Thermodynamic Calculations Research Articles

Carboxylic acid-based deep eutectic solvent for efficient desulfurization: Experimental and computational thermodynamics

The improvement of fuel quality requires the reduction of sulfur content. The main challenge of catalytic cracking diesel extraction desulfurization is to find low-price and good-performance extractants. Based on experimental research, this work further explores the separation mechanism of DES for thiophene (TP) and benzothiophene (BTP). First, the COSMOS-RS model was used to predict the separation performance of 10 HBAs and 10 HBDs for TP and BTP. The results showed that the low-cost carboxylic acid based DES had excellent separation performance. Secondly, the effect of experimental conditions on the separation performance of three carboxylic acid based DESs was investigated. When the molar ratio of DES to TP and BTP was 3:1, after three stage extraction, the extraction rates of TP and BTP by TEAC: PrA(1:3) were 98.06 % and 98.53 %, respectively. Finally, the structure–activity relationship was studied by using quantum chemistry and molecular dynamics simulation. It was found that EvdW plays a dominant role in the desulfurization process and does not include H-bond interactions. TEA+ was distributed parallel to the aromatic ring and has a CH···π interaction with thiophene. TP and BTP were distributed in the voids of DES and do not affect the regeneration performance of DES.

Computational Thermodynamics and Kinetics of Aluminum Nitride Precipitation in Steel—An Overview with Emphasis on Austenitic Grain Size Control

Computational Thermodynamics and Kinetics of Aluminum Nitride Precipitation in Steel—An Overview with Emphasis on Austenitic Grain Size Control

Deep removal of Sn, Pb, and Sb in refined indium by vacuum distillation

To deeply separate the azeotropic impurities from the refined indium, three novel processes of vacuum distillation by considering the variables of vacuum pressure, loading mass, distillation time, temperature, and the effective vacuum evaporation area are firstly presented. Thermodynamic calculations show that Pb, Sb and Sn can be separated from indium melt by vacuum distillation due to their great difference in saturated vapor pressure and separation coefficient. Experiments show that distillation at 800 ℃ for 7 h under a pressure of 10−3 Pa could achieve the Pb concentration of 0.004 ppm in indium melt by enlarging the evaporation area and small ratio of h1/h4. After 950 ℃ distillation, the concentrations of Sb and Sn in the condensing indium reduced respectively from 0.15 ppm to 0.009 ppm, and 8.1 ppm to 0.05 ppm. Multiple processes of vacuum distillation were used to achieve the 7 N purity of indium, with the removal ratio of over 99.5 %. Besides, it is found out that when the temperature dropped from 1075 ℃ to 780 ℃, the movement stroke of vapor atoms reduced from 509 mm to 209 mm.

Investigation into the effects of Na2B4O7 on the removal of titanium and vanadium from aluminium matrix

ABSTRACT This study proposes a method of adding Na₂B₄O₇ to remove titanium and vanadium impurities from primary aluminium. The effect of Na₂B₄O₇ to the aluminium melt on the removal of titanium and vanadium impurities was investigated, with a focus on the influence of varying addition amounts and holding times. According to the results, the chemical reaction occurring within the melt was postulated and a thermodynamic calculation was conducted. At 750°C and holding times of 30 min, the impurity contents of titanium and vanadium gradually decrease with an increase the amount of Na₂B₄O₇. At an addition of 0.8 wt.%, the removal rates were observed to be 53.3% and 76.3%, respectively. The impurity removal effect exhibited a positive correlation with the holding times. Holding for 90 min, the content of titanium and vanadium impurities decreased from 15 and 97 ppm to 1 and 6 ppm, with removal rates of 93.3% and 93.8%, respectively. Thermodynamic calculation results indicate that B undergoes spontaneous reaction with titanium and vanadium, forming TiB₂ and VB₂, which precipitate at the bottom, thereby explaining the observed decrease in impurities. This study provides ideas and data reference for the removal of titanium and vanadium impurities in aluminium matrix.

Novel Strategy for Efficient Recovery of CuO-Based Multiple-Metals from Copper Smelter Dust toward CO2 Electrocatalytic Reduction.

Copper smelter dust, a typical hazardous waste that is abundant in valuable heavy metals, holds the potential to be regarded as a promising resource. This study introduces a new approach that integrates chlorination roasting and cascade condensation to efficiently recover heavy metals from copper smelter dust. The findings demonstrate the successful separation of heavy metals (Cu, Pb, and Zn) as chlorides at nearly 100% efficiency while also effectively converting trivalent arsenic (As(III)) into pentavalent arsenic (As(V)) and immobilizing it in the roasting residues, thereby reducing environmental risk. Through the utilization of thermogravimetric mass spectrum analysis and thermodynamic equilibrium calculations, the chlorination process for heavy metals was investigated, revealing both direct and indirect chlorination processes. Additionally, the study resulted in the development of a CuO-based multiple-metals electrocatalyst from the oxidized roasting-recovered heavy metal chlorides, exhibiting significantly enhanced catalytic activity and faradaic efficiency for the electroreduction of CO2 into CO and CH4 compared to pure CuO electrocatalyst under similar electrocatalytic conditions. Overall, this work presents a sustainable and scalable method and new insights for addressing environmental risks while repurposing copper smelter dust.

Impact of Chemical Composition Changes during Ultrasound Atomization and Laser Powder Bed Fusion of Low Alloy Steel

This study investigates the effect of changing the chemical composition during ultrasonic atomization (UA) and laser powder bed fusion (LPBF) of low‐alloy steel. UA is used to produce a spherical powder with d50 equal to 49 μm. During UA, the chemical composition of the material changes, which is associated with selective evaporation of Mn from 1.42% to 0.35% and B from 0.0012% to <0.0001%. Thermodynamic calculations confirm that during atomization, mostly Mn and Fe evaporate. To achieve a high density of 3D printed parts, in situ remelting in LPBF is applied. A microstructure consisting of fine grains of tempered martensite and bainite in crystallized meltpools is observed. The selected high‐quality LPBF samples are austenitized in the temperature range of 900–1200 °C for 20 min and quenched in oil. The samples are characterized by light and scanning electron microscopy, as well as Vickers hardness. Changes in chemical composition result in a decrease in the hardenability of the material, and quenching only at 1200 °C produces a martensitic microstructure. LPBF samples show a hardness higher than that of the postheat‐treated sample, but still significantly lower than that of the as‐delivery condition, which is related to the change in chemical composition.

Antibiotics pollutants in agricultural soil: Kinetic, sorption, and thermodynamic of ciprofloxacin

The entry of antibiotics, as pollutants, into the environment has created great concerns. Environmental dynamics of antibiotics based on soil chemical properties need to be a better understanding of their chemical behavior. This research is focused on studying the adsorption behavior and kinetic mechanisms of ciprofloxacin (CIP) in an agricultural soil. For this purpose, a batch experiment was conducted at different times (5 min–24 h), and using initial concentrations of CIP (0–1 mmol L−1) in the soil. The adsorption processes as affected by pH and ionic strength were assessed based on the modeling with response surface methodology (RSM). According to the results, the sorption equilibrium was found within 240 min, and the pseudo second-order model was the best for describing the data. Increasing the initial CIP concentration increased CIP adsorption, but increases in ionic strength and pH had an inverse effect. Based on RSM modeling, the CIP adsorption was 7.31 and 7.03 (mg g−1) in the presence of NaCl and CaCl2 electrolytes, respectively, in the optimized conditions (pH 6.5 and ionic strength 0.01 mol L−1). The spontaneous nature of CIP adsorption was determined based on thermodynamic calculations (ΔG° = −10.8 to −12.4 kJ mol−1). The interaction of pH and ionic strength was described with the quadratic model. The obtained results contribute to understanding the CIP fate in the soil environment and facilitate decisions regarding entry and controlling soil contamination due to this antibiotic.

Synthesis of TaB2-TaC nanocomposite powders by a boro-carbothermal reduction route

This paper introduces the boron/carbon thermal reduction reaction, represented by the equation 2Ta2O5+ B4C + 11 C = 2TaB2 + 2TaC + 10CO (g), as a novel reaction pathway for synthesizing TaB2₋TaC composite powders. Subsequently, the SPS technique is employed for the fabrication of TaB2-TaC composite ceramics via sintering. The article begins by elucidating the fundamental process of this reaction and constructing a phase diagram through thermodynamic calculations. The experimental results demonstrate that adjusting the synthesis temperature and the proportion of the boron source in the raw materials enables effective control over the ratio of the two phases within the composite materials, allowing the TaB2 phase content to be tailored within the range of 38.1–60 %. Moreover, elevating the synthesis temperature and increasing the proportion of the boron source effectively mitigate the C,O impurity content in the composite powders and facilitate the TaB2 step-growth process. It is noteworthy that the hardness of TaB2-TaC composite ceramics sintered at 2000°C using the optimized complex-phase powder as the precursor reaches 21.7±0.5 GPa, and the fracture toughness attains 5.2±0.2 MPa⋅m1/2.

High-efficient removal of tebuconazole from aqueous solutions using P-doped corn straw biochar: Performance, mechanism and application

Due to the serious threat posed by tebuconazole to the aquatic ecosystem, it is imperative to develop a highly efficient adsorbent material for the sustainable remediation of tebuconazole-contaminated water. Herein, a phosphorus (P)-doped biochar from corn straw and H3PO4 was fabricated by one-step pyrolysis for tebuconazole adsorption. Results showed that the P-doped biochar produced at 500℃ (PBC500) possesses a large specific surface area (SSA=869.6 m2/g), abundant surface functional groups, and the highest tebuconazole adsorption capacity (429.6 mg/g). The adsorption of tebuconazole on PBC500 followed pseudo-second-order kinetics and Langmuir adsorption isotherm models. Thermodynamic calculations indicated that the adsorption of tebuconazole by PBC500 was a spontaneous, endothermic process with a random increase. Adsorption mechanism mainly involves pore filling, π-π interactions, hydrogen bonding, and hydrophobic interaction. Moreover, PBC500 demonstrated robust anti-interference capabilities in adsorbing tebuconazole from diverse water sources and exhibited excellent reusability, underscoring its potential for a broad array of practical applications.

Assessment of entropy accumulation in human subjects when exposed to low energy availability

Background & aimsAdequate energy availability is essential for the body to maintain its physiological functions and achieve optimal health, especially among athletes. Unfortunately, low energy availability (LEA) is common among athletes, and it has been associated with impairments in health and performance. In contrast, an energy-restricted diet has been linked to longevity, but it is unclear how LEA affects athletes’ lifespans. The goal of the present study was to assess the impact of LEA thermodynamically on the lifespan of athletes. MethodsData from seven healthy young endurance-trained athletes (24 ± 4 years) who underwent short-term low energy availability (125 (kJ/day) per kg FFM) once with low protein content (LEA-LP; 0.8 g/kg) and with high protein content (LEA-HP; 125 (kJ/day) per kg FFM, 1.7 g/kg), as well as a control diet (CON; 230 (kJ/day) per kg FFM, 1.7 g/kg), were used in the calculations. The athletes followed each diet for five days and expended 67.5 (kJ/day) per kg FFM. entropy generation-based thermodynamic calculations were performed based on the metabolic activity of the athletes, which was determined from oxygen consumption and carbon dioxide production rates. ResultsLow energy availability was successfully induced during LEA-LP (62 ± 8 (kJ/day) per kg FFM; 95%Cl: 53–70) and LEA-HP (64 ± 8 (kJ/day) per kg FFM; 95%Cl: 56–71) diets. Despite of achieving energy deficit of −6658 ± 2110 kJ/day (95%Cl: 8609-(−) 4707) (LEA-LP), −5781 ± 623 (95%Cl: 26591-(−)4707) (LEA-HP) and excessive energy of 772 ± 1915 (95%Cl: 845-2388) (CON) statistical analyses revealed no significant differences in lifespan estimations among diets (CON: 72 ± 8 years (95%Cl: 65–79), LEA-LP: 74 ± 7 years (95%Cl: 68–80), and LEA-HP: 73 ± 11 (95%Cl: 62–83)). ConclusionsThis study suggests valuable insights into the intricate relationship between energy availability, entropy generation, and lifespan among athletes. Whereas entropy generation levels and the lifespan of athletes remained stable depending on diets, the distinguished differences in energy deficiency and energy availability underline the need for a profounder investigation of underlying physiological mechanisms to improve the health and performance of athletes.

Origin of Manipulating Selectivity in Prins Cyclization by [Ga4L6]12- Supramolecular Catalysis through Host-Guest Interactions.

The host effect of the supramolecular [Ga4L6]12- tetrahedral metallocage on Prins cyclization reaction of the substrate by encapsulated citronellal has been investigated by means of molecular dynamics and quantum mechanics. The encapsulation process of the substrate into the [Ga4L6]12- cavity was simulated via attach-pull-release (APR) methods. Thermodynamic calculations and classical molecular dynamics simulations assessed the substrate's microenvironment inside the cavity, guiding DFT-level modeling of the reaction. DFT calculations show diol product predominance in acidic solution but high enol selectivity inside [Ga4L6]12-, consistent with experimental findings. [Ga4L6]12- alters the selectivity of the Prins cyclization reaction by inhibiting diol formation. The activation strain model-based decomposition analysis (ASM-DA) of the barrier difference among distortion and interaction terms indicates that the more positive interaction between a host and guest in the diol transition state than enol determines the product selectivity, particularly the fewer C-H···O and O-H···O hydrogen-bonding interactions. These theoretical insights could contribute to a deeper understanding of the nature of supramolecular catalysis and to further develop new supramolecular catalysts.

The possibility of using the Zn (II) Butadiyne-linked porphyrin nanoring for detection and adsorption of AsH3, NO2, H2O, SO2, CS2, CO, and CO2 gases

The present research aims to study the probability of applying the Zn (II)-Butadiyne-linked porphyrin (ZBPN) nanoring for detection and adsorption of some of the most important air pollutants such as AsH3, NO2, H2O, SO2, CS2, CO, and CO2 gases by using the density functional theory (DFT) method. The key results of the thermodynamic calculations indicated that ZBPN nanoring is able to absorb SO2, AsH3, NO2, and H2O gases; while, it could not strongly adsorb CS2, CO, or CO2. Subsequent to the thermodynamic results, the changes of band gaps and the frontier molecular orbital (FMO) calculations show that ZBPN nanoring might release stronger signals in the presence of SO2 (σ = 1.64(1010) s), AsH3 (σ = 1.35(1010) s), and H2O (σ = 1.11(1010) s) single molecules compared to the other considered ones. Therefore, ZBPN could be used as a relatively good sensor for detection of SO2, AsH3, and H2O (compared to CS2, CO, CO2, and NO2 gases). Regarding the key findings of this research, it hopes that in the future, the results of the work be helpful for experimental synthesis of ZBPN nanoring for adsorption and sensing of the mentioned gases.

Investigating the interdependence of microstructure and properties in low-Cu content Al-Zn-Mg alloys via thermodynamic calculation

This paper redesigned the Al-Zn-Mg alloy composition by thermodynamic calculations and experiments, and also explained the precipitation strengthening of the 7xxx alloy. At a Zn/Mg ratio of 3.3–5.3, only the η phase is present. The η phase was experimentally verified as the main contributor to precipitation strengthening. The Al-7.6Zn-2.2Mg-0.2Cu-0.2Cr-0.4Mn-0.15Zr alloy exhibited excellent mechanical properties, with yield and tensile strengths of 510 MPa and 542 MPa under T6 treatment. The low copper content 7xxx alloy designed in this study achieves a yield strength exceeding 500 MPa solely through the compositional design of the Zn/Mg ratio.

Sulfidation of Smithsonite via Microwave Roasting under Low-Temperature Conditions

This study employs microwave roasting to decompose smithsonite mineral (zinc carbonate) into zinc oxide, which then reacts with pyrite to sulfurize its surface, forming zinc sulfide. This process is beneficial for the flotation recovery of zinc oxide minerals. The surface sulfidation behavior of smithsonite under low-temperature microwave roasting conditions is examined through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermodynamic calculations. XRD and thermodynamic analysis indicate that smithsonite completely decomposes into zinc oxide at 400 °C. Introducing a small amount of pyrite as a sulfidizing reagent leads to the formation of sulfides on the surface of decomposed smithsonite. XPS analysis confirms that the sulfide formed on the surface is zinc sulfide. SEM analysis reveals that sulfides are distributed on the surface of smithsonite, and the average sulfur concentration increases with the pyrite dosage. Microwave-assisted sulfurization of smithsonite (ZnCO3) was found to significantly enhance its floatability compared to conventional sulfurization methods. The optimal mass ratio of ZnCO3 to FeS2 is approximately 1:1.5, with the best temperature being 400 °C. These findings provide a technical solution for the application of microwave roasting in the efficient recovery of smithsonite through flotation.

Force-Free Identification of Minimum-Energy Pathways and Transition States for Stochastic Electronic Structure Theories.

The accurate mapping of potential energy surfaces (PESs) is crucial to our understanding of the numerous physical and chemical processes mediated by atomic rearrangements, such as conformational changes and chemical reactions, and the thermodynamic and kinetic feasibility of these processes. Stochastic electronic structure theories, e.g., Quantum Monte Carlo (QMC) methods, enable highly accurate total energy calculations that in principle can be used to construct the PES. However, their stochastic nature poses a challenge to the computation and use of forces and Hessians, which are typically required in algorithms for minimum-energy pathway (MEP) and transition state (TS) identification, such as the nudged elastic band (NEB) algorithm and its climbing image formulation. Here, we present strategies that utilize the surrogate Hessian line-search method, previously developed for QMC structural optimization, to efficiently identify MEP and TS structures without requiring force calculations at the level of the stochastic electronic structure theory. By modifying the surrogate Hessian algorithm to operate in path-orthogonal subspaces and at saddle points, we show that it is possible to identify MEPs and TSs by using a force-free QMC approach. We demonstrate these strategies via two examples, the inversion of the ammonia (NH3) molecule and the nucleophilic substitution (SN2) reaction F- + CH3F → FCH3 + F-. We validate our results using Density Functional Theory (DFT)- and Coupled Cluster (CCSD, CCSD(T))-based NEB calculations. We then introduce a hybrid DFT-QMC approach to compute thermodynamic and kinetic quantities, free energy differences, rate constants, and equilibrium constants that incorporates stochastically optimized structures and their energies, and show that this scheme improves upon DFT accuracy. Our methods generalize straightforwardly to other systems and other high-accuracy theories that similarly face challenges computing energy gradients, paving the way for highly accurate PES mapping, transition state determination, and thermodynamic and kinetic calculations at significantly reduced computational expense.

Experimental study and thermodynamic modeling of CO2+CH4 gas mixture hydrate phase equilibria for gas separation efficiency

Gas separation is a critical application of gas hydrates, and accurately predicting separation performance is crucial. In this study, we used thermodynamic calculations to predict the equilibrium phase of gas hydrates for various mole fractions of CO2 + CH4 gas mixtures. We also determined the mole fraction of each gas component trapped within the hydrate clathrate. To predict the equilibrium points, we used the Soave–Redlich–Kwong（(SRK) equation of state for the gas phase, the nonrandom two-liquid (NRTL)model for the liquid phase, and the Chen–Guo model for the hydrate phase. We modified the hydrate fugacity formula and introduced a new function to improve the accuracy of the Chen–Guo model. By incorporating experimental equilibrium results from our study and another study, we developed a correlation based on gas mixture composition and temperature, resulting in highly accurate predictions. The use of this new correlation for hydrate fugacity calculation significantly improved precision, as evidenced by an average absolute deviation percent of calculated pressures (AADP) of 1.34% for pure CO2 and 1.25% for CH4. When considering the 27 data points of different CO2 + CH4 mixtures, the AADP% was 1.98%.To implement the model to predict equilibrium phases, we used the Chen–Guo framework to determine the mole fraction of each gas component in the hydrate mixture. Interestingly, we discovered a linear correlation between the CO2 mole fraction in the hydrate and equilibrium pressure, with a slope of approximately 0.001 and a y-intercept of less than one, for all gas compositions. Therefore, we can conclude that low thermodynamic conditions (temperature and pressure) result in a high CO2 mole fraction in the hydrate phase and great separation efficiency.

Thermally induced release and generation of CO2 and C1–C4 hydrocarbons in Opalinus Clay from Mont Terri (Switzerland)

Claystone formations are candidate host rocks for high-level heat-emitting nuclear waste (HLW). Temperatures from 90 to 150 °C at the canister surface are discussed internationally as potential emplacement and storage conditions. The thermal energy emitted from waste containers will be transported into the host rock formation, accelerating chemical reactions including the release of sorbed and dissolved gases and the generation of new gases. This study investigated gas release and generation in Opalinus Clay from Mont Terri (Switzerland) at elevated temperature and pressure conditions relevant for HLW storage and beyond. Hydrous pyrolysis experiments were conducted in Dickson-type flexible gold-titanium reaction cells and gold capsules in the temperature range of 80–345 °C and at 20 MPa. CO2(g) was the predominant product, followed by C1–C4 hydrocarbons, which decrease in abundance with increasing carbon atom number. Neither CO nor H2S was detected. H2 was generated only in high temperature experiments at 315 °C and 345 °C, respectively. A combination of CO2(g) quantification, stable carbon isotopic composition data, thermodynamic calculations and aqueous fluid composition (dissolved ions, pH) demonstrated that ≥80 % of the measured CO2(g) originated from carbonate mineral dissolution. The model calculations also suggest that the fraction of CO2(aq) in DIC increases from ∼50 % at 80 °C to nearly 100 % at higher temperatures. Thermal transformation of organic matter represented an additional source for CO2(g) and was the predominant process yielding the C1–C4 hydrocarbons. Our findings stress the importance of quantitative geochemical data for the safety assessment of potential host rocks for HLW storage. We demonstrated that two sources are involved in gas release and generation at temperatures relevant for HLW storage, e.g., in the Opalinus Clay – organic matter and carbonate minerals. Our data will contribute to numerical modelling studies and the refinement of feature, events, and processes (FEP) catalogues.

Thermodynamic study of water/solvent, bitumen/solvent, water/bitumen, and water/bitumen/solvent systems: From CPA EoS parametrization towards phase diagram construction

Various fluid phase equilibria happen in solvent-aided steam-assisted gravity drainage (SA-SAGD). An appropriate fluid model is a prerequisite for reservoir simulation, SA-SAGD operation analysis, and the design of various phase behavior experiments. Computational thermodynamics is a powerful tool for phase behavior studies in this application. We used the Cubic Plus Association Equation of State (CPA EoS) to predict equilibrium properties due to the presence of molecules with highly directional attractive forces. Calibration of the thermodynamic model is performed by parametrizing its unknown parameters versus two-phase equilibrium data. The model’s prediction capability of three-phase experimental data is evaluated, and it is used to construct the phase diagram of water/multicomponent solvent and water/multicomponent solvent/bitumen systems. For the water/multicomponent solvent system, the Txy diagram is obtained at 25 bar, and various phase equilibria regions are specified. These phase regions are presented on ternary diagrams for water/multicomponent solvent/bitumen systems at 25 bar and 475 K, 480 K, and 485 K. The steam/solvent coinjection analysis shows that at the same pressure, temperature, and steam/solvent composition, the multicomponent solvent/steam coinjection yields more aqueous phase compared to pure solvent/steam. This results in the transfer of more latent heat to bitumen, significantly contributing to its viscosity reduction. Analysis of the SA-SAGD operating conditions shows that a multicomponent solvent outperforms pure solvents in promoting steam condensation. The results aids in designing experiments, reducing the risk of failure of experiments, and saving time and resources in phase behavior studies.

Hydrogen technologies for decarbonization of ferrous metallurgy: scientific background and technical capabilities

To date, the use of ferrous hydrogen in metallurgy is considered from several positions. First, the partial or complete replacement of carbon with hydrogen reduces greenhouse gas emissions of CO2. Secondly, due to the different chemical affinity for oxygen, it becomes possible to selectively (selectively) extract components from complex complex ores and man-made materials. Thirdly, the absence of carbon in the reaction zone will make it possible to obtain a metal with a low content of carbides, which in many cases increases the demand for the product. Thermodynamic calculations of a multicomponent oxide system (Ni, Fe, P, Zn, Mn, V, Cr, O) in the presence of various reducing agents: carbon, hydrogen are performed using the TERRA software package, and their combined effects are considered. It is shown that the type of reducing agent affects the temperature of the beginning of the reduction of metals and the degree of their metallization. Thus, by selecting the type of reducing agent, its quantity, and the temperature of the process, it is possible to selectively extract some metals, and leave others in an oxidized state. Ilmenite concentrate in the form of a briquette was used in laboratory tests. The analysis of the iron reduction process using carbon or hydrogen as a reducing agent has been carried out. In comparison with the results obtained using carbon, the kinetics of iron reduction with hydrogen is higher. At the same time, the reduction proceeds with the formation of metallic iron, rutile (TiO2) and residual ilmenite. Whereas, in a carbothermic process occurring at higher temperatures (1000–1300 ℃), the reduction products are iron and iron ditanate (FeTi2O5). In addition, an important advantage of selective reduction by gas is the possibility of subsequent separation of the metallic and oxide phases by melting, without fear of secondary reduction due to solid carbon residues.

Influence of microalloying on precipitation behavior and notch impact toughness of welded high-strength structural steels

Microalloying elements such as Nb and Ti are essential to increase the strength of quenched and tempered high-strength low alloy (HSLA) structural steels with nominal yield strength ≥ 690 MPa and their welded joints. Standards such as EN 10025–6 only specify limits or ranges for chemical composition, which leads to variations in specific compositions between steel manufacturers. These standards do not address the mechanical properties of the material, and even small variations in alloy content can significantly affect these properties. This makes it difficult to predict the weldability and integrity of welded joints, with potential problems such as softening or excessive hardening of the heat-affected zone (HAZ). To understand these metallurgical effects, previous studies have investigated different microalloying routes with varying Ti and Nb contents using test alloys. The high-strength quenched and tempered fine-grained structural steel S690QL is the basic grade regarding chemical composition and heat treatment. To evaluate weldability, three-layer welds were made using high-performance MAG welding. HAZ formation was investigated, and critical microstructural areas were identified, focusing on phase transformations during cooling and metallurgical precipitation behavior. Isothermal thermodynamic calculations for different precipitations were also carried out. Mechanical properties, especially Charpy notch impact toughness, were evaluated to understand the influence of different microalloys on the microstructure of the HAZ and mechanical properties.