Nanometric powders and sintered ceramics studied by atomic force microscopy
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Nanometric powders and sintered ceramics studied by atomic force microscopy A. Dias Departamento de Engenharia Metal´urgica e de Materiais, EE-UFMG, Belo Horizonte, MG, 30160-030, Brazil
R. L. Moreira and N. D. S. Mohallem Departamentos de F´ısica e Qu´ımica, ICEx-UFMG, Belo Horizonte, MG, 30123-970, Brazil
J. M. C. Vilela and M. S. Andrade Setor de Tecnologia Metal´urgica– Fundac¸ a˜ o Centro Tecnol´ogico de Minas Gerais-CETEC, Belo Horizonte, MG, 31170-000, Brazil (Received 18 November 1996; accepted 27 May 1997)
Atomic force microscopy, as well as the Brunauer, Emmett, and Teller technique and x-ray diffraction, was used to analyze ultrafine NiZn ferrite powders hydrothermally synthesized at 200 ±C, for 5 h. The particle sizes, measured through AFM images acquired from the surface of pressed powders, were 52 6 6 nm, which were higher than those obtained by the other techniques. The particles were monodispersed in size and approximately spherical, meeting the requirements for the production of high density sintered components. The observations performed on ceramic bodies sintered at different conditions (1100–1400 ±C, 5 to 240 min) showed necks characteristic of the early stages of sintering (1100 ±C) and the expected pore curvature evolution (1400 ±C) with sintering time in the final stage of the sintering process. Using a straightforward sample preparation technique, AFM proved to be a powerful tool for direct analysis of ceramic powder particles on the nanometric scale and sintered ceramics at different sintering stages.
I. INTRODUCTION
Ferrites with spinel structure are an important group of materials, whose technological applications always require high density, low porosity, and controlled microstructure. A specific set of properties is achieved by appropriate control of powder characteristics and purity, which have a strong influence on the microstructure and properties of the sintered components. The conventional ceramic method for the preparation of ferrite powders involves high temperatures and may result in hard agglomerates of particles, with consequent deleterious effects on sintering. On the other hand, hydrothermal synthesis of ferrites has shown increasing importance due to the low energy costs and the resulting ultrafine, submicrometric, highly reactive, crystalline and impurity-free particles, which have controlled stoichiometry and size. These powder properties lead, after sintering, to ceramic bodies with suitable characteristics for applications in the electronic industry.1 The characterization of these nanomaterials requires appropriate techniques and, recently, Atomic Force Microscopy (AFM) was shown to be a powerful tool for surface analysis of nanometric powders,2,3 with good results. The technique has gained widespread acceptance due to its ability to provide high resolution topographical data of surfaces in ambient conditions. The application of AFM for the characterization of sintered ferrites from J. Mater. Res., Vol. 13, No. 1, Jan 19
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