Molybdenum (Mo) is a silvery transition metal renowned for its exceptional corrosion resistance and extremely high melting point. It is also an important micronutrient like iron or magnesium. This article will not cover the biological properties of molybdenum nor its role in body functions. Instead, we aim to offer a comprehensive overview of the chemistry and thermodynamics of molybdenum in construction and engineering applications.

Chemical Properties of Molybdenum

Atomic Number 42
Atomic Mass 95.96
Density 10.22 g/cm3
Melting Point 2623°C
Coefficient of Thermal Expansion 4.8 x 10-6 / K at 25°C

Molybdenum lies in the second transition series of the periodic table and belongs to the refractory metals group. Refractories are typically characterized by their outstanding thermophysical properties, including a low coefficient of thermal expansion (CTE) and relatively high density. Distinguishable from the likes of tungsten (W) by its ductility, relatively low density, and unmatched CTE, molybdenum is often viewed as the most economical refractory for manufacturing applications.

Pure molybdenum can withstand a wide range of non-oxidizing acids and molten materials, but will rapidly corrode in the presence of alkalis and oxidizing materials. When exposed to air at temperatures greater than 760°C, for example, the oxide layer will sublime and the base metal will succumb to corrosion. Consequently, molybdenum works best in inert/vacuum environments, or as part of an alloy system.

Background of Molybdenum

Initially confused for a lead (Pb) compound, molybdenum was first identified in 1779 when it was isolated from the mineral molybdenite (MoS2). It was discovered that molybdenum does not occur as a free metal and is instead only found naturally in oxidation states from -II to +VI. Most commercial molybdenum available today is still extracted from molybdenite via oxidation roasting or nitric acid leaching. It can also be obtained from molybdenum trioxide (MoO3) and the lead molybdate wulfenite (PbMoO4).

H.C. Starck Solutions has been heavily invested in molybdenum manufacturing for years, devoting enormous resources to refining our product development pipelines and building a robust global supply chain. We are among the world’s leading suppliers of molybdenum alloy flats, sheets, tubes, and high-purity powders for emerging applications including additive manufacturing (AM).

Common Molybdenum Alloys

Titanium-Zirconium-Molybdenum (TZM)

We consolidate our TZM alloys by either powder metallurgy or vacuum arc-casting. The inclusion of 0.50% titanium and 0.08% zirconium leads to the formation of carbides which increases both strength and creep resistance at elevated temperatures. This enables the use of TZM at service temperatures that would typically yield a loss of strength in pure molybdenum counterparts, such as in rotating anodes for X-ray tubes.

Molybdenum-Hafnium-Carbide (MHC)

Our MHC alloys boast high recrystallization temperatures, excellent strength, and good all-around thermal properties. It is an ideal molybdenum alloy for forging applications.

Molybdenum-Lanthanum (MoLa)

Incorporating small volumes of lanthanum into a molybdenum alloy alters the overall microstructure, promoting greater stability at temperatures approaching 2000°C. Additionally, MoLa alloys exhibit exceptional formability compared to all grades of pure molybdenum. They are subsequently ideal for heating elements and other furnace components.

Molybdenum-Tungsten (Mo30W)

We supply arc-cast molybdenum-tungsten alloys based primarily on the composition with 30% tungsten by weight. This combines the attractive properties of each, yielding outstanding thermodynamic performance in the most challenging working environments. Our Mo30W alloys are widely used to stir rods, components for processing molten zinc, and more.

Interested in molybdenum alloys?

Contact a member of the H.C. Starck Solutions team today if you would like to learn more about the range of alloys and products that we routinely supply.