Abstract The concentrations of stress and strain along the edges caused by the presence of geometric discontinuities in solids, such as circular, elliptical, and square shapes, have attracted the attention of the scientific community for more than a century due to their wide applicability in engineering. In this context, this research conducts a computational simulation using COMSOL Multiphysics software based on the Finite Element Method (FEM), performing a parametric study varying the dimensions of a perforated plate with a circular hole in seventy-two combinations. The plate has a constant thickness, and the combinations were obtained by varying the width (L), length (a), hole position, and radius (⌀). For a better analysis, the seventy-two combinations were divided into two groups of thirty-six, in which the influence of width (L) variation on the stress concentration factor (k) was evaluated. The results show that varying the plate width from 0.3a to 0.7a does not significantly affect the values of k. Finally, among the analyzed combinations and for the established parameters, the stress-strain curves demonstrated that the regions near the hole edge enter the plastic zone more rapidly, emphasizing the importance of analyzing strain distribution and stress concentration in structural design.
Abstract This study presents an experimental and numerical investigation of the structural performance of masonry built with Extruded, Pressed, and Fired Ceramic Blocks (BCEPQ), an emerging class of units for structural masonry systems. Despite their potential advantages, the mechanical behavior of BCEPQ units assembled through dry interlocking remains largely unexplored. An extensive experimental program was conducted, including physical and mechanical characterization of the blocks, compressive testing of prisms and small walls, and full-field deformation measurements using Digital Image Correlation (DIC). The blocks exhibited a characteristic compressive strength of 4.86 MPa and water absorption of 22.83%, while prisms and small walls reached average compressive strengths of 1.66 MPa and 0.98 MPa, respectively, with brittle failure modes governed by stress concentration and interface effects. A three-dimensional finite element model was developed in ANSYS 2024 R1 using experimentally obtained properties and linear elastic assumptions. Numerical results reproduced the main trends observed experimentally, with an average discrepancy of approximately 20%, confirming the exploratory nature of the model. The study provides unprecedented experimental data on BCEPQ masonry, highlights structural limitations associated with mortarless assembly, and offers technical insights to support future improvements in block geometry, manufacturing processes, and computational modeling of ceramic masonry systems.
Abstract This work presents the synthesis and characterization of niobium pentoxide (Nb₂O₅) obtained by combustion reaction, as well as its application as a heterogeneous catalyst in the production of biodiesel via simultaneous transesterification and esterification reaction (TES). The choice of Nb2O5 is justified by the fact that it is a material with wide applications, as a catalyst for biodiesel production; few reports in the literature can be explored. The vast majority of natural Nb2O5 is extracted in Brazil, in the city of Araxá in Minas Gerais (MG) by the Brazilian Metallurgy and Mining Company (CBMM), as it holds 98.2% of the world’s reserves. The synthesis of Nb2O5 was carried out on a laboratory scale using urea as fuel and niobium ammonium oxalate as precursor. The material obtained was characterized by XRD, FTIR, DG, BET, and SEM, showing a polyphasic structure (T-orthorhombic and TT-pseudohexagonal), polydisperse particle size distribution, surface area of 14.59 m2·g, and predominance of mesopores with a mean diameter of 7.16 nm. Subsequently, Nb2O5 was applied as a catalyst in the production of biodiesel from soybean vegetable oil and residual frying oil, using ethanol and methanol. The conversions into ethyl and methyl esters, densities, and acidity values were analyzed and compared with the standards of the National Petroleum Agency (ANP). The highest conversions were observed for soybean oil using methanol (34.74±0.79%) and residual frying oil using methanol (42.54±1.09%). Although the parameters obtained were below regulatory requirements, the results demonstrated the potential of Nb2O5 as an efficient and low-cost catalyst. The production of biodiesel using alternative and renewable materials highlights the feasibility of applying Nb2O5 in sustainable processes, with the possibility of future optimizations in synthetic routes and reaction conditions.
Abstract This study aims to enhance porcelain’s physicochemical properties by adding glass powder as flux. Kaolinitic clay, sand, and glass powder were used to formulate six grades, fired between 1140-1260ºC for 2 h. Specimens were tested for shrinkage, mass loss, water absorption, density, porosity, and mechanical strength (three-point bending). Phases were identified by X-ray diffraction and compared with industrial porcelain. The incorporation of glass powder has enabled the reduction of the firing temperature, the enhancement of densification, the augmentation of mechanical properties, and the valorizations of glass waste. The grade with 20 wt% glass (P20) fired at 1220ºC (P20-122) showed the best results: 13% shrinkage, 3.93wt% mass loss, 0.2wt% water absorption, 0.4% porosity, density 2.4 g/cm3 (46.6%). Using glass powder not only improves porcelain quality but also contributes to recycling glass waste on an industrial scale.
Abstract The use of waste materials for the production of construction materials is a sustainable alternative to their disposal, as well as a way of reducing the environmental impact of producing the materials. Geopolymer is a promising building material with attractive properties. Rice husk ash (RHA) is a potentially polluting waste material that, due to its properties, can be used to produce geopolymers. This study investigates the hardening behaviour of geopolymer mortars, incorporating up to 20 wt.% rice husk ash in the geopolymer formulations. After 28 days of curing, the samples were tested for mechanical and physical properties. Statistical analysis of the results revealed significant differences between the samples. In addition, the results showed an increase in the mechanical strength of the geopolymer mortars, reaching a value of 43.29 MPa with the simultaneous replacement of 20% metakaolin and sodium silicate with rice husk ash. The highest compressive strength reached 47.75 MPa, corresponding to an increase of 52.4% compared with the reference mixture.
Resumo Preocupações ambientais têm ganhado destaque devido à persistência de contaminantes orgânicos emergentes, como fármacos presentes em corpos d’água. Dentre os antidepressivos, a fluoxetina (FLX) é amplamente prescrita e se destaca por sua estabilidade à luz visível. Nesse contexto, a busca por métodos eficientes para a eliminação da FLX torna-se essencial para reduzir seu impacto nos ecossistemas. Este estudo avaliou estruturas porosas de ZnO, produzidas pela técnica de réplica, e submetidas à radiação UV em um reator fotoquímico, com o objetivo de analisar a fotodegradação da fluoxetina por processos oxidativos. Para a análise, foi utilizada cromatografia (HPLC UV-VIS). A presença do ZnO aumentou a taxa de remoção do fármaco em aproximadamente 20-30% nos primeiros 15 minutos de exposição, partindo de uma concentração de 10 mg/L, comparado à fotólise. Após 45 minutos, a fluoxetina foi completamente transformada em subprodutos, com comprovação do potencial de reuso dos corpos cerâmicos porosos obtidos.
Abstract This study investigates the effect of incorporating eggshell ash (ESA) into 1:3 mortars and its influence on physical, mechanical, and microstructural properties. Mortars were prepared with 0%, 5%, and 10% ESA additions relative to cement weight. Characterization techniques included XRD, SEM, compressive and flexural strength tests, modulus of elasticity, and porosity analysis. Results demonstrated that 5% ESA enhanced early and 28-day compressive strength (31.34±1.14 MPa), reduced porosity (27.95%), and improved microstructure continuity, indicating nucleation and filler effects. In contrast, 10% ESA promoted excess Ca(OH)2 and ettringite formation, increasing heterogeneity and decreasing performance (26.61±1.80 MPa). XRD confirmed secondary phase formation, and SEM images corroborated matrix densification at optimal dosage. The findings suggest that ESA is a viable, eco-friendly additive, with 5% representing an optimal content that maximizes performance without compromising durability. Excess ESA (>10%) may impair mechanical behavior due to calcium oversaturation and porosity increase, highlighting the need for dosage control.
The use of alternative materials in civil construction has grown exponentially in recent decades, driven by the demand for sustainable solutions. Among them, structural ceramic blocks stand out for combining technical performance with environmental responsibility. This study investigates the structural behavior of prisms and small walls built with Extruded, Pressed, and Fired Ceramic Blocks (BCEPQ)BCEPQ which are a promising alternative. Despite their potential, further research is needed on their mechanical propertiesMechanical properties, especially under static and dynamic loadsDynamic loads. Laboratory tests examined the failure modes, revealing a characteristic compressive strength of 4.86 MPa, in accordance with the Brazilian standard. However, water absorption reached 22.83
Abstract Alkali-activated binders represent a promising alternative for reducing the high carbon dioxide emissions associated with the cement industry. However, the influence of chemical admixtures on the workability of these materials remains insufficiently explored. This study aimed to evaluate the effect of surfactant admixtures on alkali-activated pastes composed of fly ash, basic oxygen furnace (BOF) steel slag, sodium hydroxide, and sodium silicate. Workability was assessed using the Kantro mini-slump test, alongside measurements of setting time and compressive strength. The polycarboxylate-based admixture (ADT1) and the sulfonated salt-based admixture (ADT2) improved the consistency of the material, with optimal dosages of 3% for ADT1 and 5% for ADT2, resulting in increases in mini-slump spread of 18% and 25%, respectively. The initial setting time was reduced by up to 50 minutes with the use of 5% ADT2, acting as an accelerator, while 3% of ADT1 presented a lower impact on setting time. However, compressive strength decreased by 33% with ADT1 and 27% with ADT2. Overall, ADT2 yielded better performance across all evaluated properties compared to ADT1.
Abstract The construction sector faces increasing pressure to adopt sustainable practices and reduce reliance on non-renewable and high-impact materials. This study investigates the incorporation of carnauba fibers (CFs), an abundant lignocellulosic by-product of the wax extraction industry, as reinforcement in cement-based rendering mortars. Both untreated and Ca(OH)2-treated fibers were evaluated at volume fractions of 0.5%, 1.0%, and 1.5%. A comprehensive characterization of the fibers was conducted, including physical, mechanical, spectroscopic (FTIR), structural (XRD), and thermal (TGA) analyses, to assess the effects of alkali treatment on their morphology and performance. Results demonstrated that fiber addition led to significant improvements in fresh and hardened properties of the mortars. Treated CFs exhibited increased crystallinity and reduced hemicellulose and lignin content, promoting superior fiber-matrix bonding. In the fresh state, mortars with CFs showed decreased workability and air content, accompanied by increased water retention - particularly in treated formulations. In the hardened state, mortars reinforced with CFs displayed enhanced compressive strength, lower shrinkage, and reduced elastic modulus, indicating improved toughness and energy dissipation capacity. Tensile Bond Strength was notably improved by treated fibers, meeting technical standards for both internal and external applications. The findings underscore the technical viability and environmental relevance of incorporating treated carnauba fibers into cementitious mortars, offering a low-cost, renewable alternative to synthetic reinforcements. This work contributes to the circular economy by valorizing agricultural residues and aligns with global efforts towards sustainable construction materials.
Abstract The reuse of mining wastes in ceramic production represents an important strategy for reducing environmental impacts while adding value to industrial by-products. Although black tourmaline has been explored in other ceramic and functional applications, its potential use in porcelain stoneware remains unexplored. In this context, the present study investigates the feasibility of incorporating black tourmaline-rich waste (WOS) as a partial substitute for feldspar in porcelain stoneware formulations, contributing to the sustainable management of mining residues. The waste was processed, characterized, and incorporated at levels ranging from 0 to 5 wt%, and the ceramic bodies were fired at 1150, 1175, and 1250ºC. Physical-mechanical properties, including linear shrinkage, water absorption, apparent porosity, flexural strength, and apparent density, were evaluated, complemented by SEM and XRD analyses. The results demonstrated that the waste is suitable as a ceramic raw material, with bodies containing higher waste contents fired at 1250ºC exhibiting properties compatible with the requirements of ISO 13006:2018, ISO 10545-3:2014, and ISO 10545-4:2014 for porcelain stoneware. These findings highlight the potential of black tourmaline-rich waste as an alternative raw material for high value-added ceramic applications and reinforce the role of traditional ceramics in advancing sustainable and circular production practices.
Resumo Este estudo investigou a produção de nanopartículas de hidroxiapatita a partir de escamas de peixe calcinadas em diferentes temperaturas (400, 600, 800 e 1000°C), com o objetivo de avaliar o efeito da temperatura de calcinação na cristalinidade e sua influência na liberação de fósforo para aplicações agrícolas. A análise de difração de raios X (XRD) demonstrou que temperaturas de calcinação mais altas levaram ao aumento da cristalinidade e a tamanhos maiores de cristalito. As nanopartículas calcinadas a 600°C exibiram a maior concentração de fósforo e a cinética de liberação mais favorável. Foi descoberto que as nanopartículas de hidroxiapatita fornecem uma quantidade significativa de fósforo biodisponível às plantas. No entanto, o aumento da cristalinidade nas amostras calcinadas em temperaturas mais altas mostrou-se prejudicial ao desenvolvimento da planta, possivelmente devido a efeitos citotóxicos ou disponibilidade reduzida de fósforo.
Abstract This study investigates the influence of LiF on the sintering behavior of Si3N4 ceramics with SiO2-CaO-Al2O3 at the eutectic composition. Compositions containing 90 wt. % Si3N4 were sintered at 1650-1815ºC for 1 hour. The ceramics were characterized in terms of density, microstructure, and hardness. At 1650ºC, the β/(α+β)-Si3N4 ratio rose from 28.4% (0 wt. % LiF) to 63.7% (2 wt. % LiF), exceeded 98% at 1700ºC, and reached 100% at ≥1770ºC. In LiF-free samples, higher sintering temperatures resulted in a higher relative density (95.6±0.4%) and hardness (12.99±0.42 GPa). LiF improved densification and hardness at low content and sintering temperature, yielding 89.4±0.3% relative density and 9.71±0.42 GPa hardness (1 wt. % LiF) compared to 84.1±0.5% and 6.78±0.29 GPa (0 wt. % LiF), both at 1650ºC. At higher temperatures, LiF decreased both properties, likely due to its tendency to evaporate.
Abstract Solar energy offers an eco-friendly alternative to address global energy challenges. This study develops a cost-effective dye-sensitized solar cell (DSSC) using niobium pentoxide (Nb2O5) as a photoanode and a polyaniline (PANI) composite as a counter electrode, replacing traditional titanium dioxide (TiO2) and platinum (Pt). Nb2O5 was synthesized via the Pechini method, and PANI through polymerization. The components were assembled using the Doctor Blading method in a sandwich configuration. Characterization revealed Nb2O5 with a band gap of ~3.0 eV and an orthorhombic morphology, demonstrating potential as a TiO2 substitute. DSSCs with composite electrodes outperformed those with pure PANI or niobium pentoxide electrodes. The PANI/Nb1 composite (1% Nb) achieved a Voc of 0.69 V and a current density of 0.075 mA cm−2. These findings highlight the promise of Nb2O5-enhanced PANI for efficient, low-cost solar energy conversion.
Abstract The ceramic industry continuously seeks sustainable and cost-effective raw materials to improve the product properties while minimizing environmental impact. This study investigates the utilization of heat-treated palm oil fuel ash (POFA) as a replacement for silica (SiO2) in the porcelain glaze formulation. The glaze batch prepared using SiO2, Al2O3 and Na2CO3 was modified by incorporating both raw and heat-treated POFA at varying concentrations as a substitute for SiO2. Scanning electron microscopy (SEM) images demonstrated that sample with 20 wt. % treated POFA exhibited a denser and more uniform microstructure with a hardness value of 569 MPa. X-ray diffraction (XRD) analysis revealed the presence of quartz and cristobalite in samples containing 20 wt. % POFA which are more stable phases formed from the SiO2. The results suggested that treated POFA enhanced the structural and mechanical properties of porcelain glazes, offering a sustainable alternative to traditional glaze raw materials.
This study investigates the upset forging behavior of Aluminium 7068/SiC composite (AA 7068 with 5% vol. SiC) using the Finite Element Method (FEM). The effects of length-to-diameter ratio, friction coefficient, and initial relative density on the forging process are analyzed. FEM was applied to determine the bulge profile of the deformed billets during the upset forging process. Experiments were conducted to validate analytical models concerning the cold upset forging of solid cylindrical composite materials. Finite Element Method (FEM) simulations demonstrated strong correlation with the experimental data, exhibiting acceptable error margins for key deformation parameters. The study revealed significant dependencies of both hoop strain and axial stress on the specimen’s aspect ratio. Furthermore, an improvement in the formability stress index was observed with increasing axial strain. These findings offer valuable insights into the upset forging behavior of this class of composite materials.
Abstract Hydroxyapatite is a commonly used biomaterial in medical and dental implants. While it can be synthesized, it is often extracted from bovine bone. However, challenges persist in the extraction process, such as ensuring reproducibility in particle size and distribution, crystallinity, and cost-effective large-scale production. This study employs porcine bone drilling for the first time, complemented by mechanical milling and calcination, and aims to determine the route that allows obtaining submicrometric HA powders with high crystallinity and the smallest possible particle size. Characterization of the obtained powders was performed using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and Fourier-transform infrared analysis (FTIR). The resulting material in the sequence drilling-milling-calcination shows high crystallinity and purity, although larger particle sizes were observed compared to those reported in the literature. Additionally, highly pure HA with particle sizes ranging from 160 to 510 nm (mean: 277.3 nm) was obtained via the drilling-calcination-milling sequence. This particle size range represents a significant improvement in size reduction compared to other mechanical methods reported in the literature.
Abstract In this research, medium crude metakaolinic clay (MK, Algeria) was used as raw material for the synthesis of geopolymers. Geopolymer synthesis involved mixing metakaolin with alkaline activators, with silica fume incorporated in some formulations to enhance mechanical properties. Samples were subjected to control curing at ambient and solar conditions, and their compressive and flexural strengths were evaluated at 28 days curing age, with a compressive strength of 35 MPa and flexural strength of 10 MPa. Additional tests assessed by XRD and FTIR revealed that new crystalline phases were formed in the geopolymer samples stored under ambient and sun exposure conditions; the curing condition had a significant effect on the change in the strengths of the investigation. The results indicate that the performance of geopolymer mortars can be considerably improved, even in extreme conditions, by optimizing curing protocols and material compositions.
Abstract This work aimed to evaluate the valorization potential of mollusk shell waste as a renewable source of calcium carbonate to produce calcium titanate ceramic through a solid-state reaction method. The calcium titanate ceramic powders synthesized from the molar ratio CaCO3:TiO2 (1:1) between 900 and 1200 ºC were characterized regarding the X-ray diffraction (XRD), thermogravimetric-differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR), and electrical resistivity. The results indicated that the mollusk shell waste was primarily composed of calcium carbonate in the form of aragonite. The results also showed the formation of an orthorhombic-structured calcium titanate (CaTiO3) at different synthesis temperatures. Additionally, it was found that the calcium titanate powders had an average crystallite size in the range of 43 to 49 nm and volume electrical resistivity in the range of 3.80 - 4.89 x 109 Ωcm. Therefore, the mollusk shell waste is highly promising for obtaining calcium titanate ceramic for electroceramic applications.
Abstract Nanofibers are an efficient way to enhance the catalytic activity of ceramic materials due to their large surface area, small crystallite size, and greater reactivity compared to bulk materials. In addition, the recombination of the e-/h+ pair is low in the composite nanofibers, increasing the catalytic efficiency. Interestingly, the addition of oxides and metal doping along nanofibers improves semiconductor properties, which makes their photocatalytic action and activation under visible light even stronger. This is especially true in the search for efficient photocatalytic systems that can degrade dyes in water using the principle of heterogeneous photocatalysis. Researchers have extensively studied nanofibrous composites of semiconductor oxides or decorated with metal particles due to their high reactivity, ability to absorb, and potential as photocatalysts. However, despite the technological and economic importance of these materials, there is a scarcity of reviews on the state of the art in this field.
