Resumo em Inglês:

ABSTRACT The effects of small additions of tin, zinc, calcium and boron oxides on phase composition and electrical conductivity of zirconia-10 mol% scandia were investigated. Compounds containing 1 mol% zinc, tin and calcium oxides and 1, 3 and 5 wt.% boron oxide were prepared by solid state reaction and characterized by X-ray diffraction, density measurements, scanning electron microscopy and impedance spectroscopy. Full stabilization of the cubic structure at room temperature was obtained with additions of 1 mol% calcium oxide and 2 wt.% boron oxide. Partially stabilized compounds exhibit herringbone structure, characteristic of the β-rhombohedric phase. Specimens with calcium as additive show total conductivity of 23.8 mS.cm-1 at 750ºC with activation energy of 1.13 eV. Liquid phase sintering by boron oxide addition is effective to enhance the densification of the solid electrolyte.

Resumo em Português:

RESUMO Este trabalho aborda a caracterização das propriedades físicas, químicas e mecânicas da escória de aciaria para emprego como agregado antes e após ensaio de lixiviação controlada em extrator Soxhlet. O material foi caracterizado antes de passar por processo de estabilização (escória virgem) e após lixiviação controlada em períodos distintos de 24, 56, 96, 120 horas. A escória foi submetida, em laboratório, a uma simulação de precipitação em equipamento Soxhlet visando avaliar suas propriedades físicas, químicas e mecânicas após cada período. O estudo do processo de lixiviação em escória de aciaria buscou compreender a influência do processo de lavagem no comportamento da escória. A caracterização física se deu por meio dos ensaios tradicionais de agregados graúdos, a caracterização química através dos ensaios de Microscopia Eletrônica por Varredura (MEV) completada pela análise de Espectroscopia de Energia Dispersiva (EDS) e Difração de Raio-X, a caracterização mecânica por meio de ensaios de expansão normatizado e adaptado. A amostra virgem, sem receber processo de estabilização por lixiviação controlada, apresentou resultados satisfatórios na caracterização física quando comparada a agregados convencionais, a caracterização química comprovou ser uma escória de aciaria com elevados teores de CaO, MgO e FeO, enquanto a caracterização mecânica demonstrou que, apesar do grau de expansibilidade da escória ser baixo pelos padrões atuais, este não deve ser desconsiderado em obras para pavimentação. Após lixiviação controlada a escória não apresentou perda significativa de suas propriedades físicas. Quanto aos ensaios mecânicos de expansão houve redução no potencial de expansibilidade após os períodos de lixiviação. Conclui-se que o processo de lixiviação em extrator Soxhlet é de importância no estudo das propriedades da escória de aciaria, uma vez que contemplando vários dias de lixiviação houve redução do potencial de expansão, característica limitante no uso da escória de aciaria em pavimentação.

Resumo em Inglês:

ABSTRACT This work addresses the characterization of physical, chemical and mechanical properties of steel slag as an alternative aggregation before and after leaching testing controlled Soxhlet extractor. The material it was characterized before going through the natural leaching process and after controlled leaching in different periods of 24, 56, 96, 120 hours. The steel slag was subjected in the laboratory to simulate the precipitation in Soxhlet equipment to evaluate its physical, chemical and mechanical properties after each period described. The study of the process of leaching in steel slag searched to understand the influence of the washing process in a slag behavior in such a process. The physical characterization occurred through traditional testing of coarse aggregates, the chemical characterization through the testing of Scanning Eletron Microscopy (SEM) completed by Dispersive Spectroscopy Energy (DSE) and X- ray diffraction and the mechanical characterization through testing of standardized expansion and adapted. The sample virgin, without receiving process of stabilization by controlled leaching, showed satisfactory results in the physics characterization when compared to conventional aggregates, the chemical characterization proved to be a steel slag with high contents of CaO, MgO and FeO, the mechanical characterization demonstrated that, although the degree of expansibility of the slag is low demonstrated that this should not be disregarded in the paving work. After controlled leaching the steel slag showed no significant loss of its physical properties. As the mechanical testing of expansion had decreased the potential of expansibility after leaching periods. It is concluded that the leaching process in a Soxhlet extractor is of importance in the study the properties of steel slag, once covering several days of leaching was reduced potential for expansion, limiting feature in the use of steel slag for paving.

Resumo em Inglês:

ABSTRACT Nanotechnology can significantly improve the mechanical strength and durability of concrete. At the nanoscale, good dispersion of constituent materials is an essential factor for the improvement of concrete properties. In this scenario, the objective of this research was to evaluate the mechanical properties of high performance concrete containing stabilized nano-silica. The incorporation of nano-silica to the polycarboxylate chemical admixture allowed its application in concrete, since the nano-silica was evenly dispersed in the concrete mass. For this study, three different concretes were employed: a reference concrete, one containing stabilized nano-silica and another containing a mixture of silica fume and stabilized nano-silica. The evaluated concrete mechanical properties were the axial compressive strength and secant modulus of elasticity measured in three different ages. The results indicated a substantial increase in concrete compressive strength and modulus of elasticity with the addition of stabilized nano-silica combined with a reduction in cement content. The results also showed that use of stabilized nano-silica proved to be very advantageous, especially when mixed with silica fume. When they were combined, a synergy effect occurred in the concrete that was of chemical nature in addition to the physical effect of better concrete particle packaging. Analysis by scanning electron microscopy showed the improvement in microstructure of concretes with stabilized nano-silica, which contributed to gains in mechanical properties.

Resumo em Português:

RESUMO Membranas podem ser consideradas películas poliméricas ou inorgânicas que funcionam como uma barreira semipermeável para uma filtração em escala molecular, separando duas fases e restringindo, total ou parcialmente, o transporte de uma ou várias espécies químicas (solutos) presentes na solução. Portanto, o objetivo deste trabalho é produzir membranas de poliétersulfona (PES) e poliétersulfona / argila pela técnica de inversão de fase e avaliar a presença de argila na obtenção de membranas para o tratamento de efluentes líquidos. O solvente utilizado foi a dimetilformamida (DMF) e argilas utilizadas foram Brasgel PA (MMT) e Cloisite Na (CL Na) nas proporções de 3 a 5% (em peso). Por difração de raios-X (DRX), as membranas com 3% das argilas MMT e CL Na aparentemente apresentaram estruturas parcialmente esfoliadas; para a composição com 5% de CL Na observou-se um pequeno pico, que indica que esta é, possivelmente, uma estrutura intercalada ou microcompósito. A partir dos resultados de microscopia eletrônica de varredura (MEV), visualizou-se que a superfície da membrana de PES puro apresentou uma estrutura aparentemente sem poros, no aumento utilizado e, uma superfície sem rugosidade quando comparada com às membranas com argila. As medidas de ângulo de contato indicaram que a inclusão da argila alterou a capacidade de molhamento das membranas. O fluxo com água destilada para todas as membranas iniciou alto e ao longo do tempo chegou a um patamar de estabilização. Assim, pôde-se concluir que a presença e o teor de argila alteraram a morfologia da membrana, contribuindo para um aumento do fluxo de água.

Resumo em Inglês:

ABSTRACT Membranes can be considered polymeric or inorganic films that function as a semipermeable barrier to filtration on a molecular scale, separating two phases and restricting, totally or partially, the transportation of one or more chemical species (solute) present in the solution. Therefore, the aim of this work is to produce polyethersulfone membranes (PES) and polyethersulfone/clay by phase inversion technique and evaluate the presence of clay in obtaining membranes for wastewater treatment. The used solvent was dimethylformamide (DMF) and clays were Brasgel PA (MMT) and Cloisite Na (CL Na) in the proportion of 3 to 5% (wt.). By X-ray diffraction (XRD), the membranes with 3% of MMT and CL Na clays apparently had partially exfoliated structures. For the composition with 5% of CL Na a small peak was observed, which indicates that this is possibly an intercalated structure or microcomposite. By scanning electron microscopy (SEM), visualizes that the pure suface of the pure PES membrane a structure apparently without pores was observed in the used magnification and without roughness surface when compared to membranes with clay. The measurements of contact angle indicated that the inclusion of clay altered the wetting ability of the membranes. The flow with distilled water for all membranes started high and over time reached a stabilization level. Thus, it can be concluded that the presence and the content of clay altered the morphology of the membrane, contributing to an increase in water flow.

Resumo em Português:

RESUMO A nitretação por plasma é um tratamento termoquímico que modifica as propriedades superficiais de um determinado material. Este processo aplicado em aços ferramenta resulta no aumento da dureza da superfície através da formação da zona de difusão pelo controle das variáveis de tratamento, tais como a temperatura, composição química da atmosfera de trabalho e tempo de tratamento. Neste trabalho discute-se um procedimento alternativo para o tratamento térmico de revenimento. O qual possibilita a redução nos custos de fabricação, diminuição no consumo de energia e no tempo de confecção das ferramentas. Amostras de aço ferramenta VF 800 AT foram temperadas e revenidas (três vezes) pelo tratamento térmico convencional com posterior nitretação por plasma. Em cinco outros grupos de amostras realizou-se o revenimento concomitantemente ao tratamento de nitretação. A superfície e o núcleo das amostras foram caracterizados por difração de raios x, microscopia ótica, microscopia eletrônica de varredura, microdureza Vickers e dureza Rockwell C. Os resultados mostram que o gradiente térmico entre a superfície e o núcleo das amostras afeta a microestrutura, a dureza e as fases obtidas durante o tratamento térmico de revenimento simultâneo à nitretação. Entretanto, quando dois revenimentos são realizados em forno tipo Mufla e o último tratamento ocorre simultaneamente à nitretação, obtêm-se microestruturas, fases, dureza e microdureza semelhantes ao ciclo de tratamento térmico convencional com posterior nitretação por plasma.

Resumo em Inglês:

ABSTRACT Plasma nitriding of tool steels improves the surface hardness due to formation of diffusion zone and/or compound layer. The process parameters such as temperature, gas composition and dwell time, allow us to control the layer thickness, the microstructure, the crystalline phases and the type of layer (for example white layer or diffusion zone). This paper discusses an alternative procedure for the heat treatment of tempering and surface treatment, both in plasma or combining conventional heat treatment with subsequent plasma nitriding. Carring out both treatments in plasma could enable reduction in manufacturing costs, lower energy consumption and less time for tools manufacturing. Samples of VF800AT steel were treated and characterized (at surface and core of samples) through the following technique: X-ray diffraction, optical microscopy, scanning electron microscopy, micro-hardness profile and Rockwell C measurement. Temperature measurements during the plasma treatment, show that arise thermal gradient between the surface and the core of the samples. In this work, it was observed that the surface was up to 7% hotter than the core of sample, during the plasma treatment with temperature of magnitude about 5 x 102 °C. This thermal gradient seems inherent to the plasma process, so that it can produce different microstructure, hardness and crystalline phases between core and edge of samples. However, when two tempering operations are prior carried out in a muffle furnace and the third tempering treatment is subsequently carried out simultaneously with the plasma nitriding, it is observed that the microstructure, the crystalline phases, hardness and micro hardness (in both, edge and core) are similar to treatments done in conventional mode cycle (in muffle furnace) with subsequent plasma nitriding.

Resumo em Português:

RESUMO O ponto de carga zero é uma característica eletrocinética relacionada aos materiais anfóteros, como as fibras proteicas, cuja determinação e conhecimento é crucial para os processos de tingimento e acabamento das mesmas. Esta característica influencia na adsorção do corante do tipo ácido, principal classe de corante aplicado no tingimento das fibras de seda e lã. Durante o tingimento a carga iônica das fibras proteicas é dependente do pH do banho em que se encontram. No pH correspondente ao ponto de carga zero (pHPCZ), a fibra proteica possui carga neutra. Quando em presença de um banho cujo pH é inferior ao pHPCZ, a fibra fica carregada positivamente e pode, dessa forma, formar ligações iônicas com as moléculas de corante que estão carregados negativamente. Neste artigo, o pH correspondente ao ponto de carga zero foi determinado por um método denominando “experimento dos 11 pontos”. Este método necessita de um aparato experimental mais simples e acessível do que os métodos utilizados na determinação do ponto isoelétrico, uma outra característica eletrocinética correlata dos materiais anfóteros. Para a fibra de seda e lã, foram encontrados pHPCZ iguais a 3,8 e 6,3 respectivamente. Tingimentos com corante ácido foram realizados com valores de pH acima e abaixo do pHPCZ. As amostras tingidas em pH menor que o pHPCZ, apresentaram maior intensidade colorística, evidenciando a formação de ligações iônicas entre corante e fibra. Já as amostras tingidas em pH maior que o pHPCZ, pelo contrário, resultaram em menor intensidade colorística. Estes resultados comprovam a importância de se conhecer o ponto de carga zero das fibras proteicas e assim, determinar o melhor pH de tingimento das mesmas.

Resumo em Inglês:

ABSTRACT The point of zero charge is an electrokinetic characteristic related to amphoteric materials such as protein fibers, whose determination and knowledge is crucial for the dyeing and finishing processes of the same. This characteristic influences the adsorption of acid type dye, main dye class applied in dyeing of silk and wool fibers. During the dyeing the ionic charge of the protein fibers is dependent of the pH of the bath in which they are. In the pH corresponding to the point of zero charge (pHPZC), protein fiber has a neutral charge. When in the presence of a bath whose pH is lower than pHPZC, the fiber is positively charged and can thus form ionic bonds with the dye molecules that are negatively charged. In this article, the pH corresponding to the point of zero charge was determined by a calling method "experiment of 11 points". This method requires a simpler experimental apparatus and accessible than the methods used in determining the isoelectric point, another related electrokinetic characteristic of amphoteric materials. For silk fiber and wool were found pHPZC equal to 3.8 and 6.3 respectively. Dyeing with acid dye were carried out at pH values above and below the pHPZC. The samples dyed at pH lower than pHPZC showed higher color strength indicating the formation of ionic bonds between dye and fiber. The dyed samples at pH greater than pHPZC, on the contrary, resulted in lower color strength. These results demonstrate the importance of knowing the point of zero charge of protein fibers and thus determine the best dyeing pH of the same.

Resumo em Inglês:

ABSTRACT The Amazon has a great potential of natural resources. There is a wide diversity of plant specimens and many of them can be extracted and processed such as jute, sisal and mauve fibers. It is known that usualy small communities from Amazon build their boats using a rudimentary and ecologically incorrect method, which comes from brazilian natives. This method consists in cut of trees with large trunks, which are burned and scraped until they get the desired shape. This process is not viable due to the long time spent and also it is environmentally unacceptable nowadays. Considering these facts, it was created a project at UFPA aiming to evaluate the building viability of small boats adapted to the Amazon region. These boats have been made with composite material, polymeric resin reinforced with natural fiber fabric. Hence, this paper brings the first stage of this project, treating on the build of a small boat with reduced dimensions. This prototype was experimentally studied, using strain gages, and evaluated numerically by finite element method through the software ANSYS¨. This stage was very important to optimize the parameters used in the finite element model, which was employed to analyse the model with real dimensions. As a result, the numerical models showed a good compatibility with real tests. Additionally, the designed boat demonstrated to be able to hold the imposed loads.

Resumo em Inglês:

ABSTRACT The Ni- based superalloy Inconel 625 is extensively used owing to its high strength, excellent fabricability, good weldability and outstanding resistance to high temperature corrosion against aggressive environments. However, despite its unique properties and extensive use, its wear resistance is in some cases unsatisfactory. In this study, Inconel 625 was subjected to boriding treatments at different temperature and different durations. Microstructural characterization was made by conventional methods (scanning electron microscopy, optic microscopy, X-ray diffraction analysis) and mechanical characterization was made by microhardness and micro-abrasion wear test. Micro-abrasion wear tests were conducted against a AISI 52100 steel under 5, 7.5 and 10 N load in a 25 wt.% SiC slurry at room temperature. Microstructural results revealed that multi-phase boride layer (nickel boride, chrome boride and iron boride) and silicide layer were formed. The hardness and thickness of the boride layers were found to be 1175–2432 HV 0.1 and, 6.61 – 92.03 μm, respectively. Depending on the boriding temperature and time. In spite of silicide layer formation the wear resistance of borided Inconel 625 alloy increased up to 8 times thanks to the increase in the surface hardness which was caused by boriding process. The boriding treatment caused a transition in the wear mechanism. While grooving was observed in the untreated Inconel 625 samples, mixed (grooving and rolling) and rolling type wear was predominant in the borided samples.

Resumo em Português:

RESUMO Neste trabalho apresentam-se análises do problema bidimensional de placas compostas por materiais heterogêneos com acoplamento do MEC (Método dos Elementos de Contorno) e MEF (Método dos Elementos Finitos), através de uma abordagem multi-escala. O MEC é adotado para modelar o problema definido no macro-contínuo, que neste trabalho é dado pela análise não-linear do problema bidimensional de placas, enquanto o problema de equilíbrio na micro-escala (representada pelo Elemento de Volume Representativo - EVR) é resolvido pelo MEF. É importante notar, que na formulação não-linear do MEC é adotado o operador tangente consistente ao longo do processo iterativo, a fim de reduzir o esforço computacional, que é muito importante em uma análise multi-escala. Um EVR deve estar associado a cada ponto do macro-contínuo, onde se faz necessário conhecer as tensões e o tensor constitutivo a fim de solucionar o problema não-linear da placa. Para solucionar o problema de equilíbrio do EVR, devem-se impor ao mesmo, condições de contorno em termos de flutuações dos deslocamentos. Depois de resolver o problema de equilíbrio do EVR, a passagem do micro-contínuo para o macro-contínuo é feita adotando-se técnicas de homogeneização para os campos de tensões e do tensor constitutivo, que permitem calcular os respectivos valores homogeneizados para um ponto do macro-contínuo. Nos exemplos numéricos são definidos diferentes EVRs, os quais podem ter inclusões ou vazios no seu domínio, sendo cada fase modelada por modelos constitutivos próprios. Os resultados confirmam as potencialidades de aplicação da modelagem proposta.

Resumo em Inglês:

ABSTRACT A multi-scale modelling for analyzing the stretching problem of plates composed of heterogeneous materials using a coupling BEM (Boundary Element Method) and FEM (Finite Element Method) and a multiscale approach is presented. The BEM is adopted to model the macro-continuum problem (represented by the non-linear analysis of the stretching problem) while the equilibrium problem at micro-scale (represented by the Representative Volume Element - RVE) is solved by a FEM formulation. It is important to note that in the non-linear analysis of the stretching problem the consistent tangent operator has been considered along the iterative procedure, what is very important to reduce the computational effort. One RVE has to be assigned to every point of the macro-continuum where the stresses and constitutive tangent operator are required to solve the non-linear plate problem. To solve the RVE equilibrium problem, boundary conditions in terms of displacement fluctuations have to be imposed. After solving the equilibrium problem of the RVE the micro-to-macro transition can be made by applying homogenization techniques for the fields of stress and constitutive tensor in order to compute their homogenized values for a macro-continuum point. In the numerical examples, to define the material microstructure, different RVEs composed of inclusions or voids are considered, each one modeled by properly constitutive models. The results confirm the potentialities of the proposed modeling.

Resumo em Português:

RESUMO Os estudos na área da engenharia de superfícies recebem grande importância devido ao aprimoramento que as modificações superficiais fornecem aos materiais. Com um mercado global que tem a necessidade de proporcionar às peças e equipamentos maior vida útil com baixo custo, para suportar solicitações severas e assim manter seu alto desempenho, os tratamentos superficiais tornam o que se pensava impossível na realidade. Dentre os tratamentos superficiais que têm recebido atenção, e é objeto deste trabalho, temos o processo termoquímico de boretação. O processo de boretação consiste em saturar com boro a superfície de aços e ligas metálicas. Essa saturação fornece à superfície um incremento de propriedades não intrínsecas ao metal de base, tais como: dureza, resistência à abrasão e corrosão. Embora as propriedades dos aços boretados já tenham sido estudadas, os efeitos que o processo de boretação exerce nos aços durante ou posteriormente a processos de soldagem não são conhecidos. É objetivo deste trabalho avaliar a microestrutura e resposta mecânica de um aço de baixo carbono submetido ao tratamento de boretação pré e pós-soldagem GTAW. Os resultados apontaram uma má soldabilidade metalúrgica do aço de baixo teor de carbono com camada boretada, com a presença de trincas de solidificação. Já o aço soldado previamente à boretação apresentou um núcleo mais dúctil devido ao tratamento térmico submetido pós soldagem, porém com superfície de elevada dureza. Embora os valores de dureza do núcleo tenham caído drasticamente na zona soldada após este processo, a superfície destas amostras apresentou elevada dureza devido à camada boretada, o que pode ser considerado, principalmente em aplicações visando a resistência ao desgaste.

Resumo em Inglês:

ABSTRACT Studies on surface engineering area are given great importance due to the improvement that surface modifications provide to materials. With a global market that has the need to provide parts and equipment with extended service life and low cost, to support stringent requests and thus maintain its high performance, surface treatments may bring what was impossible into reality. Among the surface treatments that have received attention recently, we have the thermochemical process of boriding. The boriding process consists of saturate the surface of steels and metal alloys with boron. This saturation provides an increase in the surface properties not inherent to the base metal, such as hardness, resistance to abrasion and corrosion. Although the properties of boriding steels have already been studied, the effects that the boriding process perform on the steel during or after the welding processes are not known. Hence, it is the purpose of this study to evaluate the microstructure of a low carbon steel treated with boriding before and after GTAW welding. The results indicated poor metallurgical weldability of low carbon steel with boride layer, with the presence of solidification cracks. Nonetheless, the steel welded previous to boring treatment presented a more ductile nucleus, with harder surface. Although the values of hardness within the nucleus of the steel had dropped drastically at the welded zone after the boring, the surface of this steel showed higher values of hardness due to the boriding layer. This fact should be considered when applications where wear resistance is needed.

Resumo em Português:

RESUMO O objetivo deste trabalho foi investigar as propriedades térmicas, mecânicas e termo dinâmico mecânicas de compósitos de polietileno de alta densidade (PEAD) com a incorporação do pó de conchas de moluscos (5, 10 e 20% em peso). A matriz pura e seus compósitos foram misturados em um misturador interno e em seguida moldados por compressão. A incorporação do pó de concha de molusco diminuiu o índice de fluidez do PEAD em uma faixa de 23 a 53%, já a cristalinidade da matriz praticamente não foi alterada. O pó da concha possui 97, 53% de CaO, tendo estrutura cristalina constituída por aragonita e calcita, ambos polimorfos do carbonato de cálcio. O estudo granulométrico mostrou que o pó da concha apresentou uma distribuição larga do tamanho das partículas, sendo também confirmada na análise da superfície de fratura dos compósitos por microscopia eletrônica de varredura. Os aspectos morfológicos mostram que nenhuma adesão foi observada entre as partículas e o PEAD. A adição da concha causou um aumento na rigidez da matriz e como também diminui a capacidade de amortecimento da matriz. A adição de 10% deslocou a temperatura de transição vítrea (Tg) do PEAD em 6 oC , enquanto o compósito com 20% do pó de concha não apresentou essa transição.

Resumo em Inglês:

ABSTRACT This work deals with an investigation of thermal, mechanical and dynamic mechanical properties of composites of high density polyethylene(HDPE) with addition of mollusk shell powder (5, 10 and 20%wt). The pure matrix and its composites were first mixed in an internal mixer and then molded by compression. The mollusk shell powder incorporation decreased the melt index within a range of 23% to 53% whereas no relevant changes in crystallinity of matrix were observed. The shell powder was composed by 97.53% of CaO and its crystalline structure was constituted of calcite and aragonite, both polymorphs of calcium carbonate. The granulometric study showed a large distribution of particle size to the mollusk shell powder, which was also confirmed by the scanning electron microscopy (SEM) analysis of the fracture surface of the composites. The morphological aspects of the composites showed a poor adhesion between HDPE matrix and shell powder. The adding of filler increased the matrix rigidity and decreased its damping capacity. The incorporation of 10%wt mollusk shell powder shifted the glassy transition temperature (Tg) of the PEAD in 6 oC, while the composite with 20%wt did not show this transition temperature.

Resumo em Português:

RESUMO A cinética de crescimento da camada superficial cristalizada em um vidro de composição do sistema LZSA, 11,7Li2O·12,6ZrO2·68,6SiO2·7,1Al2O3 (% massa), foi estudada. Para a produção do vidro, utilizou-se matérias-primas comerciais (Li2CO3, ZrSiO4, SiO2, Al2O3), as quais foram homogeneizadas e fundidas a 1550 °C por 120 min e então vazadas em molde metálico. Amostras do vidro obtido foram seccionadas e submetidas a tratamentos térmicos em diferentes temperaturas (825–925 °C) e tempos (30–150 min) para formação e crescimento da camada cristalina. Seções transversais das amostras tratadas termicamente foram lixadas e polidas, tal que imagens das camadas cristalizadas pudessem ser visualizadas e medidas por microscopia. Os resultados mostraram que é possível obter vidros do sistema LZSA com camadas cristalizadas contendo principalmente espodumênio-β e silicatos de zircônio e lítio, de espessuras entre 13 e 665 µm, as quais crescem com velocidades entre 0,4 e 4,8 µm/min no intervalo de temperatura estudado.

Resumo em Inglês:

ABSTRACT Growth kinetics of crystallized surface layer in a LZSA glass composition, 11.7Li2O·12.6ZrO2·68.6SiO2·7.1Al2O3 (wt%), was studied. For the production of the LZSA glass, it was used commercial raw materials (Li2CO3, ZrSiO4, SiO2, Al2O3) which were mixed and melted at 1550 °C for 120 min and then poured into a metallic mold. Samples of the obtained glass were cut and subjected to heat-treatments at different temperatures (825 - 925 °C) and times (30 - 150 min) for formation and growth of crystalline layer. Cross-sections of the heat-treated samples were ground and polished such that images of the formed crystallized layers could be visualized and measured by microscopy. Results showed that it is possible to obtain LZSA glasses with crystallized layers formed by β-spodumene, zircon and lithium silicate, which present thicknesses between 13 and 665 µm and grow at rates varying from 0.4 to 4.8 µm/min in the studied temperature range.

Resumo em Português:

RESUMO O óxido de zircônio (ZrO2) policristalino parcialmente estabilizado com 3%mol de óxido de ítrio (Y2O3), ou 3Y-TZP, é usado como biomaterial nas restaurações protéticas odontológicas. Esta indicação possui limitação devido à coloração branca e alta opacidade da zircônia. Para melhorar a estética sem comprometer o desempenho funcional são adicionados outros óxidos à zircônia. Esta adição modifica a coloração da zircônia para tonalidades próximas a dos dentes naturais. Este trabalho avaliou o efeito da adição do Fe2O3 na microestrutura, nas propriedades mecânicas e nas propriedades ópticas da 3Y-TZP. Foram preparados cinco grupos de amostras com diferentes percentuais de Fe2O3. A caracterização química dos grupos foi realizada por fluorescência de raios-X (FRX). As propriedades mecânicas foram determinadas em ensaios de dureza e de resistência a flexão em quatro pontos. A análise quantitativa de transformação de fases foi realizada pelo método de Rietveld dos dados dos ensaios de difração de raios-X (DRX). O MEV foi usado para caracterizar a morfologia da superfície antes e após o ensaio de flexão. Os resultados mostraram que a adição do Fe2O3 influencia na transformação de fase, aumenta a dureza e a resistência à fratura por flexão quando sua concentração se encontra entre 0,02% e 0,17% do peso total. Acima dessa faixa de concentração, as amostras apresentaram perdas no desempenho mecânico. A adição de Fe2O3 não induziu mudanças significativas na densidade e no tamanho médio de grão.

Resumo em Inglês:

ABSTRACT The zirconium oxide (ZrO2) polycristaline partially stabilized by yttrium oxide (Y2O3) at 3mol%, 3Y-TZP, has its use been increased as a biomaterial. However, as dental prosthetics, its indication is still limited because of its white color and high opacity. Seeking improvements regarding aesthetics without compromising its functional performance, oxides such as iron oxide (Fe2O3) has been added to the microstructure of zirconia in order to provide a yellow-brownish color similar to natural teeth. This study evaluated the effect of adding Fe2O3 on the microstructure and mechanical and optical properties of 3Y-TZP. Five groups were investigated containing different concentrations of Fe2O3. Firstly, a chemical characterization of each group was carried out through X-ray fluorescence test (XRF). Microstructural characterization was performed by density and average grain size measurements. Mechanical properties were evaluated by performing hardness and four points flexural strength tests. Quantitative analysis of phase transformation was done using the Rietveld method, for each group submitted to the test of X-ray diffraction (XRD). Fractography by SEM analysis were also made on the fracture surface of the samples from tensile test. The results showed that the Fe2O3 addition influenced the phase transformation process, and proportionally increased the samples hardness and flexural strength when their concentrations varied from 0.02% to 0.17% of the total weight. Above this range, the samples showed losses in their mechanical performance. The Fe2O3 additions showed no significant changes in the density and average grain size of 3Y-TZP.

Resumo em Espanhol:

RESUMEN Este artículo tiene como objetivo presentar el análisis de falla de los bujes del tornillo de una extrusora utilizada para la fabricación de pinturas en polvo. Para esto se seleccionaron dos bujes, uno de la zona de transición y otro de la zona de dosificación. Se realizaron análisis de composición química y microestructural, ensayos de dureza y un análisis detallado de las superficies falladas mediante examen visual y microscopía electrónica de barrido. Los resultados mostraron que los bujes fueron fabricados en acero DIN 1.2316 con tratamiento térmico de recocido globular, endurecido superficialmente mediante nitruración, con espesores de recubrimiento entre 45 μm y 65 μm y durezas de recubrimiento superiores a los 1400 HV. El análisis de las superficies falladas indicó que el principal mecanismo de desgaste en los bujes es desgaste por fatiga de contacto, con la presencia de micropicaduras, macropicaduras y resquebrajamiento. Este tipo de desgaste se debe al contacto entre la superficie de los bujes y las partículas de alta dureza y abrasividad de la formulación, sumado a las altas presiones desarrolladas al interior del barril y los esfuerzos cíclicos cortantes que sufren los bujes. La presencia de otro tipo de desgastes como adhesión, corrosión y abrasión fue descartada.

Resumo em Inglês:

ABSTRACT This article aims to present the failure analysis of extruder screw bushings used for the manufacture of powder paint. Two bushings, one from the transition zone and one from the metering zone were selected to carry out the study. Chemical composition and microstructural analysis, hardness testing and a detailed analysis of the failed surfaces by visual examination and SEM were performed. The results showed that both bushings were made of steel DIN 1.2316 with a globular annealing heat treatment. Also, a nitride coating 45-65 μm thick with hardness greater than 1400 HV was identified. The analysis of the failed surfaces indicated that the main wear mechanism was contact fatigue wear, with the presence of micropitting, macropitting and cracking. This type of wear is due to the contact between the bushings surface and the high hardness abrasive particles of the paint formulation, added to the high pressures developed within the barrel and the cutting cyclic stresses that the bushings have to withstand. The presence of other wear mechanism like adhesion, corrosion and abrasion was discarded.

Resumo em Português:

RESUMO Zeólitas naturais são materiais adsorventes eficientes e com baixo custo para remoção de metais pesados em relação aos métodos convencionais. Este trabalho teve como objetivo avaliar o efeito do pH na capacidade máxima de remoção de cobre (Cu+2) por zeólita natural disponível na região do planalto catarinense (zeólita basalto - ZB) comparando sua eficiência com uma zeólita comercial importada de cuba (ZC). A capacidade de troca de cátions das zeólitas foi determinada pelo método de saturação por amônio. A densidade de partículas foi feita através do método do balão volumétrico. O efeito do pH na remoção foi avaliado a pH 3,0; 4,0 e 5,0 (±0,2) e concentrações iniciais de 10 mg L−1 e 180 mg L−1. A capacidade máxima de remoção de Cu+2 foi avaliada em pH 3,0; 4,0 e 5,0 e concentrações iniciais de 10, 30, 60, 90, 180 e 270 mg L−1. A quantificação do teor de Cu+2 foi realizada por espectrofotometria de absorção atômica com sistema de atomização por chama do tipo ar-acetileno. Para a construção das isotermas foi utilizado regressão polinomial e no teste de médias da porcentagem removida de Cu+2 em diferentes valores de pH foi utilizado Scott-Knott a 5% de significância. A ZC apresentou capacidade de troca de cátions 40% superior a ZB, porém isso não se refletiu na capacidade de remoção. Houve efeito do pH somente para ZC na menor concentração adicionada. A capacidade máxima de remoção foi de 2662 mg kg−1 para ZB e 2759 mg kg−1 para ZC em pH 5,0. A capacidade máxima de remoção de Cu+2 para ZB é semelhante ao da ZC. A ZB pode ser utilizada na remoção de metais em efluentes industriais e laboratoriais com baixo custo.

Resumo em Inglês:

ABSTRACT Natural zeolites are effective adsorbent materials and low cost for removal of heavy metals compared to conventional methods. This study aimed to evaluate the effect of pH and the maximum capacity removal of copper (Cu+2) by natural zeolite available in the region of Southern Brazil (zeolite basalt - ZB) comparing its perfomance with a commercial zeolite imported from Cuba (ZC). The cation exchange capacity of the zeolites was determined by Ammonium saturation method. The particle density was taken by volumetric flask method. The effect of pH on removal was measured at pH 3.0, 4.0 and 5.0 (± 0.2) and initial concentrations of 10 and 180 mg L−1. The maximum capacity removal of Cu+2 was assessed at pH 3.0, 4,0 and 5.0 and the initial concentrations of 10, 30, 60, 90, 180 and 270 mg L−1. Quantification of Cu+2 was carried out by atomic absorption spectrometry with atomization system type air-acetylene. For the construction of the isotherms was used polynomial regression and the averaged test percentage of Cu+2 removed at different pH values was used the Scott-Knott 5% significance level. The ZC presented capacity cation exchange 40% higher than ZB, but this was not reflected in the removal capacity. There was effect of pH only for ZC in less concentration added. The maximum removal capacity was 2662 kg−1 mg for ZB and 2759 mg kg for ZC in the pH 5.0. The maximum capacity removal Cu+2 ZB is similar to ZC. The ZB can be used to remove metals in laboratory and industrial effluents with low cost.

Resumo em Português:

RESUMO Os setores da construção civil, indústria moveleira, indústria de papel e celulose buscam novas alternativas para uma utilização mais racional da madeira que possam diminuir as limitações de seu uso, a exemplo da produção dos painéis reconstituídos dessa matéria-prima, como compensados, aglomerados de partículas, sarrafos, MLC (Madeira Laminada Colada), entre outros. No presente trabalho buscou-se avaliar a eficiência da colagem em taliscas de madeira de Eucalyptus cloeziana preservadas quimicamente com Arseniato de Cobre Cromatado (CCA). Foram utilizados seis adesivos (MUF: melamina-ureia-formaldeído; PVA: poliacetato de polivinila; RF: resorcinol-formaldeído; TF: tanino-formaldeído; UF: ureia-formaldeído; PUR: poliuretano à base de mamona) e foram realizadas avaliações da interface madeira-adesivo por meio de fotomicrografias, da resistência ao cisalhamento, da porcentagem de falhas na madeira e mensuração da espessura da linha de cola. Para a visualização da interface madeira-adesivo retiraram-se cortes anatômicos de cada posição, plano transversal e plano longitudinal da junta colada, após amolecimento em água quente. Apenas nas taliscas unidas com TF não foi possível avaliar a interface. O CCA contribuiu de forma negativa nas propriedades físicas e mecânicas da madeira. O MUF apresentou os melhores resultados, representados por maiores penetrações do adesivo no material utilizado e consequentemente maiores valores de resistência ao cisalhamento e menores valores de delaminação.

Resumo em Inglês:

ABSTRACT The sectors of civil construction, furniture industry, pulp, and paper industry that use wood, seeking new alternatives for a more rational usage of wood while reducing the use limitations. Some examples of new materials are reconstituted wood panels as plywood, chipboard, blockboards, glulam (glued laminated timber), among others. This study aimed at evaluating the efficiency of bonding pieces of chemically preserved with Copper Chrome Arsenate (CCA) Eucalyptus cloeziana wood. Six adhesives were used: MUF (Melamine urea formaldehyde); PVA (polyvinyl acetate); RF (Resorcinol-formaldehyde); TF (Tannin formaldehyde); UF (Urea-formaldehyde; PUR (castor oil-based polyurethane). We evaluated the wood-adhesive interface through photomicrographs, measuring the thickness of the main glue line, shear strength, and percentage of wood flaws. In order to preview the wood-adhesive interface, we withdrew anatomical sections for each position, transverse plane and longitudinal plane of the glued joint, after softening it in hot water. We could not assess the wood-adhesive interface of the lamellas glued with TF, only. CCA contributed negatively to the physical and mechanical properties of wood. The MUF adhesive had the best results, represented by greater penetration of the adhesive into the wood and consequently higher values in the shear and delamination test.

Resumo em Português:

RESUMO A lubrificação em estampagem de peças tem um papel importante no processo de produção, auxiliando na redução do enrugamento, fratura prematura e afinamentos muito localizados da espessura da chapa. Para tal, o lubrificante deve ser capaz de reduzir o atrito a níveis baixos mas não tão baixos a ponto de promover outros tipos de defeitos como o enrugamento da chapa. Uma boa lubrificação também reduz o desgaste prematuro das ferramentas de estampagem que são utilizadas para produção de peças, assim como é essencial para se ter sucesso no processo desenvolvimento de novas peças. Neste trabalho, 4 condições de lubrificações foram avaliadas (3 lubrificantes líquidos e a ausência de lubrificantes) através do ensaio DST (Dobramento Sob Tensão) e ensaio Swift (deep drawing test). A atuação benéfica (redução do atrito) ao processo de estampagem, dos lubrificantes, foi testada através da medição da força máxima de embutimento no ensaio Swift, da força em cada lado da chapa, torque e força vertical no pino do ensaio DST. O material de estudo foi o alumínio comercialmente puro AA1100. As conclusões indicam que o lubrificante que minimiza o atrito sempre fica evidente, não importando o tipo do ensaio a que a chapa foi submetida, porém a medição do torque facilita a identificação do mesmo. É observado também que a medição da força vertical gerada no pino é menor quanto mais ineficiente for o lubrificante.

Resumo em Inglês:

ABSTRACT The lubrication in sheet metal forming plays an important role in the production process, helping to reduce the wrinkling, premature fracture and very localized thinning of the sheet thickness. To this end, the lubricant should be able to reduce friction at low levels but not so low that promote other kinds of defects such as wrinkling of the sheet. A good lubrication also reduces premature wear of the stamping tools used to produce parts, as it is essential for success in the process of developing new parts. In this work, four lubrication conditions were evaluated (3 liquid lubricants and the absence of lubricants) by the bending under tension test (BUT) and deep drawing test. The performance of the lubricants were evaluated by measuring the maximum force of deep drawing test, the forces on each side of the sheet, torque and vertical force on the pin of the BUT test. The material used was the commercially pure aluminum AISI AA1100 alloy. The results indicate that the best lubricant always show the best performance no matter what type of test, but the measurement of torque facilitates the identification of it. It was also observed that the measurement of vertical force generated at the pin is smaller the more inefficient is the lubricant.

Resumo em Espanhol:

RESUMEN De acuerdo a datos del último censo de la producción de la industria de las fundiciones [1], se observó que aproximadamente el 46% de la producción en la industria de las aleaciones ferrosas corresponde a la fundición gris. Por ello que se hace interesante el investigar la resistencia que posee este material a l a corrosión atmosférica, y así determinar el real tiempo de vida útil a la intemperie. Los del comportamiento de las fundiciones grises bajo corrosión atmosférica son escasos, debido estos toman largos periodos de tiempo para la caracterización en tiempo real. Con el propósito de validar un ensayo de corrosión atmosférica acelerada, se ha sometido a una fundición gris [2] y a un acero al carbono [3]. a 40 dí as de un ensayo acelerado [4], que involucra ciclos de humectación en cámara de niebla salina, lavado y secado, determinando el espesor co rroído en cada tiempo. Estos resultados, luego fueron comparados, con los obtenidos por Southwell et al. [5] luego de 16 años de exposición a l a intemperie en un ambiente marino (Canal de Panamá). El análisis de resultados reveló que ambos materiales presentan un comportamiento bi-modal, en concordancia con lo descrito por Melchers et al. [6, 7, 8], éste comportamiento se caracteriza por un punto de inflexión en la curva cinética de espesor corroído, lo que permite la validación de la metodología propuesta como medio para evaluar la resistencia a la corrosión atmosférica marina en poco tiempo.

Resumo em Inglês:

ABSTRACT According to data gathered in the last Metal Foundry Industrial Production Survey [1], approximately 46% of the industrial production of ferrous alloys is gray-iron. In this context the study of the atmospheric corrosion resistance of gray-iron becomes interesting to asset its useful life when subject to weathering conditions. The studies of gray-iron atmospheric corrosion behavior are scarce due to the fact that it takes long periods of time for its real-time characterization. In order to validate an accelerated atmospheric corrosion test, a gray cast iron [2] and a carbon steel [3] were subjected to a 40 days accelerated testing, that includes wetting in a saline fog chamber, washing and drying [4], measuring the corroded thickness at each exposure time. These results were then compared with those obtained by Southwell et al [5] after 16 years of exposure in a marine environment (Panamá Canal). The result analysis reveals that both materials show a bimodal behavior, in accordance with those results reported by Melchers et al [6, 7, 8]. This behavior is characterized by an inflection point in the kinetic curve of corrosion, meanly related to the presence of bacteria in the interphase metal-corrosion products. The fact that the kinetic curve of corroded thickness shows an inflection point, allows the validation of the proposed methodology as a path to evaluate the atmospheric corrosion resistance in a short time test.

Resumo em Português:

RESUMO A incorporação de resíduos de construção e demolição (RCD) como agregados em concretos requer bom conhecimento das propriedades dos materiais envolvidos. O objetivo da presente pesquisa foi caracterizar um produto específico de uma usina de reciclagem de RCD, a Usina de Recicláveis Sólidos Paraná (USIPAR), localizada em Almirante Tamandaré, PR, conhecido comercialmente como bica corrida. O agregado reciclado foi caracterizado quanto à sua granulometria e demais características físicas. A fração miúda do agregado reciclado foi escolhida para substituir o agregado natural. Demais características desta fração foram estudadas, como teor de material pulverulento, massa específica e absorção de água. Foram produzidos concretos com diferentes taxas de substituição (0%, 25%, 50%) de agregado natural por agregado reciclado. As propriedades do concreto foram então avaliadas e verificou-se que o aumento do teor de substituição de agregado natural por agregado reciclado reduziu a trabalhabilidade, a massa específica seca e saturada do concreto e o módulo de elasticidade, bem como aumentou a absorção e o índice de vazios. A massa específica real do concreto não foi influenciada pelo teor de substituição. Com relação às resistências à compressão e à tração, a substituição de agregado natural pelo agregado reciclado levou a um decréscimo na resistência do concreto. O concreto com 50% de teor de substituição obteve uma maior resistência à compressão axial que o concreto com teor de substituição de 25%, e mesma resistência à tração por compressão diametral que o concreto controle.

Resumo em Inglês:

ABSTRACT The incorporation of construction and demolition waste (C&D waste) as aggregate in concrete requires good understanding of the properties of the materials involved. The purpose of this study was to characterize a specific product of a C&D waste recycling plant, the Usina de Recicláveis Sólidos do Paraná (USIPAR), located in Almirante Tamandaré, PR. The recycled aggregate was characterized in respect to their particle size and other physical characteristics. The fine fraction of recycled aggregate was chosen to replace the natural aggregate. Other characteristics of this fraction were evaluated, such as pulverulent material content, specific weight and water absorption. Concretes were produced with different substitution rates of natural aggregate by recycled aggregate (0%, 25%, 50%). The properties of the concrete produced were analyzed and was found that increasing the substitution rate of natural aggregate by recycled aggregate reduced the workability, the dry specific weight and saturated specific weight, and modulus of elasticity of concretes, as well as in creased absorption and void ratio of concretes. The real specific weight of the concrete was not influenced by the replacement content. In regard to the compression and tension strength, the replacement of natural aggregate by recycled aggregate led to a decrease in concrete strength. The concrete with a 50% replacement level obtained a greater compressive strength than the concrete with 25% replacement level, and the same tensile strength as the reference concrete.

Resumo em Português:

RESUMO Neste trabalho, foram obtidas membranas híbridas de poliamida6 (PA6) com 1%, 3% e 5% em peso de argila na forma de filmes finos por meio da técnica de inversão de fases. As membranas híbridas foram caracterizadas por difração de raios-X (XRD), espectroscopia na região do infravermelho com transformada de Fourier (FTIR), calorimetria exploratória diferencial (DSC), microscopia eletrônica de varredura (SEM), porosimetria por intrusão de mercúrio (MIP) e ângulo de contato. Por meio do XRD, foi possível perceber que as membranas híbridas sugerem uma estrutura esfoliada e/ou parcialmente esfoliada. Os espectros de FTIR das membranas híbridas permaneceram inalterados, exceto pelo aumento na intensidade dos picos em 800, 1033 e 1095 cm−1 provavelmente referente à camada octaédrica e a vibração do estiramento do grupo Si- O-Si da argila. Por DSC foi observado que praticamente não houve alteração da temperatura de fusão cristalina das membranas híbridas em relação à membrana de PA6 pura. A partir das fotomicrografias obtidas por SEM, foi ilustrada a obtenção de membranas microporosas assimétricas com a formação de uma pele filtrante e um suporte poroso ao longo da seção transversal. Além disso, a adição da argila provocou um aumento na quantidade e distribuição uniforme dos poros existentes na superfície e seção transversal destas membranas. Por MIP, observou-se que a presença da argila nas membranas ocasionou um aumento nos diâmetros médio dos poros. Por meio do ângulo de contato, verificou-se que as membranas híbridas apresentaram maiores ângulos de contato para a água destilada quando comparadas aos ângulos obtidos com o óleo sintético. As membranas híbridas obtidas apresentaram uma morfologia com porosidade adequada para aplicação em processos de microfiltração.

Resumo em Inglês:

ABSTRACT In this research, hybrid membranes of polyamide6 (PA6) with 1%, 3% and 5% of clay were obtained in the form of thin films by phase inversion technique. The hybrid membranes were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and contact angle. By XRD, it was revealed that the hybrid membranes suggest an exfoliated and/or partially exfoliated structure. The FTIR spectra of hybrid membranes remained unchanged, except for the increase in the intensity of the peaks at 800, 1033 and 1095 cm−1 probably related to the octahedral layer and the stretching vibration of Si-O-Si clay group. By DSC, it was observed that there was almost no change in the crystalline melting temperature of the hybrid membrane to the pure PA6 membrane. By SEM photomicrographs, it was illustrated the obtaining of asymmetric microporous membranes with the formation of a filter skin and a porous support along the cross-section. Furthermore, the addition of the clay led to an increase in the amount and in the uniform distribution of the pores at the surface and cross section of these membranes. For MIP, it was observed that the presence of clay in the membrane caused an increase in average pore diameters. By means of the contact angle, it was found that the hybrid membranes showed higher contact angles for distilled water as compared to the angles obtained from the synthetic oil. The obtained hybrid membranes showed morphology with adequate porosity for use in microfiltration processes.

Resumo em Inglês:

ABSTRACT Portland cement pastes are highly heterogeneous material and exhibits heterogeneous features over a wide range of length scales. Mechanical properties of microstructure can be determined using depth-sensing indentation. Coupled indentation/SEM technique can be used to location the indents and provides a way to determine the mechanical properties of a specific phase. Thus, the present paper aims to determine the hardness of different phases of cement pastes prepared with different mineral admixtures including sugarcane bagasse ash. The microstmcture of cement pastes prepared with different mineral admixtures is analyzed by X ray diffraction, scanning electron microscopy and dynamic hardness tests on polished sections. The different backscatter coefficient allows to differentiate anhydrous phases from C-S-H, calcium hydroxide, silica fume and quartz. A grid of indentation is used to determine the hardness of the different phases and a complete phase segmentation of the different samples is achieved. The results show that the hardness of the different phases follow the sequence (from higher to lower hardness) quartz, anhydrous particles, calcium hydroxide, C-S-H and agglomerated silica fume. The presence of agglomerated silica fume is clearly observed in scanning electron microscopy images and the poor mechanical properties of these areas might compromise the cement pastes. The microstructure of cement pastes prepared with sugarcane bagasse ashes is similar to the observed in samples with crashed quartz.

Resumo em Português:

RESUMO Estimar perdas de carga devido à fricção em tubos fechados é uma tarefa importante na solução de muitos problemas práticos nos diferentes ramos da profissão de engenharia. O projeto hidráulico e análise de sistemas de escoamento de suspensão mineral são dois exemplos. Muitos consideram o modelo de Swamee – Jain promissor para avaliar as perdas de carga devido ao atrito em conduto de tubos fechados. Para investigar o fator de atrito o modelo de Swamee – Jain foi empregado para o escoamento confinado de suspensão de caulim com teor de sólidos em massa de 55% (suspensão C), 60% (suspensão B) e 65% (suspensão A) em tubulação de ferro galvanizado com 0,2; 0,3 e 0,5 metros de diâmetro com faixa de vazão de 0,02 a 0,2 m3 por segundo. Todas as suspensões de caulim o aumento do teor de solido e do diâmetro da tubulação contribui para o aumento do fator de atrito para o escoamento confinado em faixa de vazão operacional proporcionando estimativa de valores para utilização em projeto e analise de sistemas de escoamento de caulim.

Resumo em Inglês:

ABSTRACT Estimating load losses due to friction in closed pipes is an important task for solving many practical problems in the various branches of the engineering profession. Hydraulic projects and analyses of systems for transporting mineral products in suspension are two examples. Many consider the Swamee – Jain model a promising method for assesses load losses due to friction in closed pipes. In order to investigate the friction factor the Swamee – Jain model was employed for confined flow of a kaolin suspension with a concentration of solids in mass of 55% (suspension C), 60% (suspension B) and 65% (suspension A) in a galvanized iron pipe with 0.2; 0.3 and 0.5 meters in diameter with a flow ranging from 0.02 to 0.2 m3 per second. For all of the kaolin suspensions the increase in the solid content and the diameter of the pipe contributes towards increasing the friction factor for confined flow in the operational flow, providing an estimate of values for use in projects and for analyzing systems used for transporting kaolin.

Resumo em Inglês:

ABSTRACT Titanium base coatings are being used extensively for improving wear characteristics at the surface of different parts. Titanium nitride was deposited by Plasma Assisted Chemical Vapor Deposition (PACVD) techniques with purpose improve interface with substrate, as this can increase wearing of the entire part in spite of desirable wear behavior of TiN. Samples from H13 steel were prepared and they experienced plasma nitriding (PN) prior to TiN deposition. TiN coatings were deposited in different conditions of temperature (475, 500 and 525°C) and duty cycle (33, 40 and 50%). Topographic studies were preceded by Atomic Force Microscope (AFM). Surface hardness was evaluated using Vickers's micro-hardness test. In order to study the wear behavior, pin-on-disc test was chosen which included examining the sample's resistance against pins from steel and tungsten carbide-cobalt. Based on the results obtained it can be observed that increasing the deposition temperature from 475 to 525°C will lead to higher values of hardness, thus the obtained weight loss from samples decreased from 2.1 to 0 mg. In addition to that, with increasing the duty cycle of system from 33 to 50%, weight loss of the TiN coating has increased from 0 to 2mg due to an increase in the value of surface roughness.

Resumo em Português:

RESUMO O ferro nodular austemperado (ADI) é indicado para aplicações que demandam alta resistência ao desgaste abrasivo. Uma de suas variações é o CADI (Carbidic Austempered Ductile Iron), que contém em sua microestrutura carbonetos eutéticos livres. A adição de nióbio em ferro nodular também resulta em formação de carbonetos, porém mais duros e estáveis do que os carbonetos presentes em CADI. Macroadições de nióbio em ADI mostram-se promissoras. O presente trabalho estudou a influência da adição de nióbio no tratamento de austêmpera. Cinco composições distintas, ferro nodular sem adições, ferro nodular com cromo e ferro nodular com três adições de nióbio, foram austemperadas a duas temperaturas e cinco tempos distintos. Os valores de teor de austenita retida foram estimados por metalografia. A adição de nióbio provocou a formação de carbonetos primários poligonais, ao passo que a adição de cromo provocou a formação de carbonetos de padrão dendrítico encontrados nas regiões intercelulares. Verificou-se que as adições de nióbio e, mais intensamente a de cromo, aumentam o teor de austenita retida resultante do tratamento de austêmpera, bem como alteram a morfologia da microestrutura ausferrítica.

Resumo em Inglês:

ABSTRACT The austempered ductile iron (ADI) finds applications in abrasive wear resistant parts. CADI (Carbidic Austempered Ductile Iron) is one type of ADI, which contains free eutectic carbides in its microstructure. The addition of niobium in ductile iron also results in the formation of carbides, but harder and more stable than the CADI carbides. Macro additions of niobium are promising. The present work studied the influence of the addition of niobium in the austempering treatment. Five different compositions, ductile iron, ductile iron with chromium and ductile iron with three niobium additions, were austempered at two temperatures for five different times. The retained austenite were estimated by metallography. The addition of niobium caused the formation of primary polygonal carbides while the addition of chromium caused the formation of carbides of dendritic morphology in intercellular regions. The results shows that the additions of niobium and, more intensively, of chromium result in the increasing of the retained austenite content. The additions also affect the morphology of the ausferritic microstructure.

Resumo em Português:

RESUMO A zircônia Y-TZP é muito utilizada na confecção de coping como material estrutural para próteses odontológicas devido à sua cor branca/perolada opaca e resistência mecânica. Estas próteses são confeccionadas por usinagem com apoio de um software de CAM (Computer Aided Manufacturing), a partir de blocos prensados e pré-sinterizados. A pré-sinterização consiste em aquecer os blocos compactados a altas temperaturas, com uma taxa lenta de aquecimento até o início da formação dos pescoços entre as partículas, quando proporciona dureza/resistência e usinabilidade. Uma contradição, pois a dureza/resistência mecânica é necessária para proporcionar estabilidade as forças de corte, mas se muito duro, pode dificultar a usinagem então se deve encontrar uma faixa de compromisso de temperatura entre estabilidade e usinabilidade. Dessa forma, o objetivo do presente trabalho foi investigar a relação entre a microdureza e temperatura de pré-sinterização da zircônia Y-TZP e seu comportamento ao ser submetido à usinagem. O ensaio de microdureza foi escolhido como representante de resistência mecânica por ser não destrutivo e de resultado imediato. O pó de zircônia experimental foi submetido à prensagem uniaxial seguido de prensagem isostática a frio à 200 MPa e pré-sinterização entre 900°C e 950°C. Os blocos foram cortados e submetidos ao teste de estabilidade na usinagem e ensaio de microdureza Vickers sendo os dados submetidos ao teste de “normalidade” de Anderson-Darlin com p > 0,05. Foi utilizada ANOVA de um fator com o teste de Tukey-Kramer para verificar as diferenças entre as médias dos grupos. A investigação demonstrou que a diferença de 50°C na temperatura de pré-sinterização, acima de 900°C afetou significativamente a microdureza, contudo os tempos de patamar 2 e 4 horas não a influenciou significativamente. A maior temperatura de pré-sinterização dos grupos experimentais testados possibilitou um melhor comportamento na usinagem com o apoio de um software CAM, sendo a microdureza similar ao material comercial ZL.

Resumo em Inglês:

ABSTRACT Y-TZP zirconia is widely used in the manufacture of coping as a structural material for dental prosthesis due to its opaque white/pearl color and mechanical strength. Dentures are made by machining with cam (computer aided manufacturing) software support, from pressed and pre-sintered blocks. Pre-sintering consists of heating the compressed blocks to high temperatures, with a slow heating rate until the neck formation among particles, when this provides hardness/strength and machinability. There is a contradiction, because the mechanical hardness/strength is necessary to provide stability to the cutting forces, but if it is very hard, machining can be difficult, therefore must be found a compromise zone of temperature between stability and machinability. In this way, the purpose of this study was to investigate the relationship between microhardness and the pre-sintering temperature of experimental Y-TZP zirconia and its behavior to be subjected to machining. The microharness testing was chosen as representative of mechanical strength once it is nondestructive and with immediate result. The experimental zirconia powder was subjected to uniaxial pressing, subsequently cold isostatic pressing of 200 MPa and pre-sintering between 900°C and 950°C. Blocks were cut and subjected to machining stability testing and vickers microhardnes testing which the data were subjected to the anderson-darlin (p > 0.05) test for “normality”. Anova's “one way” with tukey-kramer test was used to verify the differences among the means of groups. The investigation showed that the difference of 50°C in pre-sintering temperature above 900°C significantly affect the hardness, whereas 2 to 4 hour time did not significantly affect material microhardness. The highest pre-sintering temperature of the tested experimental groups enabled better performance in machining with cam software support, which provides similar microhardness to commercial ZL material.

Resumo em Português:

RESUMO Grandes quantidades de materiais finos (na forma de pó) são coletados e armazenados nas pedreiras, constituindo um sério problema ambiental, pela falta de destinação específica para esse resíduo. No entanto, esses materiais poderiam ser utilizados como um fíler em concreto autoadensável (CAA), o qual necessita de um grande volume de finos na sua constituição. Desta forma, neste trabalho, foram investigados os efeitos do fíler calcário (empregado como referência), fíler diabásico e gnáissico, nas propriedades de CAAs. A influência da mineralogia, forma e tamanho das partículas foram avaliadas por meio de ensaios no estado fresco (monopontos e reométricos) e ensaios no estado endurecido de CAAs. Os resultados mostraram que concretos contendo fíler gnáissico ou diabásico podem apresentar propriedades reológicas similares aos concretos contendo fíler calcário, quando apresentam distribuição granulométrica e tamanho de partícula similar ao fíler calcário usualmente utilizado (d50 entre 30 e 40 µm). Além disso, CAAs contendo fíler diabásico apresentaram resistência à compressão superior aos concretos dosados com os demais fílers. Diante dos resultados, pode-se concluir que os fílers de diabásio e gnaisse apresentam potencial para serem utilizados como materiais alternativos ao fíler calcário em CAA, embora possam demandar maior quantidade de aditivo superplastificante para atingir propriedades comparáveis no estado fresco.

Resumo em Inglês:

ABSTRACT Large amounts of powders have been collected in quarries and storage of these by-product dusts is a serious environmental concern. However, these materials may be used as a filler in self-compacting concrete (SCC), which requires a large amount of fines in its composition. Thus, in this paper, the effects of limestone filler, diabase, and gneiss quarry powder on the properties of self-compacting concrete were investigated. The influence of the mineralogy, shape and particle size distribution were evaluated by rheometry, and by fresh and hardened concrete properties. SCC containing gneissic or diabasic powder can show rheological parameters values very similar to those of SCC containing limestone filler when the material has the same particle size to that of an usual limestone filer (d50 between 30 e 40 um). SCC containing diabasic powder showed higher compressive strength than that of SCC containing limestone filler or gneiss powder. It was found that diabasic and gneissic quarry powders could be used successfully for producing SCC, although a higher superplasticizer content was required than that of SCC containing limestone filler.

Resumo em Espanhol:

RESUMEN Las aleaciones de aluminio a la temperatura ambiente no experimentan comportamientos reológicos apreciables debido a su orden microestructural coherente y su alta compacidad. Sin embargo, el aumento de la temperatura genera campos de tensiones, y con ello deformaciones, que alteran el equilibrio microestructural, manifestándose el comportamiento reológico como consecuencia de la fricción interna. En las aleaciones de Al-Mg-Si la precipitación de fases provoca pérdida de coherencia produciendo fricción interna. Los objetivos de este trabajo fueron caracterizar e identificar las transformaciones microestructurales experimentadas en el aluminio AA6061 por efecto de la temperatura; estudiar la cinética no-isotérmica e isotérmica, a través de modelos atomísticos. Analizar el comportamiento reológico, manifestado en la deformación, y en la relajación de tensiones, considerando los postulados expresados por el Número de Deborah (De). El desarrollo experimental ha sido orientado y organizado a través de la resistividad eléctrica y la microscopía. Cuatro regiones de transformaciones fueron observadas: I: 20-190, II: 220-420, III: 420-520, IV: ≥ 525 °C; con energías de activación: EaI: 20 − 60, EaII: 90 − 120, EaIII: 400 − 470 kJ/mol; y conformadas de agregados de soluto y fases aciculares y cilíndricas, respectivamente. Se determinó que De ≤ 1, asociándose a un comportamiento viscoelástico. Se observó, entre 100 y 200 °C, que: 0,1 ≤ De ≤ 0,3, vinculándose a un considerable nivel de difusión, con tasa de nucleación máxima a 150 °C. Estas caracterizaciones ampliarán el entendimiento del fenómeno de difusión, los procesos de precipitación, deformación y relajación; para aplicaciones prácticas y desarrollos teóricos relacionados.

Resumo em Inglês:

ABSTRACT Aluminum alloys at room temperature not experience significant rheological behavior due to its coherent microstructural order, and its high compactness. However, the increase of the temperature generates stress fields, and thereby deformations, that alter the microstructural equilibrium, manifesting the rheological behavior as consequence of the internal friction. In the alloys of Al-Mg-Si, the precipitation of phases cause loss of coherence producing internal friction. The objectives of this work were characterize and identify the microstructural transformations experienced in the AA6061 aluminum by temperature effect; study the kinetic no-isothermal and isothermal, through atomistic models. Analyze the rheological behavior, manifested in the deformation, and in the stress relaxation, considering the postulates expressed by Deborah's Number (De). The experimental development has been oriented and organized through the electrical resistivity and microscopy. Four regions of transformations were observed: I: 20-190, II: 220-420, III: 420-520, IV: ≥ 525 °C; with activation energys: EaI: 20 − 60, EaII: 90 − 120, EaIII: 400 − 470 kJ/mol; and formed of solute aggregates and needle and cylindrical phases, respectively. It determined that De ≤ 1, associated to a viscoelastic behavior. It observed, between 100 and 200 °C, that: 0.1 ≤ De ≤ 0.3, linking to a considerable degree of diffusion, with maximum rate of nucleation at 150 °C. These characterizations will broaden the understanding of the diffusion phenomenon, the precipitation processes, deformation and relaxation; for practical applications and related theoretical developments.

Resumo em Inglês:

ABSTRACT The most commonly used inoculants for producing grey iron are ferrosilicon based, but also there are reports indicating that silicon carbide can act as inoculant. There are few published studies of fading and nucleation sites of graphite when silicon carbide is used as inoculant, thus the understanding of the inoculation effect of silicon carbide is incomplete. To study these two aspects, fading and graphite nucleation sites, an ASTM class 35B grey iron inoculated with silicon carbide was produced and characterized. The results were compared with an ASTM class 35B grey iron inoculated with a ferrosilicon base inoculant and without inoculation. It was found that the effect of the silicon carbide was comparable to the ferrosilicon base inoculant and fading was similar. In addition, the graphite nucleation sites in the grey iron inoculated with silicon carbide were irregular shaped manganese sulfides larger than the nuclei in the grey iron inoculated with ferrosilicon, which suggest a similar nucleation mechanism for both inoculants.

Resumo em Português:

RESUMO Neste trabalho apresentam-se análises de flexão de placas compostas por materiais heterogêneos através de uma abordagem multi-escala. O macro-contínuo, representado neste trabalho pela placa, é modelado por uma formulação não-linear do Método dos Elementos de Contorno (MEC), que leva em conta o operador tangente consistente (CTO). A micro-escala é representada pelo EVR (Elemento de Volume Representativo), sendo seu problema de equilíbrio definido em termos de flutuação dos deslocamentos e solucionado através do Método dos Elementos Finitos (MEF), onde a hipótese de média volumétrica das tensões e deformações é adotada para se fazer a passagem do micro-contínuo para o macro-contínuo. A cada ponto do macro-contínuo, onde se necessita conhecer as tensões e o tensor constitutivo deve estar associado um EVR, onde se podem definir inclusões e/ou vazios no interior de uma matriz a fim de representar a micro-estrutura de um material heterogêneo. Nos exemplos numéricos são considerados diferentes EVRs com inclusões elásticas dentro de uma matriz, onde os modelos de Von Mises ou Mohr Coulomb são adotados, a fim de governar o comportamento do seu material. Consideram-se diferentes frações volumétricas para as inclusões a fim de verificar a influência na resposta homogeneizada da microestrutura e, consequentemente, no comportamento mecânico do macro-contínuo. Para solucionar o problema de equilíbrio do EVR devem-se adotar condições de contorno em termos de flutuações dos deslocamentos, que nos exemplos analisados no presente trabalho serão consideradas como periódicas.

Resumo em Inglês:

ABSTRACT Analyses of the bending problem of plates composed of heterogeneous materials are performed considering a multi-scale modelling. The macro-continuum, represented in this paper by the plate, is modelled by a nonlinear formulation of the boundary element method (BEM) taking into account the consistent tangent operator (CTO) in the iterative procedure required to solve the plate equilibrium problem. The micro-scale is represented by the RVE (Representative Volume Element) being its equilibrium problem solved in terms of dis-placements fluctuations by a Finite Element Formulation (FEM), where the volume averaging hypothesis of strain and stress tensors is used to make the micro-to-macro transition. To each point of the macro-continuum where the stresses and constitutive tensor have to be computed, a RVE must be assigned, where inclusions and voids can be defined inside the matrix in order to represent the microstructure of a heterogeneous material. In the numerical examples are considered different RVEs with elastic inclusions, while for the matrix the Von Mises or Mohr-Coulomb criteria can be adopted to govern its material behavior. Different volume fractions have been adopted for the inclusions in order to verify its influence on the homogenized response of the microstructure as well as on the mechanical behavior of the macrostructure. To solve the RVE equilibrium problem, boundary conditions in terms of displacement fluctuations have to be imposed, which for the numerical examples presented in this paper will be adopted periodic.

Resumo em Inglês:

ABSTRACT Resin Transfer Molding (RTM) process is commonly used to produce high quality polymeric composites with simple or complex geometries in small to large sizes. In RTM process a preformed reinforcement is positioned inside the mold cavity. This dry reinforcement is actually a fibrous porous media whereby resin will flow. The mold is then closed and resin is injected. After complete impregnation of the reinforcement, resin cure process takes place. Numerical simulation is a very useful tool for mold design and process optimization, however resin and reinforced medium physical properties must be precisely determined. Medium permeability is probably the most important and most difficult parameter to be evaluated. In this work it is proposed a numerical/experimental methodology to determine transverse permeability in reinforcements used within RTM process. PAM-RTM software was chosen to simulate resin flow through the reinforced medium. Proposed methodology uses the inverse parameter estimation method to calculate the unknown permeability. Newton-Raphson method was used to solve the associated algebraic equation system, on which PAM-RTM software is used to calculate resin injection times. Results have shown that with previous knowledge (taken from literature or obtained experimentally) of the in-plane permeabilities (Kxx and Kyy ), physical properties of the resin (ρ, µ), medium porosity (ε) and total filling time (t) it is possible to estimate transverse permeability in thick pieces. It was also performed a numerical study about the influence of transverse permeability in resin flow inside the mold. This study predicted several possible problems that may occur when transverse permeability is much smaller than in-plane permeabilities. Finally, it is possible to state that mold design and proper fibrous reinforcement choice can be optimized when numerical techniques are used.

Resumo em Inglês:

ABSTRACT Wood flour composites main applications are represented by outdoor furnishing. Therefore, it is important to evaluate their behavior under natural ageing conditions. This work aims to investigate the natural ageing impact on the mechanical, physical, thermal e morphological properties of recycled polypropylene/ethylene vinyl acetate/wood flour composites (PP/EVA/ITA). Samples were exposed to natural ageing for 12 months in Porto Alegre (BR). Mezilaurus itauba (ITA) wood flour was used at 30 % w/w. Results showed that PP filled wood flour retained a higher fraction of the original mechanical properties after natural ageing. Crystallinity degree for composites increased from 30.9 up to 37.5% Climatic conditions affected the colorimetric and morphological characteristics of composites, indicating that there was not only photo-degradation but also thermo-oxidative and hydrolytic degradation. In this way, the use of antioxidant additives and UV photo-absorbers is recommended to avoid stress-cracking, discoloration and loss the mechanical properties.

Resumo em Inglês:

ABSTRACT Seeking the reutilization of waste from agriculture and urban sources, studies have presented an option in the inclusion of such waste into new low-cost materials that are environmentally viable. One possibility is the reutilization of sugarcane bagasse ashes (SBA), the final waste in the productive process of the Brazilian alcohol sector. In addition to the behavior of materials with the use of SBA as additions in cement-based materials under normal environmental conditions, the study of the behavior of these materials when exposed to harsh environments is required. Thus, this project evaluated the properties, the compression strength and the bulk density of cement composites with partial replacement of cement by SBA without prior treatment. Also, it analyzed the weight loss and compressive strength of the composites subjected to environments with the presence of chloride ions. A factorial design was adopted to verify the influence of the addition of SBA (5wt%, 10wt% and 15wt%) and water/cement ratio (0.45 and 0.55) in the studied properties. The interaction between the factors was significant. The values obtained from the compressive strength of the manufactured composites showed that it is possible to replace up to 15wt% of cement for in natura SBA. After a chemical attack with an acid solution of HCl 30%, it could be observed that all materials had a lower compressive strength, which can be explained by the high weight loss suffered by all composites. Based on the results of compressive resistance, density and weight loss after the attack, it was observed that the mechanical behavior of the composites in relation to the referential conditions were similar. This study showed that it is feasible, in accordance to the studied properties, to use these composites in promoting the partial replacement of cement by this type of waste and its reutilization.

Resumo em Inglês:

ABSTRACT In this work, nanobiocomposites of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) reinforced with cellulose nanofibrils (CNFs) were produced by electrospinning and solution casting process. CNFs were obtained by sulfuric acid hydrolysis from Imperata brasiliensis fibers. Nanocomposites loaded with 1 (wt. %) of CNFs were prepared using a mixture of solvents chloroform (CHCl3): N, N-dimethylformamide (DMF), in the ratio of 78:22 with 30 h of solubilization. Films by solution casting were obtained in a petri dish, at 50 °C for 1 hour, using drying casting temperature of 153 °C. Mats by electrospinning were obtained with a needle 20x10, drum collector rotation 27 rpm, and working distance of 10 cm. Films and mats were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Differential Scanning Calorimetry (DSC). It was possible to conclude that for nanobiocomposites obtained by solution casting, the addition of CNFs did not affect the transparency of the films, but provided a significant increase in the crystallization rate as observed by DSC analysis, while for electrospinning nanobiocomposites a considerable improvement in process increasing electrospinning time and quality of the mats manufactured, were observed.

Resumo em Inglês:

ABSTRACT Biocomposites reinforced with natural fibres have been extensively investigated as a promising replacing material for synthetic ones, such as the glass fibre reinforced composites. The length of natural fibres depends not only on the plant species, but also on the extraction processing. The heterogeneity of natural fibres, in terms of length, can be considered a problem for some industrial applications. A little amount of work has been conducted towards the use of short natural fibres in composite materials. In order to balance the reduction of strength due to the use of short length fibres, ceramic particles can be incorporated. This paper describes the experimental characterization of hybrid biocomposites consisted of epoxy polymer, short random sisal fibres and Portland cement particles. A full factorial design was performed to investigate the effect of the factors and levels, such as fibre length (4 mm and 8 mm) and Portland cement inclusion (0wt%, 5wt% and 10wt%) on the following properties, flexural modulus and strength (via three-point bending test), damping ratio, apparent porosity and water absorption. The fibre volume fraction was kept constant at 25%. The Design of Experiment (DoE) analysis revealed the “Fibre length” factor does not affect the responses. The interaction “Fibre length and Cement inclusion” affected only the stiffness. Portland cement particles statistically revealed a noticeable contribution to the apparent porosity and water absorption. The presence of cement particles at 5wt% provided not only the increase in the damping ratio response, but also the reduction in the flexural strength and stiffness.

Resumo em Inglês:

ABSTRACT Nowadays, there is an increasing interest in the development of eco-friendly materials. Thus, environmental challenges due to the necessity of reducing worldwide levels of CO2 emissions, to limit the energy consumption and to use industrial waste are promoting an increasing effort to find viable alternatives to minimize pollution from the main productive processes. Thus, this paper addresses the results of an investigation on the influence of stone powder, residue from the production of crushed aggregates, on the mechanical performance of concrete reinforced with steel fibers. The effect of the amount of stone powder sand was evaluated using 0%, 50% and 100% natural sand replacement. Workability and mechanical properties were evaluated by compressive, elastic modulus, four-point bending and abrasion tests. Economic impact study of the composite production was also carried out. Based on the results obtained, it is possible to conclude that the use of crushed stone sand in steel fiber reinforced concrete is beneficial in terms of the workability and abrasion resistance but was some disadvantages. For instance, when 100% manufactured sand was added, the compressive and bending strength was reduced. However, the elastic modulus was not changed. It is also important to highlight that with 100% stone powder content, the compressive strength is still higher than 30MPa and the cost for producing is about of 32% cheaper.

Resumo em Inglês:

ABSTRACT This study evaluates the thermal, morphological and mechanical behavior of polypropylene (PP) composite with different natural fibers. The fibers used were wood, sugarcane, bamboo, babassu, coconut and kenaf with and without coupling agent. The thermal, morphological and mechanical properties were evaluated, and a composite PP+GFPP (glass fiber) was used as reference. The interaction at the interface fiber-polymer matrix was studied by scanning electron microscopy (SEM) at the fractured surface of the composites, as expected the presence of maleic anhydride (MA) as coupling agent increasedthe interaction at the interface. The influence of natural fiber in the degree of crystallinity of the composites was evaluated by DSC analysis. The samples of PP+GFPP and PP+(PP-MA)+WF (wood flour) showed better temperature stability. PP+GF also presented superior flexural modulus. The thermal dynamic mechanical behavior was evaluated by DMA, a decrease in storage modulus with increasing temperature was observed, the PP+GF and the composite containing maleic anhydride and sugarcane fiber showed higher modulus. The natural fiber biocomposites studied, consistently presented lower flexural modulus and tensile strength than the reference composite, with and without the use of coupling agent. As expected the use of natural fibers lowered the density compared to the reference material.

Resumo em Inglês:

ABSTRACT Aiming to minimize the environmental pollution and reducing the production costs of the composite materials, the use of plant fibers improves their physical and mechanical properties. On the other hand, fibers have high water absorption, which may increase their volume and weaken the fiber/matrix interaction, affecting the mechanical features of the composites. Concerned with this problem, this research had the objective of making 3 and 10 millimeter-thick specimens, containing 23% (m/m) of Caroa fibers and 73% (m/m) of unsaturated polyester. Samples were withdrawn after 0, 2, 4, 7, 12 and 21 days of exposure at room temperature water (ASTM D570 − 98). Then, the test of tensile (ASTM D 3039), flexural (ASTM D 790-03) and impact (ASTM D 256) was realized and the mechanical properties were analyzed. The samples subjected to humidity had their fibers degraded and presented loss of mechanical properties, more significant in composite with 3 mm. For example, the reduction of the strengths tensile, after 21 days of test were 80% for composites with 3 mm and 60% for composites with 10 mm. Studies like this are important for long-term applications of such composites in humid environments.

Resumo em Inglês:

ABSTRACT Novel carbon/glass hybrid thermoplastic composite rods have been developed consisting of a PAN-based carbon fiber, an E-glass fiber, and a thermoplastic matrix. Three types of hybrid rods with different carbon/glass ratios were then fabricated. The surface and cross-sectional morphologies of the hybrid rods were observed using a digital microscope. Additionally, the volume fractions of carbon/glass fibers, matrix, and void were determined by specific gravity measurements and thermogravimetric analyzes. The glass fibers in the hybrid rods display a braided structure of the 2/2 twill weave. The braid angle (defined as the orientation angle of the interlacing yarns with respect to the longitudinal axis of the rod) ranged from 22.3° to 35.2°. The various volume fractions were in the ranges of 24.6-46.2% for the carbon fiber, 23.2-39.8% for the glass fiber, 23.4-25.5% for the matrix, and 7.3-10.2% for the voids. The tensile properties and fracture behavior of the hybrid rods under static and fatigue loading were also investigated. For the static tests, the stress applied to the specimen was nearly linearly proportional to the strain until the failure of all-hybrid rods. The tensile modulus, strength, and failure strain of the hybrid rods were measured in the ranges of 65-91GPa, 1.42-1.84 GPa, and 2.1-2.2%, respectively. The tensile modulus and strength increased as the volume fraction of the carbon fiber increased. However, the failure strain decreased as the volume fraction of the carbon fiber increased. For fatigue tests, the maximum applied stress-number of cycles to failure (S-N) curves for all-hybrid rods were obtained from 0.1 of the stress ratio (minimum/maximum stress) and 10 Hz of the loading frequency. The fatigue strength at 107 cycles for all-hybrid rods was less than 30% of ultimate breaking stress. The fatigue performance of the hybrid rods was significantly lower than that of conventional carbon fiber reinforced polymer matrix composites and steel rods. The voids in the hybrid rods affected the fatigue tensile properties.

Resumo em Inglês:

ABSTRACT Direct Alcohol Fuel Cells (DAFC’s) are an alternative to fuel cell systems and when is used alkaline medium this has an increase performance. The alkaline direct alcohol fuel cells (ADAFC's) have some advantages such as low-emission, high energy efficiency, improved oxidation kinetics, low crossover and in addition there is a broad range of materials that can be used as catalysts. The ethylene glycol (EG) has received attention in recent decades as an alternative fuel for ADAFC, but like others alcohols must be completed oxidized to generate full power energy. In this study we analyzed ternary PtRhNi/C electrocatalysts with different compositions, synthesized by alcohol reduction method, and compared to Pt/C ETEK. The active area, catalytic activity and stability of catalysts for ethylene glycol oxidation in alkaline medium were studied by cyclic voltammetry, CO stripping voltammetry and chronoamperometry tests. XRD technique was applied to physical characterization and it was observed the formation of alloy. The average crystallite size was calculated from the Scherrer equation. The Pt92Rh7Ni1/C electrocatalyst shows a larger electrochemically active area and consequently higher catalytic activity for EG oxidation. This response was attributed to improvement in the synergistic effect provided by the reduction of the amount of Rh and Ni in the ternary alloy when compared to Pt80Rh15Ni5/C and Pt/C ETEK electrocatalysts. However, Pt80Rh15Ni5/C electrocatalyst showed greater tolerance to poisoning by intermediate species due to the presence of Rh in greater quantity, leading to a formation of adsorbed OH species in potentials smaller than those for platinum.

Resumo em Inglês:

ABSTRACT In this work was studied the effect of nanoparticle incorporation in the dimensional stability of elastomer matrix. To avoid excessive swelling and consequently dimensional instability in the films, crosslinking has been shown to be an efficient and simple method for achieve the reducing membrane swelling and improving mechanical stability. The elastomer used was a fluorinated type, with 70% of fluor in its composition and commercial clay (Cloisite®) was the nanofiller used. The nancomposites with 0.5, 1 or 2% (wt%) of nanoclay were prepared in a open two roll mill. The fluoroelastomer was a type of Viton® (DuPont) which has low fuel permeation and suitable for use as sealant mainly for o-ring production. The incorporation of clay in the polymer matrix aimed to avoid excessive swelling and to maintain the material dimensional stability. The nanocomposites were characterized by stress-strain test to evaluated elongation and tension at break, by rheometry to analyzed maximum and minimum torques, and degree of swelling to follow dimensional size modification of nanocomposites films. There were a decreasing of the elongation at break and of degree of swelling values what can be correlated to an increase of crosslinking, and consequently formation of a networking in the nanocomposites matrix in the films evaluated

Resumo em Inglês:

ABSTRACT Concerns for the environment are recurrent in our society, and research on low impact materials such as those produced from waste is an alternative. This work is based on the reuse of scrap paper and rice hulls aiming to increase the life cycle of these waste products and to find better destination. Composites with a volumetric filler content (dispersed phase) of 80% were produced via compression molding using polyurethane (PU) based on castor oil or polyester resin as matrix, in four distinct families: polyester/rice hulls, PU/rice hulls, polyester/paper and PU/paper. The following tests were performed: water sorption, contact angle, hardness, impact and tensile testing. Scanning electron microscopy (SEM) was used for fracture morphology study. Basic visual analysis showed greater void content for the rice hull composites, making them less aesthetically appealing compared to paper. It was observed in the case of PU matrix the filler greatly influenced the rigidity since this pure material was more flexible compared to pure polyester. Filler incorporation decreased tensile strength of the polyester matrix but significantly increased that of the PU matrix.

Resumo em Inglês:

ABSTRACT Nanofibers are materials that present high elasticity, strength, porosity and surface-area-to-volume ratio. The electrospinning method is the most widely adopted technique for forming polymeric nanofibers due to repeatability, easy scale-up process and production of long and continuous nanofibers. This method produces nanofibers with diameters ranging from 10 nm to 1000 nm. The process is regulated by many parameters which significantly affecting the morphology of the nanofibers, and through the proper handling of these parameters are obtained desired nanofibers in morphology and diameters. Based on this, the objective of this work was to evaluate the size and morphology of nanofibers obtained by different conditions of the electrospinning process. The electrospinning technique will be utilized to produce nanofibers with polyacrylonitrile (PAN) polymer and solvent N, N-dimethylformamide (DMF). The polymer solutions (10% (w/v)) were injected through of the capillary with diameter 0.45; 0.55; 0.70 and 0.80 mm. The distances from the collector to the capillary were tested between 100 and 200 mm, voltage between 15 and 25 kV, and feed rate of the solution between 100 and 1000 µL/h. All of the tests were conducted at 22 °C with the relative humidity level controlled at 65±1%. The morphology and size of nanofibers were evaluated by Scanning Electron Microscopy (SEM). Thus, the development of nanofibers with small diameter and high pore volume facilitate bioactive molecules loading and / or transport of nutrients and wastes, and allow the polymeric nanofibers become important class of biomaterials.

Resumo em Inglês:

ABSTRACT Luffa Cylindrica is a tropical plant from the Cucurbitaceae family, whose fruit becomes very fibrous when fully ripened. The lignocellulosic sponges of Luffa can be suitable for use as reinforcement of epoxy matrix composites, because they have a morphology with spatial 3-D arrangement as well as are eco-friendly materials (biodegradable, and high available) and have economic advantages compared to composites reinforced with synthetic fibers derived from non-renewable sources. Surface modification of the Luffa fibers was carried out by hornification and mercerization methods and was verified by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-Ray Diffraction (XRD). For the fabrication of non-biodegradable composites by hand layup technique, the sponges were impregnated with an epoxy resin based on bisphenol in a metallic mold with dimensions 150×200×3 mm3, followed by compression at 5 MPa. The dynamic modulus of the fabricated composites were measured using the nondestructive impulse excitation technique (IET), according to the ASTM E1876 standard. Bar specimens with dimensions 80×25×3 mm3 of the laminated composites were tested at room temperature, with Sonelastic® (ATCP) equipment and its associated software. Results showed that the Luffa/epoxy composites has higher loss factor and dynamic modulus when the Luffa fiber is treated before the composite fabrication. The highest Young's modulus obtained was 4.05±0.31 GPa for mercerized Luffa/epoxy. For hornificated Luffa/epoxy composite the highest loss factor and shear modulus values obtained, were 0.0337±0.003 and 1.46±0.13 GPa respectively.

Resumo em Inglês:

ABSTRACT The Engineered Cementitious Composites (ECC) is a special type of High Performance Fibre Reinforced Cementitious Composite (HPFRCC) characterized by a high tensile ductility with a 2% maximum volume of micro fibres. ECC has a tensile strain-hardening performance that leads to multiple cracking behaviour, thus providing the high ductility to the concrete. One of the main applications of ECC is as structural reinforcement in the construction or rehabilitation of rigid and flexible pavements. In order to adapt the ECC to the Brazilian environment, polypropylene fibres have been used instead to PVA fibres. Moreover, rice husk ash (RHA) has also been used as a partial replacement to cement, aiming to produce an environmentally friendly and a more economically viable version of the ECC. This work presents the results obtained for ECC mixtures containing 10%, 20% and 30% (by volume) of non-processed rice husk ash, as a replacement to cement. An experimental study has been carried out to investigate the tensile behavior and durability issues of these ECCs. The results indicate that the use of RHA is technically viable and that the replacement of 30% cement by RHA leads to the most promising performance in terms of high ductility, resistance to crack propagation, decrease in the water absorption and voids content and heat at hydration.

Resumo em Inglês:

ABSTRACT Epoxy resin is one of the most important polymeric matrixes for diverse uses, such as aeronautical, mobile, electronics and others. Providing a material capable of self-healing microcracks will allow it to have a more reliable and longer use. In order to study this new property of self-healing to an epoxy resin, a Differential Scanning Calorimetry (DSC) study was carried out to measure physical chemical properties such as activation energy, enthalpy of polymerization, order of reaction and pre-exponential factor based on an Arrhenius equation modelling. The materials used are diglycidyl ether of bisphenol A (DGBA) as the core material, triethylenetetramine (TETA) and an aminated polydimethylsiloxane (ADM), as curing agent and poly(urea-formaldehyde) (PUF) as microcapsule wall. Tests were done by dynamic and isothermal DSC of systems containing the resin and microencapsulated curing agent and also the resin with the free curing agent. The results showed the necessity of heating for the cure and the self-healing to be initiated.

Resumo em Inglês:

ABSTRACT Pipelines are subject to a variety of defects such as wall thickness loss, grooves, dents and holes. To restore the pipe integrity, polymeric composite repairs can be used. The inspection of repaired pipes is of fundamental importance, not only to verify the initial integrity, but also to monitor their state over time. Shearography is a laser optical strain measurement technique which compares a strain image in unstressed and stressed conditions to reveal the presence of defects and provides useful information about the interface between the repair and substrate, identifying delamination, interfacial disbond and holes. In this work, two pipes repaired with composites from two different providers were submitted to shearography inspection in order to analyze the repair system integrity. The inspections were performed to verify the presence or absence of detachments between the composite repair and subtracts and/or between the layers of the repair itself. After the procedure, the repairs were removed to compare and confirm the inspection results. Repair A presented some difficulty to be removed, what is in accordance with shearography results that exhibited the presence of only some superficial defects. The pipe surface aspect after composite removal was good, without any type of corrosion. On the other hand, the shearography inspection of repair B indicated lack of adhesion between the steel pipe and the composite repair. The repair removal was very easy, corroborating the inspection results. Also, it was observed that the pipe surface presented metal oxides. Through these inspections it could be noted an excellent correlation between shearography inspection results and the degree of difficulty to remove the repairs. The results from an inspection in an offshore platform are also presented. This inspection showed that shearography is an efficient method to inspect steel pipes repaired with composite materials in field.