Dissolution Mechanism Research Articles

Reductive Dissolution Mechanisms of Manganese Oxide Mediated by Algal Extracellular Organic Matter and the Effects on 17α-Ethinylestradiol Removal.

Reductive dissolution of manganese oxide (MnOx) is a major process that improves the availability of manganese in natural aquatic environments. The extracellular organic matter (EOM) secreted by algae omnipresent in eutrophic waters may affect MnOx dissolution thus the fate of organic micropollutants. This study investigates the mechanisms of MnOx reductive dissolution mediated by EOM and examines the effects of this process on 17α-ethinylestradiol degradation. The influences of EOM concentration (1.0-20.0 mgC/L) and pH (6.0-9.0) in both dark and irradiated conditions were assessed. In the dark, EOM was found to facilitate MnOx reductive dissolution via the ligand-to-metal charge transfer (LMCT). The dissolution was further enhanced under irradiation, with the participation of superoxide ions (O2•-). Higher EOM concentrations increased the contents of available reducing substances and O2•-, accelerating the reductive dissolution. Higher pH slowed the photoreductive dissolution rates, while O2•--mediated reduction became more important. Polyphenols and highly unsaturated carbon and phenolic formulas in EOM were found to drive the reductive dissolution. Soluble reactive Mn(III) formed through reductive dissolution of MnOx effectively removed 17α-ethinylestradiol in solution. Overall, the findings regarding the mechanisms behind reductive dissolution of MnOx have broad implications for Mn geochemical cycles and organic micropollutant fate.

PH Dependence of Noble Metals Dissolution: Iridium

Iridium's stability and catalytic properties make it indispensable in a wide range of electrochemical applications including water electrolysis, yet its dissolution behavior across varying pH conditions remains poorly understood. This study addresses this gap by employing online inductively coupled plasma mass spectrometry (ICP-MS) to monitor iridium dissolution across a pH range of 1 to 12.7 under both pre-OER and OER conditions. An electrochemical protocol consisting of potential scans and holds is designed to track how potential and time affect Ir dissolution. In the pre-OER region, iridium shows consistent qualitative dissolution behavior across pH levels, although the extent of anodic and cathodic dissolution depends on the electrolyte. To explain this dependence, the thermodynamics of Ir in aqueous media, as revealed by the Pourbaix diagram, electrochemical profiles representing oxidation / reduction processes, and adsorption of electrolyte species are considered. During potential scans, kinetic effects from native oxides and phosphate adsorption lead to the absence of anodic dissolution, while prolonged holds at higher pH result in increased anodic dissolution, likely due to IrO42− formation. Iridium's cathodic dissolution is observed in all studied protocols. It decreases from acidic to neutral pH, in line with the stability window of Ir3+ ionic species in the Pourbaix diagram, and surprisingly increases in highly alkaline conditions again, suggesting the existence of species not reflected on the diagram. In the OER region, iridium remains stable in acidic to neutral conditions, with stability decreasing under alkaline conditions. Two distinct dissolution mechanisms are proposed based on pH: in acidic environments, H2O primarily acts as the reactant, leading to Ir³⁺ formation, while above pH 9, OH− becomes the main reactant, contributing to IrO42− formation and reduced stability. Under neutral conditions, buffers play a key role in maintaining local pH and supporting consistent OER rates, especially when the buffer's pKa aligns with the solution's pH. These findings improve our understanding of iridium dissolution mechanisms and support the development of more stable and cost-effective iridium-based catalysts for various electrochemical technologies.

Behavior and mechanism of element dissolution from albite by mannose: experimental and theorical study.

In this work, the release behaviors of element from albite by mannose are studied experimentally, and the corresponding decomposition mechanism is explored from a microscopic perspective via density functional theory (DFT) calculations, with the aim of promoting the development of a microbial mineral weathering theory. The sodium, silicon and aluminium in albite are released into a solution under the action of mannose, and the release of these elements makes the surface of albite rough and decreases crystallinity and interplanar spacing of the crystal. The DFT results show that the hydroxyl H atom in mannose forms a hydrogen bond with the O atom on the surface of albite, thus causing the surface atoms to move away from their original positions, destroying the stability of the silica tetrahedron. The results of this study provide insights and deepens the understanding of microbial-mineral interactions at the microscopic level. The leaching behavior of the elements in albite was evaluated through an ion concentration in a solution. The microscopic mechanism between mannose and albite was calculated based on DFT, via the CASTEP module of Materials Studio software. The GGA-PBE method is used for all the DFT calculations. Analyses of the adsorption configuration and energy, charge density difference, and Mulliken population of the mannose-albite system were carried out.

Experimental study on solid–liquid equilibrium behavior of methimazole (Form Ⅰ) in twelve mono-solvents: Measurement, modeling, Hansen solubility parameters and thermodynamic analysis

Methimazole is an active pharmaceutical ingredient, which is commonly used as an imidazole antithyroid drug. Solubility research is one of the key steps affecting the crystal quality of methimazole, which can give essential fundamental data and theoretical guidance for its downstream industries, such as preparation form, storage, transportation and clinical application. Researchers have found that there are two crystal forms of methimazole, different crystal forms may result in differences in the efficacy, pharmacology, physicochemical properties, etc. Further supplementation and improvement are urgently needed regarding the solid–liquid equilibrium data, dissolution thermodynamic properties and dissolution mechanism of methimazole. In the present work, by using a gravimetric method, the solubility of methimazole (Form Ⅰ) in twelve selected mono-solvents including 2-propoxyethanol, isopropyl acetate, anisole, 2-ethoxyethanol, 1-hexanol, 1-pentanol, ethylene glycol, butyl acetate, 2-butoxyethanol, propyl acetate, 2-methoxyethanol and ethyl butyrate was investigated from 283.15 K to 323.15 K under pressure of 0.1 MPa. The regression result between solubility and temperature showed that they were positively correlated. At 298.15 K, the obtained mole fraction solubility of methimazole (Form Ⅰ) decreased as: 2-methoxyethanol (0.2203) > 2-ethoxyethanol (0.1766) > ethylene glycol (0.1432) > 2-propoxyethanol (0.1425) > 2-butoxyethanol (0.1268) > 1-pentanol (0.0394) > 1-hexanol (0.0349) > propyl acetate (0.0223) > butyl acetate (0.0195) > anisole (0.0176) > isopropyl acetate (0.0135) > ethyl butyrate (0.0120). The maximum solubility was found in 2-methoxyethanol at 323.15 K with the mole fraction solubility value of 0.2984, while the minimum obtained value was occurred in ethyl butyrate at 283.15 K with the mole fraction solubility of 0.00786. Besides, four thermodynamic nonlinear regression models including Yaws model, UNIQUAC model, Two-Suffix Margules model and NRTL-SAC model were used to correlate the experimental solubility of methimazole (Form Ⅰ). Furthermore, to further explore the dissolution mechanism of methimazole (Form Ⅰ) in the selected twelve target solvents, the HSPs, Hirshfeld surface analysis and dissolution thermodynamic properties were calculated and analyzed.The related research in this study is of great significance for understanding the solubility behavior and dissolution mechanism of methimazole Form I in the selective solvent system, which can provide foundation data for the optimization of its crystallization conditions. At the same time, this study is helpful to provide theoretical guidance for the research of other similar drugs.

Studies on the dissolution mechanism of barium sulfate by different alkaline metal hydroxides: Molecular simulations and experiments

Studies on the dissolution mechanism of barium sulfate by different alkaline metal hydroxides: Molecular simulations and experiments

Optimizing hydrogen storage in a heterogeneous aquifer considering hysteresis and dissolution

Hydrogen (H2) is a rising solution for carbon-neutral fuel transition. Saline aquifer, ubiquitous underground, is a competitive candidate for large-scale underground hydrogen storage (UHS). This study proposed to use a heterogeneous aquifer formation for probing the functioning of UHS and optimizing its operation. By integrating geological information with lithofacies from the Ordos Basin in China, a heterogeneous triplet aquifer model was built, upon which compositional simulations of UHS operations that consider two-phase flow, relative permeability hysteresis, hydrogen and water phase behavior, rock compressibility, and dissolution mechanisms were conducted. Orthogonal array L25 (56) with mixed levels was designed to optimize the H2 recovery. Results substantiate the feasibility of storing millions of cubic meters of H2 with over 95% recovery. Ignoring dissolution and relative permeability hysteresis will result in an overestimation of the hydrogen recovery factor, with the effect of relative permeability hysteresis being more significant. Provided equal cycle length, a lower injection-withdrawal rate is suitable for long-term operation of hydrogen storage, while a higher rate can achieve a higher recovery factor during the early cycles. Measures of lowering the skin factor and pre-extracting brine could improve storage capacity and reduce water production during injection and withdrawal. The optimized case is expected to achieve an average H2 recovery of 98.8% for 30 operation cycles with moderately low saline water production. These findings provide valuable insights for developing large-scale and cost-effective UHS in saline aquifers.

Influences on the anisotropy in through-mask electrochemical micromachining processes

This contribution studies through-mask electrochemical micromachining (TMEMM) of copper, namely the interplay between current density, electrolyte flow, mask opening width, etch depth, the presence of a wetting agent, and the resulting anisotropy in sodium nitrate electrolyte. Factors strengthening the anisotropy are: High electrolyte flow rate, low overall etch depth and large feature size (150 µm > 100 µm > 50 µm), absence of wetting agent, and moderate current densities (between 20 and 40 A cm−²). A model aiming to explain all the observed interdependencies is elaborated, based on the presence of a supersaturated surface film and a local change in dissolution mechanism in dependence on local current distribution and surface film thickness. The thickness of the surface film is greatly influenced by the flow velocity, which in turn depends on the geometry of the cavity and, therefore, opening width and etch depth. In the presence of a wetting agent the differences in surface film thickness are leveled out, which results in less anisotropic etching.

Fast Dissolution of Chitin in Amino Acids Based Deep Eutectic Solvents Under the Assistance of Microwave.

Due to the abundant hydrogen bond networks, high crystallinity, and high molecular weight of chitin, it is difficult to dissolve chitin in most solvents. Meanwhile, most of the existing solvent systems have the disadvantages of high toxicity, low solubility, and high cost. Therefore, the efficient and rapid dissolution of chitin using green solvents is urgently needed. In this work, ternary DES with amino acids, urea, and 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) is prepared at first. Then chitin can be dissolved fastly with the assistance of a microwave. Compared with the conventional heating process (110°C, 6-8h), the microwave process can be shortened to only 3-10min. The successful dissolution of chitin is verified by means of fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD), rheology studies, and optical light microscope, and the dissolution mechanism contributed to the synergistic destroying of the hydrogen bond networks of chitin by amino acids and DBU. The DES solvent can be well recovered with the remaining of its dissolving ability to chitin.

Carbonate dissolution fluxes in deep-sea sediments as determined from in situ porewater profiles in a transect across the saturation horizon

Despite their importance for long-term climate regulation, the rates and mechanisms of seafloor carbonate dissolution are poorly understood, especially with respect to calcite saturation and the role of sedimentary metabolic CO2 production. Here, we present results from an in situ porewater sampler deployed at the Cocos Ridge in the eastern equatorial Pacific, where we examine seafloor carbonate dissolution in locations with bottom water Ωcalcite ranging from 1.0 to 0.84 (1600–3200 m). With cm-scale resolution from the sediment–water interface to 35 cm, we present porewater profiles of total alkalinity, pH, dissolved inorganic carbon (DIC), δ13C of DIC, Ωcalcite, [Mn], [Ca], and [Sr], as well as solid phase porosity, % CaCO3, and % organic C. These profiles provide evidence that deep-sea sedimentary carbonate dissolution occurs via sediment-side control, wherein dissolution is dominated by sedimentary processes rather than strictly bottom water saturation state. We estimate dissolution fluxes using three independent approaches: alkalinity fluxes, δ13C of DIC combined with DIC fluxes, and [Ca] fluxes. We report seafloor dissolution fluxes with uncertainties < 38 %: 40 ± 15, 98 ± 20, 100 ± 32, and 89 ± 27 μmol CaCO3/m2/day at sites 3200, 2900, 2700, and 1600 m deep, respectively. The magnitude of dissolution fluxes is a function of bottom water saturation state (Ωcalcite), bottom water dissolved oxygen, and sedimentary CaCO3 content, but not correlated with any of these parameters independently. We observe dissolution occurring at all stations, including where bottom water is saturated with respect to calcite, and present evidence that this occurs through respiration-driven dissolution within the sediment. At all sites, porewater Ωcalcite decreases below bottom water values before increasing toward saturation deeper in the sediment. Using the δ13C of DIC, we partition the DIC fluxes across the sediment–water interface and find 21–48 % of DIC is sourced from CaCO3 dissolution, with the remainder sourced from organic matter respiration. We present a sedimentary mass balance, assembled with dissolution rates and mass accumulation rates obtained through Δ14C of foraminiferal calcite, and calculate CaCO3 burial efficiencies between 2 and 67 %, inversely correlating with water depth. Our results also provide evidence that net chemical erosion of 5,000––10,000 year old carbonate is occurring at the deepest site. Aerobic organic C respiration coupled with sedimentary CaCO3 dissolution, as documented here, will provide more alkalinity to bottom waters than from undersaturation-driven dissolution alone. This process can neutralize anthropogenic CO2 at the seafloor in a larger range of saturation states than previously estimated.

Toward understanding the solid-liquid equilibrium behavior of dinotefuran by thermodynamic analysis and molecular dynamic simulation

Dinotefuran is a third-generation nicotinic insecticide with a wide insecticidal spectrum and low toxicity to humans and other mammals, which has a huge potential market. The insight into the solid–liquid equilibrium behavior of dinotefuran in various solvents could further guide the design, development, and refinement of the further crystallization process. However, the complexity and variability of the dissolution process make it very challenging to study. In this research, the solid–liquid equilibrium of dinotefuran in both mono-solvents and mixed solvents was systematically investigated through a combined approach of the experimentation and molecular dynamics simulation. Firstly, the solubility of dinotefuran in a range of solvents was ascertained using the laser dynamic monitoring method over spanning temperatures from 278.15 to 318.15 K. The results showed that the solubility of dinotefuran in mono-solvents increase with the temperature increasing, while the solubility in mixed solvents exhibited an initial increase followed by a decrease with the organic solvent molar fraction increasing. Then the experimental data were fitted using five thermodynamic models. The NRTL model has the lowest 102ARD and 104RMSD values, indicating the best correlation, validity and fit. The dissolution behavior of dinotefuran was explored by calculating the thermodynamic properties. The results indicated that dinotefuran dissolution was a spontaneous, disorder degree increase process, and dissolution an exothermic process except the isopropanol + water mixed solvents. Additionally, the influence of the physicochemical properties of the solvent on the dinotefuran dissolution process was investigated, with a particular focus on the critical role of solvent polarity. Hansen solubility and the preferred solvation parameters of dinotefuran in the solvents were also further calculated to analyze the dissolution process. For the studied mixed solvents, when the ratios of methanol, ethanol, isopropanol, and acetone reached 0.85, 0.75, 0.50, and 0.70, respectively, dinotefuran molecules turned to be preferentially solvated by the water molecules. Finally, molecular dynamics simulation was performed to reveal the mechanisms of dinotefuran dissolution, suggesting the greater solute–solvent interaction, the easier dissolution. The solid–liquid equilibrium data might provide a guidance for the development of environment-friendly and efficient formulation.

Experimental Investigation on the Evolution of Physicochemical Properties and Dissolution Mechanism of High-Siliceous Shale with Acid Treatment

Summary The investigation of the influence of acidification conditions on the modification patterns of shale and the mechanisms of shale acidification processes is an indispensable aspect of further development within the field of shale acidizing theory. Prior research on shale acidizing has predominantly used hydrochloric acid (HCl) and carbonate-rich shale, which has restricted the scope of application for shale acidizing techniques and has not thoroughly examined the reaction kinetics of acid-rock interactions under reservoir conditions. This study focuses on siliceous shale, utilizing hydrogen fluoride (HF) in rotating disk experiments to assess the kinetic parameters of acid-rock reactions under varying acidification conditions, including duration, concentration, temperature, bedding direction, and acid flow velocity. Key influencing factors such as time, temperature, concentration, and experimental methods were selected for a comprehensive analysis, incorporating mineral composition [X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS)], microstructure (SEM), pore medium characteristics [mercury intrusion porosimetry (MIP) and low-temperature nitrogen adsorption (LNA)], surface morphology (3D laser scanning), and nanoindentation testing (NIT). The findings confirm the positive role of acid treatment in enhancing the permeability of shale oil and gas and in softening the reservoir rock, while also indicating potential negative impacts on hydrocarbon extraction, such as the formation of precipitated byproducts and the exfoliation of rock layers. This paper investigates the patterns of influence of HF acidizing parameters on siliceous shale and elucidates the mechanisms of action in shale acidification transformations, thereby providing a theoretical foundation for the modification of shale oil and gas reservoirs.

Aqueous dissolution rate of nuclear waste glasses as a function of aqueous Si concentration and pH

The aqueous dissolution rate was measured precisely for two kinds of reference nuclear waste glasses, ISG and P0798, as a function of aqueous Si concentration and pH of a solution by using the micro-channel flow-through test method with Si isotopes. The glass dissolution rate determined from the Si dissolution rate decreased with increasing aqueous Si concentration at pH 9. In contrast, the dissolution rate at pH 4 was not affected by the Si concentration or increased slightly with an increase in the Si concentration. Therefore, the glass dissolution mechanism with the altered surface properties depended sensitively on pH, causing large changes in the glass dissolution kinetics.

Inhibiting irreversible Zn2+/H+ co-insertion chemistry in aqueous zinc-MoOx batteries for enhanced capacity stability

Rechargeable aqueous Zn-MoOx batteries are promising energy storage devices with high theoretical specific capacity and low cost. However, MoO3 cathodes suffer drastic capacity decay during the initial discharging/charging process in conventional electrolytes, resulting in a short cycle life and challenging the development of Zn-MoOx batteries. Here we comprehensively investigate the dissolution mechanism of MoO3 cathodes and innovatively introduce a polymer to inhibit the irreversible processes. Our findings reveal that this capacity decay originates from the irreversible Zn2+/H+ co-intercalation/extraction process in aqueous electrolytes. Even worse, during Zn2+ intercalation, the formed ZnxMoO3−x intermediate phase with lower valence states (Mo5+/Mo4+) experiences severe dissolution in aqueous environments. To address these challenges, we developed a first instance of coating a polyaniline (PANI) shell around the MoO3 nanorod effectively inhibiting these irreversible processes and protecting structural integrity during long-term cycling. Detailed structural analysis and theoretical calculations indicate that =N– groups in PANI@MoO3−x simultaneously weaken H+ adsorption and enhance Zn2+ adsorption, which endowed the PANI@MoO3−x cathode with reversible Zn2+/H+ intercalation/extraction. Consequently, the obtained PANI@MoO3−x cathode delivers an excellent discharge capacity of 316.86 mA h g−1 at 0.1 A g−1 and prolonged cycling stability of 75.49% capacity retention after 1000 cycles at 5 A g−1. This work addresses the critical issues associated with MoO3 cathodes and significantly advances the understanding of competitive multi-ion energy storage mechanisms in aqueous Zn-MoO3 batteries.

Study on several novel crystalline complexes of sorafenib with dicarboxylic acid: Nature identification and solubilization mechanism

The development of solid-state forms of drugs is an effective approach to increase solubility. This study developed three crystalline complexes of sorafenib (SF) with oxalic acid (OA) and malonic acid (MA) using a solvent method, named SF+·OA-·THF, SF+·OA-, and SF-MA. The formation of these complexes was influenced by the crystalline method, solvent polarity, and the carbon chain length of the dicarboxylic acids. Single-crystal X-ray diffraction revealed proton transfer in SF+·OA-·THF, classifying it as a channel-type salt solvate and conformational polymorph due to hydrogen bond formation. 13C solid-state nuclear magnetic resonance and X-ray photoelectron spectroscopy confirmed proton transfer in SF+·OA-·THF and SF+·OA-, but not in SF-MA, indicating that SF+·OA- is a salt while SF-MA is a co-crystal. Fourier Transform Infrared Spectroscopy further supported these findings. Compared with Form Ⅰ, SF+·OA-, SF+·OA-·THF, and SF-MA increased the apparent solubility of SF by 8.3, 7.9, and 6.4 times in pH 1.2 HCl buffer, and by 4.0, 3.1, and 4.5 times in pH 6.8 PBS buffer, respectively. All crystalline complexes exhibited a “spring and parachute” phenomenon due to the solubility difference between the drug and the dicarboxylic acids. Notably, the intermolecular forces between SF and THF in SF+·OA-·THF prolonged the “spring and parachute” process. Additionally, these crystalline complexes demonstrated good stability. This study provides valuable insights into the development and identification of crystalline complexes and their dissolution mechanisms.

Swelling and dissolution behaviors of cellulose in phosphate-based ionic liquids-H2O binary systems: In-situ observation and molecular dynamics simulation

Swelling and dissolution of cellulose in ionic liquids (ILs) as the pretreatment processes are key steps for the high-value conversion and utilization of cellulose. However, the molar ratio of H2O to ILs has a significant effect on the swelling and dissolution of cellulose, and its molecular-scale mechanism is still unclear, which limits screening out the suitable ILs and recovery of ILs from coagulation bath in the spinning process. Herein, three phosphate-based ILs were chosen to couple with water as solvents for swelling and dissolution of cellulose by combining in-situ observation and molecular dynamics (MD) simulation. The results show that the redissolution time of swollen cellulose is greatly reduced, especially [Emim]DEP-H2O has the best swelling and dissolution performance for cellulose due to its high β value and low viscosity. Meanwhile, when the molar ratio of IL to H2O was more than 1: -1, the IL-H2O system still has the ability to dissolve cellulose. While with the molar ratio further decreased, cellulose was no longer dissolved and began to swell, and the fiber diameter obtained the maximum swelling rate with 40.1% at a molar ratio of 1:3. Moreover, MD simulation was used to calculate the interaction between IL/water/cellulose, which further illustrated that the combination of IL with water molecular has a significant influence on the behavior of cellulose in IL-H2O systems at the molecular scale. Thus, the potential swelling and dissolution mechanism of cellulose in ILs-H2O binary systems was proposed based on experimental and simulation results. Furthermore, the characterization results of swollen cellulose indicate that the crystal structure and degree of polymerization (DP) were almost unchanged, but the specific surface area and pore size increased significantly, and the thermal stability and heat absorption were decreased, all the results prove that the swelling process increased the accessibility of cellulose and benefited to the subsequent dissolution. Consequently, preferable swelling and dissolving parameters of experiments and simulations will provide a new idea for the selection of suitable ILs and the recovery of ILs from a coagulation bath in the dry-wet spinning process.

Mechanisms of dissolution and crystallization of amorphous glibenclamide

Amorphous solid dispersions enhance the dissolution and oral bioavailability of poorly water-soluble drugs. However, the link between polymer properties and formulation performance has not been fully clarified yet. We studied the effect of hydroxypropyl cellulose (HPC) polymers molecular weight (Mw) on the storage stability, dissolution kinetics and supersaturation stability of spray-dried amorphous glibenclamide (GLB) formulations. The solid-state stability of amorphous GLB during storage was significantly enhanced by both the 40 kDa (HPC-SSL) and 84 kDa (HPC-L) polymers, regardless of Mw differences. In contrast, HPC-SSL maintained significantly higher aqueous drug concentrations during dissolution, compared to HPC-L (its higher Mw analogue). Dedicated dissolution experiments, in situ optical microscopy and solid-state characterization revealed that aqueous drug concentrations were determined by the interplay between crystallization inhibition, drug ionization, wetting and solubilization effects: (1) HPC prevents surface nucleation, hence inhibiting crystallization, (2) intestinal colloids (bile salts and phospholipids) increase supersaturated drug concentrations via wetting and solubilization effects and (3) pH and drug ionization severely impact the degree of supersaturation. The better performance of the lower Mw HPC-SSL was due to its superior inhibition of surface crystallization during dissolution. These insights into the molecular mechanisms of dissolution and crystallization of amorphous solids provide foundation for rational formulation development.

The evolution and dissolution mechanism of θ-Al2Cu phase and the analysis of precipitation of a novel AlCu phase during elevated aging

The evolution and dissolution mechanism of the θ-Al2Cu precipitates were investigated in this study by transmission electron microscopy (TEM) during the re-aging at high temperatures for a long time. The results advance the current knowledge of dissolution and its associated mechanisms of the θ-Al2Cu phase in AlCu alloys. In this study, the coarsening and dissolution of θ-Al2Cu phase in T6 heat-treated Al4Cu alloy during various times (0−1000h) of re-aging temperature 420 °C were studied experimentally and theoretically. The morphological characterization revealed that the θ-Al2Cu phases gradually increase in size and decrease in volume density during the aging process, which can be attributed to coarsening and dissolution phenomena occurring during re-aging. Additionally, a body-centered tetragonal AlCu phase is precipitated within the θ-Al2Cu phase during the high temperature re-aging process, which is a characteristic of this phase prior to dissolution. Moreover, the primary mechanisms responsible for the high temperature melting of the θ-Al2Cu phase are the formation of the AlCu phase and the initial melting of the Cu-poor region in the θ-Al2Cu phase. The Cu atoms in θ-Al2Cu phase dissolve and diffuse into the Al matrix, forming L12 ordered AlCu solute clusters through long-range diffusion.

Role of Niobium on the Passivation Mechanisms of TiHfZrNb High-Entropy Alloys in Hanks' Simulated Body Fluid.

A family of TiHfZrNb high-entropy alloys has been considered novel biomaterials for high-performance, small-sized implants. The present work evaluates the role of niobium on passivation kinetics and electrochemical characteristics of passive film on TiHfZrNb alloys formed in Hanks' simulated body fluid by analyzing electrochemical data with three analytical models. Results confirm that higher niobium content in the alloys reinforces the compactness of the passive film by favoring the dominance of film formation and thickening mechanism over the dissolution mechanism. Higher niobium content enhances the passivation kinetics to rapidly form the first layer, and total surface coverage reinforces the capacitive-resistant behavior of the film by enrichment with niobium oxides and reduces the point defect density and their mobility across the film, lowering pitting initiation susceptibility. With the high resistance to dissolution and rapid repassivation ability in the aggressive Hanks' simulated body fluid, the TiHfZrNb alloys confirm their great potential as new materials for biomedical implants and warrant further biocompatibility testing.

The Corrosion Fatigue Behavior and Mechanism of AerMet 100 Steel in 3.5% NaCl at Room Temperature.

AerMet 100 steel is a new type of double-hardened high-strength steel, which is often used as landing gear material in amphibious aircraft. In the present paper, the corrosion fatigue behavior and mechanism of AerMet 100 high-strength steel in a 3.5% NaCl solution was studied by stress-controlled fatigue tests and a series of subsequent characterizations of the fracture surface, microstructure, and cracks. The results indicated that the fatigue life of AerMet 100 high-strength steel decreased with a decrease in the stress level in a 3.5% NaCl solution, satisfying the relationship lgN = -2.69 × 10-3 σ + 6.49. The corrosion fatigue crack usually initiated from the corrosion pit and propagated across the martensitic flat noodles. Meanwhile, the corrosion fatigue crack tip was filled with Cr2O3, Fe2O3, and amorphous material; it propagated in the transgranular mode by a slip dissolution mechanism. This study provides some engineering significant for the fatigue performance of AerMet 100 steel in a 3.5% NaCl solution.

Dissolution behavior of calcium uranate under oxidizing and reducing conditions

Calcium uranate solid phase is a secondary mineral found in geological environments. It may form in the residues of high-level radioactive liquid waste and in the fuel debris of the TEPCO's Fukushima Daiichi Nuclear Power Plant under high-temperature conditions. To assess the chemical stability of CaUO4 in different aqueous environments, static immersion tests were performed under various redox conditions and carbonate ion concentrations. pH and Eh values, as well as concentrations of uranium, calcium, and total carbonate in the solutions, were measured after the supernatants were filtered through a membrane with a 10 kDa molecular weight cutoff. The components of the solid phase were also evaluated using X-ray diffraction and X-ray absorption fine structure analyses. The dissolution mechanism of CaUO4 was examined using data from solid and liquid analyses, along with chemical thermodynamic calculations. Under reducing conditions and without carbonate, U(VI) in CaUO4 was reduced to U(V) and the mineral was converted into non-stoichiometric CaUO4−x. The dissolved uranium was then further reduced to U(IV) in the aqueous media, forming UO2(am), which controlled the U solubility. Under oxidizing conditions and in the absence of carbonate, dissolved uranium formed metaschoepite ((UO3)·2H2O(cr)) at pH ≤ 7 and sodium diuranate (Na2U2O7·H2O(cr)) at pH > 7, which controlled uranium solubility. In oxidizing conditions with carbonate present, the apparent solubility of U was lower than predicted by the solid-phase solubility calculations. The concentration of U was constrained to levels similar to that of calcium when the calcium concentration reached saturation with CaCO3. Additionally, the dissolution of calcium from CaUO4 influenced uranium dissolution.