Partition Coefficients Of Solutes Research Articles

A computational study of solidification kinetics in multicomponent alloys

Recent advances in materials processing technologies highlight the need to understand solidification kinetics in multicomponent alloys. Using a finite interface dissipation phase field model, we investigate planar front solidification rates in ternary alloys, used as a model system, as a function of various mass transport processes and nonequilibrium conditions. Simulation results reveal that the off-diagonal diffusion coefficients play an important role in controlling the solid–liquid (S–L) interface velocity and solute partition coefficients. Specifically, under various rapid solidification conditions negative values for the off-diagonal diffusion coefficients increase the solute partition coefficients due to the depletion of liquid phase concentrations ahead of the S–L interface. Given an undercooling, the S–L interface velocity increases with decreasing the off-diagonal diffusion coefficients. In broad terms, our work quantifies the role of coupled mass transport processes and nonequilibrium effects in solidification rates of multicomponent alloys.

Purification of High-Purity Tin via Vertical Zone Refining

The present investigation delves into the potential of vertical zone refining as an effective purification technique for achieving high-purity tin (Sn) metal. The utilization of vertical zone refining offers distinct advantages over traditional horizontal zone refining, as it allows for enhanced control over the molten zone and solid–liquid interface, ultimately leading to superior impurity separation efficiency. The present study reveals that the solute partition coefficients (k0) of various impurity elements, such as Zn, Ag, Al, Mg, Ca, Ni, In, Co, Cu, As, Pb, Fe, and Bi, during the vertical zone refining process consistently demonstrate values below one. Notably, the partition coefficient of Sb deviates slightly from the others, being greater than one but approaching one. The authors achieve exceptional levels of purity in both the bottom and middle regions of the rod by subjecting the Sn melt to nine passes of vertical zone refining at a heating temperature of 405 °C and a downward pulling rate of 10 µm/s, resulting in purities exceeding 6N4. Furthermore, by evaluating the effective partition coefficients (keff), it was determined that impurity elements, such as Cu and Bi, closely approach their equilibrium partition coefficients, reaching values of approximately 0.492 and 0.327, respectively. To further enhance the purity of Sn metal and maximize product yield, we propose the utilization of electrolytic refining and vacuum distillation, with particular emphasis on the efficient separation of five specific elements, including Cu, Fe, As, Pb, and Sb. By elucidating these findings, this study not only contributes valuable insights into the efficacy of vertical zone refining as a purification technique for high-purity tin metal, but also offers important recommendations for refining strategies and impurity element separation.

Infinite Dilution Activity Coefficients and Gas–Liquid Partition Coefficients of Organic Compounds in Ionic Liquid 1-Butyl-2,3-dimethylimidazolium Thiocyanate: Measurements and LFER Calculations

Infinite dilution activity coefficients (γi∞) of 31 organic solutes (alkanes, cycloalkanes, olefins, aromatics, chlorinated alkanes, alcohols, and other polar organic solutes) in the ionic liquid (IL) 1-butyl-2,3-dimethylimidazole thiocyanate ([BMMIM][SCN]) were determined by gas–liquid chromatographic (GLC) method in the temperature range of 313.15–353.15 K. The infinite dilution partial molar excess enthalpies (H̅iE, ∞), entropies (TrefS̅iE, ∞), and Gibbs free energies (G̅iE, ∞) of the organic solutes at the reference temperature T = 298.15 K and the solubility parameters (δ3) of [BMMIM][SCN] were derived from γi∞. The gas–liquid partition coefficients (KL) of solutes at different temperatures were calculated by referring to the densities of [BMMIM][SCN]. The linear free energy relationship solvation model was used to fit the KL values, and the KL prediction model was obtained. The selectivity (Sij∞) and capacity (kj∞) of n-hexane (i)/benzene (j) and cyclohexane (i)/benzene (j) at infinite dilution at 323.15 K were calculated. The results were compared with the values of ILs with the thiocyanate anion in the literature.

Toward multiscale simulations for solidification microstructure and microsegregation for selective laser melting of nickel-based superalloys

In this study, we carried out multiscale simulations that integrate a macro-scale finite element method simulation for mass and heat transfer of the transient molten pool and a micro-scale quantitative phase-field model for dendritic growth and solute distribution based on selective laser melting (SLM) experiments. Macroscopic simulations reveal an approximately inverse coupling of solidification velocity Vs and thermal gradient G near the solid–liquid interface at the tail end of the molten pool. It was found that the maximum flow velocity of the Inconel 718 alloy melt in the molten pool exceeds 2×10−2 m/s and the maximum negative pressure reaches −5.28×10−4 Pa. Through quantitative phase-field simulations, the map about G/Vs for each solidification morphology was obtained, and it was found that solidification velocity dependent solute partition coefficients k(Vs) can strongly influence the estimated stability regions. The power law relationship of the primary dendritic arm spacing (PDAS) λ1 versus solidification velocity λ1∝Vsα agrees with the previous experimental results for lower G, and the exponent α decreases with increasing G. The PDAS λ1 versus cooling rate R following λ1∝R−0.512 is consistent with previous investigations. We found that λ1 is a nonlinear function with G−0.5Vs−0.25, i.e., λ1∝(G−0.5Vs−0.25)α, with α ranging from 0.887 to 2.466 for various G. Comparison of the predicted λ1 with Trivedi's model reveals that λ1 is still nonlinear with G−0.25Vs−0.25.

Alloy solidification: Assessment and improvement of an easy-to-apply model

• The Gong-Chen model requires no experimental parameters and is easy to apply. • It can be used as a generic solidification model up to the solid fraction (fs) of 0.9. • When fs > 0.9, its applicability depends on both solute diffusion and partition coefficient. • The Gong-Chen model requires f s Lever > 1, which has been examined and justified. • The Won-Thomas model provides the most practical predictions but requires experimental input. It has been a central task of solidification research to predict solute microsegregation. Apart from the Lever rule and the Scheil-Gulliver equation, which concern two extreme cases, a long list of microsegregation models has been proposed. However, the use of these models often requires essential experimental input information, e.g. , the secondary dendrite arm spacing ( λ ), cooling rate ( T ˙ ) or actual solidification range ( Δ T ). This requirement disables these models for alloy solidification with no measured values for λ, T ˙ and Δ T . Furthermore, not all of these required experimental data are easily obtainable. It is therefore highly desirable to have an easy-to-apply predictive model that is independent of experimental input, akin to the Lever rule or Scheil-Gulliver model. Gong, Chen, and co-workers have recently proposed such a model, referred to as the Gong-Chen model, by averaging the solid fractions ( f s ) of the Lever rule and Scheil-Gulliver model as the actual solid fraction. We provide a systematic assessment of this model versus established solidification microsegregation models and address a latent deficiency of the model, i.e., it allows the Lever rule solid fraction f s to be greater than one ( f s > 1). It is shown that the Gong-Chen model can serve as a generic model for alloy solidification until f s reaches about 0.9, beyond which ( f s > 0.9) its applicability is dictated by both the equilibrium solute partition coefficient ( k ) and the solute diffusion coefficient in the solid ( D s ), which has been tabulated in detail.

Research on solidification behavior of a high Mn steel during continuous casting based on solidification characteristic unit analysis

A novel research route combining numerical simulation and physical simulation was used to study the solidification behavior of high Mn steel continuous casting billet under different superheats in this work. The results indicated that higher super heat degree will lead to lower equiaxed crystals content and severer element segregation. Moreover, the Mn element segregation was lighter than that of the C element, and it was caused by the higher value of solute partition coefficient of Mn. Finally, the superheat degree suitable for continuous casting of high Mn steel was modified to be 10 ℃.

Unveiling the Potential of Innovative Gold(I) and Silver(I) Selenourea Complexes as Anticancer Agents Targeting TrxR and Cellular Redox Homeostasis.

A series of NHC-based selenourea Ag(I) and Au(I) complexes were evaluated for their anticancer potential in vitro, on 2D and 3D human cancer cell systems. All NHC-based selenourea complexes possess an outstanding cytotoxic potency, which was comparable or even better than that of the reference metallodrug auranofin, and were also able to overcome both platinum-based and multi-drug resistances. Intriguingly, their cytotoxic potency did not correlate with solution stability, partition coefficient or cellular uptake. On the other hand, mechanistic studies in cancer cells revealed their ability to strongly and selectively inhibit the redox-regulating enzyme Thioredoxin Reductase (TrxR), being even more effective than auranofin, a well-known TrxR inhibitor, without affecting other redox enzymes such as Glutathione Reductase (GR). The inhibition of TrxR in H157 human cancer cells caused, in turn, the disruption of cellular thiol-redox homeostasis and of mitochondria pathophysiology, ultimately leading to cancer cell death through apoptosis.

Thermal, Metallurgical and Mechanical Determinants of Laminar Nickel/Aluminum Dissimilar Alloys during Laser-material Interaction Part I: Nickel-based Superalloy

To develop in-depth understanding of metallurgical phenomena for completeness, mechanical heterogeneity is kinetically and thermodynamically explained by thorough microstructure characterization of engineering materials, e.g. polycrystalline nickel-based superalloy, for alleviation of weldability-related problems during laser-induced keyhole fabrication. Because of nonequilibrium solidification behavior inside weld pool, finer γ phase dendrite substructure is confined to partition-resistant keyhole bottom part, coarser dendrite is crystallography-independently circumscribed at partition-vulnerable neck transition region of full penetration weld, and thus microstructure is lack of homogeneity. Abundance of segregation-driven eutectic phase or intermetallic phase in the interdendrite area throughout weld is essentially attributable to nonequilibrium solidification conditions, and morphologically increases susceptibility to mechanical properties deterioration. As a result of γ phase instability, Niobium-aided Laves/γ eutectic reaction in the vicinity of dendrite interstices at terminal stage of solidification contributes to severe dendrite boundaries brittleness, impairs mechanical properties, which is consistent with metallography and fractography results, and is more deleterious to weldability, since solute redistribution and supersaturation adversely exacerbate segregation behavior in the residual interdendrite liquid, especially asymmetric weld pool shape. There is inverse parabolic relationship between secondary dendrite arm spacing and solute partition coefficient, when location varies from nail-shaped weld upper site to bottom site. Chemical, microstructural and mechanical heterogeneities are more geometrically favorable in the curvature-related neck transition region. In addition, the mechanism of thermal, metallurgical and mechanical inhomogeneities, which are attributed to asymmetric weld pool shape, is consequently proposed. Untoward metallurgical phenomena, such as microstructure heterogeneity and brittle Niobium-rich Laves/γ eutectic phases mitigate strength, ductility and toughness of weld. In order to macroscopically and microscopically satisfy superior mechanical properties requirement, chemistry and microstructure of high quality weld are metallurgically controlled. Fruitful metallurgical information and mechanical data further support the reasonable explanations. It is imperative to progressively advance welding metallurgy, weldability and fabricability of intricate shape for welding defects minimization, suppress segregation and further develop mechanical properties through viable design and control of laser processing, simultaneously.

Enzymatic Synthesis and Antioxidant Activity of Mono- and Diacylated Epigallocatechin Gallate and Related By-Products.

Ester derivatives of epigallocatechin gallate (EGCG) were enzymatically prepared by one-step transesterification with vinyl fatty acids consisting of varying acyl groups ranging from 2 to 18 carbon atoms (acetate, butyrate, caproate, caprylate, caprate, laurate, myristate, and stearate). The main acylation products were EGCG monoesters and diesters. However, due to the presence of trace amounts of water in the reaction medium, minor but noticeable hydrolysis of EGCG also occurred as a side reaction which required a prolonged purification process due to the formation of by-products such as gallic acid, epigallocatechin, and their esters. In this contribution, 8 EGCG monoesters, 7 EGCG diesters, and 7 gallic acid monoesters were isolated and purified, and the acylation positions were characterized. Meanwhile, several classical chemicals (DPPH, ABTS, FRAP, and Fe2+ chelation assays), food (β-carotene bleaching assay), and biological (LDL and DNA oxidation assays) models were conducted to evaluate and systematically compare their antioxidant efficacy. The lipophilicity of the EGCG derivatives increased with the increasing chain length of the acyl group and led to the fluctuation of their antioxidant efficacies. Three main factors, namely, the reduction potential, the partition coefficient of solute in the solvent system, and the steric hindrance of antioxidant agent and related substrates were considered to help explain the biased antioxidant performance of EGCG derivatives upon acylation modification. The results strongly suggest that the acylated EGCGs have great potential as lipophilic alternatives to the water-soluble EGCG in lipid-based matrices.

Studies on π Interactions in Liquid-Phase Separations

π interactions have recently received considerable attentions due to principal factor governing molecular recognitions and self-assemble abilities, as accumulated in the database on proximate arrangements in structures of biological systems and organic functional materials. Therefore, further deep understanding and control of π interactions will greatly facilitate the development of new functional materials. Despite the importance of π interactions, they are still challenging to study because π interactions are much weaker than most other molecular interactions, such as hydrophobic interaction, hydrogen bonding, and electrostatic bonding. On the other hand, liquid chromatography (LC) is a powerful separation technique, which is able to distinguish the partition coefficients of solutes between the mobile and stationary phases, and can sensitively reflect the strength of molecular interactions. We investigated the properties of π interactions by developing new silica-monolithic capillary columns modified with carbon materials providing strong π interactions. In this focusing review, we introduce a few specific π interactions by columns modified with fullerenes and polycyclic aromatic hydrocarbons (PAHs), which showed strong π-π interactions due to spherical recognition and multiple CH-π interactions. Furthermore, π interactions can contribute to the separation of various samples, which are difficult to achieve by the available retention mechanisms. Briefly, we applied various π interactions to specific separation analyses, and we succeeded in separating halogenated compounds, H/D isotopologue pairs, and saccharides by effective π interactions. These results indicate that π interactions contribute to practical separation science, such as removal of environmental pollutants and quantitative determination of medicinal compounds.

Phase-field modeling of dendritic growth of magnesium alloys with a parallel-adaptive mesh refinement algorithm

A two-dimensional phase field (PF) model was developed to simulate the dendritic solidification in magnesium alloy with hcp crystal structure. By applying a parallel-adaptive mesh refinement (Para-AMR) algorithm, the computational efficiency of the numerical model was greatly improved. Based on the PF model, a series of simulation cases were conducted and the results showed that the anisotropy coefficient and coupling coefficient had a great influence on the dendritic morphology of magnesium alloy. The dendritic growth kinetics was determined by the undercooling and equilibrium solute partition coefficient. A significant finding is acquired that with a large undercooling, the maximum solute concentration is located on both sides of the dendrite tip in the liquid, whereas the maximum solute concentration gradient is located right ahead of the dendrite tip in the liquid. The dendrite tip growth velocity decreases with the increase of the equilibrium solute partition coefficient, while the variation trend of the dendrite tip radius is the opposite. Quantitative analysis was carried out relating to the dendritic morphology and growth kinetics, and the simulated results are consistent with the theoretical models proposed in the previously published works.

Microstructural evolution and microsegregation in directional solidification of hypoeutectic Al−Cu alloy: A comparison between experimental data and numerical results obtained via phase-field model

The objective of the work is focused on predictions of microsegregation, solidification speed, dendritic arm spacings and dendrite morphology by phase-field model. The numerical results were compared with experimental data. The experimental values for cooling rates and effective partition coefficient were adopted during calculations. The results of microsegregation through phase-field model show excellent agreement with the experimental data. Such excellent agreement is because cooling rates, effective partition coefficient and back-diffusion of solute are considered in the model. For solidification speed, the calculation results show good agreement with the experimental data. Tertiary dendritic arm spacing calculated with phase-field model is compared with experimental data. The results show good agreement between them. The dendrite arm spacing varies with position because high cooling rates are responsible for the refinement effect on microstructure. Finally, two-dimensional simulation produced a dendrite that is similar to that found in the experiment.

Alkane/Water Partition Coefficient Calculation Based on the Modified AM1 Method and Internal Hydrogen Bonding Sampling Using COSMO-RS.

We introduce a physics-based model for calculating partition coefficients of solutes between water and alkanes, using a combination of a semi-empirical method for COSMO charge density calculation and statistical sampling of internal hydrogen bonds (IHBs). We validate the model on the experimental partition data (∼3500 molecules) of small organics, drug-like molecules, and statistical assessment of modeling of proteins and ligand drugs. The model combines two novel algorithms: a bond-correction method for improving the calculation of COSMO charge density from AM1 calculations and a sampling method to deal with IHBs. From a comparison of simulated and experimental partition coefficients, we find a root-mean-square deviation of roughly one log 10 unit. From IHB analysis, we know that IHBs can be present in two states: open (in water) and closed (in apolar solvent). The difference can lead to a shift of as much as two log 10 units per IHB; not taking this effect into account can lead to substantial errors. The method takes a few minutes of calculation time on a single core, per molecule. Although this is still much slower than quantitative structure–activity relationship, it is much faster than molecular simulations and can be readily incorporated into any screening method.

A Modified Random Sampling Method Using Unidirectionally Solidified Specimen: Solute Partition Coefficients in Fe–Cr–Ni–Mo–Cu Alloys

A random sampling method using Fe-19.9 mass% Cr-24.8 mass% Ni-4.5 mass% Mo-1.5 mass% Cu alloy quenched during unidirectional solidification was applied to examine the measurement accuracy of the solute partition coefficients between the solid and liquid phases. Better agreement between the solute profiles obtained by the random sampling and Scheil’s equation was observed at appropriate regions where the solid fraction ranged from 0.9 to 1 at quenching. The partition coefficients of Cr, Ni, Mo, and Cu were determined to be 0.95, 1.01, 0.71, and 0.84, respectively. The values obtained using the present method agreed well with the values measured using the in-situ measurement method, which is recognized to be a reliable technique. The developed technique, which uses conventional equipment and techniques such as a unidirectional solidification furnace and scanning electron microscopy/energy-dispersive X-ray spectroscopy, requires less time to determine the solute partition coefficients than conventionally used techniques. Thus, the modified random sampling method presented in this study can be used for systematic measurements of solute partition coefficients.

A Novel Approach to Determine Variable Solute Partition Coefficients

Proper characterization of solute segregation during the solidification of alloys using partition coefficients (k) is essential to understand and model solidification paths and associated microstructural evolution. Traditional methods to determine k assume a constant value over the course of solidification, which leads to improper descriptions of segregation for elements with variable partitioning behavior. In this study, a novel method to determine partition coefficients as a function of fraction solid using electron probe microanalysis point grid measurements is described. The proposed method, termed the mass balance analysis (MBA), was applied to a cast 90 wt pct Co-10 wt pct Cu alloy with well-documented segregation behavior. The resultant partition coefficients indicated that kCu decreased as a function of fraction solid, while kCo significantly increased in the terminal stage of solidification. The measured k values showed excellent agreement with those taken from the solidus and liquidus lines of Co-Cu binary phase diagram generated using Thermo-Calc. The MBA was also applied to a multicomponent austenitic commercial alloy. It showed a decrease in the partition coefficients for both Cr and Nb as a function of fraction solid and demonstrated the applicability of the MBA method to highly alloyed multicomponent systems.

Optimizing the microstructures and mechanical properties of Al-Cu-based alloys with large solidification intervals by coupling travelling magnetic fields with sequential solidification

Alloys with large solidification intervals are prone to issues from the disordered growth and defect formation; accordingly, finding ways to effectively optimize the microstructure, further to improve the mechanical properties is of great importance. To this end, we couple travelling magnetic fields with sequential solidification to continuously regulate the mushy zones of Al-Cu-based alloys with large solidification intervals. Moreover, we combine experiments with simulations to comprehensively analyze the mechanisms on the optimization of microstructure and properties. Our results indicate that only downward travelling magnetic fields coupled with sequential solidification can obtain the refined and uniform microstructure, and promote the growth of matrix phase α-Al along the direction of temperature gradient. Additionally, the secondary dendrites and precipitates are reduced, while the solute partition coefficient and solute solid-solubility are raised. Ultimately, downward travelling magnetic fields can increase the ultimate tensile strength, yield strength, elongation and hardness from 196.2 MPa, 101.2 MPa, 14.5 % and 85.1 kg mm−2 without travelling magnetic fields to 224.1 MPa, 114.5 MPa, 17.1 % and 102.1 kg mm−2, and improve the ductility of alloys. However, upward travelling magnetic fields have the adverse effects on microstructural evolution, and lead to a reduction in the performance and ductility. Our findings demonstrate that long-range directional circular flows generated by travelling magnetic fields directionally alter the transformation and redistribution of solutes and temperature, which finally influences the solidification behavior and performance. Overall, our research present not only an innovative method to optimize the microstructures and mechanical properties for alloys with large solidification intervals, but also a detailed mechanism of travelling magnetic fields on this optimization during the sequential solidification.

Study on the precipitation and coarsening of TiN inclusions in Ti-microalloyed steel by a modified coupling model

A modified coupling model, considering microsegregation, precipitation and growth of inclusion, and variable solute partition coefficient (ki), was established to investigate the precipitation and coarsening of TiN inclusion for the 0.053wt% Ti-microalloyed steel. The influence of TiN inclusion on the steel impact toughness was revealed. Results show that the effect of phase composition on both the kTi and kN is greater than the effect of temperature, and the kTi and kN are in the range from 0.20 to 0.30 and from 0.28 to 0.45 during solidification, respectively. The change of the ki in different crystalline phases significantly affects the microsegregation and TiN precipitation. The TiN precipitation is promoted by segregation and the TiN starts to precipitate around 1754K (corresponding to fs=0.82) in the mushy zone. The predicted size of TiN inclusion is between 7.57 and 16.68μm at a conventional cooling rate (1–5K/s), which is consistent with the measured results in the slab. The square or triangle TiN inclusions with large size are harmful to the impact toughness. Many TiN inclusions can be found at the junction of the cleavage cracks. To control the TiN size and ensure the impact toughness, the cooling rate for the Ti-0.053wt% steel solidification should be enhanced and greater than 10K/s. Furthermore, reducing the Ti content to 0.03wt% is a more effective way to control the TiN size.

Predicting Partition Coefficients of Neutral and Charged Solutes in the Mixed SLES-Fatty Acid Micellar System.

Sodium laureth sulfate (SLES) and fatty acids are common ingredients in many cosmetic products. Understanding how neutral and charged fatty acid compounds partition between micellar and water phases is crucial to achieve the optimal design of the product formulation. In this paper, we first study the formation of mixed SLES and fatty acid micelles using molecular dynamics (MD) simulations. Micelle/water partition coefficients of neutral and charged fatty acids are then calculated using COSMOmic as well as a MD approach based on the potential of mean force (PMF) calculations performed using umbrella sampling (US). The combined US/PMF approach was performed with both the additive, non-polarizable CHARMM general force field (CGenFF) and the classical Drude polarizable force field. The partition coefficients for the neutral solutes are shown to be accurately calculated with the COSMOmic and additive CGenFF US/PMF approaches, while only the US/PMF approach with the Drude polarizable force field accurately calculated the experimental partition coefficient of the charged solute. These results indicate the utility of the Drude polarizable force field as a tool for the rational development of mixed micelles.

<i>In-situ</i> Measurements of Solute Partition Coefficients between Solid and Liquid Phases in Fe–Cr–Ni–Mo–Cu Alloys during Solidification

The in-situ measurements of the solute partition coefficients, k, between the solid and liquid phases in Fe–Cr–Ni–Mo–Cu alloys were conducted using X-ray transmission imaging and X-ray fluorescence spectroscopy (EDS) in a synchrotron radiation facility, SPring-8.

Boundary interface conditions and solute trapping near the transition to diffusionless solidification

The process of rapid solidification of a binary mixture is considered in the framework of local nonequilibrium model (LNM) based on the assumption that there is no local equilibrium in solute diffusion in the bulk liquid and at the solid-liquid interface. According to LNM the transition to complete solute trapping and diffusionless solidification occurs at a finite interface velocity $V=V_D$, where $V_D$ is the diffusion speed in bulk liquid. In the present work, the boundary conditions at the phase interface moving with the velocity $V$ close to $V_D$ ($V \lesssim V_D$) have been derived to find the non-equilibrium solute partition coefficient. In the high-speed region, its comparison with the partition coefficient from the work [Phys. Rev. E 76 (2007) 031606] is given.