Titanium is a metal widely recognized for its strength and remarkable resistance to corrosion. While generally considered unreactive, its behavior can change under specific conditions.
Titanium’s Natural Protection: The Passive Layer
Titanium’s reputation for being unreactive stems from its ability to form a thin, protective surface layer. When exposed to air or water, it immediately reacts with oxygen to create a durable film of titanium dioxide (TiO2). This layer acts as a physical barrier, shielding the underlying metal from further chemical interaction.
This protective film is passive. An important characteristic of this layer is its self-healing property. If the surface is scratched or damaged, the oxide film rapidly reforms, reinstating the metal’s exceptional corrosion resistance. This makes titanium particularly resilient in various environments, including those containing chlorides or even in the human body.
When Titanium Does React: Specific Conditions and Substances
While highly resistant, titanium can react under specific, often extreme conditions that overcome its passive layer. Strong acids, particularly hot and concentrated varieties, can corrode titanium. For instance, hot hydrochloric and hydrofluoric acids react with titanium, forming complexes and releasing hydrogen gas. Concentrated sulfuric acid at elevated temperatures (above 80°C) can also cause significant corrosion.
Halogens, such as fluorine, chlorine, bromine, and iodine, react vigorously with titanium when heated. These reactions typically form titanium halides, like titanium(IV) fluoride (TiF4) or titanium(IV) chloride (TiCl4). The severity of these reactions depends on the specific halogen and the temperature involved.
At very high temperatures, titanium also reacts with common atmospheric gases. It combines with oxygen to form additional titanium dioxide, and with nitrogen to produce titanium nitride, which can embrittle the metal. Hydrogen can also be absorbed at elevated temperatures, leading to the formation of hydrides that may compromise titanium’s mechanical properties. Molten metals, such as aluminum or certain alloys, can interact with titanium at high temperatures, forming intermetallic compounds.
Practical Implications: Titanium’s Uses and Safety
Titanium’s reactivity profile, characterized by inertness under normal conditions but reactivity under specific extremes, dictates its wide range of applications. Its resistance to corrosion makes it a preferred material for medical implants, such as hip and dental implants, where it is well-tolerated by the human body. The metal’s combination of strength, light weight, and corrosion resistance also makes it valuable in aerospace components, including aircraft frames and engine parts.
In marine environments, titanium’s immunity to seawater corrosion makes it suitable for use in ships, submarines, and offshore platforms. The chemical processing industry also benefits from titanium’s resilience, employing it in heat exchangers, vessels, pipes, and pumps that handle corrosive chemicals.
Understanding titanium’s reactivity under extreme conditions is important for safe handling, particularly in industrial settings. While solid titanium is generally stable, fine titanium powder or dust is flammable and can be spontaneously combustible. If ignited, water should not be used to extinguish titanium fires, as it can react violently with burning or molten titanium, potentially causing explosions. This hazard primarily concerns industrial processes involving finely divided titanium, rather than everyday use of the solid metal.