Surface chemistry studies: A. Novel corrosion passivation of aluminum. B. Surface phenomena on single walled carbon nanotubes

A. The first part of this thesis is related to the corrosion properties of aluminum. We studied several techniques to improve aluminum passivation. This thesis also focuses on the creation of an oxide layer on Al which possesses superior corrosion passivation properties compared to the thermal oxide. The surface of a polycrystalline Al surface (99.999% purity) was oxidized using “active oxygen” species: H₂O+e − (discussed in Chapter 4) and O₃ (discussed in Chapter 5). •OH radicals were produced by excitation of adsorbed water molecules by 100 eV electrons. A high purity ozone flux was used for the oxidation of aluminum by ozone. The kinetics of the growth of the oxide films and saturation atomic O/Al ratios were studied using Auger electron spectroscopy. The sticking coefficient was measured using the initial slope of the uptake curves. For ozone the sticking coefficient is 3.8 times higher than for molecular oxygen on polycrystalline Al surface. The corrosion properties of these oxide films were then studied by electrochemical impedance spectroscopy (EIS) and Tafel plot analysis. The oxide films were shown to be of superior passivation properties compared to films grown from H₂O or O₂. The average improvement in the corrosion resistance measured by EIS for either electron-induced excitation of the water molecule or ozone is 10–20-fold compared to the thermal oxide with the similar oxide thickness. The production of less porous and more dense oxides is postulated in the case of H₂O+e − and O₃. The production of higher density oxide was also confirmed by high-resolution transmission electron microscopy (HRTEM). A selected area diffraction (SAED) pattern analysis of the obtained images showed that the density of the-ozone-produced film was 4% higher than that of the film grown from oxygen.; The other study focuses on the mechanism of vinyltriethoxysilane (VTES) adsorption on γ-Al₂O₃ using Fourier Transform Infrared (FTIR) spectroscopy. We showed that the mechanism of adsorption of VTES involves its reaction with surface hydroxyls. The study also showed that vinyl functional groups have superior thermal stability compared to ethoxy functional groups.; B. Part B of this thesis is focused on the study of xenon adsorption on single-wall carbon nanotubes using temperature programmed desorption (TPD), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. Carbon nanotubes were treated using (a) thermal treatment; and (b) oxidation by ozone. The thermal treatment of nanotubes increased the adsorption capacity 20-fold. This is postulated to be due to decomposition of oxygen-containing groups (carboxyl, quinone, ester), created by acid etching. These groups are formed on the defect sites of carbon nanotube walls as well as on the rims of the nanotubes. The oxygen-containing functional groups could also be produced using ozone. The adsorption kinetics were monitored using the adsorption of xenon gas. The existence of these functional groups (quinone and ester) slows down adsorption of xenon due to the interaction between the dipole of the C-O groups and xenon. An increase of the defect site size is postulated to occur with larger ozone exposures followed by thermal etching to remove the groups as CO and CO₂. The increase in the entry port size was shown to induce faster kinetics of xenon adsorption.