MOIRE METHOD TO MEASURE PENETRATION DEPTH PROFILES ON UNEVENLY CORRODED METAL-SURFACES

A system based on the moire method was successfully applied to in situ measurement of crevice penetration for high purity 18Cr-14Ni steels i n NaCl solutions at 80-degrees-C. For the growing picture element, PE( II), the dissolution rate in the first stage (stage I), V(I), and the dissolution rate in the stationary growing stage (stage II), V(II), we re measured, and current densities, i(I) and i(II), corresponding to V (I) and V(II), respectively, were determined. The effect of NaCl conce ntration on dissolution behavior at a potential just above repassivati on potential (E(R)), E(R)+, was studied in terms of the effective coff osion current density inside the crevice, i(eff), which was found to be constant regardless of bulk NaCl concentration, which could contrib ute to the concentration difference of ions inside the crevice and in bulk solution.