Resumo em Inglês:

Abstract CuCrO2 was synthesized by solution combustion synthesis (SCS) and applied as a heterogeneous catalyst to produce soybean biodiesel. The combustion reaction was carried out using urea as a fuel, and copper (II) and chromium (III) nitrates as precursors. After the powders’ obtention, these were calcined and functionalized in an acidic medium. The powders were characterized by thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), and infrared spectroscopy (IR) techniques. The TG curve revealed that the formation of the CuCrO2 in the combustion reaction remained stable up to 1000 °C. The XRD results confirmed the formation of the CuCrO2 compound. The SEM images showed that the crystallinity of the samples increased after the calcination process. The IR spectra showed the presence of delafossite characteristic bands. After the transesterification reaction, biodiesel was obtained with a yield of around 80%. Thus, catalysts based on delafossite synthesized through the combustion method and functionalized showed to be promising for the transesterification reaction of vegetable oils.

Resumo em Inglês:

Abstract The global interest in an increasingly sustainable economy, with a reduction in the consumption of raw materials and energy, can be supported by the growth in the use of lightweight concrete (LC) produced with expanded-clay aggregates (EA). The main qualities of natural self-bloating clay for the production of EA were studied, analyzing the parameters that determine the expansion during firing, which influence EA size, mechanical strength, density, and water absorption. After this step, the production and characterization of the LC were carried out. EA characteristics showed a strong influence on the mechanical strength and the main technological properties of the LC. The results pointed out the necessary attributes that clay (and EA) must have for LC production. These attributes can also be achieved by mixing different clays (blend type), which can enhance the production and use of LC with EA worldwide.

Resumo em Inglês:

Abstract The photoluminescent behavior of Eu-doped Sr3Al2O6 obtained by highly efficient solution combustion synthesis is reported. In order to understand the influence of the fuel on the synthesis, the stoichiometric quantity and an excess of fuel were evaluated. By adjusting the amount of fuel, different luminescence responses were obtained, allowing europium cations incorporation into the Sr3Al2O6 lattice to serve as effective luminescence activators in such a short time during the rapid combustion synthesis process. The higher amount of fuel in the presence of the oxidizing agent produced Sr3Al2O6:Eu particles with higher phosphorescence brightness, owing to the increase of the reduction process from Eu3+ to Eu2+. The synthesized phosphor showed an intense band emission centered at 515 nm and could be excited over a broad spectral range in the UV-visible region. Particles having nanostructured flake-type morphology were obtained, which was considered a micro-nanofunctional candidate for practical applications.

Resumo em Inglês:

Abstract This study analyzed how the compositional variability of dimension stone residues influences the characteristics of rustic porous ceramic tiles. The specimens were prepared by adding 20 wt% of dimension stone residue to the clay and sintered at 1000 °C for 1 h. The testing assays performed were physical properties and structural analysis through scanning electron microscopy. The results indicate that water absorption was lower (~9% to 14%) in samples containing silicate residues compared to carbonate residues (~16%). Apparent porosity of ~21% to 25% and shrinkage of 0.5% to 1.6% were measured in silicate samples while higher apparent porosity of ~30% and expansion of -0.04% were found in carbonate samples. Flexural strength and modulus of rupture were similar, ~16 MPa and ~330 N, respectively, for both sample sets. The samples containing silicate residues whose SiO2 content was between 48% and 58% and the sum of alkaline and alkaline earth oxides was less than 18% were suitable for manufacturing rustic porous ceramic tile, while residues with high SiO2 or carbonate contents impaired the properties of the ceramic bodies. Therefore, it is recommended that the dimension stone residues intended for use in ceramic tiles be previously separated according to chemical and mineralogical characteristics.

Resumo em Inglês:

Abstract A glass-ceramic in the SiO2-K2O-CaO-P2O5 quaternary system was prepared by substituting the Na2O component with K2O to avoid Na2Ca2Si3O9 formation upon thermal treatment since this phase decreases apatite formation kinetics on glass material. To form the glass-ceramic, a modified sol-gel method involving solution precipitation, followed by reagents encapsulation in citric acid was adopted to enable the use of sodium metasilicate as a cheap substitute for traditional alkoxysilane silica precursors. The foam replication method using polyurethane foam as a sacrificial template was used to obtain the scaffold, which on analysis gave a porosity of 92% and an average pore size of 36±6 mm. In vitro bioactivity evaluation in simulated body fluid for a maximum of 14 days indicated the formation of hydroxyapatite on the sample surface. Phase analysis showed that CaSiO3 and K2CaSiO4 crystals formed in the sintered sample as the main phases, which exhibited biodegradability in simulated body fluid (SBF). Therefore, economically-derived porous bioactive glass-ceramic scaffolds based on the current method (a simple process) are feasible.

Resumo em Inglês:

Abstract Two different reactive concentrated magnesium hydroxide (HM) pulps, produced in a lab reactor mill, and a synthetic and non-reactive HM-pulp, for comparative analyses, have been prepared and studied. Sodium polyacrylate was selected as a dispersant for improving the HM pulp fluidity, with concentrations varying from 0.42% to 2.0% on a dry basis. The two reactive pulps differed from each other mainly by the impurity level and for both, a residual MgO amount was detected, implying that the hydration reaction could proceed. Results (with and without dispersant) confirmed the formation of particle clusters as HM concentration rose until a critical value, above which the pulp behaved as a solid. Reactive HM-pulps with high impurities may represent a limiting factor in the drying operation. Among all HM-pulps studied, the purest reactive pulp with 1% dispersant presented the best flow behavior making this reactive pulp the most suitable to be tested in a pilot spray dryer.

Resumo em Inglês:

Abstract The effect of synthesis parameters on the microstructural behavior and morphology during the yttrium oxide (Y2O3) formation is reported. Y2O3 crystals were produced by a modified sol-gel route assisted by polyvinyl alcohol solution varying the calcination temperature and solution pH. The crystalline phase formation was investigated using X-ray powder diffraction combined with the Rietveld refinement method. The microstructural properties were analyzed by using the Williamson-Hall formalism. The calcination temperature followed the thermal events observed in the differential thermal analysis combined with the thermogravimetric analysis of the precursor xerogel. It was seen that the combination of PVA and pH variation can be used to minimize the calcination time and temperature. The morphological analysis showed samples with different sizes and appearances depending on pH and calcination temperature. Therefore, it was shown that the parameters in the synthesis process can be used to tailor the properties of Y2O3, such as crystallite size, degree of structural ordering, and morphology, and consequently, improve the desired application.

Resumo em Inglês:

Abstract The effect of the calcination temperature at 800 and 1000 °C on the stable formation of the tricalcium phosphate with rhombohedral structure in the system of the hexagonal crystal family was determined, while its precursor was made from limestone obtained from nature in the Lumajang district, Indonesia. The rhombohedral tricalcium phosphate samples were prepared by sol-gel routine, then examined by several tests, such as, Fourie transform infrared spectroscopy to study the deficiency of -OH, X-ray diffraction test to study the microstructure of the tricalcium phosphate with the rhombohedral structure in a hexagonal crystal system, differential scanning calorimetry and thermogravimetry tests to study thermal characteristics, scanning electron microscopy and energy dispersive spectroscopy to study the surface topography and to obtain the atomic ratio Ca/P ~1.5. Finally, the UV-vis test found the optical energy gap, Eg, from ~5.34 to ~5.41 eV for the sample calcined at 800 °C and Eg ~5.19 to ~5.21 eV at 1000 °C.

Resumo em Inglês:

Abstract Mortar coatings have a major influence on a building’s aesthetics, valorization, and habitability, with significant effects on the mechanical behavior of masonry walls. Multiple types of meshes can be embedded in plaster to enhance both masonry and coating’s mechanical behavior, restrain crack formation, enhance the bonding between layers, and increase the wall’s seismic resistance. The reinforcement technique has simple execution and is suitable for many applications, including the strengthening of non-load bearing walls, façade performance improvement, and restoration of historical buildings. However, there is an absence of guidelines and specifications for design and execution, resulting in high variability in field applications due to the many variables involved and few in-depth studies. This paper presents a systematic review of the effects of mesh reinforcement in cementitious mortar coatings and its major applications. Mortar and mesh parameters and influences, the status of analytical and simulation models, and suggestions for future research are described.

Resumo em Inglês:

Abstract For oxide semiconductors for application in dye-sensitized solar cells (DSSCs), titanium dioxide conjugated with zinc oxide thin films was synthesized and characterized. The UV (ultraviolet) spectrum characterization showed a peak of absorbance at around 355 nm, with a band gap of 3.25 eV and reflectance around 85%. Such characteristics allowed the fabrication of DSSCs with N719 dye, under simulated light of 100 mW/cm2. The highest efficiency of 1.17% was at 5% titanium dioxide and 4 h of dye immersion.