Wednesday, 3 October 2018
Universal Ballroom (Expo Center)
Coated steels have been widely used for structures and industrial products, but the coating film deteriorates due to environmental factors such as suneshine and rain, and eventually under-film corrosion occurs. Conventional methods such as tape peeling test for evaluating corrosion deterioration of coated steels are destructive and also the quantitativeness is not high. On the other hand, non-contact type surface potential measurement was proposed for degradation evaluation of coated steels. The masurement method gave the information on the position and size of the deteriorated region. However, the method is applied just for the coated steel with the coating film of under 20 цm, and it is unknown whether it is applicapable for the coated steel with thick coating film which is practically used.
The principle of surface potential measurement used in this study is almost the same as that of the Kelvin method. The contact potential difference between the measurement probe and the sample corresponding to the work function occurs by electrical connection of the both. An AC signal proportional to the charge amount is obtained by opening / closing the shutter attached between the sample and the detection electrode, and the surface potential of the sample is measured using that signal.
Carbon steels of 4 cm × 4 cm was used as a steel substrate, and coated steels with a variety of coating thicknesses were prepared by spraying transparent acrylic lacquer. Corrosion test was conducted by alternating of wet and drying using 100 μL droplet of NaCl solution. After washing away of NaCl precipitated on the surface, the surface potential distribution was measured and the surface was observed by a digital microscope. The potential of 100 µm coated steel went down to 0.1 from 0.2 V after 38 cycles. The potential became further lower with an increase of the number of cycles, and the potential change region also expanded. This means that the deteriorated position and size of the coated steels can be detected by measurement of surface potential distribution. The surface potential measurement is a powerful tool as a deterioration evaluation method of coated steels.
The principle of surface potential measurement used in this study is almost the same as that of the Kelvin method. The contact potential difference between the measurement probe and the sample corresponding to the work function occurs by electrical connection of the both. An AC signal proportional to the charge amount is obtained by opening / closing the shutter attached between the sample and the detection electrode, and the surface potential of the sample is measured using that signal.
Carbon steels of 4 cm × 4 cm was used as a steel substrate, and coated steels with a variety of coating thicknesses were prepared by spraying transparent acrylic lacquer. Corrosion test was conducted by alternating of wet and drying using 100 μL droplet of NaCl solution. After washing away of NaCl precipitated on the surface, the surface potential distribution was measured and the surface was observed by a digital microscope. The potential of 100 µm coated steel went down to 0.1 from 0.2 V after 38 cycles. The potential became further lower with an increase of the number of cycles, and the potential change region also expanded. This means that the deteriorated position and size of the coated steels can be detected by measurement of surface potential distribution. The surface potential measurement is a powerful tool as a deterioration evaluation method of coated steels.