Mother Phase Research Articles

Quantitative nondiagonal phase field modeling of eutectic and eutectoid transformations

We develop a three-phase field model for the simulation of eutectic and eutectoid transformations on the basis of a nondiagonal model obeying Onsager relations for a kinetic cross coupling between diffusion and the phase fields. This model overcomes the limitations of existing phase field models concerning the fulfillment of local equilibrium boundary conditions at the transformation fronts in the case of a finite diffusional contrast between the phases. We benchmark our model in the well understood one-sided case with diffusion only in the parent phase against results from the literature. In addition to this solidification scenario, the case of solid-state transformations with diffusion in the growing phases is investigated. Our simulations validate the relevance of the theory developed by Ankit et al. [Acta Mater. 61, 4245 (2013)], that describes in a single frame the two limiting regimes where diffusion mainly takes place whether in the mother phase or in the growing phases. In both the one-sided and two-sided cases, we verify the necessity of the kinetic cross coupling for quantitative phase field simulations.

Thermodynamic property of ternary compound MgCaSi: A study from ab initio Debye-Grüneisen model

The thermodynamic properties of MgCaSi and its mother phase Ca 2 Si are comparatively investigated from ab initio calculations and quasi-harmonic Debye-Grüneisen model. At 0 K, MgCaSi is more thermodynamically stable. Under high temperature, the advantage of higher thermodynamically stability of MgCaSi is reduced, originating from the less negative entropy contribution because the thermodynamic entropy of MgCaSi increases more slowly with temperature and the entropy values are slightly smaller. With increasing temperature, the anti-softening ability for MgCaSi is slightly smaller due to the slightly faster decrease trend of bulk modulus than that of Ca 2 Si, although the bulk modulus of MgCaSi is higher in the whole temperature range considered. The thermal expansion behaviors of both MgCaSi and Ca 2 Si exhibit similar increase trend, although thermal expansion coefficient of MgCaSi is slightly lower and the increases is slightly slower at lower temperature. The isochoric heat capacity C V and isobaric heat capacity C P of MgCaSi and Ca 2 Si rise nonlinearly with temperature, and both C V are close to the Dulong–Petit limit at high temperature due to the negligibly small electronic contribution. The Debye temperature of both phases decrease with increasing temperature, and the downtrend for MgCaSi is slightly faster. However, MgCaSi possess slightly higher Debye temperature, implying the stronger chemical bonds and higher thermal conductivity than the mother phase Ca 2 Si. The Grüneisen parameter of MgCaSi and Ca 2 Si increase slightly with temperature, the values of MgCaSi are slightly larger. The investigation of electronic structures shows that with substitution of partial Ca by Mg in Ca 2 Si, the stronger Mg Si, Mg Ca and Si Si covalent bonds are formed, and plays a very significant role for the structural stability and mechanical properties.

Effect of Solution Composition on Impurity Profile of the Crystallized Product in Oiling-Out Crystallization.

Oiling-out is a unique phenomenon that the liquid phase is separated into two parts during crystallization. The emergence of new liquid phase changes the environment where crystals nucleate and grow, we call "mother phase," because target material and impurities become distributed to each phase according to their own particular distribution ratios. In our previous study on crystallization of an intermediate compound with impurities (denoted Imp-A, -B, and -C), we found that when oiling-out was formed, incorporation of Imp-C was inhibited, because Imp-C was distributed to the mother phase less than Imp-A and -B. In this study, we explored the effect of EtOH solution composition on impurity profile of the crystallized product in oiling-out crystallization, and found that the low content of Imp-B in the EtOH solution, the higher content of Imp-C in the crystallized product. Our finding revealed that not only oiling-out but also Imp-B played a key role in inhibiting the incorporation of Imp-C into the crystals.

Кинетика роста зародыша из нанофазы

We present a theoretical analysis of the growth kinetics of a nucleus from a nano-sized mother phase with a restricted amount of material in the presence of the stopping effect due to the depletion of supersaturation. Such a regime is typical for GaAs nanowires grown by the vapor-liquid-solid mechanism from a Ga droplet and is observed by in situ growth monitoring inside a transmission electron microscope. An analytical solution is obtained for the time-dependent size of the nucleus and atomic concentration in a nano-phase. A principally new time-scale hierarchy is found, whereby the entire growth process id divided into 3 stages – (1) fast nucleus growth to the stopping size, (2) slow nucleus growth at the rate of refill of a mother phase, and (3) further refill of a mother phase to resume the initial supersaturation. A general criterion is formulated for observing the stopping effect depending on the size of a nano-phase.

Quantized Repetitions of the Cuprate Pseudogap Line

The cuprate superconductors display several characteristic temperatures which decrease as the material composition is doped, tracing lines across the temperature-doping phase diagram. Foremost among these is the pseudogap transition. At a higher temperature, a peak is seen in the magnetic susceptibility, and changes in symmetry and in transport are seen at other characteristic temperatures. We report a meta-analysis of all measurements of characteristic temperatures well above Tc in strontium-doped lanthanum cuprate (LSCO) and oxygen-doped yttrium barium copper oxide (YBCO). The experimental corpus shows that the pseudogap line is one of a family of four straight lines which stretches across the phase diagram from low to high doping, and from Tc up to 700 K. These lines all originate from a single point near the overdoped limit of the superconducting phase and increase as doping is reduced. The slope of the pseudogap lines is quantized, with the second, third, and fourth lines having slopes that are respectively 1/2, 1/3, and 1/4 of the slope of the highest line. This pattern suggests that the cuprates host a single mother phase controlled by a 2-D sheet density which is largest at zero doping and which decreases linearly with hole density, and that the pseudogap lines, charge density wave order, and superconductivity are all subsidiary effects supported by the mother phase.

On Thermodynamics of Thin Films. J Potential

This work acquaints readers with the contemporary apparatus of chemical thermodynamics in the surface and colloid science. The J potential is a new parameter, which represents a series of thermodynamic potentials and is determined for fluid systems as a grand thermodynamic potential in combination with the product of a system volume and some pressure $$p{\kern 1pt} '.$$ A classification has been given with discrimination of the classical J potential (when $$p{\kern 1pt} '$$ is an external pressure) and special J potentials (at other values of $$p{\kern 1pt} '$$). For both classes, hybrid types of the potentials have been considered, when chemical potentials are chosen as variables for one group of components, while the number of molecules or moles is selected as such for another group. The main attention has been focused on the application of all considered types of the J potential to a system containing a planar thin film. In particular, a case has been analyzed in which the pressure in the mother phase of a thin film plays the role of $$p{\kern 1pt} '$$. Resulting fundamental equations have been formulated in terms of the disjoining pressure.

On the Thermodynamics of Thin Films. The Frumkin–Derjaguin Equation

The Frumkin–Derjaguin equation, which is a fundamental relationship in the theory of thin films, relates all surface tensions associated with a wetting film to its disjoining pressure and contact angle. The published ways of proving this relationship have been reviewed and their thermodynamic drawbacks have been analyzed in this work. The relationship has been rigorously derived on the basis of two approaches. The first entails the use of a new thermodynamic potential (J potential), which is defined for fluid systems as the grand thermodynamic potential combined with the product of the system volume and some pressure $$p{\kern 1pt} '$$ (here, the pressure in the mother phase of the thin film is used as $$p{\kern 1pt} '$$). The second approach is based on the Gibbs adsorption equation and entails the use of two dividing surfaces. These approaches yield identical results and suggest that not only temperature, but also all chemical potentials of the film must be fixed when calculating the work of film thinning. The dependence of the contact angle on the disjoining pressure has been considered on the basis of the Young equation. It has been shown that, as the disjoining pressure rises, the thermodynamic surface tension of the film-containing interface increases, while the contact angle decreases. The problems encountered when calculating the contact angles via the disjoining pressure isotherms have been noted.

STUDY OF PARAMETERS AFFECTING THE COALESCENCE OF DIMETHYL DISULFIDE DROPS IN A MEROX UNIT

Abstract This study focuses on the coalescence of dimethyl disulfide drops with the mother phase at a flat aqueous-organic interface between dimethyl disulfide and different sodium hydroxide solutions. Drop coalescence is an important part of the Merox process for regenerating the solvent. A digital high-frame rate camera was used for recording drops coalescence and duration time. Drops of dimethyl disulfide were directed in different sodium hydroxide solutions as the continuous phase. Applying the experimental design method, the influences of independent variables of drop size and physical properties on coalescence time were investigated. Computational fluid dynamics (CFD) was employed to simulate the drops released from a nozzle, moving toward the interface, and the CFD results were validated by experimental data. The maximum deviation between the predicted and experimental coalescence times was 18.7%. It was found that, among the physical properties, interfacial tension plays the most important role on the coalescence time. Based on the results, a correlation for coalescence time was proposed.

Structural and mechanical properties of ternary MgCaSi phase: A study by density functional theory

The structural, elastic, and electronic properties of multi-performance ternary phase MgCaSi have been investigated by density functional theory. The present results show that MgCaSi is thermodynamically and mechanically stable. The derived elastic constants indicate that the c axis is the easiest to compress, followed by the a and b axes. The bulk, shear, and Young’s moduli of MgCaSi are higher than these of the mother phase Ca2Si, demonstrating that the hardness of MgCaSi has been favorably improved. The higher Debye temperature of MgCaSi also indicates stronger interatomic interactions and better thermal conductivity. Although MgCaSi exhibits less brittleness based on Pugh’s empirical formula, Poisson’s ratio, and the Cauchy pressure, orthorhombic MgCaSi possesses lower anisotropy than Ca2Si based on several criteria. To reveal the bonding nature of MgCaSi, the electronic structures are further investigated. It is found that the strong Si−Si bond plays a significant role for structural stability and elastic properties.

Effect of Oiling-Out during Crystallization on Purification of an Intermediate Compound

When oiling-out occurs, a second liquid phase is formed, and the composition of “the mother phase”, where crystals nucleate and grow, changes because the target material and impurities are distribu...

Retained austenite phase detected by Mössbauer spectroscopy in ASTM A335 P91 steel submitted to continuous cooling cycles

Samples of ASTM A335 P91 steel submitted to continuous cooling at different rates were analyzed in the form of foils and powders by means of Mössbauer spectroscopy. The Continuous Cooling Transformation (CCT) diagram of steel ASTM A335 P91 displays two basic microstructural domains at low temperatures – ferritic and martensitic – whose limits depend on the austenite holding temperature, the precise chemical composition and the cooling conditions from the austenite mother phase. Under certain conditions, the martensitic transformation may not be completed, leading to a final microstructure with a non-negligible percentage of the austenite phase retained in a metastable state. This retained austenite could be detrimental for the mechanical properties of the steel.Mössbauer analysis suggested that powdering process promotes the retained austenite transformation to martensite; in particular, in the present case, all the austenite transformed into martensite during powdering. Foil samples instead displayed retained austenite whose relative fraction was determined as a function of the cooling rate. At the same time, the carbon content of retained austenite was estimated for the faster cooled samples; a preliminary explanation for the observed trends is given.

Immiscibility of Nucleating Aluminum Oxide Nanoparticles in Vapor

Multistep pathways in nucleation are now known to be ubiquitous and thus crucial to understand crystal formation processes. In a supersaturated mother phase, many types of source molecules are coagulated to form an amorphous or liquid-like intermediate, which subsequently transforms to a crystal. Such an intermediate possibly has a chemical formula that is inconsistent with that of the bulk crystal. Even in relatively simple vapor-phase homogeneous nucleation, the roles of the multicomponent mixtures at the nanoscale remain unknown. Here, by combining an experimental approach using in situ infrared (IR) measurements of homogeneous nucleation in the vapor phase and automatic quantum-chemical explorations of reaction routes, we show that a liquid-like nature of nucleating nanoparticles in the Al–O binary system induces immiscible phase separation. In an oxygen-deficient atmosphere, aluminum oxide nanoparticles form from supersaturated vapor with a unique shape composed of an Al metal head and an anisotropic Al2O3 crystalline tail. The anisotropic nanoparticles are larger than spherical Al2O3 nanoparticles formed in an atmosphere with sufficient oxygen. This indirectly shows that fewer nuclei are available in the precursor gas, indicating that homogeneous nucleation is initiated by oxygen-bearing species. We propose that miscible O-rich species act as seeds, and subsequently, the phase separation is induced in the liquid-like nanoparticles. This is supported by quantum-chemical calculations that show aggregation of Al atoms in oxygen-deficient (AlO)n clusters of as few as 16 molecules. In situ IR measurements revealed that the degree of anisotropy continues to increase even after the source gas molecules are exhausted, suggesting that oxygen-bearing species migrate to the tail through the molten Al-rich head. Liquid-like nature of nucleating nanoparticles is the key to control shapes and structures of nanomaterials and to elucidate the origin of cosmic dust.

Highly Concentrated Mg(TFSA)2–MgCl2–Triglyme Electrolytes Toward High Potential Mg Rechargeable Batteries

There is a growing demand for large scale batteries applying to electric vehicles and stationary energy storage systems. Although lithium ion batteries are currently used for these purpose, further innovative batteries in terms of energy density and safety are required. Then, magnesium rechargeable batteries (MRBs) can be a promising candidate because Mg metal has several attractive features, such as its high specific capacity (2205 mAh g- 1), low electrode potential (-2.38 V vs. SHE), and dendrite-free electrodeposition. However, the sluggish Mg diffusion in cathode materials and the limited choice of electrolytes make it difficult to construct full-cell MRBs with high cell voltage. Recently, our group has reported that some spinel oxides (e.g., MgCo2O4) can work as 2–3 V class cathode materials, by utilizing the spinel-to-rocksalt transition with Mg insertion into spinel mother phase [1]. In the previous work, we used a CsTFSA-based ionic liquid as the electrolyte, and the operating temperature was set at 150°C to facilitate Mg diffusion in the spinel oxides. However, Mg metal anode is readily passivated in such electrolytes due to the decomposition of TFSA, which causes a large drop of the cell voltage. Recently, it was reported that the addition of MgCl2 is effective to suppress the passivation of deposited Mg in some ether based solutions of Mg(TFSA)2 [2–4], but the electrolytes that exhibit stable Mg dissolution behavior with a low overpotential as well as high thermal stability at elevated temperatures are not established yet. In this work, we reveal that the Mg deposition/dissolution behavior in the Mg(TFSA)2–MgCl2/Triglyme (G3) solutions can be improved by restricting the amount of G3. Large amounts of MgCl2 salt can be dissolved in highly concentrated Mg(TFSA)2/G3 solutions at elevated temperatures around 150°C, by utilizing the chelating ability of G3 to Mg2+ ions and certain Shrenk-like reactions with Mg(TFSA)2. In particular, as for the mixture of Mg(TFSA)2:MgCl2:G3 = 1:1:2 (molar ratio), where the amounts of Mg and G3 are equimolar, the evaporation of the G3 solvent is efficiently suppressed even at 150°C. In addition, the mixture is crystallized by cooling down to room temperature without any phase separation or recrystallization of MgCl2. The behavior indicates that all G3 molecules coordinate to Mg2+ ions to form equimolar complexes as in the case of the so-called solvate ionic liquids [5], and it is also supported by Raman spectroscopy. More importantly, in the electrochemical measurements at elevated temperatures, the passivation of Mg is markedly suppressed in such highly concentrated solutions, in comparison to in the dilute solutions such as Mg(TFSA)2:MgCl2:G3 = 1:1:10 (molar ratio). In this presentation, we will discuss the solvation structure of Mg2+ ions in the highly concentrated solutions based on the results of Raman spectroscopy and powder-XRD measurements to grasp the origins of the improved Mg deposition/dissolution behavior. To assess the feasibility for MRBs operating at 150°C, battery tests are conducted using full-cells with MgCo2O4 cathodes and Mg metal anodes. We demonstrate that the cell with the electrolyte of Mg(TFSA)2:MgCl2:G3 = 1:1:2 delivers the highest cell voltage of about 2 V during a discharge process among the several electrolytes examined (Figure 1). We will mention how to design electrolytes with high potential cathodes to achieve high performance MRBs.

β-Na2TeO4: Phase Transition from an Orthorhombic to a Monoclinic Form. Reversible CO2 Capture.

The present work concerns the tellurate Na2TeO4 which has a 1D structure and could then present a CO2 capture ability. It has been synthesized in a powder form via a solid-state reaction and structurally characterized by thermal X-ray diffraction experiments, Raman spectroscopy, and differential scanning calorimetry. The room temperature structure corresponds to the β-Na2TeO4 orthorhombic form, and we show that it undergoes a reversible structural transition near 420 °C toward a monoclinic system. Ab initio computations were also performed on the room temperature structure, the Raman vibration modes calculated, and a normal mode attribution proposed. In agreement with our expectations, this sodium oxide is able to trap CO2 by a two-step mechanism: Na+/H+ exchange and carbonation of the released sodium as NaHCO3. This capture is reversible since CO2 can be released upon heating by recombination of the mother phase.

Effects of different surfactants and physical properties on the coalescence of dimethyl disulfide drops with mother phase at the interface of sodium hydroxide aqueous solutions

This study is concerned on the coalescence behavior of dimethyl disulfide drops and its mother-phase at the planar interface of sodium hydroxide aqueous solutions. This phenomenon is an essential part of the well-known Merox process. Three surfactant types of non-ionic Tween 20, anionic sodium dodecyl sulfate (SDS) and cationic cetyl trimethyl ammonium bromide (CTAB) were used to examine the effect of surfactants on the coalescence process. Critical micelle concentrations (CMC) of the surfactants in caustic solutions were obtained by the interfacial tension measurement. The drop coalescence times were measured using a high-speed digital camera. It was found that Tween 20 was the most effective surfactant in the reduction of interfacial tension for which the coalescence time was reduced by 85.2% under its CMC of 75.4 mg/L. The results also revealed that increase in the concentration of surfactants promoted the interface deformation. Furthermore, the effects of physical properties of the phases on the coalescence time were studied. Accordingly, a correlation was proposed based on the obtained data in which effective parameters and physical properties were involved with a maximum deviation of 15.1% and an average deviation of 7.8%. The results were compared with the so far reported correlations for coalescence times.

Composition, morphology, and growth of clusters in a gas of particles with random interactions.

We use Langevin dynamics simulations to study the growth kinetics and the steady-state properties of condensed clusters in a dilute two-dimensional system of particles that are all different (APD) in the sense that each particle is characterized by a randomly chosen interaction parameter. The growth exponents, the transition temperatures, and the steady-state properties of the clusters and of the surrounding gas phase are obtained and compared with those of one-component systems. We investigate the fractionation phenomenon, i.e., how particles of different identities are distributed between the coexisting mother (gas) and daughter (clusters) phases. We study the local organization of particles inside clusters, according to their identity-neighbourhood identity ordering (NIO)-and compare the results with those of previous studies of NIO in dense APD systems.

A chemical redox reaction to generate rock salt-type materials: the case of Na3V2O5.

Chemical redox reactions are extremely efficient to prepare fully reduced or oxidized phases that are formed during the topotactic insertion/extraction of alkaline ions. Herein, we report these reactions and discuss the possibility to generate new ordered or disordered rock salt-type structures depending on the structure of the mother phase. We have shown that a disordered rock salt-type structure is formed when the transition element is located at the tetrahedral site, as exemplified by the formation of Na3V2O5 upon chemical reduction of V2O5.

Phase transformation surfaces around a crack tip for a shape memory alloys

Depending of the shape of the crack tip e.g. with or without curvature, the size of the phase transformation surface between a mother phase A (austenite) and a producted phase M (martensite) is different. The presentation is focussed to the modes I and II (opening and shearing modes). The elastic stress field around the crack tip without curvature is known in the litterature and the use of Linear Elastic Mechanical Theory is consistent with the deformations amplitude associated the beginning of the phase transformation (A \(\Rightarrow\) M). In order to take into account the curvature at the crack tip, one uses the approximated expressions of Creager and Paris (1967). A special attention is devoted to take into account the asymmetry between tension and compression behavior in the surfaces prediction.

Use of Topotactic Phase Transformations To Obtain Solutions of the Crystal Structures of Highly Disordered Materials

A straightforward procedure is outlined for prediction of the complete three-dimensional coordinate set for a highly disordered phase. For a mother and daughter phase, where one of the pair has an “unsolvable” structure, one needs only to (a) establish the topotaxy using previously published techniques, (b) obtain the topotactic transformation matrix, φ, between the ordered and highly disordered phase, and (c) apply the transpose of φ–1 to obtain a trial set of coordinates for refinement using the reflection data set of the highly disordered phase. For the inclusion compound [Fe(η-C5H5)]·3(NH2)2CS (1), which contains highly disordered ferrocene molecules above 160 K (polymorph 1_I), we found a more ordered structure at low temperature. At 135 K (polymorph 1_II), two ferrocene moieties are present in the thiourea channel in an approximately 1:1 ratio. One is nearly orthogonal (87.0°) to the channel axis, while the other is tipped 16.2° from that direction. Using steps (a–c) outlined above, a trial structure may be obtained for 1_I, and refinement leads to R1 = 4.25%. The structure of 1_1, containing 12-fold disordered ferrocene molecules, is similar to that found at temperatures below the phase transition, with a greater amount of the orthogonal orientation (55:45 vs 51:48), consistent with, but lower than, amounts found using solid-state NMR techniques. The low temperature polymorph is a trill, with an approximately 3:1:1 ratio of twin components. The exact alignment of the mother phase and the three daughters has been established using the methods of topotactic analysis described previously.

Self-narrowing of size distributions of nanostructures by nucleation antibunching

We study theoretically the size distributions of ensembles of nanostructures fed from a nanosize mother phase or a nanocatalyst that contains a limited number of the growth species that form each nanostructure. In such systems, the nucleation probability decreases exponentially after each nucleation event, leading to the so-called nucleation antibunching. Specifically, this effect has been observed in individual nanowires grown in the vapor-liquid-solid mode and greatly affects their properties. By performing numerical simulations over large ensembles of nanostructures as well as developing two different analytical schemes (a discrete and a continuum approach), we show that nucleation antibunching completely suppresses fluctuation-induced broadening of the size distribution. As a result, the variance of the distribution saturates to a time-independent value instead of growing infinitely with time. The size distribution widths and shapes primarily depend on the two parameters describing the degree of antibunching and the nucleation delay required to initiate the growth. The resulting sub-Poissonian distributions are highly desirable for improving size homogeneity of nanowires. On a more general level, this unique self-narrowing effect is expected whenever the growth rate is regulated by a nanophase which is able to nucleate an island much faster than it is refilled from a surrounding macroscopic phase.