Titanium, a high-performance metal, exhibits superior resistance to pitting corrosion compared to stainless steel and aluminum alloys. However, with the increasing application of titanium in hot concentrated chloride solutions, incidents of pitting corrosion in titanium equipment are on the rise.
Pitting corrosion in titanium is less likely to occur compared to crevice corrosion, with the latter often leading to localized pitting corrosion on crevice surfaces.
Electrochemical techniques can determine the pitting corrosion potential of metals, aiding in evaluating their susceptibility to pitting corrosion.
Factors influencing titanium pitting corrosion
Sensitivity increases with temperature in chloride or bromide solutions.
pH has a minor impact on titanium's pitting corrosion resistance.
In chloride solutions, titanium's breakdown potential is approximately 8-10V, potentially lower in bromide or iodide solutions, increasing the likelihood of pitting corrosion.
Influence of iron content
Elevated iron content decreases titanium's resistance to pitting corrosion, with Ti-Fe phases often serving as nucleation sites for pitting corrosion.
Surface pre-treatment effects
Vacuum annealing and anodization enhance titanium's pitting corrosion potential, reducing susceptibility.
Wet sandpaper polishing increases the likelihood of pitting corrosion.
Other factors
Surface roughness and contact with certain metals like zinc, iron, aluminum, manganese, and copper promote pitting corrosion.
Certain anions such as sulfate, nitrate, chromate, phosphate, and carbonate ions enhance titanium's resistance to pitting corrosion.
Development Stages of Pitting Corrosion
Pitting corrosion typically progresses through nucleation, growth, and repassivation stages.
Nucleation occurs when the potential of titanium surpasses the breakdown potential of the oxide film.
Growth involves the observable enlargement of corrosion pits over time.
Repassivation can halt pitting corrosion development, sometimes preventing progression to the passivation stage and effectively stopping pit growth.
