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Adsorption kinetic, thermodynamic and desorption studies of phosphate onto hydrous niobium oxide prepared by reverse microemulsion method

RODRIGUES, Liana Alvares; SILVA, Maria Lucia Caetano Pinto da
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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A type of Nb(2)O(5)center dot 3H(2)O was synthesized and its phosphate removal potential was investigated in this study. The kinetic study, adsorption isotherm, pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order rate model very well. The phosphate adsorption tended to increase with a decrease of pH. The adsorption data fitted well to the Langmuir model with which the maximum P adsorption capacity was estimated to be 18.36 mg-Pg(-1). The peak appearing at 1050 cm(-1) in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The positive values of both Delta H degrees and Delta S degrees suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. Delta G degrees values obtained were negative indicating a spontaneous adsorption process. A phosphate desorbability of approximately 68% was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive sites on the surface of the adsorbent. The immobilization of phosphate probably occurs by the mechanisms of ion exchange and physicochemical attraction. Due to its high adsorption capacity...

Construção e avaliação de eletrodos de Nióbio/Óxido de Nióbio para determinações potenciométricas; Construction and evalution of Niobium/Niobium Oxide electrodes for potentiometric determination

Jardim, Wolney de Jesus
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 17/10/2008 PT
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A construção de sensor potenciométrico, utilizando Nióbio acoplado a eletrodo de referência de prata/cloreto de prata num mesmo instrumento, possibilita o acompanhamento da variação de potencial que ocorre durante uma reação ácido-base em meio aquoso. Foi utilizado eletrodo de vidro combinado, cuja membrana de vidro foi danificada fisicamente, porém com sua referência interna em pleno funcionamento. O eletrodo de Nióbio foi confeccionado com metal polido ou então com a superfície modificada com óxido eletrodepositado. O crescimento de óxido sobre o Nióbio foi obtido por eletrólise em meio a H3PO4 diluído. O metal ou o par metal/óxido foi fixado no eletrodo de vidro contendo uma solução eletrolítica. O eletrodo de Nióbio não apresenta boa sensibilidade quando utilizado como indicador em potenciometria direta, mas é sensível às variações de potenciais que ocorrem em titulações ácido-base. O eletrodo de Nióbio metálico pode substituir o eletrodo de vidro combinado na determinação do teor de acidez de vinagres.; The construction of potentiometric sensors, using Niobium combined with the reference electrode silver / silver chloride in a single instrument, allows the variation of potential monitoring that occurs during an acid-base reaction in aqueous media. It was used a combined electrode glass...

Síntese de nanopartículas de óxido de nióbio hidratado via microemulsão inversa; Synthesis of hydrous niobium oxide nanoparticles by reverse microemulsion

Rodrigues, Liana Alvares
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 03/02/2009 PT
Relevância na Pesquisa
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Com o objetivo de gerar um material mais homogêneo quanto à forma e tamanho das partículas formadas (nanopartículas), o presente trabalho visa o estudo das variáveis de preparação do Nb2O5.nH2O via microemulsão inversa (ME). Por meio de um planejamento fatorial completo, estudou-se a influência da concentração do agente precursor, da ordem de adição das microemulsões e da razão água/surfatante (W) no tamanho das partículas formadas. Para análise comparativa, Nb2O5.nH2O também foi preparado pelos métodos da precipitação convencional (PC) e da precipitação em solução homogênea (PSH). Os materiais preparados foram caracterizados por difratometria de raios X (DRX), termogravimetria (TG), microscopia eletrônica de varredura (MEV) e de transmissão (MET), espectrômetria de energia dispersiva (EDS), espectroscopia de absorção no infravermelho por transformada de Fourier (FTIR) e análise de área superficial específica pelo método B.E.T. A adsorção de íons fosfato em Nb2O5.nH2O foi estudada. A melhor forma de preparação do Nb2O5.nH2O via ME foi a utilizada no experimento 2. As micrografias MEV confirmam que os materiais preparados pelo método ME possuem partículas esféricas menores que as dos materiais preparados pelos métodos PC e PSH. Dos modelos cinéticos estudados...

Desenvolvimento de novos compósitos baseados em polietileno e híbridos gerados a partir de resíduos agrícolas modificados com óxido de nióbio; Development of new composites based on polyethylene and hybrids generated from agricultural residues modified with niobium oxide

Ottoboni, Fabíola Silva
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/02/2011 PT
Relevância na Pesquisa
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As fibras naturais estao ganhando espaco no mercado como materia-prima por apresentarem caracteristicas desejaveis para aplicacoes industriais, por ser um material renovavel, biodegradavel e de baixo custo. Neste sentido, a exploracao da celulose vem crescendo, inclusive no estudo de compositos polimericos reforcados com fibras naturais. Este trabalho visa primeiramente a obtencao de hibridos celulose/oxido de niobio hidratado a partir do tratamento e modificacao do bagaco de cana-de-acucar, e posteriormente a geracao de compositos de matriz de polietileno de baixa densidade (PEBD) e carga de celulose modificada. O Nb2O5.nH2O foi gerado pelo metodo da precipitacao convencional, partindo-se de niobio metalico. Os hibridos foram produzidos nas proporcoes de 10, 20, 30 e 40% de oxido e caracterizados utilizando-se as seguintes tecnicas: difracao de raios X (DRX), espectroscopia de absorcao no infravermelho com transformada de Fourier (FTIR), termogravimetria (TG), calorimetria exploratoria diferencial (DSC) e microscopia eletronica de varredura (MEV). Os resultados indicam que houve boa interacao entre a fibra de celulose e o oxido de niobio hidratado em todas as proporcoes estudadas. Pelas curvas DSC em atmosfera oxidativa pode-se observar que o Nb2O5.nH2O agiu como um agente retardante a chamas. A proporcao do hibrido definida para a geracao dos compositos foi 90Cel/10Nb2O5.nH2O. Inicialmente foram fabricados os compositos reforcados apenas com celulose branqueada...

Caracterização óptica de filmes finos de NbOx obtidos por sputtering reativo; Optical characterization of NbOx thin films obtained by reactive sputtering

Scheidt, Guilherme
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 02/12/2014 PT
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Filmes finos de óxido de nióbio têm sido usados em muitas aplicações tecnológicas. Existem pelo menos três óxidos estáveis de nióbio: NbO, NbO2 e Nb2O5 e cada um deles tem propriedades específicas. O Nb2O5 é a forma termodinamicamente mais estável e apresenta propriedades físicas e químicas únicas, como alto índice de refração, band gap largo, excelente estabilidade química e resistência à corrosão, baixa absorção óptica no campo da luz visível até regiões próximas ao infra-vermelho, sendo amplamente utilizados como filtros de interferência óptica de alta qualidade. Neste trabalho foram depositados filmes de óxido de nióbio por meio da técnica de sputtering reativo sobre substratos de silício e borossilicato. Os filmes finos foram obtidos com vazão de oxigênio variando entre 15 e zero sccm. O objetivo deste trabalho foi a caracterização das propriedades ópticas dos filmes. Foram avaliados o índice de refração e a espessura pela técnica de elipsometria, o band gap pelo método de Tauc e a razão atômica e a densidade superficial por meio de Espectrometria de Retroespalhamento Rutherford (RBS). Foram obtidos espectros de transmitância e refletância por Espectrofotometria UV/Vis/NIR e o coeficiente de extinção foi calculado pelo método de Hong. Todos estes parâmetros são importantes para aplicação em dispositivos ópticos. Nos filmes depositados com vazão de oxigênio de 15 sccm foi observado que o índice de refração aumenta com o aumento da espessura dos filmes e que o composto formado foi Nb2O5. Para uma vazão de 2...

Preparation and characterization of cellulose/hydrous niobium oxide hybrid

Maschio, Leandro Jose; Fernandes Pereira, Paulo Henrique; Caetano Pinto da Silva, Maria Lucia
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 992-996
ENG
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A composite of cellulose extracted from bagasse with Nb2O5 center dot nH(2)O in three different proportions (16.67, 37.5 and 50.0 wt%) was prepared using the co-precipitation method. The materials were characterized by X-ray diffractometry (XRD), Fourier transform infra-red spectroscopy (FTIR), thermogravimetric analysis (TG/DTG), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). TG data obtained show that the presence of inorganic material influenced slightly the stability of the hybrid material. The precipitation of 16.67 wt.% of oxide was sufficient to inhibit the combustion peaks present in the DSC curve of cellulose. This work will help find new applications for these materials. Published by Elsevier Ltd.

Influence of addition of calcium oxide on physicochemical properties of Portland cement with zirconium or niobium oxide

Tanomaru-Filho, Mario; Garcia, André Cresto; Bosso-Martelo, Roberta; Berbert, Fabio Luis Camargo; Reis, José Maurício dos Santos Nunes; Guerreiro-Tanomaru, Juliane Maria
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 105-108
ENG
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Context: Calcium oxide (CaO) may be added to mineral trioxide aggregate (MTA) or Portland cement (PC) to improve physicochemical and biological properties. Aims: To evaluate the physicochemical properties of PC associated with radiopacifiers and CaO. Materials and Methods: MTA Angelus, PC + 30% zirconium oxide (Zr), or 30% niobium oxide (Nb) associated with 10 or 20% of CaO were evaluated. Gilmore needles were used to evaluate initial and final setting time. Compressive strength was evaluated after the periods of 24 hours and 21 days. pH was analyzed after 3, 12, 24 hours, 7, 14, 21 days. Solubility and flow tests were performed based on the ISO 6876. The data obtained were submitted to analysis of variance and Tukey tests (P ≤ 0.05). Results: The associations with 10% CaO showed greater strength that the associations with 20% CaO. The shortest initial setting time was observed for the association PC + Zr + 20% CaO and MTA. All the cements presented alkaline pH. The flow of all cements was similar. The highest solubility was found in the associations with 20% CaO. Conclusion: The addition of CaO to PC favored the alkaline property and the PC + Zr + 20% CaO presented setting time similar to MTA.

Radiopacity and cytotoxicity of Portland cement associated with niobium oxide micro and nanoparticles

Mestieri, Leticia Boldrin; Tanomaru-Filho, Mário; Gomes-cornélio, Ana Livia; Salles, Loise Pedrosa; Bernardi, Maria Inês Basso; Guerreiro-Tanomaru, Juliane Maria
Fonte: Faculdade De Odontologia De Bauru - USP Publicador: Faculdade De Odontologia De Bauru - USP
Tipo: Artigo de Revista Científica Formato: 554-559
ENG
Relevância na Pesquisa
58.200522%
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); ObjectiveMineral Trioxide Aggregate (MTA) is composed of Portland Cement (PC) and bismuth oxide (BO). Replacing BO for niobium oxide (NbO) microparticles (Nbµ) or nanoparticles (Nbη) may improve radiopacity and bioactivity. The aim of this study was to evaluate the radiopacity and cytotoxicity of the materials: 1) PC; 2) White MTA; 3) PC+30% Nbµ; 4) PC+30% Nbη. Material and MethodFor the radiopacity test, specimens of the different materials were radiographed along an aluminum step-wedge. For cell culture assays, Saos-2 osteoblastic-cells (ATCC HTB-85) were used. Cell viability was evaluated through MTT assay, and bioactivity was assessed by alkaline phosphatase activity assay. ResultThe results demonstrated higher radiopacity for MTA, followed by Nbµ and Nbη, which had similar values. Cell culture analysis showed that PC and PC+NbO associations promoted greater cell viability than MTA. ConclusionIt was concluded that the combination of PC+NbO is a potential alternative for composition of MTA.

Bioatividade de vidros contendo nióbio : estudo experimental in vivo; Bioactivity of glasses composed by niobium : an experimental in vivo study

Lucas Pereira Lopes de Souza
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 31/07/2014 PT
Relevância na Pesquisa
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Alguns estudos mostram que a introdução do óxido de nióbio (Nb2O5) na composição do Bioglass® poderia ser uma solução para melhorar sua resistência mecânica, mantendo sua biocompatibilidade e bioatividade, porém, apesar da melhora na resistência mecânica causada pela adição deste óxido ser bem documentada na literatura, suas propriedades bioativas ainda são pouco conhecidas. Neste contexto, o objetivo do presente estudo foi avaliar experimentalmente as propriedades bioativas do óxido de nióbio em ratos albinos (Rattus norvegius) da linhagem Wistar. Para isso, bastões vítreos compostos por diferentes concentrações do Nb2O5 foram implantados na tíbia de ratos. Além disso, cada vidro teste, na forma de pó, foi implantado no músculo de ratos para análise de suas propriedades pró-angiogênicas, usando o Bioglass 45S5 (Bioglass®) como controle. As eutanásias foram realizadas 14 e 28 dias pós-cirurgias. Lâminas histológicas de cortes transversais das tíbias foram coradas a H&E para mensuração da área de osso subperiostal existente na cortical adjacente ao implante e a quantidade de osso esponjoso formado ao redor do bastão vítreo nos grupos de 14 dias, bem como da espessura da lâmina óssea formada ao redor do bastão nos grupos de 28 dias. Foi ainda realizada marcação imuno-histoquímica e a razão entre a área total do implante em mm2 e o número total de vasos sanguíneos contados manualmente num aumento de 400x para verificação a capacidade do material de estimular a angiogênese. A avaliação histológica revelou a ausência total de inflamação tanto após 14 quanto após 28 dias de implante. Os resultados das comparações entre as áreas de osso subperiostal dos grupos após 14 e 28 dias (feitas através de um teste ANOVA com post hoc tukey) e da quantidade de osso esponjoso formado ao redor do implante nos grupos 14 dias (feitas através do teste Kruskal-Wallis com Mann-Whitney como post hoc) mostraram que o BGPN1.3 apresentou maior capacidade de induzir a formação óssea do que o grupo controle...

Preparation and electrochemical characterization of Pt nanoparticles dispersed on niobium oxide

Mello,R. L. S.; Mattos-Costa,F. I.; Villullas,H. de las M.; Bulhões,L. O. de S.
Fonte: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP Publicador: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2003 EN
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Electrodes consisting of Pt nanoparticles dispersed on thin films of niobium oxide were prepared onto titanium substrates by a sol-gel method. The physical characterization of these electrodes was carried out by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The mean size of the Pt particles was found to be 10.7 nm. The general aspects of the electrochemical behavior were studied by cyclic voltammetry in 1 mol L-1 HClO4 aqueous solution. The response of these electrodes in relation to the oxidation of formaldehyde and methanol in acidic media was also studied.

Adsorption of phosphoric acid on niobium oxide coated cellulose fiber: preparation, characterization and ion exchange property

Pavan,Flávio A.; Francisco,Maria Suzana P.; Landers,Richard; Gushikem,Yoshitaka
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2005 EN
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The preparation procedures for a hybrid organic-inorganic cellulose-niobium oxide (Cel/Nb2O5) and its derivative, Cel/Nb2O5/phosphate, are described. The precursor reagent of the metal oxide was the very convenient water soluble niobium oxalate compound, NH4[NbO(C2O4)2)(H 2O)2].nH2 O. Phosphate ion was adsorbed on the Cel/Nb2O5 by immersing this solid in an aqueous solution of phosphoric acid. Textural analyses carried out by using scanning electron microscopy (SEM) connected to an energy dispersive detector (EDS) revealed that the niobium oxide particles are, within the magnification used, uniformly dispersed on the cellulose matrix surface. Phosphoric acid is adsorbed on the material surface through the Nb-O-P linkage. The X-ray photoelectron and 31P NMR spectra showed that the adsorbed phosphate on the surface is the (H2PO4)- species. The ion exchange isotherms obtained using the material Cel/Nb2O5/H2PO4- showed good affinity for retaining Na+, K+ and Ca2+ when in contact with these ions in an aqueous solution.

THE INFLUENCE OF NIOBIUM ON THE ACIDITY AND STRUCTURE OF GAMMA-ALUMINA-SUPPORTED VANADIUM OXIDES

Sathler,M.N.B.; Eon,J.G.
Fonte: Brazilian Society of Chemical Engineering Publicador: Brazilian Society of Chemical Engineering
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/1998 EN
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Gamma-alumina-supported niobium oxide was used as a support for vanadium oxides. The influence of the addition of niobium oxide was studied by looking for changes in the structure and acid-base character of superficial species. Vanadium oxide was deposited using the continuous adsorption method; niobium oxide was impregnated using the incipient wetness method. The catalysts were characterized by XPS, UV-visible and IR spectroscopy. Catalytic tests were performed using propane oxidation reaction at 400oC. For coverage below the monolayer, both vanadium and niobium oxides were observed in slightly condensed superficial species. The presence of vanadium oxide on the support was found to increase the Lewis acidity and create some Bronsted acidity. Higher catalytic activity and selectivity for propene were associated with vanadium oxides. The presence of niobium did not contribute to the modification of the chemical properties of superficial vanadium but did decrease the adsorption of vanadium on the alumina.

Radiopacity and cytotoxicity of Portland cement associated with niobium oxide micro and nanoparticles

MESTIERI,Leticia Boldrin; TANOMARU-FILHO,Mário; GOMES-CORNÉLIO,Ana Livia; SALLES,Loise Pedrosa; BERNARDI,Maria Inês Basso; GUERREIRO-TANOMARU,Juliane Maria
Fonte: Faculdade De Odontologia De Bauru - USP Publicador: Faculdade De Odontologia De Bauru - USP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2014 EN
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58.200522%
Objective Mineral Trioxide Aggregate (MTA) is composed of Portland Cement (PC) and bismuth oxide (BO). Replacing BO for niobium oxide (NbO) microparticles (Nbµ) or nanoparticles (Nbη) may improve radiopacity and bioactivity. The aim of this study was to evaluate the radiopacity and cytotoxicity of the materials: 1) PC; 2) White MTA; 3) PC+30% Nbµ; 4) PC+30% Nbη. Material and Methods For the radiopacity test, specimens of the different materials were radiographed along an aluminum step-wedge. For cell culture assays, Saos-2 osteoblastic-cells (ATCC HTB-85) were used. Cell viability was evaluated through MTT assay, and bioactivity was assessed by alkaline phosphatase activity assay. Results The results demonstrated higher radiopacity for MTA, followed by Nbµ and Nbη, which had similar values. Cell culture analysis showed that PC and PC+NbO associations promoted greater cell viability than MTA. Conclusions It was concluded that the combination of PC+NbO is a potential alternative for composition of MTA.

A Highly Sensitive Enzyme-Amplified Immunosensor Based on a Nanoporous Niobium Oxide (Nb2O5) Electrode

Lee, Chang-Soo; Kwon, Dohyoung; Yoo, Jeng Eun; Lee, Byung Gun; Choi, Jinsub; Chung, Bong Hyun
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 25/05/2010 EN
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We report on the development of an enzyme-amplified sandwich-type immunosensor based on a thin gold film sputtered on an anodic nanoporous niobium oxide (Au@Nb2O5) electrode. The electrocatalytic activity of enzymatically amplified electroactive species and a stable electrode consisting of Au@Nb2O5 were used to obtain a powerful signal amplification of the electrochemical immunobiosensor. The method using this electrochemical biosensor based on an Au@Nb2O5 electrode provides a much better performance than those based on conventional bulk gold or niobium oxide electrodes. Our novel approach does not require any time-consuming cleaning steps to yield reproducible electrochemical signals. In addition, the strong adhesion of gold films on the niobium oxide electrodes offers a very stable substrate during electrochemical biosensing. Cyclic voltammetry measurements indicate that non-specific binding of proteins to the modified Au@Nb2O5 surface is sufficiently low to be ignored in the case of our novel system. Finally, we demonstrated the ability of the biosensor based on an Au@Nb2O5 offering the enhanced performance with a high resolution and sensitivity. Therefore, it is expected that the biosensor based on an Au@Nb2O5 has great potential for highly efficient biological devices.

Síntese e caracterização de CuNb2O6 e CuNbC através de reação sólido- sólido e gás- sólido a baixa temperatura; Synthesis and characterization of CuNb2O6 and CuNbC through reaction solid-solid and gas-solid low temperature

Souto, Maria Veronilda Macedo
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Ciência e Engenharia de Materiais; Processamento de Materiais a partir do Pó; Polímeros e Compósitos; Processamento de Materiais a part Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Ciência e Engenharia de Materiais; Processamento de Materiais a partir do Pó; Polímeros e Compósitos; Processamento de Materiais a part
Tipo: Dissertação Formato: application/pdf
POR
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The refractory metal carbides have proven important in the development of engineering materials due to their properties such as high hardness, high melting point, high thermal conductivity and high chemical stability. The niobium carbide presents these characteristics. The compounds of niobium impregnated with copper also have excellent dielectric and magnetic properties, and furthermore, the Cu doping increases the catalytic activity in the oxidation processes of hydrogen. This study aimed to the synthesis of nanostructured materials CuNbC and niobium and copper oxide from precursor tris(oxalate) oxiniobate ammonium hydrate through gas-solid and solid-solid reaction, respectively. Both reactions were carried out at low temperature (1000°C) and short reaction time (2 hours). The niobium carbide was produced with 5 % and 11% of copper, and the niobium oxide with 5% of copper. The materials were characterized by X-Ray Diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), X-Ray Fluorescence Spectroscopy (XRF), infrared spectroscopy (IR), thermogravimetric (TG) and differential thermal analysis (DTA , BET and particle size Laser. From the XRD analysis and Rietveld refinement of CuNbC with S = 1.23, we observed the formation of niobium carbide and metallic copper with cubic structure. For the synthesis of mixed oxide made of niobium and copper...

Avaliação cinética e potencial do Nb2O5 obtido a partir de um complexo de nióbio para formação do oleato de metila através da reação de esterificação do ácido oleico; Evaluation of the kinetic and potential Nb2O5 obtained from a niobium complex to the formation of methyl oleate by esterification of oleic acid

Oliveira, Samuel Alves de
Fonte: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais Publicador: Universidade Federal do Rio Grande do Norte; BR; UFRN; Programa de Pós-Graduação em Engenharia Química; Pesquisa e Desenvolvimento de Tecnologias Regionais
Tipo: Dissertação Formato: application/pdf
POR
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Among the heterogeneous catalysts materials made from niobium show up as an alternative to meet the demand of catalysts for biodiesel production. This study aims to evaluate the potential of a heterogeneous catalyst derived from a complex of niobium in the reaction of methyl esterification of oleic acid. The catalyst was synthesized after calcination at different temperatures of a niobium complex ((NH4)3[NbO(C2O4)3].H2O) generating a niobium oxide nanostructure with a different commercial niobium oxide used to synthesize the complex. The commercial niobium oxide, the complex niobium and niobium catalyst were characterized by thermogravimetry (TG and DTA), surface area analysis (BET), scanning electron microscopy (SEM) and X-ray diffraction (XRD), showing the catalyst has researched morphological and crystallographic indicating a catalytic potential higher than that of commercial niobium oxide characteristics. Factorial with central composite design point, with three factors (calcination temperature, molar ratio of alcohol/oleic acid and mass percentage of catalyst) was performed. Noting that the optimal experimental point was given by the complex calcination temperature of 600°C, a molar ratio alcohol/oleic acid of 3.007/1 and the catalyst mass percentage of 7.998%...

Thermal, Structural and Crystallization Study of Niobium Potassium Phosphate Glasses

Lima,Clarissa Luiza Justino de; Pastena,Brenno; Nardi,Rachel Prado Russo Delorenzo; Gouvêa Junior,José Tadeu; Ferrari,Jefferson Luis; Cassanjes,Fábia Castro; Poirier,Gael
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
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New glass compositions were investigated in the binary system KPO3-Nb2O5. The glass forming domain was determined by melt-quenching of the starting nominal compositions and it has been experimentally observed that glass samples can be obtained between the molar compositions 95KPO3-5Nb2O5 and 50KPO3-50Nb2O5. Chemically stable compositions from 80KPO3-20Nb2O5 to 50KPO3-50Nb2O5 were characterized by DSC for determination of characteristic temperatures Tg, Tx, Tp and Tf. Glass transition temperatures strongly increase with Nb2O5content whereas thermal stability against devitrification progressively decreases. Thermal data were used to suggest a structural model in which NbOx polyhedra are inserted inside the phosphate chains of PO4 units. For higher Nb2O5 contents, NbOx units progressively link together to form amorphous NbOx clusters, responsible for the yellow color and lower thermal stability against devitrification. For the composition 50KPO3-50Nb2O5, it has been found that the first crystallization peak is related with precipitation of hexagonal Nb2O5 in the glass matrix whereas the high temperature exothermic peak is due to both phase transition of hexagonal niobium oxide to monoclinic niobium oxide and precipitation of niobium potassium phosphate K2Nb6P4O26.

Niobium oxides and niobates physical properties; Propriedades físicas de óxidos de nióbio e de niobatos

Nico, Cláudio Miguel Silva
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Tese de Doutorado
ENG
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Niobium oxides have been pointed as an alternative to tantalum in the production of solid electrolytic capacitors, with advantages regarding the dielectric constant, density and price. In this work, it is intended to create a new family of niobium oxides based capacitors, adapting the technology and production line currently used with tantalum. Despite the known potentialities of niobium oxides, and many types of niobates, in several technological applications, the understanding of these oxide systems is still noticeably insufficient. Hence, a careful bibliographic review is shown, which evidences the complexity of these materials, the difficulty in identifying of their different phases and polymorphs, as well as in the interpretation of their properties. In this context, several fundamental studies on niobium oxides are presented, namely structural, microstructural, optical and electrical characterizations, which allow not only to contribute in an important way for the general knowledge of the physical properties of these materials, but also to advance to a sustained development of the niobium oxides based solid electrolytic capacitors. Several processing parameters were studied, clearing the way towards the creation of a prototype. It was also decided to perform a preliminary study on the synthesis and characterization of other oxide systems based in niobium...

Electrochemical and electrocatalytic studies of toluidine blue immobilized on a silica gel surface coated with niobium oxide

Santos,Antonio S.; Pereira,Arnaldo C.; Kubota,Lauro T.
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2002 EN
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The electrochemical behavior of toluidine blue (TB) adsorbed on a silica surface modified with niobium oxide (SN) was investigated using a modified carbon paste electrode. The presence of SN gave the electrode high stability, avoiding the leaching out of the mediator from the electrode surface. The formal potential (E0') of the adsorbed TB was --113 mV vs. SCE, indicating a shift of almost 100 mV towards more positive potential values, compared to TB dissolved in aqueous solution or adsorbed on carbon paste. The stability and formal potential remained constant upon changing the solution pH in the range 5 to 8. In these solution pH values the electrocatalytic activity remained almost constant with a sensitivity of 1.2 10-4 A L mol-1 cm-2 and a K Mapp of 4.9 10-5 mol L-1. A linear response range for NADH concentration between 2.0 10-4 and 4.0 10-3 mol L-1 at pH 7.0, with a detection limit of 3.4 10-5 mol L-1 was observed for the sensor. A response time of 2 s and a precision of 1.0 %, expressed as relative standard deviation for 10 replicates, were observed for the sensor developed.

Ammonium complex of niobium as a precursor for the preparation of Nb2O5/Al2O3catalysts

Noronha, Fábio Bellot; Schmal, Martin; Mendes, Fabiana M. Teixeira; Perez, C. A. C.
Fonte: Instituto Nacional de Tecnologia Publicador: Instituto Nacional de Tecnologia
Tipo: Artigo de Revista Científica
EN
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CAtalysis today, 78 (1-4): 449-458 Fev 28, 2003.; Ammonium oxalate complex of niobium was investigated as an aqueous precursor for the preparation of x% Nb2O5/Al2O3 (x=5, 10, 20 and 30 wt.%) samples. Catalysts with the same Nb2O5 contents were also prepared from the traditional niobium oxalate/oxalic acid aqueous solution. The catalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), temperatureprogrammed reduction (TPR), infrared spectroscopy of chemisorbed pyridine and X-ray photoelectron spectroscopy (XPS). A comparison with the preparation method using the niobium oxalate salt was performed. The results showed that the niobium precursor influence the species growing leading to phases with different reducibility. The XPS revealed the presence of multilayers of niobium oxide on the Nb2O5/Al2O3 samples prepared by using niobium ammonium oxalate complex, while the ones obtained from niobium oxalate led to Nb2O5 particles islands. The addition of niobium oxide decreased the fraction of Lewis acid sites and increased the fraction of Brønsted acid sites, independent of the precursor salt. However, the creation of BAS was more pronounced on the Nb2O5/Al2O3 samples prepared from niobium oxalate.