Influence of the anodizing process variables on the acidic properties of anodic alumina films

In the present work, the effect of the different variables involved in the process of aluminum anodizing on the total surface acidity of the samples obtained was studied. Aluminum foils were treated by the electro-chemical process of anodic anodizing within the following variable ranges: concentration=1.5-2.5 M; temperature=303-323 K; voltage=10-20 V; time=30-90 min. The total acidity of the samples was characterized by two different methods: acid-base titration using Hammet indicators and potentiometric titration. The results showed that anodizing time, temperature and concentration were the main variables that determined the surface acid properties of the samples, and to a lesser extent voltage. Acidity increased with increasing concentration of the electrolytic bath, whereas the rest of the variables had the opposite effect. Theresults obtained provide a novel tool for variable selection in order to use synthetized materials as catalytic supports, adding to previous research based on the morphology of alumina layers.Fil: Boldrini, Diego Emmanuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Yañez, Maria Julia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; ArgentinaFil: Tonetto, Gabriela Marta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; Argentin

Gold nanotube membranes: fabrication of controlled pore geometries and tailored surface chemistries

This study concerns the fabrication, chemical modification and characterisation of gold nanotube membranes using porous alumina (PA) membranes as templates. Electroless deposition was used to finely coat membranes with gold, forming gold nanotubes within the pores. PA templates were fabricated with straight and shaped pores thus allowing the fabrication of a wide range of gold nanotube geometries. The gold deposition process provides control over the pore size of the membrane, where pore sizes can be reduced to molecular dimensions. Chemical sensitivity was introduced into the membrane through the addition of self assembled monolayers (SAMs) of thiols. Characterisation of thiol assembly within the pores of the membrane was investigated using confocal Raman

Optofluidic study of the pore widening in nanoporous alumina membranes

En este trabajo se utiliza una técnica optofluídica para estudiar el ensanchamiento químico de los poros de membranas de alúmina nanoporosa. La técnica optofluídica consiste en medir la evolución de la reflectancia de luz láser producida por la membrana durante la imbibición capilar de la misma con un líquido de propiedades conocidas. El cambio en la proporción aire-líquido a medida que la membrana se llena modifica el índice de refracción efectivo de la membrana produciendo sucesivamente interferencias constructivas y destructivas. La señal obtenida puede relacionarse con el volumen de líquido que penetró en la membrana utilizando una teoría de medio efectivo. Realizando las medidas de llenado capilar en ambas direcciones de la membrana es posible caracterizar la morfología del poro. Los resultados obtenidos indican que los poros de las membranas utilizadas son inicialmente cónicos y que el ensanchamiento por ataque químico con soluciones diluidas de H3PO4 es uniforme a lo largo de los mismos y proporcional al tiempo de ataque. Los resultados obtenidos son consistentes con los que produce la caracterización de las membranas por técnicas estándar de elipsometría y demuestran que esta nueva técnica optofluídica constituye una forma simple y rápida de caracterizar membranas nanoporosas. La porosidad de las membranas obtenida con esta técnica difiere de la encontrada a partir del análisis de imágenes de las muestras. Se sugiere que parte del líquido que ingresa en la membrana ocupa una sub-porosidad formada por defectos en la matriz de alúmina.In this paper we use an optofluidic technic for study the chemical pore widening process of nanoporous alumina membranes. This technic consists in measure the time evolution of the membrane reflectance during capillary imbibition of a liquid with known properties. The change in the proportion air-liquid inside the membrane, modify the effective refractive index producing successively constructive and destructive interferences. Using an effective medium theory, the obtained signal can be related with the liquid volume inside the membrane. Additionally, this information can be processed to characterize the morphology of the pores. The obtained results indicate that, initially, the pores are conical and the chemical etching with diluted H3PO4 solutions is produced in an axially uniform way at constant rate. These results are consistent with those obtained with standard ellipsometry technics and show that this novel optofluidic technic is simple, fast and suitable for characterization of nanoporous membranes. However, the porosity value obtained differs with those obtained from SEM images analysis. This result suggests that a portion of the liquid used enters to a sub-nano porosity formed by defects in the alumina matrix.Fil: Elizalde, Emanuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Rahman, M.M.. Universitat Rovira I Virgili; EspañaFil: Urteaga, Raul. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; ArgentinaFil: Berli, Claudio Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; ArgentinaFil: Koropecki, Roberto Roman. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Física del Litoral. Universidad Nacional del Litoral. Instituto de Física del Litoral; Argentin

Influence of Anodizing Parameters on Surface Morphology and Surface-Free Energy of Al2O3 Layers Produced on EN AW-5251 Alloy

The paper presents the influence of the surface anodizing parameters of the aluminum alloy EN AW-5251 on the physicochemical properties of the oxide layers produced on it. Micrographs of the surface of the oxide layers were taken using a scanning electron microscope (SEM). The chemical composition of cross-sections from the oxide layers was studied using energy dispersive spectroscopy (EDS). The phase structure of the Al2O3 layers was determined by the pattern method using X-ray diffractometry (XRD). The nanomorphology of the oxide layers were analyzed based on microscopic photographs using the ImageJ 1.50i program. The energetic state of the layers was based on the surface-free energy (SFE), calculated from measurements of contact angles using the Owens-Wendt method. The highest surface-free energy value (49.12 mJ/m2) was recorded for the sample produced at 293 K, 3 A/dm2, in 60 min. The lowest surface-free energy value (31.36 mJ/m2) was recorded for the sample produced at 283 K, 1 A/dm2, in 20 min (the only hydrophobic layer). The highest average value nanopore area (2358.7 nm2) was recorded for the sample produced at 303 K, 4 A/dm2, in 45 min. The lowest average value nanopore area (183 nm2) was recorded for the sample produced at 313 K, 1 A/dm2, in 20 min

A study on the dissolution of non-porous alumina films on aluminium

The dissolution behaviour in sulphate solutions of so-called non-porous anodic alumina films and films formed in dry oxygen and i n a moist oxygen atmosphere on chemically polished aluminium has "been investigated. Evidence is presented which indicates that the non-porous anodic films, formed at 7-30 volts, consisted of two regions, a thin, less soluble region adjacent to the metal and a thicker, more soluble outer region into which hydroxyl ions were incorporated. The structure might be related to the initial method of surface preparation adopted. It is suggested that films formed in dry oxygen at 500 C consist of crystalline Y-alumina, whilst those formed in the moist oxygen atmosphere a t 500 C possibly consist of amorphous alumina with someadsorbed water and are less faulted than the crystalline oxide. Again, there is some indication that the structure of these filmsis strongly influenced by the initial method of surface preparation used. The dissolution behaviour of the anodic films and films formed in dry oxygen at 500 C can be understood in terms of the extent of sulphate ion adsorption, apparently greater under the same conditions for the former type, and its effect on rate of transfer of protons, hydroxyl ions and water across the oxide/solution interface. A reaction scheme, proposed earlier to account for the behaviour during dissolution of the barrier layer of porous films formed anodically in sulphuric acid, appears adequate to explain the dissolution behaviour observed in the present studies. However, the type of behaviour, although rather similar for both' anodic non-porous and films formed in dry oxygen at 500 C, was quite different from the barrier layer of porous films formed anodically in sulphuric acid

Rodzaj zużywania warstw tlenkowych w zależności od parametrów wytwarzania

The article presents the type of wear of Al2O3 layers produced on the aluminium alloy EN AW-5251 depending on the production parameters. Oxide layers were produced by using DC anodizing in a ternary electrolyte at variable current density and electrolyte temperature. The layer scratch tests were carried out using a Micron- Gamma microhardness tester. The scratches of oxide layers were tested for the geometric structure of the surface using a Form TalySurf 2 50i contact profilograph. Contact thickness measurements were also made using a Dualscope MP40 device based on the eddy-current method. Using a scanning microscope (SEM), photos of the sample surfaces were taken to show and compare the surface morphology of the anodized layers in various parameters. Based on the research, it can be concluded that changes in the conditions of the production process of Al2O3 layers (electrolyte temperature and current density) have an impact on the type of tribological wear and changes in layer thickness. The largest thickness of the oxide layer (19.44 μm) was measured for Sample B produced at a current density of 3A/dm2 at an electrolyte temperature of 283 K, which was also characterized by the lowest value of the ratio of parameters f1 to f2 (0.584). The smallest thickness (5.32 μm) was measured for the Sample C anodized at 1 A/dm2 at 303 K, this sample had the largest ratio f1 to f2 (1.068) for the produced Al2O3 layers. Thanks to the parameters f1 and f2 and the calculation of their ratio, the wear process for Sample B was determined as scratching and microcutting, while for Sample C as grooving

Recycling chocolate aluminum wrapping foil as to create electrochemical metal strip electrodes

The development of low-cost electrode devices from conductive materials has recently attracted considerable attention as a sustainable means to replace the existing commercially available electrodes. In this study, two different electrode surfaces (surfaces 1 and 2, denoted as S1 and S2) were fabricated from chocolate wrapping aluminum foils. Energy dispersive X-Ray (EDX) and field emission scanning electron microscopy (FESEM) were used to investigate the elemental composition and surface morphology of the prepared electrodes. Meanwhile, cyclic voltammetry (CV), chronoamperometry, electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV) were used to assess the electrical conductivities and the electrochemical activities of the prepared electrodes. It was found that the fabricated electrode strips, particularly the S1 electrode, showed good electrochemical responses and conductivity properties in phosphate buffer (PB) solutions. Interestingly, both of the electrodes can respond to the ruthenium hexamine (Ruhex) redox species. The fundamental results presented from this study indicate that this electrode material can be an inexpensive alternative for the electrode substrate. Overall, our findings indicate that electrodes made from chocolate wrapping materials have promise as electrochemical sensors and can be utilized in various applications