In recent years, the use of lignocellulosic natural fibers (LNFs) as reinforcements in composites has increased significantly [1,2]. This trend is driven by environmental concerns and the need to reduce dependence on petroleum reserves [3]. Consequently, there is a growing interest in environmentally friendly materials aligned with the principles of sustainable development. LNFs are considered a promising alternative due to their low cost, renewability, biodegradability, and low specific weight [4,5]. As a result, these fibers have been employed across various technological sectors, particularly in engineering applications. Hybrid composites combining natural and synthetic fibers are being investigated to enhance mechanical performance while reducing weight and cost, balancing the advantages and disadvantages of each constituent. Thus, the present study investigates the influence of different stacking configurations involving aramid fabric and jute fibers, and separately, aramid fabric and sisal fibers, as reinforcement components in composite materials. These composite systems were subjected to ballistic testing using .22 caliber ammunition. Based on the measurements of impact and residual velocities, the absorbed energy and the ballistic limit velocity of the projectile were calculated. Preliminary results indicated that the incorporation of aramid layers into the sisal-based composites enhanced the energy absorption under projectile impact, likely due to modifications in the fracture mechanisms of the composites. In contrast, the jute-based composite did not exhibit significant changes.

Cold Sintering Process (CSP) was employed to densify hydroxyapatite (HAp) using phosphoric acid (H₃PO₄) as a transient liquid phase at low temperature. HAp powders synthesized by aqueous precipitation were CSP-processed at 200 °C under 600 MPa for 30 min with H₃PO₄ contents of 5 or 10 wt% at 1 or 2 M. Apparent density (Archimedes), biaxial flexural strength (three-ball method, ABNT NBR ISO 6872), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were used to correlate processing, microstructure, and properties. Despite the low thermal budget, CSP achieved apparent densities of 2.44–2.55 g cm⁻³, corresponding to 77.64–84.21% of the theoretical density. The 5%–2 M condition reached the highest densification (84.21%), whereas 10%–1 M delivered the best mechanical performance (σ_f = 36.08 ± 8.88 MPa), indicating that strength is not governed by densification alone. XRD confirmed predominance of the HAp phase (ICDD 00-009-0432) for all groups; average crystallite sizes ranged from 34.35 to 56.92 nm, with specific surface area increasing as crystallite size decreased (up to 87.53 m² g⁻¹). SEM revealed a microstructural evolution consistent with dissolution–reprecipitation: from porous, weakly coalesced networks (5%–1 M) to denser, better-bridged grains (10%–1 M), while excessive acidity (10%–2 M) promoted local fragility. Overall, tailoring the chemistry of the transient liquid phase enables efficient, phase-preserving, and energy-saving densification of HAp via CSP, offering a viable route for bioceramics where low processing temperatures and controlled microstructures are required.

For composite production, commercial corn starch plasticized with 30% glycerol was used. Ubim fibers were sourced from the local market in Belém (PA) and subjected to peeling and milling processes to optimize adhesion to the polymer matrix. The composites were processed using a single-screw extruder in five TPS/fiber ratios (0, 5, 10 and 15 wt.%). Films and test specimens were molded by hot pressing under standardized parameters. The composites were characterized through density, hardness (ASTM D2240), tensile strength (ASTM D638), and impact tests, as well as microstructural analyses by scanning electron microscopy (SEM) and phase evaluation by X-ray diffraction (XRD).

The results showed that the addition of ubim fibers to the thermoplastic starch composites significantly increased tensile strength, demonstrating the effectiveness of natural reinforcement in enhancing the mechanical properties of the polymer matrix. SEM analyses revealed morphological changes, highlighting good interfacial adhesion between the ubim fibers and TPS, which is essential for efficient stress transfer. XRD indicated the presence of semi-crystalline structures influenced by fiber incorporation. These findings confirm that the use of natural fibers, such as ubim, is a promising strategy for developing biodegradable composites with improved performance. Such materials exhibit high potential for sustainable plastic packaging applications, combining mechanical performance with reduced environmental impact.

The growing demand for sustainable solutions in civil construction, particularly in tropical regions facing a shortage of natural aggregates, has encouraged the use of mining waste as an alternative raw material for the production of artificial aggregates (Cabral et al., 2008). This study investigates the mineralogical interactions between sandy and silty textured soils and a clayey mining sludge, subjected to calcination processes aimed at forming reactive phases.

The methodology involved the formulation of mixtures with varying proportions of clayey sludge, subjected to calcination at temperature ranges defined based on mineralogical and thermal analyses. The samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), following established practices for assessing the reactivity of calcined clays (Pinheiro et al., 2023; Monteiro et al., 2004).

Preliminary results indicated the formation of potentially pozzolanic phases, such as amorphous aluminosilicates, at temperatures above 700 °C, corroborating literature findings on the influence of firing temperature on clay activation (da Silva et al., 2015). The microstructure observed via SEM showed good integration between the constituents of the mixtures after calcination, suggesting the feasibility of combining soils and mining residues for pavement applications.        

This study investigated the consolidation of hydroxyapatite (HAp) ceramics with different graphene oxide (GO) contents (0–1.00 wt.%) via the Cold Sintering Process (CSP), aiming to evaluate their effects on densification, mechanical properties, thermal stability, and microstructure [1]. CSP was performed at 200 °C under 300 MPa using diluted phosphoric acid as a transient liquid phase. Vickers hardness, fracture toughness, flexural strength, SEM/EDS, TGA/DSC, XRD with Rietveld refinement, FTIR, and Raman spectroscopy were employed for characterization.

GO addition increased the relative density from ~84.7% (pure HAp) to ~87.3% (HAp1.00GO), with the best mechanical performance observed for HAp0.50GO, which showed a hardness of 2.81 GPa, fracture toughness of 0.77 MPa·m⁰·⁵, and flexural strength of 51.63 MPa—up to 79% higher than pure HAp. These improvements were attributed to the lamellar morphology and oxygenated functional groups of GO, which promoted chemical interactions with dissolved HAp ions, enhancing precipitation-driven densification and interparticle cohesion [2].

Morphological analysis revealed that HAp0.50GO exhibited the most homogeneous and dense microstructure with well-formed interparticle bridges, while higher GO contents (0.75–1.00 wt.%) led to agglomeration and heterogeneity, impairing mechanical performance [3].

Thermal analysis indicated that GO incorporation improved thermal stability and reduced degradation related to β-TCP formation. XRD confirmed the preservation of the crystalline HAp phase in all compositions, with no secondary phases detected. Rietveld refinement showed decreased crystallite size and increased specific surface area for intermediate GO contents (0.25 and 0.50 wt.%), suggesting higher surface reactivity and potential bioactivity [4].

FTIR confirmed the preservation of HAp’s chemical structure, while Raman spectroscopy detected D and G bands from GO in samples with ≥0.50 wt.%, confirming its incorporation and revealing variations in carbon structural order with increasing GO content. The lowest ID/IG ratio (0.57) for HAp0.75GO indicated greater graphitic order, whereas HAp1.00GO displayed the highest disorder (ID/IG = 0.92), likely due to agglomeration.

Overall, the optimal GO content was ~0.50 wt.%, balancing densification, microstructural integrity, mechanical strength, and thermal stability without compromising crystallinity. These results demonstrate the feasibility of producing HAp/GO ceramics via CSP at low temperature with enhanced properties for advanced biomedical applications, such as synthetic bone grafts with improved mechanical resistance and stability [5].

The shortage of natural aggregates in tropical regions has driven the development of alternative materials for road infrastructure applications. Among these, artificial aggregates produced through clay calcination have been investigated for their mechanical properties and pozzolanic reactivity potential (Cabral, 2008; da Silva et al., 2015; Friber et al., 2023). This study proposes the production of artificial aggregates from soil–waste mixtures, incorporating a clay-rich mining sludge, aiming to add value to mineral waste and reduce reliance on conventional materials.

The formulations were defined based on preliminary mineralogical analyses using X-ray diffraction (XRD) and scanning electron microscopy (SEM), with the objective of identifying the phases formed and microstructural changes induced by calcination (Monteiro et al., 2004; Pinheiro et al., 2023). The calcination temperature was selected to maximize the formation of amorphous cementitious phases. After calcination, the aggregates were used to mold cylindrical specimens using split molds, which were then subjected to repeated load triaxial tests to determine the permanent deformation a key parameter for assessing the mechanical performance of materials used in pavement base and subbase layers.

Initial results indicated that the artificial aggregate exhibits elastic behavior compatible with that of traditional pavement materials, reinforcing its potential as a technically and environmentally sustainable solution.

Niobium is a strategic material for Brazil, a country that holds the largest global reserves of this element. However, its sintering presents significant challenges, mainly due to the high reactivity of the metal, which promotes oxide formation and hinders consolidation. This study aimed to investigate the feasibility of cold sintering of niobium at different temperatures, seeking to minimize oxidative effects and enable new technological applications. The material used was supplied by CBMM (Companhia Brasileira de Metalurgia e Mineração), and experiments were conducted at temperatures of 125 °C, 150 °C, and 175 °C. To promote the formation of a transient liquid phase, niobium powders were mixed with 10 wt.% of absolute ethanol. Sintering was performed under a simultaneous pressure of 300 MPa, with a holding time of 30 minutes at each specified temperature. After processing, the samples were characterized through density measurements, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analyses. The results indicated that cold sintering of niobium was effective even at the relatively low temperatures employed. XRD analysis revealed only minor peaks corresponding to the NbO phase, indicating a low incidence of oxidation during the process. These findings demonstrate the feasibility of cold sintering pure niobium, paving the way for the development of new components and applications, with advantages in reducing processing temperatures and preserving metallic properties. The use of cold sintering techniques thus represents a promising alternative for processing highly reactive metals such as niobium.