Titanium is the ninth most abundant element in the Earth’s crust, yet it sells for roughly thirty times the price of structural steel. The scarcity is not geological. It is thermodynamic. Titanium bonds to oxygen with extraordinary enthusiasm. That is what makes it corrosion resistant in service, and what makes it agonising to extract. Iron oxide surrenders its oxygen to carbon in a blast furnace, which is why steel is cheap. Titanium dioxide does not. Carbon simply forms titanium carbide, and any oxygen left dissolved in the lattice embrittles the metal at concentrations measured in hundreds of parts per million. So the ore takes a detour through chlorine. The Kroll process, unchanged in its essentials since 1940: - Rutile or ilmenite is reacted with coke and chlorine gas at around 1000 degrees Celsius, producing titanium tetrachloride, a volatile liquid - The tetrachloride is fractionally distilled to remove iron, vanadium and silicon chlorides, reaching purity beyond 99.9 percent...