Structural refinement, optical and electrical properties of [Ba1-x Sm-2x/3](Zr0.05Ti0.95)O-3 ceramics

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effect of calcium on the structural properties of Ba(1-x)Ca (x) TiO3 particles synthesized by complex polymerization method

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effect of Eu substitution on the crystallographic and magnetic properties of the BiMn2O5 oxide obtained by urea combustion

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

Lead-free BaBi4Ti4O15 ceramics: Effect of synthesis methods on phase formation and electrical properties

The processing of ferroelectric BaBi4Ti4O15 (BBT) ceramics from powders prepared by conventional solid state reaction (SSR) and mechanochemical activation (MA) has been investigated. It was shown that MA synthesis reduces the synthesis temperature of BBT powders, leading to smaller particles with reduced anisotropy and consequently to smaller grain size of ceramics. Dielectric properties were investigated in a wide range of temperatures (20-800 degrees C) and frequencies (1.21 kHz to 1 MHz). The relative dielectric permittivity at Curie temperature was higher for solid state obtained ceramics than for the mechanically treated ones. The conductivity of sintered samples was studied, suggesting decreasing of conductivity of BBT-MA in comparison with BBT-SS ceramics. The influence of the grain and the grain boundaries contribution to the dielectric behavior in both ceramics was analyzed through impedance spectroscopy. A well-defined ferroelectric hysteresis loop was obtained for both samples. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Aplicabilidade das equações isotermas de Freundlich e Langmuir na interação biossortiva de corantes têxteis com Saccharomyces cerevisiae liofilizada

This paper presents a study of the applicability of adsorption isotherms, known as Langmuir and Freundlich isotherm, between the biosorptive interaction of yeast lyophilized Saccharomyces cerevisiae and textile dyes. To that end, we prepared stock solutions of the textile dyes Direct Red 23 and Direct Red 75 in the concentration of 1.000μg/mL and a yeast suspension at 2,5%. We did experiments for two cases, firstly for the case that we have a fix concentration of yeast at 0,500mg/mL and an variable concentration of dye range from40, 50, 60, 80 and 100μg/mL, then for the case that we fixed the concentration of dye at 100μg/mL and the yeast concentration was variable range from 0,250, 0,500, 0,750, 1,000, 1,250mg/mL. For the dye Direct Red 23 we did analysis in the pH 2,5, 4,5 and 6,5; for the Direct Red 75, we just did for the pH 2,5. We leave the dye solution in contact with the yeast for 2 hours at a constant temperature of 30°C and then centrifuged and analyzed the sample in a spectrophotometer and finally made and analysis of parameters for the removal and study of the isotherms. After the biosorption, was observed that for the Direct Red 23 in the pH 2,5 was needed 1,407mg/mL of yeast for total removal, while for the pH 4,5 was needed 8,806mg/mL and in pH 6,5 was 9,286mg/mL; for the Direct Red 75 in pH 2,5 was needed 1,337mg/mL. This difference can be explain by the adsorption isotherms, was observed that in the case when the yeast was fix when we had in a acid pH the behavior of the system was compatible with the Langmuir isotherm, and thus, an monolayer pattern. And that when we decrease the acidity of the medium the system became more compatible with a Freundlich isotherm, and thus, a multilayer pattern; for the case that the yeast was variable this is not much evident, however for the pH 2,5 she became compatible with a Langmuir isotherm... (Complete abstract click electronic access below)

Effects of the addition of ions barium on the structural and electrical properties of PZT ceramic

Lead zirconate titanate, with Zr/Ti ratio of 53/47 was prepared by the polymeric precursor method. It was investigated the barium (II) modification at 0.0, 0.2, 0.4 and 0.6 mol% in substitution to the lead (II) cation in A site of perovskite structure. The powder samples were characterized by XRD and the diffraction patterns were used to Rietveld refinement. The percentages of tetragonal and rhombohedral phases and a systematic study of the effect of barium (II) on the morphology and the dielectric properties of PZT were carried out. The results showed that the tetragonal phase is favored and the ceramic density is improved with the barium (II) insertion. The Curie temperature (Tc) is increased besides the slight reduction of dielectric constant (Kc).

Adsorção de antibióticos em meio aquoso utilizando diferentes adsorventes

Pós-graduação em Ciência dos Materiais - FEIS

The role of oxygen vacancies and their location in the magnetic properties of Ce1-xCuxO2-delta nanorods

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Adsorção de cádmio em Latossolos sob vegetação de mata nativa e cultivados

Heavy metals are found naturally in soils at low concentrations, but their content may be increased by human activity, making them one of the barriers in management of tropical soils. These chemical elements can be found in the composition of organic and inorganic fertilizers, insecticides, fungicides, mine tailings, and urban waste, and may cause serious damage to the environment and human health. Thus, adsorption studies are essential in assessing the behavior of heavy metals in the soil. The objective of this study was to evaluate the influence of soil chemical, particle size, and mineralogical properties on adsorption of cadmium (Cd), evaluated by Langmuir and Freundlich models, in Latossolos (Oxisols) with or without human activity. Soil samples were collected from the surface layer, 0.00-0.20 m, and chemical, particle size, and mineralogical analyzes were performed. In the adsorption study, concentrations of 0, 5, 25, 50, 100, 200, 300, and 400 mu g L-1 of Cd were used in the form of Cd(NO3)(2). The empirical mathematical models of Langmuir and Freundlich were used for construction of adsorption isotherms. Data were analyzed by means of multivariate statistical techniques, Cluster Analysis and Principal Component Analysis. The data from the adsorption experiment showed a good fit to the Langmuir and Freundlich models. Soils with a lower goethite/hematite ratio and greater cation exchange capacity and pH, showed higher maximum adsorption capacity of Cd.

Utilização de turfa para remoção de metais potencialmente tóxicos de uma empresa recicladora de plásticos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Emprego de carvão ativado e resinas de troca ionica na remoção de substâncias orgânicas contaminantes do alcool etílico

This work had with objective to characterize and evaluate the performance of the combined system, involving activated charcoal and ionic exchange resins in the removal of substances organic contaminating of the ethyl alcohol from the fermentation of the cassava starch. To testing was used ethyl alcohol PA 96 oGL, conductivity of 0.90 μS/cm at 25 oC, acidity of 60 mg/L and Barbet test of 43 minutes at 15 oC. The contaminated alcohol was composed of ethyl alcohol additive of higher alcohols, organic acids, ester, diol, aldehydes, ketone and ether. Contaminated alcohol was added 2% activated charcoal and after the adsorption isotherm in ionic exchange resins was tested. The adsorption with activated charcoal was performed in a Water Bath at 30 oC for one hour and a half and shaking. Already adsorption ionic exchange columns occurred at room temperature on columns of 93,4 cm in filling height and diameter of 2.29 cm, for flows of 180 mL/min and 90 mL/min. Samples were collected in the tests with charcoal and with each one of the resins and the following analyses were performed: conductivity, acidity and Barbet test. The medium values for conductivity, acidity and Barbet test after the adsorption in charcoal and cation and anion resins were respectively: conductivity was 240; 354 and 465 μS/cm to 25 oC; acidity of 1.081; 1.103 and 1.062 mg/L and the Barbet test was 21; 20 and 9 minutes to 15 oC. It was observed that the addition of 2% of activated charcoal and the permanence in the columns of adsorption was not sufficient to remove the organic substances contaminating of the ethyl alcohol.

Estudo da utilização de serragem de madeira como adsorvente para o tratamento de efluentes têxteis

The Brazilian textile industry has been a highlight in the global economy. Connected with this high economic performance there is the water consumption and the generation of great volumes of wastewater which present high concentrations of dyes and chemical substances. One of the main techniques used in the treatment of textile effluents is adsorption, which has the activated carbon as the main adsorbent. Recently, studies have been developed to find alternative materials to activated carbon and exhibiting good adsorption capacity of dyes. The aim of this work is to study the potential of sawdust as adsorbent of low cost to remove the dye Direct Green 26. The results of this type of dye removal were obtained through the study of adsorption isotherms obtained by spectrophotometry in the UV-visible region analyzed by the Langmuir model. Finally, a comparison was made of these results with those of other adsorbents. Results showed that the average removal of dye, using sawdust, was 78.8% for an initial concentration of 500mg / L and the maximum adsorption capacity of 119mg / g. These results demonstrate the great potential of sawdust as an adsorbent for the dye Direct Green 26.

Aplicação de sílica mesoporosa modificada com moléculas contendo bases de Lewis na pré-concentração de Cd(II) em amostras aquosas

Em razão ao uso intensivo e por ser altamente não-degradável, o metal Cd (II) tem causado uma grande preocupação na sociedade moderna devido a sua capacidade de acumular-se em matrizes ambientais manifestando toxicidade. O projeto teve como objetivo o desenvolvimento da síntese da Sílica Mesoporosa para o ancoramento do ligante Ácido Rubeânico sobre a superfície do material. A caracterização do mesmo, por espectroscopia na região do infravermelho (FTIR), após a etapa de funcionalização indicou a presença de grupamento amina, com banda em 3350 cm-1, bandas na região de 2940 e 2850 cm-1 atribuídas a grupos metileno e a atenuação da banda C-Cl (700 cm-1), devido ao ancoramento da molécula do ligante. O material foi aplicado em experimentos de batelada e o efeito de tempo de contato e do pH sobre a adsorção de íons Cd (II) foi avaliado. O material apresentou cinética rápida, a qual foi alcançada em 1 minuto e a maior adsorção foi atingida em pH 6 (próximo ao ponto de carga zero) para ambos os metais. As condições ótimas obtidas foram aplicadas para a determinação da capacidade máxima de adsorção. Os dados obtidos da isoterma de adsorção foram aplicados à Equação Linearizada de Langmuir, fornecendo 0,03 mmol g-1, com o coeficiente de determinação dos dados sendo R² de 0,9961. Na segunda etapa, o material modificado foi aplicado em sistema de fluxo contínuo, ajustando as melhores condições como massa de amostra, tipos de eluente bem como o volume de eluato. Os resultados das concentrações do metal foram obtidos por determinação direta por espectrometria de absorção atômica

Influence of thermal parameters on the dendritic arm spacing and the microhardness of Al-5.5wt.%Sn alloy directionally solidified

As ligas Al-Sn são amplamente utilizados em aplicações tribológicas. Nesse estudo, análises térmica, microestrutural e dureza (HV) foram realizadas ao longo de um lingote da liga Al-5,5%Sn, obtido por solidificação direcional horizontal transitória. Os principais parâmetros analisados incluem a velocidade de deslocamento da isoterma liquidus (V_L) e a taxa de resfriamento (T_R). Esses parâmetros térmicos desempenham um papel fundamental na formação da microestrutura. A microestrutura dendrítica foi caracterizada através dos espaçamentos dentríticos primários (λ₁), os quais foram determinados, experimentalmente, e correlacionados com V_L, e T_R. O comportamento apresentado pela liga Al- 5,5% Sn, durante a solidificação,é semelhante ao de outras ligas de alumínio, isto é, observa-se rede dendrítica mais grosseira com a diminuição da taxa de resfriamento, indicando que a imiscibilidade entre o alumínio e estanho não tem um efeito significativo sobre o relação entre o espaçamento dendrítico primário e taxa de resfriamento. A dependência da microdureza em V_L, T_R e no λ₁ foi também analisada. Verificaram-se menores valores de HV para maiores T_R. Por outro lado, os valores HV aumentam com valores crescentes de λ₁.

Comportamento higroscópico de partes aéreas de pimenta-de-macaco (Piper aduncum L.)

Isotermas de dessorção de pimenta-de-macaco foram determinadas pelo método gravimétrico estático nas temperaturas de 35, 45 e 55 ºC, com umidade relativa variando de 5,5-81%. Três modelos matemáticos foram aplicados para analisar os dados experimentais. O modelo de GAB modificado apresentou o melhor ajuste aos dados experimentais. O calor isostérico e a entropia diferencial foram determinados pela aplicação das equações de Clausius-Clapeyron e Gibbs-Helmholtz, respectivamente. O calor isostérico e a entropia da isoterma de dessorção apresentaram comportamento similar. A teoria da compensação entalpia-entropia foi aplicada às isotermas indicando que o mecanismo de dessorção de umidade das partes aéreas de pimenta-de-macaco é controlado pela entalpia.