Application of Mlolybdenum
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- Category: Molybdenum knowledge
- Published on 27 August 2014
- Written by jwy
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Alloys
About 86% of molybdenum produced is used in metallurgical applications such as alloys, with the rest of molybdenum used as compounds in chemical applications. Estimated fractional global industrial use of molybdenum is structural steel 35%, stainless steel 25%, chemicals 14%, tool & high-speed steels 9%, cast iron 6%, molybdenum elemental metal 6%, and superalloys, 5%.
The ability of molybdenum to withstand extreme temperatures without significantly expanding or softening makes it useful in applications that involve intense heat, including the manufacture of armor, aircraft parts, electrical contacts, industrial motors and filaments.
Most high-strength steel alloys (example 41xx steels) contain 0.25% to 8% molybdenum. Despite such small portions, more than 43,000 tonnes of molybdenum are used as an alloying agent each year in stainless steels, tool steels, cast irons and high-temperature superalloys.
Molybdenum is also used in steel alloys for its high corrosion resistance and weldability. Molybdenum contributes further corrosion resistance to "chrome-moly" type-300 stainless steels (high-chromium steels that are corrosion-resistant already due to their chromium content, but in reality "chrome-moly" is not a type-300 stainless, but instead a 41xx series that is not stainless) and especially so in the so-called superaustenitic stainless steels (such as alloy AL-6XN). Molybdenum acts by increasing lattice strain, thus increasing the energy required to dissolve out iron atoms from the surface.
Because of its lower density and more stable price, molybdenum is sometimes used instead of tungsten. An example is the 'M' series of high-speed steels such as M2, M4 and M42 as substitution for the 'T' steel series, which contain tungsten. Molybdenum can be implemented both as an alloying agent and as a flame-resistant coating for other metals. Although its melting point is 2,623 °C (4,753 °F), molybdenum rapidly oxidizes at temperatures above 760 °C (1,400 °F) making it better-suited for use in vacuum environments.
TZM (Mo (99%), Ti (0.5%), Zr (0.08%) and some C) is a corrosion-resisting molybdenum superalloy that resists molten fluoride salts at temperatures above 1300C. It has about twice the strength of pure Mo, and is more ductile and more weldable, yet in tests it resisted corrosion of a standard eutectic salt (FLiBe) and salt vapors used in molten salt reactors for 1100 hours with so little corrosion that it was difficult to measure.
Other molybdenum-based alloys that do not contain iron have only limited applications. For example, because of the corrosion resistance against molten zinc, both pure molybdenum and the molybdenum/tungsten alloy (70%/30%) are used for piping, stirrers and pump impellers which come into contact with molten zinc.
Other applications as the pure element
Molybdenum powder is used as a fertilizer for some plants, such as cauliflower.
Elemental molybdenum is also used in NO, NO2, NOx analyzers in power plants for pollution controls. At 350 °C (662 °F) the element acts as a catalyst for NO2/NOx to form only NO molecules for consistent readings by infrared light.
Molybdenum anodes replace tungsten in certain low voltage X-ray sources, for specialized uses such as mammography.
The radioactive isotope molybdenum-99 is used to generate technetium-99m, which is used for medical imaging.
Compounds (14% of global use)
Molybdenum disulfide (MoS2) is used as a solid lubricant and a high-pressure high-temperature (HPHT) antiwear agent. It forms strong films on metallic surfaces and is a common additive to HPHT greases — in the event of a catastrophic grease failure, a thin layer of molybdenum prevents contact of the lubricated parts. It also has semiconducting properties with distinct advantages over traditional silicon or graphene in electronics applications. MoS2 is also used as a catalyst in hydrocracking of petroleum fractions containing nitrogen, sulfur and oxygen.
Molybdenum disilicide (MoSi2) is an electrically conducting ceramic with primary use in heating elements operating at temperatures above 1500 °C in air.
Molybdenum trioxide (MoO3) is used as an adhesive between enamels and metals. Lead molybdate (wulfenite) co-precipitated with lead chromate and lead sulfate is a bright-orange pigment used with ceramics and plastics.
Ammonium heptamolybdate is used in biological staining procedures.
Molybdenum coated soda lime glass is used for CIGS solar cell fabrication.
Phosphomolybdic acid is a stain used in thin layer chromatography.
Molybdenum-99 is a parent radioisotope to the daughter radioisotope technetium-99m, which is used in many medical procedures. The isotope is handled and stored as the molybdate.
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