Estudo de materiais a base de bismuto (III) : sistema Bi2O3-V2O5 modificado pela incorporação de metais alcalinos terrosos

AUTOR(ES)

Marta Eloisa Medeiros

DATA DE PUBLICAÇÃO

1995

RESUMO

In the present work, we have studied a material with unusual properties, bismuth vanadate, BiVO4. The synthesis of this material was performed through the oxide method and the non-hydrolytic sol-gel method. This was done, in order to obtain information about the influence of these methods on the structural, thermal, compositional, morphological, and color characteristics of these materials. We have also introduced II metal (Mg, Ca, Sr and Ba) into the monoclinic structure of BiVO4, resulting in the composition BiVO4.xMO. These were obtained with two distinct molar proportions: 0.11.0. These different phases were studied with respect to the structural changes observed. Color properties of all the obtained phases were studied to determine the viability of their use as pigments. The following techniques were used to study the materiais: X-ray diffractometry, infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, differential scanning calorimetry, x-ray fluorescence spectroscopy, density by gas displacement, diffuse reflectance ultra-violet spectroscopy, and scanning electron microscopy. The main results show us that: i) the monoclinic BiVO4 can be prepared by both the proposed methods, but the resulting materiais present different structural, thermal, and color properties; ii) the vanadates groups in materials prepared by both routes present distortions. Raman spectroscopy shows that there is a greater structural disordering in the material obtained via oxide. The VO4 consists, in both cases, of three V-O bonds with 1.70 Å bond length, and another V-O bond with a bond length of 1.77 Å; iii) the phases that were modified with II metals show structural modifications that depend on the ionic radius and the amount of II metal incorporated into the crystal lattice; iv) the vanadate group, in all the modified phases, is distorted, and in some cases we observed important symmetry lowering, particularity when x>0.8. The modification of the BiVO4 phase with II metais causes great changes in the color tone of the materiaIs. These differences vary with the II metal, the precursor, and the value of x.

ASSUNTO(S)

bismuto - analise

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