Sintering study of ferrites, BaTiO3 and their ceramic composites

Abstract

Traditional solid-state sintering studies of cobalt ferrite are extremely rare in the literature [1]. Differences in thermal coefficients and ultimately lead to delamination, micro-cracking or pore formation in the ceramic materials. Phase changes as a result of sintering (e.g. tetragonal to cubic in BaTiO3) can also contribute to sintering mismatch [2]. Cobalt ferrite and nickel cobalt ferrite powders were prepared using solid-state ceramic processing. Calcination of the ferrite powders was carried out with a heating rate of 5°C/min up to 1050°C and 240 min hold at 1050°C. The calcined powders were uniaxially pressed in the shape of Rectangular bars (20mm X 5mm X 4mm) and cold iso-statically pressed for use as samples for dilatometric thermal analysis. The dilatometry tests of the ferrites, the BaTiO3 (TB), and ferrtite-TB samples were carried out, some samples with constant heating rate and some samples simulating sintering with 2h hold time at a certain temperature. Based on the dilatometry results, sintering thermal cycles for both ferrites and TB were proposed. The microstructure of the sintered samples was evaluated by scanning electron microscopy and their densities were measured by the Archimedes’ method. The results were discussed relating the density and grain size of the samples to the sintering parameters. The same was done with nickel cobalt ferrite and TB to obtain the composite. The sintering study were did to devise a maximum theoretical density of >90%.