Made available in DSpace on 2015-03-03T15:15:28Z (GMT). No. of bitstreams: 1 RodolfoBS_DISSERT.pdf: 2972614 bytes, checksum: 2be8de04b2ac1f09c7c087cfcd17803d (MD5) Previous issue date: 2010-09-10 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Samples of lanthanum Ortoferrites doped with strontium were synthesized in a single phase by the sol-gel method. Two samples were prepared, one by varying the concentration of strontium in lanthanum ortoferrites La1?xSrxFeO3?? with (0 ? x ? 0.5), and another batch of samples of type, La1/3Sr2/3FeO3??, now varying only the temperature of calcination. Our samples were obtained by Pechini method and sintered in air and oxygen atmospheric. Their crystal structures were determined by x-ray diraction (XRD), scanning electron microscopy (SEM), where we observed that the samples (0 ? x ? 0.3) have orthorhombic symmetry and the volume of the single cell decreases with the increasing of concentration of strontium. For x = 0.5 it is only observed the simple phase when that is sintered in O2 atmospheric. Their magnetic characteristics were obtained by the M?ssbauer spectroscopy and magnetic measurements. The magnetization measurements for samples La1?xSrxFeO3?? with (0 ? x ? 0.5) revealed that the magnetization decreases with increasing concentration of strontium, but for the sample x = 0.4 the magnetization shows a high coercive field and a ferrimagnetic behavior, which is attributed to a small amount of strontium hexaferrite. As for the samples La1/3Sr2/3FeO3?? calcined between 800 oC e 1200 oC. The hysteresis curves revealed two distinct behaviors: an declined antiferromagnetic behavior (Canted) for samples calcined between 800 oC and 1000 oC and a paramagnetic behavior for the samples calcined at 1100 oC e 1200 o C. Thermal hysteresis and sharp peaks around the N?el temperature (TN), over the curves of specific heat as a function of temperature was only observed in calcined samples with 1100 oC and 1200 oC. This eect is attributed to the charge ordering. These results indicate that the charge ordering occurs only in the samples without oxygen deficiency. Magnetic measurements as a function of temperature are also in agreement with this interpretation / ?Amostras de ortoferritas de lant?nio dopados com estr?ncio foram sintetizados na forma de fase simples pelo m?todo Sol-Gel. Dois lotes de amostras foram preparadas, um variando a concentra??o do estr?ncio nas ortoferritas de lant?nio La1?xSrxFeO3?? com (0 ? x ? 0.5), e um outro lote de amostras do tipo La1/3Sr2/3FeO3??, agora variando somente a temperatura de calcina??o. Nossas amostras foram obtidas pelo m?todo Pechini, e sinterizados em atmosfera de oxig?nio. Suas estruturas cristalinas foram determinadas por difratometria de raios -x (DRX), microscopia eletr?nica de varredura (MEV), onde observamos que as amostras (0 ? x ? 0.3) possuem simetria ortorr?mbica, e o volume da c?lula unit?ria diminui com o aumento da concentra??o de estr?ncio. Para x=0.5 somente ? observada fase simples quando esta ? sinterizada na atmosfera de O2. Suas caracter?sticas magn?ticas foram obtidas por meio de espectroscopia M?ossbauer e medidas de magnetiza??o. As medidas de magnetiza??o para as amostras La1?xSrxFeO3?? com (0 ? x ? 0.5) revelaram que a magnetiza ??o decresce com o aumento da concentra??o de estr?ncio, contudo para a amostra x=0.4 a magnetiza??o mostra um alto campo coercivo e um comportamento ferrimagn?tico, o qual ? atribuido a uma pequana quantidade de Hexaferrita de estr?ncio. J? para as amostras La1/3Sr2/3FeO3??, calcinadas entre 800 oC e 1200 oC , as curvas de histerese revelaram dois comportamentos distintos: Um comportamento antiferromagn?tico declinado (Canted) para as amostras calcinadas entre 800 oC e 1000 oC e um comportamento paramagn?tico para as amostras calcinadas em 1100 oC e 1200 o C. Histereses t?rmicas e picos acentuados em torno da temperatura de N?el (TN), sobre as curvas de calor espec? co em fun??o da temperatura foi observada apenas nas amostras calcinadas com 1100 oC e 1200 oC . Este efeito ? atribuido ao ordenameto de carga. Estes resultados indicam que o ordenamento de carga ocorre somente nas amostras sem de ci?ncia de oxig?nio. Medidas de Magnetiza??o em fun??o da temperatura tamb?m est?o de acordo com esta interpreta??o.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2018-03-12T13:04:19Z No. of bitstreams: 1 RafaelChavesLima_DISSERT.pdf: 15500276 bytes, checksum: 4f1a759afd6ed9c7eeb174d02f229d3e (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2018-03-13T20:23:09Z (GMT) No. of bitstreams: 1 RafaelChavesLima_DISSERT.pdf: 15500276 bytes, checksum: 4f1a759afd6ed9c7eeb174d02f229d3e (MD5) / Made available in DSpace on 2018-03-13T20:23:09Z (GMT). No. of bitstreams: 1 RafaelChavesLima_DISSERT.pdf: 15500276 bytes, checksum: 4f1a759afd6ed9c7eeb174d02f229d3e (MD5) Previous issue date: 2018-01-30 / O Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico - CNPq / A assimila??o do modo como uma ze?lita ? formada partindo de um sistema amorfo e o controle sobre tamanho e morfologia dos produtos de s?ntese s?o aspectos fundamentais para a ?engenharia zeol?tica?. Um sistema para a s?ntese da ze?lita mordenita foi estudado, o qual possibilitou a obten??o de fase MOR sem indica??o da presen?a de qualquer outra fase. Foram realizadas varia??es nos par?metros: condi??o de tratamento t?rmico, temperatura, tempo, dilui??o do gel, teor e grau de pureza da ?gua, teor de s?dio, envelhecimento e tipo de s?lica, visando o estabelecimento da rela??o entre o tamanho e a morfologia dos produtos de s?ntese com as modifica??es efetuadas. A temperatura de cristaliza??o mostrou ser um fator primordial com rela??o ao tamanho de part?culas e cristalitos. A dilui??o do gel de s?ntese (50% m/m) proporcionou uma redu??o na agrega??o dos cristalitos e a varia??o do teor de ?gua na s?ntese implicou em mudan?as nas taxas de zeolitiza??o. O teor de s?dio modificou o crescimento dos cristais e o aumento de intercrescimentos e agrega??es de part?culas. Mudan?as na fonte de s?lica incrementaram a taxa de crescimento dos cristais e contribuiram para altera??es no tamanho dos mesmos. Cristais maiores foram obtidos a partir de sistemas com maior concentra??o de c?tions s?dio enquanto agregados de nanocristalitos. Agregados de pequenos cristalitos de mordenita pura de at? cerca de 50 nm foram obtidos com s?nteses realizadas a 150 ?C e com a dilui??o do gel j? preparado. Menores teores de s?dio e ?gua e o uso de fontes de s?lica de maior ?rea espec?fica (relativa a este tipo de material) tamb?m tendem ? resultar em menores cristalitos. Condi??es opostas viabilizaram o maior crescimento, gerando cristais de at? 1 ?m em m?dia. Os resultados mostraram que ? poss?vel exercer algum controle sobre o tamanho de part?cula e de cristalitos da ze?lita mordenita atrav?s do ajuste de par?metros inerentes ao sistema convencional de s?ntese. / The assimilation of the way a zeolite is formed from an amorphous system and the control over size and morphology of the synthesis products are fundamental aspects for "zeolitic engineering". A system for the synthesis of the mordenite zeolite was studied, which made it possible to obtain MOR phase without indicating the presence of any other phase. Variations were made in the parameters: thermal treatment condition, temperature, time, gel dilution, water content and degree of purity, sodium content, aging and type of silica, aiming to establish the relationship between product size and morphology with the modifications made. The crystallization temperature showed to be a prime factor with respect to particle size and crystallites. Dilution of the synthesis gel (50% w / w) provided a reduction in the crystallite aggregation and the variation of the water content in the synthesis implied changes in zeolitization rates. The sodium content modified the growth of the crystals and the increase of intergrowths and aggregations of particles. Changes in the silica source increased the growth rate of the crystals and contributed to changes in their size. Larger crystals were obtained from systems with higher concentrations of sodium cations as nanocrystallite aggregates. Aggregates of small pure mordenite crystallites of up to about 50 nm were obtained with syntheses performed at 150 ? C and with the dilution of the already prepared gel. Lower sodium and water content and the use of silica sources with a greater specific area (relative to this type of material) also tend to result in smaller crystallites. Opposite conditions enabled the highest growth, generating crystals up to 1 ?m on average. The results showed that it is possible to exert some control over the particle size and crystallites of the mordenite zeolite by adjusting parameters inherent to the conventional synthesis system.

Made available in DSpace on 2014-12-17T15:42:31Z (GMT). No. of bitstreams: 1 BrunaVL_TESE.pdf: 4965695 bytes, checksum: f511eb063b5cd567f364bc0ec9385727 (MD5) Previous issue date: 2014-05-28 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Sustainable development is a major challenge in the oil industry and has aroused growing interest in research to obtain materials from renewable sources. Carboxymethylcellulose (CMC) is a polysaccharide derived from cellulose and becomes attractive because it is water-soluble, renewable, biodegradable and inexpensive, as well as may be chemically modified to gain new properties. Among the derivatives of carboxymethylcellulose, systems have been developed to induce stimuli-responsive properties and extend the applicability of multiple-responsive materials. Although these new materials have been the subject of study, understanding of their physicochemical properties, such as viscosity, solubility and particle size as a function of pH and temperature, is still very limited. This study describes systems of physical blends and copolymers based on carboxymethylcellulose and poly (N-isopropylacrylamide) (PNIPAM), with different feed percentage compositions of the reaction (25CMC, 50CMC e 75CMC), in aqueous solution. The chemical structure of the polymers was investigated by infrared and CHN elementary analysis. The physical blends were analyzed by rheology and the copolymers by UV-visible spectroscopy, small-angle X-ray scattering (SAXS), dynamic light scattering (DLS) and zeta potential. CMC and copolymer were assessed as scale inhibitors of calcium carbonate (CaCO3) using dynamic tube blocking tests and chemical compatibility tests, as well as scanning electron microscopy (SEM). Thermothickening behavior was observed for the 50 % CMC_50 % PNIPAM and 25 % CMC_75 % PNIPAM physical blends in aqueous solution at concentrations of 6 and 2 g/L, respectively, depending on polymer concentration and composition. For the copolymers, the increase in temperature and amount of PNIPAM favored polymer-polymer interactions through hydrophobic groups, resulting in increased turbidity of polymer solutions. Particle size decreased with the rise in copolymer PNIPAM content as a function of pH (3-12), at 25 ?C. Larger amounts of CMC result in a stronger effect of pH on particle size, indicating pH-responsive behavior. Thus, 25CMC was not affected by the change in pH, exhibiting similar behavior to PNIPAM. In addition, the presence of acidic or basic additives influenced particle size, which was smaller in the presence of the additives than in distilled water. The results of zeta potential also showed greater variation for polymers in distilled water than in the presence of acids and bases. The lower critical solution temperature (LCST) of PNIPAM determined by DLS corroborated the value obtained by UV-visible spectroscopy. SAXS data for PNIPAM and 50CMC indicated phase transition when the temperature increased from 32 to 34 ?C. A reduction in or absence of electrostatic properties was observed as a function of increased PNIPAM in copolymer composition. Assessment of samples as scale inhibitors showed that CMC performed better than the copolymers. This was attributed to the higher charge density present in CMC. The SEM micrographs confirmed morphological changes in the CaCO3 crystals, demonstrating the scale inhibiting potential of these polymers / O desenvolvimento sustent?vel ? um dos principais desafios da ind?stria do petr?leo, que tem despertado crescente interesse por pesquisas para obten??o de novos materiais provenientes de fontes renov?veis. A carboximetilcelulose (CMC) ? um polissacar?deo derivado da celulose, que se destaca por ser sol?vel em ?gua, renov?vel, biodegrad?vel, de baixo custo e por apresentar possibilidades de modifica??es em sua estrutura qu?mica. Dentre os derivados de carboximetilcelulose, alguns sistemas t?m sido desenvolvidos para induzir propriedades est?mulos-responsivos e ampliar a aplicabilidade desses materiais multirresponsivos. Embora esses novos materiais sejam atualmente objeto de estudo, a compreens?o de suas propriedades f?sico-qu?micas, tais como viscosidade, solubilidade e tamanho de part?culas em fun??o do pH e temperatura ainda ? muito limitada. Esta tese descreve sistemas de misturas f?sicas e copol?meros ? base de carboximetilcelulose e poli (Nisopropilacrilamida) (PNIPAM) com diferentes composi??es percentuais de alimenta??o reacional (25CMC, 50CMC e 75CMC), em solu??o aquosa. A estrutura qu?mica dos pol?meros foi investigada por infravermelho e an?lise elementar CHN. As misturas f?sicas foram analisadas por reologia e os copol?meros foram analisados por UV-vis?vel, espalhamento de raios-X a baixos ?ngulos (SAXS), espalhamento de luz din?mico (DLS) e potencial zeta. CMC e copol?mero foram avaliados como inibidores de incrusta??o de carbonato de c?lcio (CaCO3) usando os testes de compatibilidade qu?mica e precipita??o din?mica em capilar, assim como a microscopia eletr?nica de varredura (MEV). As misturas f?sicas 50% CMC_50% PNIPAM e 25% CMC_75% PNIPAM em solu??o aquosa, nas concentra??es de 6 e 2 g/L, respectivamente, apresentaram comportamento termoviscosificante dependente da concentra??o de pol?mero e da composi??o. Para os copol?meros, o aumento da quantidade de PNIPAM e da temperatura favoreceu as intera??es pol?mero-pol?mero atrav?s dos grupos hidrof?bicos, resultando no aumento da turbidez das solu??es polim?ricas. O tamanho das part?culas diminuiu com o aumento do teor de PNIPAM na composi??o dos copol?meros em fun??o do pH (3-12), a 25 ?C. Maiores quantidades de CMC resultaram em um efeito mais forte do pH nos tamanhos das part?culas, exibindo um comportamento pH-responsivo. Assim, 25CMC n?o foi afetada pela mudan?a de pH, apresentando comportamento similar a PNIPAM. Al?m disso, a presen?a de aditivos de car?ter ?cido ou b?sico influenciou no tamanho das part?culas, que foram menores na presen?a desses aditivos do que em ?gua destilada. Os resultados de potencial zeta tamb?m sofreram maior varia??o para os pol?meros em ?gua destilada do que na presen?a de ?cidos e bases. A temperatura consoluta inferior (LCST) da PNIPAM determinada por DLS foi concordante com o valor obtido por UV-visible. Os dados de SAXS mostraram para PNIPAM e 50CMC uma transi??o de fase quando a temperatura aumentou de 32 para 34 ?C. Um aumento do car?ter polieletrol?tico foi observado em fun??o do aumento da CMC na composi??o dos copol?meros. A avalia??o das amostras como inibidores de incrusta??o mostrou que a CMC apresenta um melhor desempenho do que o copol?mero. Isto foi atribu?do a maior densidade de cargas presente na CMC. As micrografias do MEV confirmaram mudan?as morfol?gicas dos cristais de CaCO3, indicando o potencial desses pol?meros para inibi??o de incrusta??o