Correlation research of phase angle variation and coating performance by means of Pearson's correlation coefficient

The impedance characteristic and degradation process of two epoxy coatings in 3.5 % NaCl solution and seawater environment were studied by using electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and infrared spectroscopy (FTIR) methods. Pearson's correlation coefficient (r) method was used to analyze the correlation between the phase angles in different frequencies and the impedance at low frequency end (vertical bar Z vertical bar(0.01)( )(Hz)) for epoxy coatings. The results show that in a middle frequency range (about 1-100 Hz) the phase angles have a strong positive correlation with vertical bar Z vertical bar(0.01)( )(Hz) (r > 0.90-0.95). Based on the good linear relationship (log (vertical bar Z vertical bar(0.01)( )(Hz)) = A + B x theta) between the phase angle in middle frequency range and the vertical bar Z vertical bar(0.01)( )(Hz) values, it is suggested that the phase angle at 10 Hz (theta(10Hz)) is a suitable parameter to rapidly evaluate the degradation degree and the protective performance of the coatings.