Zirconium

Zirconium is an expensive and fairly reactive metal that is similar to hafnium, which is below it on the Periodic Table. A self-healing oxide film forms readily on the surface of zirconium in environments with available oxygen; this film protects against corrosion and wear. Zirconium is generally resistant to water and water vapor at regular and higher temperatures, although prolonged exposure to hot water may lead to rapid corrosion of the metal. It is also resistant to salt solutions, seawater, and polluted water. More specifically, zirconium is resistant to uniform, pitting and crevice corrosion in seawater.

Zirconium is also resistant to many acids and bases, including most mineral and organic acids and strong alkalis. Specifically, it is resistant to hydrochloric, nitric, acetic, formic, citric, lactic, and tannic acids, among others. Zirconium is susceptible to hydrofluoric acid, chromic acid and strong hydrochloric and sulfuric acids at higher temperatures. Its resistance to alkalis remains, even at higher temperatures, and has only a moderate corrosion rate when exposed to fused alkalis and liquid sodium.

Ferric chloride (FeCl3) and cupric chloride (CuCl2) environments will often cause pitting to occur on the surface of zirconium, but it is resistant to some molten salts. In general, zirconium is resistant to oxidizers in the absence of halides, but it is susceptible to corrosion, for example, in a humidified chlorine gas. A further threat to zirconium is hydrogen embrittlement.

Impurities in the composition influence the corrosion resistance of zirconium. For example, impurities such as nitrogen, aluminum, titanium, and dissolved ferric and cupric chlorides) degrade the resistance of zirconium to water and steam. Nuclear grades of zirconium do not contain hafnium and have better corrosion resistance in water at higher temperatures.