Sistemas Nanoestruturados: Heteroestruturas Quasi-Periódicas de Nitretos e Cálculos Ab initio em Polimorfos CaCO3

The physical properties and the excitations spectrum in oxides and semiconductors materials are presented in this work, whose the first part presents a study on the confinement of optical phonons in artificial systems based on III-V nitrides, grown in periodic and quasiperiodic forms. The second part of this work describes the Ab initio calculations which were carried out to obtain the optoeletronic properties of Calcium Oxide (CaO) and Calcium Carbonate (CaCO3) crystals. For periodic and quasi-periodic superlattices, we present some dynamical properties related to confined optical phonons (bulk and surface), obtained through simple theories, such as the dielectric continuous model, and using techniques such as the transfer-matrix method. The localization character of confined optical phonon modes, the magnitude of the bands in the spectrum and the power laws of these structures are presented as functions of the generation number of sequence. The ab initio calculations have been carried out using the CASTEP software (Cambridge Total Sequential Energy Package), and they were based on ultrasoft-like pseudopotentials and Density Functional Theory (DFT). Two di®erent geometry optimizations have been e®ectuated for CaO crystals and CaCO3 polymorphs, according to LDA (local density approximation) and GGA (generalized gradient approximation) approaches, determining several properties, e. g. lattice parameters, bond length, electrons density, energy band structures, electrons density of states, e®ective masses and optical properties, such as dielectric constant, absorption, re°ectivity, conductivity and refractive index. Those results were employed to investigate the confinement of excitons in spherical Si@CaCO3 and CaCO3@SiO2 quantum dots and in calcium carbonate nanoparticles, and were also employed in investigations of the photoluminescence spectra of CaCO3 crystal

Polaritons em materiais magnéticos nanoestruturados

In this work we present a theoretical study about the properties of magnetic polaritons in superlattices arranged in a periodic and quasiperiodic fashíons. In the periodic superlattice, in order to describe the behavior of the bulk and surface modes an effective medium approach, was used that simplify enormously the algebra involved. The quasi-periodic superlattice was described by a suitable theoretical model based on a transfer-matrix treatment, to derive the polariton's dispersion relation, using Maxwell's equations (including effect of retardation). Here, we find a fractal spectra characterized by a power law for the distribution of the energy bandwidths. The localization and scaling behavior of the quasiperiodic structure were studied for a geometry where the wave vector and the external applied magnetic field are in the same plane (Voigt geometry). Numerical results are presented for the ferromagnet Fe and for the metamagnets FeBr2 and FeCl2

Análise do potencial genotóxico da superfície de titânio modificada por plasma

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Aspectos clínicos, radiográficos e histológicos da superfície oclusal de molares decíduos com e sem lesão de cárie: estudo in vitro

Fundação de Amparo a Pesquisa do Estado de São Paulo

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

Aplicação de sabões de ácidos graxos epoxidados como inibidores de corrosão em oleoduto

Corrosion usually occurs in pipelines, so that it is necessary to develop new surface treatments to control it. Surfactants have played an outstanding role in this field due to its capacity of adsorbing on metal surfaces, resulting in interfaces with structures that protect the metal at low surfactant concentrations. The appearance of new surfactants is a contribution to the area, as they increase the possibility of corrosion control at specific conditions that a particular oil field presents. The aim of this work is to synthesize the surfactants sodium 12 hydroxyocadecenoate (SAR), sodium 9,10-epoxy-12 hydroxyocadecanoate (SEAR), and sodium 9,10:12,13-diepoxy-octadecanoate (SEAL) and apply them as corrosion inhibitors, studying their action in environments with different salinities and at different temperatures. The conditions used in this work were chosen in order to reproduce oil field reality. The study of the micellization of these surfactants in the liquid-gas interface was carried out using surface tensiometry. It was observed that cmc increased as salt concentration was increased, and temperature and pH were decreased, while cmc decreased with the addition of two epoxy groups in the molecule. Using the values of cmc and the Gibbs equation, the values of Gibbs free energy of adsorption, area per adsorbed molecule, and surface excess were calculated. The surface excess increases as salt concentration and temperature decreases, increasing as pH is increased. The area per adsorbed molecule and the free energy of adsorption decrease with salt concentration, temperature, and pH increase. SAXS results showed that the addition of epoxy group in surfactant structure results in a decrease in the repulsion between the micelles, favoring the formation of more oblong micellar structures, ensuring a better efficiency of metal coverage. The increase in salt and surfactant concentrations provides an increase in micellar diameter. It was shown that the increase in temperature does not influence micellar structure, indicating thermal stability that is advantageous for use as corrosion inhibitor. The results of inhibition efficiency for the surfactants SEAR and SEAL were considered the best ones. Above cmc, adsorption occurred by the migration of micelles from the bulk of the solution to the metal surface, while at concentrations below cmc film formation must be due to the adsorption of semi-micellar and monomeric structures, certainly due to the presence of the epoxy group, which allows side interactions of the molecule with the metal surface. The metal resistance to corrosion presented values of 90% of efficiency. The application of Langmuir and Frumkin isotherms showed that the later gives a better description of adsorption because the model takes into account side interactions from the adsorbing molecules. Wettability results showed that micelle formation on the solid surface occurs at concentrations in the magnitude of 10-3 M, which isthe value found in the cmc study. This value also justifies the maximum efficiencies obtained for the measurements of corrosion resistance at this concentration. The values of contact angle as a function of time suggest that adsorption increases with time, due to the formation of micellar structures on metal surface

A energia e suas implicações no ensino-aprendizagem da química

The area of Education in Chemistry in Brazil has appeared over 30 years and its growth has been accelerated by the need of comprehension of the processes of teaching and learning in chemistry. Many researches, in this area, has among its investigation objects the teaching tools like teaching materials and the learning processes of students in high school and basic education, but when dealing with higher levels of education, they are seldom portrayed. This study aimed to investigate the General Chemistry textbooks with respect to approach the concept of energy; know the main ideas of graduate students in Chemistry on the relation of the concept of energy and chemical transformations; finally, developing a cicle of studies with the proposition of an approach wich inter-relate the concept of energy and its implications in the teaching-learning process of a chemical transformation. To do so, we used as instruments a questionnaire, press conference, conceptual map and experimental activities. All activities of the study cicle were videotaped and recorded, transcribed and the results organized in tables. For the activities of the study cicle texts that have been developed and inter-relating concepts of chemistry and energy, which in turn gave theoretical support to the activities in the cycle. In the analysis it was used as a theoretical content the analysis of Laurence Bardin. The results revealed that the analysis of the book might be perceived that not always the concept of energy is used in order to generate the abstract thought of chemical transformations, but that the main macroscopic thermodynamic variables are present in the explanation of these transformations. During the study cicle, were studied two chemical reactions: the first one, made possible to approach the macroscopic dimension to quantify the concept of energy and the second one, made possible to demonstrate the macro and microscopic dimension of the concept of energy during a chemical transformation. In all reactions proposed, students used, in most of the times, as explanations, only macroscopic observations of the reactions under study and failed to realize that the concept of energy can be used to explain macro and microscopic chemical transformation. As a final action of the study cicle, students requested further discussion, to clarify the link between the concept of energy and the meanings constructed in the process of studying the reactions. This is done through an oral explanation, during the cycle, and registered in this thesis and attempts to show the interrelationship existing conceptual

Confecção e caracterização físico-química de filmes compósitos autossustentáveis NaAlg-TiO2-WO3

A new self-sustainable film was prepared through the sol-gel modified method, previously employed in our research group; sodium alginate was used as the polymer matrix, along with plasticizer glycerol, doped with titanium dioxide (TiO2) and tungsten trioxide (WO3). By varying WO3 concentration (0,8, 1,6, 2,4 and 3,2 μmol) and keeping TiO2 concentration constant (059 mmol), it was possible to study the contribution of these oxides on the obtained films morphological and electrical properties. Self-sustainable films have analyzed by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XDR), Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and Electrochemical Impedance Spectroscopy (EIS). By the IR specters, it was possible identify the TiO2, and posteriorly WO3, addition has provided dislocation of alginate characteristics bands to smaller vibrations frequencies indicating an electrostatic interaction between the oxides and the polymer matrix. Diffractograms show predominance of the amorphous phase in the films. SEM, along with EDX, analysis revealed self-sustainable films showed surface with no cracks and relative dispersion of the oxides throughout the polymer matrix. From Impedance analysis, it was observe increasing WO3 concentration to 2,4 μmol provided a reduction of films resistive properties and consequent improvement of conductive properties

Caracterização e aplicação de vermicultura natural e quimicamente modificada na adsorção de azul de metileno

Chemical modification of clays has been extremely studied in the search for improvements of their properties for use in various areas, such as in combating pollution by industrial effluents and dyes. In this work, the vermiculite was chemically modified in two ways, characterized and evaluated the adsorption of methylene blue dye. First was changed with the addition of a surfactant (hexadecyltrimethylammonium bromide, BHTA) making it an organophilic clay and then by adding an acid (HCl) by acid activation. Some analyzes were performed as X-ray fluorescence (FRX), X-ray diffraction (DRX), adsorption isotherms of methylene blue dye, infrared (FTIR) , scanning electron microscopy (SEM), thermal gravimetric analysis and spectroscopy energy dispersive (EDS). Analysis by FRX of natural vermiculite indicates that addition of silicon and aluminum, clay presents in its structure the magnesium, calcium and potassium with 16 % organic matter cations. The DRX analyzes indicated that the organic vermiculite was an insertion of the surfactant in the space between the lamellae, vermiculite and acid partial destruction of the structure with loss of crystallinity. The adsorption isotherms of methylene blue showed that there was a significant improvement in the removal of dye to the vermiculite with the addition of cationic surfactant hexadecyltrimethylammonium bromide and treatment with acid using HCl 2 mol/L. In acid vermiculites subsequently treated with surfactant, the adsorption capacity increased with respect to natural vermiculite, however was much lower compared vermiculite modified with acid and surfactant separately. Only the acidic vermiculite treated with surfactant adjusted to the Langmuir model. As in the infrared spectrometry proved the characteristics of natural vermiculite. In the organic vermiculite was observed the appearance of characteristic bands of CH3, CH2, and (CH3)4N. Already on acid vermiculite, it was realized a partial destruction with decreasing intensity of the characteristic band of vermiculite that is between 1074 and 952 cm-1. In the SEM analysis, it was observed that there was partial destruction to the acid treatment and a cluster is noted between the blades caused by the presence of the surfactant. The TG shows that the higher mass loss occurs at the beginning of the heating caused by the elimination of water absorbed on the surface between layers. In the organic vermiculite also observed a loss of mass between 150 and 300 °C caused decomposition of the alkylammonium molecules (surfactants)

Síntese e caracterização de óxidos de zinco e de magnésio suportados em A1SBA-15 para produção de biodiesel

To overcome the challenge of meeting growing energy demand in a sustainable way, biodiesel has shown very promising as alternative energy can replace fossil fuels, even partially. Industrially, the biodiesel is produced by homogeneous transesterification reaction of vegetable oils in the presence of basic species used as catalysts. However, this process is the need for purification of the esters obtained and the removal of glycerin formed after the reaction. This context, the alternative catalysts have that can improve the process of biodiesel production, aiming to reduce costs and facilitate its production. In this study, the AlSBA-15 support with Si / Al ratio = 50 was synthesized, as like as the heterogeneous catalysts of zinc oxide and magnesium supported on mesoporous AlSBA-15 silica, in the concentrations of 5, 10, 15 and 30 %, relative to the support. The textural properties and structural characterization of catalysts and supports were determined by techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) coupled to the chemical analyzer, adsorption / desorption of N2, thermal analysis (TG / DTG), absorption spectroscopy in the infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Characterization results indicated that the support AlSBA-15 retained the hexagonal ordered after the incorporation of zinc oxide and magnesium oxide in the holder. For heterogeneous catalysts, ZnO-AlSBA-15, that was observed the presence of zinc oxide nanoparticles dispersed in the surface and interior channels of the mesoporous and microporous support. The catalytic activity was evaluated by the transesterification reaction of sunflower oil via methylic route, and some reaction parameters were optimized with the most active catalyst in biodiesel production by sunflower oil. For the series of heterogeneous catalysts, the sample with 30 % ZnO supported on AlSBA-15 showed a better conversion of triglyceride to methyl esters, about 95.41 % of reaction conditions: temperature 175 °C, with molar ratio of 42:1, stirring at 200 rpm and under a pressure of 14 bar for 6 h. The catalyst MgO-AlSBA-15 showed no catalytic activity in the studied reactions

Estudo do desempenho de resinas poliméricas para remoção de H2S do gás natural

The natural gas (NG) is a clean energy source and found in the underground of porous rocks, associated or not to oil. Its basic composition includes methane, ethane, propane and other components, like carbon dioxide, nitrogen, hydrogen sulphide and water. H2S is one of the natural pollutants of the natural gas. It is considered critical concerning corrosion. Its presence depends on origin, as well as of the process used in the gas treatment. It can cause problems in the tubing materials and final applications of the NG. The Agência Nacional do Petróleo sets out that the maximum concentration of H2S in the natural gas, originally national or imported, commercialized in Brazil must contain 10 -15 mg/cm3. In the Processing Units of Natural Gas, there are used different methods in the removal of H2S, for instance, adsorption towers filled with activated coal, zeolites and sulfatreat (solid, dry, granular and based on iron oxide). In this work, ion exchange resins were used as adsorbing materials. The resins were characterized by thermo gravimetric analysis, infrared spectroscopy and sweeping electronic microscopy. The adsorption tests were performed in a system linked to a gas-powered chromatograph. The present H2S in the exit of this system was monitored by a photometrical detector of pulsing flame. The electronic microscopy analyzes showed that the topography and morphology of the resins favor the adsorption process. Some characteristics were found such as, macro behavior, particles of variable sizes, spherical geometries, without the visualization of any pores in the surface. The infrared specters presented the main frequencies of vibration associated to the functional group of the amines and polymeric matrixes. When the resins are compared with sulfatreat, under the same experimental conditions, they showed a similar performance in retention times and adsorption capacities, making them competitive ones for the desulphurization process of the natural gas

Estudo do desempenho de resinas poliméricas para remoção de H2S do gás natural

The natural gas (NG) is a clean energy source and found in the underground of porous rocks, associated or not to oil. Its basic composition includes methane, ethane, propane and other components, like carbon dioxide, nitrogen, hydrogen sulphide and water. H2S is one of the natural pollutants of the natural gas. It is considered critical concerning corrosion. Its presence depends on origin, as well as of the process used in the gas treatment. It can cause problems in the tubing materials and final applications of the NG. The Agência Nacional do Petróleo sets out that the maximum concentration of H2S in the natural gas, originally national or imported, commercialized in Brazil must contain 10 -15 mg/cm3. In the Processing Units of Natural Gas, there are used different methods in the removal of H2S, for instance, adsorption towers filled with activated coal, zeolites and sulfatreat (solid, dry, granular and based on iron oxide). In this work, ion exchange resins were used as adsorbing materials. The resins were characterized by thermo gravimetric analysis, infrared spectroscopy and sweeping electronic microscopy. The adsorption tests were performed in a system linked to a gas-powered chromatograph. The present H2S in the exit of this system was monitored by a photometrical detector of pulsing flame. The electronic microscopy analyzes showed that the topography and morphology of the resins favor the adsorption process. Some characteristics were found such as, macro behavior, particles of variable sizes, spherical geometries, without the visualization of any pores in the surface. The infrared specters presented the main frequencies of vibration associated to the functional group of the amines and polymeric matrixes. When the resins are compared with sulfatreat, under the same experimental conditions, they showed a similar performance in retention times and adsorption capacities, making them competitive ones for the desulphurization process of the natural gas

Síntese, caracterização e estudo fotofísico de complexos de 4,4- diaminoestilbeno-2,2-dissulfonato com íons lantanídeos

This is a work involving fundamental studies of chemistry where the synthesis and structural characterization, as well as a possible future application of these new compounds as luminescent sensors or sunscreen agents, complexes with 4,4 diaminostilbene-2,2-disulfonic (DSD) and trivalent lanthanide ions La3+, Nd3+, Eu3+, Gd3+ and Yb3+, were synthesized in the ratio of 3 mmol: 1 mmol (DSD: lanthanides). The complexes obtained with these ions were present in powder form and were characterized by complexometric titration with EDTA CHN Elemental analysis, molecular absorption spectroscopy in the ultraviolet region, the absorption spectroscopy in the infrared, thermal analysis (TG / DTG), Nuclear Magnetic Resonance - NMR 1H and Luminescence Spectroscopy. The complexometric titration and CHN analysis, confirmed the TG / DTG which suggest that these complexes have the following general chemical formulas: [La2(C14H12S2O6N2)2(H2O)2Cl2].7H2O,[Nd2(C14H12S2O6N2)2(H2O)2Cl2].6H2O,[Eu2(C14 H12S2O6N2)2(H2O)2Cl2].7H2O,[Gd2(C14H12S2O6N2)2(H2O)2Cl2].4H2O e [Yb2(C14H12S2O6N2)2(H2O)2].6H2O. The disappearance of the bands in the infrared spectrum at 2921 cm-1 and 2623 cm-1 and the displacement of the bands in the spectra of the amine complex indicate that the lanthanide ion is coordinated to the oxygen atoms and the sulfonate groups of the nitrogens amines, suggesting the formation of the dimer. The disappearance of the signal and the displacement signal SO3H amines in the 1H NMR spectrum of this complex are also indicative coordination and dimer formation. The Thermogravimetry indicates that the DSD is thermally stable in the range of 40º to 385°C and their complexes with lanthanide ions exhibit weight loss between 4 and 5 stages. The Uv-visible spectra indicated that the DSD and complexes exhibit cis isomers. The analysis of luminescence indicates that the complexes do not exhibit emission in the region of the lanthanides but an intense emission part of the binder. This is related to the triplet states of the ligand, which are in the lowest energy state emitting lanthanide ions, and also the formation of the dimer that suppress the luminescence of ion Eu3+. The formation of dimer was also confirmed by calculating the europium complex structure using the model Hamiltonian PM6 and Sparkle

O impacto dos custos não-gerenciáveis na determinação das tarifas de energia elétrica: um estudo nas companhias distribuidoras do nordeste que tiveram revisão tarifária nos exercícios de 2003 e 2004

This work presents results derived from a study related to impact on non-controllable costs in the determination of energy taxes. This is done analyzing tax review practiced by concessionaries responsible for the distribution of electrical energy located in the Northeastern Region of Brazil, between 2003 and 2004. This Region was chosen as a study area due to the researcher s expectation in congregating companies that deliver services to markets that have similar social-economical profiles. A brief explanation related to the restructuring of the electrical sector in Brazil is presented, pointing out that there was privatization of the great majority of these companies. The study also points out the definition of regulating rules in service delivery process. The components of taxes that are practiced by these companies aimed at final consumers, as well as the market as a whole and the revision process that is executed by Agência Nacional de Energia Elétrica ANEEL for the definition of these taxes are demonstrated in the research. A brief historical of the concessionaires that were focus of the research is presented, totaling five companies. Some data used by ANEEL in the tax review process was analyzed as well as data on components of approved taxes. It is concluded that as a media 47, 49% of the components of taxes in the researched companies correspond to the non-controllable costs. These is done considering previous classification by ANEEL in the tax review process. Although, if it is considered that these companies since 2006, by the means of participation in energy auctions are able to negotiate energy prices for their own needs, it is concluded that these concession contracts guarantee the delivery of the service to the costumer in the total tribute. The percentage of non-controllable costs is 16, 27% average of the tax. This means, amongst other information, that the government has a great deal of responsibility in the formation of price practiced by these companies and its target markets

Impacto do racionamento nos resultados das empresas concessionárias do serviço público de distribuição de energia elétrica: um estudo nas empresas privadas da Região Nordeste

This work verifies the impact caused by the Emergencial Program of Reduction of Consumption of Electric Energy (energy-rationing program) in the results of the concessionary private companies of the public service of electric energy distribution localized in the Northeast Area. As the rationing invigorated from June 2001 to February 2002, its effects are diluted in the results presented by these companies in the second semester of 2001 and first quarter of 2002, with prominence for the last quarter of 2001, when the revenue of extraordinary tariff restore was instituted by the National Agency of Electric Energy (ANEEL), consequence of the so-called General Agreement of the Electric Sector made between the federal government and the companies of the electric sector. The structure of a generic electric sector and a historical review of the Brazilian electric sector from the time it was controlled by the private enterprises, including the State control period, about 1960, and returning to the control of the private enterprises in 1990, under a new regulation structure are presented. An explanation of the models of economic regulation that Brazil used for the electric sector is made, with prominence for the price cap that is the actual effective model. The process of tariff revision foreseen in the concession contracts signed by the federal government and the concessionary companies is presented, highlighting its two stages: the tariff rebalancing that defines the new price cap and the calculation of the factor X that establishes the efficiency goals for the companies. There is made a presentation of the Emergencial Program of Reduction of Consumption of Electric Energy and of the consequent General Agreement of the Electric Sector, which created the revenue of extraordinary tariff restore. A conceptual revision on reviews is presented, regarding to concepts, accomplishment and recognition. A brief review of the six companies that made part of the worked sample is also presented. Analyzing the quarters historical review and of amount of sold energy, it was possible to conclude that the energy-rationing altered the results of the studied companies significantly and that alteration was masked by the accounting process of the revenue of extraordinary tariff restore