Sorption between microbial cells and clay minerals was determined by measuring changes in particle size distribution with an electronic particle counter. Sorption increased as the valency of the cations present on the clay and in the suspending electrolyte increased. Neither the size, motility, or Gram reaction of bacteria nor the size of the clay appeared to influence sorption. Sorption occurred between bacteria and montmorillonite homoionic to monovalent cations only at pH 2 to 4, but did not occur at any pH with yeast cells, which sorbed only in the presence of trivalent cations. Heat-killed cells of yeast lost their ability to sorb, whereas cells killed with benzalkonium chloride did not. The possible implications of these results in sorption of microorganisms in natural habitats are discussed.
Flocculation of clay minerals by microbial metabolites was determined by measuring changes in particle‐size distribution. No floculation occurred when clay and metabolite mixtures were analyzed in sodium metaphosphate as the suspending electrolyte. When the mixtures were analyzed in electrolytes containing the chloride salt of the cation to which montmorillonite was made homoionic, all metabolites caused flocculation in the presence of trivalent cations, some with divalent cations, but none with monovalent cations. Similar results were obtained with purified rhizobial polysaccharides, which, however, also flocculated kaolinite homoionic to Na. The degree of flocculation of the clays differed with the source of the metabolites. A nonionic polyacrylamide (Separan) flocculated both montmorillonite and kaolinite, regardless of the type of cation present. The possible implications of these results in the aggregation of soil by microorganisms are discussed.
Ao meu Orientador, Dr Almir Oliveira Neto, por toda paciência apoio, orientação e por me dar a oportunidade de ir para Tenerife. Ao meu primeiro Orientador, Dr. Marcelo Linardi, por abrir as portas do mundo acadêmico para mim. À minha Coorientadora, Dra Christina A. Leão Guedes de Oliveira Forbicini, pela paciência e apoio. Ao Dr. Estevam Vitorio Espinacé, pelo apoio. À Coorientadora na Universidad La Laguna, Dra Elena M. Pastor Tejera, por iluminar meu caminho em breves momentos difíceis que tive com meu trabalho, no início de minha estância, em Tenerife. Ao Dr. José Luis Rodríguez, pelo auxílio nos meus experimentos. Aos colegas de trabalho e amigos do IPEN que de 2005 a 2009 deixaram meus dias mais divertidos. Aos colegas de trabalho e amigos de Tenerife que fizeram com que minha estância na ilha fosse muito agradável.
The solid oxide fuel cell (SOFC) is an electrochemical device generating of electric energy, constituted of cathode, electrolyte and anode; that together they form a unity cell. The study of the solid oxide half-cells consisting of cathode and electrolyte it is very important, in way that is the responsible interface for the reduction reaction of the oxygen. These half-cells are ceramic materials constituted of strontium-doped lanthanum manganite (LSM) for the cathode and yttria-stabilized zirconia (YSZ) for the electrolyte. In this work, two solid oxide half-cells have been manufactured, one constituted of LSM cathode thin film on YSZ electrolyte substrate (LSM - YSZ half-cell), and another constituted of LSM cathode and LSM/YSZ composite cathode thin films on YSZ electrolyte substrate (LSM - LSM/YSZ - YSZ half cell). The cathode/electrolyte solid oxide half-cells were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results have been presented with good adherence between cathode and electrolyte and, LSM and YSZ phases were identified.
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