Materials Science Forum Vol. 509

Abstract: Zirconia-alumina composites with additions of a CaO-SiO2 glass are prepared by uniaxial pressing and sintering. In order to promote bioactivity, the composites are biomimetically treated. The effect of immersion time in simulated body fluids (SBF) and that of the presence of a wollastonite powder bed, as a calcium ion provider, on the apatite forming ability are investigated. The influence of replacing the simulated body fluids each 7-day-period for a more concentrated solution is also studied. A bonelike apatite layer is observed after 21 days of immersion when the SBF is renewed, whether the bed of wollastonite powder is present or not. However, a thicker layer is formed by using wollastonite and the agglomerates of the apatite layer are finer on the composites containing CaO-SiO2 glass.

Abstract: Cordierite has been synthesized by heating mixtures of kyanite and talc, using kyanite powders of two different sizes. The reaction is studied by thermogravimetric and differential thermal analysis. Phase changes are followed by X-Ray diffraction of samples fired between 750 °C and 1400 °C. The evolution of the reaction starts with the dehydration of talc at approximately 880 °C. The kyanite decomposes at approximately 1140 °C. The first traces of α-cordierite appear at around 1200 °C. The influence of the kyanite particle size on the kinetics and microstructure is analyzed.

Abstract: The present work describes the fabrication of monolithic ceramics of different geometries through direct extrusion of ceramic pastes. Using this technique, ceramic rods with triangular, hexagonal, honey-like and tubular cross sections have been produced. The shape of some of these monolithic materials allows piling them up for building big catalytic reactors. After extruding and sintering, all processed ceramics have appropriate characteristics such as homogeneous texture, and controlled density and porosity. These results suggest the feasibility of using the extruded ceramics for different catalysis and filtering applications. Some features of the monolithic ceramics and the fabrication process will be analyzed.

Abstract: A titanium base alloy and a cobalt base alloy have been subjected to a biomimetic process. Samples of titanium and cobalt alloys have been immersed in 10M and 5M NaOH solutions, respectively, then the samples have been heat treated and finally, immersed in either a simulated body fluid (SBF) with ionic concentration close to human blood plasma or in a simulated body fluid with an ionic concentration 1.5 times that of the SBF (1.5SBF) for a period of 21 days. An apatite layer has been observed after the immersion of the samples in SBF for both Ti and Co base alloys. The apatite layer observed on the Ti alloy samples is more homogeneous and thicker than that observed on the Co alloy samples. However, the apatite layer on both samples is not continuous and homogeneous along the surface. The layer of apatite formed is thicker on samples immersed in 1.5SBF. This is attributed to the higher ion concentrations, mainly of calcium and phosphorus. The Ca/P ratios measured in the apatite layers are close to that of bone.