Study on the effect of halloysite nanotubes on the adhesion and corrosion protection of epoxy coatings on carbon steel

Halloysite nanotubes (HNT) are naturally occurring clay minerals with abundant reserves, commonly employed as carriers for corrosion inhibitors in protective coatings. However, the direct influence of HNT on the physico-mechanical properties and corrosion resistance of coatings has received limited attention. In this study, a procedure for dispersing HNT into an epoxy binder was established, and the effect of HNT loading on adhesion strength and corrosion protection was subsequently evaluated, using pull-off adhesion tests and electrochemical measurements. The results demonstrated that HNT was uniformly dispersed in the epoxy via a sequential process consisting of ultrasonic agitation in a solvent, mechanical stirring, and subsequent ultrasonication in the epoxy mixture. Experimental results indicated that epoxy coatings incorporating HNT exhibited 1.84–2.64 times higher adhesion strength than neat epoxy coatings, with adhesion increasing progressively as HNT content rose from 1 to 3 wt.% and showing negligible variation upon further increase to 5 wt.%. Moreover, the corrosion rate of carbon steel was markedly reduced in the presence of HNT, reaching a minimum value of 0.0328×10-3 mm/y at 3 wt.% HNT loading. It was shown that a relatively low HNT loading was sufficient to enhance adhesion strength and corrosion resistance of epoxy coatings, highlighting the potential of this nanomaterial for protective coatings.