Effective Partition Coefficient Research Articles

Ice zone melting method for probing ion-specific partitioning at frozen interface

When water freezes, impurities are expelled from the ice crystals and accumulate in the grain boundary space. Salts are a major impurity common to aqueous systems and, upon freezing, are dissolved in the liquid phase at temperatures above the eutectic point. Some constituent ions remain near the ice interface, but some readily diffuse away from the interface. The behavior of ions depends on their properties and affects the progress of freezing. Therefore, although the equilibrium and dynamic behavior of ions at this interface is important for understanding water freezing, nothing is known because of the lack of a suitable approach to this aspect. We extend zone melting, which is used for the purification of metal and semiconductor materials, to frozen aqueous systems. The partition behaviors of anions (F−, Cl−, Br−, and NO3−) between frozen and thawed zones are evaluated using ice zone melting followed by ion chromatographic determination of ions. The effective partition coefficients of the ions are determined from the zone melting measurements of frozen aqueous solution. Differences in the effective partition coefficient between anions are observed. The ratios for anions reveal the ion-specific behaviors at the interface between the freeze concentrated solution (FCS) and melting zone. Poorly hydrated ions tend to be thermodynamically distributed well in the FCS. However, as zone melting proceeds, F− shows a different trend from that predicted by ion hydration. This characteristic behavior of F− is understood by considering its lower diffusivity than other halide anions. Thus, ice zone melting provides information on the equilibrium and dynamic features of ions at the frozen aqueous interface.

Containment of phenol-impacted groundwater by vertical cutoff wall with backfill consisting of sand and bentonite modified with hydrophobic and hydrophilic polymers

A novel soil-bentonite backfill is proposed for use in vertical cutoff walls to contain phenol in groundwater at contaminated sites. The backfill consists of sand and bentonite modified with tetramethylammonium and carboxymethylcellulose, labeled as STCMB backfill. Flexible-wall permeability and double-reservoir diffusion tests were conducted to investigate the impact of phenol solution on hydraulic conductivity (k), effective diffusion coefficient (D*) and partition coefficient (Kp) of the backfill, respectively. The permeability results showed k of the STCMB backfill decreased by 0.91 times when the permeating liquid was changed from tap water to phenol solution. The diffusion testing results showed that D* values for the STCMB and conventional backfill (labeled as SCB backfill) were 4.0 × 10−10 m2/s and 3.0 × 10−10 m2/s, respectively, whereas Kp values for the STCMB and SCB backfills were 2.0 mL/g and 0.75 mL/g, respectively. The octanol-water partition coefficient model is suitable for estimating Kp for nonpolar organics. Furthermore, a series of solute transport simulations using Pollute V7 program was performed to evaluate the performance of vertical cutoff walls comprising STCMB and SCB backfills in containing phenol in lateral flowing groundwater. Overall, the STCMB backfill has demonstrated superior effectiveness in containing phenol in groundwater.

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.

Modeling the Phase Equilibria of Associating Polymers in Porous Media with Respect to Chromatographic Applications.

Associating copolymers self-assemble during their passage through a liquid chromatography (LC) column, and the elution differs from that of common non-associating polymers. This computational study aims at elucidating the mechanism of their unique and intricate chromatographic behavior. We focused on amphiphilic diblock copolymers in selective solvents, performed the Monte Carlo (MC) simulations of their partitioning between a bulk solvent (mobile phase) and a cylindrical pore (stationary phase), and investigated the concentration dependences of the partition coefficient and of other functions describing the phase behavior. The observed abruptly changing concentration dependences of the effective partition coefficient demonstrate the significant impact of the association of copolymers with their partitioning between the two phases. The performed simulations reveal the intricate interplay of the entropy-driven and the enthalpy-driven processes, elucidate at the molecular level how the self-assembly affects the chromatographic behavior, and provide useful hints for the analysis of experimental elution curves of associating polymers.

Effective 137Cs+ and 90Sr2+ immobilisation from groundwater by inorganic polymer resin Clevasol® embedded within a macroporous cryogel host matrix

The conservative fission products 137Cs and 90Sr are of concern when present in groundwater, as they present a radiological hazard to organisms and can be transported long distances from their source. To provide an interceptive permeable reactive barrier (PRB) solution which accommodates the throughflow of groundwater whilst removing 137Cs+ and 90Sr2+, we report the synthesis of a novel composite cryogel which performs as a permeable hierarchical sorbent. This material incorporates the ion-exchanger Clevasol® into a PVA-based cryogel host matrix with interconnected macropores, producing a composite cryogel (Clevasol®-PVACC). Clevasol®-PVACC enables the in-situ deployment of an ion-exchanger with rapid uptake kinetics for 137Cs+ and 90Sr2+, inside of a robust and permeable scaffold with green chemistry. Clevasol®-PVACC has a facile, one-pot and scalable synthesis, and can possibly also be used at other stages of the nuclear fuel cycle, such as radioactive liquor treatment. Critically, the incorporated Clevasol® resin is vitrifiable, which is optimal for long-term storage and geological disposal if high activities are adhered onto the resin. The effective partition coefficients (kd) and effective Langmuir uptake capacities (qmax) of the Clevasol® resin in Sellafield groundwater simulant are respectively 105 mL/g and 298 mg/g for Cs+, and >104 mL/g and 128 mg/g for Sr2+.

Mechanism of heterogeneous distribution of Cr-containing dispersoids in DC casting 7475 aluminum alloy

The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill (DC)-casting ingot of 7475 aluminum alloy are obtained. Meanwhile, by analyzing the microstructure, the mechanism of the heterogeneous distribution of E (Al18Mg3Cr2) dispersoids in this DC ingot is revealed. The results show that the actual effective partition coefficients of Mg and Cr are 0.650 and 1.392, respectively, and they describe the heterogeneous distributions of Mg and Cr along the direction of radius of the cross-section of the dendrite arm of the alloy. After homogenization treatment at 470 °C for 24 h, Mg diffuses uniformly, but Cr hardly diffuses. Both the concentrations of Mg and Cr and the sites of heterogeneous nucleation in the alloy are the determinants of the formation of E dispersoids simultaneously. The heat treatment at 250 °C for 72 h provides a large number of the sites of heterogeneous nucleation of the formation of fine E dispersoids that will be formed in the center of the cross-section during the subsequent heat treatment at higher temperature.

Application of directional freezing for seawater desalination: Parametric analysis using experimental and computational methods

Directional freezing is valuable due to their capability to provide excellent relocation of impurities away from ice crystals and thus produce higher desalination efficiency. In this work, desalination of surrogate seawater using directional freezing in radial and vertical directions of a cylindrical crystallizer was assessed experimentally and numerically. Experiments on the effect of different brine concentration and freezing direction on the salinity at various spatial locations was conducted. Moreover, a transient computational fluid dynamics model of multispecies flow which allows for solidification and melting was developed in order to simulate the experimental set-up. Subsequently, a modified model was developed to investigate the role of stirring on the solutes distribution during the directional ice growth. The developed model showed good agreement with the experimental results. The model also showed a successful directional freezing by obtaining the anticipated salinity gradient due to salt diffusion away from the ice growth layer. Performance metrics such as effective partition coefficient, removal efficiency and energy consumption of the desalination process were evaluated. Results showed that better partition and removal efficiency were achieved under lower salinity brine, top freezing instead of bottom or radial freezing, and with stirred flow versus stagnant configurations. Freeze desalination (FD) consumed less energy as compared to multi-stage flash distillation (MSH), humidification-dehumidification (HDH). The FD consumed 11.34 kWh/m3 as compared to MSH and HDH which require 24.6kWh/m3 and 123kWh/m3, respectively. Although the energy consumed in FD (11.34 kWh/m3) was more that of reverse osmosis (RO) (8.2 kWh/m3), it was relatively close.

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.

Revealing the influence of high magnetic field on the solute distribution during directional solidification of Al-Cu alloy

The effect of the high magnetic field (MF) on the distribution of solute concentration during directional solidification of Al-Cu alloy under low growth speed was experimentally investigated. The amount of non-equilibrium eutectic is quantified via X-ray computed tomography (XCT) and demonstrated to reduce with the application of MF. Further, experimental results reveal that the MF alleviates the microsegregation and increases the average Cu concentration in solid solution, leading to the increases of the effective partition coefficient ke. It was also found that Cu concentration in solid solution increases continuously with the increasing intensity of MF, following the strengthening of micro-hardness. The change of ke under the MF is demonstrated to attribute to the thermoelectric magnetic convection (TEMC) in the mushy zone and the thermoelectric magnetic force (TEMF) acting on the solid. The TEMC is supposed to cause secondary convection owing to the inequality in flow velocities of circulation in different positions of dendrite stem. And the vacancies created by the proliferation and movement of dislocations induced by TEMF in the matrix is supposed to be able to capture solute atoms and thus enhance the solute concentration in the solid solution.

Multiscale model for flow and transport in CO2-enhanced coalbed methane recovery incorporating gas mixture adsorption effects

In this work we develop a multiscale model for flow and transport problem in CO2-enhanced coalbed methane recovery. The coalbed methane reservoir is characterized by two levels of porosity associated with nanopores in the matrix and cleat network. Mass conservation equations for fluid mixture (CH4 and CO2) in the matrix at the microscale are rigorously derived by using the formal homogenization technique taking into account the gas mixture adsorption in the nanopores. The Density Functional Theory (DFT) is used to compute the gas adsorption isotherms and the solvation force acting on the nanopore wall, showing a much more pronounced adsorption capacity of CO2 compared to CH4. The average transport equations in the matrix together with the multiphase flow problem in fracture network (gas mixture and water) are homogenized giving rise to a macroscopic model ruled by the effective conductivities, partition and transfer coefficients. The cleat permeability evolution due to deformation is taken into account through a three-scale poromechanical model reported in a previous work. Computational simulations illustrate the macroscopic laws underlying the gas pressure distributions, cleat closure phenomena and CH4 production curve enhanced by CO2 injection.

Magnetic-Field-Induced Liquid–Solid Interface Transformation and Its Effect on Microsegregation in Directionally Solidified Ni-Cr Alloy

The transformation of liquid–solid interface induced by the steady magnetic field (SMF) in the directionally solidified Ni-10 wt pct Cr alloy was studied experimentally. At the moderate pulling rate (50 μm s−1), it could be observed that the interface morphology gradually transformed from planar to cellular shape with increasing the SMF intensity (0 T, 3 T, 6 T). However, the cellular interface at the high pulling rate (100 μm s−1) was not influenced by the SMF. 3D numerical simulations suggested that the transformation of interface morphology originated from the thermoelectric magnetic convection near the wavelike interface at the early stage of solidification. From the composition measurement, it was found that the formation of microsegregation at the moderate pulling rate was associated with the interface morphology. Under the 3 T SMF, the liquid–solid interface remained planar and the microsegregation level increased in comparison with that without the SMF. Under the 6 T SMF, the liquid–solid interface became cellular and the microsegregation level was reduced. The factors affecting microsegregation were evaluated. The effective partition coefficient was estimated based on composition data. It was revealed that the effective partition coefficient increased with the 6 T SMF due to the thermoelectric magnetic and magnetic damping effects within the cellular structure. Additionally, the solid diffusivity was measured using the diffusion couple technique. It was found that the interdiffusion coefficient of Cr decreased with increasing the SMF intensity. The modified Brody model was used to predict the microsegregation behavior in the SMF. The predicted results were in agreement with experimental observation. It could be concluded that the decrease in solid diffusivity enhanced the formation of microsegregation for the planar interface, whereas the increase in effective partition coefficient in the SMF was beneficial for alleviating the extent of microsegregation for the cellular interface.

Progressive Freeze Concentration of Coconut Water and Use of Partial Ice Melting Method for Yield Improvement.

Coconut water is a highly nutritious liquid food which is a by-product of the desiccated coconut industry. Freeze concentration is the most suitable concentration method for coconut water since the low-temperature operation for concentration does not deteriorate the original quality of coconut water. Suspension freeze concentration (SFC) and progressive freeze concentration (PFC) are the available FC methods, and SFC is a complex and expensive method compared with PFC. PFC is a novel freeze concentration technique to concentrate liquid food by using a simple system. The limitation of PFC is the lower product yield than SFC, and to overcome the problem, the partial ice-melting technique can be used. A simple cylindrical apparatus was used for PFC which consists of a sample vessel, agitator system, and a cooling bath (at −23°C ± 2°C temperature). The final concentration of the liquid product was directly affected by the apparatus agitator speed and sample vessel dipping speed. PFC agitator speed of 290 rpm and dipping speed of 1.3 cm h−1 were reported as the optimum operating conditions to achieve the highest concentration for the PFC apparatus used in this study. Using optimized agitation speed and dipping speed, coconut water was concentrated up to Brix 8.5° from the initial concentration of Brix 3.5°. PFC coconut water achieved 73.56% of total yield, 2.42 of concentration ratio, 0.7° of ice phase concentration, and 0.08 of effective partition coefficient. The partial melting technique was successfully explored by recovering initial ice fractions with high solute concentrations, and the total yield was improved up to 80%.

The Effect of the Cooling Rate on the Microstructure and Microsegregation: An Experimental and Numerical Investigation of Solidification in Hypoperitectic Cu − 20 wt.% Sn Alloy

Abstract Hypoperitectic Cu − 20 wt.% Sn alloy was solidified under different cooling rates and solidification growths using directional solidification system. The effects of cooling rate and solidification growth on the microsegregation profiles and tertiary dendritic arm spacing (λ3) were experimentally investigated along the casting. A mathematical model known as phase-field was applied to simulate microstructure and microsegregation during solidification in system Cu-Sn liquid. In this paper the applicability of the phase-field model to the solidification problem in a real alloy system was systematically explored. Microsegregation profiles and realistic dendritic structures were obtained using the phase-field model. The results calculated by phase-field model show various solidification features consistent with our experiment. The calculated tertiary dendritic arm spacing (λ3) and microsegregation profiles were compared with experimental values from directional solidification system. Since the calculated microsegregation profiles using the equilibrium partition coefficient (keq) can yielded discrepancies from the experimental results, an effective partition coefficient (kef) as a function of solidification growth, is proposed in phase-field model, showing a good agreement with the experimental data for any case examined.

The seawater Sr/Ca ratio in the past 50 Myr from bulk carbonate sediments corrected for diagenesis

The strontium/calcium (Sr/Ca) ratio in paleoseawater is important for evaluating the global fluxes of continental weathering products and carbonate deposition in the oceans. Existing reconstructions of the paleoseawater Sr/Ca ratio using different methods give conflicting results. We use a modeling approach to estimate paleo-Sr/Ca for the past 50 million years that uses pore fluid chemistry and bulk sediment measurements of carbonate ooze and chalk from the Ontong Java Plateau as input. The effects of diagenesis in modifying the Sr/Ca ratio recorded in bulk carbonate sediments are estimated using a reactive transport model, and those effects are accounted for in determining the initial Sr/Ca ratio of the biogenic carbonate sediments. The Sr/Ca of the paleo-oceans is calculated based on an effective partition coefficient (KSrbio=0.198) inferred from Sr/Ca in modern sediments. The model simulates deposition of sediments on the seafloor, reactions between pore fluid and solid (dissolution and precipitation of calcite), and diffusion within the pore fluid. Measured pore fluid Sr, Ca and sulfate concentrations provide input for the Sr model. This approach, applied to four Ocean Drilling Program (ODP) sites (803, 805, 806, 807) that have long Cenozoic records of carbonate deposition, indicates that the Sr/Ca ratio of seawater has increased slowly over the past 50 million years from a value of about 8 mmol/mol to the modern value of 9.4, with fluctuations of about ±1 over 10 Myr periods. This result is consistent with previous estimates based on foraminifera and coral aragonite, but differs from recent estimates obtained with other approaches. The near-constant seawater Sr/Ca over the past 50 million years is consistent with likely weathering sources to the oceans. The fluctuations suggest that there were modest shifts in the aragonite/calcite ratio of marine carbonate.

A case study of cesium sorption onto concrete materials and evaluation of wash agents: Implications for wide area recovery

To support the viability of a wash-down approach to mitigating nuclear contamination, this study presents a characterization of the aggregate of a common concrete by optical microscopy and the sorption-desorption characteristics of cesium from these into potential wash solutions. Various minerals with weathered surfaces displayed strong affinity for 137Cs with an effective partition coefficient Kd = 120 mL/g for micas, >25–90 mL/g for feldspars, and >25–30 mL/g for amphiboles. The desorption Kd into 0.1 M NH4Cl varied greatly but for amphiboles, sandstones, granite, and fine-grained quartzite it was >200 mL/g as a result of irreversible sorption. These same mineral phases are prevalent in all types of building materials, extending our conclusions more broadly to the problem of wide-area urban decontamination. In contrast, ionic solutions desorbed up to 98% of 137Cs from cement, suggesting that fresh concretes with an intact surface layer of cement could be more easily decontaminated if Cs+ interactions with the underlying minerals could be avoided. For practical applications common, non-hazardous chemicals such as sodium, potassium, and ammonium salts are as effective or more effective than harsher chemicals and expensive chelating agents. For example, when treated shortly after exposure, on time-scales commensurate with early response phase activities, 0.5 M KCl could remove nearly 50% of bound 137Cs from concrete aggregate. Statistical analyses showed that desorption from the fine aggregate benefited from higher K+ and NH4+ concentrations. These results suggest that contamination in large areas of the urban environment can be dramatically reduced using common chemicals obtained readily from local stores.

Numerical Modelling of Transport Phenomena and Macrosegregation during Ternary Alloy Solidification: Solutal Undercooling Effects

In this paper, a macroscopic mathematical model is developed for simulation of transport phenomena during ternary alloy solidification processes, taking into account non-equilibrium effects due to solutal undercooling. The model is based on a fixed-grid, enthalpy-based, control volume approach. Microscopic features pertaining to non-equilibrium effects on account of solutal undercooling are incorporated through a novel formulation of a modified partition coefficient. The effective partition coefficient is numerically modeled by means of macroscopic parameters related to the solidifying domain. Numerical simulations are performed for ternary steel alloy by employing the present model and the resulting convection and macrosegregation patterns are analyzed. It is observed that the consideration of non-equilibrium solidification in the present mathematical approach is able to capture the thermo-solutal convection and leads to prediction of accurate value of macrosegregation. The results from the present model matches well with the experimental observations published in the literature.

Investigation of Thermal Parameters Effects on the Microstructure, Microhardness and Microsegregation of Cu-Sn alloy Directionally Solidified under Transient Heat Flow Conditions

The microstructure and mechanical properties of cast materials are strongly dependent on the thermal history during solidification process. The global casting industry has faced major challenges, i.e., customers increasingly demand completely finished cast parts as well as complexity of casting alloys are rising. Therefore, the previous knowledge the solidification conditions effects on the as-cast ingot microstructure and mechanical properties resulting is very useful in the casting industry in order to improve the casting quality. In this present paper, the thermal parameters effects on the microstructure, microhardness and microsegregation of a Cu- 20 wt.% Sn alloy under transient heat flow conditions were experimentally investigated. The experimental observations indicate that the tertiary dendritic arm spacing (λ3), microsegregation and microhardness are affected by the thermal parameters (solidification speed and cooling rate). Solidification speed (SS) associated with increasing cooling rate (RC) are found to contribute to the decreasing tertiary dendritic arm spacing (λ3). However, cooling rates from 11.36 °C/s to 0.65 °C/s were not found to affect significantly the microhardness along the ingot length. The solute concentration (Sn) in solid region were calculated by Scheil and Clyne-Kurz equation, and used in the predictions of microsegregation profiles. The results calculated by equations, have shown deviations from the experimental data. It is well known that it is very difficult to calculate these concentration profiles using the equilibrium partition coefficient, since frequently castings solidify under non-equilibrium conditions and the solidification process is known as non-equilibrium solidification. For this reason, effect of solidification speed (SS) was considered into equations through effective partition coefficient (kef) that has been determined for the range of solidification speed experimentally examined between 0.19 and 0.89 mm/s. However, results calculated by Scheil and Clyne-Kurz equation using the effective partition coefficient (kef), yielded discrepancies from the experimental results. Because of its deviations between calculated and experimental data, an experimental equation with effective partition coefficient (kef), is considered in present work, showing an excellent agreement with the experimental data.

Spinodal Decomposition in Lead-free Piezoelectric BaTiO3–CaTiO3–BaZrO3 Crystals

Polycrystals and centimeter-sized BaTiO3-based single crystals were grown by top seeded solution growth from the BaTiO3–CaTiO3–BaZrO3 system. High effective partition coefficients of Zr ranging from 15 to 6 with small Zr content have been calculated from Castaing microprobe measurements, whereas those of Ca increase slightly from 0.45 to 0.7. A spinodal decomposition mechanism is emphasized during the growth leading to the emergence of two phases with close compositions. Chemical analysis displayed periodical Zr and Ca content fluctuations within the whole boules, and Rietveld measurements highlighted two phases belonging to perovskite structures with tetragonal P4mm and orthorhombic Amm2 space groups. Samples with various calcium and zirconium contents were characterized by means of dielectric and piezoelectric measurements. Most efficient samples are indistinctly polycrystals or oriented single crystals where electromechanical performances are compositional-dependent. Polycrystalline samples and single crystals oriented along (001)pc and (110)pc displayed Curie temperatures ranging from 50 to 111 °C. Electromechanical coupling factor up to 58% and piezoelectric charge coefficient d33 = 496 pC·N–1 were obtained at room temperature. The miscibility gap between the two perovskite solid solutions as well as Ca and Zr element content variation in single crystals lower crystal piezoelectric response that remains nonetheless of the same efficiency compared to that of ceramics of the same composition.

Effect of Cooling Rate on Microsegregation During Solidification of Superalloy INCONEL 718 Under Slow-Cooled Conditions

The solidification sequence, microstructural evolution, solid-liquid interface variation, interdendritic segregation, and elemental distribution of as-cast IN718 alloy at three slow-cooling rates (5, 10, and 20 °C/min) were investigated by differential scanning calorimetry (DSC), confocal laser scanning microscopy (CLSM), optical microscopy (OM), field-emission scanning electron microscopy (FESEM), and electron-probe microanalysis (EPMA) techniques. The results indicate that as the cooling rate decreases, the constitutional supercooling at the solidification front affects the solid-liquid interface more significantly, and the size and quantity of the Laves phase increase. However, the composition of the Laves phase is insensitive to the cooling rate in the range of conditions studied here. In dendrite core, the contents of Ni, Cr, Fe, and Al follow a slight downward trend with an increasing cooling rate, whereas the Nb, Mo, and Ti contents show an upward trend. Additionally, Mo shows a stronger propensity to segregate under slow-cooling conditions because its effective partition coefficient almost linearly decreased with decreasing cooling rate, which is same as Nb. Using the parameters experimentally determined in this study and the Clyne–Kurz equation, we achieved reasonable agreement between the calculated and measured liquid composition change during the solidification process at different cooling rates. All experimental and theoretical programs in this research were undertaken with the aim of gaining further understanding of the microsegregation behaviors in large-scale IN718 ingots, whose cooling rates are within a lower range.

Experimental Investigation of Ternary Al-Si-Cu Alloy Solidified with Unsteady-State Heat Flow Conditions

Ternary Al-9.0wt%Si-4.0wt%Cu alloy was solidified in a vertical directional solidification system under unsteady-state heat flow conditions. The resulting dendritic morphology and microsegregation were investigated. A more detailed analysis was dedicated to the microsegregation phenomena where a multielement interaction was observed. The solidification parameters such as: solidification speed (VL) and cooling rate (T˙) were determined from the cooling curves obtained during the solidification process. The thermal variables effect on the dendritic morphology is presented. The measurements of tertiary dendrite arm spacing (λ3) and microsegregation were performed for different positions along the casting. The experimental curves for microsegregation were obtained for Si and Cu from the center of dendritic tertiary arm to the next nearest tertiary arm. The solidification speed (VL) influence is built the effective partition coefficient (Kef_Cu and Kef_Si) that has been determined for the range of VL and microsegregation curves are calculated by Scheil's equation for comparison with experimental data. Good agreements of the Scheil's equation with experimental data on microsegregation curves of the Si and Cuwere obtained when effective partition coefficient (Kef_Cu and Kef_Si) is taken into consideration. The multielement interaction effect on the Si microsegregation is investigated. Experimental results show that, Cu-rich dendrites were accompanied by minute amounts of Si. The concentration profiles obtained experimentally point to a strong negative correlation between Si and VL on ternary Al-9.0wt%Si-4.0wt%Cu alloy.