Evaluation of parameters affecting adhesive strength of high build epoxy coatings on textured and plasma treated metallic substrates

Epoxy coating systems have been used throughout the years for protecting critical industrial assets. To ensure superior coating adhesion and longevity, abrasive blasting has been traditionally employed to texture metallic surfaces. Though a large variety of abrasives are available in the industry, coal slag (aluminium silicate) and garnet (mineral abrasive) have remained popular choices until now owing to their easy availability. However, depleting reserves of coal slag owing to stricter environmental regulations and shortage of good quality garnet have fueled the need to identify substitutes. This work is focused on evaluating the effect of surface texturing on adhesive strength of epoxy coatings using two novel abrasive types–olivine (obtained from dunite rock) and calcium silicate (iron furnace slag) which are available in abundance and present an excellent alternative. The surface textures of various blast cleaned mild steel (A36) and stainless steel (316L) substrates were evaluated using a combination of techniques namely, optical profilometry (spatial parameters), replica tape method as per ASTM D 4417 (Method C) (height parameter) and scanning electron microscopy (Secondary electron imaging/energy dispersive X-ray spectroscopy analyses) for embedded particle composition analysis. Correlations were drawn to the wettability of metallic substrates textured using the selected abrasives. Adhesive strength tests on high build epoxy coatings, performed in accordance with ASTM D4541 revealed exceptional performance using various grades of both olivine and calcium silicate abrasives. The effect of air plasma treatment on adhesive strength of epoxy coatings applied on mild steel substrates were also studied.