Molybdenum and molybdenum alloy Overview and Applications

Overview

Molybdenum is a chemical element with symbol Mo and atomic number 42. It is a silvery-white lustrous metal with reminiscent of tin. It has a density of 10.22 g/cm3 and is very much lighter when compared to tungsten, but with high boiling point of 5,560 °C and a melting point of 2,620 °C. Molybdenum does not occur naturally as a free metal on Earth, but rather in various oxidation states in minerals. It is a hard, tough and high-strength material with low degree of thermal expansion, low heat resistance, and superior thermal conductivity. These properties make it the right material for applications that require great heat protection and excellent thermal conductivity. Molybdenum is a silvery-white, hard, transition metal with a very high melting point, high level of thermal conductivity, high corrosion resistance and a low coefficient of thermal expansion. It does not visibly react with oxygen or water at room temperature. In nature, it does not occur as a free metal, but rather in various oxidation states in minerals. Owing to the diverse functions of molybdenum enzymes, molybdenum is also a required element for life in all higher organisms (eukaryotes). With its good performance, molybdenum is widely used in alloys, chemicals, electrical products, fertilizers, medical imaging and so on.

Molybdenum is used for making steel strong and corrosion-resistant and is required wherever steel faces tough, challenging conditions, such as offshore drilling rigs, power plants, ships, turbine engines, tools, hospital equipment and desalination plants. It plays an important role in environmental protection, since it is included in nuclear reactors and oil and gas pipelines to prevent leaks and as a catalyst in oil refining to reduce sulfur in fuels. Molybdenum is also valued as a special high-performance lubricant and is a component in flame retardants, fertilizers and even vitamin supplements. The silvery-white and pretty hard metal has the sixth highest melting point of all metals and is often used to create high-strength alloys and superalloys. When added to steel and cast irons, it improves strength, hardness and weldability, while also elevating temperature strength and corrosion resistance. As an addition to nickel-based alloys, it enhances resistance to corrosion and high-temperature deformation.

Because of its lower density and more stable price, molybdenum is sometimes used instead of 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.

Applications

Molybdenum is a valuable alloying agent in various steels, as it not only contributes to their toughness, but also improves the corrosion resistance and weldability of the steels. Approximately 80% of this metal is used in the production of various steels, such as structural steels, stainless steels, high-speed steels, tool steels and so on. Structural steels account for 35% of all molybdenum demand. Molybdenum is used in structural steels because of its corrosion resistance, strength and durability. Such steels are very useful in protecting metals against chloride corrosion, thus they are used in a wide range of marine environment applications, as well as oil and gas pipelines. Stainless steels, which value the metal's ability to strengthen and inhibit corrosion, consume about 25% of molybdenum supply.

Molybdenum in these steels can increase their hardness and resistance to wear and deformation at high temperatures. High-speed steels are used to produce cutting tools and drills, whereas superalloys are used to produce jet engines, turbo chargers and power generation turbines. Molybdenum is also used in certain nickel-based alloys because it can improve the strength of steel at high temperatures. When alloyed with nickel, molybdenum forms heat and corrosion-resistant materials used in the chemical industry.

Molybdenum is also used in medical field. For example, the radioactive isotope molybdenum-99 is used to generate technetium-99m, which is used for medical imaging. High-purity molybdenum metal is used in a range of applications from powder coatings to solar cells and flat panel display coatings. Because molybdenum has a high melting point, it is used to produce the electrodes of electrically heated glass furnaces. Some electrical filaments are also made from molybdenum.

Molybdenum alloys have excellent strength and mechanical stability at high temperatures (up to 1900°C). Their high ductility and toughness provide a greater tolerance for imperfections and brittle fracture than ceramics.

The unique properties of molybdenum alloys are utilised in many applications:

High temperature heating elements, radiation shields, extrusions, forging dies, etc;

Electrodes of glass melting furnace and components that are resistant to molten glass;

Heat sinks with thermal expansivity matching silicon for semiconductor chip mounts;

Sprayed coatings on automotive piston rings and machine components to reduce friction and improve wear.

For specialised applications, Mo is alloyed with many other metals:

Tungsten molybdenum alloys are noted for exceptional resistance to molten zinc;

Mo is clad with copper to provide electronic circuit boards of low expansion and high conductivity .