KCl Solution Research Articles

Divalent cation contributions to the co-transport and deposition of functionalized multi-walled carbon nanotubes in porous media in the presence of bentonite or goethite nanoparticles: Experiment and simulation

This work investigates the influence of cation type (Ca2+ as compared to K+) on the co-transport and deposition of functionalized multi-walled carbon nanotubes (MWCNTs) with negatively (bentonite nanoparticles, BNPs) or positively (goethite nanoparticles, GNPs) charged natural nanoparticles under the same ionic strength (IS = 1 mM) conditions. In packed column tests with quartz sand (QS), the co-transport of MWCNTs was slightly increased by BNPs and inhibited by GNPs in both CaCl2 and KCl solutions, whereas the co-transport of BNPs or GNPs was facilitated by MWCNTs in both solutions. However, the co-transport of MWCNTs in the presence of BNPs or GNPs exhibited a different dependency on the cation type in quartz crystal microbalance with dissipation (QCM-D) tests. No deposition of MWCNTs and BNPs was observed in QCM-D studies in the presence of KCl, while enhanced deposition of MWCNTs and GNPs occurred in this same solution. In contrast, the deposition of both MWCNTs and BNPs or MWCNTs and GNPs increased in QCM-D in the presence of CaCl2. In both column and QCM-D studies, Ca2+ exhibited a more significant impact on co-transport than K+, especially for MWCNTs with GNPs than BNPs. Results from molecular dynamic simulations, aggregation studies, and interaction energy calculations indicate that non-DLVO interactions (e.g., H-bonding and cation-π interaction) between two nanoparticles (MWCNTs with BNPs or GNPs) played a non-negligible role in interpreting the deposition and co-transport in the presence of the divalent cation Ca2+. Mathematical modeling of breakthrough curves and retention profiles and aggregation results suggest that both straining and competitive blocking were enhanced and played dominant roles in the co-transport of MWCNTs in the presence of BNPs or GNPs in QS, especially in the presence of Ca2+. This work sheds novel insights on the contribution of divalent cations to interactions between two colloids and their co-transport in porous media. This information is needed to assess the environmental fate and risks of engineered nanoparticles (ENPs) and natural nanoparticles in aquatic and soil environments with abundant divalent cations.

Analytical treatment of ion-exchange permselectivity and transport number measurements for high accuracy

We analyse electromotive force measurements of concentration cells using non-equilibrium thermodynamics, and determine the transference coefficients of ion-exchange membranes in aqueous KCl solutions. By taking advantage of the analytical expression for the permselectivity, we extract transport coefficients with high accuracy. The transport number of K+ and the transference coefficient of water in the Selemion CMVN cation-exchange membrane are found to be 100tK+=99.59±0.56 and tw=3.69±0.40 respectively, while for the Selemion AMVN anion-exchange membrane they are 100tCl−=100.21±0.37 and tw=−3.75±0.27. These results suggest that the membranes are perfectly selective to the target ion, and that each ion carries 3-4 water molecules through the membrane, which reduces the membrane permselectivity. In these concentration cells, the electrical potential contribution of the membrane alone was more easily isolated with bare Ag/AgCl electrodes without reference solutions and liquid junction plugs. Additionally, we find a large contribution to the measured concentration cell voltage from concentration gradients across the porous plug of the reference electrode, which cannot be explained by Henderson’s equation alone. For most of the concentration range, the transport number of the porous plug is determined to be 100tK+=49.43±0.78 with negligible water transport, similar to literature values for bulk electrolyte. In dilute electrolyte solutions with concentrations below 0.1 mol kg−1, the plug shows anomalous behaviour consistent with an increase in K+ selectivity and water co-transport.

Multielectrode Arrays at Wafer-Level for Miniaturized Sensors Applications: Electrochemical Growth of Ag/AgCl Reference Electrodes

In this study, a range of miniaturized Ag/AgCl reference electrodes with various layouts were successfully fabricated on wafer-level silicon-based substrates with metallic intermediate layers by precisely controlling the electrochemical deposition of Ag, followed by electrochemical chlorination of the deposited Ag layer. The structure, as well as the chemical composition of the electrode, were characterized with SEM & EDS. The results showed that the chlorination is very sensitive to the applied electric field and background solution. Potentiostatic chlorination, in combination with an adjusted mushroom-shaped Ag sealing deposition, enabled the formation of electrochemical usable Ag/AgCl layers. The stability of the electrodes was tested using open circuit potential (OCP) measurement. The results showed that the reference electrodes stayed stable for 300 s under 3 M KCl solution. The first stage study showed that the stability of the Ag/AgCl reference electrode in a chip highly depends on chip size design, chlorination conditions, and a further protection layer.

Effect of K+ Concentration on the Direct pH Measurement of Peat Matrix by Sb Electrode pH Sensor and Compensation Methods

pH of the substrate for soilless cultures is crucial information. As comparison to laboratory analysis, direct pH measurement with an all-solid-state pH sensor is quicker, more cost-effective, and more accurate. There are a variety of impacting factors and measuring inaccuracies, though. Peat was utilized as the test item in order to examine the variables and regulations affecting the measurement error and minimize it. Using KCl solution, substrate specimens with various mass water contents (MWC) and K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> concentrations (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K+</sub> ) were created. Using an alumina substrate, a Sb working electrode and an Ag/AgCl reference electrode were created to form an all-solid-state pH sensor. On the basis of the direct pH measurements of peat substrate, it was used to investigate the error patterns of MWC and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K+</sub> . A statistical examination of the measured pH values revealed that MWC and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K+</sub> clearly affected the pH of the peat’s direct measurement error. The greatest inaccuracy is 0.98 pH units when C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K+</sub> is 0 M and MWC is 0.2, and it progressively declines as MWC is increased. The inaccuracy is 0.39 pH units when C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K+</sub> is 0.1 M. From 0 to 0.1 M, the measurement error falls linearly as C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K+</sub> is increased. A double compensation model of MWC and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K+</sub> was constructed using statistical analysis, and after compensation, the maximum error of the pH of peat substrate was decreased from 1.05 to 0.41. For the purpose of furthering the development of an all-solid-state pH sensor in practice, the work offers a theoretical and experimental foundation.

Experimental Study on the Effects of Applied Electric Field on Liquid Infiltration into Hydrophobic Zeolite

A nanofluidic energy absorption system (NEAS) is composed of nanoporous material and functional liquid with high energy absorption density. Applying an electric field to adjust the energy absorption characteristics of a nanofluidic system will open broader prospects for its application. In the current work, ZSM-5 zeolite was adopted as the nanoporous material and water, a 25% KCl solution, and a saturated KCl solution were adopted as functional liquids to configure NEASs. Pressure-induced infiltration experiments were carried out to study the infiltration and defiltration characteristics of the NEASs under the action of an applied electric field. The results show that the introduction of an applied electric field can weaken the hydrogen bonds between molecules, thus reducing the equivalent surface tension and contact angle, changing the infiltrability of liquid molecules into the nanopores, and reducing the infiltration pressure of the system. In an electrolyte solution/zeolite system, the anions and cations move close to the two plate electrodes under the action of an external electric field, and the fluid properties in the central zone of the pressure chamber are close to the water/zeolite system. For both an ultra-low conductivity liquid and an electrolyte solution/zeolite system, applying an electric field can effectively improve the relative outflow rate of liquid, thus improving the reusability of the system.

Separation of Palladium from Alkaline Cyanide Solutions through Microemulsion Extraction Using Imidazolium Ionic Liquids.

In this paper, three imidazolium-based ionic liquids, viz., 1-butyl-3-undecyl imidazolium bromide ([BUIm]Br), 1-butyl-3-octyl imidazolium bromide ([BOIm]Br), and 1-butyl-3-hexadecyl imidazolium bromide ([BCIm]Br), were synthesized. Three novel microemulsions systems were constructed and then were used to recover Pd (II) from cyanide media. Key extraction parameters such as the concentration of ionic liquids (ILs), equilibration time, phase ratio (RA/O), and pH were evaluated. The [BUIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion system exhibited a higher extraction percentage of Pd (II) than the [BOIm]Br/n-heptane/n-pentanol/sodium chloride and [BCIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion systems. Under the optimal conditions (equilibrium time of 10 min and pH 10), the extraction percentages of these metals were all higher than 98.5% when using the [BUIm]Br/n-heptane/n-pentanol/sodium chloride microemulsion system. Pd(CN)42- was separated through a two-step stripping procedure, in which Fe (III) and Co (III) were first separated using KCl solution, then Pd(CN)42- was stripped using KSCN solution (separation factors of Pd from Fe and Co exceeded 103). After five extraction-recovery experiments, the recovery of Pd (II) through the microemulsion system remained over 90%. The Pd (II) extraction mechanism of the ionic liquid [BUIm]Br was determined to occur via anion exchange, as shown by spectral analysis (UV, FTIR), Job's method, and DFT calculations. The proposed process has potential applications for the comprehensive treatment of cyanide metallurgical wastewater.

Electrochemically-stimulated nanoscale mechanochemical wear of silicon

AbstractMechanochemical reactions at the sliding interface between a single-crystalline silicon (Si) wafer and a silica (SiO2) microsphere were studied in three environmental conditions: humid air, potassium chloride (KCl) solution, and KCl solution with an applied voltage. Compared to that from humid air, mechanochemical material removal from the silicon surface increased substantially in the KCl-immersed condition, and further increased when electrochemistry was introduced into the tribological system. By measuring the load dependence of the material removal rate and analyzing the results using a mechanically assisted Arrhenius-type kinetic model, the activation energy (Ea) and the mechanical energy (Em), by which this energy is reduced by mechanical activation, were compared qualitatively under different environmental conditions. In the KCl-immersed condition, mechanochemistry may decrease the required effective energy of reactions (Eeff = Ea − Em) and promote material removal mainly through improved catalysis of the mechanochemical reactions facilitated by greater availability of water molecules compared to the humid air condition. Thus, the effectiveness of the mechanochemistry is improved. In the electrochemical condition, electrochemically-accelerated oxidation of the silicon surface was confirmed by the X-ray photoelectron spectroscopy (XPS) characterization. The results strongly suggest that electrochemistry further stimulates mechanochemical reactions primarily by increasing the initial energy state of the surface via the facilitated formation of interfacial bonding bridges, i.e., a surface oxidation/hydroxylation process.

Determination of the error of measurements obtained by the optical micrometry

We present the results of measuring the volume of polyvinyl alcohol polymer granules crosslinked with epichlorohydrin in water and in aqueous solutions of KCl, MgCl2 and their mixtures, obtained by optical micrometry, and consider the main sources of errors in the measurement errors. The purpose of this study is to analyze and evaluate the effect of the main sources of errors on the accuracy of determining the relative volumes of granules, as well as to search for techniques that can minimize the resulting measurement errors. The diameters of the granules were determined using specialized software implementing machine vision algorithms from the images obtained by optical microscopy. Their volumes were calculated using the formula for the volume of the ellipsoid of revolution. The maximum accuracy of volume determination is known to be achieved when the measured granule has a sphere shape. It is shown that deviation from this shape, for example, in case of an ellipsoid, gives errors in determining the third axis of the ellipsoid, invisible in the image, which creates an error in determining the relative volume of the granule. The instrument error is determined and a statistical estimate of the error attributed to the non-sphericity of the granules is given. It is shown that a typical instrument error in determining the relative volumes of granules is 0.4%. The non-sphericity of the measured granules increases the measurement error up to 3.5%. The error for a single granule can be reduced to 2.3% by combination of methodological techniques and statistical processing of the results, whereas and for an ensemble of at least 5 granules — up to 1.5%. The reproducibility of the properties of polymer granules in cyclic measurements was studied. It is shown that the degree of swelling the granules is reproduced with an error of 1%, which allows the sensor to be used repeatedly. The results obtained can be used in experiments and data processing for analytical applications.

Thermodynamic Modeling of Methane Hydrate Phase Equilibria in Chloride and Bromide Solutions

The formation of hydrates is a major issue in the oil and gas industry. Injection of electrolytes is considered one of the best ways to prevent its formation. A thermodynamic model is developed from the Klauda and Sandler model, PRSV EoS, and Pitzer’s correlation to study the phase equilibria of methane hydrate in chloride and bromide electrolyte solutions. The model employs the parameters reported by Pitzer and Mayorga to calculate the Debye–Huckel coefficient and the second and third virial coefficients at 25 °C. The %AAD in predicted equilibrium pressures from experiments is 3.70 when the hydrate formed in NaCl, KCl, MgCl2, and CaCl2 solutions, whereas it is 2.33 in NaBr, KBr, MgBr2, CaBr2, and ZnBr2 solutions. The inhibition effect of any electrolyte on methane hydrate formation at 1 wt % is small, slowly increases at 3 wt %, and then pronounces at 5, 10, and 15 wt %. The cage occupancies have been found to increase and the activity of water has been found to decrease with the increase in electrolytes concentration. The freezing point depression of water in the presence of the strongest inhibitor MgCl2 has been observed to be −12.82 °C, whereas in the presence of the weakest inhibitor ZnBr2 it is −4.22 °C, both at 15 wt % concentration. Based on the phase equilibrium results and the freezing point depression of water, the order of the methane hydrate inhibition effect among all of the electrolytes studied here is MgCl2 > NaCl > CaCl2 > KCl > NaBr > ZnCl2 > MgBr2 > KBr > CaBr2 > ZnBr2.

Electrospraying deposition and characterization of potassium chloride targets for nuclear science measurements

Natural and isotopically enriched KCl targets were prepared using specially formulated KCl solutions, deposited by electrospraying on thin (1.5μm) gold backings, followed by a short annealing in a preheated (350–450 °C) furnace. Various techniques, such as X-ray fluorescence (XRF), scanning electron microscopy (SEM) imaging, and energy-dispersive X-ray spectroscopy (EDS), were used to characterize the produced targets. A white neutron beam at the Los Alamos Neutron Science Center (LANSCE) facility was also used to verify the estimated atomic percentages of the enriched 40KCl targets. KCl was deposited relatively uniformly as large particles rather than films on the gold surface. This method can be broadly extended to make stable targets that are difficult to produce with other methods and more exotic radioactive targets required for research in fundamental sciences and applications.

Estimation of the swelling strain and swelling pressure of compacted bentonite using electrical conductivity

Estimation of the swelling strain or swelling pressure is important for predicting the behavior of compacted bentonite barriers. In this study, the electrical conductivity of compacted bentonite was measured under free-swell and confined conditions to investigate the predictability of swelling strain or swelling pressure from the measured electrical conductivity. The evolution of electrical conductivity by water penetration was qualitatively consistent with that of swelling strain or swelling pressure, implying that monitoring electrical conductivity could be used to detect the initiation and termination of swelling process or any internal changes in compacted bentonite. The relationships between normalized swelling strain and normalized electrical conductivity, and between normalized swelling pressure and normalized electrical conductivity were developed based on the results of Ca-bentonite hydrated with NaCl solution, and those were verified using the results of Ca-bentonite hydrated with KCl and CaCl2 solutions, and Na-bentonite hydrated with NaCl solution. Finally, the limitations and possibilities of using electrical conductivity in estimating swelling parameters and monitoring swelling process were discussed in this study.

Environmental factors strongly influence the leaching of di(2-ethylhexyl) phthalate from polyvinyl chloride microplastics

Phthalic acid esters (phthalates) are an important group of additives (plasticizers) to ensure the flexibility and stability especially of polyvinyl chloride (PVC) and to enable its processing. However, phthalates like di(2-ethylhexyl) phthalate (DEHP) are harmful for aquatic organisms due to their endocrine disrupting effects and toxicity. For the assessment of exposure concentrations, thorough understanding of leaching kinetics of phthalates from PVC (micro-) plastics into aqueous environments is necessary. This study investigates how environmental factors influence the leaching of phthalates from PVC microplastics into aquatic systems. The leaching of phthalates from PVC microplastics into aqueous media is limited by aqueous boundary layer diffusion (ABLD) and thus, process-specific parameters can be affected by environmental factors such as salinity and the flow conditions. We conducted batch leaching experiments to assess the influence of salinity and flow conditions (turbulence) on the leaching of DEHP from PVC microplastics into aqueous media. DEHP is salted out with increasing salinity of the solution and a salting-out coefficient for DEHP of 0.46 was determined. The partitioning coefficient of DEHP between PVC and water KPVC/W increased with increasing salinity from 108.52 L kg−1 in a 1 mM KCl solution to 108.75 L kg−1 in artificial seawater thereby slowing down leaching. Increasing flow velocities led to higher leaching rates because the ABL thickness decreased from 1315 µm at 0 rpm shaking speed (no-flow conditions) to 38.4 µm at 125 rpm (turbulent conditions). Compared to salinity, turbulence had a more pronounced effect on leaching. Increasing the flow velocity led to a 35-fold decrease in the leaching rate, while increasing salinity led to a 2-fold increase. By calculating specific leaching times, that is, leaching half-lives (t1/2), time frames for leaching in different aquatic systems such as rivers and the ocean were determined. Given ABLD-limited leaching, DEHP is leached faster from PVC microplastics in rivers (t1/2 > 49 years) than in the ocean (t1/2 > 398 years). In both systems, PVC microplastics are a long-term source of phthalates.

Melamine-Based Nanocomposites for Selective Dopamine and Uric Acid Sensing

The formation process of carbon dots (CDs) is mostly polymerization; recently, studies on the polymerization of carbon families (graphene oxide and C60) have been receiving exciting attention. Herein, a protocol of prepolymerization and electropolymerization of monomer (melamine) and nanomonomer (CDs fixed melamine residues) was proposed to prepare a nanocomposite for selective dopamine (DA) and uric acid (UA) sensing. The nanomonomer was prepared by hydrothermal prepolymerization of melamine, and then the nanocomposite was formed in situ by electropolymerization of the CDs/carboxylated multiwalled carbon nanotubes (MWCNTs-COOH)-modified glassy carbon electrode (GCE) in KCl solution. Scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry were used to characterize the properties of the nanocomposite. Under optimal conditions, the electrochemical sensor shows selectivity and a wide linear range from 0.1 to 10 μM for DA and 0.1 to 200 μM for UA, with the detection limit of 0.023 and 0.064 μM (S/N = 3) in the presence of AA, respectively. In addition, the proposed sensor was also applied to selectively test DA and UA in the presence of 500 μmol/L AA in real samples with satisfactory recovery.

Graphene Nanopores Enhance Water Evaporation from Salt Solutions: Exploring the Effects of Ions and Concentration.

With increased water stress, the development of clean water technologies is an active area of research. Evaporation-based solutions offer the advantage of low energy consumption, and recently a 10-30 fold enhancement in water evaporation flux has been observed through Å-scale graphene nanopores (Lee, W.-C., et al., ACS Nano 2022, 16(9), 15382). Herein, using molecular dynamics simulations, we examine the suitability of Å-scale graphene nanopores in enhancing water evaporation from salt solutions (LiCl, NaCl, and KCl). Cation-π interactions between ions and the surface of nanoporous graphene are found to significantly influence ion populations in the nanopore vicinity, leading to varied water evaporation fluxes from different salt solutions. The highest water evaporation flux was observed for KCl solutions, followed by NaCl and LiCl solutions, with the differences reducing at lower concentrations. Relative to the bare liquid-vapor interface, 4.54 Å nanopores exhibit the highest evaporation flux enhancements ranging from 7 to 11, with an enhancement of 10.8 obtained for 0.6 M NaCl solution, which closely resembles seawater compositions. Functionalized nanopores induce short-lived water-water hydrogen bonds and reduce surface tension at the liquid-vapor interface, thereby lowering the free energy barrier for water evaporation with a negligible effect on the ion hydration dynamics. These findings can aid in developing green technologies for desalination and separation processes with low thermal energy input.

Defect-rich hierarchical porous carbon prepared by homogeneous activation for high performance capacitive deionization

Defect engineering has emerged as an effective approach for modulating the electronic structure and physicochemical properties of carbon materials. Porous carbon materials with abundant defects are regarded as prospective electrode materials for capacitive deionization. Nevertheless, constructing defect-rich carbon materials and revealing the relationship between desalination capacity and intrinsic defects remains a daunting challenge. Herein, the defect-rich interconnected hierarchical porous carbon (IHPC) was fabricated via sol-gel method to form a supramolecular hydrogel containing highly dispersed K+ using coal, polyvinylpyrrolidone, and KOH as raw materials, followed by homogeneous activation. The spectroscopic studies coupled with density functional theory calculations demonstrate that the introduction of intrinsic defects can optimize the distribution of electron density to promote charge transfer, thereby enhancing saline ions adsorption. The plentiful adsorption sites, robust charge transfer kinetics and rapid ion diffusion derived from the multiple advantageous characteristics of IHPC facilitate a high desalination capacity of 31.25 mg g−1 in 800 mg L−1 NaCl solution. Meanwhile, it also presented excellent desalination performances in KCl (31.42 mg g−1), CaCl2 (29.55 mg g−1), and MgCl2 (26.65 mg g−1) solutions. The higher desalination capacity, rapid salt adsorption rate as well as outstanding cycling stability rank the IHPC as a potential candidate for capacitive deionization applications.

Adsorption characteristics, isotherm, kinetics, and diffusion of nanoemulsion in tight sandstone reservoir

Nowadays, nanoemulsions have shown a high application potential in improving hydrocarbon recovery from tight reservoirs. However, the adsorption characteristics, isotherms, kinetics of nanoemulsions onto reservoir rocks surface and the diffusion behavior into reservoir matrix are still not been systematically clarified. In this work, nanoemulsion was prepared by diluted microemulsion method using two nonionic surfactants, isopropanol, limonene and 2.0 wt% KCl solution. The static adsorption capacity measurement under different influencing factors were carried out, and the adsorption process was characterized through equilibrium isotherms and kinetic studies. Also, the diffusion behavior of nanoemulsion in the sandstone reservoir matrix were evaluated by core flooding experiments. Results indicated that the nanoemulsion was successfully synthesized and the droplet size mainly distributed between 8 and 18 nm. It had been found that the optimal static adsorption experimental parameters for 0.1 wt% nanoemulsion were 1:8 solid–liquid ratio and 50/60 mesh rock powder. Equilibrium adsorption results indicated that Langmuir model yielded a better fit which means that single-layer coverage of the surfactants composed of nanoemulsion onto the rock surfaces was more probable. Meanwhile, it was concluded that the pseudo-second order model could better describe the kinetic behavior of nanoemulsion adsorption onto the rock surfaces, which revealed that the adsorption rate was positively correlated with the nanoemulsion concentration. Dynamic adsorption experiments showed that the adsorption amount is inversely proportional to the core permeability, while the diffusion coefficient increases with the increase of permeability. Moreover, the advantage of nanoemulsions over sole surfactant is that the oil nucleus in the nanoemulsions enable control the release of the attached surfactants, and there is a competitive adsorption relationship between oil nucleus and rock surface for the free surfactants in the solution, which offers a possibility for reducing the surfactant adsorption loss and extending the invasion distance in the reservoir matrix. The findings obtained in this study can help for better understanding of the interaction mechanism between nanoemulsions and reservoir rocks, and provide guidance for selecting appropriate nanoemulsions for the enhanced oil recovery (EOR) project in tight sandstone reservoirs.

Achieving exceptionally high strength and rapid degradation rate of Mg-Er-Ni alloy by strengthening with lamellar γ′ and bulk LPSO phases

As-extruded Mg-Er-Ni alloys with different volume fractions of long-period stacking ordered (LPSO) phase and density of lamellar γ′ phase were prepared, and the microstructure, mechanical, and degradation properties were investigated. Coupling the bulk LPSO phase and the lamellar γ′ phase, and controlling the dynamic recrystallization processes during deformation by adjusting the volume fraction of LPSO and the density of the γ′ phase, a synergistic increase in strength and degradation rate can be achieved. On the one hand, the increase in corrosion rate was related to the increased volume fraction of the bulk LPSO phase and the densities of the lamellar γ′ phase, which provide more galvanic corrosion. Moreover, high densities of the lamellar γ′ phase can provide more corrosion interface by inhibiting the recrystallization process to refine dynamic recrystallized (DRXed) grains during the hot extrusion. On the other hand, the ultimate tensile strength (UTS) and tensile yield strength (TYS) of the Mg-Er-Ni alloy increased from 345 and 265 MPa to 514 MPa and 358 MPa, respectively, which was mainly attributed to grain boundary and texture strengthening, bulk LPSO phase and lamellar γ′ phase strengthening. Overall, Mg-14Er-4Ni alloy, which contains the highest volume fraction bulk LPSO phase and the densities of lamellar γ′ phase, realized a synergistic enhancement of strength and degradation rate. The UTS, TYS, and degradation rate of Mg-14Er-4Ni were 514 MPa, 358 MPa, and 142.5 mg cm–2 h–1 (3 wt% KCl solution at 93 ℃), respectively. This research provides new insight into developing Mg alloys with high strength and degradation rates for fracturing tool materials in the application of oil and gas exploitation in harsh environments.

The microstructure, mechanical behaviour, and dissolvability of novel Al-Cu-Zn-Mg-based alloys

ABSTRACT The use of dissolvable alloys (DAs) in hydraulic fracturing is increasing, particularly in low-permeability reservoirs. However, existing DAs based on Al or Mg alloys have limited mechanical properties despite their desirable dissolvability. This studyaims to explore new Al-based DAs with good dissolvability and mechanical strength. Four Al-Zn-Cu-Mg based alloys with various additional elements (Ag, Ga, In, Sn, Zr, Ti, V, and Cr) were prepared using the melting and casting technique. The microstructures of DAs were analysed using X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy. Immersion corrosion tests were conducted to evaluate the dissolvability of DAs at 90°C in KCl solutions. Hardness and tensile testing were performed to assess the mechanical properties of the alloys. The resulting phases in the as-cast microstructure included η-MgZn2, Mg2Sn, θ-Al2Cu, Al3Zr, and Al45Cr7, as predicted using the Calphad method. There was a trade-off observed between dissolvability and mechanical properties, with the alloys containing low melting point intermetallic phases exhibiting greater dissolvability but reduced mechanical strength. DA18 withthe highest Ga, In, and Sn (GIS) content, showed intense corrosion but had the lowest mechanical properties. The presence of In-containing phases was identified as the primary cause of Al degradation, while coarse phases reduced the alloy's strength. Overall, all DAs were reported to be brittle with limited elongation.

Synthesis of Bi-Pr-O Composite Nanoflakes with Good Electrochemical Performance

Bi-Pr-O composite nanoflakes were synthesized with the aid of polyvinyl pyrrolidone (PVP) as the surfactant. The characterization of Bi-Pr-O composite nanoflakes was performed by X-ray diffraction and electron microscopy. The prepared nanoflakes consisted of tetragonal Bi2O3, hexagonal Pr2O3, and hexagonal Bi0.4Pr0.6O1.5 with smooth surface. The size of whole nanoflakes is less than 1 μm and thickness is less than 100 nm. The formation of the Bi-Pr-O composite nanoflakes can be explained by a PVP-assisted growth mechanism. A systematic study of electrochemical catalysis of L-cysteine using a Bi-Pr-O-composite-nanoflake-modified electrode was carried out. A pair of quasi-reversible anodic and cathodic peaks are observed at −0.69 and +0.02 V, respectively, on the Bi-Pr-O-composite-nanoflake-modified electrode in 2 mM L-cysteine and 0.1 M KCl solution. The current response of the Bi-Pr-O-composite-nanoflake-modified electrode is proportional to the L-cysteine concentration in the range of 0.001—2 mM with a detection limit of 0.33 μM. In addition, the Bi-Pr-O composite nanoflakes display satisfactory reproducibility and stability for the detection of L-cysteine.

Development and characterization of a clay-HDTMABr composite for the removal of Cr(VI) from aqueous solutions with special emphasis on the electrochemical interface

This research aims to study the removal of chromium in its toxic form, Cr (VI), from wastewater, using clay and modified clay with Hexadecyltrimethyl ammonium bromide (HDTMABr)as adsorbents. The modified clay is obtained by impregnating a known quantity of HDTMABr into the clay. The two materials were characterized by different techniques, such as X-ray diffraction, which is used to determine the inorganic composition and the phyllite structures it contains. Thermal analysis TGA isused to understand the thermal behavior as function of the sintering temperature. Nitrogen adsorption/desorption is used to get the pores' size and surface area, using the Brunauer-Emmett-Teller (BET) theory. Scanning electron microscopy (SEM) coupled with Energy Dispersive X-ray Spectroscopy (SEM/EDAX) is used to study the surface morphology of the bare clay and the HDTMABr/clay. The operating conditions, such as contact times, pH, and adsorption temperatures, were studied, and optimized to improve the efficiency of the adsorption process. The adsorption is favored in acidic medium and room temperature, giving adsorption capacities for Cr(VI) of 12 mg/g and 250 mg/g for the clay and clay/HDTMABr, respectively. The reaction kinetics were studied and found to fit a pseudo-second-order model. The standard entropy (ΔS°), enthalpy (ΔH°), and Gibbs free energy (ΔG°) changes indicate that the chromium (VI) adsorption process is a physical, spontaneous, endothermic process. Cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS) are used for the electrochemical characterization of the raw clay and clay/HDTMABr in [Fe(CN)6]3-/4-/ 0.1 M KCl solution. The linear scan anodic stripping voltammetry (LSASV) is used for the reduction the Cr(VI) to Cr(III), indicating that Cr(VI) accumulates better at the surface of clay/HDTMABr compared to the bare graphite and the raw clay.