Na2SO4 Solution Research Articles

Transport Properties of Solutions in γ–FeOOH/CSH Pores of Steel Fiber-Reinforced Concrete (SFRC) Derived Using Molecular Dynamics

Steel fiber-reinforced concrete structures designed for marine environments can become compromised by the ingress of water and ions. Water and ion transport through the pores between steel fibers and concrete gels significantly affects the durability of such structures, but the mechanisms of this transport are not sufficiently understood. Reported here is a molecular dynamics-based investigation of the transport of water, NaCl, Na2SO4, and mixed solutions of NaCl and Na2SO4 through γ–FeOOH/CSH pores. The effect of pore width on the capillary transport of NaCl + Na2SO4 solutions was also investigated and reported. It is shown that the depth of water penetration in NaCl solution increases parabolically with time. It is further shown that the CSH surface forms bonds with different ions to form Na–OCSH, Cl–CaCSH, and S–CaCSH compounds, which results in reduced rates of solution transport. The mixed NaCl + Na2SO4 solution was found to have the lowest transport rate. A reduction in pore width was found to reduce the transport rate of water molecules and diminish the transport of ions. In pores smaller than 2.5 nm in width, the immobilized ions aggregate into clusters, occupying pore inlets and blocking more ions from entering the channels. Compared with the matrix on both sides, solutions are transported significantly faster along the CSH side than along the γ–FeOOH side, indicating that the addition of steel fibers can effectively slow down the transport of water molecules and ions in concrete. These data on the difference in the transport of solutions along the two sides of the matrix may provide molecular-level insights to support studies on the durability of concrete materials.

Characterizing Ferrihydrite Transformation Products in Near‐Saturated Brine Environments: Implications for Fe‐Oxide Formation on Mars

AbstractFerrihydrite has been observed within the Martian regolith; therefore, ferrihydrite transformation pathways are likely critical to iron cycling and mineral transformation on Mars and other extraterrestrial systems. Data from Mars rovers and orbiters indicate that ferrihydrite is associated with significant salt deposits. Previous studies show these salts likely formed as the planet desiccated and may rehydrate to form modern brines today that strongly influence(d) mineral alteration. We hypothesize that the salts observed on Mars' surface may help preserve ferrihydrite for longer periods than typically observed on Earth. This study investigates the effects of brine chemistry on ferrihydrite alteration through laboratory experiments. Lab‐synthesized ferrihydrite was reacted with near‐saturated brines and ultra‐pure water at 20°C for 30 days in a series of batch reactor experiments. X‐ray diffraction and Raman spectroscopy showed that ferrihydrite was preserved without evidence of dissolution/transformation in near‐saturated solutions of MgSO4, Na2SO4, and NaClO4, while additional iron‐oxyhydroxide phases formed in other brines. We also compared mineral reaction products formed from freeze‐dried ferrihydrite and undried ferrihydrite slurry. The freeze‐dried ferrihydrite was more likely to be preserved, whereas ferrihydrite in a slurry resulted in the precipitation of goethite and lepidocrocite, indicating that particle aggregation and/or drying history affect ferrihydrite stability and alteration. Overall, ferrihydrite remained largely unaltered in the presence of concentrated sulfate and perchlorate brines. In the context of soils/regolith observed on Mars, our research demonstrates that ferrihydrite is more likely to be preserved when found in areas where these salts are dominant, and desiccated in a cold/arid environment prior to brine exposure.

Kinetic Modeling and Assessment of a CO2 Nanobubble-Enhanced Hydrate-Based Sustainable Water Recovery from Industrial Effluents

Abstract This study evaluates the effectiveness of CO2 nanobubble-enhanced hydrate-based desalination (HBD) to treat industrial effluents from the mining and metals industry. Testing was conducted in a high-pressure reactor apparatus that employed CO2 as the gas hydrate former at 274.15 K and 3.58 MPa. CO2 nanobubbles (NBs) were used to promote hydrate formation, aiming to streamline an HBD process without separation steps for the additives/chemicals used. Due to the limited studies on hydrate formation in sulfate-containing aqueous solutions, this research focused on the kinetics of hydrate formation in varying concentrations of Na2SO4 and MgSO4 (0.1 and 0.5 M). The results showed that CO2 NBs significantly enhanced hydrate formation in both Na2SO4 and MgSO4 solutions, with CO2 consumption increasing by up to approximately 51% and 35%, respectively. Additionally, a kinetics study on a real effluent from the mining and metals industry showed that the presence of CO2 NBs increased CO2 consumption by around 20% after 180 min. This research also evaluated water recovery and desalination efficiency in a 3-stage HBD process applied to the effluent, the concentration of which exceeded the operating range of reverse osmosis. The results indicated an improvement in water recovery from 25.13 ± 2.04% to 40.16 ± 1.43% with CO2 NBs, underscoring their effectiveness in treating highly saline water. Moreover, desalination efficiencies of 49.54 ± 2.39% and 42.03 ± 3.43% were achieved without and with CO2 NBs, respectively. This study represents the successful demonstration of the efficient application of the CO2 NBs-boosted HBD method to treat high-salinity effluents and recover clean water for reuse. Graphical Abstract

Regeneration of NaOH from the Spent Na2SO4 Solution by Two-Compartment Bipolar Membrane Electrodialysis

With the recent introduction of various environmental policies focused on carbon neutrality has made recycling a crucial task in the electric vehicle industry. In particular, the recycling of lithium-ion batteries, a critical component of EVs, is becoming increasingly important. The process of recovering valuable metals such as lithium (Li), cobalt (Co), manganese (Mn), and nickel (Ni) from spent batteries typically involves leaching, precipitation, solvent extraction, and crystallization. However, these processes generate a significant amount of Na2SO4 wastewater. To address this issue, bipolar membrane electrodialysis (BMED) has been developed to recover H2SO4 and NaOH from Na2SO4. The conventional method uses a three-compartment configuration to simultaneously recover acid and base components, This approach, however has drawbacks such as high initial installation costs due to the expensive membranes and low current efficiency. To overcome these limitations, a two-compartment constant voltage method using cation exchange membranes and bipolar membranes was employed in this study. The effects of various process parameters on the recovery rate of NaOH, current efficiency, flux, and energy consumption were evaluated. Based on the optimal conditions from the experiment, a flow rate of 950 mL/min, a feed solution of 1.30 M Na2SO4 at 1.5 L, and an initial base solution of 0.1 M NaOH at 0.50 L resulted in an base recovery rate of 67.59%, with 0.91 L of 2.96 M NaOH recovered.

Preparation of Magnetic Photocatalyst Fe3O4@SiO2@Fe-TiO2 and Photocatalytic Degradation Performance of Methyl Orange in Na2SO4 Solution

In this study, Fe3O4@SiO2@TiO2 (FS-FT (0 g)) photocatalysts, featuring a magnetic core–shell structure, and Fe-doped Fe3O4@SiO2@Fe-TiO2 (FS-FT (x g)) photocatalysts, were fabricated via the sol–gel method. Structural and compositional analyses of the processed samples were systematically conducted through X-ray diffraction (XRD), transmission electron microscopy (TEM) with selected area electron diffraction (SAED), surface-sensitive X-ray photoelectron spectroscopy (XPS), and optical property assessment via UV-Vis diffuse reflectance spectroscopy (UV-DRS). The results show that TiO2 on the outer layer of FS-FT (0 g) and FS-FT (x g) has an anatase structure, and that Fe is doped into FS-FT (x g). The photodegradation of methyl orange (MO) using FS-FT (0 g) and FS-FT (x g) with various Fe doping levels was evaluated in both pure MO (C0 = 10 mg/L) and MO-Na2SO4-blended solutions. Under irradiation with high-pressure mercury lamps, the removal rates of MO using FS-FT (0 g) and FS-FT (0.36 g) in pure MO solution reached 90.25% and 99% at 25 min, respectively, which indicates that FS-FT (0.36 g) can enhance photocatalytic performance. The removal rates of MO using FS-FT (0 g) and FS-FT (0.36 g) in MO-Na2SO4-blended solution (C0 = 10 mg/L, CNa2SO4 = 12.5 g/L) reached 92.38% and 97.16% at 25 min, respectively. The removal rate of MO using FS-FT (0.36 g) decreased in MO-Na2SO4-blended solution in the previous 25 min, which indicates that Na2SO4 can inhibit degradation using FS-FT (0.36 g). The degradation experiments of MO-Na2SO4-blended solutions with different concentrations of Na2SO4 using FS-FT (0.36 g) showed that as the concentration of Na2SO4 increases, the inhibitory effect becomes more pronounced. Recovery and recycling experiments confirmed that the photocatalyst exhibited robust degradation performance over multiple cycles. Kinetic analysis of the photocatalytic data, based on a first-order model, was conducted to explore the underlying degradation principles.

Puncture-resistant hydrogels with high mechanical performance achieved by the supersaturated salt.

Sufficient mechanical performance is the basic requirement for load-bearing and damage-resistant materials. However, the simultaneous optimization of mechanical properties is usually difficult in a single hydrogel. Herein, a supersaturated salt was employed to enhance the mechanical performance and damage resistance of hydrogels. By immersing the pre-formed hydrogel based on hydrophobic associations into supersaturated Na2SO4 solution (3.3 M), high-density and strong hydrophobic associations were constructed simultaneously in the network due to the contraction of hydrophilic chains and improvement of hydrophobic associations. Compared to the pristine hydrogel, this salt-treated hydrogel was transparent and showed a simultaneous enhancement in stiffness (E of 253 ± 7 MPa), strength (σ of 12.65 ± 0.07 MPa), and toughness (Γ of 19.6 ± 3.2 MJ m-3). It also displayed remarkable puncture and tear resistance with a puncture force of 66 N, a puncture energy of 370 mJ, and a tearing energy of 34 kJ m-2. This work provides a simple method to simultaneously optimize the contradictory mechanical properties and puncture resistance in a single hydrogel.

Rutile solubility in aqueous sodium salt solutions at high pressures and temperatures: in-situ observations using a diamond anvil cell

Knowledge of rutile (TiO2) solubility in aqueous fluids at high pressures and temperatures is of primary importance to a quantitative understanding of the high field strength elements (HFSE) transport in subduction zones. We attempted to redetermine rutile solubility in aqueous NaF solution and newly assess rutile solubility in aqueous Na2CO3 and Na2SO4 solutions through in-situ optical observations of the complete dissolution of a rutile grain in a hydrothermal diamond anvil cell (HDAC) at 823–974 °C and a pressure of approximately 0.9–1.8 GPa. The reproducibility of the experimental results in Na2CO3 solution was confirmed across individual experiments and repeated cycles within a single experiment. The rutile solubility in the aqueous sodium salt solutions was significantly higher than the previously reported solubility in pure H2O obtained with weight loss techniques using a piston–cylinder apparatus. While the increase in the solubility with added NaF was consistent with previous findings, the present results suggest that the solubility-promoting effect is smaller than previously reported. The high solubility in the aqueous sodium salt solutions may be attributed to the formation of Ti(IV) complexes with potential ligands (e.g., OH−, CO32−, SO42−, and F−) and sodium that remain to be characterized. Our findings indicate that sodium carbonate and sulfate-bearing fluids in subduction zone lithologies may play a role in efficiently transporting HFSE. A pertinent example of this could be the occurrence of carbonate and sulfate minerals in rutile-rich veins and fluid inclusions from high-pressure metamorphic rocks.

Equipotential lines in liquids

Understanding the potential distribution in liquids is critical due to its significant differences from general media. The main problem addressed in this research is the lack of clarity on how electrode polarization affects potential distribution in liquid electrolytes. To investigate this, we experimentally measured the potential distribution characteristics in liquids under DC and AC voltages, explaining the variability through electrode polarization theory. Our action included introducing electrode polarization potential correction in COMSOL software simulations, which showed strong agreement with our experimental results. Further, we investigated the potential distribution characteristics in Na2SO4 solutions with varying concentrations, using ionic potential to explain voltage formation inside the liquids. The results highlight the improved accuracy in modeling potential distributions in liquid electrolytes, which is significant for advancing various electrochemical processes.

Preparation of Crown Ether-Containing Polyamide Membranes via Interfacial Polymerization and Their Desalination Performance.

The large-scale application of aromatic polyamide (PA) thin-film composite (TFC) membranes for reverse osmosis has provided an effective way to address worldwide water scarcity. However, the water permeability and salt rejection capabilities of the PA membrane remain limited. In this work, cyclic micropores based on crown ether were introduced into the PA layer using a layer-by-layer interfacial polymerization (LbL-IP) method. After interfacial polymerization between m-phenylenediamine (MPD) and trimesoyl chloride (TMC), the di(aminobenzo)-18-crown-6 (DAB18C6) solution in methanol was poured on the membrane to react with the residual TMC. The cyclic micropores of DAB18C6 provided the membrane with rapid water transport channels and improved ion rejection due to its hydrophilicity and size sieving effect. The membranes were characterized by FTIR, XPS, SEM, and AFM. Compared to unmodified membranes, the water contact angle decreased from 54.1° to 31.6° indicating better hydrophilicity. Moreover, the crown ether-modified membrane exhibited both higher permeability and enhanced rejection performance. The permeability of the crown ether-modified membrane was more than ten times higher than unmodified membranes with a rejection above 95% for Na2SO4, MgSO4, MgCl2, and NaCl solution. These results highlight the potential of this straightforward surface grafting strategy and the modified membranes for advanced water treatment technologies, particularly in addressing seawater desalination challenges.

The Influence of Alkaline Earth Metal Cations on the Performance of Platinum Electrodes during Brine Electrolysis.

The performance of platinum electrodes towards the hydrogen evolution reaction (HER) during pH-neutral brine electrolysis was investigated in the presence of alkaline earth metal cations, with a focus on Mg2+ ions. This study aimed to understand the impact of these cations and/or their hydroxide deposits on electrode performance. Electrochemical measurements, including chronoamperometry and polarization curves, were conducted in pH-neutral electrolytes with varying Mg2+ concentrations (0 mM to 55 mM) in 1 M Na2SO4 solution. Contrary to concerns that Mg(OH)2 deposits might impair performance, Pt electrodes exhibited improved HER activity across all Mg2+ concentrations compared to Mg-free electrolytes. To distinguish the effects of hydroxide deposits from solvated cation interactions with the electrocatalyst, other divalent cations (Ca2+, Sr2+, Mn2+) with varying solubility product constants were also tested. All cations enhanced HER performance, including those unlikely to form deposits under the tested conditions. Our results point to cation acidity and Gibbs free energy of hydration as effective descriptors for predicting the role of divalent cations in HER kinetics. In situ image analysis revealed that Mg(OH)2 deposits are periodically removed by evolving hydrogen bubbles, preventing the blockage of active sites. In situ Raman spectroscopy further confirmed the formation of Mg(OH)2 deposits during HER.

Transient Liquid Induced Hierarchical Structure Contributes to High Thermoelectric Performance in Ag2Se.

Owing to the intrinsic high thermoelectric performance, Ag2Se is a promising alternative for traditional near-room temperature Bi2Te3-based materials. In this study, a Na2SO3 solution has been used as the transient liquid during the modified cold sintering process to induce a hierarchical structure, including micropores, nanopores, sub-nanopores, and additional nanoscale Na2SO3 residuals. Such a hierarchical structure contributes to an ultralow lattice thermal conductivity of 0.18W m-1 K-1 at ≈300 K in the Ag2Se-30%Na2SO3. Additionally, extra Se vacancies further optimize the carrier concentration to ≈5.6 × 1018cm-3, leading to a high power factor of ≈25 µW cm-1 K-2 at ≈300 K in the Ag2Se-30%NS. Consequently, due to the synergistic effects of high power factor and low lattice thermal conductivity, an ultrahigh room-temperature figure of merit of 1.04 in the Ag2Se-30%Na2SO3. The study demonstrates that introducing transient liquid solutions in the modified cold sintering process can effectively achieve specific structural engineering and high thermoelectric performance.

Identifying the influence of nanomodifiers on the structure formation process regularities in the gypsum-alumina cement system

Gypsum alumina cement is resistant to magnesium solutions, seawater, and concentrated Na2SO4 and Mg2SO4 solutions, but it is less resistant to sodium chloride solutions. One of the ways to improve the gypsum alumina cement durability and enable its use in aggressive calcium chloride waters is to design a composition by incorporating modifiers. Thus, the composite is applicable for well-casing under conditions involving aggressive water exposure. However, such cements have their limitations: they are not suitable for processing at high temperatures in autoclaves. Up to now, the ettringite phase stability dependence on curing conditions and temperature has remained an unresolved issue. It has been theoretically proven and experimentally confirmed that the optimal calcium sulfate content in gypsum alumina cement and gypsum grade G-5 (GAC+G5) compositions, according to calculations, ranges from 28 % to 38 % of the mass of the alumina binder. That makes it possible to increase ettringite formation and obtain cement stone structure with predefined characteristics. As a result of modification with nano additives, the strength indicators of the composite materials have been improved: gypsum alumina cement GAC gypsum grade G-5:G (70:30) %+0.18 % nanotubes+0.4 % Sika – up to 70.2 MPa compared to 14.67 MPa in the reference composition. The scope of practical application includes the development of road surfaces and waterproofing materials, as well as hydraulic engineering. A condition for the practical implementation of results is the temperature range from –15 to 80 °С. Expected effects of application are shrinkage deformation reduction, improved crack resistance, increased strength, and enhanced durability of concrete articles under challenging operating conditions

Sol-Gel Electrophoretically Deposited TiO2-Multiwalled Carbon Nanotube-SiO2 Thin-Film Electrode with High Photoelectrochemical Activity.

Hydrogen production via water splitting has been extensively researched for its environmental friendliness, energy efficiency, and renewability. This study describes the development of TiO2-multiwalled carbon nanotube (MWCNT)-SiO2 composite thin-film electrodes via electrophoretic deposition (EPD) from a 2-propanol solution of MWCNTs including TiO2 and SiO2 gels. The TiO2 and SiO2 gels were prepared via the sol-gel method and by mixing in varying weight ratios to enhance the efficiency of photoelectrochemical water splitting. Dual sol-gel EPD incorporates MWCNTs with a C/TiO2 molar ratio of ≥0.25 while varying the TiO2/SiO2 molar ratio from 5 to 14; the electronic conductivity is improved owing to the pristine graphene structure of the MWCNTs along with hydrophilicity imparted by SiO2. In addition, the volume of SiO2 sol influences the anatase-to-rutile ratio, the TiO2 crystal size, and chemical bonds, thereby affecting the formation of new energy levels. The optimal volume of SiO2 sol results in elevated ultraviolet-visible absorbance, attributed to midgap states generated by a high anatase-to-rutile ratio and Ti-O-Si formation, further leading to a substantial effective carrier density for the photoelectrochemical water-splitting reaction. Furthermore, the valence band maximum (VBM) and conduction band minimum, estimated using ultraviolet photoelectron and ultraviolet-visible spectroscopies, exhibited a downward shift with increasing SiO2 sol volume, followed by an upward shift; meanwhile, the Fermi level in a Na2SO4 solution under stimulated solar light deepened. The highest photoelectrochemical performance is achieved at the optimal SiO2 sol volume, where the VBM is deep enough to minimize the water-splitting overpotential, and the flat-band potential aligns with the set potential, thereby reducing band bending with a negligible hole depletion layer at the TiO2-solution interface. The best TiO2-MWCNT-SiO2 composite exhibits a photocurrent ∼7.4 times higher than that of a TiO2-MWCNT electrode.

New insight into the salt role during preparing α‐hemihydrate gypsum in atmospheric salt solution: Particle size control

AbstractThe synergistic control of the crystal morphology and size of α‐hemihydrate gypsum (α‐HH) was achieved by adjusting the Na2SO4 concentration and maleic acid content. Maleic acid primarily regulated the α‐HH morphology through surface adsorption. The concentration of Na2SO4 determined crystal size by tailoring the maximum relative supersaturation (Smax) during α‐HH crystallization. Higher Na2SO4 concentrations led to higher Smax and smaller crystal sizes. The Smax of α‐HH in a 9% Na2SO4 solution was 4.5 times that in a 6% solution, resulting in a significant decrease in crystal size from approximately 40–18 µm as the Na2SO4 concentration increased from 6% to 9%, while maintaining similar crystal morphology (average aspect ratio of about 1.0). This study filled the gap in research on particle size control during the preparation of α‐HH using the salt solution method under atmospheric pressure, contributing to a more systematic and comprehensive understanding of this method.

Salt Crystallization and Heritage Materials: Improving Durability by Understanding Porosity and Mineral Composition

ABSTRACT The current research examines the role of salt crystallization, a major factor in atmospheric pollution in coastal regions, on the degradation of biocalcarenite stones used in monuments in the Rabat-Salé area of Morocco. Focusing on Bouknadel and Bouskoura stones samples, the study conducted seven cycles of imbibition and desiccation with Na2SO4 and NaCl solutions (70 g/L and 100 g/L) to simulate marine aerosol effects. Additionally, capillary absorption was measured, and mass changes were documented after immersion in distilled water. X-ray diffraction and scanning electron microscopy were utilized to evaluate the chemical, mineralogical, and textural properties of the stones. The findings revealed that Bouknadel stone, despite its higher porosity (38 ± 9%), exhibited greater resistance to salt damage than Bouskoura stone (25 ± 5% porosity). This variation in response is attributed to differences in mineral composition, notably the presence of quartz in Bouknadel stone and sulfur in Bouskoura stone. Bouskoura stones faced significant deterioration, especially with Na2SO4, linked to the crystallization of thenardite. In contrast, Bouknadel stones maintained structural integrity despite halite crystal formation. These results underscore the importance of mineralogical composition and porosity in assessing stone susceptibility to salt degradation, offering critical insights for the conservation of cultural heritage in coastal ecosystems.

A New Type of Self-Compacting Recycled Pervious Concrete Under Sulfate Drying-Wetting Exposure.

Traditional pervious concrete poses significant challenges in optimizing both mechanical properties and permeability. To address this issue, a novel type of self-compacting recycled pervious concrete (SCRPC) featuring vertical and penetrating channels has been developed. The vertical channels were created by pulling out the reinforcement in the pre-drilled holes that were artificially created in the mold, after the concrete had been poured. However, whether this concrete has superior durability and can be employed in different sulfate drying-wetting situations remains to be investigated. This study explored the sulfate resistance and permeability of SCRPC under five drying-wetting exposure regimes: full soaking in Na2SO4 solution with drying-wetting ratios of 3:18, 9:12, and 18:3; semi-soaking in Na2SO4 solution; and full soaking in MgSO4 solution. The results showed that the SCRPC soaked in MgSO4 solution suffered the largest compressive strength loss (13.4%) after 150 drying-wetting cycles. Furthermore, as the drying-wetting ratio increased, the sulfate degradation of the SCRPC increased. Despite the comparable relative dynamic modulus of elasticity of SCRPC after full soaking (95.54%) and semi-soaking (92.89%), ettringite and gypsum were identified as the predominant sulfate deterioration products of SCRPC, respectively. In contrast to the two stages for traditional pervious concrete, the effective porosity of SCRPC was divided into three stages during sulfate attack: an initial rapid decline stage, a subsequent increase stage, and a final slow decline stage. The permeability coefficient of SCRPC varied from 6.00 to 6.82 mm/s under different sulfate drying-wetting exposures. In summary, SCRPC has superior sulfate resistance and permeability, and it could be more applicable in environments containing Na2SO4 compared to MgSO4. This study provides basic data for the enhancement and application of pervious concrete with artificial vertical and penetrating channels.

Effects of zeolite and palm fiber on the weathering resistance and durability characteristic of cement soil

This paper aims to investigate the effects of zeolite and palm fiber on the strength and durability of cement soil. Based on the findings of previous research, optimal proportions of zeolite, palm fiber, and cement, as well as the appropriate curing age, were determined. Subsequently, unconfined compressive strength tests, dry-wet cycle tests, and freeze-thaw tests were conducted, utilizing NaCl and Na2SO4 solutions over the specified curing period. The strength and durability characteristics of the samples were evaluated by assessing mass and strength loss, taking into account the combined effects of NaCl and Na2SO4 solution erosion. The test data also provide a fitting relationship between strength and the number of cycles under the influence of different solutions, thereby offering a basis for theoretical predictions without the need for additional experiments. Finally, the microscopic mechanisms were analyzed using scanning electron microscopy (SEM). The results indicate that the cement soil composite of zeolite and palm fiber, when combined in optimal proportions, exhibits the best durability and minimal loss of strength and mass, irrespective of whether exposed to clean water or salt erosion, as well as during dry-wet or freeze-thaw cycles.

Durability and microscopic mechanisms of coal gangue-calcium carbide residue geopolymer binder material

To evaluate the durability of coal gangue (CG)–calcium carbide residue (CCR) geopolymer in aggressive environments, full immersion tests were performed in H2SO4, Na2SO4, and MgSO4 solutions. Changes in compressive strength, mass loss, and performance degradation were examined. Degradation mechanisms were studied using XRD, FTIR, TGA, MIP, and SEM to analyze erosion products, microstructure, and pore evolution. An optimal liquid-to-solid ratio of 0.45 was identified for CG–CCR geopolymers. The material exhibited excellent resistance to Na2SO4 due to ettringite and C-A-S-H gel formation, enhancing pore structure and bonding strength. However, resistance to H2SO4 and MgSO4 was poor, driven by aluminum and calcium leaching and C-A-S-H transformation into non-cementitious M-A-S-H gels. A dense protective layer and corrosion-resistant C-A-S-H gel provided superior durability compared to OPC, with CCR addition further improving structural integrity and C-A-S-H gel generation. These findings highlight the potential of industrial waste-based geopolymers for durable, sustainable construction.

An Experimental Assessment and Numerical Simulation of the Corrosion Behavior of Aluminum Welded Joints in Diverse Environments

The corrosion behavior of stud-welded AA5083-H321/AA6061-T6 joints was examined. The electrochemical demeanor of the resultant joint was scrutinized in 3.5% NaCl, ASTM seawater, and Na2SO4 solutions using scanning electron microscopy (SEM), optical microscopy (OM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). COMSOL Multiphysics version 5.6 software was used to predict the galvanic corrosion of AA5083-H321/A6061-T6 in different solutions, using the software finite element (FE) kit. The results indicated that drawn arc stud welding (DASW) enhanced the corrosion resistance of the welding zone, with the highest resistance observed in the Na2SO4 solution. This process also influenced the pitting corrosion rate and minimized alterations in pit morphology, with the order of corrosion resistance decreasing from Na2SO4 to 3.5% NaCl and ASTM seawater. Among the base metals, the AA6061-T6 side of the weld exhibited superior corrosion resistance compared to the AA5083-H321 side across all tested solutions. The results from the numerical simulation of the corrosion behavior of the welded joint support the experimental assessment.

Electrochemical behavior of FeCoNiAl0.75Cr1.25 high-entropy alloy in Na2SO4 solution with acidic pH

Electrochemical behavior of FeCoNiAl0.75Cr1.25 high-entropy alloy in Na2SO4 solution with acidic pH