Solution Conductivity Influence on Pitting Corrosion Studies by SVET

摘要

The controversial statements about the solution conductivity changes occurring above the pitsappeared on corroded Al alloy surface were verified. Original local conductometric measuringtechnique was employed together with SVET to evaluate the solution conductivity influence on theSVET results, completely dependent on the solution conductivity (IRsolution ohmic drop). Bare andchromated AA 7075-T6 aerospace aluminum alloy specimens were employed in 5 % NaCl solutionsfor the conductometric/SVET measurements. Artificial its(Pt spots) with known dimensions wereused for the SVET measuring instrument calibration. Solution conductivity variations of about 4.8 %above the non-chromated specimenssurfaces were registered at a distance of 30 m 5 minutes afterthe specimensimmersion, against less than 1% changes above the chromated specimens at sameconditions. A special noise reduction technique was applied allowing distinguishing of the smallchanges of the SVET signal caused by the conductivity influence.