Molybdenum:

• Is a naturally occurring element identified in 1778 by Carl Wilhelm Scheele, the Swedish scientist who also discovered oxygen in air.
• Has one of the highest melting points of all the elements yet its density is only 25% greater iron.
• Is contained in various ores, but only molybdenite (MoS2) is used in the production of marketable molybdenum products.
• Has the lowest coefficient of thermal expansion of any engineering material.

Where does it come from:

• The principal molybdenum mines are found in Canada, USA, Mexico, Peru and Chile. In 2008, the ore reserve base totalled 19,000,000 tonnes (source: US Geological Survey). China has the largest reserves followed by USA and Chile.
• Molybdenite can occur as the sole mineralisation in an ore body, but is often associated with the sulfide minerals of other metals, notably copper.

How is it processed:

• The mined ore is crushed, ground, mixed with a liquid and aerated in a flotation process to separate the metallic minerals from the rock.
• The resulting concentrate contains between 85% and 92% industrially useable molybdenum disulfide (MoS2). Roasting this in air at 500 to 650 °C produces roasted molybdenite concentrate or RMC (Mo03), also known as technical Mo oxide or tech oxide. Some 40 to 50% of molybdenum is used in this form, mainly as an alloying element in steel products.
• 30-40% of RMC production is processed into ferromolybdenum (FeMo) by mixing it with iron oxide and reducing with ferrosilicon and aluminium in a thermite reaction. The resulting ingots are crushed and screened to produce the desired FeMo particle size.
• About 20% of the RMC produced worldwide is processed into a number of chemical products such as pure molybdic oxide (Mo03) and molybdates. Ammonium molybdate solution can be converted to any number of molybdate products and further processing by calcinations produces pure molybdenum trioxide.
• Molybdenum metal is produced by a two-stage hydrogen reduction process to give pure molybdenum powder.

What is it used for:

• About 20% of new molybdenum, produced from mined ore is used to make molybdenum-grade stainless steel.
• Engineering steels, tool and high speed steel, cast iron and superalloys collectively account for an additional 60% of molybdenum use.
• The remaining 20% is used in upgraded products like lubricant grade molybdenum disulfide (MoS2), molybdenum chemical compounds and molybdenum metal.

Material benefits and uses:

Stainless steel

• Molybdenum improves the corrosion resistance and high temperature strength of all stainless steels. It has a particularly strong positive effect on pitting and crevice corrosion resistance in chloride-containing solutions, making it essential in chemical and other processing applications.
• Molybdenum-containing stainless steels are exceptionally resistant to corrosion and are commonly used in architecture, building and construction, giving great design flexibility and extended design lives.
• A wide range of products are manufactured from molybdenum-containing stainless steel for increased protection against corrosion, including structural components, roofing, curtain walls, handrails, swimming pool liners, doors, light fitments and sunscreens.

Superalloys

These comprise of corrosion resistant alloys and high temperature alloys:

• Corrosion resistant nickel-based alloys containing molybdenum are used in applications exposed to highly corrosive environments in a wide range of process industries and applications, including the flue gas desulfurization units used to remove sulfur from power station emissions.
• High temperature alloys are either solid-solution strengthened, which provide resistance to damage caused by high temperature creep, or age-hardenable, which provide additional strength without significantly reducing ductility and are very effective in reducing the coefficient of thermal expansion.

Alloy steels

• Just a small amount of molybdenum improves hardenability, reduces temper embrittlement and boosts resistance to hydrogen attack and sulfide stress cracking.
• The added molybdenum also increases elevated temperature strength and improves weldability, especially in high strength low alloy (HSLA) steels. These high performance steels are used in a variety of applications, from lightweighting cars to improved efficiency in buildings, pipelines and bridges, saving both the quantity of steel required and the energy and emissions associated with its production, transportation and fabrication.

Other uses

Specialized examples of molybdenum uses include:

• Molybdenum-based alloys, which have excellent strength and mechanical stability at high temperatures (up to 1900°C) in non-oxidizing or vacuum environments. Their high ductility and toughness provide a greater tolerance for imperfections and brittle fracture than ceramics.
• Molybdenum-tungsten alloys, noted for exceptional resistance to molten zinc
• Molybdenum-25% rhenium alloys, used for rocket engine components and liquid metal heat exchangers which must be ductile at room temperature
• Molybdenum clad with copper, for making low expansion, high conductivity electronic circuit boards
• Molybdenum oxide, used in the production of catalysts for the petrochemical and chemical industries, widely deployed in the refining of crude oil to reduce the sulphur content of refined products
• Chemical molybdenum products used in polymer compounding, corrosion inhibitors and high-performance lubricant formulations