Min Of Anodization Research Articles

Comparison of the Growth of $${\text {TiO}}_{2}$$ TiO 2 Nanotubes in Different Solutions

The kinetics of growth of tubular nanostructures of titanium dioxide ( $${\text {TiO}}_{2}$$ ) obtained by means of the physic-chemical method of electro position under potentiostatic conditions is studied. For this investigation, four tests were carried out where some synthesis parameters were varied in chemical solution: water/fluorhydric acid/ammonium fluoride/ethylene glycol $$(\text {H}_{2} \text {O/HF/NH}_{4}\text {F/EG})$$ as well as the conditions of anodization. Therefore, the chemical attack in the anodization process is produced by the $$\text {NH}_{4}\text {F}$$ and $$\text {HF}$$ ions. The morphology of the resulting nanotubes was analyzed through scanning electron microscopy (SEM). The average length of the nanotubes was established, with a maximum value of 980 nm. By means of X-ray diffraction of the samples the structure was analyzed, obtaining a mixed phase of anatase and titanium. Using ultraviolet–visible spectroscopy (UV–Vis), the energy gap of the tests was found at different times of anodization. At 60 min of anodization, the energy gap of the samples varied between 3.56 and 3.68 eV. For a time of 30 min anodization, the energy gap of the samples varied between 3.58 and 3.63 eV with the same parameters of chemical synthesis. With obtaining of the curves of the current as a function of the time of anodization (I vs. t), the different stages of growth of the nanotubes and the regions that these stages define were determined. Analyzing of the behavior the current–time graphs and SEM measurements, it was observed that the best solution of the 4 tests used in this work was that of test 1.

The initial products of the anodic oxidation of galena in acidic solution and the influence of mineral stoichiometry

The oxidation products retained at the surface of galena samples from Broken Hill (lead-rich) and Missouri (sulphur-rich) following mild anodic treatment in acetate solution of pH 4.6 have been determined by X-ray photoelectron spectroscopy (XPS) using excitation both by Al K α X-rays and by synchrotron radiation (SR). Elemental sulphur was found to be the major oxidation product on both galenas. For short anodization times, S 0 could only be detected by the more surface sensitive SR-XPS. Electrochemical studies showed that the quantity of sulphur on a Missouri galena surface did not decrease significantly when the galena was held for 40 min at open circuit. This contrasts with previous studies on Broken Hill galena in which the sulphur coverage was found to decrease to a low value in this time period, a behaviour that was assigned to diffusion of lead atoms from the bulk. The different behaviour of the two galenas can be explained by the different stoichiometry of the Broken Hill and Missouri minerals. According to SR-XPS measurements, the intensity of the S 0 component in S 2p spectra for galena surfaces held for 40 min at open circuit following anodization at 0.3 V for 20 s was less than for the equivalent spectra carried out within 7 min of anodization. The S 0 intensity was negligible for the Broken Hill mineral in agreement with electrochemical studies. A small but significant decrease in the S 2p intensity was also observed for Missouri galena and this was assigned to accumulation of the sulphur product into clusters. S 2p components at the binding energies expected for lead polysulphide were also observed in the spectra for the Missouri mineral. Conventional XPS revealed a significant variability in the S 0 2p intensity following short anodization times and this could also arise from sulphur clustering.

Oxide Film Formation on a Microcrystalline Al Alloy in Sulfuric Acid

The differences in the electrochemical behavior of a rapidly solidified, two‐phase (matrix and dispersoid) Al‐based alloy containing Fe V and Si (FVS0812 alloy) and the bulk form of its matrix and dispersoid phases were investigated in sulfuric acid FVS0812 exhibited generally higher electrochemical activity than the matrix material due to the presence of the very active dispersoid phase in the alloy. Impedance studies indicated that the properties of thin films formed on the FVS0812 and matrix substrates during only 5 min of anodization are similar, whereas the film formed on the alloy during 2.5 h of anodization was substantially less resistive and contained a thinner and/or damaged underlying barrier oxide compared to a comparable film formed on the matrix. Compared to the classical structure of porous Al oxide films with underlying barrier oxide, the oxide film on FVS0812, as seen by TEM, was thinner, with an intermittent banner oxide underlying a porous oxide of contorted morphology. Evidence is seen for the loss of dispersoids from the oxide film, leaving voids throughout its structure, perhaps the reason for its lack of physical adherence and its limiting thickness.