Simulação numérica do perfil de microssegregação na solidificação rápida de um sistema Ag-Cu

A model was used to simulate solute distribution during rapid solidification of a system Ag-15%massCu with initial undercooling of 5 K, 10 K and 30 K. Boettinger et al (1987) measured the microsegregation profile in Ag-Cu alloys superficially treated with a focused electron beam (resolidification). In that work, they found an irregular variation for Cu concentration in cross sections of the resolidified microstructures. In some cases, the profile of concentration versus radius presented a W shape. Current models of microsegregation predict a monotonic variation the concentration depending on the cell radius, which are apparently not in accordance with the acquired measurements. The present study used a numeric model to evaluate the solidification of Ag-Cu alloy under same conditions to the Boettinger´s experiment. Numerical results are for a metallic spherical drop, initially liquid, cooled by convection. Solidification starts in the center of the droplet in a given undercooling. The algorithm used here is based on a model in volumetric average of the quantities and the balance equations in a representative elementary volume for treating a solid/liquid mixture. Inside the droplet transport of energy and mass are repurely diffusive processes of average quantities. The algorithm used permitted a global analysis of the phenomena occurring during the solidification process, as well as a local analysis of the quantities involved, which has been shown to be a prerequisite for the prediction of non-monotonic profiles of microsegregation, such as those measured in the experiment mentioned above.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESFoi utilizado um modelo para simular a distribuição de soluto durante a solidificação rápida de um sistema Ag-15%Cu com superresfriamentos iniciais de 5 K, 10 K e 30 K. Boettinger et al (1987) mediram o perfil de microssegregação em ligas Ag-Cu tratadas superficialmente com um feixe de laser (resolidificação). Nesse trabalho, os autores constataram uma variação irregular para a concentração de cobre em seções transversais de células nas microestruturas resolidificadas. Em alguns casos um perfil de concentração ao longo do raio em forma de W foi medido. Os modelos de microssegregação atuais, em geral, preveem uma variação monotônica da concentração em função do raio da célula, o que aparentemente não está de acordo com as medições obtidas. No presente trabalho, foi usado um modelo numérico para avaliar a solidificação de uma liga Ag-Cu em condições análogas às do experimento de Boettinger. Os resultados numéricos são para uma gota metálica esférica, inicialmente líquida, resfriada por convecção. A solidificação tem início no centro da gota em um superresfriamento dado. O algoritmo usado foi desenvolvido previamente para um modelo baseado na tomada de médias volumétricas das grandezas e das equações de balanço descritivas em um volume elementar representativo para tratar com uma mistura sólido/líquido. No interior da gota, os transportes de energia e massa são processos puramente difusivos de grandezas médias. O algoritmo usado permite não apenas uma análise global dos fenômenos que ocorrem durante o processo de solidificação, mas também uma análise local das grandezas envolvidas, o que demonstrou ser condição necessária para a previsão dos perfis não monotônicos de microssegregação, tais como os medidos no experimento mencionado acima

Montmorilonita como suporte para remoção de proteínas no processo de clarificação/estabilização dos vinhos e para obtenção de pigmentos híbridos

Adsorption of organic molecules in the clays minerals can lead to the formation of the hybrid materials and/or nanocomposites through different interaction mechanisms, making these materials interesting for several applications. The present work presents two different applications for a montmorillonite clay : as a support for the removal of proteins in the process of wine clarification/stabilization and as a support to obtain new pigments, investigating the structural modifications and emphasizing the interactions between the organic compounds and the surface of the inorganic material. In the first study, the nanocomposites based on the adsorption of a model protein and a polyphenol of interest on the surface of the montmorillonite, in a model hydroalcoholic solution, were investigated. The amount of the organic part was determined by ultraviolet-visible (UV-VIS) and thermal (TG/DTG) analysis. X-ray diffraction (XRD) and transmission electronic microscopy (TEM) analyzes reported on the stacking/exfoliation of the layers in the nanocomposites. Nuclear magnetic resonance (NMR) and infrared spectroscopy (ATR-FTIR) methods emphasized the formation of a complex between the protein and the polyphenol before adsorption on the claymineral. The motility/stiffness of the organics was determined by time resolved fluorescence spectroscopy. In the second study, pigments were prepared based on the carminic acid and alizarin organic dyes loaded under montmorillonite pillarized with of Al or Tications, at different pH. The stability of the pigments formed was tested under light for 340 h. The pillarization process was investigated by X-ray diffraction, textural analysis, transmission electronic microscopy and nuclear magnetic resonance in the solid state of 27Al. The interactions between the dyes and the inorganic support were highlighted by infrared spectroscopy, 13C and 27Al solid nuclear magnetic resonance and time resolved fluorescence. The spectra confirmed the complexation between the structure of the dyes and the modified clay, through different adsorption sites. Hybrid pigments based on Al-pillared montmorillonite were more stable under light than the Ti-based hybrids. In oil paint formulations, the pigments were shown to be stable even over a long period of irradiation.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESA adsorção de moléculas orgânicas nas argilas pode levar à formação dos materiais híbridos e/ou nanocompósitos através de diferentes mecanismos de interação, tornando estes materiais interessantes para diversas aplicações. O presente trabalho apresenta duas diferentes aplicações para uma argila montmorilonita: como suporte para remoção de proteínas no processo de clarificação/estabilização dos vinhos e como suporte para obtenção de novos pigmentos, investigando as modificações estruturais e ressaltando as interações entre os compostos orgânicos e a superfície do material inorgânico. No primeiro estudo, foram investigados os nanocompósitos baseados na adsorção de uma proteína modelo e um polifenol de interesse na superfície da montmorilonita, em uma solução hidroalcoólica modelo. A quantidade da parte orgânica foi determinada por análise de ultravioleta-visível (UV-VIS) e térmica (TG/DTG). As análises de difração de raios-X (DRX) e microscopia eletrônica de transmissão (MET) informaram sobre o empilhamento/esfoliação das camadas nos nanocompósitos. Os métodos de espectroscopia de ressonância magnética nuclear (RMN) e infravermelho (ATR-FTIR) enfatizaram a formação de um complexo entre a proteína e o polifenol antes da adsorção no argilomineral. A mobilidade/rigidez das partes orgânicas foi determinada por espectroscopia de fluorescência resolvida no tempo. No segundo estudo, foram preparados pigmentos à base dos corantes orgânicos ácido carmínico e alizarina carregados sob montmorilonita pilarizada com cátions de Al ou Ti, em diferentes pH. A estabilidade dos pigmentos formados foi testada sob luz durante 340 h. O processo de pilarização foi investigado por difração de raios-X, análise textural, microscopia eletrônica de transmissão e ressonância magnética nuclear no estado sólido do 27Al. As interações entre os corantes e o suporte inorgânico foram destacadas por espectroscopia de infravermelho, ressonância magnética nuclear no estado solido do 13C e 27Al e fluorescência resolvida no tempo. Os espectros confirmaram a complexação entre a estrutura dos corantes e o argilomineral modificado, através de diferentes sítios de adsorção. Os pigmentos híbridos baseados em montmorilonita pilarizada com Al foram mais estáveis sob luz do que os híbridos à base de Ti. Em formulações de pintura a óleo, todos pigmentos se mostraram estáveis mesmo sob um longo período de irradiação

Monitoring diclofenac adsorption by organophilic alkylpyridinium bentonites

International audienceOrganoclays have been applied as efficient adsorbents for pharmaceutical pollutants from aqueous solution. In this work, dodecylpyridinium chloride (C12pyCl) and hexadecylpyridinium chloride (C16pyCl) cationic surfactants were used for the preparation of organobentonites destined for diclofenac sodium (DFNa) adsorption, an anionic drug widely detected in wastewater. The organofunctionalization of the clay samples was performed under microwave irradiation at 50 °C for 5 min with surfactant amounts of 100% and 200% in relation to the cation exchange capacity (CEC) of the pristine bentonite. The amount of incorporated ammonium salts based on CHN elemental analysis was higher for all samples prepared with 200% of the CEC. The basal spacings of the organoclays ranged from 1.54 to 2.13 nm, indicating the entrance of organic cations into the interlayer spacing of the clay samples, and the spacing depended on the size of the alkyl organic chain. The hydrophobic character of the organobentonites was verified by thermogravimetry and infrared spectroscopy (FTIR). The adsorption isotherms showed that the drug capacity adsorption was influenced by the amount of surfactant incorporated into the bentonite, the packing density and the arrangement of the surfactants in the interlayer spacing. Zeta potential measurements of the organobentonites and FTIR analysis after drug adsorption suggested that electrostatic and nonelectrostatic interactions contributed to the mechanism of adsorption

Going through the wine fining: Intimate dialogue between organics and clays

International audienceWine chemistry inspires and challenges with its complexity and intriguing composition. In this context, the composites based on the use of a model protein, a polyphenol of interest and montmorillonite in a model hydroalcoholic solution have been studied. A set of experimental characterization techniques highlighted the interactions between the organic and the inorganic parts in the composite. The amount of the organic part was determined by ultraviolet-visible (UV–VIS) and thermal analysis. X-ray diffraction (XRD) and transmission electronic microscopy (TEM) informed about the stacking/exfoliation of the layers in the composites. Vibrational and nuclear magnetic resonance spectroscopies methods stressed on the formation of a complex between the protein and the polyphenol before adsorption on the clay mineral. The mobility/rigidity of the organic parts were determined by fluorescence time resolved spectroscopy. Changes in the secondary structure of the protein occured upon complexation with polyphenol on clay mineral due to strong interactions. Although not representating faithfully enological conditions, these results highlight the range and nature of mechanisms possibly involved in wine fining

Hybrid Pigments from Bixin Dye and Inorganic Matrices

Annatto dye is a natural organic dye belonging to carotenoids, whose main components are bixin and norbixin. Due to its low stability, it is convenient to protect the dye molecules with other materials. The use of clay minerals is an alternative, which are phyllosilicates with attractive physico-chemical properties, such as high specific surface area, cation exchange capacity, mechanical/chemical stability and non-toxicity. The main purpose of this work was to develop hybrid materials, using annatto dye and clay mineral modified with different inorganic cations, and then, to evaluate the stability of the new pigments. The process of preparing the modified clay minerals involved mixing a synthetic montmorillonite in solutions containing the precursor salts of the metal cations. Subsequently, the dye was dissolved in a solution containing water and alcohol, followed by filtration and mixed with the modified clay, giving rise to the hybrid pigments. Through the characterizations, it was noted that a variety of colors were obtained, and the sample containing aluminum was the one that most adsorbed the dye and showed a significant increase in stability at high temperatures. This hybrid material was better to dye than its pure form. Therefore, the bixin/montmorillonite pigments are promising for replacing artificial colors in practical applications such as in the cosmetics, food or pharmaceutical industries

Facile Synthesis of Ni-Doped ZnO Nanoparticles Using Cashew Gum: Investigation of the Structural, Optical, and Photocatalytic Properties

This work adopted a green synthesis route using cashew tree gum as a mediating agent to obtain Ni-doped ZnO nanoparticles through the sol–gel method. Structural analysis confirmed the formation of the hexagonal wurtzite phase and distortions in the crystal lattice due to the inclusion of Ni cations, which increased the average crystallite size from 61.9 nm to 81.6 nm. These distortions resulted in the growth of point defects in the structure, which influenced the samples’ optical properties, causing slight reductions in the band gaps and significant increases in the Urbach energy. The fitting of the photoluminescence spectra confirmed an increase in the concentration of zinc vacancy defects (VZn) and monovacancies (Vo) as Zn cations were replaced by Ni cations in the ZnO structure. The percentage of VZn defects for the pure compound was 11%, increasing to 40% and 47% for the samples doped with 1% and 3% of Ni cations, respectively. In contrast, the highest percentage of VO defects is recorded for the material with the lowest Ni ions concentration, comprising about 60%. The influence of dopant concentration was also reflected in the photocatalytic performance. Among the samples tested, the Zn0.99Ni0.01O compound presented the best result in MB degradation, reaching an efficiency of 98.4%. Thus, the recovered material underwent reuse tests, revealing an efficiency of 98.2% in dye degradation, confirming the stability of the photocatalyst. Furthermore, the use of different inhibitors indicated that •OH radicals are the main ones involved in removing the pollutant. This work is valuable because it presents an ecological synthesis using cashew gum, a natural polysaccharide that has been little explored in the literature

The Role of Clay Mineral-Derived Photocatalysts in Insights of Remediation

Clay minerals have advantages to be used as supports for obtaining new catalysts, in which colloidal and surface characteristics play a significant role. In addition to their favorable physicochemical properties, clay minerals allow different modifications to form structures with broad photochemical capabilities. This review collects pertinent works of semiconductor nanoparticles loaded onto clay minerals and their potential application in hazardous contaminant photodegradation. Web of Science, Scopus, and Science Direct were used for bibliographic research databases. The sol–gel method is the most frequent technique used to obtain semiconductors immobilized onto clay minerals, but other methods have also proven helpful in forming these structures. Thence, the types of synthesis and different parameters that influence their photocatalytic efficiency will be discussed. Pillared clay minerals have been applied to photo-oxidation reactions involving photodecomposition of environmental contaminants. The homogeneous dispersion of nanoparticles on the surface of clay minerals, reduction of fine particles, its non-toxicity, and the generation of a suitable suspension for photocatalytic reactions may be the main characteristics of these inorganic supports to obtain successful photoactive materials

The Role of Clay Mineral-Derived Photocatalysts in Insights of Remediation

Clay minerals have advantages to be used as supports for obtaining new catalysts, in which colloidal and surface characteristics play a significant role. In addition to their favorable physicochemical properties, clay minerals allow different modifications to form structures with broad photochemical capabilities. This review collects pertinent works of semiconductor nanoparticles loaded onto clay minerals and their potential application in hazardous contaminant photodegradation. Web of Science, Scopus, and Science Direct were used for bibliographic research databases. The sol–gel method is the most frequent technique used to obtain semiconductors immobilized onto clay minerals, but other methods have also proven helpful in forming these structures. Thence, the types of synthesis and different parameters that influence their photocatalytic efficiency will be discussed. Pillared clay minerals have been applied to photo-oxidation reactions involving photodecomposition of environmental contaminants. The homogeneous dispersion of nanoparticles on the surface of clay minerals, reduction of fine particles, its non-toxicity, and the generation of a suitable suspension for photocatalytic reactions may be the main characteristics of these inorganic supports to obtain successful photoactive materials

Antimicrobial efficacy of building material based on ZnO/palygorskite against gram-negative and gram-positive bacteria

This study investigated ZnO nanoparticles immobilized in palygorskite clay mineral (Pal) that acted as an inorganic antimicrobial agent in a commercial mortar aiming to control microorganisms and improve safety and stability for building applications. ZnO/Pal nanocomposites were obtained by sol-gel methods at pH 7 and 11 and were calcined at 250 °C and 400 °C to evaluate different synthesis parameters. The mortar/ZnO/Pal composite was obtained using 5% (by weight) ZnO/Pal hybrid mixed with a commercial mortar. The results show that pH and calcination temperature influenced the properties of ZnO/Pal. ZnO was observed in the ZnO/Pal samples during the wurtzite phase by analyzing the XRD patterns. FTIR spectra illustrated the interactions between ZnO nanoparticles and the fibrous clay mineral. TG-DTG analysis showed the thermal events of Pal before and after zinc incorporation. Scanning electron microscopy (SEM) evaluated ZnO morphology as spherical in shape and dispersed on the fibers of the clay minerals, which presented needle-like morphology. ZnO/Palygorskite showed a possible antibacterial effect when used in mortar formulation. The mortar/ZnO/Pal composites were effective against Escherichia coli and Staphylococcus aureus bacteria when tested by the direct contact method in darkness and in visible light and could be an alternative antimicrobial material for building surfaces.info:eu-repo/semantics/publishedVersio

Clays as Vehicles for Drug Photostability

Clay minerals are often used due to their high adsorption capacity, which has sparked interest in their biological applications to stabilize drugs and pharmaceutical products. This research aims to summarize information about the stability of drugs, cosmetics, dermocosmetics, and pharmaceutical compounds incorporated in the structure of different clay minerals. The databases used to search the articles were Web of Science, Scopus, PubMed, and Science Direct. Photostabilization of these compounds is reviewed and its importance demonstrated. For biological applications, the increase in solubility and bioavailability of clay minerals has proven useful for them as drug carriers. While their natural abundance, low toxicity, and accessible cost have contributed to classical applications of clay minerals, a wide range of interesting new applications may be facilitated, mainly through incorporating different organic molecules. The search for new functional materials is promising to challenge research on clay minerals in biological or biotechnological approaches