RESUMO
We present the preparation, structural and magnetic properties of nanosized magnetite obtained by the crystallization of a series of Fe-containing borosilicate glasses. Several compositions with the ratio Fe2O3/SiO2 spanning from 0.37 to 0.67 were investigated as a function of two nucleators Cr2O3 and P2O5, respectively, and modifiers and intermediates (Al2O3 and MgO). Mössbauer spectroscopy revealed the degree, the type and the location of disorder induced by a specific composition and nucleators. In addition to magnetite, it was also revealed the presence of large amounts of Fe-rich paramagnetic phases. The magnetic response is analysed in relation with the amount of Fe ions which remain dispersed in the glassy matrix as noninteracting (paramagnetic) ions. We discuss the role of the nucleators on the disorder in both tetrahedral and octahedral sites of the magnetite.
Assuntos
Cristalização/métodos , Vidro/química , Nanopartículas de Magnetita/química , Nanopartículas de Magnetita/ultraestrutura , Substâncias Macromoleculares/química , Campos Magnéticos , Teste de Materiais , Conformação Molecular , Tamanho da Partícula , Propriedades de SuperfícieRESUMO
The paper presents a short history of the cataract intervention, starting from the lens luxation in vitreum and going to the implant of artificial lens. From the three classes of artificial lenses, up-to-date options are the posterior chamber artificial lenses. Today, in 80% of the cases, artificial lens implant is done, 80% of the implanted lenses being posterior chamber lenses. The paper also exposes various operatorial techniques, post-operatorial evolution and the results obtained.
