Добірка наукової літератури з теми "Local anodizing"

A search through the literature reveals that the vast majority of studies about aluminum anodizing were conducted at the macroscale (i.e., from cm2 up to m2), while those focused on local anodizing (i.e., on surfaces of less than 1 mm2) are rare. The last ones either used insulating masks or were conducted in an electrolyte droplet. The present study describes on the one hand a new way to prepare aluminum microelectrodes of conventional disk-shaped geometry, and on the other hand the local anodizing of their respective aluminum micrometric top-disks. The influence of the anodizing voltage on anodic film characteristics (i.e., thickness, growth rate and expansion factor) was studied during local anodizing. Compared with the values reported for macroscopic anodizing, the pore diameter appears to be significantly low and the film growth rate can reach atypically high values, both specificities probably resulting from a very limited increase in the temperature on the aluminum surface during anodizing.

In 100-times diluted synthetic seawater at 298 K (pH 8.2), the effect of anodizing on the galvanic corrosion resistance of AA5083 coupled to pure Fe, Type 430, or 304 stainless steel was investigated by measuring the galvanic current densities and electrode potentials. Anodizing in H 2 SO 4 effectively suppressed the galvanic corrosion of AA5083. It was shown that an increase in pitting potential by anodizing alone could not determine whether galvanic corrosion would occur or not. The cathodic activity on Al 6 (Fe, Mn), which causes alkalization on and around Al 6 (Fe, Mn) particles, decreased as the anodizing time and voltage increased. And, the anodic oxide film on the Al-matrix in alkaline environments became stable as the thickness of the oxide film increased. A comparison of these two factors revealed that the dissolution resistance of surface oxide film on Al-matrix contributed the galvanic corrosion prevention of anodized AA5083 coupled to pure Fe. In the case of AA5083 anodized at 16 V for 180 s, no galvanic corrosion damage was observed on the AA5083 coupled to Type 430 or 304.

Anodized aluminum oxide (AOA) is applied in many technological areas such as formation of decorative or anticorrosive coating, hydrophobic and hydrophilic surfaces, development of functional micro- and nanomaterials. Due to unique properties of porous structure (most direct, regular and through pores with size in a narrow range) AOA films can be used for membrane separation. The morphological features of such films mainly depend on synthesis conditions. This review consists of the models of pore formation on the aluminum surface and the correlation parameters of films with anodizing conditions. Particular attention is paid to the influence of synthesis factors (electrolyte composition, voltage, temperature conditions, etc) on the porous structure of AOA and the film thickness that determines the mechanical strength of membranes. The optimal voltage values for the porous structure arraingment of anodized aluminum oxide were indicated for each electrolyte. It is noted formation of cylindrical shaped pores with controllable pore diameters, periodicity and density distribution can be produced during two-stage anodizing. The pre-treatment of the metal surface and stage of separation of the formed film from its surface are also considered. Modern research are mainly aimed to synthesis of porous AOA membranes in new anodizing electrolytes and determining pore formation factors on the aluminum surface. The new anodizing conditions in most popular electrolytes (oxalic, sulfuric, phosphoric acids) for obtaining of porous AOA with the required morphological features is also under investigation. Such conditions include, for example, a lower voltage or higher temperature in case for a particular electrolyte. To avoid of local heating the electrolytes with additional components, for example, organic additives is also studied. Some practical aspects of AOA membrane utilization obtained under certain conditions are considered.

The formation process of a petal-like morphology on the surface of porous anodic alumina (PAA) is discussed in detail. During the anodizing process, the electronic current is produced within the growing oxide, which results in the oxygen evolution at the pore bottom. The pressure of the oxygen bubbles increases along with the anodizing process, and their high pressure acts as a driving-force of the micro-gas-flow, resulting in the micro-liquid-flow in the pores of PAA. The micro-liquid-flow can flow into each other between a center pore and the nearest neighboring pores. The nanogroove between two pores can be formed due to the dissolving effect during the process of micro-liquid-flow between the two pores. This leads to the formation of the petal-like morphology on the PAA surface. As the micro-liquid-flow leaves off the pore bottom, there a local vacuum is formed. This local vacuum behaves as a driving-force of the micro-liquid-flow, making the electrolyte renovated in the nanopores. The renovated electrolyte can provide enough anions or impurity centers, which are the cause of the generation of the electronic current. The self-organizing for the petal-like morphology on PAA surface is mainly dependent upon the high pressure of the oxygen bubbles and the local vacuum produced at the pore bottom. The present results may help us to understand the nature of the self-organization in the porous anodic oxides.

The local wastes, which are sources of SiO2, Al2O3 and CaO, are rice husk ash, waste sediment from aluminum anodizing process and dreg from pulp production, respectively. The wastes are mixed in three different compositions in ranges of 20-50 SiO2, 20-35 CaO and 20-45 Al2O3, wet milled, slip casted and then fired at 1,100 °C. Characterization of the fired bodies reveals the formation of calcium-aluminosilicate compounds: gehlenite and anorthite as major phases, in accordance with the SiO2-CaO-Al2O3 ternary diagram. Their bulk densities and % water absorption lies between 0.95-1.42 g/cm3 and 37.40-67.95%, respectively. While flexural strength and coefficient of thermal expansion are between 4.09-9.56 MPa and 6.14 - 10.1 x 10-6 °C-1, respectively. By simple thermal conductivity comparison, the materials themselves have thermal conductivity comparable to alumina ceramics. These wastes, therefore, may be used as precursors for the production of some insulating refractory members, in place of minerals from natural resources.

The morphology and microstructure of the columnar niobium oxide nanostructures were investigated. The dependences of their morphological sizes on the anodization voltages (100–450 V) and anodic alumina pore diameters (40–150 nm) were established. The features of ion transfer in the process of niobium local anodizing were investigated and the transport numbers of electrolyte anions and niobium cations were calculated. The formation and growth mechanism was proposed and discussed. The phase composition and electrophysical properties of the column nanostructures were investigated.

L'anodisation de l'aluminium est un traitement de surface connu et étudié depuis près d'un siècle. Toutefois, de façon surprenante, très peu de travaux ont concerné l'anodisation locale de l'aluminium, c'est-à-dire sur des surfaces inférieures au mm². Le premier but de ce travail a consisté à fabriquer des microélectrodes unitaires en aluminium, ce qui n'avait jamais été réalisé auparavant. Des essais ont été réalisés selon trois approches d'élaboration, à savoir la fusion du métal, l'étirage simultané et l'enrobage du fil conducteur. Au final, un protocole expérimental maîtrisé, répétable et innovant permet à présent la fabrication de microélectrodes d'aluminium 1050 de type disque-plan dont la surface active constitue un disque de 125 µm de diamètre, et le Rg, c'est-à-dire le rapport entre le diamètre total de l'électrode et le diamètre du métal, variant entre 2,5 et 9,5. Le deuxième objectif résidait dans l'anodisation de ces microélectrodes d'aluminium, en étudiant dans ce cas l'influence de différents paramètres opératoires clés (tension, composition de l'électrolyte et sa température) sur les caractéristiques des films anodiques. Les résultats ont d'une part confirmée des évolutions "classiques" de la porosité ou du diamètre des pores, mais ont d'autre part révélé des vitesses de croissance atypiques, associées spécifiquement à l'échelle microscopique. Le troisième et dernier challenge visait à tester la faisabilité d'élaborer un réseau de nanoélectrodes métalliques à l'intérieur des pores des films anodiques élaborés précédemment à l'extrémité des microélectrodes. Dans cette optique, différentes expérimentations ont été menées afin de réduire la couche barrière et limiter la réduction de l'eau, en vue d'électrodéposer du nickel métal dans la porosité. Au final, les présents travaux constituent l'initiation d'une voie d'élaboration prometteuse vers une nouvelle génération potentielle de capteurs tirant parti des propriétés d'un réseau d'ultramicroélectrodes ayant chacune la dimension d'un pore unitaire, soit un diamètre de 100 nm
Aluminum anodizing is a surface treatment that has been known and studied for nearly a century. However, in a surprising manner, very few works have been published about the local anodizing of aluminum, meaning on surfaces lower than a mm². The primary goal of this work consisted in fabricating unitary aluminum microelectrodes, which has never been reported. Tests have been carried out using three different approaches, that is using melted aluminum, the simultaneous pulling of a glass capillary, and the coating of a conducting wire. Ultimately, a controlled experimental procedure, repeatable and innovative, now allows the manufacturing of disk-shaped aluminum 1050 microelectrodes, the active surface of which is a 125 µm diameter disk and the Rg, which is the electrode total diameter on the metal diameter ratio, varying between 2,5 and 9,5. The second objective lied in the anodizing of these aluminum microelectrodes, while studying in this case the role of different key operating parameters (voltage, nature of the electrolyte and its temperature) on the anodic film characteristics. The results have, for one part, confirmed the "standard" evolution of the porosity and the pores diameter, but for the other part have also revealed extraordinary growth speed of the anodic film, which has specifically been associated with the microscopic scale. The third and last challenge was to test the possibility of elaborating a metal nanoelectrode array inside the pores of the anodic films previously achieved at the tip of the microelectrodes. In this context, various experiments have been carried out to thin the barrier layer and restrict the reduction of water with the idea of electrodepositing metallic nickel in the porous film. Finally, the present work represents the first step to a promising way of elaborating a potential new generation of sensors using the properties of an ultramicroelectrodes array, every single one of which having the dimension of a single pore, with a diameter of 100 nm

The process of Quick Plastic Forming (QPF) developed by General Motors involves hot aluminum forming at ∼450°C, and has formability advantages over conventional stamping of aluminum or steel. However, there are still no fully satisfactory solutions for the problem of local interaction/sticking between the aluminum blank and the tool, and the eventual transfer of some aluminum to the steel tool after repeated forming cycles. In this paper we show that the process of anodizing aluminum prior to forming greatly diminishes the interaction of aluminum with steel at QPF forming temperatures. Significantly improved tribological behavior of the aluminum surface after anodization as compared to lubricated aluminum was shown on a laboratory scale with flat-on-flat reciprocating experiments.