Corrosion Resistance of Pure Titanium - Knowledge

Core Reason for the Excellent Corrosion Resistance of Pure Titanium

The primary reason for pure titanium's outstanding corrosion resistance lies in its spontaneous formation of a dense, adherent, and self-healing passive oxide film (primarily TiO₂) on its surface when exposed to air or an aqueous environment. This oxide layer is extremely thin (typically a few nanometers to tens of nanometers thick) and chemically inert, acting as an impenetrable barrier that prevents the underlying titanium metal from reacting with most corrosive media. Even if the film is damaged mechanically, it can rapidly regenerate in the presence of oxygen or moisture, restoring its protective function.

Can Pure Titanium Withstand Strong Acid and Strong Alkali Environments?

Pure titanium's performance in strong acid and strong alkali environments varies significantly depending on the type of reagent, concentration, temperature, and presence of impurities:

Strong acids

It exhibits excellent resistance to most cold dilute strong acids (e.g., dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid) because the passive film remains stable under these conditions.

However, in hot concentrated strong reducing acids (such as concentrated hydrochloric acid above 30% at high temperatures, boiling concentrated sulfuric acid), the passive film is prone to dissolution, leading to significant corrosion of pure titanium. Notably, pure titanium has exceptional stability in concentrated nitric acid (even at high temperatures) due to the enhanced passivation effect of nitrate ions.

Strong alkalis

Pure titanium has good corrosion resistance in cold dilute strong alkali solutions (e.g., dilute sodium hydroxide solution).

In hot concentrated strong alkali environments (e.g., concentrated NaOH or KOH solutions above 100°C), the passive oxide film reacts with hydroxide ions to form soluble titanates (e.g., Na₂TiO₃), resulting in severe intergranular corrosion or uniform corrosion of pure titanium, accompanied by the release of hydrogen gas that can cause hydrogen embrittlement of the metal.