Materials Science Forum Vols. 798-799

Abstract: This study has evaluated the influence of dispersant additives on the interaction of sodium bentonite clay in aqueous dispersion. Measurements of apparent viscosity (AV) and plastic viscosity (PV) for the dispersions, before and after additive, were done in a Fann 35A viscometer at ambient temperature and after thermal ageing (366K during 57600 seconds in Fann Roller Oven). The dispersions were prepared with clay contents of 0.04 and 0.08 kg/10^-3m³ of water and the dispersants (sodium polyacrylate and sodium polyphosphate) with 0.02 and 0.04 kg/10^-3m³ of water. Was observed that the dispersions prepared with clay and dispersant at ambient temperature presented, very likely, associations between particles of the type face to face, characterized by the low values of viscosity when compared to the ones of the dispersions containing only clay. Comparing the dispersions at ambient temperature with the aged ones, an increase of VA and VP was observed, wherein the dispersion was in a flocculated state, with associations of the types face-to-edge and/or edge-to-edge.

Abstract: Niobia is used as a sintering additive in alumina processing because it lowers the sintering temperature. This work investigated the influence of sintering dwell time at 1400^oC on the properties of 4 wt% niobia doped alumina. The sintered ceramics were characterized by scanning electron microscopy (SEM), and X rays diffraction (XRD) with Rietveld refinement. Measurements of density, average grain size, hardness, and elastic constants were also performed. The results showed that the porosity depend on the time sintering and this influence on the elastic properties. Longer sintering times improved densification and with this the Young's Modulus.

Abstract: This paper examines the use of active lock-in thermography and optical microscopy coupled with digital image processing as a production-time quality control tool for porcelain tile manufacturing. We demonstrate that it is possible to associate physical properties such as density, porosity and water absorption capacity with internal defects such as thermal delamination in ceramics. Defective and intact samples were subjected to active lock-in thermography and digital microscopy analysis on a workbench developed to simulate the conditions found in production lines. The images were collected and processed using morphological operators, image enhancement and thresholding to detect the presence of defects. These methods were compared with methods that analyze the physical properties of the materials to demonstrate that it is possible to detect the presence of defects.

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: Medicine seeks increasingly to treat problems related to bone regeneration and tissue in order to minimize surgical trauma and some bone diseases. The technology advancement in the biomaterials field allows develop materials that assist in reconstructive procedures of body parts and increase treatments improving the life quality of human beings. Due to the biodegradability, biocompatibility and biofunctionality characteristics, chitosan has attracted attention of researchers in order to obtain new materials. Its unique features promote the incorporation of other materials such as calcium phosphate ceramics which are used in this bone replacement and bone regeneration due to submit biocompatibility, bioactivity, osteoconductivity in addition to allowing the bone cells proliferation, collagen and proteins in their surfaces, thus allowing tissue regeneration. This study aimed to develop biodegradable chitosan membranes with 1%, 3% and 5% calcium phosphate for use in bone regeneration. The composites were prepared and Characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and angle contact wettability. The results indicates the composite formation and show an increased crystallinity in the chitosan membrane through the phosphate incorporation, besides confirming the composites hydrophilicity. Preliminary results indicates that the composite is a promising biomaterial.

Abstract: In the context of green economy supported and widespread by United Nations (UN), the renewable energy sources are the unique mechanism to universalize the access to energy. Face to this strategic direction of change is essential to develop efficient components for saving energy such as porous ceramics that associate light with mechanical strength. Thus, the objective of this work concerns to improve the homogeneity of porous size distribution of yttria porous ceramics by evaluating their morphology during replica processing. Samples were subject to immersion into 30vol% yttria aqueous suspensions during an interval from 1min to 120min and sintered through careful thermal conditions. Based on the results, the weight and morphology of porous structure samples were directly influenced by immersion time, whereby intervals from 30-120min showed the best final products.

Abstract: This work investigated the sintering behavior of alumina doped with 4wt% niobia. Three sintering temperatures were investigated: 1400°C, 1450°C and 1500°C. The first temperature leads to solid-phase assisted sintering (SSS) while the other ones develop liquid-phase assisted sintering (LPS). The presence of liquid phase in the second case is due to an eutectic reaction occurring at 1440°C ± 20°C in the alumina-niobia system. The sintering behavior was assessed by measuring the final densities. The results indicated that the 1400°C solid-state sintering, comparatively, was better. This paper proposes that defects associated to the substitution of Al⁺³ by Nb⁺⁵ in the alumina cation sub-lattice, fostered diffusion and SSS. Sintering at 1500°C presented the lowest density, apparently due to niobate (liquid phase) loss, at this temperature as observed by XRD results.

Abstract: The effects of adding polysiloxane (polymethylsilsesquioxane) on the sintering behavior, microstructure and hardness of alumina ceramics have been studied. The sintering kinetics of cold-pressed specimens was studied by dilatometry. Polymer sintering aid was used for alumina based ceramics sintered at 1650o C. The sintered materials were characterized using helium picnometry, x-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectrometry and Vickers indentation. The addition of polymethylsilsesquioxane yielded alumina/Si₂Al₄O₄N₄ composites. The sintering studies in nitrogen atmosphere (1650 °C/1h) revealed that the highest densities were obtained for specimens with 1wt% PMS. The materials prepared with ceramic polymer precursors had higher hardness than the standard specimen. The preparation of ceramic composites using small amounts of polymer precursors is suited for alumina based ceramics. The processing route being simple, it has the potential to enable the manufacture of complex shaped pieces.

Abstract: The SrTiO₃ is a ceramic with thermoelectric properties, i.e., it can generate electrical voltage between its terminals when subjected to a temperature gradient, and this behavior is known as Seebeck effect. One parameter for quantifying the efficiency of converting thermal energy into electric energy is through the value of the Figure of Merit (ZT). STO nanostructured powders were synthesized by ultrasonic irradiation (USS), and the effects of USS in STO synthesis were evaluate, and it was compared with the conventional route of solid-state reaction (SSR). USS powders were produced by solubilization of Ti (C₄H₉O)₄ and SrCO₃ in acid solution and following the posterior precipitation by adding NH₄OH solution. After drying process, the precipitated was added to a KOH solution and was subjected to ultrasonic irradiation to promote the STO formation. DRX analysis revealed that from USS method it was possible to obtain exclusive STO phase. SEM characterization showed that the USS powder presented particle size about 100nm, which was much lower than that obtained by SSR, about 250nm.

Abstract: Ceramic filters processed by the replica method have been the subject of increasing research during the late years. In this research, ceramic filters of both 10 and 20 ppi of the systems Al₂O₃-LZSA and Al₂O₃-SiC, obtained by the replica method, have been mechanically evaluated using the compression test. The results of mechanical strength have been compared to Gibson and Ashby model. This paper proposes an adaptation of this model to explain the results.