Scielo RSS <![CDATA[Superficies y vacío]]> http://www.scielo.org.mx/rss.php?pid=1665-352120150004&lang=pt vol. 28 num. 4 lang. pt <![CDATA[SciELO Logo]]> http://www.scielo.org.mx/img/en/fbpelogp.gif http://www.scielo.org.mx <![CDATA[Desulfuración oxidativa de dibenzotiofenos con catalizadores de tungsteno soportados en Al <strong><sub>2</sub></strong> O <strong><sub>3</sub></strong> o Al <strong><sub>2</sub></strong> O <strong><sub>3</sub></strong> -TiO <strong><sub>2</sub></strong>]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212015000400102&lng=pt&nrm=iso&tlng=pt Resumen: Catalizadores de óxido de tungsteno soportados en Al2O3 o Al2O3-TiO2 fueron evaluados en la reacción de desulfuración oxidativa (ODS) de compuestos dibenzotiofénicos usando H2O2 como agente oxidante. Los catalizadores fueron preparados por impregnación incipiente de metatungstato de amonio con diferentes contenidos de tungsteno y se caracterizaron por difracción de rayos X (DRX), microscopía electrónica de barrido con análisis elemental de energía dispersiva de rayos X (SEM-EDX) y reducción a temperatura programada (TPR). Los resultados de actividad muestran que al agregar titania al soporte de alúmina la producción de sulfonas aumenta y que las especies de W parcialmente reducidas son más activas en la ODS que el WO3.<hr/>Abstract: Tungsten oxides based catalysts on alumina or mixed oxide alumina-titania were carried out in oxidative desulfurization (ODS) of dibenzothiophene compounds using H2O2 as oxidant agent. The catalysts were prepared by incipient impregnation method using different loading of tungsten and characterized by x-ray diffraction (XRD), scanning electronic microscopy (SEM-EDX) and temperature programmed reduction (TPR). The results show ODS activity was improved in catalysts containing titania and using W species partially reduced. <![CDATA[MWCNTs synthesis from butanol, diethyl ether, ethyl acetate and hexane by chemical vapor deposition with a stainless steel core as catalyst]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212015000400108&lng=pt&nrm=iso&tlng=pt Abstract: A stainless steel core catalyst with several green precursors, butanol, diethyl ether, ethyl acetate and hexane, were used to obtain multi-walled carbon nanotubes via chemical vapor deposition. Argon was used as carrier gas at 50-90 ml/min rates. Samples were synthetized at 680-850 ºC, according to the precursor used. The characterization techniques were scanning electronic microscopy, X-ray diffraction, energy dispersive, Fourier transformed infrared and Raman spectroscopy. The micrographs showed tangled carbon nanotubes formation with different diameters from 50-300 nm. Elemental analysis indicated carbon atomic percentages ranging from 93-99 %, 1.0-4.5 % iron and less than 1% of manganese, chrome and silicon. X-Ray diffraction demonstrated the characteristic carbon nanotubes peak (002) at 26°. G and D carbon nanotubes distinctive bands were confirmed by Raman spectra for all samples. <![CDATA[MWCNTs oxidation by thermal treatment with air conditions]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212015000400111&lng=pt&nrm=iso&tlng=pt Abstract: A functionalization process has to occur in order to employ carbon nanotubes, generally by using certain types of acids. Multiwalled carbon nanotubes synthetized from benzene and ferrocene were oxidized at different temperatures between 270-600 °C through thermal treatment at atmospheric conditions. Samples were characterized by SEM, EDS, XRD, FTIR and Raman. The weight loss is shown with fluctuations from 0-78% according to different temperature conditions. FTIR analysis demonstrated presence of carbonyl groups and decrease of CHx. <![CDATA[Synthesis by wet chemistry and characterization of LiNbO <strong><sub>3</sub></strong> nanoparticles]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212015000400115&lng=pt&nrm=iso&tlng=pt Abstract: Actually, lithium niobate (LiNbO3) has been used for optical wavelength conversion and ultrafast optical signal processing because of its outstanding rapid nonlinear optical response behavior, low switching power and broad conversion bandwidth. LiNbO3 nanoparticles, which belong to the ferroelectric oxide class, were synthesized by chemical reaction with wet chemistry. Their size distribution was centered around 200 nm. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to further investigate the quality of the obtained LiNbO3 powders. The present work shows that by employing this chemical method the correct stoichiometric phase was obtained. This was corroborated by XPS (X-Ray Photoelectron Spectroscopy) results. Also, the nanoparticles showed a defined crystallinity and uniform morphology. This way of obtaining nanoparticles is innovative because of its low cost and simple way to reproduce it. It is an important method of increasing the surface area, controlling the phase purity and reducing the particle size distribution. The samples were obtained under low temperature annealing at 500, 650 and 800 ºC. Those features can be controlled using variables such temperature, time of synthesis, and calcination. In previous works it was found that hydrothermal methods offer many advantages over conventional ceramic synthesis methods. <![CDATA[Crecimiento de Películas de TiO <strong><sub>2</sub></strong> por electrodeposición pulsada: Influencia de la frecuencia de los pulsos de voltaje]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212015000400119&lng=pt&nrm=iso&tlng=pt Resumen: Se prepararon películas de TiO2 usando la técnica de electrodeposición pulsada sobre sustratos de acero inoxidable, y se estudió el efecto de la frecuencia de los pulsos de voltaje sobre la cantidad de masa depositada y la morfología de las muestras obtenidas. A la celda electrolítica utilizada se le adicionó un sistema de agitación con un motor de vibraciones microsónicas, para la eliminación de burbujas de hidrógeno producidas durante el crecimiento. Los pulsos de voltaje fueron de -2500 mV en la zona catódica y -500 mV en la zona anódica; con una frecuencia en los pulsos en el rango de 0 a 1 Hz. Posterior al crecimiento de las películas, éstas fueron deshidratadas a 120 °C por 1 hora; y sometidas a un tratamiento térmico a 450 °C por 2 horas en argón. Las propiedades estructurales y morfológicas fueron estudiadas mediante Difracción de Rayos-X y Microscopia Electrónica de Barrido. Los resultados muestran que la agitación de la solución ayuda a mantener estable la corriente durante el crecimiento. Las películas presentaron una estructura amorfa después de la deshidratación, transformándose a cristalina después del tratamiento térmico; la cual corresponde al TiO2 en fase anatasa. La masa depositada y la morfología dependen de la frecuencia de los pulsos de voltaje aplicados durante el crecimiento.<hr/>Abstract: TiO2 films were grown by pulsed electrodeposition on stainless steel substrates, and they were studied the influence of the frequency of the voltage pulse on the amount of mass deposited and the morphology of the samples. The electrolytic cell was added with a system of agitation with a motor of micro sonic vibrations for the elimination of hydrogen bubbles produced during the growth. The voltage pulses were of - 2500 mV in the cathodic zone and -500 mV in the anodic zone; the frequency of the pulses was between 0 and 1 Hz. After their growth the films were dehydrated at 120°C by one hour; and annealed at 450 °C by 2 hours. The structural and morphologic properties were studied by means of X ray Diffraction and Scanning Electron Microscopy. The results show that the agitation of the solution helps stabilizing/maintaining the current during the growth. The films had an amorphous structure after the dehydration, acquiring the anatasa crystalline structure after thermal annealing. The deposited mass and the morphology depend on the frequency of the applied voltage pulses during the growth.