Advances in electrospun composite polymer/zeolite and geopolymer nanofibers: A comprehensive review.

Política de acceso abierto: https://v2.sherpa.ac.uk/id/publication/16964Electrospinning is widely recognized as an efficient, simple, and cost-effective technique for producing nanofibers. It has successfully led to the fabrication of various ultrafine polymer composites. This method has spurred extensive research in fields such as medicine, electronics, chemistry, and physics, where producing materials via electrospinning is very promising for revolutionizing many fields. This paper presents a comprehensive review of the latest research and developments on electrospun composite polymer/zeolite nanofibers and geopolymers. The study examines processing, structure, characterization, and potential applications. Detailed information on these composites, including their specific electrospinning conditions, has been thoughtfully summarized in this work. Furthermore, we address important concerns related to the technology’s limitations and existing research challenges. In the studies analyzed, a diverse range of polymers was employed, the most frequent were polyvinyl alcohol, polycaprolactone, and polylactic acid. The applications of zeolite/polymer composites were equally varied, encompassing fields such as catalysis, filtration, adsorption, and pesticide residue analysis in food samples. Moreover, these composites were found to be useful in the medical sector, including applications in dental tissue engineering and for treating bacterial infections.Part of this study was funded by project TED2021-130756B-C31 MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” by the European Union Next GenerationEU/PRTR). Brazilian Coordination for the Improvement of Higher Education Personnel (CAPES) Project Number 88881.142487/2017-01; CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico (Grant 401697/2022-3

Estudo das propriedades mecânicas de porcelanato através da avaliação de tensões residuais microscópicas originadas durante a etapa de resfriamento do ciclo de queima

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-graduação em Ciência e Engenharia de MateriaisO porcelanato é formado por uma mistura de argilominerais, quartzo e feldspatos. Corresponde à classe de revestimento com melhor desempenho técnico. É constituído basicamente por 50-65% de fase vítrea, 10-25% de quartzo, <10% de mulita, 0-10% feldspatos não fundidos, 3-7% de porosidade fechada. A produção de porcelanato normalmente se faz por conformação por prensagem, a partir de matériasprimas finamente moídas, homogeneizadas por via úmida e granuladas por atomização. A queima ocorre em ciclos rápidos entre 40 e 60 min, com temperaturas máximas entre 1180 e 1220ºC. A etapa de resfriamento do ciclo de queima é realizada o mais rapidamente possível e com escasso controle. A única precaução tomada é reduzir a velocidade de resfriamento durante a transformação alotrópica do quartzo. Normalmente associa-se o desenvolvimento das propriedades mecânicas do porcelanato com os mecanismos de reforço atribuídos às porcelanas, mas dificilmente relacionando quais fatores que apresentam maior relevância. No presente trabalho, o desenvolvimento das propriedades mecânicas do porcelanato foi estudado com base na avaliação do desenvolvimento das tensões residuais macroscópicas e microscópicas. Diferentes magnitudes de tensões macroscópicas foram desenvolvidas por distintas velocidades de resfriamentos e alterando-se a composição de partida (caulinita, quartzo e albita). Os efeitos provocados pelas tensões microscópicas foram analisados alterando-se a composição de partida e o tamanho de partícula do quartzo. As tensões residuais macroscópicas foram medidas pelo método de relaxação de deformações por corte incremental e as tensões microscópicas por difração de raios X. A resistência mecânica e a tenacidade à fratura, método SENB, foram medidas por flexão em três pontos de apoio em máquina universal de ensaios mecânicos. Os resultados demonstraram que o porcelanato desenvolve têmpera quando submetido a resfriamento rápido. Esse processo é controlado pelas mesmas variáveis da têmpera em vidros planos, constituindo dessa forma um importante mecanismo de reforço microestrutural. Paralelamente à têmpera ocorre um processo de deterioração da microestrutura que foi quantificado matematicamente através de uma equação proposta, que associa a deterioração com o crescimento do tamanho do defeito natural de Griffith. Essa deterioração mostrou ser o principal fator que distingue as propriedades mecânicas de diferentes composições. As maiores resistências mecânicas foram obtidas para aquelas misturas que associam tensão macroscópica juntamente com o efeito de reforço provocado pelas partículas de quartzo e proteção microestrutural,, contra essa deterioração, através da interconexão dos cristais de mulita. As diferenças observadas nas tensões sobre as partículas de quartzo estão relacionadas com variações na natureza da interface (sílica amorfa ou mulita/vidro de caulinita ou vidro de albita), e não podem ser associadas indistintamente com o aumento da energia de fratura sem levar em consideração os efeitos deletérios que as fases de baixo coeficiente de expansão térmica causam à matriz vítrea. A metodologia proposta para a determinação da tensão residual microscópica sobre as partículas de quartzo, juntamente com a análise dilatométrica, comprovaram que o quartzo nas composições de porcelanato está parcialmente desconectado e que este fenômeno é controlado pelo comportamento anisotrópico da célula unitária. Desse modo, o quartzo apresenta dois diâmetros críticos a partir dos quais as partículas se desprendem parcial ou totalmente da matriz. The porcelain tile is composed by clay minerals, quartz and feldspars. It is the best ceramic tile considering the technical properties. Basically it is constituted by 50-60% glassy phase, 10-25% quartz, <10% mullite, 0-10% non-fused feldspar and 3-7% of close porosity. Manufacturing is normally done by dry pressing from fine wet grid raw materials which are spray-dried. Sintering is carried out by fast firing, i.e., 40-60 min, and maximum temperature between 1180 and 1220ºC. Cooling stage is done as fast as possible, with a lack of specific control. Only a little decrease is done on the cooling rate during the quartz allotropic transition. The mechanism of developing mechanical properties of porcelain tile is normally associated with that of technical porcelain, but it is not so evident what the most relevant mechanism is. In the present work, the mechanical properties of porcelain tile was evaluated based on the developing of macroscopic and microscopic residual stress. Different levels of macroscopic residual stress were produced by changing the cooling rate and the initial composition (kaolinite, quartz, albite). The effect of microscopic residual stress was evaluated by changing the initial composition and the particle size of quartz. The macroscopic residual stress was measured by deformation-relaxation method with incremental cuts and the microscopic residual stress by x-ray diffraction. The mechanical strength and fracture toughness, SENB method, was measured by three points bending using a universal test machine. The results show that porcelain tile develops tempering when submitted to fast cooling rate. This process is controlled by the same factors of those in float glass, them it can be considered a kind of reinforcing mechanism. As the tempering occurs, a microstructural deterioration also occurs, which was quantified by a proposed model based on an increasing of the Griffith flaw size. This deterioration is the most important mechanism that differs the mechanical properties all the studied composition. The high strength was obtained for those compositions with macroscopic residual stress, matrix reinforced by quartz particles, but with no deterioration during fast cooling. The deterioration was least for those microstructures where interconnected mullite crystal was observed. The observed changing in microscopic residual stress on the quartz particles was related with changes in the interface nature (amorphous silica, mullite/ kaolinite glass or albite glass) and can not be directly associated with matrix reinforced by increasing the fracture energies without considering the deleterious effect of those low thermal expansion phases. The proposed methodology for determination of microscopic residual stress under quartz particle together with dilatometric experiments, could confirm that the quartz particles in porcelain tile are partially disconnected. This phenomenon is controlled by anisotropic behavior of the quartz unit cell. In this way, the quartz presents two critical diameters and the particles can be completely or partially disconnected

Modelagem matemática aplicada ao controle dimensional de placas cerâmicas de monoqueima processadas por via úmida

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Ciência e Engenharia de Materiais.As placas cerâmicas devem ser produzidas dentro de tolerâncias dimensionais estabelecidas por normas. É crescente o uso de técnicas de modelagem matemática com o objetivo de quantificar a influência das variáveis de controle de processo. O modelo desenvolvido leva em consideração variáveis independentes e foi inspirado na teoria da incerteza máxima de medição, equacionado a partir de expansão em série de Taylor. Foram avaliados o material e o processo de duas empresas que produzem revestimentos de monoqueima pelo processo via úmida. O planejamento experimental foi executado avaliando-se cada variável individualmente, em condições industriais e laboratoriais. Os ensaios estão baseados em medidas de tamanho, massa e densidade aparente dos corpos-de-provas. A definição dos limites ideais depende do tamanho das peças e da realidade de cada processo, mas pode-se dizer que variações maiores que 50g de massa da peça, 2ºC de temperatura de queima, 0,5% de umidade do pó atomizado e 8 kgf/cm2 de pressão de compactação aumentam de forma significativa a variação do tamanho final das placas cerâmicas. Para a granulometria, é desejável que as frações classificadas em finos, médios e grossos não sofram variações maiores do que 20%. O retardo de extração foi a variável que apresentou menor influência sobre a variação dimensional

Influence of composition on mechanical behaviour of porcelain tile. Part III: Effect of the cooling rate of the firing cycle

This paper is the third part of a study focusing on determining the influence of the porcelain tile composition on mechanical behaviour of sintered bodies. Tile compositions were prepared according to a simplex-centroid mixture design set out in Part I of this research, in which the microstructural characterisation of sintered specimens was carried out. In Part II the influence of the starting composition on the mechanical properties of sintered porcelain tile was evaluated on the basis of the linear elastic fracture mechanics. Finally, in this last Part, ceramic bodies from seven compositions were subjected to fast cooling after firing, in order to reproduce the industrial cooling rates. The main objective was to analyze the influence of the mineralogical composition of the starting mixture on the development of macroscopic residual stress and growth of flaw size. When the pieces were subjected to fast cooling, flaw size was the main factor determining the variation of the mechanical strength. This increase in flaw size can be interpreted from the Weibull modulus, from 6 to 8 in those mixtures, with high deterioration of mechanical properties. The mullite hypothesis as a strengthening mechanism in triaxial porcelains was clearly manifested when the samples are fast cooled. This mechanism was the main responsible for the strengthening, what contrasts with the increase in flaw size. The microscopic residual stress caused by the thermal expansion mismatch of the phases also acted as a reinforcement mechanism.

Influence of composition on mechanical behaviour of porcelain tile. Part II: mechanical properties and microscopic residual stress

The influence of the starting composition on the mechanical properties of sintered porcelain tile was evaluated based on the linear elastic fracture mechanics. Tile compositions were prepared according to a simplex-centroid mixture design set out in part I of this research. Results were analyzed based on the linear elastic fracture mechanics. The Irwin equation and the experimental data were treated according to a Taylor's series expansion. This methodology made it possible to evaluate the mechanisms which are more relevant for strengthening and the role of each component of the system. It was observed that the phase composition affects markedly the mechanical strength of porcelain tile mainly by changes in fracture energy. Young's modulus and flaw size have also a notable but less important influence. Wide variations in flaw size can cause a more severe impact on the mechanical strength. In turn, the fracture energy is equally affected by the state of microscopic residual stress and the deflection in crack propagation. Regarding to the contributions of the each phase component, it was noticed that mullite and kaolinite glass significantly worsen the fracture energy while quartz particles have a decisive contribution on increasing the fracture energy. Finally, the results confirm once again that the Selsing equation can be used for estimating microscopic residual stress on quartz particles in porcelain tile

Influence of composition on mechanical behaviour of porcelain tile. Part I: microstructural characterization and developed phases after firing

The porcelain tile is a ceramic product with high technical and aesthetic performance, whose composition is formulated from a mixture of clay or kaolin, quartz and feldspar. This paper is the first part of a study focusing on determining the influence of the porcelain tile composition on mechanical behaviour of sintered bodies. Seven compositions were prepared according to a simplex-centroid mixture design for a triaxial mixture, comprised of kaolinite, quartz and albite. The mixtures were processed reproducing industrial conditions: wet mixing followed by spray-drying, forming by pressing and fast firing with maximum temperatures ranged from 1210 to 1260 °C. The presence of kaolinite increases the dry apparent density in a significant way up to 30 wt%. Because of the fast firing, the microstructure is directly influenced by particle packing after forming. The internal porosity presented little change as a function of starting composition in the tested intervals. The surface porosity of the polished product increased with higher amounts of quartz. The results obtained in this first part of the study showed how the starting and end composition could generate the microstructure and suggest its influence on the mechanical properties of the porcelain tile, which will be later analysed in the second part of this paper