Zinc Surface Functionalization: Artificial Patination with CO2

Abstract

Material processing technologies are required to be increasingly cleaner and safer for the globe to prevent excessive exposure to toxins and pollutants. This work presents a solution for two processes that currently use such harmful chemicals. The method uses pressurized carbon dioxide (CO<SUB>2</SUB>) to produce an artificial patina on metallic zinc. The artificial patina shows promise in enhancing corrosion protection and promoting adhesion of organic coatings applied on hot-dip galvanized steels that are currently treated with other chemicals for the same effect. Additionally, the artificial patina can be converted into distinct zinc oxide (ZnO) nanostructures that could have applications in, e.g. antibacterial surfaces, gas sensors or solar cells.

The thesis details a holistic description of the treatment method by exploring the fundamental interactions and formation mechanisms of the artificial patina. The artificial patina could be formed uniformly throughout a substrate surface using a supercritical carbon dioxide (scCO<SUB>2</SUB>) treatment together with only water or with the addition of catalysts. The supercritical treatment was able to form a homogeneous layer of the artificial patina on the substrate surfaces. The formed artificial patina was composed of zinc carbonate (ZnCO<SUB>3</SUB>) as well as a new kind of zinc hydroxy carbonate compound with a nanowire morphology.

The chemistry and structure of the carbonates were advantageous for applying organic coatings onto the hot-dip galvanized surfaces, and they created a dense barrier layer that could help prevent corrosion. The artificial patina could be converted to ZnO with a simple heat-treatment which produced semiconducting ZnO nanostructures. Therefore, this method could help by reducing the usage of harmful chemicals significantly, achieving a comparable outcome only CO<SUB>2</SUB> and water in a facile and environmentally-friendly process.