1990 Volume 39 Issue 12 Pages 688-696
Scanning vibrating electrode technique (SVET) system was applied to measure corrosion current density profiles around Pt foil embedded in epoxy resin except its edge, which was used to simulate intergranular corrosion. The system was calibrated under the condition of uniform current. Output voltage, V, became larger with decreasing conductivity of the test solution, κ, and increasing vibrating amplitude of sensor probe, a. Measuring sensitivity did not depend on frequency of vibration, f, under the condition of uniform current. Laplace equation could be applied for corrosion current distributions around foil-shape electrode with width of t. When height of sensor probe from the specimen surface, h, could be decreased down to h≤t/2, condition A, corrosion current distribution could be considered to be uniform and net corrosion current density, i0, could be determined as i0=πip/2, where ip was the corrosion current density just above the center of the electrode. When h was larger than t/2, condition B, corrosion current flowed out in all directions from the electrode and identification sensitivity of ip=ti0/πh became better with decreasing h. Corrosion current profiles around Pt foil electrode were measured under various conditions of f, h and width of Pt foil, t. Measuring sensitivity became improved with increasing f and then leveled off after a f-value of 300Hz. Because V was unstable under the conditions with f=50n(Hz) (n=7, 8, 9…) under the influence of AC power source (f=50Hz), f=370Hz was adopted in this work. Relationship between ip and h satisfied the Laplace equation under condition B. With regard to corrosion current flowing out from two Pt foils at the distance of d, h was required to be less than d/2 to detect two peaks of corrosion current and to determine the positions of Pt foils. These strong dependency on h of the measured intergranular corrosion current profiles are attributed to the adopted conditions which remains within condition B.