Dilatometric studies of (SiO2-RE2O3-Al2O3) silicon carbide ceramics

Silicon carbide is an important structural ceramic and finds applications as abrasives, as a refractory and in automotive engine components. This material can attain high densities during liquid phase sintering if suitable additives are used. Silicon carbides containing silica, alumina and rare earth oxides have suitable characteristics to promote liquid phase sintering. In this paper, the sintering behavior of silicon carbide ceramics with additives based on the (SiO2-RE2O3-Al2O3) system (RE = Y, Dy) has been studied. Samples with different compositions and containing 90 vol.% SiC were sintered in a dilatometer at 1950 °C/1h and in a graphite resistance furnace from 1500 °C/1h up to 1950 °C/1h. The shrinkage behavior as a function of rare earth oxide used and additive composition was also studied. The sintered materials were characterized by density and weight loss measurements. The crystalline phases were identified by X-ray diffraction analysis. The sintering kinetics of these materials can be related to the formation of secondary crystalline phases

A study of the consolidation method with albumin to obtain porous beta-TCP ceramics

In many 'in-vivo' and 'in-vitro' studies, the behavior of calcium phosphate ceramics like beta - tricalcium phosphate in biological environments has been reported to be predictive and positive. In terms of bone tissue growth, these ceramics are attractive biomaterials due to their porous microstructures. To obtain biomaterial quality ceramics, in this investigationbeta- TCP porous ceramics were prepared by a special consolidation method with albumin as a foam generating agent. This technique enables a variety of formats with complex geometries to be prepared. To obtain porous samples using albumin, heat had to be introduced into the system during the consolidation stage. After consolidation, the samples were sintered at 1250 °C for 30 minutes and characterized using X ray diffractometry, scanning electron microscopy and mercury porosimetry. The foams that were obtained by this method exhibited spherical and interconnected pores, characteristics desirable in biomedical implants

Complex-shaped ceramic composites obtained by machining compact polymer-filler mixtures

Research in the preparation of ceramics from polymeric precursors is giving rise to increased interest in ceramic technology because it allows the use of several promising polymer forming techniques. In this work ceramic composite pieces were obtained by pyrolysis of a compacted mixture of a polysiloxane resin and alumina/silicon powder. The mixture consists of 60 vol% of the polymer phase and 40 vol% of the filler in a 1:1 ratio for alumina/silicon, which was hot pressed to crosslink the polymer, thus forming a compact body. This green body was trimmed into different geometries and pyrolised in nitrogen atmosphere at temperatures up to 1600 °C. X-ray diffraction analysis indicated the formation of phases such as mullite and Si2ON2 during pyrolysis, that result from reactions between fillers, polymer decomposition products and nitrogen atmosphere. The porosity was found to be less than 20% and the mass loss around 10%. The complex geometry was maintained after pyrolysis and shrinkage was approximately 8%, proving pyrolisis to be a suitable process to form near-net-shaped bulk ceramic components