A.C.F.M. Costa

Avaliação da microestrutura e das propriedades magnéticas de ferritas Ni-Zn dopadas com cobre

An evaluation was made of the microstructure and magnetic properties of Ni0.5-xCuxZn0,5Fe2O4 ferrites with x = 0.1, 0.2, 0.3 and 0.4 prepared by combustion reaction with particle sizes 23 to 29 nm. The resulting powders were uniaxially compacted at 385 MPa into pellets and sintered at 1000 oC/2 h. The samples were characterized by apparent density and porosity measurements, X-ray diffraction, scanning electron microscopy and M-H magnetic measurements. The X-ray diffraction revealed crystalline inverse spinel as the major phase in all the specimens and a small amount of hematite (a-Fe2O3) as the secondary phase in the x = 0.1 and 0.4 samples. An increase in the amount of copper caused a slight increase in grain size (0.65 to 0.68 µm), a decrease in the apparent porosity (33.7% to 6.6%) and a reduction in saturation magnetization from 69 to 54 emu/g.

Obtaining of Chitosan/ZNAL1,9EU0,05O4 Film for Application as Biomaterial

This work reports the development and characterization by SEM, XRD, FTIR, emission and excitation chisonan/ZnAl1.9Eu0.05O4 films with a mass proportion of 1:1. The powders were deagglomerated and passed 325 mesh screens and added to the diluted chitosan in 1% acetic acid. The materials were filtered and placed in petri dishes and placed in an oven at 60°C for solvent evaporation. After drying the film, a solution of 1M sodium hydroxide was added in order to obtain a film with neutral pH. With the XRD, it has been verified that the chitosan/ZnAl1.9Eu0.05O4 films presented the chitosan peaks and ZnAl2O4. Through the SEM, it has been observed that the chitosan/ZnAl1.9Eu0.05O4 presented a protruding surface. The results presented in emission and excitation spectra suggest that the film chitosan/ ZnAl1.9Eu0.05O4 exhibit good luminescence properties, and are promising to be applied as a luminescent marker in future applications in the field of biomaterials.

Síntese, por reação de combustão em forno de microondas, de nanoferritas de níquel dopadas com cromo

Chromium-doped nickel nanoferrite powder was prepared by combustion reaction, using microwave energy as the external heating source, and the influence of the Cr3+concentration on the NiCrxFe2-xO4 system was investigated. The powder, which was prepared according to the concept of propellant chemistry, was heated in a microwave oven under a power of 980 W. The resulting material was characterized by XRD, BET, SEM, helium picnometry and magnetic measurements. The results indicate that it was possible to obtain chromium-doped nickel ferrite nanopowders and that raising the chromium concentration caused an increase in particle size (from 15 nm to 55 nm), and a reduction in the magnetic parameters.

Preparação e caracterização de catalisadores ácidos de zircônia sulfatada para aplicação na esterificação do óleo de algodão

This work aimed to produce zirconia by combustion synthesis, to analyze the structure and morphology comparatively with a commercial monoclinic ZrO2, as well as, to investigate the sulfation, aiming to obtain acid catalysts for its use in the esterification of cotton oil for biodiesel. The samples were characterized by X-ray diffraction, scanning electron microscopy (SEM), specific surface area by BET method, infrared spectroscopy (FTIR), thermal analysis (TG/DrTG/DTA), granulometric distribution, pH and chromatography. The synthesized sample evidenced the formation of the monoclinic phase with traces of the orthorhombic phase, while in the commercial sample only the monoclinic phase was observed. In the sulfation process, traces of the tetragonal phase, typical of sulfated zirconia, were observed with the presence of the monoclinic phase in the two samples. With the impregnation of the sulfate ion on the surface of the samples, an increase in the particle size was observed, as seen in the characterization of BET, granulometric distribution and SEM, which also indicated a homogeneous morphology consisting of fine particles of approximately spherical shape for both samples. The chromatography indicated conversion of 65.5 and 91.8% in methyl esters to the synthesized and commercial SO4 2-/ZrO2, respectively. The results indicated that the sulfation increased the acidity, which was evidenced by the decrease in the pH, ranging from 5.12 to 2.65, which contributed significantly to the increase of the conversion, indicating that the SO4 2-/ZrO2 is a promising catalyst in the esterification.

Evaluation of Current in Composites PVAL/Ceramics for Detection of Leakage Current Generated in Electrical Insulators

This research aims to prepare composites of polyvinyl alcohol (PVAL) with ceramic nanoparticles loads (NPs) of Ti1.95Eu 0.05O2; ZnAl2O4 and Ni0.5Zn0.5Fe2O4 to evaluate the detection of leakage current generated in electrical insulator. The composites were prepared in the proportion of 6/1.5 g of the PVAL/ceramics and characterized by XRD, FTIR, SEM and measurements of the current as a function of applied voltage. The results show for the composites with Ti1.95Eu0.05O2 and ZnAl2O4 a homogeneous morphology, while the structure of the composite formed by Ni0.5Zn0.5Fe2O4 resulted in a heterogeneous and porous morphology. The determination of the current as a function of the applied voltage has shown that there is a dependence of morphology and the semiconductor characteristic of the load used and the best results are therefore assigned for the composite produced with the Ti1.95Eu0.05O2 load with homogeneous morphology and high current values as a function of the applied voltage.

Estudo do efeito da diluição nas propriedades microestruturais e magnéticas de ferritas Mn0,65Zn0,35Fe2O4 por reação de combustão

As ferritas Mn-Zn vem sendo utilizadas em diversas areas tecnologicas por apresentarem propriedades atrativas no âmbito tecnico-cientifico. Este trabalho teve como objetivo sintetizar ferritas Mn0,65Zn0,35Fe2O4 por reacao de combustao e avaliar o efeito da diluicao dos reagentes em agua destilada sobre as caracteristicas microestruturais e magneticas. As amostras foram caracterizadas por difracao de raios X, microscopia eletronica de varredura e transmissao, temperatura de Curie e por medidas magneticas. Foi observado que o aumento da diluicao em agua durante a sintese por reacao de combustao foi favoravel para obtencao da ferrita Mn0,65Zn0,35Fe2O4 monofasica. Tambem favoreceu a diminuicao do tamanho de aglomerado e aumento da temperatura de Curie com valor maximo de magnetizacao de saturacao de 62 emu/g para a amostra diluida na proporcao 1:10.

Avaliação catalítica dos espinélios ZnAl2O4 e ZnAl1,9Eu0,1O4 na transesterificação metílica do óleo de soja

Este estudo objetivou avaliar o efeito da dopagem de europio na estrutura e na morfologia do espinelio ZnAl1,9Eu0,1O4 e seu desempenho como catalisador na transesterificacao metilica do oleo de soja. Os pos do espinelio ZnAl1,9Eu0,1O4 foram sintetizados por meio da reacao de combustao e caracterizados por difracao de raios X (DRX), espectroscopia de absorcao optica na regiao do infravermelho com transformada de Fourier (FTIR), microscopia eletronica de varredura e analise termogravimetrica. As reacoes de transesterificacao foram conduzidas a 160 e 180 oC, razao molar oleo/alcool 1:15, 2% de catalisador e tempo de reacao 3 h. Os resultados das caracterizacoes por DRX e FTIR indicaram a fase espinelio do aluminato e duas bandas de absorcao entre 450 e 700 cm-1, caracteristicas da estrutura de espinelio. Os resultados das reacoes de transesterificacao mostraram que a dopagem de ZnAl2O4 com 0,1 mol de europio favoreceu um aumento na conversao catalitica de 15,8% para 68,7%, indicando que os ions europio tornam o catalisador mais ativo. Aumentando a temperatura da reacao de 120 para 180 oC promoveu um aumento consideravel na conversao catalitica de 18,4 para 68,7%, utilizando o catalisador dopado com europio. A conversao do catalisador reutilizado ZnAl1,9Eu0,1O4 mostrou uma reducao em cerca de 31% quando foi utilizado pela terceira vez.

Study of Nanoferrites Ni0,5Zn0,5Fe2O4 and Ni0,1Cu0,4Zn0,5Fe2O4 as Catalysts in the Methyl Transesterification of Soybean Oil

Research with emphasis on substitution of energy sources used in worldwide for renewable energy undoubtedly indicates that the use of biodiesel would be an option to increase the income in rural areas, reduction in oil derivatives spending and also new opportunities for job creation. Soon, in purpose to contribute with the research growth, this research proposes to evaluate the new catalysts performance as nanoferrites Ni0,5Zn0,5Fe2O4 (pure) and Ni0,1Cu0,4Zn0,5Fe2O4 (doped with 0.4 mol of Cu2+) in transesterification reactions of soybean oil methyl. For both samples were synthesized by chemical method in the stoichiometry of the combustion reaction, using urea as a fuel source and a resistance heating coil. During synthesis were measured time and combustion temperature. Later they were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), textural analysis (BET) and subjected to catalytic tests bench. The reaction conditions used in the transesterification were: 10 g of oil, 2 h reaction time, molar ratio of 1:20 oil and alcohol, 4% (w/w) of catalyst and reaction temperature of 160°C. Finally, the reaction product was characterized for conversion into methyl esters by gas chromatography. Results has shown only the presence of the inverse spinel phase, characteristic of Ni-Zn ferrite for both samples, with crystallite size of 26 and 29 nm, respectively. The thermogravimetric analysis has shown that samples are thermally stable, with a weight loss of 4.9 and 3.7%, respectively. The surface area and particle size were 48.89 m2g-1 and 23 nm, and 18.06 m2g-1 and 62 nm, respectively. The conversion results obtained by the transesterification reaction were 13 and 50% Ni0,5Zn0,5Fe2O4 and Ni0,1Cu0,4Zn0,5Fe2O4, respectively, indicating that sample with presence of copper was 26% more effectively, thus being one promising catalyst for the transesterification reaction, which aims to obtain biodiesel.

Synthesis, Characterization and Catalytic Performance of Nanoferrites Subjected to the Esterification Reaction

Ni0.5Zn0.5Fe2O4, Mn0.5Zn0.5Fe2O4 and Ni0.2Cu0.3Zn0.5Fe2O4 nanoferrites were synthesized, characterized and evaluated in terms of their performance as catalysts in the methyl esterification reaction of soybean oil. The nanoferrites were synthesized by combustion and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The XRD patterns show the presence of inverse spinel B(AB)2O4 phase. The EDX results confirmed the stoichiometry of the nanoferrite systems, whose morphology consisted of large block-like agglomerates with a brittle aspect and a wide agglomerate size distribution. The results indicate that the Ni0.5Zn0.5Fe2O4 nanoferrite was the most active catalyst in the esterification reaction, with conversion rates ranging from 40 to 91%.

Nanoferrites Ni-Zn Silanized with 3-Aminopropyltrimethoxysilane Using the Reflux Method

In this paper we propose nanoferrites Ni-Zn silanization with 3-aminopropyltrimethoxysilane using the method of reflux and evaluate the effect of silanization on the structure, morphology and magnetism of the magnetic nanoparticles aimed at biological applications. The samples as synthesized and after silanization were characterized by XRD, FTIR, SEM and testing magnetic attraction. The results indicated a single phase inverse spinel Ni-Zn ferrite, high intensity of diffraction peaks and a high basal width of all reflections observed, indicating that the samples are crystalline, and formation of nanoparticles. Morphologically, for nanoferrites Ni-Zn synthesized observed formation of large agglomerates in the form of spongy blocks of frail and after silanization was observed with respect dense pellets, indicating that most particles were rigidly connected by the presence of the agent silane. The characteristic bands of the spinel were observed for the Ni-Zn nanoferrites before and after silanization, and also observed the characteristic bands of silane in confirming the ferrites silanized functionalization of ferrites with the silane agent. Nanoparticles ferrite as synthesized and after silanized were strongly attracted by the presence of a magnet, immediately after the presence thereof indicating that the silane is effective is not interfere with the magnetic particles, maintaining the same magnetic behavior.