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.        

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 resilient modulus—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.

Sustainable polymer matrix composites have gained prominence as an eco-friendly alternative to conventional materials, especially those based on biodegradable thermoplastics. Among them, thermoplastic starch (TPS) stands out for its abundance, low cost, and biodegradability, although its mechanical limitations require reinforcement for more demanding applications [1]. In this context, the use of natural fibers emerges as a viable and environmentally responsible solution. Ubim fiber, originating from the Amazon region and extracted from the leaves of the Geonoma baculifera palm, presents itself as a promising reinforcement due to its lightness, strength, and renewability [2,3]. This study investigates the potential of TPS composites reinforced with ubim fibers, aiming to improve mechanical properties and promote materials aligned with the bioeconomy and the valorization of sustainable Amazonian forest resources.

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.

Natural fiber-reinforced polymer composites have emerged as a sustainable alternative to conventional materials, particularly those utilizing biodegradable thermoplastics. Thermoplastic starch (TPS) is a notable candidate due to its renewability, low cost, and biodegradability; however, its limited mechanical strength necessitates reinforcement for broader applications [1]. Among natural reinforcements, guarumã fiber, derived from the Ischnosiphon koern plant native to the Amazon, offers excellent potential owing to its lightweight nature, mechanical resistance, and ecological appeal [2,3]. This research explores the development of TPS-based composites reinforced with guarumã fibers, aiming to enhance mechanical performance while fostering sustainable material solutions aligned with bioeconomic principles and the valorization of Amazonian biodiversity.

The composites were produced using commercial corn starch plasticized with 30% glycerol, incorporating guarumã fibers processed through peeling and milling to improve interfacial compatibility. Five formulations were prepared via single-screw extrusion, varying fiber content up to 30 wt.%. Standardized hot-pressing techniques were applied to obtain films and specimens, which were subsequently characterized by density, hardness (ASTM D2240), tensile (ASTM D638), and impact testing, alongside SEM and XRD analyses.

The incorporation of guarumã fibers led to notable improvements in tensile strength and modified the composite morphology, as evidenced by SEM, which also revealed satisfactory interfacial adhesion. XRD results indicated semi-crystalline structures influenced by fiber content. These outcomes highlight guarumã fiber as an effective reinforcement for biodegradable TPS composites, supporting their application in sustainable plastic packaging with enhanced mechanical properties and reduced environmental footprint.

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.

Natural lignocellulosic fibers (NLFs) have been widely studied as sustainable alternatives to synthetic fibers, standing out for being renewable, biodegradable, economically viable and for presenting good specific mechanical properties [1-3]. In this context, the present study aimed to evaluate the flexural strength of polyester matrix composites reinforced with short jute and piassava fibers. The fibers were used in their natural form, without surface treatment, cut to a length of 15 mm, and incorporated into the matrix by manual molding (hand lay-up) using silicone molds, without the application of pressure. The specimens were produced with randomly distributed discontinuous fibers, with mass fractions adjusted to the mold volume. The bending tests indicated that the pure polyester composite presented a bending stress of 112.12 ± 17.58 MPa, while the composites reinforced with jute and piassava fibers reached 59.16 ± 8.37 MPa and 62.48 ± 5.89 MPa, respectively, representing reductions of approximately 47% and 44% in relation to the pure matrix. Fractographic analysis of the rupture surfaces revealed that the failure of the composites was predominantly governed by fiber pull-out and low interfacial adhesion between fiber and matrix, also associated with the presence of internal voids resulting from the manual molding process. These factors contributed to the reduction of the mechanical efficiency of the composites, highlighting the need for surface treatments of the fibers and improvements in processing to optimize structural performance.

Potassium ferrite was synthesized through the sol-gel auto-combustion [1] chemical route, aiming to evaluate the influence of calcination temperature on the formation of crystalline phases. The obtained samples were subjected to calcination temperatures of 0°C (post-combustion), 300°C, 550°C, 750°C, and 950°C. Structural characterizations were performed using X-Ray Diffraction (XRD), where the crystallite size was calculated from the most intense peak at each calcination temperature using the Scherrer equation [2]. Micrographs were also obtained to assess grain size, along with analyses by Mössbauer Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), and Raman Spectroscopy. The results demonstrated that the synthesis of potassium ferrite was successful; however, an increasing formation of additional phases of potassium ferrite and magnetite was observed with rising calcination temperatures. Therefore, it is concluded that the sol-gel auto-combustion method is not recommended for applications requiring a specific crystalline phase predominance, due to the simultaneous generation of secondary phases with higher thermal treatment temperatures [3]. Additionally, as the temperature increased, a reduction in grain size was observed, attributed to the combustion of residual fuel traces.

This study investigated the Cold Sintering Process (CSP) [1] of potassium ferrite, previously synthesized by the sol-gel auto-combustion method. To date, there have been no reported cases of potassium ferrite sintering; therefore, two solutions were tested for transient phase formation: acetic acid at a 5 molar concentration and pure ethanol, both applied at 5 wt% of the sample's weight. After consolidation of the specimens, an average material loss of 20 wt% was observed in both cases. Structural characterization by X-Ray Diffraction (XRD) indicated that the use of acetic acid resulted in a poorly defined crystalline phase, highlighting the inadequacy of this solvent for the studied method, despite achieving bulk formation. On the other hand, the use of ethanol revealed significant microstructural changes, confirmed by Scanning Electron Microscopy (SEM) images. It was observed that the initial microstructure, characterized by typical grains resulting from combustion synthesis, evolved into a lamellar (plate-like) structure [2,3], leading to an improvement in the mechanical strength of the material when compared to specimens produced with acetic acid. These results demonstrate that ethanol is an effective solvent for optimizing the microstructural and mechanical properties of potassium ferrite obtained through cold sintering process.

A growing demand for research about ballistic armor shields follows the increase of violence around the world. Ultimately, different composite materials with polymeric matrices have already presented the minimum performance as an individual protection required with cheaper and lower density, such as those reinforced with natural lignocellulosic fiber (NLF). The Cyperus malaccensis, a type of sedge fiber, is already used in simple items like ropes, furniture, and paper, but has not yet been investigated as composite reinforcement for possible ballistic protection applications. Therefore, composite plates were prepared for the ballistic tests, based on the condition of 30 vol% alkali treated sedge fibers. A total of seven plates have been subjected to seven test-shots  using 7.62 mm commercial ammunition. The fibers were embedded under pressure in the epoxy resin matrix and cured at room temperature for 24 hours. The tested specimens were examined by scanning electron microscopy. Besides, analysis of variance (ANOVA) was performed and the absorbed energy of all specimens were evaluated, based on a confidence level of 95%.

A growing demand for research about ballistic armor shields follows the increase of violence around the world. Ultimately, different composite materials with polymeric matrices have already presented the minimum performance as an individual protection required with cheaper and lower density, such as those reinforced with natural lignocellulosic fiber (NLF). The Cyperus malaccensis, a type of sedge fiber, is already used in simple items like ropes, furniture, and paper, but has not yet been investigated as composite reinforcement for possible ballistic protection applications. Therefore, composite plates were prepared for the ballistic tests, based on the condition of 30 vol% sedge fibers coated by graphene oxide. A total of seven plates have been subjected to seven test-shots  using 7.62 mm commercial ammunition. The fibers were embedded under pressure in the epoxy resin matrix and cured at room temperature for 24 hours. The tested specimens were examined by scanning electron microscopy. Besides, analysis of variance (ANOVA) was performed and the absorbed energy of all specimens were evaluated, based on a confidence level of 95%.

A growing demand for research about ballistic armor shields follows the increase of violence around the world. Ultimately, different composite materials with polymeric matrices have already presented the minimum performance as an individual protection required with cheaper and lower density, such as those reinforced with natural lignocellulosic fiber (NLF). The Cyperus malaccensis, a type of sedge fiber, is already used in simple items like ropes, furniture, and paper, but has not yet been investigated as composite reinforcement for possible ballistic protection applications. Therefore, composite plates were prepared for the ballistic tests, one for each condition of 10, 20 and 30 vol% sedge fibers. Each plate has been subjected to 5 test-shots  using 7.62 mm commercial ammunition. The fibers were embedded under pressure in the epoxy resin matrix and cured at room temperature for 24 hours. The tested specimens were examined by scanning electron microscopy. Besides, analysis of variance was performed and the absorbed energy of all specimens were evaluated.

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.

Given the growing demand for sustainable solutions in pavement engineering, the use of agricultural waste as soil reinforcement material has emerged as a technically and environmentally viable alternative. Among these residues, banana fiber shows high potential due to its low cost and wide availability in tropical regions. This study aims to investigate the potential application of banana fiber as a reinforcement material for soils used in pavement subgrades. Initially, physicochemical analyses were conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM) on both untreated and chemically treated fibers to assess structural modifications and determine the need for treatment to enhance fiber–soil adhesion. Subsequently, preliminary permanent deformation tests were performed using a repeated load triaxial apparatus to evaluate the effectiveness of the fiber as reinforcement and identify the optimal fiber content that provides the best mechanical performance. The results indicate that banana fiber can significantly improve soil strength and reduce permanent deformations, provided that adequate fiber content is used and, if necessary, the fibers undergo prior treatment. These findings are consistent with results reported in the literature, which highlight improvements in shear strength and bearing capacity of clayey soils through the incorporation of natural fibers (Finu John et al., 2018; Bawadi et al., 2020; Guimarães et al., 2024). This research contributes to the advancement of more sustainable subgrade stabilization techniques, offering both environmental and economic benefits.

Hydroxyapatite is a mineral composed of hydrated calcium phosphates. As it is the main mineral component of human bone, it is widely used in the fabrication of alloplasts for bone tissue regeneration treatments, known as scaffolds [1][2]. Scaffolds serve as a cellular matrix for the development of new bone tissue; therefore, they must have a porous structure, adequate mechanical strength, and be composed of biocompatible material [3]. To meet these criteria, additive manufacturing techniques, such as fused deposition modeling (FDM) 3D printing, are employed as an alternative for controlling structure and mechanical strength. However, if the printer operates by extruding thermoplastic material, it is necessary to synthesize polylactic acid (PLA) filament loaded with hydroxyapatite to incorporate the bioceramic into the scaffold [4]. Hydroxyapatite can be obtained through various synthesis routes or from synthetic or natural resources. In this study, hydroxyapatite was extracted from the byproduct of the Arapaima gigas fish and used to produce filaments for 3D printing. The scales were subjected to chemical treatment with NaOH and thermal treatment with sintering at 600 ºC in an oxygen-rich environment. The characterizations performed were TG, DTG, DSC, FTIR, and SEM. After these characterizations, the sample was subjected to a thermal treatment at 700 ºC, followed by the same analyses. The filaments were produced by extrusion and were loaded with 1% w/w of hydroxyapatite extracted from the scales of Arapaima gigas. The filaments were subjected to tensile testing according to ASTM C1557-20. Thermal analysis revealed that the sample sintered at 600 ºC did not undergo complete removal of organic volatiles, with mass losses of 3.6% in the range of 75 ºC – 100 ºC due to residual water; 1.1% in the range of 280 ºC – 700 ºC due to collagen residue; and 2.93% between 600 ºC – 742 ºC due to the loss of structural water from hydroxyapatite. The sample sintered at 700 ºC showed little mass loss, with a total loss of 1.68%, and a maximum degradation temperature at 619 ºC, related to the structural water present in hydroxyapatite. In both samples, FTIR analyses revealed the characteristic bands of PO₄³⁻ anions at 1091 cm⁻¹; 1022–1018 cm⁻¹; 602–563 cm⁻¹, and the presence of CO₃²⁻ ions at 1450 cm⁻¹, 1411 cm⁻¹, and 871 cm⁻¹. Scanning electron microscopy (SEM) micrographs showed that the samples sintered at 600 ºC presented agglomerates of inorganic particulates without a defined morphology. Sintering at 700 ºC promoted the growth of particulates larger than 200 µm with polygonal shapes, tending toward hexagonal formation.

Solid solution strengthening is an essential process for increasing the strength of metals. It occurs when solute atoms are introduced into a crystalline matrix [1,4]. The interaction between dislocations and solute atoms — which may occupy interstitial sites or substitute lattice positions — generates distortions that hinder dislocation motion, thus enhancing mechanical resistance [2,5]. Substitutional solutes cause spherical distortions in the lattice, creating compressive or tensile stress fields, while interstitial solutes, due to their smaller size, produce more significant distortions and interact more effectively with dislocations [1,6]. The elastic misfit energy resulting from these distortions is a fundamental component of the strengthening mechanism [4,7]. The mathematical modeling of these interactions allows for the estimation of interaction energy based on elastic theory, taking into account parameters such as solute concentration, atomic radius mismatch, and modulus difference [3,8]. Recent studies emphasize the importance of optimizing the concentration and type of solute atoms, as well as processing conditions such as temperature and strain rate, to maximize the strengthening effect in advanced metallic alloys [5–7].

The growing global demand for product customization, coupled with the long lead times associated with traditional manufacturing processes, has driven the industry to adopt faster and more flexible production methods. In this context, additive manufacturing (AM) — particularly material extrusion-based 3D printing (FFF) — stands out as a technological advancement by enabling the fabrication of customized geometries and multi-material parts with minimal waste. Among the polymers used in AM, polyamides are widely recognized for their mechanical strength, thermal stability, rigidity, and wear resistance. When reinforced with carbon fibers, these properties are significantly enhanced, making nylon-based composites highly suitable for high-performance applications, including in the defense sector. However, the mechanical performance of parts produced via FFF depends directly on process parameters such as extrusion temperature, print speed, and layer thickness, which influence material flow and interlayer adhesion. This study investigates the effects of extrusion speed, nozzle temperature, and infill orientation on the mechanical and thermal behavior of a carbon fiber-reinforced polyamide processed on the Bambulab X1E printer. Tensile and Differential Scanning Calorimetry (DSC) tests were conducted to evaluate the influence of these parameters, and an Analysis of Variance (ANOVA) was applied to validate the statistical significance of the results and support the selection of optimal printing conditions.

The growing impacts of climate change, combined with the high demand for environmentally responsible practices, have encouraged the scientific community and the industrial sector to seek sustainable alternatives for the development of new materials [1]. In this context, natural fiber-reinforced composite materials have emerged as a promising alternative to synthetic composites, not only due to their lower environmental impact but also because they offer economic and functional advantages in various applications [2]. The Amazônica region, rich in plant biodiversity, holds significant potential for the use of fibers extracted from native species in the development of sustainable composites. This contributes to reducing dependence on synthetic materials while also promoting the appreciation of the forest’s natural resources through responsible extractive practices [3]. The incorporation of these natural fibers into materials—especially in the construction sector—represents a significant step forward in the development of sustainable cities, while also promoting the growth of the regional bioeconomy, technological innovation, and local infrastructure [4]. In this study, polyester matrix composite materials reinforced with guaruman fibers were analyzed for their flexural mechanical properties. Test specimens were produced using silicone molds and sanded to meet the specifications of ASTM D790 for flexural strength testing. Specimens were fabricated with 10%, 20%, and 30% guaruman fiber volume fractions in polyester resin. The results were validated through ANOVA statistical variance analysis. The flexural mechanical results indicated a slight increase in the average strength. Regarding the flexural modulus, there was an increase in material stiffness as the fiber content increased. ANOVA indicated no statistically significant differences in the strength results among the composites. Although no significant differences in strength were observed, it is important to highlight the reduction in resin content required to produce composites with 30% fiber volume, without compromising strength.

Hydroxyapatite (HA), an inorganic ceramic biomaterial, presents itself as a promising and active bone substitute in this scenario, as it presents characteristics similar to the mineral apatite, found in human bones and teeth. Thus, the aim of this work is to synthesize and characterize synthetic hydroxyapatite, using chicken eggshell residue as a source of calcium. The analysis of the egg shell was carried out using X-ray Diffraction (XRD) and Fourier Transform Spectroscopy (FTIR) techniques. The characterization of the hydroxyapatite powder was performed by X-Ray Diffraction (XRD), Fourier Transform Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The results for eggshell revealed the presence of absorption bands of hydroxyl groups and carbonates and phases corresponding to calcium hydroxide and calcium oxide. The HA sample showed vibration bands of hydroxyl, carbonate and phosphate groups, and hydroxyapatite and calcium oxide phases. SEM analysis indicated irregular morphological formations with dimensional variations. The EDS semiquantitatively revealed percentages of Oxygen, Phosphorus and Calcium. According to the results, type B hydroxyapatite was obtained using eggshell residue, which was also a good source of calcium in this study.

Titanium alloys are widely used as aerospace structural materials because of their low density, high strength and excellent corrosion resistance at low-to-moderate temperatures. However, when the working temperature is over 400°C, titanium alloys usually show a poor oxidation resistance because of the fast diffusion of oxygen through the nascent TiO_2–X surface oxide layer[1]. On the other hand, SiO₂ shows considerable promise as a protective oxide layer, for both high temperature oxidation corrosion; however, the most successful application so far of Si–based oxides to Ti–alloys is the preprocessed amorphous (or ‘enamel’) SiO₂ coating [2]. Ti–based Multi-Principal Element Alloys with added Si potentially provide a novel opportunity to find new alloy compositions which could form an SiO₂–based layer spontaneously at elevated temperatures [3]. Boron has also been suggested as a further alloying addition, that could avoid the possible issue of pesting of formed silicide compounds in such MPEAs at intermediate temperatures [4].

This research builds an equimolar TiCrAlNb MPEA alloy system with different ratios of Si and/or B content and characterizes their microstructure, before and after oxidation, to study the influence of the addition of silicon and boron. The oxidation resistance of such alloys shows in general a significant improvement compared with a typical Ti-6Al-4V Ti–alloy. Furthermore, Niobium shows a higher tendency to form compounds with silicon/boron. In addition to such silicide/boride compounds, some laves phases were also observed and the addition of silicon showed a significant influence on the microstructure, the addition of B refines the lamellar microstructure while the addition of Si transfers the structure into an equiaxed dendritic structure.
 

Corrosion is a natural phenomenon that degrades the properties of materials when they are exposed to environmental elements. This issue is especially prevalent in steel structures, where it can result in substantial economic losses, structural failures, and even pose risks to human safety. The corrosion of steel can be triggered by various factors, including environmental conditions, mechanical stress, and the presence of impurities. This study investigates the macroscopic corrosion of steel under potentiostatic conditions through a combination of electrochemical experiments and probabilistic modeling. A probabilistic cellular automata (PCA) model was developed in MATLAB to predict the propagation and penetration of corrosive material in steel. The model was refined using experimental data obtained from a three-electrode corrosion cell. Various steel specimens were subjected to corrosion under different environmental conditions, and their mechanical strengths were assessed. The refined model's predictions were validated using finite element analysis (FEA) and tensile testing of the corroded specimens. The FEA results showed a strong correlation with the tensile testing outcomes across three different specimen designs. This thesis enhances the understanding of steel corrosion under potentiostatic conditions and offers a predictive tool for assessing the corrosion behavior and mechanical properties of steel in such environments.

Plasma treatment of ores, and ore concentrates is used most often to improve the separation performance of ore minerals and non-metallic gangue, as well as for the “plasma grinding” (softening) of ores to reduce the time of subsequent mechanical grinding and energy costs. Non-equilibrium, low-temperature plasma of dielectric barrier discharge (LTP-DBD), characterized by high pressure (hundreds of Torr), high electron temperatures (electron temperatures can reach several electron volts), and low temperature of the process gas (close to the temperature of dielectric barriers) [1] is considered the most precise, efficient, and safe tool for modifying the composition, structure, and properties of the surfaces of various materials, including geomaterials [2–5]. A DBD occurs in a gas under the action of an alternating voltage applied to the conducting electrodes, provided that at least one electrode is covered with a dielectric layer on the side of the discharge gap. The discharge can be carried out in oxygen or air at atmospheric pressure, room temperature, and natural air humidity, i.e., under normal conditions and without the use of a special plasma gas. For practical applications, the problem of obtaining a diffuse discharge in air at atmospheric pressure is relevant, since in this case the effect of the DBD plasma spreads uniformly over the largest possible area [1,3]. During the our experiments, the mineral samples filled the gap between the active metal electrode and the dielectric barrier and were separated from the electrode by a small air gap. The mineral particles were affected by the following DBD factors: a high-strength pulsed electric field, ionic wind, and low-temperature plasma products in the form of chemically active compounds, such as ozone O₃, and other agents. When conducting experiments on the effect of DBD on the structural and physicochemical properties of minerals, the following rational parameters of pulses initiating a barrier discharge we established in [3]: duration of the leading edge of the pulse 250–300 ns, pulse duration 8µs, voltage on the electrodes in the barrier discharge cell 20 kV, repetition frequency of the pulses initiating the discharge ~15 kHz, time range of plasma minerals treatment was t_treat=10–150 s. The dimensions of the electrodes of the DBD discharge cell significantly exceeded the length of the interelectrode gap, which was 5mm. According to SEM, defects of a regular triangular shape formed on the surface of galena samples due to the removal of microcrystalline fragments due to ponderomotive forces in the region of a strong electric field. On the surface of chalcopyrite, the formation of irregularly shaped defects was observed, and on the surface of sphalerite, microchannels of electrical breakdown formed, bordered by the sinter formation material of oxide microphases. The change in the morphology of the surface of sulfides caused softening, and a significant decrease in the microhardness of minerals as a whole by 20–30%. Short (t_treat=10 s) treatment of pyrrhotite caused a shift in the electrode potential of the mineral to negative values (φ=−60mV, at pH 9.7–12) [4], which predetermines the effect of reducing the sorption activity of pyrrhotite with respect to xanthate, hence its flotation recovery reduction. In [5] rational conditions were determined for t_treat=30–40s) plasma pretreatment, in which the efficiency of pyrite and arsenopyrite separation in monomineral flotation increased considerably: an increase in pyrite recovery was 27% while the yield of arsenopyrite decreased by 10–12%. Thus, the method of plasma-chemical processing of geomaterials with using of DBD has great prospects for practical applications in the processes of selective separation of semiconductor ore minerals (sulfides, oxides). In rock-forming minerals, the following features of changes in surface properties when exposed to DBD were established [3]. With increasing plasma treatment time of the quartz samples t_treat=10–150s, smoothing of surface irregularities and the formation of microdefects of irregular shape (≤3µm) occurred This caused weakening and a monotonous decrease in the microhardness of the mineral from 1420 up to 1320 kgf/mm² in the original and modified at t_treat=150 s states, respectively. The maximum relative change (decrease) in microhardness ∆HVmax was ~7%. The contact angle of wetting the quartz surface with water changed nonmonotonically. As a result of short-term exposure (t_treat=10–30s), the contact angle increased from 44° to 53°, which indicates an increase in the hydrophobicity of the mineral’s surface, while with an increase in t_treat, a gradual decrease in the contact angle was observed to initial values. The possibility of modifying the hydrophobicity of quartz by energy impacts can be used in industrial processes for separating the mineral from impurities and selective (reverse) flotation of ferruginous quartzites.

The production of quality castings requires the use of modern computer programs that serve to simulate foundry processes as a tool for optimizing proposed production technologies. This paper focuses on the analysis of a computer simulation concerning the casting of a brake disc at a Slovak foundry. Notably, this brake disc has experienced issues such as shrinkages and micro shrinkages, which adversely affect the internal quality of the casting. Through this study, we aim to enhance our understanding of these challenges and explore solutions to improve the overall quality of cast components, making the process more efficient and cost-effective. Defects were identified in the ribs located in the upper section of the casting beneath the feeders. To address this issue, a comprehensive computer simulation was conducted, replicating the actual conditions of the casting and solidification process. The results revealed that the initially designed gating system, along with its feeder configuration, was inadequate in preventing the formation of these defects. 

In response, a new feeder layout was proposed, which successfully eliminated the defects based on the simulation outcomes. The input parameters for this simulation were meticulously set to reflect the actual requirements of the foundry closely. To facilitate this process, 3D models of the assemblies were created using SolidWorks CAD software, and filling and solidification simulations were carried out using the NovaFlow & Solid CV 4.6r42 simulation program. This approach ensured a thorough analysis and resolution of the issues at hand.

The largest amount of input raw materials in the foundry is silica sand, which constitutes more than 90% of the molding mixture, which is necessary for the production of molds necessary for the production of castings. Almost all silica sand that enters the foundry ends its material cycle in a landfill, either after a single use (molding mixture with an organic binder) or after a certain period of time. Three types of waste with a high SiO₂ content are generated in the foundry: dust from handling the molding mixture (preparation of the molding mixture, molding and framing of castings), dust from blasting of castings, the non-magnetic part of which contains a high proportion of SiO₂, and the used molding mixture. The paper proposes methods for treating and utilizing these wastes containing SiO₂ either directly in the foundry or in other industrial sectors. Dust extracted from the molding mixture preparation workplace can be returned to the process in limited quantities without impairing the properties of the molding mixtures. Dust obtained from blasting castings can be separated by magnetic separation into a non-magnetic component containing a high proportion of SiO₂ and can be returned to the process, and the used molding mixture was added as a substitute for building sand in the preparation of concrete.

In technological and analytical practice, in preparative chemistry, halogenide complexes of platinum group metals play an important role. Available information concerning Pd(IV) chloride complexes is limited due to the instability of PdCl₄ [1-3], which exists in an individual state only as dichloride. Chlorination of metallic palladium in molten alkali metal chlorides at high temperatures (630-980 °C) and at elevated chlorine pressures (8-10 atm) allows, according to our data, obtaining palladium in rapidly cooled and solidified salt melts based on CsCl mainly in the tetravalent state in the form of Cs₂PdCl₆. However, in RbCl- and KCl-based solidified melts there are complex compounds both of Pd(II) and of Pd(IV), and in solidified melts containing NaCl and LiCl only divalent palladium is present in the form of M₂PdCl₄ compounds.

The ratio of valence forms (II, IV) of palladium chlorides in salt melts and in solidified fusions at different stages and process regimes can be conveniently and quickly monitored by changing the ratio of intensities of the bands of the groupings [PdCl₆]^2- (O_h): n₁(A_1g) ~ 315, n₂(E_g) 290, n₅(F_2g) ~ 170 cm^-1 and [PdCl₄]^2- (D_4h): n₁(A_1g) ~ 300, n₂(B_1g) ~ 270, n₄(B_2g) ~ 200 cm^-1 of the chloride complexes of M₂[PdCl₆] and M₂[PdCl₄] in the Raman spectra, recorded using a Renishaw U1000 spectrometer [4]. 

The use of low-temperature chlorination of Pd(II) compounds in solidified fusions with alkali and alkaline earth metal chlorides (exposed in liquid chlorine for several days at room temperature and for 10-12 hours at 100 °C) made it possible to obtain known hexachloropalladates(IV): M₂[PdCl₆] with M=Cs, Rb, K and new low-stability compounds Na₂[PdCl₆], Li₂[PdCl₆] and Ba[PdCl₆]. The experimental vibration frequencies are within the ranges of 309-323 - n₁(A_1g), 283-295 - n₂(E_g) and 169-176 cm^-1- n₅(F_2g), with a tendency to increase in a series from Cs₂[PdCl₆] to Li₂[PdCl₆] and to Ba[PdCl₆].

 Pd(IV) chloride complexes with chlorides of other alkaline earth metals did not form under the conditions of this study.

Low-melting molten mixtures of sulfur chlorides with chlorides of other elements are promising for use in power sources and environmentally friendly processes for obtaining noble and rare metals [1]. Sulfur in compounds with chlorine may have different valences. The higher (IV, for chlorides) valence state of sulfur is unstable already at room temperature, at which SCl₄ dissociates into SCl₂ and Cl₂ even in the presence of the strongest oxidizer - liquid chlorine. The higher valence state of sulfur can be stabilized by the inclusion of sulfur in the composition of outer-sphere cations SCl₃⁺ in compounds of the [SCl₃]_k·[M_mCl_n] type, where M = Al, Sb, Zr, Nb, Fe, Au, Ir  and some other [1-3].

In the present work, a search for new chloride complexes was carried out. Sulfur together with the corresponding element (Be, In, Ga, V, Ti, Sn, Ge), red phosphorus or some chlorides (ZnCl₂, PbCl₂, GaCl₃, AlCl₃, HfCl₄) were kept for several days at 18–150 °C in sealed quartz ampoules with anhydrous liquid or gaseous Cl₂ at elevated pressures (up to 60 atm). Under these conditions, the indicated elements were chlorinated. Some of the chlorides formed (SCl₂, GaCl₃, VCl₄, TiCl₄, SnCl₄, and GeCl₄) are highly soluble in liquid chlorine. 

The formation of ionic compounds of the [SCl₃]_k·[M_mCl_n] type, which have low solubility in liquefied chlorine and therefore crystallize from solutions, was recorded by the appearance of characteristic bands of their SCl₃⁺ complex cations and M_mCl_n^k– anions in the Raman spectra of solid samples [4]. They were recorded using a Renishaw U1000 spectrometer microscope (laser power 25 mW, λ = 514.5 nm) directly through the glass walls of sealed reactionary ampoules with liquid Cl₂. 

Several new and known compounds have been synthesized according to the described method, for example [SCl₃]^.[BeCl₃],  [SCl₃]^.[AlCl₄], [SCl₃]^.[GaCl₄], [SCl₃]^.[Ga₂Cl₇], [SCl₃]^.[InCl₄], [SCl₃]^.[Ti₂Cl₉], [SCl₃]₂^.[SnCl₆], [SCl₃]₂^.[HfCl₆], [SCl₃]^.[Hf₂Cl₉], containing the pyramidal group SCl₃⁺ [4]. It was established, in particular, that sulfur chlorides do not form complex compounds with germanium and vanadium tetrachlorides, since the Raman spectra of solutions at room temperature only show bands of chlorides of these metals, sulfur dichloride and chlorine. Accordingly, crystalline deposits were also not observed. 

The spectroscopic characteristics of all synthesized chloride complexes, in which the highest valence state (IV) of sulfur is stabilized as a result of complex formation, have been systematized.