Papers by Author: Jose B. de Campos

Abstract: The mechanical properties and creep resistance of the Al₂O₃ have been improved with the use of other oxide ceramics, among these the Y₃Al₅O₁₂ (YAG - "yttrium aluminum garnet"), to obtain the Al₂O₃-YAG composite. The aim of this work is to study the effect of addition of Nb₂O₅ at low sintering temperatures of the composite, starting from the eutectic composition Al₂O₃-Y₂O₃. In this work, the compositions were produced by powder mixtures of Al₂O₃-Y₂O₃ and Al₂O₃-Y₂O₃-Nb₂O₅ using high energy ball milling. The green bodies were pressed at 70 MPa and sintered at 1000, 1100, 1200 and 1300°C for 2 h. The materials were characterized by shrinkage and X-Ray Diffraction (XRD) using the Rietveld method. The presence of Nb₂O₅ does not show any improve neither for the YAG phase formation nor for the shrinkage of the sintered samples in the temperature range studied.

Abstract: Al₂O₃-Nb₂O₅ has been widely explored as one of the most used material for sintering mixing in the literature, due to its excellent hardness properties, used in armor. In this study, Al₂O₃-Nb₂O₅ and Y₂O₃-Nb₂O₅ powders were prepared, with 50% in mole fraction of each oxide. The mixtures were subjected to high energy milling in an eccentric ball mill for 3 h, dried and sieved in a sieve vibrator. The green bodies were compacted at 70 MPa and sintered from 1250 to 1650 °C for 3 h, at 100 °C steps. The materials were characterized by quantitative X-Ray diffraction (XRD) using Rietveld method and by mass loss. The Al₂O₃-Nb₂O₅ mixtures experienced a weight loss of 84% at sintering temperatures of 1550 and 1650 °C.

Abstract: In the present work, apatite powders were synthesized at pH 10, pH 11 and pH 12 in order to give rise to biphasic and triphasic bioceramics after sintering. A modified gelcasting process, including polyethylene wax spheres addition to the suspension, is proposed in comparison to the original gelcasting method. The aim of the addition is the creation of uniform, open and interconnected pores in the body of samples.

Abstract: The present work suggests a modified gel casting process, including polyethylene wax spheres addition to the suspension with the objective of creating uniform and interconnected pores in the body of samples. In the present study, apatite powders were synthesized at pH 10 and pH 12 in order to give rise to biphasic and triphasic bioceramics after sintering.

Abstract: Calcium phosphates are widely used in medicine and dentistry. However, synthesis of these substances through precipitation methods still presents problems regarding reproducibility. Alginate is a polymer extracted from brown algae, whose monomers are D-mannuronic and L-guluronic acids, and is suitable for biomedical applications. The aim of this paper is to investigate how the poly-ionic nature of alginate affects phase composition of calcium phosphate obtained through a precipitation method.