Tungsten, molybdenum and their alloys
In the periodic table, tungsten and molybdenum have silver gray luster on the surface of VIB group elements, and the powder is dark gray. Their commonness it is characterized by high melting point, strength and modulus of elasticity, small expansion coefficient, low vapor pressure, good conductivity and thermal conductivity, and superior corrosion resistance. Its disadvantages are low temperature embrittlement and high temperature oxidation.
Tungsten was discovered as early as the tenth century in China, which was called "heavy ore". In 1783, tungsten was made from a mixture of tungstic acid and carbon powder. At the end of the 19th century, tungsten was used as an additive of steel in metallurgical industry. Tungsten was used as filament in 1908. With the appearance of industrial production method of ductile tungsten, tungsten metal has been widely used in electrical industry. At present, tungsten and tungsten alloys are used in modern industries such as aerospace industry with plates, rods, wires and various shaped parts.
In the periodic table, tungsten and molybdenum have silver gray luster on the surface of VIB group elements, and the powder is dark gray. Their commonness it is characterized by high melting point, strength and modulus of elasticity, small expansion coefficient, low vapor pressure, good conductivity and thermal conductivity, and superior corrosion resistance. Its disadvantages are low temperature embrittlement and high temperature oxidation tungsten was discovered as early as the tenth century in China, which was called "heavy ore". In 1783, tungsten was made from a mixture of tungstic acid and carbon powder. At the end of the 19th century, tungsten was used as an additive of steel in metallurgical industry. Tungsten was used as filament in 1908. With the appearance of industrial production method of ductile tungsten, tungsten metal has been widely used in electrical industry. At present, tungsten and tungsten alloys are used in modern industries such as aerospace industry with plates, rods, wires and various shaped parts.
Molybdenum was found in 1778. Ten years later, molybdenum was obtained by reducing molybdic acid with carbon. At the beginning of the 19th century, more pure molybdenum was obtained by hydrogen reduction. Molybdenum was found to significantly improve the properties of steel in 1910. Since then, molybdenum has become the main addition element of various structural steels and corrosion-resistant steels. Molybdenum has good ductility, which makes it applied in electronic and electrical industry. At present, molybdenum and its alloys are being used in industrial and agricultural production, science and technology with plates, rods, wires and various special-shaped parts.
Molybdenum is mainly used as an additive of stainless steel, tool steel, low alloy steel and other steel. When molybdenum is added to the steel, the grain refinement, grain coarsening temperature and hardenability, toughness, high temperature strength and creep properties of the steel can be improved.
Because of its high melting point, good conductivity and thermal conductivity, molybdenum can be used as heating element and reflection screen material of high temperature furnace. The working temperature of the electric furnace with molybdenum as the heat generator can reach 1700 ° C, and the furnace has long service life and low cost. In the electronic and electrical industry, the cathode, grid, high-voltage rectifier components of the electronic tube and the conductor of the semiconductor film integrated circuit can be made; in the metal processing industry, the extrusion die, die-casting die and casting core can be made, and the piercing plug of the seamless steel pipe can be rolled (it has higher strength under the piercing temperature, and the oxide film is generated to play a lubricating role). Molybdenum alloy has high strength, excellent formability and specific strength. Under the protection of coating, it can be used to make nozzles, flame baffles and fins of attitude control engine. Due to its small thermal neutron absorption cross section, high endurance strength, stability to nuclear fuel and resistance to liquid metal corrosion, molybdenum and its alloys can be used as cladding materials and core structural materials for gas cooled reactors in the atomic energy industry. In addition, molybdenum can also be used to make chemical equipment, operating parts and structural parts in corrosion-resistant media, additives, carbonators and lubricants for coating materials, etc.
In the future, the research and development of tungsten, molybdenum and their alloys will focus on further improving high-temperature strength, recrystallization temperature, low-temperature plasticity and oxidation resistance, improving production technology, expanding varieties, reducing costs, and making them more widely used.
