Investigation on aluminum treatment for enhancing surface properties and for fabrication of high-sensitive capacitive humidity sensor

Abstract

One of the engineering metals applied to a wide range of industries is aluminum (Al) because of its excellent properties such as ductility, light weight, and high electrical conductivity. Since the surfaces of aluminum are exposed to extremely high/low temperature, dry/wet condition, or corrosive environments, an appropriate surface modification is required for ensuring an operating time. Therefore, the purposes of this study are to understand the relationship between surface structure and physical properties as well as to design and synthesize nanostructured solid-state materials to impart specific properties on the surface of Al. This dissertation is composed of 5 chapters. Chapter 1 (Introduction) is a comprehensive survey that explains the capacitive humidity sensor and the wettability on the surface of metal oxides, starting with the various kinds of anti-corrosive coating technologies presented to date. The introduction also includes the detailed information on the operation and performance indicators of nano-porous anodized aluminum oxide (AAO) humidity sensor. In chapter 2, the anti-corrosive and electrically conductive behaviors of aluminum coated by polysiloxane-graphene composite were investigated. Through electrochemical analysis, the corrosion rate and inhibition efficiency of aluminum before and after anti-corrosive coating were numerically evaluated. In addition, the dual properties enhancement of the barrier film was developed as a function of graphene filler contents in the matrix. In chapter 3, we fabricated freestanding nano-porous anodized aluminum oxide (AAO) template for high-sensitive capacitive humidity sensor. The relationship between H2O adsorption properties and the porosity as well as the anion impurities on AAO surface was considered in detail. In chapter 4, we synthesized super-hydrophilic hierarchical boehmite surfaces on two-step anodized Al substrates by immersing in a boiling water. The relationship between a number of hydroxyl groups on the surface of metal oxides and wetting behavior of H2O was intensively studied. In the last chapter (Chapter 5), the findings were summarized.