Resumo em Inglês:

Abstract In this work, natural and thermally modified Chocolate B clays were used for batch adsorption of Pb2+ and Zn2+ from an aqueous solution. The materials were characterized by X-ray diffraction, X-ray fluorescence spectroscopy, nitrogen adsorption, and cation exchange capacity. The tests were performed in a finite bath following a 22 factorial design, with the variables: pH and initial concentrations of metal. Results revealed that the thermal treatment caused alterations on the Chocolate B clay structure and decreased the specific surface area. Affinities between Pb2+ or Zn2+ and Chocolate B clay were found with adsorption capacities up to 3.36 and 3.72 mg.g-1, respectively. The maximum adsorption capacities were 6.79 mg.g-1 for Pb2+ and 3.35 mg.g-1 for Zn2+ using thermally activated clay. The Langmuir and Freundlich models were used for the adsorption equilibrium analysis, and the Langmuir model provided the best fit for sorption isotherms. The adsorption kinetics was evaluated by two models: pseudo-first-order and pseudo-second-order. The pseudo-first-order kinetic model represented well the mechanism of interaction involved during Pb2+ adsorption into the pores of the clay. However, the two models represented well the mechanism of interaction of Zn2+ adsorption into the pores of the clay.

Resumo em Português:

Resumo Desenvolveu-se uma placa cerâmica porosa utilizando resíduo de vidro e lama de cal e simulou-se a aplicação em fachada ventilada. O resíduo de vidro foi usado como substituto total (100%) do feldspato. A lama de cal foi usada como material porogênico. Foi realizado um planejamento experimental com variações de 20% a 40% de lama de cal e temperatura de queima entre 860 e 1020 °C. As placas obtidas foram submetidas a testes de tensão da ruptura à flexão e porosidade total. Na melhor condição experimental, a placa contendo 40% de lama de cal queimada a 1020 °C apresentou tensão de ruptura à flexão de 7,25 MPa, porosidade total de 37,5% e absorção de água de 21,8%. No ensaio de desempenho quanto ao isolamento térmico das placas, esta amostra apresentou melhor desempenho térmico em relação à amostra comercial avaliada.

Resumo em Inglês:

Abstract A porous ceramic plate was developed using glass residue and lime mud and simulated application on a ventilated facade. The glass residue replaced 100% feldspar. Lime mud was used as a porogenic material. An experimental design was carried out with variations of 20% to 40% of lime mud and firing temperature between 860 and 1020 °C. The obtained plates were submitted to tests of flexural strength and total porosity. In the best experimental condition, the plate containing 40% of lime mud fired at 1020 °C had a flexural strength of 7.25 MPa, total porosity of 37.5%, and water absorption of 21.8%. In the thermal insulation performance test of the plates, this sample presented a better thermal performance in relation to the commercial sample evaluated.

Resumo em Inglês:

Abstract The capability to recycle waste materials, such as steel slag, has appealed to the construction industry, as the cement industry faces a major challenge to reduce carbon dioxide (CO2) emissions into the atmosphere. This paper investigated the obtainment of cement pastes with Kanbara reactor desulfurization waste slag (KR slag) through alkaline activation using silicate and sodium hydroxide solutions. The mixtures were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), compressive strength, and physical property tests. The FTIR, XRD, and TGA results pointed to chemical activation, forming C-S-H and C-(A)-S-H gels. The formation of these compounds indicated the possibility of using KR slag in cementitious composites for civil construction.

Resumo em Inglês:

Abstract Materials by the modified proteic method based on calcium doped LaMnO3 and LaNiO3, with perovskite structure were prepared. The X-ray diffraction patterns revealed the presence of the perovskite phase in all materials, whose specific surface area values varied between 27 and 37 m2.g-1. The materials presented efficiency for the removal of Congo red dye and those with site B occupied by nickel presented better adsorptive efficiency. The incorporation of calcium on LaMnO3 or LaNiO3 materials caused an improvement in the performance of the materials for the dye removal from water. The materials maintained perovskite structure after the adsorption tests, allowing their reuse in new adsorption tests with high efficiency.

Resumo em Inglês:

Abstract The viability of preparing cellular ceramics suitable for external wall insulation of buildings was investigated using granite dust, ball clay, plantain peels, sodium silicate, and sodium hydroxide. The predetermined compositions of the raw materials were mixed homogeneously and then subjected to uniaxial pressing at 10 MPa. The formulated samples were oven-dried and sintered in a gas kiln at 850 °C for 3 h. The obtained cellular ceramics were then subjected to standard property tests. The results revealed water absorption of 19.5-41.7%, bulk density of 1.39-1.86 g/cm3, apparent porosity of 36.4-66.7%, thermal conductivity of 0.09-0.62 W/(m.K), and compressive strength of 0.9-18.4 MPa. From the results, the optimum sample of the cellular ceramics prepared is a potential thermal insulation material for load-bearing applications such as walling systems in buildings, where not only low thermal conductivity but also high mechanical strength is required.

Resumo em Inglês:

Abstract Zinc oxide, which has photocatalytic activity, is used as a white pigment in cosmetics. With cosmetics containing zinc oxide, some sebum on the skin is broken down by the UV rays of the sun. In this study, in order to suppress the photocatalytic activity of zinc oxide, zinc oxide was added to an aqueous solution of sodium pyrophosphate and shaken, so that novel white pigment coated with zinc phosphate having no photocatalytic activity was prepared for use in cosmetics. The chemical composition, powder properties, photocatalytic activity, hue (visible light reflectance and L* a* b* values), and smoothness of the resulting powder material were studied. Part of the zinc oxide reacted to zinc phosphate by this pyrophosphate treatment. The photocatalytic activity of zinc oxide was suppressed by this zinc phosphate coating. The resulting sample had sufficiently high reflectance in the visible light region and a high L* value in the L*a*b* color space. The treated samples had lower static friction resistance than the original zinc oxide. Judging from the results of photocatalytic activity, L* value, and smoothness, the optimum conditions were the molar ratio P/Zn of 1/4 for 6 h of shaking the mixture.

Resumo em Inglês:

Abstract The advantages of using zeolites are lower costs and better durability, but it requires longer setting time and slower strength development. Chemical and thermal methods have been developed to overcome these disadvantages and to enhance the reactivity of natural zeolite. This paper addressed through a parametric experimental pozzolanic reactivity, the strength and setting time by varying the cure temperature and the amount and type of chemical activators. To this end, several mixtures of natural zeolite-lime pastes were made with two concentrations of chemical activators including 4% and 8% of NaOH, NaCl, and CaSO4.2H2O. The produced pastes were cured at 20, 40, and 80 °C. The blends were also analyzed by X-ray diffraction and infrared spectroscopy. The results showed that curing at high temperatures accelerated the pozzolanic reactivity and increased the compressive strength. The use of CaSO4.2H2O led to an increase in the consumption of Ca(OH)2 and strength. Adding NaCl improved slightly the compressive strength at high curing temperatures. The addition of 8% NaOH at 40 °C significantly improved reactivity and strength. Setting time was accelerated by adding chemical activators to the blends. The raw zeolite had good pozzolanic activity, but the addition of CaSO4.2H2O enhanced it.

Resumo em Inglês:

Abstract This paper discussed the synthesis of LTA zeolite from Pinheiro clay (PIN) aiming for adsorption of CO2. To obtain the LTA-PIN zeolite, the PIN was submitted to acid treatment, followed by calcination and hydrothermal treatment. These treatments promoted the reorganization of the crystalline structure of the PIN, leading to the LTA-PIN zeolite with 95.79% purity confirmed by XRD, SEM, XRF, and FTIR results. The performance of the LTA-PIN zeolite was similar to the one of the standard LTA zeolite. The CO2 adsorption by the zeolites could be properly described by the pseudo-second-order kinetic and Freundlich isotherm models, suggesting that physisorption was the main mechanism responsible for the deposition of CO2 at the surface of the zeolites. According to regeneration results, LTA-PIN zeolite can be reused five times without significant loss of CO2 adsorption capacity, contrary to the 12% reduction in CO2 adsorption capacity presented by the LTA-standard zeolite.

Resumo em Inglês:

Abstract Mesoporous TiO2 nanoparticles were synthesized by the sol-gel method and using hydrothermal treatment at 200 ºC during different time intervals, which allowed the evaluation of the time or the treatment on the structural, morphological, and optical properties of the oxides. TEM micrographs showed that the morphology of the materials was characterized by the presence of spherical clusters, while the crystalline phases of the anatase and brookite mixtures were analyzed by X-ray diffraction and Raman spectroscopy. A type IV profile was identified from the results of specific surface area, which is characteristic of the mesoporous material with strong and weak affinity. The band gap in the range of 3.29 and 3.40 eV, estimated by the Kubelka-Munk function, showed a gradual increase as a result of oxide crystallization. It was found that 8 h of treatment in a hydrothermal system was sufficient to synthesize a photocatalyst with optimal photocatalytic performance. This efficiency was probably based on a good correlation between physical and chemical factors, such as high surface area and porosity, the improved capability of photon adsorption in the visible range, crystallinity, and a favorable content of brookite.

Resumo em Português:

Resumo O uso de pesticidas, como o fipronil, visa o aumento da produtividade, melhoria na qualidade dos produtos gerados e a diminuição de prejuízos. Contudo, os resíduos acumulados podem ser lavados durante as chuvas, ocasionando a contaminação de águas superficiais e subterrâneas. Nesse aspecto, a combinação entre semicondutores na forma de heteroestruturas é uma alternativa para degradação de tais poluentes. Heteroestruturas BiVO4/CePO4 e CePO4/BiVO4 foram sintetizadas pelo método de coprecipitação seguido de tratamento hidrotérmico assistido por micro-ondas, a 130 °C por 30 min. Os estudos de difração de raios X demonstraram a formação das heteroestruturas com estruturas de fase hexagonal (CePO4) e tetragonais scheelita e zircônia (BiVO4). Os resultados obtidos por microscopia eletrônica de transmissão e espectroscopia de infravermelho sugeriram a formação de uma região de interface, a qual contribuiu na sinergia entre os catalisadores. As heteroestruturas BiVO4/CePO4 e CePO4/BiVO4 apresentaram degradação de 80,06% e 99,50%, respectivamente, frente ao pesticida fipronil.

Resumo em Inglês:

Abstract The use of pesticides, such as fipronil, aims to increase productivity, improve the quality of agricultural products generated, and reduce losses. However, pollutants accumulated can be loaded during rains, causing contamination in the surface and groundwater. Therefore, the combination of different semiconductors to form heterostructures can potentiate the degradation of such pollutants. BiVO4/CePO4 and CePO4/BiVO4 heterostructures were synthesized by co-precipitation method plus microwave-assisted hydrothermal treatment at 130 °C for 30 min. X-ray diffraction studies demonstrated the formation of heterostructures containing hexagonal phase (CePO4) and scheelite and zircon-type tetragonal phases (BiVO4). The obtained results by transmission electron microscopy and Fourier transform infrared spectroscopy results suggested the formation of an interface that contributed to the synergy between catalysts. BiVO4/CePO4 and CePO4/BiVO4 heterostructures showed degradation of 80.06% and 99.50%, respectively, of pesticide fipronil.

Resumo em Inglês:

Abstract Coating layers based on Ca3Si3O9, Ca2ZnSi2O7, and ZnSiO4 on 3Y-TZP ceramics were obtained by the dip coating process, using SiO2-CaO-P2O5-ZnO glass suspensions with Zn contents in the range of 0-20 mol%. The influence of the Zn content in the dip coating slips, the slip solid loading, and the 3Y-TZP surface porosity on the layer formation rate was studied. The Zn content of the dip coating slips as well as the slip solid loading greatly affected the slip viscosity, and consequently the liquid entrainment mechanism at the initial stage. The low dissolution rate of 20 mol% Zn-containing slips decreased the dip coating slip viscosity, whereas the lower stability of 10 mol% Zn-containing slips increased the slip viscosity. A significant increase in the initial layer thickness was produced either by using 10 mol% Zn-containing slips or by increasing the slip solid loading. The casting rate for longer immersion times was markedly accelerated by increasing the 3Y-TZP surface porosity. Sintered layers based on ZnSiO4 having the lowest thickness values were produced using the glass containing 20 mol% Zn. On the other hand, the 0 and 10 mol% Zn-containing glass produced thicker sintered layers mainly composed of Ca3Si3O9 and Ca2ZnSi2O7, respectively.

Resumo em Inglês:

Abstract Ceramics compositions (1-x)Pb(Zr0.53Ti0.47)O3-xGdMnO3 (x= 0, 0.01, 0.02, 0.03, 0.04, and 0.05) were synthesized by solid-state route and sintered at 1180 °C for 2 h. Structural, microstructural, and dielectric properties of the system were investigated. X-ray structural analysis of the materials confirmed their formation in a single phase with a tetragonal crystal structure. The PZT ceramics doped with 0.04 moles of GdMnO3 exhibited denser and finer microstructures, which produced a high relative density of 7.22 g/cm3 (~98% of the theoretic density). Scanning electron microscopy showed uniform distribution of grain and grain boundaries. Comparing with the undoped ceramics, the dielectric properties of the GM-doped PZT specimens are significantly improved. The maximum dielectric constant (εr=475324) and the minimum dielectric loss (6%) were observed for 0.04 moles of GdMnO3, which indicated that the PZT-GM ceramics are promising to lead to practical applications.

Resumo em Inglês:

Abstract Wastes management studies concerning slaker grits, a rich calcium carbonate landfilled residue from the pulp and paper industry, are focused on their application in the construction field due to their calcareous nature. To the best of our knowledge, slaker grits addition in a high calcium content ceramic frit formulation and their behavior as a glaze has not yet been explored, being the aim of this work. Grits were added as a calcium oxide source in 0, 50%, and 100%, and the frits were analyzed regarding their chemical composition, devitrification, sintering behavior, morphology, colorimetric coordinates, and scratch resistance. By means of comparison, the commercial frit was also characterized. The glazes were analyzed by their physical and thermal properties and scratch resistance. Grits did not prevent the vitreous phases obtention and, compared to the commercial frit, presented a similar behavior, although resulted in higher wollastonite devitrification that directly affected glazes’ thermal properties, sintering contraction, linear thermal expansion coefficient, among others. A great outcome was the quartz scratch resistance of the glaze containing the highest grits content, revealing an optimized behavior. Grits residue proved to be a promising alternative raw material capable of generating sustainable and economic perspectives for the ceramic coating sector.

Resumo em Português:

Resumo As cerâmicas porosas podem ser utilizadas nas mais diversas aplicações, como na indústria petroquímica e na área da saúde. No entanto, é difícil produzir cerâmicas com formas complexas usando processos convencionais. Neste trabalho, diferentes termoplásticos (PEBD, ABS e PLA) foram utilizados para a extrusão de filamentos com alumina submicrométrica. Estes filamentos foram extrudados com e sem ácido esteárico que, posteriormente, foram utilizados na manufatura aditiva para a impressão de estruturas porosas (scaffolds) pelo método de fabricação por filamento fundido. Foram obtidas imagens por microscopia eletrônica de varredura das amostras com e sem o ácido esteárico, antes e após a sinterização. Estas imagens mostraram que a presença do ácido esteárico reduziu a formação de defeitos, pois além de atuar como dispersante também facilitou a posterior remoção do veículo orgânico do scaffold, antes da sinterização final.

Resumo em Inglês:

Abstract Porous ceramics can be used in the most diverse applications, such as in the petrochemical industry and in the health area. However, it is difficult to produce ceramics with complex shapes using conventional processes. In this work, different thermoplastics (LDPE, ABS, and PLA) were used for the extrusion of filaments with submicrometric alumina. These filaments were extruded with and without stearic acid and, subsequently, were used in additive manufacturing for printing porous structures (scaffolds) by fused filament fabrication. Scanning electron microscopy images of the samples with and without stearic acid were obtained before and after sintering. These images showed that the presence of stearic acid reduced the formation of defects since, in addition to acting as a dispersant, it also facilitated the subsequent removal of the organic vehicle from the scaffold, before final sintering.