M.H. Prado da Silva

Síntese e caracterização do compósito Al2O3 -YAG e do Al2O3-YAG e Al2O3 aditivados com Nb2O5

The Al2O3-YAG composite exhibits high corrosion and creep resistance in aggressive environments, which provides quite glimpse attractive applications such as jet engine vanes and as gas turbines. This composite also shows high hardness and wear resistance allowing its use in ballistic armor. In this study, precursor powders of Al2O3, Y2O3 and Nb2O5 were homogeneously mixed in a planetary ball mill for 4 h, dried in an oven at 120 oC for 48 h, sieved and deagglomerated. The Al2O3-YAG composite was produced from mixtures of Al2O3-Y2O3 at 1300 oC for 2 h. Samples of Al2O3-YAG, Al2O3-YAG with Nb2O5 and Al2O3 with Nb2O5 were produced. Each powder composition was uniaxially pressed at 70 MPa. Sintering was performed at 1400 and 1450 oC. The powders as received and as processed were characterized for specific surface area and particle size. The sintered materials were characterized by apparent density and porosity by the Archimedes method and evaluated for shrinkage and loss of mass. The obtained results showed that further adjustments are needed in the sintering conditions of Al2O3-YAG composition with Nb2O5 in order to improve the densification and shrinkage, which were low, 60% and 3%, respectively. The Al2O3 with Nb2O5 addition, on the other hand, presented a satisfactory densification of 96% and shrinkage around 15%.

Processamento e caracterização morfológica do compósito Al2O3-YAG aditivado com nióbia

The Al2O3-YAG composite has high mechanical strength at high temperatures which allows its use in air craft applications, since it increases the thermal efficiency of jet engines and helps the development of high performance gas turbines. This composite also exhibits some favorable properties toward military applications such as armor, due to its high hardness. In this study, Al2O3-YAG and Al2O3-YAG with 4wt.% Nb2O5 (niobia) samples were produced. The precursors powders were ground in a planetary ball mill for 4 h, dried in an oven at 120 oC during 48 h, deagglomerated and sieved. The powder mixtures were then uniaxially pressed at 70 MPa. Sintering was carried out at 1450 oC for 2, 3, and 4 h, with heating and cooling rates of 10 oC/min. The materials were characterized by scanning electron microscopy (SEM) in order to characterize the microstructure. X-ray diffraction with Rietveld refinement was performed to determine and quantify the structural phases, whereas density was measured by the Archimede´s method. The samples with niobia addition revealed approximately 5wt.% of yttrium niobate (YNbO4) phase. It is worth pointing out that there is no citation in the literature involving niobia addition to the Al2O3-YAG composite. On the other hand, the obtained results indicated that additional experiments regarding the sintering conditions are necessary to optimize density.

Evaluation of Hardness and the Fracture Toughness of Composite Biphasic Alumina-YAG

Currently the composite two-phase Al2O3-YAG laser has been widely exploited by having good properties such as high abrasion resistance and deformation in harsh environments. Thus, one can predict that this material has very attractive applications such as fins of jet engines and gas turbines. In this study, five mixtures were processed Y2O3-Al2O3-Nb2O5, in proportions of 0, 1, 5, 15 and 35 wt% Y2O3 and 4% by weight of Nb2O5. These samples were sintered at 1550 to 1650 °C in air where it was detected by X-Ray Diffraction (XRD) with Rietveld refinement training YAG and also two intermediate stages, and AlNbO4 YNbO4. Finally they were characterized by hardness by Vickers microindentation and fracture toughness. The highest hardness and fracture toughness were 15 GPa and 5.5 MPa.m1/2, respectively.

Thermal Analysis of Two Niobo-Phosphate Glasses

In the present study, two new biocompatible glasses, with the same components, but in different proportions, were produced.The thermal behavior of both glasses was analyzed and the glass transition temperatures (Tg) were determined by differential scanning calorimetry (DSC) for both glasses. The DSC analyses showed that the bioactive glass with Ca/P = 1.68 showed higher Tg than the bioactive glass with Ca/P = 1.33.

Ostrich eggshell as calcium source for the synthesis of hydroxyapatite and hydroxyapatite partially substituted with zinc

In the present study, hydroxyapatite and Zn-substituted hydroxyapatite powders were synthesized using ostrich eggshell as a calcium source. The samples were analyzed by scanning electron microscopy with field emission gun, and X-ray diffraction (XRD) to identify the present phases, and X-ray fluorescence spectroscopy for quantitative chemical analysis of the synthesized and heat treated powders. The Fourier transform infrared spectroscopy technique was used before and after heat treatments at 700, 900 and 1100 °C in order to identify the functional groups present, as an additional technique to the XRD analysis. The results presented in this study represent a promising method for synthesis of hydroxyapatite and hydroxyapatite partially substituted with zinc, since the results showed no undesirable phases or impurities in the produced powders. It was observed that Zn-substituted hydroxyapatite showed higher thermal stability, when compared to pure hydroxyapatite.