Papers by Author: Sonia Regina Homem de Mello-Castanho

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Authors: Thomaz Augusto Guisard Restivo, D.W. Leite, Sonia Regina Homem de Mello-Castanho
Abstract: Anodes composed of Ni-YSZ (yttria-stabilised zirconia) cermets are the key material to allow direct biofuel feeding to Solid Oxide Fuel Cell (SOFC) devices due to its internal reforming capability. The main challenge among these materials is related to carbon deposition poisoning effect when C-bearing fuels are feed. The work deals with these issues by alloying Ni with some metals like Cu to conform a multi-metallic anode material. Mechanical alloying (MA) at shaker mills is chosen as the route to incorporate the metal and ceramic powders in the anode material, also leading to better sintering behaviour. A projected cermet material is conceived where a third metal can be added based on two criteria: low Cu solubility and similar formation enthalpy of hydrides regarding Ni. Refractory metals like Nb, W and Mo, seems to fulfil these characteristics, as well as Ag. The MA resulted powder morphology is highly homogeneous showing nanometric interpolated metal lamellae. The sintering behaviour is investigated by conventional dilatometry as well as by stepwise isothermal dilatometry (SID) quasi-isothermal method to determine the sintering kinetic parameters. Based on these tools, it is found the Cu additive promotes sintering to obtain a denser anode and therefore allowing lower process temperatures. The consolidation is achieved through the sintering by activated surface (SAS) method allied to liquid phase sintering process, where the third metal additive also has influenced. The final cermet can be obtained at one sole process step, dispensing pore-forming additives and reduction treatments. The sintered microstructure demonstrates the material is homogeneous and possesses suitable percolation networks and pore structure for SOFC anode applications.
Authors: Sonia Regina Homem de Mello-Castanho, Antônio Carlos da Silva, Wilson Acchar, Ana M. Segadães
Abstract: The vitrification process is an attractive route for the inertization treatment of hazardous industrial wastes. The corrosion resistance of this kind of materials is one of the most important requirements to ensure the long term retention of the toxic metals. In this work, silicate glasses with various waste concentrations were obtained using a galvanic sludge from metallurgical activities and glass forming rejects from ceramic activities. Glasses with several galvanic waste concentrations were obtained. The corrosion behaviour of the vitrified materials under various pH media was evaluated. The FTIR technique was used to investigate the glass structural modifications. Glasses containing 40 wt.% galvanic waste additions show higher resistance to corrosion media than those without waste additions.
Authors: Luiz Fernando Grespan Setz, Sonia Regina Homem de Mello-Castanho
Abstract: Lanthanum Chromite may used as interconnect for SOFC’s applications due its particular intrinsic properties as stability in both oxidant and reducing environments and electrical conductivity. However to manufacture these devices that generally present complex shapes as grooved plates and fine pipes, they are necessary the use of the conformation techniques such as screen printing, slip casting, tape casting, extrusion moulding, etc. that are related with colloid processing. Independent of the processing techniques chosen the control of the suspension conditions is important to obtain reproducibility and homogeneous products as final result. In this sense, all contribution to understand the behaviour of the LaCrO3 fine particles in liquid suspension as the surface state using the Zeta’s Potential concepts may supplies information by the forecast of the behaviour during the shaped processing. The aqueous suspensions behaviour was studied utilizing doped lanthanum chromite powders, attained by combustion synthesis. The eletrophoretic mobility measurements of particles in suspension, prepared with the different conditioned powders were made. The electrolyte compositions as function of the pH varying from 2 to 12 were tested. The Zeta potentials and the stability conditions for stable suspensions prepared were determined. The viscosity curves are also appraised.
Authors: Antônio Carlos da Silva, J.J. Reinosa, J.S. Moya, J.F. Fernandez, Sonia Regina Homem de Mello-Castanho
Abstract: Green stoneware tiles have been produced by the incorporation of galvanic waste to industrial compositions processed from kaolinitic clay, feldspar, quartz. Some compositions with recycled domestic glass are also prepared. The galvanic waste required a calcination step to eliminate the gas forming species prior its incorporation into industrial processes. The effective absorption of metal from the galvanic waste was attained through the formation of crystalline phases. The presence of chromite type particles in the porcelain matrix acts as “in situ” to form pigments. The crystallization process also produces a higher consume of metal cations in the surrounded area of the crystalline pigments. The followed procedure allowed to effectively immobilized up to 20 wt% metal waste in a porcelain stoneware that satisfy both the mechanical and the chemical standards required to massively commercialize such a product.
Authors: Wilson Acchar, G.C.L. Silveira, Sonia Regina Homem de Mello-Castanho, Ana M. Segadães
Abstract: The use of industrial waste materials as additives in the manufacture of ceramic products has been attracting a growing interest from researchers in recent years and is becoming common practice. The continued depletion of natural resources throws a new light on the potential use of some industrial wastes and natural sub-products as full-fledged alternative ceramic raw materials. This work describes the research carried out on the low temperature manufacturing of alumina bodies using, as additive, granite reject as-produced by an ornamental stone processing industry that saws granite stones into blocks and slabs in Rio Grande do Norte, Brazil. This reject is produced in significant amounts and is discarded in sedimentation lagoons, landfill areas or simply thrown in rivers, resulting in environmental pollution. Samples containing up to 30 wt% granite reject and 5 wt% manganese oxide (constant) were uniaxially pressed and sintered in air in an electric furnace (1150-1350 °C, for 1 hour). Sintered test pieces were characterized by X-ray diffraction, apparent density, open porosity and flexural strength. The results showed that the addition of granite reject and manganese oxide enables low temperature sintering and remarkably improves the cold mechanical properties of the alumina body.
Authors: Sonia Regina Homem de Mello-Castanho, D.M. Ferreira, Sandra Maria Cunha
Authors: Thomaz Augusto Guisard Restivo, Sonia Regina Homem de Mello-Castanho
Abstract: A new integrated method for direct preparation of cermet materials is proposed consisting of a powder processing method allied to a special sintering step. The powder is obtained by mechanical alloying route where a specific morphologic design is searched to yield thin metal plated ceramic particles. These have the proper characteristics to engage the sintering by activated surface (SAS) consolidation method. The last is triggered by partial evaporation and reactive sintering of thin metal layers, therefore exposing high active surfaces with superior sinterability. Refractory sacrifice metal components are found to play an important role. The application of the integrated method to Ni-ZrO2 cermet with selected metal additives is investigated. Sintering temperatures can be reduced by more than 300°C for the same final density range. The resulted powders and pellets microstructures are analysed accordingly to the projected expected ones. The thermophysical and electrical properties measurements are performed for evaluate phases percolation.
Authors: Luiz Fernando Grespan Setz, Laís Koshimizu, Sonia Regina Homem de Mello-Castanho, Márcio Raymundo Morelli
Abstract: The pure oxides (yttria, zirconia, titania, alumina, etc.) pastes ceramics production by concentrate suspensions is interesting because differently than plastic ceramics (clays), where these behaviours are often empirical available, the rheological suspensions behaviour are extensively studied. Thus, controlling the concentrate slips rheological parameters, is possible extend these analysis for better understand and control the plastic pastes production, providing subsidies to obtain after shaping process, such as extrusion and calendering, suitable products for the desired application. Thus, alumina suspensions rheological behaviour, with high solids loading (> 50 vol.%) adequately stabilized, slip cast shaped are available in this work. High solids loading suspensions, up to 60 vol.%, presents adequate flow for thickeners/plasticizers elements adds to produce ceramic plastic pastes.
Authors: S.C. Santos, L.F.G. Setz, Chieko Yamagata, Sonia Regina Homem de Mello-Castanho
Abstract: Yttria (Y2O3) has been used in many technological applications areas as luminescence material, high temperature and strength structural material, owing to its excellent optical and refractory characteristics. Applying conformation techniques using Y2O3 concentrated suspensions is adequated, if it is well controlled, so that assisting to obtain homogeneous ceramic bodies, reproductive and with complex geometry. Studies involving superficial behavior, stability conditions of suspensions and the behavior related to conformation give important information to control the processes in manufacturing ceramic components. In this work is presented a rheological study of Y2O3 aqueous suspensions, which concerns to solids and dispersant concentration and pH of media. Preparation of Y2O3 aqueous suspensions with solids concentration of 30vol% was possible, using 1wt% of ammonium polyacrylate (PAA) that was enough to gain the lowest viscosity of the suspensions.
Authors: M.C. Ferreira, Wilson Acchar, Ana M. Segadães, Sonia Regina Homem de Mello-Castanho
Abstract: Brazil has one of the world’s most important Bauxite deposits, the raw material for the aluminium extraction metallurgy. This work is focused on finding a suitable application for the white dross residue (WDR), a second-generation waste material produced during the metal recovery from the slag left after the primary extraction of aluminium from the ore. A commercial lime-silica based glass frit was used, to which WDR additions were made (up to 30 wt.%), aimed at studying the devitrification process of the glasses produced. Such mixtures were melted at temperatures varying from 1100 to 1500°C and the resulting fritted glasses were heat treated at 900°C. The starting materials and the mixtures thereof were characterized before and after thermal treatment by differential thermal analysis, X-ray diffraction and fluorescence, and scanning electron microscopy. The results obtained showed that the WDR is easily incorporated into the glass matrix and causes easy devitrification after short heat treatment periods at low temperature.
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