The applications of molybdenum in powder metallurgy and chemistry


The applications of molybdenum in powder metallurgy

The metal molybdenum is generally produced with the technology of powder metallurgy. The molybdenum powder is pressed into green by hydrostatic pressure and is sintered in about 2,100 degrees celsius. It is under thermal processing in the range of 870~1260 degrees celsius. Molybdenum will form the volatile oxides in about more than 600 degrees celsius when heated, so its advanced application is limited in the environment of non-oxidation and vacuum. The alloys of molybdenum have good strength and mechanical stability when the temperature reaches 1900 degrees celsius. Due to their high ductility and toughness, their tolerance of defects and brittle rupture are higher than ceramic.

Molybdenum improves the corrosion resistance of stainless steel and it also can enhance the corrosion resistance and mechanical property of nickel-base alloys. Many nickel-base alloys which contain high content of molybdenum and have strong corrosion resistance are widely used in many fields. Molybdenum is a very effective matrix enhancer in the super alloy which can make jet engine become a reality. When the content of molybdenum reaches 5 percent, it can intensify the nickel substrate and expand its work by using precipitated phase and setting apart the nickel base and γ. These alloys are widely used in rotating components, such as turbine disc of turbine bucket and jet engine. High molybdenum alloy, such as x-alloy (contains 9 percent of molybdenum) is applied in many stationary combustion components. The current super alloy occupies more than 1/3 weight of the jet engines. Stellite21, a kind of cobalt-based alloy investment casting containing 5 percent molybdenum, has good corrosion resistance to liquid and is widely used in making artificial limbs.

The chemical application of molybdenum

Molybdenum base chemicals have various properties which can transform in the oxidation state of 4, 5 and 6. The materials made by molybdate including the oxidation catalysts, have light sensitivity and semiconducting properties. Through the study of molybdenum chemical property, many properties of molybdenum can provide opportunities of development and new industrial applications for it. Molybdenum compound often can be used as a safe alternative to toxic elements.

Molybdenum based catalyst has a wide application. It can be used in the oil industry when combined with cobalt and nickel as it can wipe off the sulphide of the organosulphide compounds that usually exists in the crude oil. Due to further expansion of world crude oil supply and the decrease of sweet crude, the application of molybdenum based catalyst will be increased. When the molybdenum catalysts are associated with sulphide, it can transform the hydrogen and carbon monoxide which are generated by the high decomposition of waste into alcohol. Otherwise it can cause the poisoning of noble metal catalysts. Molybdenum can also convert the coals into liquid state. Molybdenum can not only be used as the economic fuel refining, but also makes contribution to provide a safe environment for us as its row of sulphur content is little. Being a composition of selective oxidation catalyst, molybdenum can convert propylene, ammonia water and air into acrylonitrile, acetonitrile and other chemicals. These materials are important for the industries of plastic and textile.

Molybdenum disulfide is the most common natural form of molybdenum which can be directly used as the lubricants after the extraction and purification from the minerals. Because of the layered structure of molybdenum disulfide, it is a kind of very effective lubricant. These hierarchies can slide against each other and allow them to flow freely on the surface of steel and other metals. They work the same even under pressure, such as the bearing surface. As molybdenum disulfide is formed by geothermal heat, it has chemical stability under hot pressing. A small content of sulphide can react with iron and form a sulphide layer which is compatible with molybdenum disulfide and can keep lubricating film. Molybdenum disulfide has inertness with many chemicals and can complete its lubrication action under vacuum. However, the graphite cannot do that.