Local Electrochemical Probe For Detecting Inner Coating Defects In Metal Can In Atmosphere

Metal can in the food packaging industry has a wide range of applications.Different kinds and thickness of coating exhibit different performance. Coatingselection is particularly important. Coating defects in metal can would significantlyshorten shelf life of food and lower its quality. In order to solve the problem of innercoating defects in metal can, locating and detecting defect area are helpful toimprove metal cans’ production process and products’ quality. To this end, a localelectrochemical probe for detecting inner coating defects in metal can in cylindricalspace is needed. This device is going to locate and detect inner coating defects. Itshould be able to scan electrochemical information in planar and cylindrical area inmetal can, and quickly and accurately locate and evaluate defect area.For the purpose of locating and detecting inner coating defects in metal can, asolid Ag/AgCl reference electrode was prepared in this paper. The solid Ag/AgClreference electrode had good potential stability in3.5%NaCl solution. It could meetthe requirements for open-circuit potential and electrochemical impedancespectroscopy test in metal can. Using the homemade solid Ag/AgCl referenceelectrode, a local electrochemical probe for detecting inner coating defects in metalcan in atmosphere was developed in this paper, and XYZθ scan coordinate system infour-dimensional was also constructed. It could get the electrochemical informationof metal can’s inner coating, locating and evaluating coating defects by using OCPand EIS measurements. In this test, firstly detecting of average EIS of metal can in5%NaCl solution was needed to determine whether there is coating damage. Formetal can which has coating defects, the value of OCP and EIS at defect area aresignificantly different from the non-defect region. By measuring OCP value inatmosphere, it could pinpoint the location of the damaged area, and by measuringEIS, it could further analysis electrochemical information.In this paper the value of OCP and EIS at bottom shrinkage area, weld area, bottom area and sidewalls were detected respectively. The result showed that thisdevice could accurately locate and evaluate the status of coating defects in planarand cylindrical area in metal can in atmosphere, and had a high resolution andprecision. In addition, this paper also studied coating with different defect size, andthe result showed that under the same condition, the larger the damaged area, thelower the impedance values. The result also illustrated that this probe can distinguishdifferent sizes of coating defects with high sensitivity. In summary, the localelectrochemical probe had high practical value in laboratory.