Materials Science Forum Vols. 660-661

Abstract: Many ceramic materials are being studied for application as cathodes in Solid Oxide Fuel Cells (SOFCs), especially aiming to reduce the operating temperature. Several ceramic materials can act as cathodic components, including Strontium-Doped Neodymium Manganite (Nd1-XSrXMnO3). This work contributes to the aforementioned studies by analyzing the main physical, chemical and microstructural characteristics of Nd1-XSrXMnO3 powders, where x = 0.10, 0.30, and 0.50. These powders were obtained by the method of ceramic solids mixture. The homogeneity of the powder particles was found to be suitable for the preparation of suspensions, which can be evaluated rheologically and subsequently molded to the surface of the solid electrolyte.

Abstract: The aim of the present work is to verify experimentally the influence of the charge level on collection efficiency during the first stages of filtration. A charge classifier was used to measure the charge level of the aerosol as a function of particle diameter. The filter was made of polypropylene with diameter of 0.047 m and a thickness of 2.6 mm. The solid particles used as test dust were a phosphate rock powder (density 2940 kg/m3 and average Stokes diameter of 3.40 m). The aerosol was dispersed by a TSI Venturi type generator. The particle charging was achieved by a corona charger. In all the tests performed, a linear relation between the particles acquired charge and their diameter was observed. A gradual increase of the charge level was observed with an increase of the tension in the corona charger (0, -3, -6 kV). The filtration results indicated that the global collection efficiency of the filter was very sensitive to the variation of the charge level of the particles. Both efficiency and pressure drop increased when the charge level increased. During the tests, the small increase in pressure drop indicated that the cake had not yet been formed.

Abstract: The organo-clays have important industrial uses between others are: rheological additives for drilling fluids in oil bases, inks, glues, lubricants and cosmetics. At the moment and in a growing way, these materials are considered as important reinforcement fillers in the structuring of nano-composites clays/polymers. They are obtained by the smectite clay reaction with quaternary ammonium salts. In this work an organophillic clay sample prepared by a dry process at the PMT – EPUSP – Metallurgic and Materials Engineering Department of the Polytechnic School at the University of São Paulo, had been characterized basically by techniques of XRD, IR, Thermal Analysis, and by swell capacity of the clays in some oils and organic solvents.

Abstract: This paper presents a study of a stabilization/solidification (S/S) process of a tannery waste containing chromium. In this process a mixture of cement, water and the waste is solidified during hydration of the former. Stabilization occurs by the reaction of the chromium components of the waste with the calcium hydroxide formed during the process. A rigid block is obtained with low hazardous of contamination of soil and groundwater after its disposal into industrial landfill. Mixtures were prepared adding dried tannery waste in 10, 15 and 20% of the Portland cement mass. Sodium bentonite and organoclays in 5 % of cement mass were used as additives. Solidified specimens were analyzed after 28 days of hydration time by solid-state 29Si nuclear magnetic resonance (NMR) spectroscopy and unconfined compressive strength analysis. The increase of tannery waste content and the presence of the additives reduce silica polymerization as well as the mechanical strength of the solidified bodies.

Abstract: The paper describes the technique developed for applying garnet powder abrasive ultra-high pressure water jet advanced technology (AWJ) to build accurate models of artistic objects. The objects to be modeled have been selected through a cooperative initiative between the University of Sao Paulo and entities of the private sector. The first application was the reproduction of the artistic floor of marble at the St. Mark's Basilica, Venice, Italy. The other application was the production of official trophies for a technical awards ceremony for a national symposium that took place in Brazil. The trophies were made in stainless steel, whilst the floor reproduction was made in ceramic tiles. The floor was reproduced from high-definition photography of the original floor. The design concept and the blueprints of the trophies were originally conceived by the symposium organizers. Both models have been built using OMAX® CAD/CAM Software, which controls an AWJ unit installed at the University of São Paulo, where the procedures for building both models have been developed and executed with high success.

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.