M. A. Zaghete

Composites PVDF-TrFE/BT used as bioactive membranes for enhancing bone regeneration

In this paper a piezoelectric composite membranes were developed for charge generator to promoter bone regeneration on defects sites. Is known that the osteogenesis process is induced by interactions between biological mechanisms and electrical phenomena. The membranes were prepared by mixing Barium Titanate (BT) powders and PVDF-TrFE (PVDF:TrFE = 60:40 mol%) on dimethylformamide medium. This precursor solution was dried and crystallized at 100oC for 12 hours. Composites membranes were obtained by following methods: solvent casting (SC), spincoating (SP), solvent extraction by water addition (WS) and hot pressing (HP). The microstructural analysis performed by SEM showed connectivity type 3-0 and 3-1 with high homogeneity for samples of ceramic volume fraction major than 0.50. Powder agglomerates within the polymer matrix was evidenced were observed for composites with the BT volume fraction major than 40%. The composite of ceramic fraction of 0.55 presented the best values of remanent polarization (~33mC/cm2), but the flexibility of these composites with the larger ceramic fraction was significantly affected. For in vivo evaluation PVDF-TrFE/BT 90/10 membranes with 3cm larger were longitudinally implanted under tibiae of male rabbit. After 21 days the animals were sacrificed. By histological analyses were observed neo formed bone with a high mitotic activity. In the interface bone-membrane was evidenced a pronounced callus formation. These results encourage further applications of these membranes in bone-repair process.

Effect of Nb on barium titanate prepared from citrate solutions

The influence of the addition of dopants on the microstructure development and electrical properties of BaTiO3 doped with 0.2, 0.4, 0.6, 0.8 mol% of Nb and 0.01 mol% of Mn based compounds was studied. Doped barium titanate was prepared using the polymeric precursor method from citrate solutions. The powders calcined at 700°C for 4 hours were analysed by infrared (IR) spectroscopy to verify the presence of carbonates, and by X-ray diffraction (XRD) for phase formation. The phase composition, microstructure and dielectric properties show a strong dependence on the amount of added niobium.

Influência do oxalato de amônio na formação do precursor columbita obtido pelo método Pechini

The synthesis of PMN (Pb3MgNb2O9) using the columbite route allows for reduction of secondary phases. The Pechinix92s method was used for preparing MN powders to obtain powders with suitable chemical homogeneity and high surface area. In this work it is showed that impurity content and calcination conditions affect the synthesis of MN contained MgNb2O6 single phase. The presence of ammonium oxalate residue affected the organic matter decomposition stage and the synthesis temperature of MN. The results obtained by TG/DTA and XRD show that columbite phase mechanism formation is influenced by the concentration of the ammonium oxalate in the Pechini precursor. A columbite precursor with crystalline single phase and high surface area could be obtained using citrate solution completely absent of impurities and calcination at 900 °C for 2 hours.

Influence of oxygen atmosphere on LiNbO/sub 3/ thin films prepared by Pechini process

Thin films of lithium niobate were deposited on the Pt/Ti/SiO/sub 2/ (111) substrates by the polymeric precursor method (Pechini process). Annealing in static air and oxygen atmosphere was performed at 500/spl deg/C for 3 hours. The films obtained were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The dielectric constant, dissipation factor and resistance were measured in frequency region from 10 Hz to 10 MHz. Electrical characterizations of the films pointed to ferroelectricity via hysteresis loop. The influence of oxygen atmosphere on crystallization and properties of LiNbO/sub 3/ thin films is discussed.