Bulk processing of ZnO nanostructures via microwave assisted oxidation of mechanically seeded Zn dust for functional paints and coatings

Abstract

Micron sized metallic zinc dust (99.9%, Davg=40μm) was mechanically milled to have zinc oxide seed nuclei on its surface, eventually transforming it into ZnO nanostructures by microwave irradiation for 15min. Effect of milling on the growth of seed layer, oxidation kinetics, particle size distribution, nano ZnO morphologies, phase purity, dispersion and UV absorption properties were studied and reported. ZnO rods with length 5–6μm and diameter of nearly 200nm were successfully synthesized in bulk through this facile route. The products were systematically characterized and studied with the motive to design multifunctional nano-products. A paint formulation was made by blending the as-synthesized nano ZnO with a natural organic resin; cashew nut shell liquid (CNSL) and surface coatings were developed over glass and metal substrates. ZnO–CNSL paint coatings were further studied for NIR reflectance, optical transparency and hydrophobic surface property. Its effective corrosion resistance has been validated with highly corrosive Mg-alloy substrates, an upcoming key material for automobiles. The ZnO–CNSL paint developed showed about 33% enhancement in NIR shielding and about 156% improvement in corrosion resistance when compared to their uncoated counterparts. The study strongly recommends microwave accelerated oxidation as a technologically competent process for the bulk preparation of multifunctional nano ZnO.