Arrhenius Equation Research Articles

Cu0-Functionalized, ZIF-8-Derived, Nitrogen-Doped Carbon Composites for Efficient Iodine Elimination in Solution

The development of copper-based materials with a high efficiency and low cost is desirable for use in iodine (I2) remediation. Herein, Cu0-nanoparticles-functionalized, ZIF-8 (Zeolite Imidazole Framework-8)-derived, nitrogen-doped carbon composites (Cu@Zn-NC) were synthesized by ball milling and pyrolysis processes. The as-prepared composites were characterized using SEM, BET, XRD, XPS, and FT-IR analyses. The results showed that the morphology of ZIF-8 changed from a leaf-like structure into an irregular structure after the introduction of a copper salt and carbonization. The copper in the pyrolysis samples was mainly in the form of Cu0 particles. The presence of an appropriate amount of Cu0 particles could increase the specific surface area of Cu@Zn-NC. The subsequent batch adsorption results demonstrated that the as-fabricated composites showed high I2 adsorption amounts (1204.9 mg/g) and relatively fast dynamics in an iodine–cyclohexane solution when the Cu content was 30% and the pyrolysis temperature was 600 °C, outperforming the other Cu-based materials. The isothermal adsorption followed both Langmuir and Dubinin–Radushkevich isotherm models, while the kinetics of I2 adsorption followed a pseudo-second-order kinetic model. The activation energy (Eα) of the adsorbent was determined to be 47.2 kJ/mol, according to the Arrhenius equation. According to the experimental and DFT analyses, I2-Zn interactions and I2-Cu0 chemisorption jointly promoted the elimination of iodine. In general, this study provided an operative adsorbent for the highly effective capture of iodine in solution, which might be worth applying on a large scale.

Influence of ultrasonication during soaking on water absorption and Softness characteristics in the cooking process of cowpea.

Owing to the long duration of cooking legumes, which limits their consumption and utilization, soaking has been used to reduce cooking time, save energy consumption, and diminish their hardness. However, limited studies have reported the influence of cooking and soaking treatment along with ultrasonication on hydration, hardness, and cooking time reduction of legumes. Therefore, this study investigated the impact of cooking and soaking treatments on Dr. Saunder cowpea's water absorption, hardness, and cooking time reduction with and without ultrasonication. Samples of Dr. Saunder's cowpea were first soaked at 30°C and 50°C for 15 - 90min (with and without ultrasonication), after which they were cooked at 100°C and 121°C for 15 - 120min. The absorbed water and hardness of the tested samples under these treatments were measured. Hydration and softening behaviors were modeled from the obtained data using Ibarz-Augusto and first-order equations, respectively. Arrhenius equation was used to describe the kinetics of the hydration and softening process. Results showed that ultrasonic treatments accelerated water absorption and reduced the hardness of the samples; consequently, in a shorter time, using less energy will receive the desired hardness as the final product. The Ibartz-Augusto and first-order equations perfectively fit the sigmoidal and decaying exponential behavior of the absorbed water and hardness data with high prediction performance (R2 ≈ 1) marked by minimal error values. The deployment of ultrasonication and increased cooking temperature were observed to reduce the kinetic parameter (water absorption) and elevate the softening rates and activation energy (for hydration and softening). A synergy of the trio treatments reduced the total cooking duration from 120min to 90min (25%), thus promoting the benefit of deploying ultrasonication to soften cowpeas and other seeds rapidly.

Comprehensive Investigation of Ti-Doped Sr3CoSb2O9 Triple Perovskite: Structural, Morphological, Optical, and Dielectric Characteristics

We report a comprehensive investigation of the doped Ti4+ and the pristine Sr3CoSb2O9 triple perovskite material. By conducting a solid-state reaction in the air at room pressure, a stabilized single orthorhombic Immm (SG 71) phase is obtained. For series samples Sr3CoSb2−xTixO9 (x = 0.0, 0.1, 0.3, 0.5), using Rietveld refinements of powdered x-ray patterns, we reach to the conclusion that the Ti4+ doping at B-site has considerable impact on its structural parameters. The microstructure of the series samples was studied using FESEM and associated with EDS mapping for compositional analysis. The optical characteristics studied via optical absorbance measurements indicate that with an increasing doping concentration of Ti4+, the optical bandgap increases for 0.1 sample and then decreases up to 1.50 eV for 0.5 sample. As a result, they can be considered potential candidates for technological applications like photocatalytic systems and solar cells due to their suitable bandgap values and optical absorption-related applications. The FTIR analysis aimed to examine the bond forms and vibrational modes of the synthesized samples. Moreover, the space charge polarization mechanism explains a detailed analysis of temperature-dependent dielectric properties in the 1 KHz-2 MHz frequency range. The dielectric loss behavior is described by the thermally activated relaxation process tailored by the Arrhenius law and characterized by doping Ti4+ ions into the material’s structure. The existence of Co in Co2+ and Co3+ oxidation states, while Sb3+ state is stabilized with doping confirmed by X-ray photoelectron spectroscopy research. The current study thereby advances our knowledge of how these materials’ structural, morphological, optical, and dielectric characteristics are related.

Description of steady-state creep rate with continuously varying stress sensitivity parameter and upper limits of applied stress.

The steady-state creep rate increases with working temperature according to the Arrhenius law and with applied stress according to the power law. The dependence on both the variables is usually expressed as the product of the Arrhenius law and the power law, where a constant value of the apparent activation energy is assumed. As the exponent of the power law, called the stress sensitivity parameter and dependent on the deformation micromechanism, a specific integer is taken. A deeper study of empirical results shows that the apparent activation energy depends significantly on the applied stress and the deformation mechanism can change if the temperature varies over a wide range. Taking these two facts into account, a new equation for the dependence of the steady-state creep rate on the working temperature and on the applied stress was derived and verified using real creep measurement results. Moreover, the convexly bent curves representing the dependence of the creep rate on the applied stress in bilogarithmic plot do not need to be described using the questionable sinhx function, but it is sufficient to assume the existence of upper limits of the applied stress leading to immediate fracture.

Structural and dielectric properties of green synthesized SnO2 nanoparticles

Abstract The present research study provides an analysis of the structural and dielectric characteristics of SnO2 nanoparticles (SnO2-NPs) synthesized by the green synthesis approach. Powder x-ray diffraction (PXRD) investigation indicates the existence of a single tetragonal phase with the P42/mnm space group. The crystallite size and lattice strain of the tetragonal SnO2-NPs were determined through x-ray peak broadening analysis. The average crystallite size calculated by high-resolution transmission electron microscopy (HR-TEM) was 16 nm. Fourier transform infrared spectroscopy (FTIR) within the 530 to 644 cm−1 range confirms the vibration modes of Sn-O-Sn and Sn-O. The vibrational modes observed in the Raman spectra confirm the tetragonal rutile-type structure of the synthesized SnO2-NPs. The dielectric characteristics of SnO2-NPs were investigated within a temperature range of 353–433 K and a frequency range of 50 Hz –5 MHz. The total conductivity exhibits frequency dependence according to Jonscher’s power law ( σ t ω = σ dc + A ω s ) . The correlated barrier hopping (CBH) model is found to be the dominant conduction mechanism in the studied material. The direct current (DC) conductivity appears to be thermally activated, with an activation energy of 307 mev. The analysis of dielectric characteristics demonstrated that the real (ε′) and imaginary (ε″) parts of the dielectric constant drop with frequency and increase with temperature. The dielectric modulus indicates the presence of non-Debye relaxation within the material. The relaxation time, based on the analysis of the imaginary component of the modulus (M″), follows the Arrhenius equation. An equivalent-circuit model was used to analyze the impedance spectroscopy results, which indicated the existence of a temperature-dependent electrical relaxation phenomena of the non-Debye nature.

Mechanistic origins of temperature scaling in the early embryonic cell cycle.

Temperature profoundly impacts organismal physiology and ecological dynamics, particularly affecting ectothermic species and making them especially vulnerable to climate changes. Although complex physiological processes usually involve dozens of enzymes, empirically it is found that the rates of these processes often obey the Arrhenius equation, which was originally derived for single-enzyme-catalyzed reactions. Here we have examined the temperature scaling of the early embryonic cell cycle, with the goal of understanding why the Arrhenius equation approximately holds and why it breaks down at temperature extremes. Using experimental data from Xenopus laevis, Xenopus tropicalis, and Danio rerio, plus published data from Caenorhabditis elegans, Caenorhabditis briggsae, and Drosophila melanogaster, we find that the apparent activation energies for the early embryonic cell cycle for diverse ectotherms are all similar, , which corresponds to a value of . Using computational models, we find that the approximately Arrhenius scaling and the deviations from the Arrhenius relationship at high and low temperatures can be accounted for by biphasic temperature scaling in critical individual components of the cell cycle oscillator circuit, by imbalances in the values for different partially rate-determining enzymes, or by a combination of both. Experimental studies of cycling Xenopus extracts indicate that both of these mechanisms contribute to the general scaling of temperature, and in vitro studies of individual cell cycle regulators confirm that there is in fact a substantial imbalance in their values. These findings provide mechanistic insights into the dynamic interplay between temperature and complex biochemical processes, and into why biological systems fail at extreme temperatures.

Electrical performance of calcium ferrite in sintering by the assimilation melt breakover method

Abstract The quality of sintering ore and the efficiency of the blast furnace are both heavily dependent on the high-temperature performance and compatibility of iron ores. A novel characterization technique, the Assimilation Melt Breakover method, is proposed to test the electrical performance during assimilation in sintering. Utilizing the two-electrode method, the electrical resistance of mixtures of ferrite oxide and calcium oxide was measured during their assimilation. A rise in temperature is associated with a reduction in electrical resistance, adhering to the principles of Arrhenius Law. The changes in conductivity observed during the assimilation process accurately reflect the mineral phase transformations, encompassing alterations within the solid state and transitions from solid to melt. The transition is marked by a substantial reduction in electrical resistance, specifically from several thousand to a few dozen Ohms in melting assimilation, along with notable variations in the activation energy associated with conductance. This research has the potential to swiftly differentiate between the assimilation characteristics of different iron ores, as well as to assist in the utilization of an electric field in iron ore sintering.

Atomistic Transport Mechanisms in Lithium Salt‐Doped Ionic Covalent Organic Framework Electrolytes

Ionic covalent organic frameworks (iCOFs) have garnered significant attention as potential single‐ion conductive solid‐state electrolytes, where researchers have made great efforts in designing iCOF‐based composites, aiming to improve their intrinsic low conductivity. One successful case is to fill iCOF channels with lithium salts, such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). However, the ion transport mechanisms in these composite electrolytes are still largely unknown, hindering their further improvement. Here molecular dynamics simulations were employed to systematically predict the ion diffusivity in iCOF (e.g., TpPa‐SO3Li COF)‐LiTFSI composite electrolytes with varying LiTFSI compositions at different temperatures. A positive correlation was seen between Li+ diffusivity and LiTFSI:iCOF ratio, which was also verified by our experiments. Interestingly, the Li+ diffusion energy barrier obtained by the Arrhenius equation exhibited nearly no dependency on the LiTFSI concentration, indicating the importance of temperature insensitive microstructural related factors. Radial distribution functions show that with a higher LiTFSI proportion, the coordination number of SO3‐ decreases, while that of TFSI‐ increases, suggesting a competition between these two species in the Li+ solvation shell. Furthermore, configurational entropy and bond orientational order parameter calculations examined the degree of disorder in the Li+ solvation structure. These results should improve our mechanistic understandings of iCOF‐based electrolytes.

Metabolic rearrangement enables adaptation of microbial growth rate to temperature shifts.

Temperature is a key determinant of microbial behaviour and survival in the environment and within hosts. At intermediate temperatures, growth rate varies according to the Arrhenius law of thermodynamics, which describes the effect of temperature on the rate of a chemical reaction. However, the mechanistic basis for this behaviour remains unclear. Here we use single-cell microscopy to show that Escherichia coli exhibits a gradual response to temperature upshifts with a timescale of ~1.5 doublings at the higher temperature. The response was largely independent of initial or final temperature and nutrient source. Proteomic and genomic approaches demonstrated that adaptation to temperature is independent of transcriptional, translational or membrane fluidity changes. Instead, an autocatalytic enzyme network model incorporating temperature-sensitive Michaelis-Menten kinetics recapitulates all temperature-shift dynamics through metabolome rearrangement, resulting in a transient temperature memory. The model successfully predicts alterations in the temperature response across nutrient conditions, diverse E. coli strains from hosts with different body temperatures, soil-dwelling Bacillus subtilis and fission yeast. In sum, our model provides a mechanistic framework for Arrhenius-dependent growth.

Kinetics and energetics of biodiesel oxidation stability: The impact of Uapaca kirkiana‐derived natural antioxidants

AbstractDespite considerable progress in understanding biodiesel autoxidation inhibition, the kinetics and energetics of the inhibition reactions involving natural antioxidants remain underexplored. Most existing research on natural antioxidants has focused on enhancing oxidation stability and other fuel properties. This study aimed to investigate the oxidative stability of croton biodiesel (CBD) and assess the kinetics and energetics of natural antioxidants derived from the roots, pulp, and fruit peels of the Uapaca kirkiana plant. The oxidation stability of biodiesel samples was assessed using the OXITEST method at temperatures of 90, 100, 110, and 120 °C. These tests enabled the calculation of kinetic parameters such as reaction rates and activation energies, crucial for understanding the inhibition role of antioxidants during oxidative degradation. Activation energy for antioxidant consumption, determined using the Arrhenius equation, was found to be 81.39 kJ mol−1 for fruit peel extracts, 77.73 kJ mol−1 for pulp extracts, and 63.85 kJ mol−1 for root bark extracts. The higher activation energy for fruit peel extracts suggests that they are more effective at preventing oxidation, especially under high‐temperature conditions. Enthalpy, entropy, and Gibbs free energy parameters were calculated using the Eyring equation, indicating a nonspontaneous endothermic process for the antioxidant samples. The study found an inverse relationship between antioxidant concentration and rate constants, demonstrating the antioxidants' effectiveness in slowing down the oxidation process. These kinetics and energetics analyses provide detailed insights into how antioxidants function, facilitating the optimization, selection, and validation of their efficiency in stabilizing biodiesel.

Peroxydisulfate Persistence in ISCO for Groundwater Remediation: Temperature Dependence, Batch/Column Comparison, and Sulfate Fate

The persistence of peroxydisulfate anion (S2O82−) in soil is a key factor influencing the effectiveness of in situ chemical oxidation (ISCO) treatments, which use S2O82− (S2O82− based ISCO) to remediate contaminated groundwater. However, only a few studies have addressed aspects of S2O82− persistence, such as the effect of temperature and the fate of sulfates (SO42−) generated by S2O82− decomposition in real soil and/or aquifer materials. Additionally, there are no studies comparing batch and dynamic column tests. To address these knowledge gaps, we conducted batch tests with varying temperatures (30–50 °C) and initial S2O82− concentrations (2.7 g/L and 16.1 g/L) along with dynamic column experiments (40 °C, 16.1 g/L) with comprehensively characterized real soil/aquifer materials. Furthermore, the principal component analysis (PCA) method was employed to investigate correlations between S2O82− decomposition and soil material parameters. We found that S2O82− decomposition followed the pseudo-first-order rate law in all experiments. In all tested soil materials, thermal dependence of S2O82− decomposition followed the Arrhenius law with the activation energies in the interval 65.2–109.1 kJ/mol. Decreasing S2O82− concentration from 16.1 g/L to 2.7 g/L led to a several-fold increase (factor 2–11) in bulk S2O82− decomposition rate coefficients (k′) in individual soil/aquifer materials. Although k′ in the dynamic column tests showed higher values compared to the batch tests (factor 1–3), the normalized S2O82− decomposition rate coefficients to the total BET surface were much lower, indicating the inevitable formation of preferential pathways in the columns. Furthermore, mass balance analysis of S2O82− decomposition and SO42− generation suggests the ability of some systems to partially accumulate the produced SO42−. Principal Component Analysis (PCA) identified total organic carbon (TOC), Ni, Mo, Co, and Mn as key factors influencing the decomposition rate under varying soil conditions. These findings provide valuable insights into how S2O82− behaves in real soil and aquifer materials, which can improve the design and operation of ISCO treatability studies for groundwater remediation.

Effect of biochar content and particle size on mechanical and water absorption properties of landscaping waste/polylactic acid composites

The high-value utilization of landscaping waste to produce wood-plastic composites provides a promising approach to waste management, yet remains a challenge. In this study, wood-plastic composites were prepared using landscaping waste and polylactic acid (PLA) through an extrusion-molding process, with biochar (BC) as the reinforcing material. First, the effects of biochar content (0.5 %, 1 %, 2 %, 3 %, 4 %) and particle size (100mesh, 300mesh, 800mesh, 1200 mesh) on the physico-mechanical and dynamic thermo mechanical properties of the composites were analyzed. A multivariate nonlinear model was employed to fit the flexural properties of the composites. Additionally, the water absorption properties were investigated under immersion conditions at three different temperatures (20°C, 35°C, 50°C). The results demonstrated that biochar significantly improved the interfacial compatibility between landscaping waste and PLA, enhancing the mechanical properties of this composite. When the biochar content was 1 % and particle size was 100 mesh, flexural strength reached 25.16 MPa, respectively, representing increases of 19.20 % over composites without biochar, while the change in impact strength was small. In addition, the water absorption process of composites with 1 % BC were well fitted by Fick's law. SEM morphology observation indicated that interfacial bonding was reduced after water absorption, which was consistent with the test results. Combined with Arrhenius equation and Fick's law, the water absorption model of the composites at each water immersion temperature was obtained, which can predict the water absorption behavior at 60°C.

Synthesis and ionic conductivity of Na1+2xMxZr2-x(PO4)3 (M – Mg, Mn) NASICON-type ceramic materials

Ceramics of the Na1+2xMxZr2-x(PO4)3 (M – Mg, Mn) composition were synthesized by the co-precipitation technique with subsequent annealing. The samples were characterized using X-ray diffraction with the Rietveld refinement, scanning electron microscopy, and impedance spectroscopy. The studied phosphates belong to the NASICON type structure. The solid solutions (0 ≤ x ≤ 1.0) were shown to be formed in the investigated systems. To study the effect of the chemical composition and sintering additive on conductivity, two series of ceramics were prepared for each phosphate: with and without ZnO (2 wt.%) additive. The ionic conductivity of the studied phosphates followed the Arrhenius law and passed through a maximum with x growth. It was shown that the addition of zinc oxide also leads to partial substitution of zirconium in the lattice and an increase in ionic conductivity. The highest conductivity was achieved for the Na2.6Mg0.8Zr1.2(PO4)3 ceramic with 2 wt.% ZnO additive (6.8∙10-3 S∙cm-1 at 673 К).

The Preservation of HBV, HCV, HIV Viral Nucleic Acids in Plasma by Dry Spot Method and the Duration of Preservation

To establish a method for preserving viral nucleic acids in plasma using a blood collection card based on the dry spot method, to predict the duration of nucleic acid preservation by establishing the Arrhenius equation, and to demonstrate the feasibility of this preservation method for the re-testing of nucleic acids in blood samples retained by blood banks. Plasma samples positive for HBV, HCV, and HIV nucleic acids were prepared into preservation cards in the form of dry plasma spots for storage. The prepared preservation cards were placed under accelerated storage conditions at 37, 45, 50, and 55 ℃. The preservation cards were periodically retrieved from each temperature condition for nucleic acid extraction, and the nucleic acid samples were purified for subsequent PCR testing, with the recorded CT values. An Arrhenius equation model was established between the expiration time and the storage temperature, thereby predicting the validity period of nucleic acid preservation in blood collection cards under specified storage temperature conditions. For the plasma samples positive for HBV, HCV, and HIV nucleic acids preserved using the dry spot method, the regression equations for the duration with temperature were as follows: y=-11546 x + 31.74 for HBV, y=-12949x + 36.88 for HCV, and y=-12204x + 34.48 for HIV, with the correlation coefficient r greater than 0.98 for all. It was predicted that at a storage temperature of 4 ℃, the preservation periods for HBV, HCV, and HIV viral nucleic acids using the dry spot method would be 20 792 days, 19 289 days, and 14 285 days, respectively. At a storage temperature of 20 ℃, the preservation periods would be 2 135 days 1 502 days, and 1 289 days, respectively. The nucleic acids of the three common viral pathogens in blood samples, when preserved using the dry spot method, conform to a first-order reaction pattern in the accelerated degradation experiment. The relationship between the rate of nucleic acid degradation and the absolute temperature of storage is consistent with the Arrhenius equation. Based on the calculations using this equation, the stability and validity period of plasma nucleic acid samples preserved using the dry spot method can reach a minimum of 3.5 years under storage conditions not exceeding 20 ℃, which essentially meets the requirements for the preservation period of blood samples retained by blood banks.

Enhanced luminescence and quenching mechanisms in Na⁺ Co-doped K₇CaY₂(B₅O₁₀)₃:Tb3+ phosphors under UV radiation.

This study investigates the structural and luminescent properties UV radiation of Tb³⁺-doped K₇CaY₂(B₅O₁₀)₃ (KCYBO) phosphors prepared using a microwave-assisted sol-gel method, with a focus on the impact of Na⁺ co-doping. Tb³⁺ ions were effectively integrated as evidenced by X-ray diffraction (XRD) and Rietveld analysis, without disrupting the crystal structure. Photoluminescence (PL) analysis showed intense green emissions at 542nm, which are due to the 5D₄ → 7F₅ transition in Tb³⁺. Optimal luminescence was observed at 3wt% Tb³⁺, beyond which concentration quenching effect was driven by non-radiative cross-relaxation between adjacent Tb³⁺ ions. Na⁺ co-doping enhanced PL intensity by improving energy transfer and reducing non-radiative losses. CIE chromaticity coordinates demonstrated a tunable color shift towards warmer tones with increasing Na⁺ concentration. Thermal stability was assessed through the Arrhenius equation, with an activation energy of 0.31eV, indicating the material's potential for high-temperature optoelectronic applications.

Kinetics of human insulin degradation in the solid-state: an investigation of the effects of temperature and humidity.

With the increasing development of oral peptide dosage forms, a comprehensive understanding of factors affecting peptide drug stability in the solid-state is critical. This study used human insulin, as a model peptide, to examine the individual and interactive effects of temperature and humidity on its solid-state stability. Insulin was stored at temperature (25°C, 40°C, and 6 °C) and humidity (1%, 33% and 75%) over 6 months. Primary degradation pathways were deamidation and covalent aggregation. Degradation product formation rates were determined empirically and modelled using the humidity-corrected Arrhenius equation. Temperature had a major impact on deamidation and covalent aggregation rates, with the reaction rates increasing with temperature. The effect of humidity was temperature dependent. Moisture induced degradation was minimal at 25°C and 40°C, but an important factor at 60°C. Dynamic vapour sorption analysed determined a clear differences in insulin moisture sorption characteristics at 60°C relative to 25°C and 40°C. The findings suggest that the effect of moisture on insulin deamidation and covalent aggregation rates was not a function of water content but the nature of the insulin moisture interaction.

Toughening mechanisms taking into account growth kinetics of SiC whiskers for bionic ceramic cutting tool materials

The growth mechanism and kinetic characteristics of SiC whiskers for novel bionic ceramic cutting tools were analyzed by modified Arrhenius equation, which reveals the regulation effect of SiC whisker growth on the microstructure evolution. Furthermore, the influence of the growth mechanism on the toughening mechanism under shear and indentation failure was investigated. The results showed that the formed transition area at the bonding interface can improve the residual thermal stress distribution. The synergistic effect of multiple macro/micro-toughening mechanisms and interfacial strengthening mechanisms enabled the bionic ceramic cutting tool materials to exhibit excellent fracture resistance under shear and indentation failure.

Kinetics and Mechanism of the Thermal Isomerization of Cyclopropane to Propene: A Comprehensive Theoretical Study.

The kinetics of the homogeneous gas-phase thermal isomerization of cyclopropane to propene has been studied theoretically to clarify existing discrepancies regarding the interpretation of its mechanism. High-level ab initio and density functional theory calculations were used to determine the branching ratios of the biradical and carbene reaction channels over wide temperature and pressure ranges. For this, relevant molecular and thermochemical properties of the proposed intermediates and related transition states were computed and compared with literature values. The Arrhenius equation, derived between 400 and 1400 K in the high-pressure limit at the CCSD(T)/6-311++G(3df,3pd)//CCSD/6-311++G(d,p) level of theory, is given by log10(koverall,∞/s-1) = (15.60 ± 0.06) - (65.70 ± 0.17) kcal mol-1 (2.303 RT)-1. This expression is in very good agreement with the available experimental data. According to these results, the biradical pathway is the predominant mechanism, while the carbene pathway contributes 1-2% at higher temperatures. The G4//B3LYP/6-311++G(3df,3pd) and G4//M06-L/6-311++G(3df,3pd) levels showed comparable Arrhenius parameters. Low-pressure limit rate coefficients and falloff curves were also estimated to evaluate the effect of pressure on the reaction. Additionally, the possibility of a concerted path is considered, but calculations showed unstable wave functions, suggesting that this mechanism would not be plausible.

Evaluating the Reaction Kinetics on the H2 Reduction of a Manganese Ore at Elevated Temperatures

This study investigates the hydrogen reduction of Nchwaning manganese ore at elevated temperatures to enhance understanding of reaction kinetics and optimize industrial applications. Experimental investigations were conducted across temperatures ranging from 600 °C to 900 °C to observe reduction behavior and identify rate determining steps. Thermogravimetric analysis (TGA) was employed to monitor manganese ore weight loss, facilitating precise measurement of reduction rates. Various kinetic models validated experimental outcomes for H2 reduction, revealing an apparent activation energy (Ea) of 65.76 kJ/mol and an apparent pre-exponential factor (k0) of 319.66 min⁻1. The rate constant (k) exhibited a significant temperature-dependent increase, following the Arrhenius equation where rates approximately doubled every 100 °C, rising from 0.037 min⁻1 at 600 °C to 0.377 min⁻1 at 900 °C. Morphological and compositional analyses using scanning electron microscopy (SEM) and X-ray diffraction (XRD) assessed structural changes post-reduction. Results demonstrated that pre-reduction temperature critically influences the physical and microstructural properties of the ore particles, particularly above 700 °C, where a notable reduction in BET (Brunauer–Emmett–Teller) surface area and pore volume indicated sintering within the ore. The rate determining step for this reduction process is most likely the chemical reaction at the gas–solid interface between hydrogen and the manganese ore. These findings highlight advancements in efficient manganese ore reduction processes, with significant implications for metallurgical practices and the hydrogen economy.Graphical

Kinetic and Thermodynamic Aspects of the Degradation of Ferritic Steels Immersed in Solar Salt.

The study and improvement of the corrosion resistance of materials used in concentrated solar power plants is a permanent field of research. This involves determining their chemical stability when in contact with heat transfer fluids, such as molten nitrate salts. Various studies indicate an improvement in the corrosion resistance of iron-based alloys with the incorporation of elements that show high reactivity and solubility in molten nitrate salts, such as Cr and Mo. This study analyzes the kinetic and thermodynamic aspects of the beginning of the corrosion process of ferritic steels immersed in Solar Salt at 400, 500, and 600 °C. The analysis of the kinetic data using the Arrhenius equation and the Transition State Theory shows that an increase in the Cr/Mo ratio reduces the activation energy, the standard formation enthalpy, and the standard formation entropy. This indicates that its incorporation favors the degradation of steel; however, the results show a reduction in the corrosion rate. This effect is possible due to a synergistic effect by the formation of insoluble Fe-oxide layers that favor the formation of a Cr oxide layer at the Fe-oxide-metal interface, which limits the subsequent oxidation of Fe.