Evaluation and Investigation of Surface Treatment of Industrial Coatings by Impedance Spectroscopy

Abstract

Three organic coatings of commercial grade (zinc rich epoxy-polyamide) were applied to steel substrates and immersed for up to 2160 h in 0 . 5M NaCl at 25uC. These coated plates were assessed by ac impedance in the frequency range 100 kHz to 1 mHz. The coatings were evaluated in salt spray and humidity tests according to ASTM B117 and D-2247. X-ray diffraction and X-ray fluorescence techniques were applied to analyse the coated surface. Electrolytic penetration through the coating changes the dynamic characteristics of the conduction and resistance of the coating film of the protected system over time. Equivalent circuits were used to interpret the physical and electrochemical properties of the changes so, for each coating system, equivalent circuits were appointed using analysis of impedance curves. The numerical quantities of elements were estimated by the Boukamp method. The mechanism and kinetics of the electrochemical systems were assessed by studying the changes in electrochemical parameters v. time. The qualities of the coatings can be compared by measuring the fluctuations in capacitance, dielectric constant and percentage of water uptake. The results obtained from impedance and salt spray tests were compared. Results showed that the best quality coatings can be introduced by measuring the capacitance, water uptake and dielectric constant. SE/S297Mr Neshati (neshatyj@ripi.ir) and Mr Fardi (fardimr@ hotmail.com) are in the Corrosion Department, National

Atomic spectrometry update. X-Ray fluorescence spectrometry

“…The effects of current density and electrolyte temperature on surface roughness and grain size distribution were used by Jiang et al 475 in their characterisation of films of Sn electrodeposited on steel substrates. Neshati and Fardi 476 subjected organic coatings of commercial grade Zn rich epoxy polyamide on steel to salt spray and humidity tests, as described in ASTM B117 and D-2247. XRD and XRF analysis were then used to reveal the best quality coatings.…”

Electrochemical Impedance Spectroscopy Investigation on the Corrosive Behaviour of Waterborne Silicate Micaceous Iron Oxide Coatings in Seawater

“…This is mainly due to the fact that some assumptions, such as intactness of coating main structure, linear transmission of corrosive media and so forth, are needed to apply the corresponding relationship [34] between Q c and the water absorption of the coating. However, these conditions cannot be met in most cases for inorganic coatings-it will result in an obvious deviation between the water absorption calculated from the coating capacitance value and the actual water absorption [35][36][37][38]. Therefore, to effectively evaluate the protective performance of the inorganic coatings, new evaluation parameters and methods need to be found.…”

A Novel Application of EIS for Quantitative Coating Quality Assessment During Neutral Salt Spray Testing of High-Durability Coatings

“…[7][8][9] Excellent coatings have resistance values 10 8 -10 12 Ωcm 2 and poor corrosion protection properties are exhibited when resistance intensity drops below 10 5 Ωcm 2 . 13 The appearance of coating defects is observed when coating impedance value falls below 10 6 Ωcm 2 . 14 Impedance greater or equal to 10 9 Ω corresponds to excellent protecting properties of coatings which provide almost purely capacitive behaviour over long exposure periods.…”

“…14 Impedance greater or equal to 10 9 Ω corresponds to excellent protecting properties of coatings which provide almost purely capacitive behaviour over long exposure periods. 15 The described EIS model may be applied to various industrial coating types and thicknesses providing a universal tool for coating quality and protective ability comparison [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] .…”