Gibbs Free Energy Of Reaction Research Articles

Conductive Metal-Organic Framework Microelectrodes Regulated by Conjugated Molecular Wires for Monitoring of Dopamine in the Mouse Brain.

Herein, we demonstrated a strategy to regulate the conductive metal-organic framework (MOF) surface, by the conjugated molecule wires for selective and sensitive determination of dopamine (DA) in the live brain. The MOFs were decorated at the carbon fiber electrode deposited by Au nanoleaves as the upper electric transducer to provide rich electrocatalytic sites for electron transfer of neurochemicals at the electrode surface, leading to greatly enhanced sensitivity for detection of neurochemicals. On the other hand, the conjugated molecular wire, 4-(thiophen-3-ylethynyl)-benzaldehyde (RP1), was synthesized and assembled as an underlying bridge to regulate the electrochemical processes at the MOF-based electrode, specifically decreasing the reaction Gibbs free energy of DA oxidation, thus selectively promoting the heterogeneous electron transfer of DA from the MOF layer to the electrode surface. Owing to the electrocatalytic activity for DA oxidation, the present microsensor exhibited high selectivity for real-time tracking of DA in a good linear relationship in the range of 0.004-0.4 μM with a detection limit of 1 nM. Eventually, this functionalized electrode was successfully applied for in vivo monitoring of DA in mouse brains with Parkinson's disease (PD) model. The results indicated that the levels of DA were obviously decreased in both acute and subacute PD models. Moreover, the level of DA strongly depended on the amount of uric acid (UA), a physiological antioxidant, which rose as the UA amount was lower than 200 mg kg-1 but was downregulated again after treatment by a higher amount of UA.

Computing the Differences between Asn-X and Gln-X Deamidation and Their Impact on Pharmaceutical and Physiological Proteins: A Theoretical Investigation Using Model Dipeptides

Protein deamidation is a degradation mechanism that significantly impacts both pharmaceutical and physiological proteins. Deamidation impacts two amino acids, Asn and Gln, where the net neutral residues are converted into their acidic forms. While there are multiple similarities between the reaction mechanisms of the two residues, the impact of Gln deamidation has been noted to be most significant on physiological proteins while Asn deamidation has been linked to both pharmaceutical and physiological proteins. For this purpose, we sought to analyze the thermochemical and kinetic properties of the different reactions of Gln deamidation relative to Asn deamidation. In this study, we mapped the deamidation of Gln-X dipeptides into Glu-X dipeptides using density functional theory (DFT). Full network mapping facilitated the prediction of reaction selectivity between the two primary pathways, as well as between the two products of Gln-X deamidation as a function of solvent dielectric. To achieve this analysis, we studied a total of 77 dipeptide reactions per solvent dielectric (308 total reactions). Modeled at a neutral pH and using quantum chemical and statistical thermodynamic methods, we computed the following values: enthalpy of reaction (ΔHRXN), entropy (ΔSRXN), Gibbs free energy of reaction (ΔGRXN), activation energy (EA), and the Arrhenius preexponential factor (log(A)) for each dipeptide. Additionally, using chemical reaction principles, we generated a database of computed rate coefficients for all possible N-terminus Gln-X deamidation reactions at a neutral pH, predicted the most likely deamidation reaction mechanism for each dipeptide reaction, analyzed our results against our prior study on Asn-X deamidation, and matched our results against qualitative trends previously noted by experimental literature.

Behavior of the components of carbon-containing ash from the combustion of power coals under the conditions of chlorination roasting

On the basis of thermodynamic calculations of interaction reactions between mullite, oxides of titanium, iron, and Cl2 (gas) in the presence of carbon, the values of the Gibbs free energy are determined in the current work. It has been established that the probability of reactions occurring in the temperature range 1073–1473 K is very high. The most negative value ΔG°Т = –1029.9 kJ/mol is typical for the titanium oxide reduction reaction at the roasting tem- perature (1100 °С). The value of the Gibbs free energy of the destruction reaction of mullite (Al2SiO5), which is important for practice, is ΔG°Т = –269.2 kJ/mol. This makes it possible to predict the complete decomposition of mullite from ash to easily soluble aluminum chloride under the conditions of chlorination roasting. The study of the behavior of carbon under the conditions of chlorination roasting of ash with CaCl2 in an oxidizing atmosphere is also important. The results of the differential thermal analysis of the non-magnetic fraction of ash, previously separated from the TPP ash by magnetic separation, showed clearly defined manifestations on the DTA, DTG and TG curves, caused by the presence of various types of reactions in the system. Low-temperature (20–115 °C) sample dehydration and ash dehydration were determined in the temperature range of 115–375 °C. In the range of further heating of the sample (375–685 °C), an exothermic projection was found on the DTA curve, which is characteristic of the oxidation of thermally active carbon present in the powder. The amount of carbon removed from the ash established as 6.75% by weight of the sample. The research was carried out within the framework of grant funding from the Committee of Science of the Ministry of Education and Science of the Republic of Kazakhstan for 2021–2023 in the priority area “Geology, mining and processing of mineral and hydrocarbon raw materials, new materials, technologies, safe products and structures” of project No. АР09259637 “Development of a highly efficient wastefree technologies for the utilization of ash from coal combustion with the production of marketable products.

Theoretical study on the organic acid promoted dissolution mechanism of forsterite mineral

Olivine-type minerals are the most probable minerals for vast carbon dioxide sequestration since their abundant and wide distribution around the world. Nevertheless, mineral dissolution rate is the key factor restricting its carbon dioxide sequestration process. In this study, first principles calculation combined with the scanning electron microscope (SEM) were used to investigate different types of organic acids that promoted mineral dissolution mechanism of Mg2SiO4, including the adsorption configuration, adsorption energy, and electronic properties. Thermodynamics calculations on the complexation paths between organic acid molecules and the Mg(OH)2 or Si(OH)4 groups are studied. Results show that cations on the olivine surface prefer bonding with carbonyl O of the carboxyl group after the organic acid molecule was adsorbed onto the surface with charge transferred and orbital hybridization. The H - O bond in the carboxyl group will be broken up, resulting in the mineral surface hydroxylation. A greater number of carboxyl groups will be better for the mineral dissolution with more etch pits appearing. Multiple types of complexes formed by ionized organic acid molecules and Mg2+ coexist with different reaction paths and Gibbs free energy from thermodynamics calculations. The strong interaction between the dissolved cations and carbonyl O of the carboxylate radical was the first time to predicted, which could be useful to find reasonable additives to improve the mineral dissolution kinetics.

Guaiacol oxidation: theoretical insight into thermochemistry of radical processes involving methoxy group demethylation

Guaiacol (2-methoxyphenol) is naturally occurring phenolic compound essential in various research areas. Oxidative transformation of guaiacol can lead to the formation of various products, including 1,3-benzodioxole or ortho-quinone. Therefore, this study is focused on the investigation of the reaction enthalpies of experimentally observed guaiacol oxidation pathways in gas-phase, as well as in non-polar environment and aqueous solution. Corresponding Density Functional Theory (DFT) calculations were carried out using two hybrid functionals (M06-2X and B3LYP-D3). All reaction enthalpies, as well as Gibbs free energies, were also calculated using composite ab-initio G4 method. M06-2X and G4 results show mutual agreement and the best accordance with available experimentally determined reaction enthalpies. Obtained Gibbs free reaction energies indicate that formation of ortho-quinone is thermodynamically preferred to formation of 1,3-benzodioxole at 298 K in studied environments. Moreover, all computational methods confirm that the reaction enthalpy of methoxy group demethylation, i.e., O–C bond dissociation enthalpy (BDE), is substantially lower in comparison to the enthalpy of hydrogen atom transfer from phenolic OH group. In the case of phenoxide anion of guaiacol, which can be formed in ionization supporting solvents, O–C BDE shows further significant decrease, exceeding 50 kJ mol−1, in comparison to parent molecule.

An ultra-strength SiC ceramic joint with an in-situ formed high-entropy carbide interlayer via diffusion bonding by spark plasma sintering

A novel Ta0.5HfZrTi refractory high-entropy alloy instead of the traditional single refractory metal was chosen as an interlayer for diffusion bonding of silicon carbide (SiC) ceramics by spark plasma sintering. The microstructural evolution and mechanical properties of SiC joints processed at 1400–1700 °C for 5–20 min under a pressure of 30 MPa were investigated. The phase constitutes in the reaction layer varied with the joining conditions and mainly consisted of (TaHfZrTi)C, (TaHfZrTi)xSiyCz, and (TaHfZrTi)xSiy. The initial reaction phases exhibited metallic element segregation owing to the different Gibbs free energies of the interfacial reactions. The crystalline structure of the diffusion-formed (TaHfZrTi)C was identified as face-centered cubic sphalerite. A near-full (TaHfZrTi)C reaction layer was successfully achieved at 1700 °C for 20 min due to the fast formation of a relatively dense (TaHfZrTi)C layer and the decomposition of (TaHfZrTi)xSiyCz at elevated temperatures. The maximum joint hardness and shear strength at the same conditions were significantly improved to 2552.1 ± 357.1 HV and 326.2 ± 9.9 MPa, respectively.

Selective sulfidation-vacuum volatilization processes for tellurium and bismuth recovery from bismuth telluride waste thermoelectric material

Bismuth telluride-based alloy materials are currently the best performing thermoelectric materials at near room temperature; however, their production and use generate waste (e.g., cutting waste and failed grains). There is also lack of efficient recycling strategies for the generated waste. In this study, a selective sulfidation-vacuum volatilization method is proposed for recovering bismuth telluride waste. The Gibbs free energies of the sulfidation reaction of bismuth telluride are calculated, the saturated vapor pressure of each substance is analyzed, and the composition of the products is predicted. Based on the differences among the sulfidation and volatile properties of bismuth and tellurium, by adding sulfur to bismuth telluride waste, the composition of the substances was regulated, and efficient separation of tellurium and bismuth was achieved. We combined theoretical calculations and experimental studies to investigate the effect of process conditions on the separation and recovery of tellurium and bismuth. The results show that bismuth was thoroughly sulfereted and tellurium was a pure metal when the mass ratio of sulfur to bismuth telluride was 0.168, the sulfidation temperature was 573 K, and the holding time was 60 min. After sulfidation of the bismuth telluride waste, the sulfides were telluride and bismuthous sulfide. The sulfides, that resulted from sulfureted bismuth telluride production, were treated via vacuum volatilization. The optimal vacuum volatilization condition was 873 K for 120 min. The purities of tellurium and bismuth sulfide obtained by the selective sulfidation-vacuum volatilization experiment were >99%. The distribution ratios of tellurium and bismuth were 98.46% and 99.59%, respectively. The method thoroughly separated tellurium and bismuth from bismuth telluride waste, considerably reducing the environmental and economic costs compared with those of the conventional processes.

Base-catalyzed hydrolysis of spectinomycin in aqueous solutions: Kinetics and mechanisms

Hydrolysis plays an imperative role in the abiotic transformation process of antibiotics in aqueous solutions. However, little information is available on the hydrolysis process of spectinomycin (an aminocyclitol antibiotic). This study systematically investigated the spectinomycin hydrolysis kinetics and mechanisms under different pH via experiments and density functional theory (DFT) computation. Hydrolysis was first conducted in a pure water system under pH of 4.0–9.0 and temperature of 25 °C, 50 °C and 70 °C, respectively. Results showed that hydrolysis was highly dependent on pH and temperature. When pH > 6.0, spectinomycin hydrolysis was accelerated by the catalysis of OH−. Meanwhile, the hydrolysis rate increased with the elevation of temperature. Then, for the reference of the practical environment, the general base-catalyzed hydrolysis and mechanisms were studied under environmental pH 6.0–8.0 and 25 °C. DFT calculation demonstrated that base-catalyzed hydrolysis of spectinomycin could be more thermodynamically and kinetically favorable based on the lower Gibbs free energies of reaction and Gibbs free energies of activation. Further, instead of specific base catalysis (OH−), the general base catalysis (e.g., phosphate buffer) was also found to promote hydrolysis efficiency. The antibacterial activity and ecotoxicities of the hydrolysis product were analyzed to be lower than the precursor, thereby decreasing the environmental impact of spectinomycin.

Preparation of corn stover hydrothermal carbon sphere-CdS/g-C3N4 composite and evaluation of its performance in the photocatalytic co-reduction of CO2 and decomposition of water for hydrogen production

In this paper, a composite photocatalyst based on g-C3N4/CdS/corn straw hydrothermal carbon spheres was prepared by one-pot thermal synthesis method and applied for photocatalytic reduction of CO2 and hydrogen production. The morphology and structure of CdS/g-C3N4/ corn straw hydrothermal carbon spheres were characterized, which confirmed that the corn straw hydrothermal carbon spheres were successfully loaded into the heterojunction of g-C3N4 and CdS nanosheets. Through the study of photoelectric characteristics and DFT simulation, it was found that the energy band of g-C3N4/CdS/corn straw hydrothermal carbon spheres composite is reduced by 2.04 eV compared with that of pure g-C3N4 and CdS, and the photogenerated carrier transfer rate is accelerated. The Z-scheme heterostructure between g-C3N4 and CdS and the graphitized hydrothermal carbon spheres increase the surface active sites of the composite, leading to the generation of synergistic photocatalytic reaction. The photocatalytic experiment showed that g-C3N4/CdS/corn straw hydrothermal carbon spheres composite exhibited synergistic photocatalytic performance, while pure g-C3N4 and CdS did not. When the mass ratio of g-C3N4/CdS/corn straw hydrothermal carbon spheres was 1:0.1:0.5, the synergistic reaction efficiency was the highest, and the H2 yield was 250 μ mol·h−1·g−1, CO yield was 100 μ mol·h−1·g−1, and CH4 yield was 25 μ mol·h−1·g−1. By calculating the Gibbs free energy of the photocatalytic reaction and determining the possible mechanism of the synergistic reaction of g-C3N4/CdS/corn straw hydrothermal carbon spheres, it was inferred that the key step in the reaction was generation of CO.

Effects of operating temperature on photoelectrochemical performance of CuWO4 film photoanode

Photoelectrochemical (PEC) water splitting is a kind of strategy to produce hydrogen by using renewable energy. Copper tungstate (CuWO4) with a suitable bandgap (∼2.3 eV) is a potential candidate, but its poor charge transfer ability limits the real performance. According to the fact that the real reaction temperature is different from the normal temperature (298 K) in the laboratory, the testing temperature was considered as a potential influence factor for the PEC performance of photoelectrodes. In this study, the effects of temperature on the PEC properties of CuWO4 photoanode were discussed from the viewpoint of charge transfer in the photoanode, specific conductance and pH of the electrolyte, and the reaction Gibbs free energy. An increasing photocurrent is achieved by increasing the testing temperature, which is from 0.11 mA/cm2 (1.23 V vs RHE) at 5 ℃ to 0.31 mA/cm2 at 70 ℃. A similar increasing trend was seen between the carrier concentration and photocurrent, indicating the main influence factors are considered as improved carrier concentration and accelerated charge transfer ability of semiconductors. At higher temperatures, the risk of collisions of electrons and holes increases, although this negative effect is smaller than the positive effect brought on by greater carrier densities, as indicated by the smaller rise in current density compared to that of carrier density at 60/70/80/90 °C. This research suggests that a real-world factor favoring PEC water splitting is an increase in temperature.

Electrostatic Potential-Induced Co-N4 Active Centers in a 2D Conductive Metal-Organic Framework for High-Performance Lithium-Sulfur Batteries.

The use of single-atom catalysts is a promising approach to solve the issues of polysulfide shuttle and sluggish conversion chemistry in lithium-sulfur (Li-S) batteries. However, a single-atom catalyst usually contains a low content of active centers because more metal ions lead to generation of aggregation or the formation of nonatomic catalysts. Herein, a 2D conductive metal-organic framework [Co3(HITP)2] with abundant and periodic Co-N4 centers was decorated on carbon fiber paper as a functional interlayer for advanced Li-S batteries. The Co3(HITP)2-decorated interlayer exhibits a chemical anchoring effect and facilitates conversion kinetics, thus effectively restraining the polysulfide shuttle effect. Density functional theory calculations demonstrate that the Co-N4 centers in Co3(HITP)2 feature more intense electron density and more negative electrostatic potential distribution than those in the carbon matrix as the single-atom catalyst, thereby promoting the electrochemical performance due to the lower reaction Gibbs free energies and decomposition energy barriers. As a result, the optimized batteries deliver a high rate capacity of over 400 mA h g-1 at 4 C current and a satisfying capacity decay rate of 0.028% per cycle over 1000 cycles at 1 C. The designed Co3(HITP)2-decorated interlayer was used to prepare one of the most advanced Li-S batteries with excellent performance (reversible capacity of 762 mA h g-1 and 79.6% capacity retention over 500 cycles) under high-temperature conditions, implying its great potential for practical applications.

Insight into the weak interaction between organic primary amine and propionic acid or phenol solvents in solvent extraction

The essence of solvent extraction is to change the interaction degree between extracted molecules and solvents in the system. The study of solvent extraction at the molecular level has important guiding significance for further design. Here, taking the extraction of organic weak acid (phenol/propionic acid) by primary amines N1923 through hydrogen bond association as an example, the quantitative calculation parameters of reactive molecules were discussed, such as the charge distribution, potential distribution, average local ionization energy (ALIE) distribution and abbreviated Fukui function, while the polar index and polar area percentage were calculated. Moreover, the region and intensity of weak interaction were analyzed and visualized by electronic density difference and Van der Waals (VDW) radius. At the same time, the electron density of the critical point of bond (BCP) and the corresponding predicted value of hydrogen bonding energy are calculated. Finally, the solubility energy of primary amines and the Gibbs free energy of extraction reaction were calculated, and the results show that the interaction between organic amine and propionic acid is stronger by the hydrogen bond mechanism. This study provides a set of systematic cases to analyze the interaction between extraction molecules. It provides a new perspective for understanding the essence of solvent extraction, thus promoting the theoretical development of separation science.

Separation and recovery of tin and copper from tin refining sulfur slag using a new process of airtight sulfuration – Vacuum distillation

Sulfur slag is a high-value hazardous waste produced during the refining process of crude tin. To reduce the emission of wastewater, harmful gas, and hazardous residue, a theoretical and experimental investigation was carried out to develop a new process for converting metal to metal sulfide that utilizes physical differences (saturated vapor pressure) for separation. Here, a sulfur slag processing approach based on airtight sulfuration-vacuum distillation is proposed. In this paper, the Gibbs free energies of the sulfuration reaction of tin and cuprous sulfide and the decomposition reaction of copper sulfide are calculated, the saturated vapor pressure of each substance is analyzed, and the composition of the products is predicted. By adding sulfur to sulfur slag, the composition of the substances in the slag was regulated, and efficient separation of tin and copper was achieved based on the difference in volatility of the compounds. The optimum sulfur addition amount, sulfuration temperature and time, and volatilization temperature and time were investigated using airtight sulfuration and vacuum distillation experiments. The results show that tin and cuprous sulfide were thoroughly sulfurated when 20 g sulfur was added, the airtight sulfuration temperature was 573 K, and the holding time was 4 h. Stannous sulfide volatilizes violently above 941 K and volatilizes completely at 1273 K. The purities of stannous sulfide and cuprous sulfide obtained by the airtight sulfuration-vacuum distillation experiment were 99.02% and 99.30%, respectively. The direct recovery rates of tin and copper were 99.93% and 99.91%, respectively. The removal rate of copper in the volatiles was 99.84%, and the removal rate of tin in the residue was 99.96%. The method thoroughly separated tin and copper from sulfur slag, significantly reducing the environmental and economic costs compared to those of the traditional process.

Stability of Carbocyclic Phosphinyl Radicals: Effect of Ring Size, Delocalization, and Sterics.

In this computational study, we report on the stability of cyclic phosphinyl radicals with an aim for a systematical assessment of stabilization effects. The radical stabilization energies (RSEs) were calculated using isodesmic reactions for a large number of carbocyclic radicals possessing different ring sizes and grades of unsaturation. In general, the RSE values range from −1.2 to −14.0 kcal·mol–1, and they show practically no correlation with the spin populations at the P-centers. The RSE values correlate with the reaction Gibbs free energies calculated for the dimerization of the studied simple radicals. Therefore, the more easily accessible RSE values offer a cost-effective estimation of global stability in a straightforward manner. To explore the effect of unsaturation on the RSE values, delocalization energies were determined using appropriate isodesmic reactions. Introducing unsaturations beside the P-center into the backbone of the rings leads to an additive increase in the magnitude of the delocalization energy (∼10, 20, and 30 kcal·mol–1, respectively, for radicals with one, two, and three C=C bonds in the conjugation). Parallelly, the spin populations at the P-centers also dwindle gradually by ∼0.1 e in the same order, indicating that the lone electron delocalizes over the π-system. Radicals containing exocyclic C=C π-bonds were also investigated, and all of these radicals have rather similar stabilities independently of the ring size, outlining the primary importance of the two exocyclic π-bonds in the conjugation. Among the radicals involved in our study, those with the best electronic stabilization are the unsaturated three-, five-, six-, and seven-membered rings containing the maximum number of conjugated vinyl fragments. The largest delocalization energy of 31.5 kcal·mol–1 and the lowest obtained spin population of 0.665 e were found for the fully unsaturated seven-membered radical (phosphepin derivative). Importantly, the electronic stabilization effects alone are insufficient for stabilizing the radicals in monomeric forms epitomized by the exothermic dimerization energies (−40 to −58 kcal·mol–1). Therefore, it is essential to apply sterically demanding bulky substituents on the α-C-atoms. Tweaking the steric congestion enabled us to propose radicals that are expected to be stable against dimerization and, consequently, may be realistic target species for synthetic investigations. The effects contributing to the stability of radicals having sterically encumbered substituents have also been explored.

Network Thermodynamics-Based Scalable Compartmental Model for Multi-Strain Epidemics

SARS-CoV-2 continues to upend human life by posing novel threats related to disease spread and mutations. Current models for the disease burden of SARS-CoV-2 consider the aggregate nature of the virus without differentiating between the potency of its multiple strains. Hence, there is a need to create a fundamental modeling framework for multi-strain viruses that considers the competing viral pathogenic pathways. Alongside the consideration that other viral pathogens may coexist, there is also a need for a generalizable modeling framework to account for multiple epidemics (i.e., multi-demics) scenarios, such as influenza and COVID-19 occurring simultaneously. We present a fundamental network thermodynamics approach for assessing, determining, and predicting viral outbreak severity, which extends well-known standard epidemiological models. In particular, we use historical data from New York City’s 2011–2019 influenza seasons and SARS-CoV-2 spread to identify the model parameters. In our model-based analysis, we employ a standard susceptible–infected–recovered (SIR) model with pertinent generalizations to account for multi-strain and multi-demics scenarios. We show that the reaction affinities underpinning the formation processes of our model can be used to categorize the severity of infectious or deceased populations. The spontaneity of occurrence captured by the change in Gibbs free energy of reaction (∆G) in the system suggests the stability of forward occurring population transfers. The magnitude of ∆G is used to examine past influenza outbreaks and infer epidemiological factors, such as mortality and case burden. This method can be extrapolated for wide-ranging utility in computational epidemiology. The risk of overlapping multi-demics seasons between influenza and SARS-CoV-2 will persist as a significant threat in forthcoming years. Further, the possibility of mutating strains requires novel ways of analyzing the network of competing infection pathways. The approach outlined in this study allows for the identification of new stable strains and the potential increase in disease burden from a complex systems perspective, thereby allowing for a potential response to the significant question: are the effects of a multi-demic greater than the sum of its individual viral epidemics?

DFT+U study and in-situ TEM investigation of high-entropy titanate pyrochlore (Lu0.25Y0.25Eu0.25Gd0.25)2Ti2O7

High-entropy pyrochlore has become a promising immobilization matrix due to its ability to immobilize multiple nuclides especially for high-level radioactive waste. This work adopts first principle method to analyze the formation possibility of (Lu0.25Y0.25Eu0.25Gd0.25)2Ti2O7 (HTP-1). By calculating the Gibbs free energy of possible chemical reactions, we predict that the driving force to synthesize HTP-1 is greater than the driving force to form single-component pyrochlore at temperatures above 1225 K. The characterization results show that the HTP-1 sample is successfully prepared by the solid-state reaction at the predicted temperature. To investigate the radiation resistance of HTP-1, the sample is irradiated by 800 keV Kr2+ ions, and the microstructure evolution is characterized by in-situ TEM. HTP-1 sample achieves complete amorphous at 0.26 dpa, indicating that its radiation resistance is between Eu2Ti2O7 and Y2Ti2O7, which is proved by the calculation results of xO48f and antisite defect formation energy.

A promising new class of high-entropy ceramics: High-entropy oxycarbides with good oxidation resistance

(Hf0.25Zr0.25Nb0.25Ti0.25)(C0.5O0.5) high-entropy oxycarbides (HECO-1) with good oxidation resistance, as a promising new class of high-entropy ceramics, were synthesized by a facile carbothermic reduction method for the first time. The results showed that the as-synthesized HECO-1 samples had the single-phase rock-salt structure and high compositional uniformity. Compared to the as-synthesized (Hf0.25Zr0.25Nb0.25Ti0.25)C high-entropy carbides, the as-synthesized HECO-1 samples possessed the higher initial oxidation temperature and slower oxidation rate to show the better oxidation resistance, making them the promising applications in extreme environments, which was attributed to their higher oxidation activation energy and Gibbs free energy of oxidation reaction.

Prediction of surface termination preference of out-of-plane ordered double-transition metal MXenes (o-MXenes) from first-principles calculations

Surface terminations greatly affect the MXene performance. On the basis of the first-principles thermodynamic calculations, the surface termination preference of 33 different out-of-plane ordered double-transition metal MXenes when prepared by etching the o-MAX phases with HF acid is revealed. By calculating the reaction enthalpy and reaction Gibbs free energy at finite temperature, it is concluded that when the outermost transition metal is a 3d-orbital transition metal, the surface termination is dominated by -F, and when the outermost transition metal belongs to 4d or 5d-orbital transition metal, the surface termination is mainly -O. And this preference law may be related to whether the outermost transition metal can donate enough electrons to surface groups.

THERMODYNAMIC ANALYSIS OF THE CHEMICAL RESISTANCE OF CERAMIC MATERIALS IN THE RO- Al2O3-SiO2 SYSTEM

Operational characteristics, properties of modern aircraft and aerospace devices and their technical characteristics owe a lot to the radio engineering systems that are installed on them. Therefore, their protection and the selection of the necessary ceramic material, which will ensure the protection of electronic devices from interaction with the external environment, is an important task of modern materials science.
 In order to substantiate the choice of a crystalline phase as the basis of a radio-transparent ceramic material that will be used in aggressive environments, it is advisable to conduct thermodynamic calculations, namely changes in the Gibbs free energy of chemical reactions of the interaction of the crystalline phase with an aggressive environment. To carry out thermodynamic calculations of chemical stability reactions, the three-component system RO- Al2O3-SiO2 (RО – SrО, BaО) was chosen and the crystalline phases that can exist within them were determined. When choosing experimental crystalline phases, a complex of physico-chemical and operational requirements for radio-transparent materials was taken into account. From the point of view of thermodynamics, the corrosion behavior of the selected crystalline phases: celsian BaO·Al2O3·2SiO2, slavsonite SrO·Al2O3·SiO2, SrO·SiO2, and 2SrO·SiO2 is considered.
 The paper presents the results of thermodynamic calculations of changes in enthalpy, entropy, and Gibbs free energy of reactions to determine acid resistance (HСl, H2SO4, HNO3) and alkali resistance (NaОН, Na2CO3) of these compounds under standard conditions. It was established that all considered compounds have a thermodynamic probability of corrosion resistance to the action of alkaline reagents. In relation to an acidic environment, under normal conditions, celsian and slavsonite show acid resistance to hydrochloric acid, and they are least prone to interaction with sulfuric acid, but are able to actively interact with HNO3. Regarding the investigated binary compounds SrO·SiO2 and 2SrO·SiO2, all calculated reactions are thermodynamically favorable, i.e. interaction with acidic reagents occurs.
 The obtained results are analyzed and the correlation of the calculations of the reaction of celsian and hydrochloric acid with experimental data is given. It was concluded that it is rational to plan the production of ceramic products based on celsian and slavsonite or their heterophase mixture with a minimum content of binary oxides of strontium and barium.

Desulfurization of Cu-Fe Alloy Obtained from Copper Slag and the Effect on Form of Copper in Alloy.

In order to realize the high-value utilization of copper slag, a process for preparing Cu–Fe alloy through the reduction of copper slag is proposed. The sulfur in the alloy exists in the form of matte inclusions, which is different from sulfur in molten iron. The reaction of CaO with Cu2S is difficult. It is necessary to add a reducing agent to promote desulfurization. To avoid the introduction of other elements, Fe–Mn and CaC2 additions were used as desulfurizers for the desulfurization of Cu–Fe alloy. The thermodynamics of the desulfurization reaction were calculated and the experimental process was studied. It was found that the Gibbs free energy of desulfurization reactions was negative for Fe–Mn and that CaC2 can reduce the sulfur in the alloy to 0.0013% and 0.0079%, respectively. The desulfurization process affected the shape of copper in the alloy. Part of copper in this alloy exists in the form of nano-copper spheres, and the size of the spheres is found to increase after desulfurization. Reducing agents can facilitate the desulfurization process of stable sulfides.