Liquid-solid Transformation Research Articles

Chiral Separation of the Phenylglycinol Enantiomers by Stripping Crystallization.

Stripping crystallization (SC) is introduced in this work for chiral purification of R-phenylglycinol from the enantiomer mixture with an initial concentration ranging from 0.90 to 0.97. As opposed to the solid–liquid transformation in melt crystallization, the three-phase transformation occurs in SC at low pressures during the cooling process. SC combines melt crystallization and vaporization to produce a crystalline product and mixture vapor from a mixture melt due to the three-phase transformation. Thermodynamic calculations were applied to determine the operating pressure for the three-phase transformation during the cooling process in the SC experiments. To consider the possible deviations between the calculated and the actual three-phase transformation conditions, the product purity and the recovery ratio of R-phenylglycinol were investigated within a range of operating pressures during the cooling process.

Thermodynamics and kinetics of nucleation in binary solutions

A new approach that is a combination of classical thermodynamics and macroscopic kinetics is offered for studying the nucleation kinetics in condensed binary solutions. The theory covers the separation of liquid and solid solutions proceeding along the nucleation mechanism, as well as liquid-solid transformations, e.g., the crystallization of molten alloys. The cases of nucleation of both unary and binary precipitates are considered. Equations of equilibrium for a critical nucleus are derived and then employed in the macroscopic equations of nucleus growth; the steady state nucleation rate is calculated with the use of these equations. The present approach can be applied to the general case of non-ideal solution; the calculations are performed on the model of regular solution within the classical nucleation theory (CNT) approximation implying the bulk properties of a nucleus and constant surface tension. The way of extending the theory beyond the CNT approximation is shown in the framework of the finite-thickness layer method. From equations of equilibrium of a surface layer with coexisting bulk phases, equations for adsorption and the dependences of surface tension on temperature, radius, and composition are derived. Surface effects on the thermodynamics and kinetics of nucleation are discussed.

High-sensitivity determination of cadmium and lead in rice using laser-induced breakdown spectroscopy

Stability and sensitivity of toxic elements determination is still unsatisfactory in agricultural product using laser-induced breakdown spectroscopy (LIBS). A simple and low cost sample pretreatment method named solid–liquid-solid transformation method was proposed in this work. The target analytes of cadmium (Cd) and lead (Pb) from rice samples were prepared through ultrasound assisted extraction in hydrochloric acid solution. The solution was dropped on the glass slide after centrifuging process and was further dried on a heater. Finally, the glass slide contained the analytes was carried out for LIBS determination. Compare with conventional pellet method, the spectral intensity of Cd and Pb element were enhanced significantly using LIBS. The limits of detection were 2.8 and 43.7 μg/kg, respectively. The limits of quantification were 9.3 and 145.7 μg/kg, respectively. The results demonstrated that LIBS coupled with ultrasound assisted extraction should be a promising tool to detect toxic elements in rice.

An improved modified embedded-atom method potential to fit the properties of silicon at high temperature

An improved modified embedded-atom method (MEAM) potential for Si was optimized. The potential could quite well fit the potential energy curve and the elastic constants of diamond Si, the pair correlation function, the structure factor and the bond angle distribution function of liquid Si. The potential could also well fit the melting point and the solid-liquid phase transformation enthalpy. The potential could be used to study the solid-liquid transformation behaviors and the liquid structure of Si, and it could also be used to develop a MEAM potential for the binary Al-Si alloy.

Extraction of triclosan and methyltriclosan in human fluids by in situ ionic liquid morphologic transformation

Herein, we established an ionic liquid (IL)-based liquid-solid transformation microextraction (IL-LTME) combined with HPLC-UV detection for the simultaneous determination of triclosan (TCS) and its methylated product, methyltriclosan (MTCS), in human fluids. The IL-LTME method was based on an in situ metathesis between hydrophilic IL and ion-exchange salt to form a solid hydrophobic IL. According to the above principle, a hydrophilic IL, [C12MIM]Br, was selected as the extractant, and NH4PF6 as ion-exchange salt. The prominent advantages of the newly developed method are: (1) the in-situ reaction between the extractant [C12MIM]Br and ion-exchange salt NH4PF6 changed the IL from hydrophilic to hydrophobic that avoiding the stick of ionic liquid on the tube wall; (2) bubbling with NH3 greatly increased the contact area between IL-extractant and analytes resulting in improved extraction recovery; and (3) solidification of the [C12MIM] PF6 provided a good separation and avoided the use of specialized equipment. A series of main parameters were optimized by single-factor screening and central composite design as follows: 0.9 mL of NaOH, 2.0 min of second ultrasonically time, 10 min of centrifugation time, 21 mg of extractant [C12MIM]PF6, 2.4 min of ultrasonic time, 65 mg of NH4PF6 and 13.8 min of cooling time. Under the optimized conditions, the limits of detection for TCS and MTCS were 0.126–0.161 μg L−1 in plasma samples, and 0.211–0.254 μg L−1 in urine samples, respectively. The extraction recoveries for TCS and MTCS were in the range of 94.1–103.8%. The intra-day and inter-day precisions were 1.00–4.74% and 1.02–5.21%, respectively. In general, the IL-LTME method is environment-friendly, time-saving, economical, high efficient and robust with low detection limits and high recoveries. Thus, the newly developed method has excellent prospects for sample pretreatment and analysis of trace TCS and MTCS in blood and urine samples.

Monotropic polymorphism in a glass-forming metallic alloy

This study investigates the crystallization and phase transition behavior of the amorphous metallic alloy Au70Cu5.5Ag7.5Si17. This alloy has been recently shown to exhibit a transition of a metastable to a more stable crystalline state, occurring via metastable melting under strong non-equilibrium conditions. Such behavior had so far not been observed in other metallic alloys. In this investigation fast differential scanning calorimetry (FDSC) is used to explore crystallization and the solid–liquid–solid transition upon linear heating and during isothermal annealing, as a function of the conditions under which the metastable phase is formed. It is shown that the occurrence of the solid–liquid–solid transformation in FDSC depends on the initial conditions; this is explained by a history-dependent nucleation of the stable crystalline phase. The microstructure was investigated by scanning and transmission electron microscopy and x-ray diffraction. Chemical mapping was performed by energy dispersive x-ray spectrometry. The relationship between the microstructure and the phase transitions observed in FSDC is discussed with respect to the possible kinetic paths of the solid–liquid–solid transition, which is a typical phenomenon in monotropic polymorphism.

Crystalline modification of a rare earth nucleating agent for isotactic polypropylene based on its self-assembly.

In this paper, the crystalline modification of a rare earth nucleating agent (WBG) for isotactic polypropylene (PP) based on its supramolecular self-assembly was investigated by differential scanning calorimetry, wide-angle X-ray diffraction and polarized optical microscopy. In addition, the relationship between the self-assembly structure of the nucleating agent and the crystalline structure, as well as the possible reason for the self-assembly behaviour, was further studied. The structure evolution of WBG showed that the self-assembly structure changed from a needle-like structure to a dendritic structure with increase in the content of WBG. When the content of WBG exceeded a critical value (0.4 wt%), it self-assembled into a strip structure. This revealed that the structure evolution of WBG contributed to the Kβ and the crystallization morphology of PP with different content of WBG. In addition, further studies implied that the behaviour of self-assembly was a liquid–solid transformation of WBG, followed by a liquid–liquid phase separation of molten isotactic PP and WBG. The formation of the self-assembly structure was based on the free molecules by hydrogen bond dissociation while being heated, followed by aggregation into another structure by hydrogen bond association while being cooled. Furthermore, self-assembly behaviour depends largely on the interaction between WBG themselves.

Liquid-solid surface phase transformation of fluorinated fullerene on monolayer tungsten diselenide

Hybrid van der Waals (vdW) heterostructures constructed by the integration of organic molecules and two-dimensional (2D) transition metal dichalcogenide (TMD) materials have useful tunable properties for flexible electronic devices. Due to the chemically inert and atomically smooth nature of the TMD surface, well-defined crystalline organic films form atomically sharp interfaces facilitating optimal device performance. Here, the surface phase transformation of the supramolecular packing structure of fluorinated fullerene (C60F48) on single-layer (SL) tungsten diselenide (WSe2) is revealed by low-temperature (LT) scanning tunnelling microscopy (STM), from thermally stable liquid to solid phases as the coverage increases. Statistical analysis of the intermolecular interaction potential reveals that the repulsive dipole-dipole interaction induced by interfacial charge transfer and substrate-mediated interactions play important roles in stabilizing the liquid C60F48 phases. Theoretical calculations further suggest that the dipole moment per C60F48 molecule varies with the surface molecule density, and the liquid-solid transformation could be understood from the perspective of the thermodynamic free energy for open systems. This study offers new insights into the growth behaviour at 2D organic/TMD hybrid heterointerfaces.

Solidification microstructure evolution and its corresponding mechanism of metastable immiscible Cu80Fe20 alloy with different cooling conditions

Undercooling greatly influences the resultant solidification microstructure of an alloy, especially for metastable immiscible Cu-Fe alloy. In the present paper, solidification microstructure evolution of metastable immiscible Cu80Fe20 alloy was studied under different cooling conditions. For the first time, it is found that the liquid-liquid phase separation in Cu-Fe alloy is triggered by constitutional undercooling ahead of the solid-liquid interface. When the cooling rate is about 50–100 K/s, the liquid-solid transformation primarily takes place, and the liquid-liquid phase separation only exists in a small region or the interdendritic region about several tens to hundreds of microns. The liquid-liquid phase separation is ascribed to the large constitutional undercooling according to the calculation and occurs behind the liquid-solid transformation, which is different than found in previous studies. However, only normal liquid-solid transformation occurs and the morphology of the Fe-rich phase remarkably changes from cellular to developed dendrites in a cooling rate range of 350–560 K/s. The results provide significant guidance for industrial preparation and a necessary consideration for the study of metastable immiscible Cu-Fe alloy.

Exergy analysis of a flat plate solar collector with latent heat storage by phase change material for water heating applications at low temperature

An exergy analysis has been performed to determine the potential for useful work in a latent heat storage system with phase change material (PCM) for a flat-plate solar collector. Commercial paraffin wax is used as PCM to store and release energy in the solid-liquid transformation; this material is located in metal containers under the absorber plate on the bottom insulation of the collector. The exergy analysis is performed in outdoor conditions for days of the low, medium and high radiation taken from October 2016 to March 2017 at Barranquilla city (latitude: 10º 59' 16" N, longitude: 74º 47' 20" O, Colombia). The system is evaluated throughout charge and discharge periods. The energy and exergy balance equations based on the first and second law of thermodynamics is formulated and solved for each element of the collector system as well as for the PCM. Results obtained show the energy distribution and energetic destruction for each system component and its variation as a time function. It was observed that the average energy and energetic efficiency are 28.7 %, 13.2 % for of low radiation days. 26.9%, 20.56% for of medium radiation days, and 23.2%, 18.6% for of high radiation days, respectively. Results of the analysis are shown in detail in the present paper.

Fragile-to-strong transition in metallic glass-forming liquids

It has been observed that many glass-forming liquids are transformed from fragile to strong liquids in a supercooled region upon cooling. This is the so-called fragile-to-strong (F-S) transition. Since its discovery in water, the F-S transition, as a frontier problem, as well as a hot issue, in condensed matter physics and material science, has aroused the considerable interest of researchers. It has been generally accepted that the F-S transition might be a universal dynamic behavior of metallic glass-forming liquid (MGFL). Studying the F-S transition is important not only for better understanding the nature of glass transition, uncovering the microstructural inheritance during the liquid-solid transformation, clarifying the structural competition during crystallization, improving the stability of MGs, but also for promoting the standardization during the production and treatment technology of MGs. In this paper, the general and special features of the F-S transition for bulk and marginal MGFLs are studied and described in terms of a physical model. A characteristic parameter f is introduced to quantify the F-S transition. With two relaxation regimes, on the basis of Mauro-Yuanzheng-Ellison-Gupta-Allan model, we propose a generalized viscosity model for capturing the liquids with the F-S transition. Using this model, we calculate the F-S transition temperature for metallic glass. From the calculation results, the F-S transition might occur around (1.36±0.03) Tg. By using the hyperquenching annealing-calorimetric approach, we find that the anomalous crystallization behavior occurs in both LaAlNi and CuZrAl glass ribbons. This phenomenon implies the existence of a thermodynamic F-S transition, which could be used as an alternative method of detecting the F-S transition in MGFLs. To date, the origin of the F-S transition is far from understanding. We find that the F-S transition in CuZr(Al) GFLs is attributed to the competition among the MRO clusters composed of different locally ordering configurations. By comparing the parameter f with the parameter r that characterizes the competition between the α and the slow β relaxations in 19 MGFLs, we find that the slow β relaxation plays a dominant role in the F-S transition and the extent of the F-S transition is mainly determined by the degree of the comparability in structure units between the α and the slow β relaxations. The existence of the liquid-liquid phase transition might also be the root of the F-S transition. The tendency of investigation of the F-S transition is also evaluated.

Rapid solidification and liquid-phase separation of undercooled CoCrCuFexNi high-entropy alloys

Fluxing and cyclic superheating technique was used to investigate the rapid solidification behavior of CoCrCuFexNi (x = 1.0, 1.5, 2.0, molar concentration) high-entropy alloys in this study. The microstructures of CoCrCuFexNi (x = 1.0, 1.5, 2.0) high-entropy alloys solidified at different undercoolings (ΔT) were investigated. Liquid-phase separation leading to Cu-rich and Cu-depleted regions, were obtained in the solidified microstructure from highly undercooled melt. This occurs when the melt undercooling exceeds a critical undercooling (ΔTcrit) of 160 K for CoCrCuFeNi, 190 K for CoCrCuFe1.5Ni and 293 K for CoCrCuFe2Ni alloy. However, typical dendrites and interdendritic regions were observed in rapid-solidified CoCrCuFexNi alloys prepared from melts with a small undercooling (ΔT < ΔTcrit). Conversely, a large amount of Cu-rich spheres and even egg-type structures were observed in alloys solidified from melts with large degree of undercooling, ΔT in excess of the critical value, ΔTcrit. A large amount of Cu-rich nano-phases were found in the matrix, possibly, due to the precipitation of Cu-rich phase from the supersaturated solid solution obtained during solidification. The positive enthalpies of mixing between Cu and the other elements in the multi-component alloys resulted in the occurrence of liquid-phase separation prior to the liquid–solid transformation starts. The sluggish diffusion effect of high-entropy alloys and rapid solidification play an important part in the precipitation of nanophase during the solid-state transformation in the Cu-based matrix. Similar to other immiscible alloys, liquid-phase separation occurred when a critical undercooling was exceeded. Differently, nanophases were found in the microstructures of multi-component CoCrCuFexNi (x = 1.0, 1.5, 2.0) alloys.

Modelling and Analysis of Phase Transformations and Stresses in Laser Welding Process / Modelowanie I Analiza Przemian Fazowych I Naprężeń W Procesie Spawania Laserowego

The work concerns the numerical modelling of structural composition and stress state in steel elements welded by a laser beam. The temperature field in butt welded joint is obtained from the solution of heat transfer equation with convective term. The heat source model is developed. Latent heat of solid-liquid and liquid-gas transformations as well as latent heats of phase transformations in solid state are taken into account in the algorithm of thermal phenomena. The kinetics of phase transformations in the solid state and volume fractions of formed structures are determined using classical formulas as well as Continuous-Heating-Transformation (CHT) diagram and Continuous-Cooling-Transformation (CCT) diagram during welding. Models of phase transformations take into account the influence of thermal cycle parameters on the kinetics of phase transformations during welding. Temporary and residual stress is obtained on the basis of the solution of mechanical equilibrium equations in a rate form. Plastic strain is determined using non-isothermal plastic flow with isotropic reinforcement, obeying Huber-Misses plasticity condition. In addition to thermal and plastic strains, the model takes into account structural strain and transformation plasticity. Changing with temperature and structural composition thermophysical parameters are included into constitutive relations. Results of the prediction of structural composition and stress state in laser butt weld joint are presented.

Kinetic study of phase transformation of n-octane using hydrothermal diamond anvil cell

A kinetic study of phase transformation of n-octane has been performed using a hydrothermal diamond anvil cell. The results show that pressure has a negative effect on the solid–liquid reaction rate. The increase of pressure can accelerate the liquid–solid transformation rate. Upon the liquid–solid transformation, the light transmittance showed a decreased trend with time in the early stage, which was caused by the formation of a large quantity of crystal nuclei. In the later stage, the light transmittance almost remained the same, thus indicating a growth stage of crystal nuclei. The activation volume yields a value of 2.16×10−5 and –1.35×10−5 m3/mol for the solid–liquid and liquid–solid transformations. Based on the obtained activation energy, the solid–liquid transformation is dominated by the interfacial reaction and diffusion, and the liquid–solid transformation is controlled by diffusion. This technique is an effective and powerful tool for the transformation kinetics study of n-octane.

Anisotropic in Situ Metal Matrix Composite Reinforced with VC Carbide Fibres

Abstract A eutectic reaction is a basic liquid-solid transformation, which can be used in the fabrication of high-strength in situ composites. In this study an attempt was made to ensure directional solidification of Fe-C-V alloy with hypereutectic microstructure. In this alloy, the crystallisation of regular fibrous eutectic and primary carbides with the shape of non-faceted dendrites takes place. According to the data given in technical literature, this type of eutectic is suitable for the fabrication of in-situ composites, owing to the fact that a flat solidification front is formed accompanied by the presence of two phases, where one of the phases can crystallise in the form of elongated fibres. In the present study an attempt was also made to produce directionally solidifying vanadium eutectic using an apparatus with a very high temperature gradient amounting to 380 W/cm at a rate of 3 mm/h. Alloy microstructure was examined in both the initial state and after directional solidification. It was demonstrated that the resulting microstructure is of a non-homogeneous character, and the process of directional solidification leads to an oriented arrangement of both the eutectic fibres and primary carbides.

Graphite and Solid Fraction Evolutions during Solidification of Nodular Cast Irons

Ductile iron casting production is strongly affected by austenite and graphite distribution obtained after the solidification process. At the same time it is accepted that solidification behavior can be considered as hypo-, hyper- or eutectic depending on the chemical composition; there is still some misconception about the growth evolution of graphite nodules and about solid fraction progression. Quenching experiments were performed on two different carbon equivalent compositions using inoculated and non-inoculated thermal analysis standard samples with the aim of freezing the existing phases at different solid fractions for each alloy. As a result of these experiments, it was possible to study the structural features found at different locations of each sample and at different stages of solidification. Additionally nodule evolution during the liquid-solid transformation was also analyzed and discussed regarding the chemical and processing characteristics of the prepared alloys.

Measuring Solid Liquid Interfacial Energy by Grain Boundary Groove Profile Method (GBG)

The solid liquid interfacial energy plays important role in the liquid solid transformation, thus it is very important to have quantitative values of the interfacial energy as this will help gain more knowledge into the structural nature of the interface. It will assist in gaining fundamental knowledge into the physics of interfaces and also in improving the technology in the crystal growth and foundry. Gündüz designed a radial heat flow apparatus in applied temperature gradient to produce grain boundary groove profile in 1984[2]. Based on the design by Gündüz, a novel radial heat flow apparatus is designed. To obtain the solid liquid interfacial energy, Gibbs Thomson coefficient value is required. To obtain accurate values of Gibbs Thomson coefficient, the interface groove profile, temperature gradient in solid and thermal conductivity values for the solid and liquid must be known.

The Solid-liquid Transformation of Low-grade Solid Potash Deposit in Dalangtan Basin and the Simplification of the Liquid Phase System

We studied the solid-liquid transformation of low-grade solid potash deposit in Dalangtan Basin and simplified the liquid phase system.We did experiments to optimize conditions of the solid-liquid transformation.The Suitable

Friction stir additive manufacturing for high structural performance through microstructural control in an Mg based WE43 alloy

Structural performance is a key challenge pertinent to additive manufacturing. A majority of the current techniques employed for metallic materials involve liquid–solid transformation and their performance is limited by solidification microstructures. Depending on the type of metallic alloy, this can be a serious impediment to structural properties. In this regard, solid-state additive manufacturing techniques have lagged behind. This study is focused on friction stir additive manufacturing (FSAM) as a potential technique to attain structurally efficient magnesium alloys. In this study, a multilayered stack of an Mg based WE43 alloy was built using FSAM at two different welding parameters. Formation of defects is sensitive to the heat input. In addition, dynamic recrystallization led to finer grain size (2–3μm). Such fine grain size coupled with desirable precipitate characteristics culminated in superior mechanical properties. Maximum hardness of 115HV was obtained in as-fabricated state and increased to 135HV after aging. These levels are similar to Al 2XXX alloys. In fact, in terms of strength, it translates to 400MPa and 17% ductility and is significantly higher than the base material subjected to aging. Mechanical properties have been correlated with detailed microstructural observations. Texture is discussed for a higher heat input sample using orientation imaging microscopy.

Modification of microstructures for hypoeutectic, eutectic and hypereutectic Al–Cu binary alloys

Al–Cu alloys of compositions near eutectic point [hypoeutectic (Al–19Cu), eutectic (Al–33Cu) and hypereutectic (Al–35·5Cu) and (Al–36Cu)] were chemically modified by adding 0·6 wt-%Al–Ti5–B1 master alloy. In addition, the specimens of unmodified and chemically modified eutectic alloy were heat treated at 500°C for different holding times (4, 24, 48 and 72 h for the unmodified and 4 and 29 h for the modified ones) followed by water quenching. The structure of chemically treated alloy was changed from large dendrites to fine rosette shaped α-Al grains inside fine eutectic matrix. For these alloys, the liquid–solid transformation temperature was shifted to a higher value. The addition of Al–Ti5–B1 master alloy to the eutectic (Al–33Cu) alloy transforms it into hypoeutectic one of fine lamellar eutectic structure. The chemically treated hypereutectic alloy (Al–35%5Cu) was changed into full eutectic alloy.