Efeito da Gália como aditivo de sinterização em eletrólitos cerâmicos à base de céria sintetizados pelo método de complexação de cátions

Fuel cells are considered one of the most promising ways of converting electrical energy due to its high yield and by using hydrogen (as fuel) which is considered one of the most important source of clean energy for the future. Rare earths doped ceria has been widely investigated as an alternative material for the electrolyte of solid oxide fuel cells (SOFCs) due to its high ionic conductivity at low operating temperatures compared with the traditional electrolytes based on stabilized zirconia. This work investigates the effect of gallium oxide (Gallia) as a sintering aid in Eu doped ceria ceramic electrolytes since this effect has already been investigated for Gd, Sm and Y doped ceria electrolytes. The desired goal with the use of a sintering aid is to reduce the sintering temperature aiming to produce dense ceramics. In this study we investigated the effects on densification, microstructure and ionic conduction caused by different molar fraction of the dopants europium (10, 15 and 20%) and gallium oxide (0.3, 0.6 and 0.9%) in samples sintered at 1300, 1350 and 1450 0 C. Samaria (10 and 20%) doped ceria samples sintered between 1350 and 1450 °C were used as reference. Samples were synthesized using the cation complexation method. The ceramics powders were characterized by XRF, XRD and SEM, while the sintered samples were investigated by its relative density, SEM and impedance spectroscopy. It was showed that gallia contents up to 0.6% act as excellent sintering aids in Eu doped ceria. Above this aid content, gallia addition does not promote significant increase in density of the ceramics. In Ga free samples the larger densification were accomplished with Eu 15% molar, effect expressed in the microstructure with higher grain growth although reduced and surrounded by many open pores. Relative densities greater than 95 % were obtained by sintering between 1300 and 1350 °C against the usual range 1500 - 1600 0 C. Samples containing 10% of Sm and 0.9% of Ga reached 96% of theoretical density by sintering at 1350 0 C for 3h, a gain compared to 97% achieved with 20% of Sm and 1% of Ga co-doped cerias sintered at 1450 0 C for 24 h as described in the literature. It is found that the addition of gallia in the Eu doped ceria has a positive effect on the grain conductivity and a negative one in the grain boundary conductivity resulting in a small decrease in the total conductivity which will not compromise its application as sintering aids in ceria based electrolytes. Typical total conductivity values at 600 and 700 °C, around 10 and 30 mS.cm -1 respectively were reached in this study. Samples with 15% of Eu and 0.9 % of Ga sintered at 1300 and 1350 °C showed relative densities greater than 96% and total conductivity (measured at 700 °C) between 20 and 33 mS.cm -1 . The simultaneous sintering of the electrolyte with the anode is one of the goals of research in materials for SOFCs. The results obtained in this study suggest that dense Eu and Ga co-doped ceria electrolytes with good ionic conductivity can be sintered simultaneously with the anode at temperatures below 1350 °C, the usual temperature for firing porous anode materials

África Austral: Los minerales como recurso estratégico para los intereses de Estados Unidos y China, período 2000-2010

La región de África Austral emerge como un nuevo escenario geopolítico complejo, en el que la lucha por la adquisición de los derechos de exploración, extracción y distribución de minerales estratégicos ha intensificado la presencia del número de actores estratégicos en esta zona. En este sentido, es interesante analizar el juego de poder que se desarrolla entre Estados Unidos y China con el fin de neutralizar la debilidad estratégica que representa la carencia de estos recursos naturales, esenciales para el desarrollo de sus industrias, así como también la oportunidad que representan como mecanismo para ampliar las esferas de influencia extra continental. Así pues, la presente investigación analiza a partir de la explotación de los minerales como recursos estratégicos, los efectos de la geoestrategia reciente de estos dos jugadores activos del sistema internacional contemporáneo en la relación con los Estados que conforman la región meridional del continente africano, durante el periodo 2000-2010.

Complexes of rare earth perchlorates with di-2-pyridyl ketone

Abstract is not availabe.

Spectroscopy and photochemistry of hydrogen peroxide and its complexes in solid rare gases

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2,6-Lutidine-N-oxide complexes of rare-earth bromides

2,6-Lutidine-N-oxide (LNO) complexes of rare-earth bromides of the composition $$MBr_3 .(LNO)_{4_{ - n} } .nH_2 O$$ wheren = l for M = La, Pr, Nd, Sm, Gd, Ho, Er; andn = 0 for M = Y have been prepared and characterised by analyses, conductance and infrared data. Infrared spectra of the complexes indicate that the coordination of ligand to the metal ion takes place through the oxygen of the ligand, and the water molecule in the complexes present is coordinated to the metal. A coordination number of seven has been suggested to all the rare-earth metal ions.

Lanthanide coordination in dimethyl sulphoxide and antipyrine complexes of rare earth nitrates

Abstract is not available.

3-Picoline-N-oxide complexes of rare-earth bromides

3-Picoline-N-oxide (3-PicNO) complexes of rare-earth bromides of the formulaMBr3(3-PicNO)8–n·nH2O wheren=0 forM=La, Pr, Nd, Sm Tb or Y andn=2 forM=Ho or Yb have been prepared. Infrared and proton NMR studies indicate that the coordination of the ligand is through oxygen. Conductance data in acetonitrile suggest that two bromide ions are coordinated to the metal ion. Proton NMR studies suggest a bicapped dodecahedral arrangement of the ligands around the metal ion in solution for Pr(III), Nd(III) and Tb(III) complexes.

4-Picoline-N-oxide complexes of rare-earth bromides

In continuation of our work on the effect of the anion on the coordination chemistry of the rare-earth metal ions, we have now extended our studies to 4-picoline-N-oxide (4-Pie NO) complexes of rare-earth bromides. By ohangi~ the method of preparation Harrison and Watsom (1) have prepared two types of Sm(IIl) complexes and three types of Eu(III) complexes of 4-pioollne-N-Oxide in the presence of perchlorate ions. We have isolated two types of pyridine-N-Oxide complexes of rare-earth bromides, also by changing the method of preparation (2). The effect of the change of the preparative method on the composition of the lanthanide complexes is exhibited in the case of other complexes also (3-6). But our attempts to prepare 4-picoline-N-Oxide of rare-earth bromides having different stoichiometries were unsucessful . The composition of the complexes is the same for all the complexes prepared. The results of the physico-chemical studies on these 4-Pic NO complexes of rare-earth bromides are discussed in the present paper.

Antipyrine complexes of rare-earth nitrates

Antipyrine complexes of eight rare-earth nitrates of the composition M(C11H12N2O)3 (NO3)3 where M = La, Ce, Pr, Nd, Sm, Gd, Er, and Y, have been prepared by a new, simple method and characterised. The complexes undergo exothermic decomposition at ~3oo°C. Infrared and U.V. spectral studies of the complexes indicate that antipyrine coordinates to metal through oxygen. The nature of the nitrate bonding is discussed in the light of infrared evidence, and conductivity studies in nitromethane and dimethylformamide.

Antipyrine complexes of rare earth perchlorates

Rare earth perchlorate-antipyrine (ap) complexes of the formula Ln (ClO4)3.6 ap have been prepared and characterised. Infrared and electronic spectra showed the co-ordination through carbonyl oxygen. Conductivity and molecular weight data indicated a co-ordination number of six for these complexes.

Dimethyl sulphoxide complexes of rare-earth perchlorates

Dimethylsulphoxide (DMSO) complexes of rare-earth perchlorates of the formula M(ClO4)3·n DMSO (M = La, Ce, Pr and Nd, n = 8; M = Sm, Gd and Y, n = 7) have been prepared. I.r. studies indicate co-ordination through oxygen. Cryoscopic and conductivity data show co-ordination number of 7 and 8.

Dimethyl formamide complexes of rare-earth nitrates

Dimethyl formamide complexes of five rare-earth nitrates, M(DMF)4(NO3)3 where M = La, Pr, Nd, Sm or Y have been prepared and their infra-red spectra and conductivities in nitromethane and DMF studied. It is suggested that the co-ordination number of the metal ion in these complexes is nine.