Navegando por Palavras-chave "Niobium"
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- ItemSomente MetadadadosAcetalization of acetone with glycerol catalyzed by niobium-aluminum mixed oxides synthesized by a sol-gel process(Elsevier Science Bv, 2016) Rodrigues, Raphael; Mandelli, Dalmo; Goncalves, Norberto Sanches [UNIFESP]; Pescarmona, Paolo P.; Carvalho, Wagner A.Niobium-aluminum-based catalysts were synthesized by a sol-gel process and successfully applied to the reaction of acetalization of acetone with glycerol yielding 2,2-dimethyl-1,3-dioxolane-4-methanol (solketal) and 2,2-dimethyl-1,3-dioxan-5-ol. The synthesis procedure was developed using high throughput techniques and the materials prepared with molar ratio1 Metal (1Nb:xAl): 100H(2)O: 1.5NH(4)OH (in which x =1, 0.6, 0.3, 0.1 and 0.05) were selected to be further investigated. The obtained series of mixed oxides displayed high catalytic activity reaching glycerol conversion up to 84%, with 98% of selectivity towards solketal. The physicochemical properties of the investigated catalysts were characterized by N-2-adorption/desorption, thermal analysis, X-rays diffraction, FTIR and Raman spectroscopy, and by adsorption of pyridine monitored by FT-IR spectroscopy and TGA. The catalysts are truly heterogeneous and can be reused in consecutive runs without loss of activity. (C) 2016 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosEvaluation of the resistance to oxidation of niobium treated by high temperature nitrogen Plasma Based Ion Implantation(Elsevier Science Sa, 2017) Oliveira, Rogerio M.; Hoshida, Lilian; Oliveira, Aline C. [UNIFESP]; Silva, Matheus M. N. F.; Pichon, Luc; Santos, Nazir M.Niobium is a technological material used in very distinct applications. Most of them as an alloying element, making part of superconducting radio frequency cavities, nuclear reactor components, missiles, rockets, aviation and space-system engineering. Nevertheless, although refractory, pure niobium presents as the main drawback the poor oxidation resistance in moderate and high temperatures. Different treatment methods have been used to mitigate this issue, as is the case of cementation, conventional nitridation, CVD and PVD processes. The evaluation of the resistance to oxidation of Nb treated by high temperature nitrogen plasma based ion implantation (HTPBII) has been described herein. The implanted nitrogen in this case easily diffuses to inner layers of niobium heated up to 1250 C-o during treatment, reaching depths of about 7 pm, while its atomic concentration of about 25% remains stable for almost the whole treated surface. This allows the formation of thick nitride layers. The produced interstitial nitrides have outstanding properties as the high hardness and strength, like ceramics, and high thermal and electrical conductivities, like metals. In addition, these refractory nitrides also present good chemical resistance and superior resistance against oxidation. The investigation performed herein includes a series of characterization performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), glow discharge optical emission spectroscopy (GDOES), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The oxidation of the ion-implanted niobium was retarded in comparison with the untreated counterpart in about 130 C-o. Isothermal analysis revealed reduced oxidation rate when treatment time was extended from 4 h to 8 h. (C) 2016 Elsevier B.V. All rights reserved.
- ItemSomente MetadadadosInvestigação Do Efeito Do Nióbio Em Aços De Médio Carbono Para Fabricação De Rodas Ferroviárias Forjadas(Universidade Federal de São Paulo (UNIFESP), 2017-02-22) Zucarelli, Tiago Alegretti [UNIFESP]; Reis, Danieli Aparecida Pereira [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)This research aims to study the effect of niobium in railway wheels materials, demonstrating the metallurgical mechanism of improvement in the mechanical properties. The primary motivation for this study is the application of niobium as an industrial component, once the world’s largest mine of it is located in Brazil. The use of this element is very low due to the scarcity of studies, and the international research if focused on similar element such as vanadium and titanium which are found in many countries. There are a lot of studies about the use of niobium in association with other elements (e.g. silicon, chrome, and molybdenum) and especial heat treatment parameters to lead to more desirable mechanical properties. However, there are few studies about the effect of isolated niobium and the mechanical and metallurgical mechanisms. In the present work, were forged two railway wheels (P-33 American design) according to AAR M-107. One wheel was manufactured using the class C traditional material and the second wheel was made using the same base (class C) but with micro-addition of niobium (0.0175% Nb – percentage per weight). The micro-addition of niobium is allowed by manufacturing standards. The mechanical tests were according to European standard EN 13262 (test, location of the samples ad number of test). The results are extremely significant, with an increase of 57% in ductility, increase of 13% in toughness fracture and better performance regarding high cycle fatigue.These properties are linked to safety. It was not observed a significant reduction in material strength (yield strength -4%), what is normally expected with the increase of ductility and toughness fracture. About the hardness, it was demonstrated a little increase in the heat treatment area. After the mechanical tests, it was started the investigation to study the metallurgical mechanism by TEM/SEM. Based on the mechanical results and the metallurgical characteristics, it was possible to determine that benefits of micro addition of niobium in railway wheels improve the safety properties without reducing the mechanical strength.
- ItemAcesso aberto (Open Access)Remoção de fenol proveniente do óleo cru em água de mar por fotocatálise heterogênea utilizando catalisador de NiNb e Pt(Universidade Federal de São Paulo, 2022-06-13) Costa, Kimberly Gomes da [UNIFESP]; Asencios, Yvan Jesus Olortiga [UNIFESP]; http://lattes.cnpq.br/3495814590644361; Universidade Federal de São Paulo (UNIFESP)Durante o refino de petróleo é gerada a água produzida, que se define como a água associada ao óleo cru, e tem uma complexa composição química, contendo hidrocarbonetos aromáticos, óleos e graxas, sais, metais e gases dissolvidos. Sua presença é abundante, inevitável e seu tratamento é um desafio. Objetivo: O presente trabalho visa a síntese, caracterização do catalisador denominado NiNb com Platina depositada e a estudar sua aplicação na Fotocatálise heterogênea para degradar o fenol em água de mar. Métodos: O material foi sintetizado a partir do oxalato amoniacal de nióbio na presença de nitrato de níquel hexahidratado, resultando na heteroestrutura de Niobato de Sódio (NaNbO3/ NaNb3O8) e Óxido de Nível (NiO), com Platina depositada (Pt). O catalisador foi caracterizado por Difração de raios-X (DRX), Espectroscopia de Refletância Difusa (DRS), Microscopia Eletrônica de Varredura (MEV), Fluorescência de Raios X por Reflexão Total (TXRF), Espectroscopia de raios x por dispersão de energia (EDX) e Área superfícial BET (SBET). Foi testada a atividade fotocatalítica na degradação de um efluente fenólico modelo, de alta salinidade, similar às condições encontradas na água produzida do petróleo, na presença e na ausência de luz UV-C (germicida, de 254 nm), nos ensaios de remoção de fenol, alguns parâmetros como: dosagem de platina, pH da solução inicial e tempo de exposição à radiação foram analisados. Verificou-se também a reutilização do catalisador e o mecanismo fotocatalítico foi investigado por testes com agentes oxidantes. Resultados: As caracterizações do material confirmam a formação da heteroestrutura, resultando em material com características similares a outros materiais usualmente empregados em Fotocatálise, apresentando energia de band gap igual a 3,0 eV. Os resultados dos estudos fotocatalíticos, demonstraram que o catalisador NiNb/Pt, atingiu um desempenho melhor em água do mar, cerca de 65% de remoção de fenol e 57% em água destilada, em 5h de reação, ambos na presença de luz UV-C, comprovando que a alta salinidade e os derivados fenólicos formados, não comprometeram a atividade fotocatalítica. O catalisador foi empregado diferentes pH, porém a partir do pH 10 seu desempenho é afetado. Os estudos com espécies oxidantes demostraram que os radicais superóxido aniônicos (O2●−) e radicais hidroxila •OH têm mais influência na degradação do fenol, podendo assim verificar o mecanismo reacional. Conclusão: O catalisador proposto apresentou resultados adequados para o tratamento de águas com alta salinidade contaminadas com fenol, apesar do catalisador NiNb não ser por si só tão eficaz no processo de remoção, e ser necessária a adição de pequenas quantidades de platina, a reutilização do material sem adição de mais platina torna sua aplicação viável.
- ItemSomente MetadadadosSíntese E Caracterização De Cimentos De "-Tcp Aditivados Com Vidros Bioativos(Universidade Federal de São Paulo (UNIFESP), 2018-12-04) Silva, Luciana Pereira Da [UNIFESP]; Motisuke, Mariana [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)Regenerative Medicine Is Becoming An Emerging Field Due To Population Aging In The Last Decades. Therefore, It Is Possible To Visualize Its Impacts On The Development Of New Treatments For Patients With Orthopedic And Dental Diseases. Calcium Phosphate Cements (Cpc), Besides Of Being Resorbable, Is Also Injectable And Can Be Molded Into Any Form, Which Ensures Complete Filling Of Bone Defects Cavities, Reducing The Number Of Surgical Interventions Or Even Eliminating Their Need. Several Studies Have Shown That The Incorporation Of Other Additives Into Cfcs May Lead To Changes On Their Properties. Bioactive Glasses (Bgs) Have Been Extensively Investigated For Bone Repair. The Dissolution Of The Silicate Network Together With The Formation Of A Silica Gel Rich Layer Would Be The Path For The Formation Of An Apatite Layer On Bg"S Surface. There Are Few Studies On The Incorporation Of Bgs Into Cpcs Where The Introduction Of Bgs Was Aimed To Increase The Materials Bioactivity And Osteogenic Potential. Nevertheless