Iron and steel 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 the strength and toughness of high temperature, improve the corrosion resistance of steel in acid-base solution and liquid metal, improve the wear resistance of steel and improve hardenability, weldability and heat resistance. Molybdenum is a good carbide-forming element that does not oxidize in the steelmaking process and can be used alone or in combination with other alloying elements. The consumption of molybdenum in special steel is increasing regularly, and the consumption of molybdenum per ton of special steel has reached the level of 0.201 kg.
Molybdenum is used in different types of stainless steels, tool steels, high-speed steels, and alloy steels along with chromium, nickel, manganese, and silicon. The stainless steel made of stainless steel has good corrosion resistance, which can be used for corrosion-resistant steel pipes for oil exploitation, and a stainless steel with molybdenum about 6% can also replace titanium for seawater desalination devices.
Ocean-going vessels, offshore oil and gas pipelines. This type of stainless steel can also be used in automotive housings, sewage treatment equipment, etc. Molybdenum-containing tool steels are twice as efficient as tungsten tools, with excellent performance, low cost and low weight. Molybdenum series high-speed steel has the advantages of carbide inhomogeneity, wear resistance, good toughness, and strong plasticity at high temperature, and is suitable for manufacturing forming tools. Molybdenum-containing alloy steels are used in the manufacture of structural components for machine tools, industrial vehicles, and bulldozing equipment. Molybdenum-containing alloy steel with fine pearlite structure in the rolled state is an important steel in the construction of rails and bridges.
Molybdenum, as an alloy additive for iron, helps to form a completely pearlite matrix, which can improve the strength and toughness of cast iron, improve the uniformity of the microstructure of large castings, and also improve the quenchability of heat-treated castings. Molybdenum-containing gray cast iron has good wear resistance, and can be used as brake wheels and brake pads for heavy vehicles.
Agricultural fertilizer: molybdenum is one of the necessary "trace elements" in the plant, 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 leguminous plants, forages and other crops. This is mainly due to the fact that molybdenum promotes the fixation of nitrogen in the air by rhizobia and other nitrogen-fixing organisms, and further converts nitrogen into proteins required by plants. Molybdenum also promotes the absorption of phosphorus by plants and exerts its effects in plants. Molybdenum can also accelerate the formation and transformation of carbohydrates in plants, improve the content and stability of plant 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, large effect and low cost, which is an important measure to improve agricultural harvest, especially 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 molybdenum production plants in China. Electronic and electrical molybdenum has good electrical conductivity and high temperature properties, especially the thermal expansion coefficient of glass is very similar, and is widely used in the manufacture of the core wire, lead wire, hook, bracket, side rod and other components of spiral filament in light bulbs, and as gate and anode support materials in electron tubes. In very large integrated circuits, molybdenum is used as a metal oxide semiconductor gate, and the "bimetallic effect" can be eliminated by mounting the integrated circuit on molybdenum. The ultra-thin seamless molybdenum tube (about 15 μm) can be used as an anode holder for the picture tube of high-definition televisions, which have 1,125 image scanning lines, which is twice as high as that of ordinary televisions. Molybdenum discs can also be used as substrates and heat sinks for power transistor heat shields and silicon rectifiers.
In addition to the use of pure molybdenum in the modern electronics industry, Mo-Re alloy can be used as the structural material of electron tubes and special bulbs, and Mo-50Re and TZM alloy can also be used as a thermionic cathode structural element in high-power microwave tubes and millimeter wave tubes, with an operating temperature of up to 1200°C and a current density of up to 10 amperes/cm2. In recent years, some people have developed the addition of elements such as Si, k and C to increase the recrystallization temperature and produce "high-temperature molybdenum wire". The addition of rare earth elements yttrium, cerium and lanthanum in the production process of molybdenum oxide can effectively increase the recrystallization temperature and overcome the problem of high-temperature embrittlement of materials. Molybdenum wire containing 0.1-0.3% zirconium and 0.1% scandium is nitrided at 1200 °C to diffuse the scandium into the entire alloy, and the tensile strength of this molybdenum wire can reach 1400 million Pascal at 20 °C.
The rapid development of the mold industry, so that the EDM technology has been widely used, molybdenum wire is the ideal EDM wire cutting machine tool electrode wire, can cut a variety of steel and cemented carbide, processing extremely complex shape of parts, its EDM stability, can effectively improve the accuracy of the mold. The above are the two most widely used molybdenum wires, the development of the bulb manufacturing industry and the rise of the mold manufacturing industry by leaps and bounds. According to the statistics of China Lighting Association, in 2001, the national production of molybdenum wire reached 3.15 billion meters, and the actual output was estimated to reach 4 billion meters, consuming nearly 800 tons of molybdenum bars, which is very considerable. Among them, the output 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 tool electrodes, but in recent years, research has been carried out on the use of molybdenum instead of tungsten as electrodes, and the results show that the corrosion resistance of tungsten-based and molybdenum-based electrodes is different with the content of copper (≤ 50% by weight). In the presence of heating pulses and mechanical load pulses, this corrosion resistance mainly depends on the brittleness process, and the ductile-brittle transition temperature of molybdenum is lower than that of tungsten, so the brittleness is small and the corrosion resistance is stronger. Molybdenum-copper, molybdenum-silver pseudoalloys are resistant to ablation and have 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 number of discrete molybdenum particles on the continuous copper body, has uniform microstructure, good thermal conductivity and conductivity, and can be used as a metal core in multilayer circuit boards.
Recently, we have also developed color-changing molybdenum trioxide, which changes color under strong light and can be easily restored, and can be used in optical memory elements of electronic computers and multi-use photocopying materials.
Automotive spraying
Molybdenum has a melting point of up to 2620 °C, and has good high temperature performance and corrosion resistance, and molybdenum has strong binding force with steel, so it is the main thermal spraying material in the production of automotive parts. Automobile parts generally use molybdenum wire high-speed flame spraying, the gas mixing injection device of the spray gun produces high-temperature gas combustion, and the specially designed combustion chamber and gas injection mixing chamber make the molybdenum wire sprayed on the surface of the workpiece at a very high speed before it is completely melted, and the density of the sprayed molybdenum can reach more than 99%, and the bonding strength is close to 10 kg/mm2. This process effectively improves the wear resistance of the abrasion surface 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, synchronizer rings, forks and other worn components, as well as to repair worn crankshafts, rolls, shafts and other mechanical components. According to the data, the annual sales volume of sprayed molybdenum wire in the European market can reach 1,000 tons, the annual consumption of the United States is also about 600 tons, Japan also consumes 30-40 tons of molybdenum wire every year, and the market capacity of sprayed molybdenum wire in China is still less than 30 tons per year. However, with the development of China's automobile industry, the thermal spraying of automobile gears and other parts will have a great development, and the sales volume of sprayed molybdenum wire will increase significantly.
High-temperature elements
Molybdenum's high purity, high temperature resistance, and low vapor pressure make it often used to make heating elements and structural materials for high-temperature furnaces. In the production process of tungsten molybdenum and cemented carbide, molybdenum wire heating is mostly used to make reduction furnace and sintering furnace, and molybdenum rod heating is used as a heating element for continuous sintering of some iron products, and molybdenum rod heating row is suspended on both sides of the furnace with molybdenum hooks. This type of furnace is generally a reducing atmosphere or a non-oxidizing atmosphere, and molybdenum wire can be used to close to the melting point in hydrogen and decomposed ammonia, and up to 2000°C in nitrogen. When used above 1700°C, TZM alloy or molybdenum lanthanum alloy with higher recrystallization temperature and better 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, with only 7.8 grams lost per ton of glass molybdenum electrode produced, and the service life can be as long as more than a year. In addition to being used as an electrode, molybdenum is also used as a high-temperature structural material for glass melting, such as guide troughs, tubes, crucibles, spouts, and stirring rods for rare earth smelting. The use of molybdenum instead of platinum in the glass fiber drawing furnace has a good effect, which greatly reduces the production cost. The newly developed nuclear fuel sintering furnace is heated by molybdenum mesh, and the three-phase mesh heater is woven into a three-phase mesh heater with 0.8mm molybdenum wire, and the working temperature can reach 1800-2000 °C. In addition, molybdenum and its alloys can also be used as hot isostatic pressing furnaces, heat shields, sintered and steam-coated boats, SmCo magnets and uranium dioxide sintering pads, thermocouples and their protective sleeves, etc.