Papers by Keyword: Niobia

Abstract: Compounds of alumina APC-2011 SG with niobia, silica and magnesia were sintered at 1400°C/3h, in order to evaluate their ballistic performance. The content of niobia (Nb₂O₅) was 4.0 to 8.0 wt.%; silica (SiO₂) was 0.8 wt.%; and magnesia (MgO) at 0.15 wt.%. Sintered samples were characterized by hardness, densification and energy absorption at impact. Ballistic tests were performed by ceramic discs firmly glued to steel plates and then subjecting the target to impact using 7.62 mm projectile shot from a rifle with a throw distance of 5 m. The energy absorbed by the disintegration of the ceramic discs was estimated by the residual velocity. The fracture surfaces of the samples were observed by scanning electron microscopy. It was verified for the first that the addition of high amounts of Nb₂O₅ to the alumina with the presence of SiO₂ and MgO increases the presence of vitreous phase in the contours of alumina grains and improved the properties of the material for use in ballistic protection.

Abstract: Niobia has been successfully used as sintering additive to alumina in order to lower its sintering temperature. This effect can also be obtained by reducing the ceramic particle size. This work investigated the effect of the particle size on the ceramic final density of alumina with 4 wt% niobia. For that two milling media were used. The as-received powders were submitted to ball and planetary milling and then sintered at 1450°C. The planetary milling medium was more efficient in reducing particle size when compared to ball milling. However, planetary milling caused significant contamination in the niobia powder, from the alumina balls used as milling agents. It forced composition balance in order to keep the original proposed formulation. The planetary milled sintered samples showed better densification and lower grain size in comparison with ball milled ones. It could be concluded that the milling medium choice directly affected both microstructure and properties of the sintered alumina with 4wt% of niobia. .

Abstract: Turbine blades of airplanes and thermoelectric plants work in adverse conditions, with corrosive environment and high temperature and pressure. One way to improve the life or the working temperature of the blades is by the use of special coatings over metallic material applied by Electron Beam – Physical Vapour Deposition (EB-PVD). The most usual material for this application is zirconia doped with yttria. Addition of niobia, as a co-dopant in the Y2O3-ZrO2 system, can reduce the thermal conductivity and improve mechanical properties of the coating. The purpose of this work is to show the influence of the addition of niobia on microstructure of ceramic coating taking in to consideration X-ray diffraction and scanning electron microscopy observations. First result shows a columnar structure with only tetragonal phase in the ceramic coating in the chemical composition range studied.