engleski

AC interference impact on EIS assessment of organic coatings using dummy cells, calibration foils and field exposed coated samples

Field application of EIS to intact and scarcely degraded high-performance protective coatings is challenging because of ambient electromagnetic fields, which cause stochastic variations in the phase angle and, to a lesser extent, in the impedance modulus of the coating spectra. AC interferences with amplitudes between 10 and 800 mV were induced on dummy cells and calibration foils to systematically investigate the effects of interference impact on the accuracy and precision of measurements with the EIS setup intended for use on coatings in the field. For EIS signal amplitudes between 10 and 250 mV and the AC interference amplitudes ≤250 mV, the measurement accuracy and precision were limited by the synergistic influence of the AC interferences and the imprecision of the EIS instrument. For systems with impedance ≥ GΩ, the accuracy of the impedance logarithm was 97.8% at signal amplitudes ≥190 mV, and the precision increased from nearly 95% to 99% as the signal amplitude increased from 10 to 150 mV, indicating that very accurate and precise measurements can be obtained at higher signal amplitudes. An example of EIS measurements on coated samples exposed in the area of AC railway interferences is given. Although the quantitative conclusions may be instrument specific, they reflect well the declared capabilities of today's high-end EIS devices. The universal explanation is given in the context of equivalent circuit theory of the observed scatter in the EIS spectral data. The coating assessment was commented on in terms of the unique properties of the mean and relative standard deviation of impedance expressed on the logarithmic scale.

EIS ; coating ; polyester ; AC interferences

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