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    Crescimento de óxidos nanoestruturados sobre liga de Ti7Nb para processos fotocatalíticos
    (Universidade Federal de São Paulo, 2018-10-05) Gomes, Mariany Ludgero Maia [UNIFESP]; Rodrigues, Christiane de Arruda [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)
    This work presents the production of nanotubular photocatalytic oxides on Ti7Nb alloy, made in two ways: as-cast and material subjected to quenching starting at 1000°C and cooled in melting ice, both without going through the process of homegenization. Initially, a study of the alloy substrate was held by undergoing Vickers Microtoughness test, Optical Microscopy test, EDS, DRX and FRX. It was verified the presence of the following phases in both alloys: α, α`, β e ω. The latter was detected by means of Microtoughness tests, and was present in greater quantity in the alloy that was subjected to quenching. The nanotubular photocatalytic oxides were grown by the anodizing process using an aqueous solution containing Fions and a voltage difference of 20V, and were subjected to MEV-FEG and EDS analyses. It was obtained, for all samples, a continuous and regular oxide layer comprising of nanotubes with a mean length of 321 nm and mean internal diameter of 88 nm. EDS trials demonstrated a greater solubility of the Nb on the substrate that undergone to quenching, such that, in the as-cast alloy, regions rich in Nb appeared. Due to the amorphous characteristics of these nanoscale oxides, they were subjected to a thermal treatment to obtain a highly ordered crystalline phase. Heat treatment temperatures varying from 450°C to 650°C were investigated aiming to obtain crystalline nanotubular oxides with high photoactivity. The presence of Nb delayed the transition temperature from anatase to rutilo, and the best temperatures for the crystallization of samples of Ti7Nb in the as-cast form and quenched at 1000°C were 450°C and 550°C, respectively. Studies of the optical properties were performed using DRS techniques, and it was possible to verify that there was an increase in the photocatalytic efficiency of the oxide grown on the alloys in relation to the TiO2 due to a shift of the absorption into the visible region (alloy under quenching) and due to the reduction of the recombination rate of the photogenerated charges (as-cast alloy), confirmed by the RAMAN spectroscopy techinique. A study of the stability of the oxide layer grown on the Ti7Nb alloy prepared under quenching at 1000°C was carried out and no changing was observed. Photocurrent values of the oxide nanolayer grown on the Ti7Nb alloys were higher than that of the TiO2, both in the visible and in the UV-Vis light, with higher efficiency for the as-cast alloy. This efficiency was confirmed on the photocatalytic degradation of the Reactive Blue 4 (RB4) textile dye, where a reduction of 99.99% on the solution coloring and a reduction of 86.13% of the organic load was obtained after 180 min of photoelectrocatalytic treatment, under 1.2V and 80W UV radiation.