Leandro da Conceição

Compósitos magnéticos baseados em hidrotalcitas para a remoção de contaminantes aniônicos em água

In this work the adsorption features of hydrotalcites (Al, Mg- CO3) and the magnetic properties of iron oxides have been combined in a composite to produce a magnetic adsorbent. These magnetic composites can be used as adsorbents for anionic contaminants in water and subsequently removed from the medium by a simple magnetic process. The magnetic hydrotalcites were characterized by XRD, magnetization measurements, N2 adsorption isotherms and Mossbauer spectroscopy. These magnetic adsorbents show remarkable adsorption capacity for anionic contaminants in water.

Solid-state Synthesis of La0.7Sr0.3MnO3 Powders using Different Grinding Times

Sr-doped lanthanum manganites (LSM) have been studied as promising materials for cathodes in solid oxide fuel cells (SOFC). In the present work La0.7Sr0.3MnO3 powders were synthesized by solid-state method evaluating the influence of dry or wet (using isopropanol) routes and different grinding times on the morphological and microstructural properties of LSM. The results of the synthesis of LSM powders pointed out that the use of solvent during homogenization results in poor crystallinity and only 6 hours of grinding at low speed in the ball mill is enough to obtain nano-sized crystalline phase by dry route. Scanning electron micrographs showed formation of agglomerates of fine primary particles. The electrical conductivity of the sintered LSM (La1xSrxMnO3, x= 0.2, 0.3 and 0.4) pellets with about 35% of porosity was measured by the two probe technique, showing a slight increase in the conductivity with strontium content.

Structural Characterization of Sr-doped LaMnO3 and LaCrO3 Powders Synthesized by Combustion Method

Lanthanum strontium manganite (LSM) and chromite (LSC) are good candidates for cathode and interconnect application in SOFC, respectively. This paper reports the synthesis of LSM and LSC powders from nitrate precursors by the combustion method, using two different fuels (urea and glycine). The ignition of the reagent mixture with urea takes a longer time and the maximum temperature is higher than using glycine. However, the adiabatic flame temperatures using urea are lower. X-ray diffraction patterns showed formation of only perovskite phase for the samples synthesized with urea, whereas secondary phases were also found for the samples prepared from glycine. The crystallite size calculated using the Scherrer equation is in the range of 23-31 nm. Thermogravimetric analysis revealed that the weight loss is much higher for manganites, with complete burn out of organics at 850900 o C. Scanning electron microscopy showed the presence of agglomerates, formed by fine particles of different shapes.

Transmission electron microscopy characterization of protective La0.7Sr0.3MnO3−delta coatings prepared by electrostatic spray deposition on ferritic alloy

The effect of La0.7Sr0.3MnO3−δ (LSM) coating on SS446 steel on air oxidation at 800∘C was investigated by transmission electron microscopy. Dense and crack free thin LSM films were prepared by electrostatic spray deposition. The microstructural characterization was carried out on coated and uncoated interconnectors. A thin chromia scale at the alloy interface along with two spinel phases were observed after long term oxidation in both cases. Specimens exhibit, in addition, an SiO2 layer at the interface with steel due to the high content of Si in the steel. Significant changes in the thickness, morphology and composition occurred in the reaction layer for the LSM coated steel. These effects are explained on the basis of changes in the diffusive fluxes during exposure to the oxidation treatment. The implications of these effects for the degradation mechanism of LSM-based interconnects are discussed.