Made available in DSpace on 2014-10-09T12:29:09Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:58Z (GMT). No. of bitstreams: 1 01008.pdf: 794494 bytes, checksum: d63c1a441a7027bff0b1b37bc88c461b (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

<p> Solar cells were made by diffusing impurities into the rough or backside of commercially available silicon wafers to form a junction. The properties of these solar cells were compared to solar cells made by diffusing impurities into the polished surface of similar silicon wafers. The processing steps involved in preparing each type of solar cell were identical. </p> / Thesis / Master of Engineering (MEngr)

<p> The frequency spectrum of a diatomic linear chain with randomly placed isotopic impurities is calculated using a Green's function formalism. The calculation follows a method devised by Langer, and yields the density of states exactly to first order in the concentration of impurities. It is found that polarisation mixing causes no problem and the results are analogous to those of Langer for the monatomic chain. Results are presented for various ratios of impurity mass to replaced mass, for which impurity bands are found above the optical band and in the gap between the accoustic and optical bands. A self consistent calculation is also discussed.</p> / Thesis / Master of Science (MSc)

Yes / Captured carbon dioxide flowing in pipelines is impure. The impurities contained in the carbon dioxide fluid impact on the properties of the fluid. The impact of each impurity has not been adequately studied and fully understood. In this study, binary mixtures containing carbon dioxide and one impurity, at the maximum permitted concentration, flowing in pipelines are studied to understand their impact on pipeline performance. A hypothetical 70 km uninsulated pipeline is assumed and simulated using Aspen HYSYS (v.10) and gPROMS (v.5.1.1). The mass flow rate is 2,200,600 kg/h; the internal and external diameters are 0.711 m and 0.785 m. 15 MPa and 9 MPa were assumed as inlet and minimum pressures and 33 oC as the inlet temperature, to ensure that the fluid remain in the dense (subcritical or supercritical) phase. Each binary fluid is studied at the maximum allowable concentration and deviations from pure carbon dioxide at the same conditions is determined. These deviations were graded to rank the impurities in order of the degree of impact on each parameter. All impurities had at least one negative impact on carbon dioxide fluid flow. Nitrogen with the highest concentration (10-mol %) had the worst impact on pressure loss (in horizontal pipeline), density, and critical pressure. Hydrogen sulphide (with 1.5-mol %) had the least impact, hardly changing the thermodynamic properties of pure carbon dioxide.

Master of Science / Department of Civil Engineering / Kyle Riding / Some limestone coarse aggregate in concrete pavement can break down under repeated freeze-thaw cycles. Application of rock salt may increase the severity of exposure conditions because of trace compounds, such as calcium sulfate, in rock salt. Subsequently, limestone aggregate in concrete was subjected to freeze-thaw cycling in two methods: salt-treating the aggregate before batching concrete, and half-immersing concrete specimens in rock salt solution during freeze-thaw cycling. Concrete and saw-cut limestone specimens were also subjected to wet-dry cycles in varying salt solutions to examine the influence of trace compounds in rock salt. Freeze-thaw test results indicate that the test methods used were not severe enough to determine if a limestone aggregate was durable or not. The wet-dry testing was also not severe enough to determine the effects of trace compounds in salt solution.

No description available.

Graphene, the thinnest material with a stable 2D structure, is a potential alternative for silicon-based electronics. However, zero band gap of graphene causes a poor on-off ratio of current thus making it unsuitable for logic operations. This problem prompted scientists to find other suitable 2D materials. Creating vacancy defects or synthesizing hybrid 2D planar interfaces with other 2D materials, is also quite promising for modifying graphene properties. Experimental productions of these materials lead to the formation of possible defects and impurities with significant influence in device properties. Hence, a detailed understanding of the effects of impurities and defects on the properties of 2D systems is quite important. In this thesis, detailed studies have been done on the effects of impurities and defects on graphene, hybrid graphene/h-BN and graphene/graphane structures, silicene and transition metal dichalcogenides (TMDs) by ab-initio density functional theory (DFT). We have also looked into the possibilities of realizing magnetic nanostructures, trapped at the vacancy defects in graphene, at the reconstructed edges of graphene nanoribbons, at the planar hybrid h-BN graphene structures, and in graphene/graphane interfaces. A thorough investigation of diffusion of Fe adatoms and clusters by ab-initio molecular dynamics simulations have been carried out along with the study of their magnetic properties. It has been shown that the formation of Fe clusters at the vacancy sites is quite robust. We have also demonstrated that the quasiperiodic 3D heterostructures of graphene and h-BN are more stable than their regular counterpart and certain configurations can open up a band gap. Using our extensive studies on defects, we have shown that defect states occur in the gap region of TMDs and they have a strong signature in optical absorption spectra. Defects in silicene and graphene cause an increase in scattering and hence an increase in local currents, which may be detrimental for electronic devices. Last but not the least, defects in graphene can also be used to facilitate gas sensing of molecules as well as and local site selective fluorination.

The recovery of ethylene glycol from its crude solutions in the production of polyethylene terephthalate (PET) has become important recently because of the rising cost of feedstocks for the manufacture of synthetic fibers and other polymeric materials. This work dealt with procedures for separation of ethylene glycol from its crude solutions and also with the identification of impurities, primarily phenols. The separation was carried out by fractional distillation techniques using three different additives: kerosene, hexachloronaphthalene, and naphthalene. The best additive was found by comparing the amounts of· recovered glycol. The identification of impurities was done by infrared spectroscopy and nuclear magnetic resonance spectroscopy.

Compostos de fósforo insolúveis em água, como os do tipo Fe - K - P podem ser formados em fertilizantes fosfatados totalmente acidulados (FFTA). Em superfosfatos dois dos mais comuns são os compostos Fe3KH8(PO4)6.6H2O (H8) e Fe3KH14(PO4)8.4H2O (H14). Elevadas quantidades de rocha fosfática são descartadas a fim de garantir que FFTA apresentem na fração citrato neutro de amônio (CNA) + água, 90% de P2O5 solúvel em CNA, como prevê a legislação brasileira de fertilizantes. Experimentos anteriores mostraram que os FFTA não necessitam, obrigatoriamente, conter alta solubilidade em água. Estudos anteriores indicaram que rochas fosfáticas poderão ser melhores utilizadas conhecendo-se a performance agronômica das impurezas insolúveis em água. Para adicionar informações a este assunto, os compostos H8 e H14 foram sintetizados em condições de laboratório. Os precipitados foram analisados através de análise química elementar, difratometria de raios-x, microscopia eletrônica de varredura e espectrometria de energia dispersiva (EED). As análises efetuadas confirmaram a correta precipitação de ambos compostos. Um experimento de hidrólise foi conduzido usando soluções de NaCl 0,01; 0,05 e 0,1 mol L -1 com pH variando de 3,0 a 7,5. Amostras do H8, H14 e de FR de Catalão foram agitadas utilizando-se as soluções até pH de equilíbrio. O pH da solução foi ajustado adicionando-se NaOH ou HCl. Depois de atingido o pH de equilíbrio, as soluções foram filtradas, e as concentrações de P, Fe, K, S, Na e Cl determinadas analiticamente e utilizado o programa MINTEQ para calcular a atividade dos íons ortofosfato (H2PO4 - e HPO4 2- ). Os precipitados que ficaram retidos no papel de filtro foram analisados analiticamente e submetidos a raios-x e EED. As quantidades de H8 e H14 sintetizadas foram suficientes para o estudo de hidrólise. Os resultados indicaram que a porcentagem de P liberada dos compostos do tipo Fe - K - P aumentava com o aumento do pH. Quantidades mais elevadas de P foram liberadas do composto H14 quando comparado ao H8. Também, a atividade dos íons ortofosfato foi mais elevada para o H14 quando comparado ao H8. Observou-se uma tendência a elevação da atividade dos íons ortofosfato com a diminuição da força iônica para ambos compostos. Para o H8 ocorreu um aumento da atividade com o aumento do pH para NaCl 0,01 mol L -1 . Para o H14 a tendência foi o aumento da atividade até pH 5,0 para NaCl 0,05 e 0,1 mol L -1 e pH 6,0 para NaCl 0,01 mol L -1 . Após estes valores a atividade tendeu a diminuir devido provavelmente à formação do par NaHPO4 - . As análises químicas, raios-x e EED dos precipitados oriundos do estudo de hidrólise mostraram que os resultados de composição e raios-x são similares ao do composto H8, atestando novamente baixa porcentagem de liberação de P deste composto. Para o composto H14 verificou-se a formação de um novo composto, possivelmente estrengita amorfa. Os dados obtidos neste estudo indicam que elevadas quantidades de P liberado de compostos do tipo Fe - K - P a solução não significam necessariamente elevada atividade. Os resultados confirmam que o composto H14 pode apresentar melhor eficiência agronômica do que o H8. / Water-insoluble P compounds, as of the type Fe-K-P, can be formed in totally acidulated phosphate fertilizers (TAPF). In superphosphates two of the most common are the Fe3KH8(PO4)6.6H2O (H8) and the Fe3KH14(PO4)8.4H2O (H14). High amounts of phosphate rock (PR) are discarded in order to produce APF with about 90% of P2O5 neutral ammonium citrate (NAC) soluble fraction in the available P fraction (NAC + H2O), as indicated by the brazilian fertilizer legislation. Previous experimental data have shown that TAPF do not necessarily need to always contain high water solubility. Studies have indicated that PR will be better utilized by accessing the agronomic performance of water-insoluble P impurities. To add information related to this topic H8 and H14 compounds were synthesized at laboratory conditions. The precipitates were exposed to elemental chemical analysis, x-ray, scanning electron microscope and energy-dispersive spectroscopy (EDS). All chemical plus instrumental analysis confirmed the correct precipitation of both compounds. A hydrolysis experiment was conducted using 0,01; 0,05 and 0,1 mol L -1 NaCl solution with pH ranging from 3 to 7.5. Sub samples of the H8, the H14 and a PR from Catalão were agitated with each solution until certain equilibrium was achieved. Solution pH was adjusted by adding NaOH or HCl. After equilibrium the solutions were filtered, the concentrations of P, Fe, K, S, Na and Cl determined and the software MINTEQ used to calculate the activity of the orthophosphate ions (H2PO4 - and HPO4 2- ). The precipitate remaining in the filter paper was also analyzed for the same elements and submitted to x-ray and EDS. The amounts of H8 and H14 synthesized were enough for the hydrolysis study. The results indicated that the amount of P released from both Fe-K-P compounds increased in higher solution pH. More P was released from the H14 than the H8 compound. Also, the activity for the orthophosphate ions was higher for the H14 than for the H8 compound. There was a trend to obtain higher activity of the ions orthophosphate with lower ionic strength for both compounds. For the H8 it was obtained higher activity as the solution pH increased when the ionic strength was of 0,01 mol L -1 NaCl. For the H14 the trend was for the activity to increase until pH 5 for the 0,05 and 0,1 mol L -1 NaCl solution and until pH 6 for the 0,01 mol L -1 . After these values the activity tended to decrease most likely due to the formation of the NaHPO4 - ionic par. The elemental chemical composition, x-ray and EDS of the precipitates after the hydrolysis study showed composition and x-ray results similar to the H8 compound attesting low hydrolysis in this situation. For the H14 compound it was found the formation of a new compound, most likely an amorphous strengite. Data obtained in this study indicate that higher amounts of P released from compounds of the type Fe-K-P as the solution pH increases does not necessarily mean higher activity. The results confirm that the H14 compound should be of higher agronomic effectiveness than the H8.

Neste trabalho estudamos as propriedades eletrônicas e as estabilidades estruturais do cristal de ZrO2 e dos defeitos de vacância de oxigênio e impureza substitucional de cério. As investigações foram efetuadas através de simulações computacionais baseadas em métodos de primeiros princípios dentro do formalismo da teoria do funcional da densidade e utilizando o método APW + lo (Aumengted Plane Waves plus local orbitals), implementado no código computacional WIEN2k, dentro do esquema de supercélula, com relaxações atômicas tratadas de modo apropriado. A zircônia apresenta 3 fases estruturais, dependendo da temperatura. Sua fase mais estável é a monoclínica e, a altas temperaturas, ela apresenta as fases tetragonal e cúbica, sendo estas duas últimas as mais importantes para aplicações tecnológicas. Ela pode ser estabilizada em uma condição metaestável em uma estrutura quase cúbica quando crescida na forma de pós nanocristalinos, com tamanhos menores que um certo tamanho crítico. Outra maneira de se estabilizar as estruturas cúbica e tetragonal, a temperatura ambiente, é através da adição de dopantes, entre eles o cério. Nesses casos, estão sempre presentes vacâncias de oxigênio. Neste trabalho, para o cristal puro de ZrO2, foram calculadas as propriedades das estruturas cristalinas cúbica e tetragonal, constatando-se que a estrutura quase cúbica, proposta em várias investigações relatadas na literatura, pode ser interpretada como uma estrutura tetragonal de corpo centrado, com pequenos deslocamentos dos átomos de oxigênio na direção k . Destes resultados, propomos que nas análises dos dados experimentais obtidos por difração de raios-X e EXAFS (Extended X-ray Absorption Fine Structure) sejam utilizadas simulações onde a estrutura tetragonal de corpo centrado seja considerada como uma possível estrutura para o cristal. Dos estudos da vacância de oxigênio, obtivemos que sua presença quebra a simetria local do sistema e faz com que existam três diferentes distâncias entre um átomo de Zr e os átomos primeiros vizinhos de oxigênio, podendo, também, explicar resultados experimentais de difração de raios-X e EXAFS. Para o centro de impureza substitucional de Ce no sítio do átomo de Zr, nossos resultados apresentam uma possível explicação de porque as impurezas de Ce, em diferentes concentrações, estabilizam o ZrO2 nas estruturas tetragonal e cúbica. / In this investigation we studied the electronic properties and the structural stabilities of zirconia (ZrO2), as well as oxygen vacancy and Ce substitutional impurity. The investigations were carried by computational simulations using ab initio methods, based on the density functional theory and the APW + lo (Aumengted Plane Waves plus local orbitals) method, as implemented in the WIEN2k code, considering the supercell approach and atomic relaxations. Concerning the ZrO2 bulk, the tetragonal (quasi-cubic) phase is not thermodynamically stable at room temperature, but it can be retained in a metastable condition in nanocrystalline powders with crystallite sizes smaller than a certain critical size, or throught addition of dopants, for example cerium. In this cases, oxygen vacancies are always present. In this work we have obtained the properties of the cubic and tetragonal phases of ZrO2. From the results, we propose that the quasi-cubic structure presented in many articles can be understood as a body centered tetragonal structure, with small oxygen atoms displacement perpendicular to the k direction. Those results suggest that the analysis of the X-ray and EXAFS (Extended X-ray Absorption Fine Structure) data should include in the crystallographic model the body-center tetragonal structure. The results of the structural and electronic properties of the oxygen vacancy suggest that its presence could explain the different models of the Zr first neighbor oxygen shell. For the Ce substitutional impurity, our results present a possible explanation why these impurities, in several concentrations, are able to stabilize the ZrO2 in the tetragonal and cubic phases.