Materials Science Forum Vol. 1012

Abstract: The increase in researches related to nanomaterials has provided innovation and enhancement of the properties of innumerous materials. Among the materials frequently studied, magnesium oxide can be cited because of its many industrial applications, mainly in the chemical and electronics sectors. Magnesium oxide nanoparticles, as well as other nanomaterials, can be produced by several routes of synthesis, and the characteristics of the route chosen may change the microstructure and properties of the nanoparticles. However, despite the general consensus that the synthesis variables affect the characteristics and properties of the nanoparticles, much still needs to be studied. Among these variables, the reactive environment is one of the factors that influence considerably and about which there are still few studies. In this work, it was evaluated, using the sol-gel synthesis method, how the modification of the solvent, water or ethyl alcohol, affects the morphology and purity of the magnesium oxide nanoparticles, as well as the yield of the synthesis reactions. The nanoparticles were characterized by XRD, surface area analysis via BET, FEG-MEV and EDS. The results indicated that the nanoparticles obtained by route using ethyl alcohol as solvent have a larger crystallite and particle size, besides the synthesis reactions have a higher yield. In addition, by the analysis of surface area and pore volume, they present a lower surface area and lower pore volume, in relation to the route that uses water as solvent. Thus, it was possible to conclude that altering the solvent of the reaction, even if all other synthesis conditions are maintained, significant modifications are observed in the morphology of the magnesium oxide nanoparticles and also in the reaction yield.

Abstract: TiO₂-based nanotubes are a very promising material with many applications in solar cells, biomedical devices, gas sensors, hydrogen generation, supercapacitors, and lithium batteries, among others. Nanotube thickness is a very important property since it is related to electronic and surface mechanics. In this sense, transmission electron microscopy (TEM) can be used. However, it can be difficult to acquire a good TEM image because the transversal section of the nanotubes needs to be visible. In this work, TiO₂-based nanotubes obtained via hydrothermal synthesis were studied using X-ray line profile analysis. Scherrer and Single-Line methods provided consistent results for the thickness of the nanotubes (≃ 5 nm) when compared with TEM. Additionally, Single-Line method was also applied to estimate the microstrain. The advantage of using XRD is given by the fact that it is a quick and statistically significant analysis when compared with TEM. The results show that XRD can be used as a rapid and reliable alternative for the thickness estimation of nanotubes.

Abstract: In this work are presented analyzes from calcination and sintering of zinc niobate ceramics by microwave processing. In order to obtain minimum processing parameters, the behavior of the material was first studied for the calcination at different temperatures in the range of 450 to 1150°C, with duration time of 10 minutes. The sintering was carried out between 950 and 1050°C. The results showed that the crystalline structure of the calcined and sintered samples was influenced by the temperature, because, according to the increase in temperature, the evolution of the formed crystalline phases was observed and only the Zn₃Nb₂O₈ and ZnNb₂O₆ phases prevailed in the final microstructure. The densification of the sintered ceramics was influenced by the time and temperature of the heat treatment, with lower residual porosity and grain growth with the increase of the sintering temperature in the microwave oven.

Abstract: A study was carried out on the behavior during the sintering of Al₂O₃ ceramics with pre-sintering of the additives Nb₂O₅ and LiF at different temperatures. It was observed through XRD and DSC the formation of the LiNb₃O₈, Nb₃O₇F and LiNbO₃ phases during the pre-sintering of the additive powders and the formation of the LiAl₅O₈, AlNbO₄ phases during the sintering of the samples The samples showed densities around 91% of the theoretical density, and pre-sintered samples showed low growth in grain size.

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: A brief review of the characteristics and properties of cubic boron nitride (cBN) is presented, including different processing methods. The influence of bonding substances, as well as other ceramic composites, is also discussed. Finally, it is highlighted the great practical importance of the cBN as a ceramic with elevated hardness in substitution for the diamond in cutting tools.

Abstract: In this work it was investigated the influence of CTAB surfactant concentration on the synthesis of the compound Mn_0.75Zn_0.25Fe₂O₄ by the coprecipitation method. It was also compared the influence of hydrothermal treatment on the synthesized materials. The magnetic properties were characterized by AC susceptometry for the determination of the magnetic susceptibility and magnetic density energy. The phases, crystal structure and morphology of the nanoferrites were determined by Rietveld analysis of X-ray diffraction data. It was found the presence of two phases: Franklinite and Akaganeite and it was shown that the samples synthesized only by coprecipitation presented the tendency to increasing the crystallite sizes of the akaganeite phase and decreasing of crystallite sizes of the Franklinite phase as a function of CTAB concentration. The samples submitted to subsequent hydrothermal treatment presented a tendency to decreasing the crystallite sizes of both phases and increasing in Franklinite phase fraction, compared to the samples synthesized only by coprecipitation, suggesting that the hydrothermal treatment was effective in obtaining nanostructured materials of smaller particles.

Abstract: Civil construction is a sector of extreme impact on the Brazilian economy, both in terms of jobs as well as consumption of raw material and waste generation. Civil construction waste (CCW) represents a large part of the total mass of municipal solid waste in a medium and large city. An alternative to diminish these released wastes is to reuse them. In this work, a study was carried out using CCW both to produce concrete with sand substitution and as a small aggregate for use in mortar. The compression strength of structural concrete and mortar, with total and partial replacement of sand, was analyzed. In addition, the consistency of mortar with the replacing was also studied. The results of the compression test indicate superior quality for concretes (75wt% CCW) and mortar with CCW incorporation. The required amount of water for good workability in the modified mortar is 310 g, against 270 g for the reference mortar.

Abstract: In the south of Ceará (Brazil), Cariri region, there is a production center for roof tiles and bricks. At that same region, there has been an expressive mining of laminated limestone, known as Pedra Cariri (Cariri Stone), which has produced large amounts of CaCO₃-rich waste, that causes undesirable impacts to the environment. This work aimed to analyze the feasibility of producing rustic ceramic tiles, made up of clayey masses used in the region with the addition of this waste, aiming at the diversification of red ceramic products in a sustainable way. The mixtures were pressed, fired in maximum firing temperature which varies from 750° to 1150oC and had their physical-mechanical characteristics tested. The results indicated that the clayey mass is composed of kaolinite, feldspar and quartz, while montmorillonite and/or vermiculite is only found in roof tile clayey mass. The waste is mainly made of calcite. In general, the values of water absorption were compatible with porous rustic ceramic tile and the addition of Pedra Cariri waste provided lower values of firing shrinkage as well as the increase of the flexural strength. The samples of roof tile clayey mass (10% of waste at 850°C and at 1150°C) obtained physical-mechanical property values that match Brazilian technical norms to BIII type ceramic tile. Therefore, the mixture formulated with tile clayey mass and limestone waste presents potential to be utilized in the manufacture of ceramic roof tiles.

Abstract: Moisture and water transport in clay bricks are essential contributing factors towards brick decay in buildings. Experimental work is reported comparing water absorption and porosity of handmade and solid fired clay bricks from Paraguay. Their respective porosities were estimated by gravimetric test and, their pore distribution, degree of anisotropy and morphology were examined by SEM. Although it was found that both samples have a common composition (XRD), a higher degree of porosity was found in handmade bricks, which also absorb water at a higher rate accelerating the decay process. Experimental data is reported on the exponential kinetics behavior of water absorption similar to the one observed in capillary tubes, but with an additional diffusive process. A phenomenological model is proposed for water absorption in both types of bricks which compared with the standard model of water absorption available in the literature, produces a better representation of the experimental data.