Navegando por Autor "Souto, Maria Veronilda Macedo"

Agora exibindo 1 - 6 de 6

Carbeto de tântalo nanoestruturado: produção e caracterização à baixa temperatura
(Associação Brasileira de Metalurgia, Materiais e Mineração, 2015) Lima, Maria José Santos; Souto, Maria Veronilda Macedo; Silva, Ariadne Souza; Gomes, Uílame Umbelino; Souza, Carlson Pereira de
O carbeto de Tântalo (TaC) é um material extremamente duro, apresentando elevada dureza, elevado ponto de fusão, elevada estabilidade química, boa resistência ao ataque químico e choque térmico e excelente resistência à oxidação e corrosão. Desta forma, este trabalho teve como objetivo a obtenção de TaC nanoestruturado a partir do precursor tris(oxalato)oxitantalato de amônio hidratado, através de reação gás-sólido a baixa temperatura (1000°C) e curto tempo de reação. Os materiais obtidos foram caracterizados através de difração de Raios-X (DRX), Refinamento Rietveld, Microscopia Eletrônica de Varredura (MEV), Espectroscopia de Infravermelho (espectroscopia IV), Termogravimétrica (TG). Através das analises de DRX e do refinamento Reitiveld para o TaC com S = 1,1584 observou-se a formação do carbeto de tântalo puro com estrutura cúbica e tamanho médio de cristalitos na ordem de 12,5 nanômetros
Obtaining and characterization of W-Cu composite powder produced by mixing and sintering of Ammonium Paratungstate (Apt) and copper nitrate
(ABM, ABC, ABPol, 2017-05-18) Lima, Maria José Santos; Silva, Fernando Erick Santos da; Souto, Maria Veronilda Macedo; Mashhadikarimi, Meysam; Silva, Ariadne Sousa; Gomes, Uílame Umbelino; Souza, Carlson Pereira de
The objective of this work is obtaining W-30 wt% Cu composite powder from ammonium paratungstate hydrated (APT) and hydrated copper nitrate and investigating the influence of some production process parameters of W- 30 wt% Cu in particles form which results in high sinterability and densification of W-30 wt% Cu composite. To achieve this objective, the powder was obtained by manually mixing the APT and copper nitrate and reducing under a hydrogen atmosphere at 800 °C and then compacting at 500 MPa and sintering in a tubular furnace at 1200 °C for 60 minutes. The obtained materials were characterized by XRD, SEM, EDS, particle size analysis, density and microhardness measurements. The composite powder showed a good homogenization of Cu in W with very fine and agglomerated particles and a mean crystallite size of 25.64 nm. SEM coupled with EDS with mapping analysis revealed a homogeneous distribution of Cu and W in the sintered sample. The composite had a relative density of 96.77% and a microhardness of 523.66 HV. Therefore the method of obtaining the composite powder is feasible to sinter W-30 wt% Cu powder due to a greater dispersion and homogenization of phases and the average particle size
On the synthesis of molybdenum carbide with cobalt addition via gas-solid reactions in a CH4/H2 atmosphere
(Brazilian Society of Chemical Engineering, 2016) Araujo, Camila Pacelly Brandão de; Souza, Carlson Pereira de; Maia, Lucas Mateus Dantas; Souto, Maria Veronilda Macedo; Barbosa, Cleonilson Mafra
Due to ever more severe environmental regulations regarding SOx, NOx and other pollutants' emissions, there has been an interest in developing new and improved catalysts for hydroprocessing reactions. Mo2C has been reported to display good selectivity and activity for those reactions, especially for HDS. Addition of another metal to the carbide structure may improve catalytic properties. Mo2C with low cobalt addition (2.5 and 5%) was obtained via gas-solid reaction in a fixed bed reactor with CH4 (5%)/H2 atmosphere. XRD and TG/DTA analysis of the precursors were carried out in order to understand its mass loss profile, doping metal presence and phase distributions. CoMoO4 as well as MoO3 were identified after calcining doped precursors at 600 °C/180min. SEM, XRD, XRF, TOC, BET and laser granulometric analysis of the reaction products were also performed. Compositions verified by XRF and theoretical values were compatible. At 700 °C both carbide (Mo2C) and oxide (MoO2) phases are present, as identified in XRD analysis and observed by SEM. At 750 °C only single phase Mo2C was verified by XRD, indicating Co dispersion on the carbide matrix. Morphology at this temperature is compatible with pure Mo2C, though XRF indicates Co presence on the material
Síntese e caracterização de CuNb2O6 e CuNbC através de reação sólido- sólido e gás- sólido a baixa temperatura
(Universidade Federal do Rio Grande do Norte, 2013-10-31) Souto, Maria Veronilda Macedo; Souza, Carlson Pereira de; ; http://buscatextual.cnpq.br/buscatextual/visualizacv.do?id=K4781094H3; ; http://lattes.cnpq.br/7937371965888298; Silva, Ariadne de Souza; ; http://lattes.cnpq.br/5623381698478389; Silva, Paulo Sérgio Gomes da; ; http://lattes.cnpq.br/9463069127508798; Gomes, Uilame Umbelino; ; http://lattes.cnpq.br/9858094266525225
Os carbetos de metais refratários têm se revelado importantes no desenvolvimento de materiais de engenharia devido as suas propriedades, tais como: alta dureza, alto ponto de fusão, alta condutividade térmica e alta estabilidade química. O carbeto de nióbio apresenta essas características. Os compostos de nióbio impregnados com cobre também possuem excelentes propriedades dielétricas e magnéticas e, além disso, a dopagem com Cu aumenta a atividade catalítica em processos de oxidação de hidrogênio. Este trabalho teve como objetivo a síntese dos materiais CuNbC e óxido de nióbio e cobre nanoestruturados a partir do precursor tris(oxalato)oxiniobato de amônio hidratado, através de reação gás-sólido e sólido-sólido, respectivamente. Para ambos, as reações foram realizadas a baixa temperatura (1000°C) e curto tempo de reação (2 horas). O carbeto de nióbio foi produzido com 5% e 11% de cobre e o óxido de nióbio e cobre com 5% de cobre. Os materiais obtidos foram caracterizados através dos ensaios de Difração de Raios X (DRX), Refinamento Rietveld, Microscopia Eletrônica de Varredura (MEV), Espectroscopia por Fluorescência de Raios-X (FRX), Espectroscopia de Infravermelho (IV), Termogravimétrica (TG), Análise Termodiferencial (DTA), BET e granulometria a Laser. A partir das análises de DRX e do refinamento Reitiveld para o CuNbC com S= 1,23, observou-se a formação do carbeto de nióbio e cobre puro com estrutura cúbica. Na síntese realizada do óxido misto de nióbio e cobre correu a formação de duas fases distintas: CuNb2O6 e Nb2O5, embora a última tenha sido formada em pequena quantidade
Synthesis and characterization of CuNb2O6 from an oxalic precursor via solid state reaction
(ABM, ABC, ABPol, 2016) Souto, Maria Veronilda Macedo; Lima, Maria José Santos; Barbosa, Cleonilson Mafra; Gomes, Uílame Umbelino; Souza, Carlson Pereira de; Araújo, Camila Pacelly Brandão de
The present paper's objective was to synthesize and characterize both the oxalic niobium precursor (NH4)3NbO(C2O4)3.H2O, and the product of its doping with Cu and calcining, CuNb2O6. In order to obtain the niobium precursor, commercially available niobium oxide (Nb2O5) was subject to fusion with potassium bisulfate (KHSO4). Once leached with water, the powder was complexed with oxalic acid and ammonium oxalate. The as produced material was manually mixed with copper nitrate Cu(NO3)2.2H2O (25% Cu molar) and calcined at 1000°C in a muffle furnace. CuNb2O6 was then obtained. The precursor was characterized by XRD, SEM, FT-IR, XRF, TG/DTG. The calcination product was characterized by XRD, XRF and SEM. Results show that single phase CuNb2O6 could be obtained by this method without Nb2O5 contamination
Synthesis and characterization of niobium carbide with copper addition obtained via gas solid reaction
(ABM, ABC, ABPol, 2018-02-26) Borges, Filipe Martel Magalhães; Souto, Maria Veronilda Macedo; Araujo, Camila Pacelly Brandão de; Lima, Maria José Santos; Gomes, Uilame Umbelino; Souza, Carlson Pereira de
The use of niobium containing materials' has gained much attention of the scientific community in the late years due its various applications in diverse fields. NbC is a highly versatile material. Copper addition may alter several of its properties, such as morphology, crystal structure etc. as well as enhance its catalytic behavior. Nanostructured NbC with copper addition synthesis' presented here had the precursor [(NH4 )3[NbO(C2O4)3]xH2O] as starting material, which was doped with Cu(NO3)2at 5% and 10% (molar) ratios. Doped NbC was obtained via gas solid reaction in fixed bed reactor at lower temperature (980°C) and with shorter reaction time (2h) than traditional methods. Reaction products' were characterized by XRD, crystal sizes were estimated according to HWL method, and SEM, XRF, BET and laser particle size analysis were performed. XRD indicated the formation of NbC and Cu phases with cubic crystal structure of ~20nm. SEM showed slight morphological change upon increasing copper content, indicating a less porous structure, which is consistent with BET data (43.7m2/g for 5%Cu-NbC and 37m 2/g for the 10% Cu-NbC). Crystal size calculations showed that increasing dopant content particle sizes were also increased, probably due to the presence of the dopant, in some extent, in the crystal structure

SIGAA

Navegando por Autor "Souto, Maria Veronilda Macedo"