Papers by Keyword: Anodizing

Abstract: The morphology of porous anodic alumina (PAA) formed by anodizing in inorganic electrolytes is reported. An impure aluminum was anodized in sulfuric acid, phosphoric acid and chromic acid at room temperature with a constant applied potential 2 – 30 V. The formation of porous anodic alumina was carried out by one and two steps anodization. It is clearly noted that anodizing impure aluminum at room temperature provide higher kinetic of oxide dissolution compared to oxide growth. Two steps anodizing aluminum in sulfate electrolyte always resulted in random porous alumina, while phosphate electrolyte provided strong anodization producing irregular porous alumina with average diameter of 61.6 nm. Two steps anodizing aluminum in chromate electrolyte produce better pore ordering with relatively large size pore distributions. The average pore diameter of alumina increases linearly with applied voltage, with proportionality factor l_p 0.83 nmV^-1. Annealing the sample increased the interpore distance, removed stresses providing lower activation energy for pore formation.

Abstract: The injection of ozone into the air mixture for a barbotage of electrolyte at anodization of an aluminum alloy D16 in 5 % aqueous solution of sulfuric acid increases final thickness of oxide coating by 45 - 53 %, and simultaneous ultrasonic affecting and bubbling of electrolyte by the ozone-aerial mixture - only on 30 - 35 %, however in the latter case microhardness and wear resistance of coating increase. The additional applying of vibration decreases thickness, microhardness and wear resistance of an oxide layer.

Abstract: In this study, porous anodic alumina was formed on aluminium alloy substrate with increasing manganese content, from high purity aluminium with 0 wt% Mn to aluminium alloy with 2.0 wt% manganese by anodizing. Substrates were anodized at 50 V in 0.3 M oxalic acid of 15°C for 60 minutes. Images from the optical microscope revealed that no secondary phase existed in high purity aluminium and aluminium substrate with 0.5 wt% manganese while two phases were observed when the manganese contents were higher than 0.5 wt%. Element dispersive X ray spectroscopy spot analysis suggested that the secondary phase consists of both aluminium and manganese. Well ordered porous anodic alumina was obtained on high purity aluminium and aluminium substrate with 0.5 wt% manganese while pore arrangement of porous anodic alumina was significant disturbed when aluminium alloys with manganese contents higher than 0.5 wt% were anodized.

Abstract: In this study, oxide dissolution treatment was used for the formation of well ordered porous anodic alumina. Porous anodic alumina was formed on mechanically polished high purity aluminium by anodizing at 50 V in 0.3 M oxalic acid of 15°C for 60 minutes. It is observed that the pore arrangement of as anodized porous anodic alumina was randomly distributed and showed no ordered hexagonal cell structure. As anodized porous anodic alumina were then subjected to oxide dissolution treatment of increasing exposure duration, up to three minutes. Micrographs were captured by using scanning electron microscope. Pore arrangement of porous anodic alumina subjected to oxide dissolution treatment up to two minutes were similar to one another where no ordered periodic structures were formed. .When porous anodic alumina subjected to oxide dissolution treatment for three minutes, a perfect hexagonal pore arrangement was obtained.

Abstract: In this study, Fast Fourier Transform (FFT) analysis was conducted on the images of scanning electron microscope of morphology of the porous anodic alumina formed on high purity aluminium. High purity aluminium substrates were anodized at 50 V in 0.3 M oxalic acid of 15°C for 60 minutes. As anodized porous anodic alumina were then subjected to oxide dissolution treatment of increasing exposure duration, up to three minutes. Micrographs were captured by using scanning electron microscope and the images were analyzed using FFT. It was found that the FFT images of as anodized porous anodic alumina and porous anodic alumina subjected to oxide dissolution treatment up to two minutes were similar, which were disc shaped white forms, indicating no ordered periodic structures were formed. When porous anodic alumina subjected to oxide dissolution treatment for three minutes, FFT image showed six distinct spots at the edges of a hexagon, indicating a perfect hexagonal pore arrangement was obtained for porous anodic alumina subjected to oxide dissolution treatment for three minutes.

Abstract: In this work, the effect of temperature of distilled water on the morphology of ZnO nanoporous thin films formed by anodizing was studied. ZnO nanoporous thin films were formed by anodizing of Zn plates at voltage 30 V in 500 ml distilled water of temperature ranged from 5 °C to 25°C. As anodized zinc plates were characterized by using SEM and XRD. Characterization of as anodized Zn plates using SEM showed that the morphologies of the as anodized Zn plates were significantly influenced by the temperature of distilled water. Nanoporous ZnO thin films were formed when 15 °C to 25 °C were used while ZnO thin films without nanoporous structures were formed when 5°C and 10 °C were used. XRD analysis indicated the ZnO thin films formed in distilled water of 5 °C to 25°C were of hexagonal wurtzite structures.

Abstract: In this work, ZnO nanoporous thin films were formed by anodizing of Zn plates in 500 ml distilled water of 25°C at voltage ranged from 10 V to 30 V. As anodized zinc plates were characterized by using SEM and XRD. Characterization of as anodized Zn plates using SEM showed that the morphology of the as anodized Zn plates were significantly influenced by the anodizing voltages. Nanoporous ZnO thin films were formed when 25 V and 30 V were used while ZnO thin films without nanoporous structures were formed when 10 V, 15 V and 20 V were used. XRD analysis indicated the ZnO thin films formed at 10 V to 30 V were of hexagonal wurtzite structures.

Abstract: An oxide film was prepared on AZ91D magnesium alloy by anodizing in solution containing sodium metavanadate (NaVO₃). The corrosion resistance of the substrate was investigated at a fixed current density 10 mA/cm² for 5 mins with different concentration of solution in the range of 0 – 1.0 g/l. The surface morphology, phase structure and corrosion resistance of oxide film were studied by optical microscope, scanning electron microscope (SEM) and energy dispersive spectrometry (EDS) and X-ray diffractometer (XRD), potentiodynamic polarization technique and corrosion test.

Abstract: Colour of the anodised Al-Mg-Si alloys was quantified by spectrophotometric method defining L* (lightness), a* (greenness-redness) and b* (blueness- yellowness) values. All alloys exhibited yellow and green colour. The yellowness of the anodised surfaces increased significantly with the increase of Cu while increasing Mn reduced the greenness. Effect of trace elements V and Ni was negligible while Zn caused slightly yellowness. Fe reduced the lightness of the surfaces, while its effect on colour was insignificant. Smut layer being formed during alkaline etching (prior to anodising) was desmutted/deoxidised in different acid solutions, some of which failed to clean the etched surfaces. Remaining smut however caused minor effect on colour.

Abstract: Antibacterial layer was prepared on the aluminum surface by anodizing pure Al and electrodepositing Cu in the pores of the anodic aluminum oxide (AAO) membrane. The AAO membrane was generated by a two-step anodization process in oxalic acid solution. The electrodeposition of Cu was conducted in copper sulfate solution using alternating current. The structural characterizations by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and energy-dispersive spectrometer (EDS) show that Cu nanowires with an average diameter of 70 nm are assembled in the pores of the AAO membrane. The tests of antimicrobial properties against two typical bacteria of Escherichia coli (E. Coli) and Staphylococcus aureus (S. Aureus) indicate that surface antibacterial layer of aluminum possesses excellent antimicrobial properties and the maximum value of the antibacterial rate can reach 99.9% both for E. coli and S. aureus.