Polaritons de exciton em super-redes semicondutoras

In this work we study the spectrum (bulk and surface modes) of exciton-polaritons in infinite and semi-infinite binary superlattices (such as, ···ABABA···), where the semiconductor medium (A), whose dielectric function depends on the frequency and the wavevector, alternating with a standard dielectric medium B. Here the medium A will be modeled by a nitride III-V semiconductor whose main characteristic is a wide-direct energy gap Eg. In particular, we consider the numerical values of gallium nitride (GaN) with a crystal structure wurtzite type. The transfer-matrix formalism is used to find the exciton-polariton dispersion relation. The results are obtained for both s (TE mode: transverse electric) and p (TM mode: transverse magnetic) polarizations, using three diferent kind of additional boundary conditions (ABC1, 2 e 3) besides the standard Maxwell's boundary conditions. Moreover, we investigate the behavior of the exciton-polariton modes for diferent ratios of the thickness of the two alternating materials forming the superlattice. The spectrums shows a confinement of the exciton-polariton modes due to the geometry of the superlattice. The method of Attenuated Total Reflection (ATR) and Raman scattering are the most adequate for probing this excitations

Reavaliação da eficiência de óleo de coco saponificado e de sua microemulsão como inibidores de corrosão em uma célula eletroquímica

An interesting development in surfactants science and technology is their application as corrosion inhibitors, since they act as protective films over anodic and cathodic surfaces. This work aims to investigate the efficiency of saponified coconut oil (SCO) as corrosion inhibitor and of microemulsified system (SCO + butanol + kerosene oil + distilled water), in saline medium, using an adapted instrumented cell, via techniques involving linear polarization resistance (LPR) and mass loss coupons (MLC). For this, curves of efficiency versus SCO concentration (ranging between 0 and 75 ppm) have been constructed. According to the obtained results, the following efficiency levels were reached with OCS: 98% at a 75 ppm concentration via the LPR method and 95% at 75 ppm via the MLC method. The microemulsified system, for a concentration of 15 ppm of SCO, obtained maximum inhibition of 97% (LPR) and 93% (MLC). These data indicate that it is possible to optimize the use of SCO in similar applications. Previous works have demonstrated that maximal efficiencies below 90% are attained, typically 65% as free molecules and 77% in microemulsified medium, via the LPR method in a different type of cell. Therefore, it can be concluded that the adapted instrumented cell (in those used methods) showed to be an important tool in this kind of study and the SCO was shown effective in the inhibition of the metal

Estudo da corrosão no aço carbono 1020 protegido com óleo de coco saponificado: análise físico-química do comportamento químico do tensoativo

Corrosion inhibitors in solution are utilized to minimize processes from corrosion in steel. Of the present dissertation was evaluated the efficiency by inhibition from the surfactant saponified coconut oil (OCS) in the carbon steel 1020 through in linear polarization electrochemistry technique, well as, studied the process from adsorption through from the isotherms from Langmuir, Frumkin and Temkin. The corrosion current was determined through in Tafel extrapolation from the curves in the polarization, and then, was calculated the efficiency in the inhibitor to each concentration and temperature. Were studied four concentrations (12,5 ppm, 25 ppm, 50 ppm, and 75 ppm) in the inhibitor OCS and one in the NaCl salt (10.000 ppm) in six temperatures (301 K, 308 K, 313 K, 318 K, 323 K, and 328 K) in triplicate. By the results obtained observed that the technique applied can evaluated with rapidity and efficiency corrosion inhibitors. In relation to the isotherms, the than best appropriated was the in Langmuir and in the concentrations studied, the that obtained the best efficiency was the concentration of 75 ppm

Inibição à corrosão do aço AISI 1020, em meios ácido e salino, por tensoativos e substâncias nitrogenadas microemulsionados

Corrosion inhibition efficiency of saponified coconut oil (SCO) and sodium dodecilbenzene sulfonate (DBS) surfactants in AISI 1020 carbon steel was evaluated by electrochemical methods. These surfactants were also evaluated as microemulsion systems (SCO-ME and DBS-ME), of O/W type (water-rich microemulsion), in a Winsor IV region. They were obtained according to the following composition: 15% SCO, 15% butanol (30% Co-surfactant/Surfactant C/T), 10% organic phase (FO, kerosene) and 60% aqueous phase (FA). These systems were also used to solubilize the following nitrogenated substances: Diphenylcarbazide (DC), 2,4-dinitro-phenyl-thiosemicarbazide (TSC) and the mesoionic type compound 1,3,4-triazolium-2-thiolate (MI), that were investigated with the purpose of evaluating their anticorrosive effects. Comparative studies of carbon steel corrosion inhibition efficiencies of free DBS and DBS-ME, in brine and acidic media (0.5%), showed that DBS presents better inhibition results in acidic media (free DBS, 89% and DBS-ME, 93%). However, the values obtained for DBS in salted solution (72% free DBS and 77% DBS-ME) were similar to the ones observed for the SCO surfactant in brine (63% free SCO and 74% SCO-ME). Analysis of corrosion inhibition of the nitrogenated substances that were solubilized in the SCO-ME microemulsion system by the linear polarization method in brine (0.5% NaCl) showed that such compounds are very efficient an corrosion inhibitors [DC-ME-SCO (92%), TSC-ME-SCO (93%) and MI-ME-SCO (94%)]

Estudo das ligas titânio-zircônio resultantes do processo de fundição plasma-skull para aplicações como biomateriais

The aim of this work was to study a series of 11 different compositions of Ti-Zr binary alloys resistance to aggressive environment, i. e., their ability to keep their surface properties and mass when exposed to them as a way to evaluate their performance as biomaterials. The first stage was devoted to the fabrication of tablets from these alloys by Plasma-Skull casting method using a Discovery Plasma machine from EDG Equipamentos, Brazil. In a second stage, the chemical composition of each produced tablet was verified. In a third stage, the specimen were submitted to: as-cast microstructure analysis via optical and scanning electron microscopy (OM and SEM), x-ray dispersive system (EDS) chemical analysis via SEM, Vickers hardness tests for mechanical evaluation and corrosion resistence tests in a 0.9% NaCl solution to simulate exposition to human saliva monitored by open circuit potential and polarization curves. From the obtained results, it was possible to infer that specimens A1 (94,07 wt% Ti and 5,93% wt% Zr), A4 (77,81 wt % Ti and 22,19 wt % Zr) and A8 (27,83 wt% Ti and 72,17 wt% Zr), presented best performance regarding to corrosion resistance, homogeneity and hardness which are necessary issues for biomaterials to be applied as orthopedic and odontological prosthesis

Estudo da eficácia do tensoativo sorbitano tween 80 veiculado em nanoemulsão contendo óleo de soja, como inibidor de corrosão

Nowadays, the use of chemicals that satisfactorily meet the needs of different sectors of the chemical industry is linked to the consumption of biodegradable materials. In this context, this work contemplated biotechnological aspects with the objective of developing a more environmentally-friendly corrosion inhibitor. In order to achieve this goal, nanoemulsion-type systems (NE) were obtained by varying the amount of Tween 80 (9 to 85 ppm) a sortitan surfactant named polyoxyethylene (20) monooleate. This NE-system was analyzed using phase diagrams in which the percentage of the oil phase (commercial soybean oil, codenamed as OS) was kept constant. By changing the amount of Tween 80, several polar NE-OS derived systems (O/W-type nanoemulsion) were obtained and characterized through light scattering, conductivity and pH, and further subjected to electrochemical studies. The interfacial behavior of these NE-OS derived systems (codenamed NE-OS1, S2, S3, S4 and S5) as corrosion inhibitors on carbon steel AISI 1020 in saline media (NaCl 3.5%) were evaluated by measurement of Open Circuit Potential (OCP), Polarization Curves (Tafel extrapolation method) and Electrochemical Impedance Spectroscopy (EIS). The analyzed NE-OS1 and NE-OS2 systems were found to be mixed inhibitors with quantitative efficacy (98.6% - 99.7%) for concentrations of Tween 80 ranging between 9 and 85 ppm. According to the EIS technique, maximum corrosion efficiency was observed for some tested NE-OS samples. Additionaly to the electrochemical studies, Analysis of Variance (ANOVA) and Principal Component Analysis (PCA) were used, characterization of the nanoemulsion tested systems and adsorption studies, respectively, which confirmed the results observed in the experimental analyses using diluted NE-OS samples in lower concentrations of Tween 80 (0.5 1.75 ppm)

Obtenção de novos sistemas nanoautoemulsificantes a partir do óleo das sementes de Azadirachta indica A Juss e suas aplicações como inibidores de corrosão

Corrosion is a natural process that causes progressive deterioration of materials, so, reducing the corrosive effects is a major objective of development of scientific studies. In this work, the efficiency of corrosion inhibition on a AISI 1018 carbon steel of the nanoemulsion system containing the oil of the seeds of Azadirachta indica A. Juss (SNEOAI) was evaluated by the techniques of linear polarization resistance (LPR) and weight loss (CPM), a instrumented cell. For that, hydroalcoholic extract of leaves of A. indica (EAI) was solubilized in a nanoemulsion system (SNEOAI) of which O/W system (rich in aqueous phase). This nanoemulsion system (tested in different concentrations) was obtained with oil from the seeds of this plant species (OAI) (oil phase), dodecylammonium chloride (DDAC) (surfactant), butanol (cosurfactant) and water, using 30 % of C/T (cosurfactant/surfactant), 0.5 % of oil phase and 69.5 % of aqueous phase, and characterized by surface tension, rheology and droplet sizes. This systems SNEOAI and SNEOAI-EAI (nanoemulsion containing hydroalcoholic extract - EAI) showed inhibition efficiencies in corrosive environment in saline (1 %), for the method of LPR with significant value of 70.58 % (300 ppm) to SNEOAI, 74.17 % (100 ppm) and 72.51 % (150 ppm) to SNEOAI-EAI. The best efficiencies inhibitions were observed for the method of CPM with 85.41 % for the SNEOAI (300 ppm) and 83.19 % SNEOAI-EAI (500 ppm). The results show that this formulation could be used commercially for use as a corrosion inhibitor, this research contributed to the biotechnological applicability of Azadirachta indica, considering the large use of this plant species rich in limonoids (tetranortriterpenoids), especially azadirachtin

Caracterização dos eletrocatalisadores LaMnO3, LaFeO3, LaFe0,2Mn0,8O3 E La0,5Fe0,5MnO3 preparados por autocombustão assistida por microondas para cátodos de células a combustível do tipo SOFC

Materials consisting of perovskite-type oxides (ABO3) have been developed in this work for applications in fuel cell cathodes of solid oxide type (SOFC). These ceramic materials are widely studied for this type of application because they have excellent electrical properties, conductivity and electrocatalytic. The oxides LaMnO3, LaFeO3, LaFe0.2Mn0.8O3 e La0.5Fe0.5MnO3 were synthesized by the method of microwave assisted combustion and after sintering at 800°C in order to obtain the desired phases. The powders were characterized by thermogravimetry (TG), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and voltammetric analysis (cyclic voltammetry and polarization curves). The results obtained by XRF technique showed that the microwave synthesis method was effective in obtaining doping oxides with values near stoichiometric. In general, powders were obtained with particle size less than 0.5 μm, having a porous structure and uniform particle size distribution. The particles showed spherical form, irregular and crowded of varying sizes, according to the analysis of SEM. The behavior of the oxides opposite the thermal stability was monitored by thermogravimetric curves (TG), which showed low weight loss values for all samples, especially those of manganese had its structure. By means of Xray diffraction of the samples sintered at 800°C was possible to observe the formation of powders having high levels of crystallinity. Furthermore, undesirable phases such as La2O3 and MnOx were not identified in the diffractograms. These phases block the transport of oxygen ions in the electrode/electrolyte interface, affecting the electrochemical activity of the system. The voltammetric analysis of the electrocatalysts LF-800, LM-800, LF2M8-800 e L5F5M-800 revealed that these materials are excellent electrical conductors, because it increased the passage of electrical current of the working electrode significantly. Best performance for the oxygen reduction reaction was observed with iron-rich structures, considering that the materials obtained have characteristics suitable for use in fuel cell cathodes of solid oxide type

Degradação eletroquímica de benzeno, tolueno e xileno via oxidação eletroquímica utilizando eletrodo Ti/Pt

This work is directed to the treatment of organic compounds present in produced water from oil using electrochemical technology. The water produced is a residue of the petroleum industry are difficult to treat , since this corresponds to 98 % effluent from the effluent generated in the exploration of oil and contains various compounds such as volatile hydrocarbons (benzene, toluene, ethylbenzene and xylene), polycyclic aromatic hydrocarbons (PAHs), phenols, carboxylic acids and inorganic compounds. There are several types of treatment methodologies that residue being studied, among which are the biological processes, advanced oxidation processes (AOPs), such as electrochemical treatments electrooxidation, electrocoagulation, electrocoagulation and eletroredution. The electrochemical method is a method of little environmental impact because instead of chemical reagents uses electron through reactions of oxide-reducing transforms toxic substances into substances with less environmental impact. Thus, this paper aims to study the electrochemical behavior and elimination of the BTX (benzene, toluene and xylene) using electrode of Ti/Pt. For the experiment an electrochemical batch system consists of a continuous source, anode Ti/Pt was used, applying three densities of current (1 mA/cm2, 2,5 mA/cm2 and 5 mA/cm2). The synthetic wastewater was prepared by a solution of benzene, toluene and xylene with a concentration of 5 ppm, to evaluate the electrochemical behavior by cyclic voltammetry and polarization curves, even before assessing the removal of these compounds in solution by electrochemical oxidation. The behavior of each of the compounds was evaluated by the use of electrochemical techniques indicate that each of the compounds when evaluated by cyclic voltammetry showed partial oxidation behavior via adsorption to the surface of the Ti/Pt electrode. The adsorption of each of the present compounds depends on the solution concentration but there is the strong adsorption of xylene. However, the removal was confirmed by UV-Vis, and analysis of total organic carbon (TOC), which showed a percentage of partial oxidation (19,8 % - 99,1 % TOC removed), confirming the electrochemical behavior already observed in voltammetry and cyclic polarization curves

Termodinâmica de um gás de fótons no contexto de eletrodinâmicas não-lineares

The objective of this dissertation is the development of a general formalism to analyze the thermodynamical properties of a photon gas under the context of nonlinear electrodynamics (NLED). To this end it is obtained, through the systematic analysis of Maxwell s electromagnetism (EM) properties, the general dependence of the Lagrangian that describes this kind of theories. From this Lagrangian and in the background of classical field theory, we derive the general dispersion relation that photons must obey in terms of a background field and the NLED properties. It is important to note that, in order to achieve this result, an aproximation has been made in order to allow the separation of the total electromagnetic field into a strong background electromagnetic field and a perturbation. Once the dispersion relation is in hand, the usual Bose-Einstein statistical procedure is followed through which the thermodynamical properties, energy density and pressure relations are obtained. An important result of this work is the fact that equation of state remains identical to the one obtained under EM. Then, two examples are made where the thermodynamic properties are explicitly derived in the context of two NLED, Born-Infelds and a quadratic approximation. The choice of the first one is due to the vast appearance in literature and, the second one, because it is a first order approximation of a large class of NLED. Ultimately, both are chosen because of their simplicity. Finally, the results are compared to EM and interpreted, suggesting possible tests to verify the internal consistency of NLED and motivating further developement into the formalism s quantum case

Propriedades estruturais e optoeletrônicas dos compostos SrSnO3, SrxBa1-xSnO3 e BaSnO3

In this work we present a study for the structural, electronic and optical properties, at ambient conditions of SrSnO3, SrxBa1

Anisotropia sísmica crustal na região de Cascavel - CE

This dissertation presents a study on crustal seismic anisotropy in Cascavel - CE. The earthquake data employed here are from the Seismological Laboratory at Universidade Federal do Rio Grande do Norte (UFRN) and were colected from 29 September 1997 to 05 march 1998 using six three-component digital seismographic stations. In general, the cause of the observed seismic anisotropy in many regions of the world is interpreted in terms of fluid-filled stress aligned microcracks in the rockmass (EDA). In other words, the polarisation direction of the faster shear-wave splitting is parallel to SHmax. However, other researches on seismic anisotropy carried out in NE Brazil have shown a remarkable consistency of the faster shear-wave polarisation direction with the direction of the Precambrian fabric. The present work is another case study that is used to investigate this issue. In order to map the Precambrian fabric we used aeromagnetic data, since the study area is mostly covered with sediments (up to 50m thick) and in-situ field mapping would be very difficult to be carried out. According to the results from the present research, the observations of the faster shear-wave polarisation directions in two seismographic stations in Cascavel region are best explained in the framework of EDA. For the remaining two stations, the observed anisotropy may have two interpretions: (i) - 90_ flips of the direction of polarisation of the faster shear-wave, since that the event-to-station ray path would be through the fracture zone and hence would travel under a higher pore pressure and (ii) - the observed seismic anisotropy would agree with the direction on the ductile Precambrian fabric

Análise de superfícies seletivas em frequência com geometria multifractal

Frequency Selective surfaces are increasingly common structures in telecommunication systems due to their geometric and electromagnetic advantages. As a matter of fact, the frequency selective surfaces with fractal geometry type would allow an even bigger reduction of the electrical length which provided greater flexibility in the design of these structures. In this work, we investigated the use of multifractal geometry in frequency selective surfaces. Three structures with different multifractal geometries have been proposed and analyzed. The first structure allowed the design of multiband structures with greater flexibility in controlling the resonant frequencies and bandwidth. The second structure provided a bandwidth increase even with the rising of the fractal level. The third structure showed response with angle stability, dual polarization and provided room for a bandwidth increase with the rising of the structural multifractality. Furthermore, the proposed structures increased the degree of freedom in the multiband designs because they have multiple resonant frequencies ratios between adjacent bands and are easy to deploy. The validation of the proposed structures was initially verified through simulations in Ansoft Designer software and then the structures were constructed and the experimental results obtained

Estudo da densidade de corrente crítica para reversão da magnetização de nanoelementos ferromagnéticos

The discovery that a spin-polarized current is capable of exerting a torque in a ferromagnetic material, through spin transfer, might provide the development of new technological devices that store information via the direction of magnetization. The reduction of current density to revert the magnetization is a primary issue to potential applications on non volatile random access memories (MRAM). We report a theorical study of the dipolar and shape effects on the critical current density for reversal of magnetization, via spin transfer torque (STT), on ferromagnetic nanoelements. The nanostructured system consists on a reference layer, in which the current will be spin-polarized, and a free layer of magnetization reversal. We observed considerable changes on the critical current density as a function of the element’s reversion layer thickness (t = 1.0 nm, 1.5 nm, 2.0 nm e 2.5 nm) and geometry (circular and elliptical), the material kind of the system free layer (Iron and Permalloy) and according to the orientation of the magnetization and the spin polarization with the major axis. We show that the critical current density may be reduced about 50% by reducing the Fe free layer thickness and around 75% when we change the saturation magnetization of circular nanoelements with 2.5 nm of thickness. We still observed a reduction as much as 90% on the current density of reversion for thin nanoelements magnetized along the minor axis direction, using in-plane spin polarization parallel to the magnetization.

Estudo de métodos de tratamento de efluentes (troca iônica e eletroquímico) separados e sequenciais para eliminação de derivados de petróleo

The produce of waste and the amount of the water produced coming from activities of petroleum production and extraction has been a biggest challenge for oil companies with respect to environmental compliance due to toxicity. The discard or the reuse this effluent containing organic compounds as BTEX (benzene, toluene, ethylbenzene and xylene) can cause serious environmental and human health problems. Thus, the objective this paper was study the performance of two process (separately and sequential) in one synthetic effluent for the benzene, toluene and xylene removal (volatile hydrocarbons presents in the produced water) through of electrochemical treatment using Ti/Pt electrode and exchange resin ionic used in the adsorption process. The synthetic solution of BTX was prepared with concentration of 22,8 mg L-1, 9,7 mg L-1 e 9,0 mg L-1, respectively, in Na2SO4 0,1 mol L-1. The experiments was developed in batch with 0.3 L of solution at 25ºC. The electrochemical oxidation process was accomplished with a Ti/Pt electrode with different current density (J = 10, 20 e 30 mA.cm-2). In the adsorption process, we used an ionic exchange resin (Purolite MB 478), using different amounts of mass (2,5, 5 and 10 g). To verify the process of technics in the sequential treatment, was fixed the current density at 10 mA cm-2 and the resin weight was 2.5 g. Analysis of UV-VIS spectrophotometry, chemical oxygen demand (COD) and gas chromatography with selective photoionization detector (PID) and flame ionization (FID), confirmed the high efficiency in the removal of organic compounds after treatment. It was found that the electrochemical process (separate and sequential) is more efficient than absorption, reaching values of COD removal exceeding 70%, confirmed by the study of the cyclic voltammetry and polarization curves. While the adsorption (separately), the COD removal did not exceed 25,8%, due to interactions resin. However, the sequential process (electrochemical oxidation and adsorption) proved to be a suitable alternative, efficient and cost-effectiveness for the treatment of effluents petrochemical.