Estudo das características magnéticas e absorvedoras das ferritas de nizn, niznmn, mnzn, nimg, nicuzn e nicuznmg obtidas via método do citrato precursor

• Autor(a) principal: Pessoa, Régia Chacon
• Data de Publicação: 2009
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UFRN
• Texto Completo: https://repositorio.ufrn.br/jspui/handle/123456789/17716
• topic: Ferritas; materiais magnéticos; materiais absorvedores de radiação - mare; Ferrites; magnetic materials; radar absorbing materials - RAM.; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA

Were synthesized systems Ni0,5Zn0,5Fe2O4, i0,2Zn0,5Mn0,3Fe2O4, Mn0,5Zn0,5Fe2O4, Ni0,5Mg0,5Fe2O4, Ni0,2Cu0,3Zn0,5Fe2O4 and Ni0,2Cu0,3Zn0,5Mg0,08Fe2O4, the precursors citrate method. The decomposition of the precursors was studied by thermogravimetric analysis and spectroscopy in the infrared region, the temperature of 350°C/3h. The evolution of the phases formed after calcinations at 350, 500, 900 and 1100ºC/3h was accompanied by X-ray diffraction using the Rietveld refinement to better identify the structures formed. The materials were also analyzed by scanning electron microscopy, magnetic measurements and analysis of the reflectivity of the material. The samples calcined at different temperatures showed an increase of crystallinity with increasing calcination temperature, verifying that for some compositions at temperatures above 500°C precipitates of second phase such as hematite and CuO. The compositions of manganese present in the structure diffusion processes slower due to the ionic radius of manganese is greater than for other ions substitutes, a fact that delays the stabilization of spinel structure and promotes the precipitation of second phase. The compositions presented with copper precipitation CuO phase at a temperature of 900 and 1100ºC/3h This occurs according to the literature because the concentration of copper in the structure is greater than 0.25 mol%. The magnetic measurements revealed features of a soft ferrimagnetic material, resulting in better magnetic properties for the NiZn ferrite and NiCuZnMg at high temperatures. The reflectivity measurements showed greater absorption of electromagnetic radiation in the microwave band for the samples calcined at 1100ºC/3h, which has higher crystallite size and consequently the formation of multi-domain, increasing the magnetization of the material. The results of absorption agreed with the magnetic measurements, indicating among the ferrites studied, those of NiZn and NiCuZnMg as better absorbing the incident radiation.