Materials Science Forum Vols. 591-593

Abstract: This work is concerning to production of quicklime (CaO) from thermal decomposition of the calcite limestone (CaCO3) using analytical and instrumental techniques (TGA and MS) to evaluate kinetic and thermodynamic effects as well as heat/mass transfer associates with the process operation. On the other hand, experiments of morphologic, structural and textural characterization (XRD, SEM and BET surface area) were carried out in order to evaluate the quality of the quicklime produced. Under experimental studied conditions it was observed that carbon dioxide (CO2) inhibits the thermal decomposition reaction rate. In addition, it was observed that steam (H2O) can catalyze this reaction but it can also cause sintering of the oxide formed. It was also observed that the calcination reaction is greatly limited by mass transfer effects and that the controlled thermal decomposition generates an increase in the solid porosity. The formed CO2 have also increased the sintering phenomena in the oxide structure, resulting in less reactive quicklime.

Abstract: The settling vessels are equipment destined to solid-liquid separation; usually have continuous operation, with a circular section, presenting one conic and one cylindrical part. They are very used in chemical industries: wastewater treatment, minerals industries; to concentrate or to remove the solids. The solid particle splitting with small granular becomes difficult through the operation of conventional sedimentation. An expedient very used in the industry is the flocculant substance addition, whose objective is to promote the precipitation of particles, with decantation speed is upper than the single one. The present work aim the study of the burst operational conditions that influence the formation and the stability of these aggregates, the flake, the effect of pH and the concentration of flocculant using kaolin suspension and genfloc, that contains aluminum sulfate, as a flocculant; and the capacity of conventional settling vessel, which area of the transversal remains constant, considering this operational conditions.

Abstract: These work present studies about influence of the high temperature at the antimicrobial properties of the Bactericide Wood Polymer Composites (BWPC) after exposition during different times at 110 oC. The composite was formulated containing Polypropylene (PP) as matrix polymeric, wood powder of the species Pinus and Triclosan additive as bactericide agent. The BWPC was exposited during different times in the ambient and submitted to microbiological tests. The Agar Diffusion tests were applied with two kind bacteria, the Echerichia coli (EC - Gram Positive) and Staphylococcus aureos (SA - Gram Negative). The FT-IR and TGA techniques were utilized to available of the temperature effect in the chemical structure of the composites BWPC. The studies showed a strong dependence of the bactericide action of the composites with exposition time at 110 oC and a constant bactericide action after 100 hours of exposition.

Abstract: Rotary dryers are commonly used to dry particulate in a range of food and mineral processing industries. The purpose of this work was to study the design and performance of a rotary dryer. It was evaluated the number of flights and operational conditions that corresponding to the optimal performance for the equipment. A set of equations to predict the solids holdup in flights with three and two segments was also evaluated. Their predictions were compared to measurements performed with a pilot plant rotary dryer. The equation generated very accurate estimations.

Abstract: Stainless steel parts have been manufactured by two different layer by layer additive processes. The first one is a standard three dimensional process, in which metal powders are bound by selective deposition of binder with a printer head. The second one is a novel process, which is based on the selective deposition of a solvent on metal-polymer granule beds. The microstructures of green and sintered parts are characterized by optical and scanning electron microscopy, and the mechanical properties evaluated by hardness and tensile tests. Solvent on granule printing allows to reach mechanical properties similar to those of metal injection moulding parts.

Abstract: This paper presents a systematic study about ceramics made of zirconium oxide and titanium oxide (ZrO2-TiO2) doped with tin oxide (SnO2), strontium oxide (SrO2) and niobium oxide (Nb2O5). These ceramics can be applied as dielectric resonators in microwave systems for telecommunications. For a good microwave performance, these ceramics must reach some parameter values as high dielectric constant and high quality factor due to the dielectric losses. The ceramics were manufactured using suitable powder mixtures of ZrO2-TiO2 with additions of 1 % of SnO2, SrO2 and Nb2O5, resulting in four different kinds of samples for analysis. The samples were compacted by an uniaxial (190 MPa) and an isostatic (300 MPa) pressing, sintered at 1200 °C for 3 hours, characterized in the chemical compound formation using X-ray Diffraction (XRD) and scanned for microstructure densification degree and grain distribution analysis in Scanning Electron Microscopy (SEM). The dielectric parameters were measured using a microwave system. The main goal of present procedure is manufacture ceramic materials for promising application as dielectric resonators.

Abstract: Diluted magnetic semiconductors (DMS), which have both semiconducting and magnetic properties, are those in which transitions metal ions substitute cations of host semiconductor materials [1]. There is a great interest for DMS for use as the material of spintronics. In this study is reported the structural and morphologic characterization of Zn1.95Co0.05O nanoparticles obtained by Pechini method and combustion reaction. The powders resulting were characterized by X-ray diffraction (XRD) for determination of the phases, crystalline phase and lattice parameter; nitrogen adsorption by BET for determination of the specific superficial area and calculation the particle size from the superficial area and scanning electron microscopy (SEM) for morphologic analysis. The XRD results demonstrated the viability of obtaining crystalline and nanosize powders by the both synthesis routes. For all samples the average crystallite sizes was nanosized, but the powders obtained by reaction combustion is smaller. The SEM micrographs shows that the powders obtained for both syntheses are constituted of soft agglomerates.

Abstract: Samples of the superconducting ceramics Hg0.82Re0.18Ba2Ca2Cu3O8+ were prepared by solid-vapor reaction technique. The preparation of the ceramic precursor started with a mixture of Ba2Ca2Cu3Ox and ReO2 powders with molar ratio 1:0.18. The precursor material was submitted to annealing under three different partial pressures of oxygen using a mixture of oxygen/argon at ratios: 5/95 (sample A), 10/90 (sample B) and 15/85 (sample C). X-ray powder diffraction analysis of the precursors identified the phases BaCuO2+x, Ba2Cu3O5+x, Ba4CaCu3O8+x, Ca2CuO3 and Ca5Re2O12 at different ratios in the samples, indicating an increment in the oxygen content from sample A to sample C. Finally, the precursors with different oxygen contents were blended with HgO at molar ratio 1:0.82 and treated in a sealed high pressure furnace to produce the high Tc superconducting ceramics. Rietveld refinement of XRD data showed differences in the crystal structures of the samples. The measurement of thermopower at room temperature resulted in distinct values, confirming the different oxygen sample doping.

Abstract: Yttria-stabilized zirconia is the most developed solid electrolyte for use in hightemperature solid oxide fuel cell (SOFC). Commercial yttria-stabilized zirconia powders reach high densification at temperatures around 1400 °C. The use of additives may increase the densification rate by means of a liquid phase formation during sintering. However, these additives should not cause any degradation on the ionic conductivity of the electrolyte. The main purpose of this work was to study the effect of Co addition on the densification and electrical conductivity of yttriastabilized zirconia. Green compacts were prepared by pressureless sintering a mixture of commercial 8 mol% yttria-stabilized zirconia with cobalt carbonate. Linear shrinkage results show that the temperature at which the shrinkage starts decreases with increasing Co content. Impedance spectroscopy measurements reveal that Co additions to stabilized zirconia decrease the total electrolyte conductivity even for Co contents as low as 0.05 mol%.

Abstract: The soil humidity sensor plays fundamental role in the monitoring of hazard areas with landflows and landslides, about which in Brazil stories exist since 1671. Nowadays, it is just known that the majority of the mass movements in the hillsides occur in rainy periods, what makes the water the most important deflagrator agent of these movements, decreasing the soil resistance, increasing its specific weight and increasing the internal pressures as well. In this direction, the sensing elements developed by Group SUCERA/LAS/INPE uses the advantages presented for ceramics, in particular metal oxides, in terms of their mechanical strength, their resistance to chemical attack and their thermal and physical stability. In this work the results of the characterization analyses of sensor elements of ZrO2-TiO2 doped with 1, 5, 10, 15 e 20 % Nb2O5 porous ceramic, sintered at 1200 °C are shown and discussed.