Aluminum In Oxalic Acid Research Articles

Periodic Oscillations of Luminescence Intensity at the Formation of Anodic Oxides on Aluminum in Oxalic Acid

The electroluminescence phenomenon observed during the formation of porous anodic oxide films on aluminum in oxalic acid solutions is studied. Periodic changes in the luminescence intensity arise during the transition from the barrier-film formation to the steady-state growth of porous oxide. The period and number of oscillations are determined by the oxidation voltage.

Porous anodic alumina optimized as a catalyst support for microreactors

This paper describes the optimization of process conditions for making porous anodic alumina as a catalyst support in monolithic microreactors. The basic process involves direct current anodization of 1100 alloy aluminum in oxalic acid. Electrolyte concentration, temperature, and anodization potential are optimized with respect to oxidation efficiency and pore density via a Box–Behnken experimental design to the values of 0.6 M, 18 °C, and 30 V, respectively. The effects of subsequent hydrothermal–thermal treatment on the surface area enhancement and surface morphology of the porous oxide are also investigated and optimized. The resulting films are employed in the fabrication of active catalytic aluminum–alumina microreactors for the decomposition of ammonia to hydrogen and nitrogen.

Study of porous oxide film growth on aluminum in oxalic acid using a re-anodizing technique

The effects of current density on the porous alumina films formed on Al foil in 4% oxalic acid have been studied using the film thickness measured with the help of a mechanical profiler with computer signal processing, and the barrier layer thickness determined by a re-anodizing technique. A digital voltmeter with a computer system was used to record the change in the anode potential with re-anodizing time. It was established that the dependence of the logarithm of the ionic current density on the electric field strength consists of two linear regions. At electric field strengths higher than 9.9MVcm−1 a decrease in the rate of ionic current density growth by 1.88 times is observed. This peculiarity of the dependence was explained by the decrease in the effective charge of mobile ions that are jumping over the energetic barrier in order to enter the oxide. At high field strengths the linear dependence of the electric field strength across the barrier layer on the inverse volume expansion factor of porous alumina films has been established.

The temperature rise and burning for high rate anodizing of aluminum in oxalic acid.

The temperature rise in the substrate as well as in the bulk solution and the development of a local brown-coloured 'burnt' region on the anodic film are the characteristics of high rate anodizing of aluminum in oxalic acid. In this study, measurement of the barrier layer thickness in both the predicted burning region and the normal region indicates that they increase simultaneously as the voltage builds up to form the secondary voltage peak on the voltage/time transient; a depletion of oxalate anions allied with the temperature rise at the pore base is thought to govern this behaviour. Characteristic strong dotted anodic glows occurred simultaneously with a slight drop of voltage, about 1V, from the secondary peak value were observed just prior to the initiation of the local burning sector; also, the local substrate temperature always rises when burning is approaching. These studies suggest that a thermal modified electronic breakdown process is responsible for the burning phenomenon.

Structural chemistry of anodic alumina

Magic angle spinning-nuclear magnetic resonance has been used as a structural probe for porous anodic films formed on aluminium in oxalic acid. The morphologically and compositionally characterized films reveal four-, five-and sixfold coordination of aluminium with oxygen. However, with controlled chemical dissolution of the distinct film morphology, the residual film unifies to sixfold coordination. Surprisingly, the sixfold coordination is not limited to the pure alumina film regions, but develops relatively rapidily, suggesting a ready transformation of the bulk film material on immersion in the anodizing electrolyte in the absence of the electric field.

Investigation of the Electrolytic Colouring of Porous Anodic Films on Aluminium using Electron Microscopy

SummaryThe colouring of porous anodic films formed on aluminium in oxalic acid, using a c deposition of silver within the pores, has been studied by electron microscopical examination of replicas taken from fracture sections of the films. Following a recovery period in which tiny incipient pores develop in and transform the initial barrier layer of the film, by thermally enhanced field assisted dissolution, metal deposits at the bases of most original pores but the nucleation and growth process occurs at different rates in different pores. It appears that the metal deposition takes place as a result of current passed through the remaining barrier layer during the cathodic half cycle, probably via flaws of various kinds, and the metal is apparently not in direct contact with the aluminium substrate. A progressively thickening anodic film, characteristic of a c anodizing in sulphuric acid, is formed beneath the original film barrier layer but its development is impeded by the metal deposition process.

The Morphology of Anodic Films Formed on Aluminium in Oxalic Acid

SummaryElectron microscopy of carbon replicas taken from outer surfaces, sections and cell base patterns of anodic films, formed in oxalic acid, has enabled relationships between the main film parameters of barrier layer thickness, cell size and pore diameter to be quantified and related to the anodizing variables. In general, the barrier layer, cell and pore dimensions are all proportional to the forming voltage and are inter-related as a result of the forming mechanism involving field-assisted dissolution and growth of the film in the barrier layer region. If the forming voltage is allowed to rise during the anodizing run at constant current density, inversely funnelled pores are produced in which the pore diameter is smaller nearer the film surface than adjacent to the barrier layer. In order to maintain this morphology it is necessaiy to restrain the electrolyte aggressiveness by controlling the acid concentration and temperature below certain limits. Transmission electron micrographs of stripped thin films have provided information on film development and pore initiation and on the transition from these transient processes to the steady-state growth stages.

非水溶媒中におけるカルボン酸誘導体によるアルミニウムの直接滴定およびアルミニウム表面処理液中のアルミニウム定量への応用

Conductometry of aluminum with EDTA and NTA as well as oxalic, succinic, and benzoic acids in DMF (dimethyl formamide) has been investigated. Chelatometry with EDTA for the determination of aluminum in aqueous solution was not easy or rapid because Al was present in various types of anion in the solution. In DMF solution, AlCl3 was present in cations such as [AlCl3-x⋅DMF]+. After a large amount of DMF was added to the solution, conductometric titration of AlCl3 was made with DMF solution of carboxylic acid derivatives (oxalic, succinic, benzoic acids, NTA, and EDTA), and 3 inflection points were observed for each solute in DMF as follows:Al: oxalic acid 2:1, 1:1, and 2:3Al: succinic acid 2:1, 1:1, and 2:3Al: benzoic acid 1:1, 1:2, and 1:3Al: NTA 3:1, 2:1, and 1:1Al: EDTA 4:1, 2:1, and 1:1However, the inflection points for EDTA 2:1 and 1:1 were considered to be weak, and Al was determined by the point of 4:1.The determination of aluminum in oxalic acid, phosphoric acid, sulfuric acid and other aluminum surface finishing solutions were rapidly determined by the present method after a large amount (10 times of the sample solution) of DMF was added.