| dc.description.abstract | Anodic aluminum oxide (AAO) films have been investigated and used in numerous
products for more than 50 years. The morphologies of the AAO films can be classified into barrier-type and porous-type. Barrier-type films consist of compact amorphous alumina,
while porous-type films comprise of a thin barrier layer next to the metal and an outer layer of porous alumina. There are limitations in the way nanoporous alumina has been
fabricated. The limitations are the freezing of the electrolyte with a temperature controlled
bath, very high potential and prolong anodizing time have also been used during AAO
fabrication. In order to overcome these shortcomings associated with the fabrication of this
porous alumina film at room temperature, this study aim to create a novel process to
fabricate nanoporous alumina film with controlled pore diameters that is externally
controlled by direct current circuit. The steps followed during the electronic circuit design
set-up involved specification, design/cost, verification and testing of the circuit. The
specification of the design is to address the issue of temperature, low potential anodization
and the value of the most critical process parameter which is current, and the less critical
parameters which are temperature and concentration of electrolyte. The next step of the
design was the identification of important components i.e. capacitors and resistors that are
crucial during the preliminary design stage. The components are cheap and provide a form
of stability and control of the circuit. The verification and testing was done by computer
simulation (PhET software kit) and practical testing of the circuit design. The computer
simulations provided the information about the most suitable circuit design under different
simulated conditions. The simulation identified a series connection of a single 60 V rated
capacitor and a 500 ohms resistor to be the most suitable circuit design to limit the
influence of the process parameters. The practical testing using different electrolyte
concentration (i.e. 0.7 M, 1.5 M, and 2.2 M), different low potentials (i.e. 10 to 50 V)
operating at room temperature identified the most critical current value to be less or equal
to 150 mA. Any current value above this failed to produce a nanoporous alumina structure.
A similar testing was also performed at higher temperature (50oC) to confirm the suitability
of the circuit to operate at higher temperatures. The functionality of the circuit design is
also equation based controlled by standard equations which can be operated via a direct
circuit supply or alternating current supply, making the entire process flexible, accurate and
precise. The room temperature and low potential anodization of aluminum were anodized
under different electrolyte conditions for 1 hour, 3 hours, and 5 hours respectively. The
scanning electron microscope (SEM) results show that the pores formed at different
potentials and concentrations of electrolytes is within the range of 10 – 200 nm. The pores
are randomly distributed all over the surface of the aluminum. As the applied voltage is
increased with time subsequently the pores also increase in diameter. This results show that
with the aid of the upgraded electrochemical cell controlled by the external dc circuit,
nanoporous alumina were successfully fabricated at room temperature and high temperature
with low potentials using a single step anodization technique which was suitable for AAO
fabrication | en_US |
