Salt spray test Fig nbsp xA
Salt spray test PND-1186 performed on epoxy coated and epoxy with copolymer composite coated steel specimens in 5.0 wt.% NaCl (pH of 6.5–7.2) at a constant temperature of 35 °C. All the coated steel panels were provided with a scribe mark across the panel and placed in a defined angle in the salt spray chamber. Fig. 13 shows the photographs of epoxy coated (EC) and epoxy with copolymer coated steel panels (OPF1, OPF2, OPF3 and OPF4) after exposure to salt spray fog of 5.0 wt.% NaCl. Fig. 13a clearly exhibits the presence of spread of corrosion along the scribe mark for epoxy coated steel panel only after 75 days of exposure to salt spray chamber. The presence of rust indicates loss of adherence of the epoxy coating during prolong exposure to salt fog. Severe blistering and pin holes are also noticed. The addition of co-polymer composite in epoxy coatings improves the corrosion resistance properties of the epoxy resin. This can be clearly noticed from the photographs (Fig. 13b–e). The epoxy coated specimen with 1.0 wt.% loading of copolymer composite (OPF1) evidenced less extended corrosion along the scribe mark (Fig. 13b). Further, almost no extension of corrosion along the scribe mark is noticed for specimen OPF2 (Fig. 13c). Specimen OPF3 also evidenced better corrosion resistance with less extended corrosion along the scribe mark (Fig. 13d). The salt spray results clearly show Lyon hypothesis the poly(aniline-co-o-toluidine)/flyash composite effectively prevents the spread of corrosion near scribe mark that exposes the steel surface. It is assumed that the copolymer composite might have promoted the adhesion of the epoxy coating to the metal substrate improving the corrosion resistance under accelerated test conditions.