カレントインターラプター法による塗膜の防食性の評価

塗膜下腐食の研究 (第1報)

抄録

The corrosion rate of coated mild steel was investigated using the technique of current interrupter method. Generally the high impedance of film had been a barrier to measure the corrosion rate of coated mild steel but this method made it easy to eliminate the impedance of film and furthermore to obtain the polarization behavior of coated mild steel. The equivalent circuit of coated mild steel immersed in a 3wt% sodium chloride solution is composed of two kinds of impedance circuit, that is, the impedance circuit of paint film and that of metal interface beneath paint film. These circuits were easily separated because of the large difference of time constants between the one circuit and another. Therefore the polarization resistance was obtained under the condition of small polarization (up to 10mV) and Tafel's coefficient was given by the relation between time and potential in decay curve of small polarization to the extent of 200mV to 300mV. And the corrosion rate of coated mild steel was calculated using Stern's equation. This method is characterised by items below. (I) Very small current was applied to paint film for a few seconds so that no damage appeared throughout measuring. (II) The impedance of film and that of metal surface under paint film were measured simultaneously. As a result, the corrosion rate of coated mild steel coincided with the appearance of underfilm corrosion throughout immersion tests.