Evaluation of blistering performance of pigmented and unpigmented alkyd coatings using electrochemical impedance spectroscopy

Importance of Surface Preparation for Corrosion Protection of Automobiles

“…For example as shown in Table 5, f b value for formulation III after 300 hrs. of exposure is 1345 Hz which is much lower compared with corresponding values 8447 Hz and 27,994 Hz for formulation I and II respectively, indicating clearly that formulation III offers much superior corrosion resistance (minimum area of delamination) followed by phosphating formulation I and II, which was also corroborated by visual observation of the panels from salts spray test [26].…”

“…The chemical stability of the phosphate coatings may be determined by exposing the coatings in dilute solution of sodium hydroxide and checking the extent of solubility [19,21]. The final corrosion performance of phosphated and painted surface maybe evaluated by accelerated tests like salts spray (ASTM-B117) and also by Electrochemical impedance Spectroscopy (EIS] [22][23][24][25][26][27]. In automotive industry, salts spray tests are widely used to evaluate the performance of phosphated (PT) and Electro-deposited primer (ED) coating.…”

“…The impedance measurements were carried out at open circuit potential using a "Schlumberger 1255 Frequency Response Analyzer" (FRA) operated under computer control. The FRA was connected to the electro chemical cell through "EG&G potentiostat/Galvanostat 273" More details of the experimental set up for impedance measurement have been reported in an earlier publication [26]. (b) In order to interpret the impedance data we have used an equivalent circuit model of painted metal/solution interface as shown in Figure 11.…”

“…The impedance data were analyzed in terms of three coating parameters viz. Pore resistance (Rpo), coating capacitance (Cc) and breakpoint frequency (fb) [26]. The results of variation of Rpo, Cc and f b as a function of salt spray exposure time are shown in Figures 12-14 respectively.…”

A model for cathodic blister growth in coating degradation using mesomechanics approach

“…It is, therefore, essential to understand the physical and metallurgical phenomenon of blistering from both scientific and engineering point of view. One of the most severe forms of blistering is known as cathodic blistering [14][15][16], which takes place when a metallic substrate with coating defects is exposed to saline environment, such as salt spray or immersion in salt solution [17][18][19][20][21].…”