Papers by Author: Wilson Acchar

Abstract: In this work aqueous-based tape casting was used to produce Ni-GDC substrates. Rheological properties of the slurries were measured at room temperature. The acrylic-based suspensions showed a pseudoplastic behavior and remained stable and homogeneous. Tapes with thickness between 100 and 220 um were produced and showed smooth and homogeneous surfaces and good flexibility. Sintered tapes showed good density and porosity values.

Abstract: Water-based suspensions from commercial Tetragonal stabilized zirconia (3Y-TZP) were produced and characterized with different contents of solids and two different dispersants. According to zeta potential measurements, 3Y-TZP particles showed basic surface characteristics and IEP of around 9 when in aqueous media. The critical volume fraction of solids was about 79.6 wt%, which hindered the processing of more concentrated slurries. Rheological measurements confirmed that well dispersed slurries could be obtained with solid content as high as 79.6 wt.%. The results showed that Triton X-114 was an effective dispersant for preparing well stabilized 3Y-TZP suspensions for the layer-wise slurry deposition process.

Abstract: This study evaluated the potential use of Sugarcane Bagasse Ashes (SBA) as a flux, replacing phyllite for the production of enamelled porcelain tile. The raw materials of the standard mass components and the SBA residue were characterized by testing by XRF, XRD, AG, DTA and TGA. Test samples were fabricated, assembled in lots of 3 units and sintered at temperatures of 1150 ° C to 1210 ° C. The results of the physical properties, mechanical properties and SEM of the sintered samples, showed that the formulation, G4 - in which applied 10% of SBA replacing phyllite, sintering temperature 1210 ° C showed better performance as the previously mentioned properties due to the formation of mullite crystals, meeting the prerequisites of standards for enamelled porcelain tile, while reducing the environmental impact and the cost of production.

Abstract: The concept of sustainable construction throughout the building life cycle has motivated several studies on the application of waste to replace partially or totally some materials such as aggregates. This study evaluated the feasibility of stone dust use, replacing the natural sand in the production of structural concrete. In the initial stage it was carried out physical and chemical characterization of the applied materials and then molded cylindrical specimens with FCK 20, 25 and 30 MPa at 28 days, in compositions at levels of 10% stone powder, 30%, 50%, 100% e 100% with additive. After curing they were subjected to compressive strength tests and mechanical tests showed that the composition with 10% presented promising results.

Abstract: During processing of zirconia blocks, where they are used for different dental implants type, most of the loosed material as a powder is subsequently discarded. Besides damage to the environment, waste of material results in financial losses, resulting in higher final cost of treatment. The yttria stabilized zirconia (Y-TZP) has a variety of applications due to it is combination of high strength and fracture toughness. The objective was to reuse zirconia waste analyzing the effects of sintering temperature. The starting materials used in this study were two different powders of ceramic system ZrO₃-Y₂O₃: commercial zirconia nanoparticle and microparticle zirconia waste. The raw material was shaped by uniaxial and isostatic pressing and then sintered at 1500, 1550 and 1600 ° C over 1 hour. The X-ray diffraction (XRD) and dilatometry were used to powder characterization. After sintering density / porosity, flexural strength, and scanning electron microscopy (SEM) were realized .The waste showed similar values of density, and grain size to commercial material studied, confirming that it can be reused.

Abstract: The aim of this study was to evaluate the dependence of sintering conditions on mechanical properties and microstructure of zirconia stabilized by yttria. Commercial blocks of pre-sintered of zirconia stabilized (DeguDent Dentsply, Germany-Cercon) were investigated in this study. The blocks belonging to group 1 were sintered under the recommended conditions by the manufacturer (1350°C for 6 hours). The blocks of group 2 were sintered under 1500°C for 6 hours. The blocks of group 3 were sintered under 1350 C for 14.5 hours. The results indicated that the sintering conditions influenced the mechanical properties and microstructure of zirconia. The three sintering conditions analyzed in this study produces zirconia bodies with properties adequate to be used in clinical function. However, the decisive factor for change in the sintering conditions should be the cost/benefit during the prosthetical process and longevity of clinical material to perform its function in the oral cavity.

Abstract: The technical porcelain is usually obtained by mixing different raw materials, which are generally clay, kaolin, quartz, and a fluxing agent, in appropriate amounts. These porcelains are used in the production of electric and electronic devices for several applications, ranging from high and low power capacitors to low, medium, high and extra high voltage insulators. In this work, we studied technological properties of dielectric porcelain, obtained from raw materials found in large quantities and excellent quality in the Rio Grande do Norte state in Brazil. Test samples were produced by powder technology for two different compositions: composition A (20% clay, 28% kaolin, 32% feldspar and 20% quartz) and composition B (15% clay, 31% kaolin, 33% feldspar and 21% quartz), and sintered at temperatures, T1=1150°C, T2=1200°C, T3=1250°C, T4=1300°C and T5=1350°C with isotherms P1=0.5 hours, P2=1 hour, P3=1.5 hours and P4=2 hours. Then after sintered, the sample microstructure was characterized by scanning electron microscopy (SEM) and analysis of dielectric strength with direct and alternating voltage. The best results for electrical properties were obtained in temperature of 1250oC for composition A, and confirms the electrotechnical porcelain production feasibility.

Abstract: Zirconia ceramic stabilized with 3% yttria (3Y - TZP) is the most used ceramic dental materials. During the machining of zirconia blocks in the laboratory to prepare the various types of prostheses, much of the material is lost in powder form, which is subsequently discarded. This study investigates the possibility to recycling of zirconium oxide powder obtained during milling of dental crowns and bridges. Uniaxial and isostatic pressed samples were prepared, sintered and compared to the commercial material. The results indicated that the isostatic pressed samples shows good physical and mechanical properties, comparable to the commercial material, demonstrating the viability to use this recycle material in the same process.

Abstract: The properties of ceramic materials can be greatly influenced when a residue is added to its composition. This article aims to study the incorporation of waste oil well drilling fluid in the standard bulk for fabrication of red ceramic. The success of the merger can reduce costs in the production of ceramic pieces and reduce the environmental impacts caused by waste. The results reveals that the use of the residue for the manufacture of the ceramic products is possible (tiles, massive bricks and hollow bricks) replacing clay up to 40%, according the requirements of the norm and in the literature for the technological properties of the final product.

Abstract: Lanthanum chromite (LaCrO₃) has been considered a promissing candidate for use as interconnect materials for solid oxide fuel cells (SOFCs), due to their excellent electrical properties. In this work, LaCr_1-xSn_xO₃ (x = 0 and 0.1) ceramic powders were prepared using the following synthesis routes: Flame spraying (FS) and microwave assisted combustion method (MCM). The powders were characterized by TGA, XRD and TEM. The TG curves showed weigh losses corresponding the dehydration of compounds as well as decomposition of secondary phases and organic matter. The XRD patterns indicated the formation of Sn doped LaCrO₃ phase by FS. The crystallite sizes of samples are in the range 20-36 nm. The TEM images revealed the presence of particles with spherical shape and uniform particle size distribution.