Journal of Chemical Technology and Metallurgy

FUNCTIONAL GROUPS AND STRUCTURAL FEATURES OF ANTIOXIDANTS: A REVIEW

Nina Ruseva — 2025-11-02

The antioxidant activity of bioactive compounds is fundamentally determined by their chemical structures and, more specifically, by the nature and positioning of key functional groups. Despite the structural diversity among natural and synthetic antioxidants, many share common molecular features that enable them to neutralize reactive oxygen and nitrogen species. The present review is an attempt to systematize the classification of antioxidants according to their functional groups. The role of redox-active moieties such as phenolic hydroxyl (-OH), thiol (-SH), amine (-NH₂), and carbonyl (C=O) groups is also highlighted. The groups facilitate electron or hydrogen donation, stabilizing free radicals and interrupting oxidative chain reactions. Conjugated π-systems, such as those found in carotenoids and polyphenols, further enhance antioxidant capacity by allowing electron delocalization across the molecule. By examining the structural basis of antioxidant mechanisms, the review underscores the critical relationship between molecular structure and biological function in oxidative stress mitigation.

ANTIOXIDANT CAPACITY OF (KLAKLAK)₂ BIOCONJUGATES ASSESSED BY THE ELECTRON-TRANSFER METHODS FRAP AND CUPRAC

Yoana Stoyanova — 2025-11-02

Oxidative stress and metal-driven redox processes are key contributors to the pathogenesis of chronic diseases and cancer, motivating the search for novel antioxidant molecules. In this study, the antioxidant potential of a series of synthetic peptides previously reported to possess antitumor and antibacterial properties was evaluated using two complementary electron-transfer assays: ferric reducing antioxidant power (FRAP) and cupric ion reducing antioxidant capacity (CUPRAC). Both assays were calibrated against caffeic acid, and results were expressed as caffeic acid equivalents (CAE).

The FRAP assay revealed substantial differences in reducing activity, with Si₈ exhibiting the highest value (0.558 ± 0.132), followed by Si₁₂ (0.478 ± 0.0240), Si₁₀ (0.293 ± 0.0220), and Si₁₅ (0.250 ± 0.0200), whereas Si₁ (0.00439 ± 0.00240) and Si₁₁ (0.00260 ± 0.000500) showed negligible responses. A comparable pattern was observed in the CUPRAC assay, where Si₈ again displayed the strongest reducing capacity (0.381 ± 0.0948), with Si₁₂ (0.290 ± 0.0225), Si₁₅ (0.262 ± 0.0223), and Si₁₀ (0.224 ± 0.0290) also demonstrating appreciable activity, while Si₁ (0.001800 ± 0.000400) and Si₁₁ (0.0132 ± 0.000500) remained inactive.

The combined application of FRAP and CUPRAC provided complementary and reproducible measures of peptide antioxidant capacity, establishing a framework for systematic characterization of redox-active peptides in relation to oxidative stress.

EFFECT OF TEMPERATURE IN THE EMULSIFICATION STEP ON THE YIELD AND QUALITY OF THE ROSE OIL FILLED UREA-FORMALDEHYDE MICROCAPSULES PREPARED BY INTERFACIAL IN SITU POLYMERIZATION METHOD

Stanislav Bayryamov — 2025-11-02

In the present work, the influence of reaction temperature in the emulsification step on the efficiency of the encapsulation process of rose oil by in situ polymerization, using urea - formaldehyde resin, forming the shell of the microcapsules, was studied. The process was carried out at the following temperatures: 40°C, 50°C, 60°C and 70°C. It was established that the effect of temperature during this step is ambiguous, as during the first sub - step (stage A) of the emulsification step, its increase leads to an increase in the efficiency of the encapsulation process, the yield and quality of the obtained microcapsules, as well as a decrease in the size of the obtained microcapsules. This is mainly due to a reduction in the size of the microdroplets obtained during this stage, determining the size of the future microcapsules. In the second stage of the emulsification step, the increase in temperature to certain
values (from 40°C to 50°C) also leads to an increase in the efficiency of the process, the yield and the quality of the obtained microcapsules. Increasing the temperature above 50°C (60 and 70°C) leads to desorption of the pre - polymer particles from the surface of the microdroplets, and from there to deterioration of the quality of the capsule shell, which leads to a decrease in the yields and quality of the microcapsules. For these reasons, the author chooses a temperature optimum of 45°C for this stage, changing the other conditions and observing the effect of this change.

RADICAL-SCAVENGING ACTIVITY OF (KLAKLAK)₂ BIOCONJUGATES WITH CAFFEIC ACID

Yоana Stoyanova — 2025-11-02

Free oxygen radicals released in the body as a result of various metabolic processes could lead to the so-called oxidative stress in cells, which is a precursor to various types of cancer. Protecting cells from oxidative stress is an important step in the prevention of cancer. Nature has a large supply of compounds with powerful antioxidant properties. One of them is caffeic acid. In the present study, caffeic acid was combined to obtain bioconjugates with analogs of the natural peptide with proven antitumor properties (KLAKLAK)₂. Here we report the antioxidant potential of these molecules as it was investigated with the well-known from the literature DPPH method, in search of a synergistic effect between the two pharmacophores of the molecule. The obtained results identify Si₁₈ (Caf-(KnLAKnLAK)₂-NH₂) as the lead candidate approaching the caffeic acid benchmark under the tested conditions with EC₅₀ = 0.0178 mM.

DETERMINATION OF ARSENIC IN COMPLEX MATRICES BY UV-Vis SPECTROSCOPY: IMPORTANCE OF pH FACTOR

Nevena Borisova — 2025-11-02

Arsenic is a widespread metalloid found in soils, sediments and waste materials. The main sources of
contamination are metallurgy, energy production from thermal power station and mining activities, which release stable forms of arsenic with different mobility depending on the pH conditions. This creates a health risk for workers exposed to contaminated materials and dust. The aim of the study is to determine the arsenic content in solid samples of industrial and natural origin by UV-Vis method with Variamine blue indicator. The results show good linearity (0.0389 - 0.649 mg L^-1, R2 = 0.99, LOD = 0.0114 mg L^-1 and LOQ = 0.0379 mg L^-1) and dependence on the pH values of the tested samples. The method is suitable for arsenic analysis, providing a short test time at a low cost and a sufficient degree of reliability of the result.

THE IMPACT OF A PICKERING EMULSION SYSTEM STABILIZED BY ZINC OXIDE AND STARCH ON THE PHYSIOCHEMICAL AND FUNCTIONAL GROUPS PROPERTIES OF YOGHURT

Marouane Chemek — 2025-11-02

The dataset extensively examines the effect of Pickering emulsion (stabilized by starch/zinc oxide) incorporation on the physicochemical and functional groups properties of set-type yogurt. The Pickering emulsion was formed with helping of ultrasonic treatment. The application of Pickering emulsions to the yoghurt structure did not significantly change the values of important textural features on the 1st, seventh and fourteenth days of storage, and the results of viscosity, pH, acidity, and antioxidant all made sense and were consistent with earlier research. Similarly, an identic FT-IR pattern with a slight changes due to the ultrasonic treatment during the addition of the Pickering emulsion was noticed in the fortified yoghurt when comparing to control samples. This study therefore suggests the development of functional yoghurt using the Pickering emulsion system as a bioactive compounds delivery system.

HYDROLYTIC STABILITY OF ADAMANTANE HYBRID MOLECULES

Antoniya Stoymirska — 2025-11-02

Herein, the hydrolytic stability of new hybrid adamantane molecules modified with amino acid cysteine (Cys) at different pH is reported. Cys is a rare proteinogenic amino acid but it is a key structural unit in proteins. Cys is the only amino acid containing thiol group in the lateral chain which make it important source of sulphur for human organism. In addition, Cys has many biological functions such as antioxidant properties, immunomodulation activity by influence of the levels of the glutathione hormone, support liver function to eliminate toxins, help the breakdown of mucus in the lungs and improve breathing, etc. Adamantane derivatives are organic compounds largely used as antiviral therapeutics for treatment of influenza virus type A as well as neurodegenerative illnesses such as Parkinson’s and Alzheimer’s diseases. The adamantane motif assures high thermic stability and resistance. The modification of many adamantane derivatives such as amantadine, rimantadine and memantine with proteinogenic amino acid Cys could lead to increasing of activity and bioavailability of newly designed molecules. It is well known that hydrolytic stability is important feature for prodrug molecules related to the ability to penetrate cell membranes and to reach the specific receptors. A series of prodrugs based on adamantane motif including Cys-S-tert.-butylamantadine, Cys-S-tert.-butylrimantadine and Cys-S-tert.-butylmemantine was studied. The hydrolytic stability was determined at two different pH 1.0 and 7.4 at 37°C, similar to these in the human stomach and blood plasma. Kinetic of hydrolysis is monitored spectrophotometrically by specifically created UV-VIS method following the concentration of non-hydrolyzed part of the compounds. The most stable compound at pH 7.4 was Cys-S-tert.-butylamantadine with t_1/2 = 8.5 h. The compound Cys-S-tert.-butylmemantine also has good hydrolytic stability with t_1/2 = 6.7 h and Cys-S-tert.-butylrimantadine has t_1/2 = 6.2 h. Almost identical are t_1/2 values at acid pH 1.0: the most stable is Cys-S-tert.-butylamantadine with t_1/2 = 4.7 h, followed by Cys-S-tert.-butylrimantadine with t_1/2 = 3.9 h and Cys-S-tert.-butylmemantine with t_1/2 = 3.5 h. However, it was revealed that hydrolytic stability of tested compounds in the two model systems at acid pH is relatively lower than those in neutral conditions.

EVALUATION OF ADHESIVE AND AGGREGATION PROPERTIES OF LACTIC ACID BACTERIA ISOLATED FROM DIFFERENT BIOTOPES

Viktoria Marinova-Yordanova — 2025-11-02

The objective of this study were fifty strains of seven lactic acid bacteria (LAB) species (L. paracasei, L. casei, L. rhamnosus, L. plantarum, L. fermentum, L. delbrueckii subsp. bulgaricus and L. koreensis), previously isolated from various biotopes (human breast milk, newborn feces, and fermented vegetables). As part of their probiotic potential, their ability for adhesion, biofilm / anti-biofilm formation, auto-aggregation and co-aggregation with different pathogenic species were evaluated.
Based on their capacity to form biofilm, strains were grouped as poor (34 %), moderate (33 %), and strong (33 %) biofilm forming bacteria (BFB). L. fermentum 18V, showed the strongest biofilm formation ability and 70 % anti-biofilm activity against P. aeruginosa. The auto-aggregation capability of LAB ranged from 12 % to 68 %. The highest auto-aggregation (85 %) was established for L. fermentum 12V and L. casei 8V (78 %). The best co-aggregation ability with all tested pathogenic species was demonstrate by L. casei 8V. The highest percentage (85 %) of co-aggregation was determined for L. paracasei strain 29V with L. innocua. The housekeeping genes (ef-Tu, eno, gap, groEl, and srtA) involved in binding mechanisms shown 100 % presence in all of the tested strains. The great ability to adhere to mucin was determined for L. koreensis 35V (1. 9 x 106 CFU mL-1). The degree of adhesion varies both between individual species and between strains belonging to the same species. The obtained results showed that the LAB possess strain- and species-specifically probiotic properties with potential applications in the food industry.

"GREEN" CEMENT COMPOSITES WITH HYBRID ADDITIVES OF MICROSILICA AND ASH SLAG MIXTURE FROM THERMAL POWER PLANT

Mastura Iskandarova — 2025-11-02

The paper presents the results of studies on determination of composition of ultra dispersed microsilica (MS) and its derivatives in composition with active ash and slag mixture (ASM) of dry ash removal Thermal Power Plant. Their chemical and mineralogical compositions and suitability for use as an additive in cement were determined by their hydraulic activity according to the Student’s t-criterion value and CaO absorption from saturated lime solution. It has been established that according to the t-criterion value, ASM meets the requirements of the Interstate standard (ISS) 31108 - 2020 for active mineral additives for cement (t - criterion - no less than 15), but MS does not correspond. Taking these data into account, the compositions of hybrid additives (HA) were formed, including active (ASM) and passive components (ASM), providing maximum replacement of the expensive clinker part in cement with the optimal ratios of the ingredients of hybrid additives and its optimal dosage found in the composition of composite Portland cements (CPC).The rate of chemical interaction of the ratio of mineral ingredients was found to be in the composition of hybrid additives: CPC exhibits high chemical activity upon contact with water with a content of 15 % ASM + 10 % MS (HA), introduced into cement in an amount of up to 35 %. The achievement of hydraulic activity of cement composites is scientifically substantiated to be higher than that of additive-free cement, providing their belonging to the class 32.5 and 42.5 in strength due to the formation of a dense microstructure. Control tests of “green” CPC in the laboratories of two large cement plants of Uzbekistan confirmed the results of research on the possibility of replacing up to 35 % of expensive clinker with available and cheap hybrid additives from local techno genic waste to obtain high durability composite Portland cement.

MODELING CONFINED ZONE EFFECT IN REINFORCED CONCRETE CORBEL STRENGTHENED BY CFRP

Veselin Stankov — 2025-11-02

Confined zone effect, which is primarily observed in reinforced concrete (RC) columns subjected to compression, is crucial for the load-bearing capacity of (RC) structures. This occurs when, despite an increase in the load, the resulting deformations are nearly zero. The same effect can be observed in structures strengthened by different types of fabrics (carbon, glass, Kevlar, etc.). It is well known that experimental studies are a high-resources and time-consuming process. Therefore, a combination of experimental study and non-linear finite element (FE) simulation strategy is considered. The structure investigated in this paper is an RC corbel strengthened by bonding carbon fibre reinforced polymer (CFRP). Two RC corbel structures were developed, one with strengthening by three layers of CFRP and one without strengthening. The experimental results were used to validate the FE simulation. The model was successfully validated and provides opportunities for future parametric investigations. The aim of this study is to model he confined zone effect in reinforced concrete corbels strengthened by CFRP. Modelling confined zone effect is a significant challenge for engineers. This study shows a new approach to FE simulation. The resulting model successfully simulates the mechanical behaviour of the structure.

PREPARATION AND CHARACTERIZATION OF COTTON FABRIC MODIFIED WITH CHITOSAN CONTAINING DICLOFENAC SODIUM FOR WOUND DRESSING

Daniela Atanasova — 2025-11-02

Due to the different types of wounds and stages of their healing, the development of bioactive textile wound dressings is a challenge. In many cases, the dressing is expected to be multifunctional. It must actively support wound healing by absorbing excess exudate, but also provide a moist environment, inhibit microbial growth, and, if necessary, deliver bioactive substances in a controlled manner.

This study aims to modify cotton fabric with a layer of chitosan crosslinked with citric acid, involving diclofenac sodium. Different methods were applied to obtain two composite materials. The first treatment used the pad-dry technique at room temperature (CRTD), and the second applied pad-cure at 80^oC for 180 min (CHTD). The new materials were characterised by optical microscopy and thermal analysis. The surface properties of the pristine cotton fabric were compared with the modified samples by determining the contact angle of a droplet of distilled water. The composites exhibit hydrophobic properties and antibacterial activity against model bacterial strains, Bacillus cereus and Pseudomonas aeruginosa. The material CHTD inhibits approximately 78.0 % of the growth of P. aeruginosa and approximately 31.6 % of B. cereus. Using gravimetric and spectrophotometric analysis, the swelling of the obtained layers on the fabric surface and the release of diclofenac sodium in phosphate buffer with pH = 7.4 at 37^oC were investigated. Therefore, the composite materials combine antibacterial efficacy with continued release of bioactive substances, making them promising for use as wound dressings.

EFFECT OF EPOXY MATRIX VISCOSITY ON THE DISPERSION OF GPL GRAPHENE LAYER SEPARATION FOR COATING APPLICATIONS

Anna Staneva — 2025-11-02

Coatings application is among the most accessible methods of surface modification. Many materials exhibit the desired bulk properties (e.g. mechanical strength), but their surface needs to be protected from the environment to have an additionally functionalized surface - heat and electrically conducting or isolating, optical or aesthetic considerations.
When adding nanosized materials to a matrix the main concern is the retention of separation of nanoparticles and the prevention of aggregation. In the following study, dispersion of Graphene nanoplatelets (GPL) in bisphenol-a based epoxy is investigated. GPL is initially sonicated in methanol and introduced into a series of liquid epoxies with varying dry weight concentration and thus, varying viscosity. The working hypothesis that increased viscosity aids to stabilize the suspension and delamination of graphene layers, has been confirmed. The samples have been characterized by Transmission Electron Microscopy (TEM) and Raman spectroscopy. TEM confirms that the best delamination is retained in the most concentrated matrix. Increased Raman signal intensity testifies to the increase of stabile suspended fraction of GPL before coating, which leads to a higher concentration of active additives in the coatings. Furthermore, adhesion and delamination testing by the crosshatch method confirms that adding GPL does not negatively affect the mechanical properties of the coatings, as compared to coatings without the addition of GPL.

EFFECT OF TEMPERATURE ON THE MODIFICATION OF COTTON FABRIC WITH CROSSLINKED CHITOSAN

Daniela Atanasova — 2025-11-02

This study aimed to compare the properties of the cotton fabric coated with a layer of chitosan crosslinked with citric acid at room temperature or after thermal treatment (at 80^oC for 180 min). The applied conditions assume the formation of ionic bonds between the coating components in the first case and their covalent interactions in the second case. Various analyses have been used to confirm this statement. The quantity of the obtained coating on the fabric and the colour characteristics of the materials was characterised with gravimetric and colorimetric analysis. The changes in the bands of functional groups in FT-IR analysis and thermal behaviour of modified fabrics compared to pristine cotton fabric were studied. The surface morphology was investigated using the contact angle measurement. It was found that after thermal treatment, the fabric surface hydrophobicity increases, and the antimicrobial activity against both Gram-negative Pseudomonas aeruginosa and Gram-positive Bacillus cereus strains also increases.

ANALYSIS OF THE NEED TO EXAMINE CYANURIC ACID LEVELS IN SWIMMING POOLS IN BULGARIA

Monika Dragneva — 2025-11-02

This study analyzes the necessity of monitoring cyanuric acid levels in swimming pools in Bulgaria, with a focus on its impact on chlorine efficiency in pool disinfection. Current Bulgarian regulations, as outlined in Instruction No. 34 (1975), do not mandate testing for cyanuric acid, despite its widespread use in pool maintenance. A dataset of 1,675 records from the period 2019-2023, collected from state health inspections in Sofia, reveals frequent non-compliance with chlorine residual standards. Statistical analysis indicates significant differences in chlorine levels between indoor and outdoor pools, with higher instability observed in outdoor pools due to UV degradation. Cyanuric acid acts as a stabilizer, slowing chlorine degradation and extending its effectiveness. However, excessive accumulation above 100 ppm can inhibit chlorine activity, increasing the risk of microbiological contamination. Given its critical role in water quality, routine monitoring of cyanuric acid is recommended to optimize disinfection efficiency and minimize health risks.

COMPARATIVE STUDY OF DISTILLERY WASTEWATER TREATMENT BY DIRECT UV IRRADIATION, UV/H2O2 AND UV-PHOTO-FENTON PROCESSES

Karima Anggita Wijayanti — 2025-11-02

The disposal of distillery stillage wastewater poses significant environmental challenges due to its high organic load and complex composition. Among the commonly used treatment methods are advanced oxidation processes (AOP) such as direct UV irradiation, UV/H₂O₂ and UV-Photo-Fenton. This study presents a comparative analysis of three methods: direct UV irradiation, UV/H₂O₂ and UV-Photo-Fenton processes, for the treatment of distillery wastewater. The effectiveness of each process was assessed by evaluating the reduction of chemical oxygen demand (COD) and biological oxygen demand (BOD₅). Direct UV irradiation alone showed limited efficacy in degrading the complex organic molecules present in the wastewater. The UV/H₂O₂ process, involving the photolysis of hydrogen peroxide, demonstrated a moderate improvement in pollutant reduction. However, the most effective treatment was achieved
with the UV-Photo-Fenton process, which combines hydrogen peroxide, ferrous ions, and UV light. This method exhibited the highest removal efficiencies, achieving significant reductions in COD (96.36 %) and BOD₅ (94.60 %). The enhanced performance is attributed to the synergistic generation of hydroxyl radicals through Fenton chemistry and UV irradiation, leading to more effective degradation of recalcitrant compounds. The study concludes that while each AOP has specific advantages, the UV-Photo-Fenton process stands out as the most promising treatment option for distillery stillage wastewater, offering an efficient and sustainable solution for mitigating the environmental impact of distillery operations.

EXPONENTIAL MOVING AVERAGE FOR AIR POLLUTION DATA: ASSESSING ITS ROLE IN PM10 MONITORING ACCURACY

Kremena Stoyanova — 2025-11-02

Accurate estimation of particulate matter (PM₁₀) concentrations is critical for assessing air quality and mitigating public health risks. Traditional monitoring data processing methods, such as simple moving averages (MA), often struggle to capture rapid fluctuations in pollutant levels due to their uniform weighting of historical data, potentially compromising real-time decision-making. This study evaluates the efficiency of the Exponential Moving Average (EMA) algorithm, which prioritizes recent observations through exponential weighting, to improve PM₁₀ concentration estimates. Using data from urban air quality monitoring stations, EMA was applied across varying time windows and compared against conventional MA approaches. Performance was assessed against ground-truth measurements. Results demonstrated that EMA significantly reduced estimation errors. The algorithm exhibited enhanced responsiveness to abrupt PM₁₀ spikes, attributed to its dynamic weighting mechanism. Sensitivity analysis revealed that optimal smoothing factors depended on the selected time window, balancing noise reduction and trend detection. These findings underscore EMA’s potential as a robust tool for air pollution monitoring data analyses, offering superior adaptability to temporal variability. Implementation of EMA in regulatory and public health frameworks could enhance early warning systems and pollution control strategies. Future research should explore integrating EMA with machine learning models and low-cost sensor networks to further optimize real-time air quality management.

PERFORMANCE AND ERROR EVALUATION OF TWO-PARAMETER ADSORPTION MODELS FOR ZINC ION REMOVAL VIA FLY ASH

Ajay Kumar Agarwal — 2025-11-02

In the present investigations, a series of batch experiments were conducted to analyze the adsorption behavior of flyash using eight two-parameter adsorption isotherm models. Each isotherm model was assessed using eleven distinct error functions to determine the most suitable model that can be used to design the adsorption process. The analysis relied on minimizing error values as the primary metric for model performance evaluation. Based on the analysis of error values, it was concluded that the ranking of the different isotherm models (in terms of accuracy and relative performance) is as follows: Temkin, Freundlich, Frenkel–Halsey–Hill, Frumkin, Elovich, Langmuir, Jovanovic, and Harkins-Jura. Amongst these, the Temkin isotherm emerged as the most reliable model for representing the adsorption process, whereas the Harkins-Jura model showed the least accuracy with the experimental data. These findings highlight the importance of error function analysis in accurately ranking isotherm models and selecting the most appropriate isotherm for specific adsorption studies.

ADSORPTIVE DESULFURIZATION OF MODEL FUELS WITH LOW-COST ADSORBENT IN DYNAMIC CONDITIONS

Daniela Angelova — 2025-11-02

The adsorption capacity of pyrolyzed rice husks was investigated with respect to individual model solutions of benzothiophene (BT) and dibenzothiophene (DBT), and a model mixture containing benzothiophene, dibenzothiophene and 4,6,-dimethyldibenzothiophene (4,6 –DMDBT). The adsorption process was carried out under dynamic conditions. The influence of temperature and initial concentration of sulfur compounds in individual model fuels was investigated. The highest adsorption capacity was achieved at 60°C and the highest initial sulfur concentration in the model fuels. Carrying out the adsorption at higher temperatures leads to an increase in the degree of desulfurization, which means that the adsorption process is not only physical in nature. The adsorption selectivity of the pyrolyzed rice husk from mixture model fuel decreases in the order DBT > 4, 6–DMDBT > BT.

SEGREGATION OF COAL PARTICLES DURING CHARGING INTO COKING TOWER

Valentyn Koval — 2025-11-02

This study investigates coal particle segregation in an industrial coking plant, analysing particle size and key quality parameters (ash, volatile matter, sulfur). Unlike previous mathematical or lab-based studies, it provides real-world data to optimize coal preparation. Findings show uneven ash distribution across size fractions: the 25 - 50 mm fraction has the highest ash content (6.8 - 32.1 %, average 13.1 %), while lower values appear in the 0.5 - 6 mm range (6.9 - 7.3 %). Fine fractions (< 0.5 mm) exhibit elevated ash levels (average 10.9 %, max. 15.1 %).
Despite stable coal charge properties during loading, variations across tower sections highlight challenges in achieving uniformity. Differences in particle size, volatile matter, and ash content from central to peripheral rows emphasize the need for improved loading strategies. This study underscores the critical role of the loading and distribution stages in preparing a uniform coal charge for coking doffers practical recommendations to enhance coal preparation and coke production efficiency.

NUMERICAL ANALYSIS OF MICROMIXING IN CONCEPTUAL COMBUSTOR

Jayeshkumar R. Parekh — 2025-11-02

When a jet is introduced into a crossflow, a key fluid dynamic phenomenon known as micromixing improves fluid mixing. In order to encourage hydrogen's mixing with air prior to burning in a diffusion flame, hydrogen is delivered perpendicularly into an airstream in this study. The purpose of the combustor design is to shed light on the behavior of micromixing and how it affects combustion properties. The micromixing process is examined and its impact on flow dynamics assessed using ANSYS Fluent. In order to maximize micromixing efficiency in both cold flow and combustion scenarios, the combustor geometry was specially designed. According to simulation data, there is better mixing in the combustor's center, which raises the temperature during combustion. Analysis of velocity and turbulence also shows how vortex generation and jet penetration contribute to improved micromixing. Better fuel-air mixing enhances combustion performance and stability, according to the study. Advanced cooling techniques will be investigated in future studies to control temperature distribution and avoid thermal hotspots. Additionally, optimization of injection parameters and combustor modifications will be considered to further enhance micromixing and overall combustion efficiency.

EFFECT OF AL CONTENT ON THE MICROSTRUCTURE, MICROHARDNESS AND CORROSION RESISTANCE Of AlxCoCrFeNiMo0.5 HIGH-ENTROPY ALLOYS

Olga Samoilova — 2025-11-02

The microstructure, microhardness and corrosion resistance (in a 1 M NaCl solution) of as-cast Al_xCoCrFeNiMo_0.5 (x = 0, 0.25, 0.5) high-entropy alloys (HEAs) were studied. The as-cast samples exhibited a dendritic microstructure in which a (CrFeMo)-type molybdenum-rich σ-phase precipitated in the interdendritic space. It was determined that Al alloying increases the microhardness from 285 HV_0.3 for CoCrFeNiMo_0.5 HEA to 628 HV_0.3 for Al_0.5CoCrFeNiMo_0.5 HEA. At the same time, aluminum has a negative effect on the corrosion resistance of the studied alloys, where an increase in Al concentration, increases the corrosion current by two orders of magnitude.

INVESTIGATION OF THE INFLUENCE OF MO, W AND V MODIFICATION ON THE STRUCTURE AND HARDNESS OF IRON-DOPED CuAl9 BRONZE IN THE CAST STATE

Maria Krasteva — 2025-11-02

Of the group of tin-free bronzes, the most widespread in foundry production is the use of so-called "aluminium" bronze, or bronze type CuAl₉. Double bronzes of this type tend to "self-anneal", resulting in a coarse-grained cast structure. To suppress this tendency, aluminium bronzes are most commonly alloyed with iron, manganese and nickel, but are also further modified with various modifiers. The aim of this development is to investigate the influence of Mo, W and V modification on the structure and hardness of iron alloyed CuAl₉ type in the cast state.

AGEING EFFECT ON TRUE STRESS-STRAIN AND FRACTURE BEHAVIOR OF COLD DEFORMED SOLDER-AFFECTED COPPER

Mohammad Salim Kaiser — 2025-11-02

Present manuscript reports the effects of minor Sn-Pb solder on the true stress true strain, impact toughness as well as mode of fracture behavior of commercially pure copper. Heat treatment of cast alloys is done by homogenizing, solution treatment and quenching those. Then the alloys are cold rolled by 75% followed by ageing at room temperature, 150°C and 400°C for one hour each. The results reveal that solder has a positive effect on the tensile properties of the alloy at lower ageing temperature, but does not offer enough benefit at higher ageing temperatures. Both Sn and Pb increase strength through solid solution strengthening, with tin performing better than lead because Sn has a different BCC crystal structure and Pb has a similar FCC structure to Cu. In addition, Pb does not form any intermetallic with Cu but Sn forms various intermetallic with Cu as well as impurities which naturally present in the cast alloys. They also have a significant impact on ductility minima of the matrix. The microstructures exhibit relatively thick grain boundaries of minor alloying elements due to the presence of different particles. Fracture surfaces also indicate such particles that inhibit dislocation movement as well as ensure high strength.

INVESTIGATION OF THE INFLUENCE OF MODIFICATION WITH B, Zr AND Ti ON THE STRUCTURE AND HARDNESS OF CUAL9FE3 ALLOY BRONZE IN THE CAST STATE

Maria Krasteva — 2025-11-02

In view of the changes occurring in the global production plan and the imposition by the business on the market for metal products and parts, there is a tendency to replace basic parts and castings made of cast iron and steel with those made of non-ferrous metals and alloys. Some of the most used metals are copper and aluminium, and their alloys. These alloys are alloyed or modified to produce alloys with better casting, performance and corrosion properties. Aluminium bronzes are of scientific interest because they are of industrial importance at a content of 6 - 12 % Al with or without the addition of other elements, crystallizing in a narrow temperature range, which determines a good thinness and a high tendency to form concentrated suctions, and alloys with a content of 9 - 15 % Al, where the mechanical strength and hardness increase with increasing aluminium content, but their ductility and impact toughness decrease. The development aims to increase the hardness, preserve or finesse the structure and change the grain shape of aluminium bronzes by adding a small amount of B, Zr and Ti as modifiers so that the resulting castings and parts of CuAl₉Fe₃B, CuAl₉Fe₃Zr and CuAl₉Fe₃Ti alloys in the cast state possess high technological, corrosion and service properties.

TRENDS IN DISTANCE LEARNING IN AN ELECTRONIC ENVIRONMENT

Monika Petrunova — 2025-11-02

This paper introduces an analysis in the forms of education and learning in the past and nowadays and especially the tendencies in distance learning in an electronic environment in COVID-19 pandemic conditions. After the brief introduction of the types of training before and during the pandemic, a comparative analysis of the problems related to the distance learning in an electronic environment identified by Institute for Educational Research /IER/ in 2021 and our private surveys in 2020 and 2023 has been done. The results in both researches show many common tendencies commented in the following parts of the paper.