Papers by Keyword: Anodic Alumina

Abstract: Ni nanopillars (Ni NPs) composite materials formation technology was presented. The morphological and structural properties of the composite material were investigated using scanning electron microscopy, atomic force microscopy, X-ray diffraction. The corrosion resistance of the nanocomposite materials has been studied by potentiodynamic polarization curves analysis. The composite represents the array of vertically ordered Ni NPs with the identical size in alumina matrix. XRD investigation indicates that Ni NPs are polynanocrystalline material. It has been shown that Ni NPs and the composite material have sufficient corrosion resistance in a 0.9% aqueous NaCl solution. Porous alumina matrix is the neutral and protective component of the composite. These nanocomposite materials can be excellent candidates for practical use in different applications.

Abstract: The morphology of anodic aluminum oxide (AAO) produced by hard anodization (HA) in oxalic acid electrolyte modified with various amount of ethylene glycol (EG) was investigated. The EG induces a considerable changes in the AAO morphology. The AAO transforms from continuous nanoporous film to separated AAO nanotubes upon addition of increasing amount of EG. In the sample II (4:1 v/v water to EG mixture) well separated nanotubes with variable wall thickness are produced. In the sample III (1:1 v/v water to EG solution) the nanotubes “imprisoned” in a partially dissolved cell skeleton with regularly spaced apertures along the cell are formed. In the electrolyte with the highest amount of EG (1:4 v/v water to EG mixture) an irregular AAO consisted of formless oxide and the oxide in a form of separated tubes of thick walls and small pores is fabricated. Based on the data obtained in this work it is concluded that the C containing ionic species originating from the EG dissociation along with the high electric field (E) operating during the HA were responsible for the separation phenomena. These ions, driven by the high E, were transported from the electrolyte to the pore base, where they were being embedded into the AAO framework generating strong mechanical stresses at cell boundaries and initiating the cell cleavage process. Moreover, some of these charged particles were ionized under the high E providing additional electrons to the overall current flow and giving rise to a sudden current density boost in the samples II and III.

Abstract: This work describes preparation process of free-standing alumina membranes used in sensor devices for separation or purification (increased selectivity, and sensitivity) purposes. Nanoporous alumina membranes were prepared using anodic oxidation of aluminium foil in two types of acidic electrolytes and characterized using scanning electron microscopy. Membranes with pore diameters of 90 nm and 30 nm and thicknesses of 115 µm and 163 µm respectively were obtained. Fabrication of membranes with different post-treatment was also done. In this post-treatment process, etching of non-anodized aluminium and opening of barrier layer were replaced with application of reversible potential with equal magnitude as anodization voltage.

Abstract: The thermal stability of anodic alumina layers made by the open circuit potential measurements and electron microscopy is discussed. The crack growth resistance of the anodic alumina layers has been studied depending on the initial aluminum alloy composition and the anodization regimes.

Abstract: Self-ordered nanoporous α-alumina membrane having uniformly sized straight pore arrays was fabricated by anodization of aluminum and subsequent through-hole and heat treatment. The detachment of thick anodic oxide film formed in oxalic acid was performed by combining preliminary loaded heating before stepwise voltage drop and cathodic polarization in phosphoric acid to prevent excess dissolution at the through-hole process. Suppression of excess dissolution of the upper layer of anodic alumina membrane acted an important role to provide symmetrical evenness of top and bottom pore density for the prevention of deformation such as warp and cracking during subsequent heating for crystallization. Thus, a thick, robust and chemically resistant nanoporous crystalline α-alumina membrane was successfully obtained by optimizing preparation conditions.

Abstract: A wide variety of metallic and metal oxide nanoflowers and other exotic patterns have been fabricated using different techniques. We have created copper and cupric oxide nanoflowers using two different techniques: electro-deposition of copper in polymer and anodic alumina templates, and cytyltrimethal ammonium bromide (CTAB)-assisted hydrothermal method, respectively. Zinc oxide and manganese oxide nanoflowers have been synthesized by thermal treatment. Characterization of nanoflowers is done in the same way as for nanowires using XRD, SEM, TEM and FESEM. Scanning Electron Microscope (SEM) images record some interesting morphologies of metallic copper nanoflowers. Field Emission Scanning Electron Microscope (FESEM) has been used to determine morphology and composition of copper oxide nanoflowers. X-ray diffraction (XRD) pattern reveals the monoclinic phase of CuO in the crystallographic structure of copper oxide nanoflowers. Nanoflowers find interesting applications in industry. There is an element of random artistic design of nature, rather than science, in exotic patterns of nanoflowers fabricated in our laboratory.

Abstract: Highly ordered through-hole anodic porous alumina membranes were fabricated by electrochemical oxidation of aluminum in a controlled two-step process. A teflon dispositive was used to ensure single side anodization. Under the most appropriate condition for the fabrication of ideally ordered anodic aluminum oxide (AAO), the voltage used was 15 V during 24 h in a 15 % w/v sulfuric acid solution. SEM, TEM and FESEM characterization shows that the as-fabricated AAO film has a defect-free array of straight parallel channels perpendicular to the surface. The thickness of the porous membrane is 20 microns, approximately. The ordered channels are formed in a honey comb arrange with a pore diameter in the range 20-30 nm, wall thickness of 10-20 nm, interpore distance of 40 nm, and high aspect ratio of 850. The pore density, quantified by image analysis, is 5.4×10¹⁰ pore/cm²; perfect ordering was maintained in the full depth of the membrane. Dimensions of this porous structure provide a convenient way to precision engineer the nanoscale morphology.

Abstract: Cu-Al₂O₃ (Co-Al₂O₃) nano-array composite structures assemblies with Cu (Co) grown in the pores of an anodic alumina membrane (AAM) were obtained by alternating current electrode position. Their transmitted spectra and polarized spectra are systematically investigated. Experimental results indicate that the transmittance of Cu-Al₂O₃ is superior to that of Co-Al₂O₃ in visible and infrared waveband, but the extinction ratio of Co-Al₂O₃ is better than that of Cu-Al₂O₃ in near infrared waveband.

Abstract: Copper is one of the most important metals in modern electronic technology. Keeping in view its role in nanoelectronics, we have fabricated copper nanowires of diameters 100 and 200nm using Anodic Alumina and polymer membranes as templates. Electrodeposition technique based on the principle of electroplating was adopted for copper nanowire fabrication in an electrochemical cell designed in our laboratory. SEM micrographs are used to calculate the aspect ratio of nanowires. The morphology of nanowires shows some interesting features.

Abstract: Effects of annealing treatments of aluminum substrate for ordered nanopore arrays formed by self-organized anodization have been investigated. To observe the relationship between microstructures of aluminum substrate and nanopore regularity formed after anodization of the aluminum substrate, aluminum specimens were annealed at 300, 400, and 500 °C. The anodic alumina layer was prepared by two-step anodizing process in oxalic acid at 40 V. The ordered arrays of nanopore on anodic alumina were shown to be strongly dependent on the annealing conditions, and nanopore regularity on alumina template increased with increasing annealing temperature and time.