Solution Chemistry inside Crevice for Stainless Steel

The relationship between pH and concentrations of CrCl₃ and FeCl₂ were measured. For CrCl₃ solutions, pH values after 500h were adopted, because it took more than 2 weeks to reach the equilibrium conditions. It was found that pH value inside crevice for stainless steel was controlled by the equilibrium of Cr³⁺+H₂O-> Cr(OH)²⁺+H⁺ in diluted solution. In concentrated solutions of CrCl₃ and FeCl₂, complex ions of CrCl²⁺ and FeCl⁺ is formed. The equilibrium constant values were determined for formations of these complex ions - Cr³⁺+Cl^--> CrCl²⁺ and Fe²⁺+Cl^--> FeCl⁺. And it was also found that pH value decreased extremely with increasing concentrations of solutions, because the activity coefficient of H⁺ increases extremely with increasing concentrations of solutions. The calculation model to simulate solution chemistry in crevice corrosion  for stainless steel immersed in NaCl solution was studied by using mass transfer model and considering formation of complex ions.