Surface science of the adhesion of an alkyd paint to a low carbon aluminium killed steel
Mohlala, Pheladi Junior
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An important factor in achieving maximum adhesion of a particular coating system to the substrate lies in the proper pre-treatment of the substrate prior to the application of the coating. The Lewis acid-base properties of the outer metal surface playa determining role in many of these applications, and the chemical reactions involved therein. In this work, the Lewis nature of the low-carbon aluminium-killed (LCAK) substrate has been significantly modified by a chemically activated surface pre-treatment. The wetting properties of the LCAK substrate was determined by contact angle measurements; the coordination of the chemical species on the surface was studied with XPS; FTIR together with the probe molecule (B(OCH3)3) was used to explain the chemical bonding on the surface. The novel combination of contact angle, XPS, FTIR and probe molecule enabled the determination of the Lewis acid-base properties of the LCAK surface before coating. The XPS spectra of the LCAK surface rinsed in warm water show that the surface species differ from that rinsed in tap water. With change in pH the wettability properties also drastically changed. The probe molecule (B(OCH3)3) did not bond to the warm water rinsed samples but bonded strongly to tap water rinsed samples as the pH decreased. In this study, the adsorption strength of oxygen and water to Fe (110) surfaces was investigated using Cambridge Sequential Total Energy Package (CASTEP) as applied in the Material Studio Software Package. This study gave theoretical information of the adsorption strength of water and oxygen to Fe surfaces and may be the first step in examining the adhesiveness of these compounds on Fe surfaces. This research has shown that Lewis acid-base properties can be significantly changed with water temperature and pH, which has important implications for industrial pre-treatment.