Effect of seed addition on SnO2-based varistors for low voltage application

The effect of seed addition on the microstructure and non-ohmic properties of the SnO2 + 1%CoO + 0.05%Nb2O5 ceramic-based system was analyzed. Two classes of seeds were prepared: 99% SnO2 + 1%CuO and 99% SnO2 + 1%CoO (mol%); both classes were added to the ceramic-based system in the amount of 1%, 5%, and 10%. The two systems containing 1% of seeds resulted in a larger grain size and a lower breakdown voltage. The addition of 1% copper seeds produces a breakdown voltage (V b) of ∼ 37 V and a leakage current (fic) of 29 μA. On the other hand, the addition of 1% cobalt seeds produced a breakdown voltage of 57 V and a leakage current of 70 μA. Both systems are of great technological interest for low voltage varistor applications, by means of appropriate strategies to reduce the leakage current. Using larger amounts of seeds was not effective since the values of breakdown voltage in both cases are close to a system without seeds. To our knowledge, there are no reports in the literature regarding the use of seeds in the SnO2 system for low voltage applications. A potential barrier model which illustrates the formation of oxygen species (O′2(ads), O′ads, and O″ads) at the expense of clusters near the interface between grains is proposed. © 2012 The American Ceramic Society.

Evaluation of mechanical and thermal properties after chemical degradation of PVC and HDPE geomembranes

Chemical compatibility between geomembranes and site-specific waste liquids should be assessed since the waste liquids are highly complex mixtures. This paper presents some considerations about the chemical compatibility of geomembranes and some results of mechanical tests in HDPE and PVC geomembranes that were exposed to leachate and chemical residue (niobium). PVC and HDPE geomembranes of two thicknesses were tested: 1.0, 2.0 mm (PVC) and 0.8, 2.5 mm (HDPE). The results obtained show that after exposure the PVC geomembranes (1.0, 2.0 mm) were more rigid and stiffer than fresh samples. The HDPE geomembranes, on the other hand, when exposed to leachate and niobium residue presented increases in deformation. Melt flow index (MFI) tests were also carried out to verify the oxidation. © 2013 ejge.

Estudos sobre a síntese de piperidinas funcionalizadas através de reações pentacomponentes, utilizando compostos de nióbio como catalisadores

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Estudo das propriedades estruturais e ópticas de vidros teluritos do sistema TeO2-Li2O-Nb2O5

Pós-graduação em Ciência dos Materiais - FEIS

Síntese e caracterização da cerâmica PZT dopada com estrôncio e com nióbio e estrôncio

Pós-graduação em Química - IQ

Síntese de templates para aplicação em piezocerâmicas livre de chumbo

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Síntese, caracterização e propriedades da matriz sílica-carbono impregnada com níquel obtida pelo método dos precursores poliméricos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo do efeito do tempo e do meio de moagem de alta energia para obtenção de pós nanométricos de hidretos de titânio e nióbio

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Cerâmica condutora à base de 'SN''O IND.2' obtida pelo método dos precursores poliméricos e sinterização por micro-ondas

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Caracterização mecânica, física e química das ligas Ti-35Nb-5Zr e Ti-35Nb-10Zr

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Ativação da ligação c-h no metano por espécies MOm n+ (M = Nb, Fe; m = 0, 1; n = 0, 1, 2): estrutura eletrônica, mecanismo de reação e reatividade

The need for renewal and a more efficient use of energy resources has provided an increased interest in studies of methane activation processes in the gas phase by transition metal oxides. In this respect, the present work is an effort to assess , by means of a computational standpoint, the reactivity of NbOm n+ and FeOm n+ (m = 1, 2, n = 0, 1, 2) oxides in the activation process of the methane C-H bond, which corresponds to the first rate limiting step in the process of converting methane to methanol. These oxides are chosen, primarily, because the iron oxides are the most experimentally studied, and iron ions are more abundant in biological mediums. The main motive for choosing niobium oxides is the abundance of natural reserves of this mineral in Brazil (98%), especially in Minas Gerais. Initially, a thorough investigation was conducted, using different theoretical methods, to analyze the structural and electronic properties of the investigated oxides. Based on these results, the most reliable methodology was selected to investigate the activation process of the methane C-H bond by the series of iron and niobium oxides, considering all possible reaction mechanisms known to activate the C-H bond of alkanes. It is worth noting that, up to this moment and to our knowledge, there are no papers, in literature , investigating and comparing all the mechanisms considered in this work. I n general, the main results obtained show different catalytic tendencies and behaviors throughout the series of monoxides and dioxides of iron and niobium. An important and common result found in the two studies is that the increase in the load on the metal center and the addition of oxygen atoms to the metal, clearly favor the initial thermodynamics of the reaction, i.e., favor the approach of the metal center to methane, distorting its electron cloud and, thereby, decreasing its inertia. Comparing the two sets of oxides, we conclude that the iron oxides are the most efficient in activating the methane C-H bond. Among the iron oxides investigated, FeO + showed better kinetic and thermodynamic performance in the reaction with methane, while from the niobium oxides and ions NbO 2+ and NbO2 2+, showed better catalytic efficiency in the activation of the methane C-H bond.

Efeito da adição de níquel nas propriedades elétricas de nanopós de niobato de potássio e estrôncio de estrutura tungstênio bronze

Pós-graduação em Química - IBILCE

Estudo sobre o uso de compostos de nióbio em reações multicomponentes de aza-Diels-Alder

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Preparação e caracterização estrutural de complexos quirais de nióbio, utilizando álcoois terpênicos quirais como ligantes

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Estudo sobre o uso do pentacloreto de nióbio em reações multicomponentes para síntese de derivados de 4-ARIL-3,4-DI-Hidrocumarinas

Pós-graduação em Ciência e Tecnologia de Materiais - FC