Development of anodised aluminium oxide nanostructure from Al-Mn alloy
Voon, Chun Hong
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This study was divided into two parts. The first part of the study was focused on the synthesis of well ordered porous AAO by using oxide dissolution treatment. The porous AAO was formed by anodising of 99.99 % aluminium in 0.3 M oxalic acid at 15 oC for 15 minutes. Anodised substrates were subjected to oxide dissolution treatment by immersing in stirred mixture of chromic acid and phosphoric acid. The effect of oxide dissolution treatment on the morphology and regularity of porous AAO was studied by using scanning electron microscope. The results showed that exposure of porous AAO to oxide dissolution treatment up to three minutes revealed the well ordered pores arrangement that formed during the steady state growth stage. Regularity of the porous AAO was improved. In the second part of the study, porous AAO was formed from aluminium manganese (Al-Mn) alloy substrates and the effect of manganese content, anodising voltage, concentration of oxalic acid, and temperature of oxalic acid on the anodising behaviour, morphology, dimensional properties and growth kinetics were studied. Results showed that the addition of Mn from 0.5 wt % to 2.0 wt % into Al substrates reduced the current density, regularity and growth kinetics of porous AAO. The pore size and interpore distance were also found to decrease with the addition of Mn. Anodising efficiency of anodising process decreased as the Mn content increased up to 1.0 wt %, but increased when the Mn content was further increased to 2.0 wt %. Analysis of XRD patterns showed that amorphous alumina was formed in substrates of all compositions and MnO2 was found to present in Al-1.5 wt % Mn and Al -2.0 wt % Mn substrates. For the study of effect of anodising voltage, anodising of Al-0.5 wt % Mn under the influence of increasing anodising voltage of 30-70V has led to higher current density, larger pore size and interpore distance and higher growth rates. The regularity of pore arrangement of porous AAO was improved when the anodising voltage was increased from 30 V to 50V, but deteriorated when further increased to 70V. Dielectric breakdown occurred when anodising was conducted at 70V. Amount of amorphous alumina was found to increase when the anodising voltage was increased from 30 V to 70 V. Anodising of Al-0.5 wt % Mn at 50 V in oxalic acid of increasing concentration from 0.1 M to 0.7 M increased the current density and growth kinetics. Well ordered porous AAOs were obtained when oxalic acid of all concentration was used, except 0.1 M. Increase of concentration of oxalic acid decreased the pore size while no significant difference in interpore distance was observed. Anodising efficiency decreased as a function of concentration of oxalic acid. The relative intensity of broad peaks in XRD patterns showed that amount of amorphous alumina increased as a function of concentration of oxalic acid. For the study of effect of temperature of oxalic acid, anodising of Al-0.5 wt % Mn was conducted at 50V in 0.5 M oxalic acid of temperature ranging from 5oC to 25oC. Current density and oxide thickness increased while regularity of pores arrangement and anodising efficiency decreased with the increasing temperature of oxalic acid. Temperature of oxalic acid did not have obvious effect on both pore size and interpore distance. Relative intensities of broad peaks increased indicating the amount of amorphous alumina increased with the increasing temperature of oxalic acid.