Scielo RSS <![CDATA[Superficies y vacío]]> http://www.scielo.org.mx/rss.php?pid=1665-352120110003&lang=es vol. 24 num. 3 lang. es <![CDATA[SciELO Logo]]> http://www.scielo.org.mx/img/en/fbpelogp.gif http://www.scielo.org.mx <![CDATA[<b>Caracterización estructural y óptica de compósitos ZnO-SiO<sub>x</sub> obtenidos por la técnica Cat-CVD</b>]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212011000300001&lng=es&nrm=iso&tlng=es Se obtuvieron compósitos de óxido de Zinc-óxido de Silicio fuera de estequiometría (ZnO-SiOx) por la técnica de depósito químico en fase vapor catalítico (Cat-CVD) a una temperatura de depósito de 950 0C. Los experimentos se llevaron a cabo en el rango de 800-1100 0C. Del análisis por difracción de rayos-X (XRD) y espectroscopia infrarroja por transformada de Fourier (FTIR), se encontró que a 800 0C se obtiene la fase de ZnO pura. Se observó que con el incremento de la temperatura de depósito, la estructura del material comienza a ser dominada por el SiOx hasta que solo se obtiene esta fase a 1100 0C. Sin embargo, se encontró que a 950 0C se obtiene el compósito de ZnO-SiOx. El cambio gradual de fase se asoció a la re-evaporación de Zinc (Zn) y al incremento en la movilidad superficial de los átomos de silicio (Si) al aumentar la temperatura. Los espectros de fotoluminiscencia (FL) muestran dos bandas de emisión: una desde 450 hasta 700 nm, y otra banda amplia de 600 a 1100 nm aproximadamente. Estas emisiones son relacionadas generalmente con transiciones radiativas debidas a la presencia de vacancias de oxígeno (Vo) en el ZnO y nanocristales de Si en el SiOx.<hr/>Zinc oxide- non-stoichiometric silicon dioxide (ZnO-SiOx) composites were obtained by catalytic chemical vapor deposition (Cat-CVD) technique at 950 0C. The experiments were carried out in the range of 800-1100 0C. From X-ray diffraction (XRD) and Fourier transformed infrared spectroscopy (FTIR) analyses, we found that pure ZnO phase is obtained at 800 0C. It was observed that increasing deposit temperature, the structure of deposited material is beginning to be dominated by SiOx until to 1100 0C, single amorphous SiOx phase is obtained. However, it was found an intermediate temperature (950 0C) to obtain ZnO-SiOx composite. The gradually phase shift was attributed to both zinc (Zn) re-evaporation, and increased surface mobility of silicon (Si) atoms. Photoluminescence (PL) spectra showed two emission bands: one from 450 until 700 nm, and the other, a broad band from 600 to 1100 nm approximately. These emissions are generally related with oxygen vacancies (Vo) in ZnO and Si nanocrystals in SiOx. <![CDATA[<b>Temperature distribution in a <i>p-n</i> thermoelectric module</b>: <b>Quadratic approximation with respect to an electrical current</b>]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212011000300002&lng=es&nrm=iso&tlng=es The temperature distribution in a p-n thermoelectric module in quadratic approximation with respect to an electrical current, when the Joule and Thomson surface and bulk effects are presented, is studied. Here were taken into account the temperature dependences of the thermal conductivity and the Seebeck coefficient, the presence of the Peltier and Seebeck surface coefficients. The partial cases are considered and the applicability criteria of the quadratic approximation in these cases was established. <![CDATA[<b>Chemical and electrical diagnosis of two configurations of dielectric barrier discharges applied to nitric oxides degradation</b>]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212011000300003&lng=es&nrm=iso&tlng=es The distinctive of non-thermal plasma (NTP) techniques is the efficient use of electrical energy through selective decomposition of the pollutant molecules. NTP processes can simultaneously treat several pollutants at atmospheric pressure with a quite good efficiency at relatively low energy consumption. In this work, NTP was used to remove nitric oxides from a mixture of air, water vapor and helium. Non thermal plasma was generated by dielectric barrier discharge at atmosphere pressure. In this work two different configurations were employed for the process: single dielectric barrier discharge (DBD) and double dielectric barrier discharge (2DBD). The aim of this work is to determine which configuration is most suitable for NOx treatment. A chemical model was developed to observe the species behavior in the plasma and results of numerical simulation demonstrated a good agreement with experimental data of the removal process, achieving more than 96% of NOx removal efficiency. From an electrical diagnosis several experimental parameters such as power, frequency, initial concentration of NOx and specific input energy were tested. To determine the electronic temperature and electronic densities in the plasma, an optical emission spectroscopy study was accomplished. <![CDATA[<b>Crecimiento en fluido fisiológico simulado de hidroxiapatita sobre películas de PMMA sílice-CaO</b>]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212011000300004&lng=es&nrm=iso&tlng=es Utilizando un fluido fisiológico simulado, se depositó hidroxiapatita sobre acero inoxidable 316L recubierto con una película híbrida PMMA-sílice-CaO sintetizada por el método sol-gel. Los sustratos recubiertos estuvieron inmersos en fluido fisiológico simulado por periodos de 10, 15, 20, 25 y 30 días y la hidroxiapatita depositada se caracterizó por Microscopia Electrónica de Barrido (SEM), Espectroscopia de Infrarrojo con Transformada de Fourier (FTIR) y Difracción de Rayos X (XRD). Por FTIR se mostró la presencia de grupos funcionales característicos de la hidroxiapatita. El análisis de SEM reveló que el material está conformado por estructuras esféricas con un tamaño del orden de 3 a 20 μm, compuestas a su vez por estructuras laminares y que el tiempo de inmersión contribuye a la formación de estructuras laminares mucho más grandes y por XRD se confirmo la presencia de la fase hidroxiapatita sobre el sustrato. El recubrimiento sintetizado tiene las características potenciales para ser usado como biomaterial.<hr/>By simulated body fluid was grown hydroxyapatite on stainless steel 316L coated with PMMA-silica hybrid coating doped with calcium methoxide synthesized by sol-gel process. The coated substrates were immersed in simulated body fluid (SBF) solutions for periods of 10, 15, 20, 25 and 30 days and the apatite deposited on the substrates was characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD). FTIR showed the presence of functional groups characteristic of hydroxyapatite. SEM analysis revealed that the material is formed for spherical structures with a size of the order of 3 to 20 μm composed of plate-like, curled fragments and the immersion time contributes to the formation of a much larger laminar structure. XRD analysis confirmed the presence of hydroxyapatite phase on the coating hybrid. The synthesized coating has the potential features to be used as a biomaterial. <![CDATA[<b>Síntesis y caracterización de una red semi-interpenetrada de poli (3-hidroxibutirato) y acrilamida obtenida por polimerización de injerto radio-inducido</b>]]> http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1665-35212011000300005&lng=es&nrm=iso&tlng=es El polihidroxibutirato (PHB) es un polímero obtenido de bacterias. En este trabajo se reporta la síntesis de un hidrogel basado en una red semi-interpenetrada (IPN, por sus siglas en inglés) de poli (3-hidroxibutirato) y acrilamida en medio acuoso. La síntesis se llevó a cabo por el método de copolimerización por injerto radio-inducido de irradiación simultánea, utilizando radiaciones gamma de 60Co. Se realizó el estudio de hinchamiento y el comportamiento térmico del material por medio de las pruebas de absorción, calorimetría diferencial de barrido y análisis termo-gravimétrico. De acuerdo con los resultados obtenidos el comportamiento térmico del PHB no es afectado de forma significativa por la formación del IPN. Adicionalmente se realizó el análisis por espectroscopia infrarrojo para verificar la formación del hidrogel. El análisis de microscopía electrónica de barrido (MEB) permitió determinar las características morfológicas del material y evidenciar la presencia de un hidrogel. El material obtenido resultó ser menos cristalino que el material de partida.<hr/>Poly (3-hydroxybutyrate) (PHB) is a polymer obtained by bacteria. Semi-interpenetrating polymer network (IPN) hydrogel of bacterial poly (3-hydroxybutyrate) and acrylamide were prepared by the radiation induced graft copolymerization reaction. It was chosen the simultaneous 60Co gamma irradiation technique. The swelling and thermal behaviors of the hydrogel were studied by means of swelling tests, differential scanning calorimetry and thermogravimetric analyses. According to the results the thermal behavior of PHB is not significantly affected by the IPN's formation. In addition fourier transform infrared studies were performed in order to demonstrate the IPN's synthesis. On the other hand, scanning electron micrograph analyses were carried out to study the IPN's morphology. The IPN's degree of cristallinity decreased with respect to PHB.