What is hafnium and hafnium alloys?

Hafnium is a lustrous silver-gray transition metal having a density of 13.31g/cm³(20 °C), a melting point of 2233 °C (2506 K, 4051 °F) and a boiling point of 4603 °C (4876 K, 8317 °F). The dense metal hafnium is inactive and reacts with air to form an oxide coating, which is stable at room temperature, while the powdered hafnium is prone to spontaneous combustion in air.Hafnium does not react with dilute hydrochloric acid, dilute sulfuric acid, and strong alkali solutions, but is soluble in hydrofluoric acid and aqua regia.Hafnium is very small in the earth's crust and often coexists with zirconium.Hafnium has high temperature resistance, corrosion resistance, oxidation resistance, easy processing, fast heat absorption and heat release and other properties, is used as atomic materials, alloy materials, high temperature resistant materials, electronic materials, etc.

Hafnium is used in alloys with iron, titanium, niobium, tantalum, and other metals. An alloy used for liquid rocket thruster nozzles, for example 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. It improves thereby the 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