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Search Results: 1 - 10 of 462014 matches for " Bibian A; "
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Modelo Matemático de la Nucleación Electroquímica con Ondas de Corriente Pulsante
Molina,Jarol E; Hoyos,Bibian A;
Información tecnológica , 2007, DOI: 10.4067/S0718-07642007000500005
Abstract: a mathematical model has been established for the description of concentration overpotential, nucleation rate and nucleus size formed on metallic substrates when four types of pulse current waveforms are used: rectangular, ramp-down, ramp-up and triangular. the mathematical model was developed considering that the species diffusion in the limit layer is the rate determining step of the process. the model predicts that when using wave current with the same current average and the same time of application, the ramp-down current produces the shortest transition time, with the highest rise of overpotential concentration, this drives to high nucleation rates with small nucleus size. for the case of current wave forms with the same pick and average current, the rectangular and ramp-down waves show practically the same transition time, with equivalent nucleation rate and deposit size.
Modelo Matemático de la Nucleación Electroquímica con Ondas de Corriente Pulsante Mathematical Model for the Electrochemical Nucleation with Pulse Current Waveforms
Jarol E Molina,Bibian A Hoyos
Información Tecnológica , 2007,
Abstract: Se presenta un modelo matemático para describir el sobrepotencial de concentración, la velocidad de nucleación y el tama o de núcleos formados sobre sustratos metálicos, cuando se emplean cuatro tipos de ondas de corriente pulsante: rectangular, rampa ascendente, rampa descendente y triangular. Para el desarrollo del modelo, se considera que la etapa que controla el proceso es la difusión de especies en la capa limite. El modelo predice que, cuando se emplean ondas con igual corriente promedio e igual tiempo de aplicación, la rampa descendente produce tiempos de transición más cortos, con mayor aumento en el sobrepotencial de concentración, lo que lleva a mayores velocidades de nucleación con tama os de núcleos más peque os. Para el caso de ondas con igual corriente pico y promedio, las ondas rectangular y descendente presentan prácticamente el mismo tiempo de transición, con velocidades de nucleación y tama o de los depósitos equivalentes. El modelo desarrollado, constituye una herramienta ágil y flexible para la determinación del tama o y la velocidad de formación de núcleos de electrodepositos y, puede ser extendida para estudiar otro tipo de ondas de corriente. A mathematical model has been established for the description of concentration overpotential, nucleation rate and nucleus size formed on metallic substrates when four types of pulse current waveforms are used: rectangular, ramp-down, ramp-up and triangular. The mathematical model was developed considering that the species diffusion in the limit layer is the rate determining step of the process. The model predicts that when using wave current with the same current average and the same time of application, the ramp-down current produces the shortest transition time, with the highest rise of overpotential concentration, this drives to high nucleation rates with small nucleus size. For the case of current wave forms with the same pick and average current, the rectangular and ramp-down waves show practically the same transition time, with equivalent nucleation rate and deposit size.
ánodos de Pt-Ru y Pt-Ir para Celdas de Combustible Alimentadas con Metano y Propano Directo
Hoyos,Bibian A; Restrepo,Ana I; Mesa,Carlos M;
Información tecnológica , 2007, DOI: 10.4067/S0718-07642007000400007
Abstract: in this paper, the effect of temperature in the performance of proton exchange membrane fuel cells feed with methane and propane, using oxygen as feed to the cathode, is presented. for the fuel oxidation in the anodes, five carbon supported catalysts were tested: pt, pt85/ru15, pt50/ru50, pt90/ir10, and pt50/ir50. carbon-supported pure platinum was used as catalysts in the cathode side. the performance of the fuel cells was evaluated by polarization curves obtained from the current-potential data. results indicate that methane oxidation is favoured at high temperatures on the pt90/ir10, pt50/ir50 and pt50/ru50 catalysts. at low temperatures the best catalysts were pt and pt85/ru15. the pt85/ru15 bimetallic mixture showed the best performance to carry out propane oxidation at 30 °c.
Electrodeposición de Níquel Duro con Ondas de Corriente Pulsante Triangulares
Hoyos,Bibian A; Martínez,Luisa F; Salazar,álvaro F;
Información tecnológica , 2007, DOI: 10.4067/S0718-07642007000400003
Abstract: in this paper it is studied the frequency and current density effect on hardness of nickel electroplating obtained by means of triangular and rectangular pulse current and their comparison with those obtained using direct current. hardness measurements were done following the astm e384 standards. morphologic qualitative description of deposits was done using a scanning electronic microcopy (sem) according with the astm e112, e3 and e93 standards. the experimental results showed that at 4 a/dm2 the hardness of deposits is affected by the current waveform, producing hardness in the order: ramp-down > rectangular > ramp-up. for the experimental conditions explored here, the highest value of hardness was obtained at t 20 a/dm2 and 60 hz. for this current waveform the hardness value diminishes when the duty cycle increases. the hardness increases up to 300% when using pulse current instead on direct current.
ánodos de Pt-Ru y Pt-Ir para Celdas de Combustible Alimentadas con Metano y Propano Directo Pt-Ru and Pt-Ir Anodes for Direct Methane and Propane Proton Exchange Membrane Fuel Cells
Bibian A Hoyos,Ana I Restrepo,Carlos M Mesa
Información Tecnológica , 2007,
Abstract: En este trabajo se evalúa el efecto de la temperatura en el desempe o de celdas de combustible de membrana de intercambio protónico alimentadas con metano y propano, utilizando oxígeno como alimentación en el cátodo. Para la oxidación de los combustibles en los ánodos, se probaron cinco catalizadores soportados en carbón: Pt, Pt85Ru15, Pt50Ru50, Pt90Ir10 y Pt50Ir50. Como catalizador en el cátodo se usó platino puro soportado en carbón. El desempe o de las celdas de combustible fue evaluado mediante curvas de polarización obtenidas a partir de los datos corriente-potencial. Los resultados indican que la oxidación de metano se ve favorecida a altas temperaturas sobre los catalizadores Pt90/Ir10, Pt50/Ir50 y Pt50/Ru50. A bajas temperaturas los mejores catalizadores resultaron ser Pt y Pt85/Ru15. La mezcla bimetálica Pt85/Ru15 fue la que presentó mejor desempe o para llevar a cabo la oxidación de propano a 30 °C. In this paper, the effect of temperature in the performance of proton exchange membrane fuel cells feed with methane and propane, using oxygen as feed to the cathode, is presented. For the fuel oxidation in the anodes, five carbon supported catalysts were tested: Pt, Pt85/Ru15, Pt50/Ru50, Pt90/Ir10, and Pt50/Ir50. Carbon-supported pure platinum was used as catalysts in the cathode side. The performance of the fuel cells was evaluated by polarization curves obtained from the current-potential data. Results indicate that methane oxidation is favoured at high temperatures on the Pt90/Ir10, Pt50/Ir50 and Pt50/Ru50 catalysts. At low temperatures the best catalysts were Pt and Pt85/Ru15. The Pt85/Ru15 bimetallic mixture showed the best performance to carry out propane oxidation at 30 °C.
Electrodeposición de Níquel Duro con Ondas de Corriente Pulsante Triangulares Electroplating of Hard Nickel With Triangular Pulse Current Waveforms
Bibian A Hoyos,Luisa F Martínez,álvaro F Salazar
Información Tecnológica , 2007,
Abstract: Se estudia el efecto de la frecuencia y la densidad de corriente sobre la dureza en electrodepósitos de níquel obtenidos mediante corrientes pulsantes triangulares y rectangulares y su comparación con los obtenidos empleando corriente directa. Las mediciones de dureza se realizaron según la norma ASTM E384. La descripción de la morfología de los depósitos se realizó mediante un microscopio de barrido electrónico (SEM) según las normas ASTM E112, E3 y E93. Los resultados experimentales muestran que a 4 A/dm2 la dureza de los depósitos está influida por la forma de onda, produciéndose durezas en el orden rampa descendente > rectangular > rampa ascendente. Para las condiciones exploradas, la mayor dureza se obtiene con onda rectangular a 20 A/dm2 y 60 Hz. Para ésta onda de corriente, la dureza disminuye al aumentar el ciclo de trabajo. La dureza tiene un aumento de hasta un 300% cuando se emplea corriente pulsante frente a los valores alcanzados con corriente directa. In this paper it is studied the frequency and current density effect on hardness of nickel electroplating obtained by means of triangular and rectangular pulse current and their comparison with those obtained using direct current. Hardness measurements were done following the ASTM E384 standards. Morphologic qualitative description of deposits was done using a Scanning Electronic Microcopy (SEM) according with the ASTM E112, E3 and E93 standards. The experimental results showed that at 4 A/dm2 the hardness of deposits is affected by the current waveform, producing hardness in the order: ramp-down > rectangular > ramp-up. For the experimental conditions explored here, the highest value of hardness was obtained at t 20 A/dm2 and 60 Hz. For this current waveform the hardness value diminishes when the duty cycle increases. The hardness increases up to 300% when using pulse current instead on direct current.
El Mecanismo de la Electro - oxidación de Metanol y Etanol una Revisión Bibliográfica
Bibian Hoyos
DYNA , 2002,
Abstract: Se presenta una revisión bibliográfica del estudio de electro-oxidación de metanol y etanol en ánodos para celdas de combustible. Se muestran las dificultades principales para la comparación cuantitativa de los diversos resultados publicados, con énfasis en el resumen del estado del arte en la determinación del área de electrodos porosos y se plantean los mecanismos de las reacciones de oxidación de metanol y etanol en metales del grupo del platino, anotando las discrepancias y consensos actuales sobre el tema. Se sugieren además nuevas direcciones de investigación para trabajos futuros
Morphological Comparison of Five Varieties of Colocasia esculenta (L.) Schott in Anambra State, Southeastern Nigeria  [PDF]
Chinelo A. Ezeabara, C. U. Okeke, J. E. Amadi, A. I. Izundu, Bibian O. Aziagba, P. T. Egboka, C. D. Udechukwu
American Journal of Plant Sciences (AJPS) , 2015, DOI: 10.4236/ajps.2015.618278
Abstract: Comparative morphological study of five varieties of Colocasia esculenta (L.) Schott present in Anambra State, Nigeria was carried out, in order to furnish plant taxonomists with information which could be of great help in delimitation of the varieties. Significant difference was established at p < 0.05. The result showed that adaxial surface of “kochuo” had a purplish dot on the centre, abaxial leaf surface had a conspicuous purplish colour at the point of attachment to the leaf, and the cormels had numerous striking vertical purple stripes on the surface. There was presence of foliaceous (leaf-like) appendages at the veins of the abaxial surface of the leaf of “ogeriobosi”. The leaf length ranged from 35.6 ± 7.70 cm (“kochuo”) to 49.9 ± 3.55 cm (“ogeriobosi”). Petiole length of “ogeriobosi” was the highest (63.3 ± 3.83 cm), whereas the least was Colocasia esculenta var. antiquorum (26.67 ± 2.20 cm). The corm length ranged from 4.10 ± 0.10 cm (Colocasia esculenta var. antiquorum) to 8.60 ± 0.35 cm (“ogeriobosi”), while the cormel length ranged from 3.70 ± 0.96 cm (Colocasia esculenta var. antiquorum) to 7.03 ± 0.36 cm (“ogeriobosi”). This work has revealed diagnostic and differential morphological characters, which could be useful for identification and description of varieties of C. esculenta. In addition, it provided additional information which might be helpful in resolving the on-going controversy in the taxonomy of Colocasia, which would, in turn, probably lead to possible delimitation of C. esculenta.
EFECTO DE LAS FORMAS DE ONDAS DE CORRIENTE PULSANTE EN LA ELECTRODEPOSITACIóN DE NANOCRISTALES
MOLINA,JAROL; HOYOS,BIBIAN;
DYNA , 2009,
Abstract: a mathematical model has been developed for describing the effect of pulse current wave forms on size and hardness of electroplated nanocrystals. the model relates in a direct form the typical wave variables (frequency, duty cycle and peak current) with harness of generated deposits by means of direct current and by four pulse current wave forms: rectangular, ramp up, ramp down and triangular. the results of the model were evaluated for duty cycles of 20 and 80%, with frequencies of 50 and 150 hz and peak currents of 4 and 8 ka/m2.the model predicts that small increases in the concentration overpotential drives to increase the nucleation rate significantly, diminishing the growth of the nanocrystals and generating a hardness increase. the increase of the duty cycle and the wave?s frequency produces a behavior increasingly close to that produced by direct current, with a diminution in the nanocrystals hardness. any modification in the waveform variables that increases the peak current produces higher hardness values.
MODELO PRIMITIVO MEJORADO PARA IONES HIDRATADOS CERCA DE UNA SUPERFICIE METáLICA: SIMULACIONES MONTE CARLO
CARMONA,JUAN; HOYOS,BIBIAN;
DYNA , 2010,
Abstract: the structure of the electrical double layer (edl) formed by solvated ions near a metal surface was studied by monte carlo simulations using an improved primitive model. the proposed model, which includes different radius and adsorption potentials for each solvating atmosphere, was applied to the interfacial system ni(111)-nicl2 (aqueous). model results show oscillations in the profiles of density and potential, and the separation and reversal of the charge in the edl. additionally, the model shows a prevalence effect of ions size over the asymmetric charge effect, producing a positive potential of zero charge (pzc) for the studied system, although the adsorption of the hydrating atmosphere of anions is more favorable than that of cations. these structural characteristics of the edl are very different from those found with simple primitive models, restricted or not.
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