Síntese e caracterização de aluminato de cobalto com diferentes estequiometrias e dopado com Cu, Mg e Ni

Abstract

Resumo: O aluminato de cobalto (C0AI2O4) é um espinélio de grande interesse industrial e tecnológico devido à sua cor azul intensa, estabilidade química, propriedades catalíticas, magnéticas e ambientais. Esta dissertação investiga a síntese e a caracterização estrutural, química e óptica deste material, analisando o impacto da temperatura de calcinação, da variação estequiométrica e da adição de dopantes metálicos na rede cristalina. Foram produzidos dois conjuntos de amostras: o primeiro com diferentes proporções de cobalto, calcinadas a 5000C via mistura de precursores e o segundo dopado com 10% de cobre (Cu), magnésio (Mg) e níquel (Ni), calcinado a 900 0C pelo método sol-gel. As caracterizações foram realiza das por difração de raios X com refinamento Rietveld, espectroscopia no infravermelho por transformada de Fourier, microscopia eletrônica de varredura, espectroscopia de energia dispersiva e espectroscopia UV-Visível. Os resultados para as amostras calcinadas a 500 0C indicaram uma formação de fase incompleta e baixa cristalinidade, com a coexistência de óxidos secundários (Al2O3 e Co3O4) que conferiram uma coloração preta às amostras, mascarando o azul característico. Em contraste, o tratamento térmico a 9000C promoveu a formação efetiva da estrutura de espinélio cúbica (Fd3m). A incorporação dos dopantes resultou em uma contração sistemática do parâmetro de rede, fenômeno atribuído à inversão catiônica parcial. O cobre atuou como agente fundente, promovendo um crescimento de grão superior (196,8 nm). As análises de UV-Vis e FTIR confirmaram que a cor azul está vinculada à coordenação tetraédrica do cobalto, enquanto a inversão catiônica induzida pela dopagem reduziu a pureza e a saturação da cor. Observou-se também que os do pantes inibiram a formação de óxidos amorfos superficiais presentes na amostra pura, que conferiram uma cor esverdeada para a amostra

Abstract: The cobalt aluminate (C0AI2O4) is a spinel of great industrial and technological interest due to its intense blue coloration, chemical stability, and its catalytic, magnetic and environmental properties. This dissertation investigates the synthesis and the structural, chemical and optical properties of this material, analysing the calcination temperature’s impact, the stoichi- ometric variation and the addition of metallic doping agents in the crystalline network. Two sets of samples were produced: the first had different percentages of cobalt, calcined at 500 °C through a mixture of precursors, and the second one doped with 10% of copper (Cu), magnesium (Mg) and nickel (Ni), calcined at 900 °C with the sol-gel method. The characteri- zations were made through diffraction of X-rays with Rietveld refinement, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy and UV-Visible spectroscopy. The results of the samples calcined at 500 °C indicated an incom- plete phase formation and with low crystallinity, with coexistence of secondary oxides (Al2O3 and Co3O4) causing a black coloration to appear on the samples, masking the characteristic blue. In contrast, the thermic treatment at 900 °C produced the effective formation of the cuboidal spinel strThe cobalt aluminate (C0AI2O4) is a spinel of great industrial and technological interest due to its intense blue coloration, chemical stability, and its catalytic, magnetic and environmental properties. This dissertation investigates the synthesis and the structural, chemical and optical properties of this material, analysing the calcination temperature’s impact, the stoichi- ometric variation and the addition of metallic doping agents in the crystalline network. Two sets of samples were produced: the first had different percentages of cobalt, calcined at 500 °C through a mixture of precursors, and the second one doped with 10% of copper (Cu), magnesium (Mg) and nickel (Ni), calcined at 900 °C with the sol-gel method. The characteri- zations were made through diffraction of X-rays with Rietveld refinement, Fourier-transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy and UV-Visible spectroscopy. The results of the samples calcined at 500 °C indicated an incom- plete phase formation and with low crystallinity, with coexistence of secondary oxides (Al2O3 and Co3O4) causing a black coloration to appear on the samples, masking the characteristic blue. In contrast, the thermic treatment at 900 °C produced the effective formation of the cuboidal spinel structure (Fd3m). The incorporation of the doping agents resulted in a sys- tematic contraction of the network parameter, a phenomenon assigned to the partial cationic inversion. The copper acted as a fusing agent, promoting a superior growth of the grain (196,8 nm). The UV-Vis and FTIR analysis confirm that the blue coloration is linked to the cobalt’s tetraedric coordination, while the cationic inversion induced by the doping reduced the purity and the color saturation. It was also observed that the doping agents inhibited the formation of surface amorphous oxides present in the pure sample, that bestowed a green hue to the sampleucture (Fd3m). The incorporation of the doping agents resulted in a sys- tematic contraction of the network parameter, a phenomenon assigned to the partial cationic inversion. The copper acted as a fusing agent, promoting a superior growth of the grain (196,8 nm). The UV-Vis and FTIR analysis confirm that the blue coloration is linked to the cobalt’s tetraedric coordination, while the cationic inversion induced by the doping reduced the purity and the color saturation. It was also observed that the doping agents inhibited the formation of surface amorphous oxides present in the pure sample, that bestowed a green hue to the sample