used in steam turbines, gas turbines, metal rolls, gear teeth, molds, automobiles and aerospace equipment.

After decades of hard work, China's molybdenum mining, smelting and processing technology has made great progress. The application and promotion of molybdenum has also achieved gratifying results, but we still feel insufficient compared with the world advanced level. We should make full use of the advantages of China's molybdenum resources, establish a reasonable production layout from mining, smelting and processing, and vigorously carry out deep processing of molybdenum products. Establish a production and research team with high technical literacy, vigorously promote the application of new equipment and new technologies, strengthen research and new product development of molybdenum, especially strengthen the application research of molybdenum, expand market capacity, and concentrate on research institutes and The technical strength of production enterprises, the establishment of specialized institutions, quickly transform scientific research results into productivity, guide market consumption, expand foreign trade exports, and make China a truly large molybdenum producing country, a major consumer and a major exporting country.

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