Use of colour change indicators to quantify iron contamination on stainless steel

Abstract

The iron contamination on stainless steels was evaluated based on a quantification of colour change after colour reaction of indicators, and the roles of phenanthroline and ferroxyl solutions as colour change indicators were compared during the quantification. The results showed that the sensitivity and the solution stability of phenanthroline solution were superior to the ferroxyl solution. The redness degree using the phenanthroline solution increased with increasing iron contamination, but decreased with increasing Cr content of stainless steels. The potentiodynamic polarisation curves showed that iron contamination deteriorated the local corrosion resistance of stainless steel. The measured values of redness degree have a linear relationship with the breakdown potentials obtained from the polarisation curves. It is supposed that the preferential corrosion of free iron particles and the surface damage induced by the particles is responsible for corrosion degradation of stainless steels.