Improvement in varistor properties of CaCu3Ti4O12 ceramics by chromium addition

The effect of chromium addition on the structure and electrical properties of CaCu3Ti4O12 is studied. Compositions based on the formula CaCu3Ti4-xCrxO12-δ (x = 0, 0.025, 0.050 and 0.075 mol%) are prepared by solid-state reaction. Pellets sintered at 1070 °C for 12 h are characterised by X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and impedance spectroscopy. Current density-electric field, dielectric loss and permittivity measurements are also carried out. Rietveld refinement showed the substitution of Cr(III) on the Ti(IV) site, with the maximum substitution for x = 0.025 mol%. The generation of electrical defects in the grain boundary region by chromium doping is responsible for increasing the electric breakdown field strength and nonlinearity coefficient at room temperature from 1723 V/cm and 5.29 for x = 0 mol% to 3431 V/cm and 8.16 for x = 0.025 mol%. This composition shows the greatest improvement in ceramic varistor parameters

Application of Zinc Oxide Nanospheres for Hybrid Solar Cell

Poly(3-alkylthiophenes), P3AT, are organic polymers formed by conjugate structures with conductive properties. Zinc oxide (ZnO) has been used as an electron acceptor in hybrid solar cells because it offers electron transport properties and can be synthesized by methods in which the variation of synthesis parameters allows morphological control. Different ZnO morphologies allow for distinct properties in terms of electronic transport at the interface of solar cells. ZnO particles were synthesized by the co-precipitation method. ZnO films were deposited by spin-coating in Fluorine Tin Oxide (FTO) and then immersed in solutions containing poly (3-hexylthiophene) (P3HT) or poly (3-octylthiophene) (P3OT) polymers. The cell was assembled in the form of a sandwich consisting of: FTO/ZnO,P3AT/Iˉ,I3ˉ/Pt/FTO. UV-vis measurements were performed for bandgap calculation, scanning electron microscopy (SEM), X-ray diffraction (XRD), and J-V curves. The ZnO/P3HT cell presented the best values of J, V and η, indicating an improvement in the electronic transfer processes, with a value of η = 0.56%. DOI: http://dx.doi.org/10.17807/orbital.v13i2.145

Optimisation of the alcoholic fermentation of aqueous jerivá pulp extract

The objective of this research is to determinate the optimum conditions for the alcoholic fermentation process of aqueous jerivá pulp extract using the response surface methodology and simplex optimisation technique. The incomplete factorial design 3³ was applied with the yeast extract, NH4H2PO4 and yeast as the independent variables and the alcohol production yield as the response. The regression analysis indicated that the model is predictive, and the simplex optimisation generated a formulation containing 0.35 g L-1 yeast extract, 6.33 g L-1 yeast and 0.30 g L-1NH4H2PO4 for an optimum yield of 85.40% ethanol. To validate the predictive equation, the experiment was carried out in triplicate under optimum conditions, and an average yield of 87.15% was obtained. According to a t-test, no significant difference was observed (on the order of 5%) between the average value obtained and the value indicated by the simplex optimisation technique.The objective of this research is to determinate the optimum conditions for the alcoholic fermentation process of aqueous jerivá pulp extract using the response surface methodology and simplex optimisation technique. The incomplete factorial design 3³ was applied with the yeast extract, NH4H2PO4 and yeast as the independent variables and the alcohol production yield as the response. The regression analysis indicated that the model is predictive, and the simplex optimisation generated a formulation containing 0.35 g L-1 yeast extract, 6.33 g L-1 yeast and 0.30 g L-1 NH4H2PO4 for an optimum yield of 85.40% ethanol. To validate the predictive equation, the experiment was carried out in triplicate under optimum conditions, and an average yield of 87.15% was obtained. According to a t-test, no significant difference was observed (on the order of 5%) between the average value obtained and the value indicated by the simplex optimisation technique.

Amylase potential of filamentous fungi isolated from sweet potato pulp

Sweet potato is a rustic culture, widely adapted and with a high starch content, thus having innumerable aptitudes. For the transformation of sweet potatoes into biofuel, some processes are necessary. The success of ethanol production from sweet potatoes depends on the transformation of starch into fermentable sugars. The most used conversion process is enzymatic hydrolysis, which uses commercially available enzymes. However, this process can be carried out through enzymes secreted by filamentous fungi. In this work, filamentous fungi that naturally colonized sweet potatoes were studied. These were isolated, tested for enzymatic activity, and identified by microculture. Fifty-one fungi from the pulp of sweet potatoes Beauregard and BRS-Amélia were isolated, 27 of them showed the ability to hydrolyze starch. Out of these, six showed an enzyme index ≥ 2.0 and were identified as Aspergillus sp. and Penicillium sp. This fact indicates the potential of these fungi in the production of amylase, an important enzyme for ethanol production

CARACTERIZAÇÃO DE LIPÍDIOS DE SEMENTES DE CANOLA NA REGIÃO DOS CAMPOS GERAIS, PARANÁ

Uma grande variedade de oleaginosas pode ser utilizada como matéria prima na produção de biodiesel, como soja, algodão e canola entre outras. A Canola (Brassica napus) é uma espécie de oleaginosa que apresenta alto teor de lipídios, sendo largamente utilizada para esse fim em alguns países da Europa. Este trabalho teve como objetivo caracterizar os lipídios de sementes de canola cultivada em Tibagi, região dos Campos Gerais, visando uso na produção de biodiesel. Foram utilizadas sementes colhidas em lavoura comercial da safra de inverno de 2013. O sistema de extração de óleo utilizado foi extração contínua por solvente.  As propriedades dos lipídios obtidos foram determinadas com relação à massa relativa de lipídios, massa específica e  estabilidade  oxidativa,  que  tiveram  média  de  370,4 g kg-1, 873 kg m-³, e 10,01 horas, respectivamente. A composição qualitativa de ácidos graxos foi avaliada pela Espectroscopia de Ressonância Magnética Nuclear de 1H. Pelas análises foi constatada a presença de ácidos Oleico (C18:1), Linoléico (C18:2) e Linolênico (C18:3)

AVALIAÇÃO DA DECOMPOSIÇÃO TÉRMICA DE ESPÉCIES DE BAMBU POR TERMOGRAVIMETRIA

Rafaela Faber de Campos[1]Pedro Henrique Weirich Neto[2]Sandra Regina Masetto Antunes3Maria Elena Payret Arrúa4 RESUMOA biomassa sempre foi uma das fontes de energia mais utilizadas pelo homem, e como consequência, principalmente, dos problemas enfrentados pelo uso de combustíveis fosseis assume, novamente, grande importância.  Vários tipos de biomassa podem ser citados, como por exemplo, a madeira de árvores, entretanto nem sempre é a mais adequada para geração de energia. O bambu entre outras plantas apresenta estrutura ímpar e, se destaca pela produtividade, podendo-se tornar uma alternativa sustentável para a geração de energia. Neste trabalho foi investigada a estabilidade térmica, consequentemente, a degradação térmica de quatro espécies de bambu in natura e na forma de carvão utilizando a termogravimetria (TGA).  As espécies avaliadas foram Phyllostachys aurea A. C. Rivière (bambu dourado), Chusquea gracilis McClure & Smith (criciúma), Chusquea mimosa McClure & Smith (caratuva) e Merostachys multiramea Hackel (taquara lixa), presentes no centro-sul do estado do Paraná - Brasil. A análise dos resultados de termogravimetria indica que a decomposição destas espécies de bambu ocorre em 3 etapas. Estas etapas são associadas a perda de umidade (primeira), decomposição da hemicelulose e celulose (segunda) e decomposição da lignina (terceira). As espécies se diferenciam na temperatura de velocidade máxima de decomposição devido, provavelmente, às suas distintas composições.    

Effect of Pr6O11 doping in electrical and microstructural properties of SnO2-based varistors

The influence of the dopant Pr6O11 was investigated with regard to the electrical and microstructural properties of the system (98.95-x)%SnO2.1.0%CoO.0.05%Ta2O5.x%Pr6O11, where x = 0.05%, 0.10%, 0.30% and 0.50% in mol. Pr6O11 doping modifies the electrical behavior of the ceramics. The electrical parameters were: α = 8.0, EB = 319 V cm-1 and Vb = 0.66 V barrier-1 for the system without Pr6O11 and α = 17.0, EB = 853 V cm-1 and Vb = 1.15 V barrier-1 with the addition of 0.10% in mol Pr6O11. The system with 0.05% in mol Pr6O11 had the same non-linearity coefficient α as the system with 0.10% in mol. However, breakdown electrical field and voltage per barrier rates were lower (EB = 708 V cm-1 and Vb = 0.98 V barrier-1). The low rates in the breakdown electrical field enabled the varistor systems under study to be used in protection systems for low-voltage energy grids. In the case of Pr6O11 concentrations above 0.10% in mol, the presence of the dopant became deleterious to the varistor’s electrical characteristics. This effect was due to an increase in praseodymium stannate (Pr2Sn2O7) secondary phase. The crystalline phase coupled to the cassiterite (SnO2) phase was found with XRD and SEM/EDS and quantified by Rietveld’s refining method.