What is Hafnium and Hafnium Alloys?

Hafnium is a lustrous silver-gray transition metal with a density of 13.31 g/cm³ (at 20°C), a melting point of 2233°C, and a boiling point of 4603°C. The dense metal is chemically inactive and reacts with air to form a stable oxide coating at room temperature, while powdered hafnium is prone to spontaneous combustion in air. Hafnium does not react with dilute hydrochloric acid, dilute sulfuric acid, or strong alkali solutions, but is soluble in hydrofluoric acid and aqua regia.

Hafnium is very rare in the earth’s crust and commonly coexists with zirconium. It has high temperature resistance, corrosion resistance, oxidation resistance, easy processing characteristics, and fast heat absorption and release properties. These qualities make it suitable for use as an atomic material, alloy material, high-temperature resistant material, and electronic material.

Hafnium is used in alloys with iron, titanium, niobium, tantalum, and other metals. One well-known alloy used for liquid rocket thruster nozzles — including the main engine of the Apollo Lunar Modules — is C103, which consists of 89% niobium, 10% hafnium, and 1% titanium. Small additions of hafnium increase the adherence of protective oxide scales on nickel-based alloys, improving corrosion resistance especially under cyclic temperature conditions that tend to break oxide scales by inducing thermal stresses between the bulk material and the oxide layer.