Resumo em Inglês:

Abstract Fused alumina is a material used in the manufacturing of abrasive tools, due to its high fusion point, great hardness, and mechanical toughness. In this context, this study addressed the influence of niobium addition on the properties of fused alumina for abrasive applications. A comparison was also made between this oxide and the brown fused alumina and the white fused alumina traditionally applied in this market, using different characterization techniques, such as particle size characterization, scanning electron microscopy, real and bulk density, chemical analysis, fracture resistance, and abrasiveness indexes. Among the main findings of this study, it was possible to observe that the addition of niobium to fused alumina significantly increased the fracture resistance and abrasiveness indexes compared to the brown and white fused alumina.

Resumo em Inglês:

Abstract In this work, the results of a multi-technique characterization of a type of pottery production with high cultural and economic relevance from the only potter town in Argentina are presented and correlated. Raw materials, a prepared paste, and ceramic samples were studied. Chemical, structural, textural, microstructural, and thermal features were assessed and described in terms of the raw materials characteristics, fabrication, and firing conditions. Some distinctive properties of this Casira ceramic production, like the thermal expansion coefficient and other technological properties, are reported for the first time. This allowed the establishment of characteristic behaviors of the ceramics under study, which also constitute the basis for their traceability.

Resumo em Inglês:

Abstract Red ceramic waste (RCW) is one of the main by-products generated by the production of ceramic materials. Its application in lightweight aggregates (LWAs) has not yet been tested. Thus, this review intends to evaluate the perspectives of using RCW in the manufacture of LWAs. The search was carried out in the ScienceDirect database. 47 articles were selected. A significant amount of data on the chemical, physical, mineralogical, and morphological properties of RCW are discussed. In most studies, the chemical constituents of RCW complied with the swelling parameters. The mineralogy of the residue usually has constituents capable of controlling the viscosity and aiding gas formation. The data of granulometry, microstructure, and loss of mass denote the need for special care with the methodology adopted for grinding and sintering of the residue. This review indicates that there is a high potential for the use of RCW in the manufacture of LWAs.

Resumo em Inglês:

Abstract Kiln geometries were developed to reach homogeneous temperatures above 900 °C, during the firing process, aiming to improve the production process of the ceramists from Vale do Jequitinhonha (MG/Brazil). Techniques of reactive flow numerical solution using the software Ansys CFX have been used to foresee the behavior of the firings. Two types of catenary geometries, simple and robust, were studied, capable of being easily reproduced. The firewood used as an energy source in the current kilns and the developed ones, in this research project, favored the control of the kiln’s atmosphere during the firing, beyond being a source found with easiness for the ceramists. The results of the numerical simulations demonstrated the energy efficiency of the kilns and the level of temperature reached. Knowing well thermal and gas dynamic behavior, some parameters of the burning could be improved, aiming for a better quality of used ceramics.

Resumo em Inglês:

Abstract Ceramic macro-needles incorporation as reinforcement in commercial refractory castable was studied. Ceramic macro-needles (Ø2x20 mm) were made from kaolinite clay and gibbsite to obtain mullite as the main crystalline phase. Specimens with the ceramic reinforcement were evaluated by compression after being treated at two temperatures (815 and 1400 °C). The results were compared with those obtained using the same commercial concrete but reinforced with steel fibers and without reinforcement. Compression values presented by specimens with ceramic macro-needles were 74% and 50% higher than specimens with steel fibers after exposition to 815 and 1400 °C, respectively. Based on these results, it was established that ceramic macro-needles are a feasible solution to improve the mechanical resistance of castables exposed to high temperatures.

Resumo em Inglês:

Abstract Nanostructured crystalline composite (activated carbon) was synthesized from residual ashes of the burning process of the sludge generated in the flotation step of a poultry slaughterhouse and was used for Allura red dye adsorption. The ashes were chemically activated using two types of reagents, H2O2 and H3PO4, and the structure, morphology, and surface of the adsorbents were characterized by different techniques such as scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), N2 adsorption/desorption isotherms with Brunauer-Emmett-Teller (BET) method and Barret-Joyner-Hallenda (BJH) method, Fourier transform infrared spectroscopy (MID/FTIR), X-ray diffraction (XRD), and the point of zero charge (PZC). The adsorbent synthesized with H3PO4 at 400 ºC displayed the best performance in removing dye molecules in 10 mg.L-1 solution, with a removal rate of approximately 100% when using a concentration of 2 g.L-1 in particle size of 0.42 mm. Besides that, the adsorbent synthesized with H3PO4 had a particle diameter of approximately 15 Å, a size corresponding to the nanometer range, presented a crystallinity structure with well-defined phases such as quartz and the major elements in the composition were carbon and silicon. The surface area of the ashes enlarged from 14.71 to 448.1 m2.g-1 when H3PO4 was used as an activator, producing a high-quality adsorbent, with an excellent cost-benefit, being it possible to be produced for a price of 9.35 USD.kg-1, a price lower than the commercial activated carbon, making it a promising candidate for application in an industrial environment.

Resumo em Inglês:

Abstract Changes in the structure of phyllosilicate microparticles of submicron fractions of polymineral clay with an average size of 290 nm, as well as changes in the positions of impurity ions of transition metals in the crystal lattice, were studied by X-ray diffraction analysis, Fourier transform infrared spectroscopy, and high-resolution electron paramagnetic resonance spectroscopy. The main composition of microparticles included clinochlore, montmorillonite, calcite, and quartz. Structural transformations were stimulated by heating the samples to 1200 K at a rate of 10 K/min. A decrease in the number of crystal structures of microparticles was recorded due to the amorphization of montmorillonite, the decomposition of calcite, and the formation of sillimanite. Structural rearrangements of crystal cells containing impurity paramagnetic ions Fe3+ and Mn2+ in submicron particles of clinochlore and montmorillonite, accompanied by displacements and changes in the chemical bonds of these ions, were recorded by the ion-electron paramagnetic resonance method. It is shown that when microparticles were heated to 1200 K, the impurity paramagnetic ions of transition metals did not go beyond their crystal cells.

Resumo em Português:

Resumo Células solares com emissor e face posterior passivada (PERC, passivated emitter and rear cell) vêm dominando o mercado fotovoltaico em razão de seu processo de fabricação ser compatível com as linhas industriais que vinham sendo utilizadas e pela produção de dispositivos de alta eficiência. Atualmente o silício tipo p é o mais utilizado pela indústria de células solares, mas o silício tipo n deve ganhar mercado nos próximos anos juntamente com o emprego de lâminas de espessura reduzida. O objetivo deste trabalho é apresentar uma revisão sistemática dos principais estudos na área de células solares base n, sendo elas do tipo PERC, PERT (passivated emitter-rear totally diffused) e TOPCon (tunnel oxide passivated contact), com ênfase para a abordagem de contatos seletivos, emissores seletivos e nos processos utilizados, bem como na análise de células solares de espessura reduzida em relação ao padrão da indústria atual.

Resumo em Inglês:

Abstract The PERC (passivated emitter and rear cell) solar cells have been dominating the competitive photovoltaic market due to their manufacturing process being compatible with the industrial lines that were being used and to produce high efficiency devices. Currently, p-type silicon is the most used by the solar cell industry, but n-type silicon should gain market in the coming years along with the use of thinner wafers. This work is a systematic review that aims to find the main recent studies in the field of n-type solar cells, like PERC, PERT (passivated emitter-rear totally diffused), and TOPCon (tunnel oxide passivated contact), with emphasis on the selective contacts and selective emitters and the processes to obtain them, as well as the analysis of solar cells of reduced thickness in relation to the current industrial standard.

Resumo em Inglês:

Abstract The rice husk, agro-industrial residue, stands out for having silica, the main oxide former of the bioactive glass. To avoid contamination in this biomaterial, substances with bactericidal properties, like silver can be incorporated. Thus, the objective of this work is the synthesis of silver nanoparticles to functionalize a bioactive glass synthesized from rice husk ash (BRHA). The bioglass was prepared by the sol-gel method from the rice husk ash as a silica source. Silver nanoparticles were synthesized from thyme extract with AgNO3 and their formation was verified by UV-vis spectroscopy. The glass powder was added to this solution and its structure was evaluated by SEM-EDS, ATR-FTIR, and microbiology. The bioglass powder appeared in the form of porous agglomerates and the addition of silver altered its superficial roughness by deposition. The chemical bonds of the glass network related to bioactivity were maintained after the incorporation of the nanoparticles. Microbiological analysis by the agar diffusion test confirmed the inhibitory action of the nanoparticles for P. aeruginosa and S. aureus. Therefore, the developed material presented great potential for biomedical applications.

Resumo em Inglês:

Abstract Hydrothermal synthesis of kalsilite was facilitated by the inclusion of potassium carbonate (K2CO3) as the source of the potassium ion. After a 24 h reaction at 220 °C, kaolin clay treated with 1.25 M K2CO3 showed the most significant peaks at 2θ of 28.5° and 34.7° by X-ray diffraction corresponding to the hexagonal kalsilite. In addition, field emission scanning electron microscopy images also revealed hexagonal particles proving the formation of the desired mineral. The orthorhombic boehmite and monoclinic bayerite were formed as the dominant phases at lower K2CO3 molarity (<1.0 M), whereas kalsilite was recognized as the minor crystalline phase. The crystallinity of hexagonal kalsilite increased at higher K2CO3 concentration (>1.0 M) while the reaction temperature remained at 220 °C. Furthermore, the energy dispersive spectroscopy pattern of kalsilite showed a significant atomic percentage of potassium in the aluminosilicate material, indicating its formation.