Crystallization Mode Research Articles

Comparative study of gravity effects in directional solidification of Al-3.5 wt.% Si and Al-10 wt.% Cu alloys

Directional solidification experiments of Al-3.5 wt.% Si and Al-10 wt.% Cu alloys were conducted under gravity and microgravity conditions using a 50-m-high drop tube. The solidification morphology of the two alloys is mainly columnar dendrites and equiaxed dendrites, respectively. The dendrite arm spacing (DAS), eutectic content, grain size, and compositional distribution of both alloys exhibit distinct characteristics under gravity and microgravity conditions. The study introduces an innovative perspective by taking solute density and its redistribution behavior into account when discussing the gravity effects during the directional solidification of alloys. The results indicate that the way gravity works on the solidification behavior of alloys depends strongly on the redistribution behavior and density of solute as well as crystallization modes, such as columnar grain or equiaxed grain. These findings are helpful in clarifying the coupling mechanism of gravity and relevant factors on the solidification of alloys, not only contributing to understanding the effect of gravity on solidification better but also offering valuable guidance for eliminating solidification segregation and producing high-performance alloys.

Dynamic instability of two-step continuous crystallization with applications to beta-lactoglobulin, lysozyme and insulin crystal growth

Abstract This study is concerned with a continuous operation mode of bulk crystallization from a supersaturated solution with allowance for the two-step mechanism of nucleation and growth of crystals. The integro-differential system of governing equations for the crystal-size distribution function and liquid supersaturation is formulated accounting for mass input into the saturated solution and withdrawal rate of product crystals from the crystallizer (mass exchange with the environment). This system contains the particles growth rate for the two-step nucleation mechanism, which is only a function of crystal radius when considering $\beta$-lactoglobulin, lysozyme and insulin crystal growth. The steady-state analytical solutions of this system are found for the Weber-Volmer-Frenkel-Zel'dovich and Meirs nucleation kinetics. The crystal-size distribution function for unsteady crystallization mode is found by means of the integral Laplace transform method. This function enables us to derive a single unsteady integro-differential equation for the liquid supersaturation. A linear instability analysis based on this equation is carried out. The amplification rate and frequency of small perturbations following from this analysis enable us to find the neutral stability curve and the domains of stable and unstable crystallization. We show that the frequency of perturbations stabilizes near the neutral stability curve when dealing with the stable mode of continuous crystallization.

Crystallization Behavior and Structure of CaO–SiO2–Al2O3 Melts Representing the Oxide Inclusions in Si‐Mn Deoxidized Steel

For further optimization of the inclusion plasticization control process of Si‐Mn deoxidized steel, the crystallization behavior and structure of CaO–SiO2–Al2O3 system inclusions are investigated. The crystallization behavior of four typical low melting point CaO–SiO2–Al2O3 inclusions at 1000 to 1250 °C is studied by steel crucible isothermal heating experiment. The obtained results reveal that the glassy stability of the inclusions is high when the composition of low melting point inclusion is located in the eutectic region of tridymite, pseudowollastonite, and anorthite in the ternary phase diagram. However, when the composition of the inclusion is located in the eutectic region of melilite, pseudowollastonite, and anorthite, it is easy to undergo glass‐crystallization transformation and precipitate wollastonite and anorthite crystalline phases when isothermal heating at 1100 to 1200 °C. In addition, the crystallization mode of these inclusions is mainly surface crystallization, and the crystallization degree of inclusions increases with the increase of heat treatment temperature and time. The activation energy of crystallization and the content of nonbridging oxygen in the silicate structure NBO/T can be used to predict the crystallization ability of inclusions. The greater the activation energy of crystallization and the smaller the NBO/T value, the higher the glassy stability of the inclusions.

Facile Characterization of Isothermal Crystallization and Microphase Separation Kinetics of Polyamide 6 (PA6)‐Based Thermoplastic Elastomers

AbstractThe facile characterization of isothermal microphase separation kinetics in polyamide 6 (PA6)‐based thermoplastic elastomers (TPAE‐6) has long posed a challenge for the development of suitable melt spinning processes. In this study, this challenge is addressed through differential scanning calorimetry (DSC) measurements. It is assumed that the enthalpy changes of TPAE‐6 during the isothermal process are a linear superposition of enthalpy changes associated with microphase separation and crystallization of PA6 in hard phases, resembling that of TPAE‐6 without soft segments (TPAE‐6‐0). The study reveals that, as the concentration of soft segments in TPAE‐6 increases, the accelerated dynamics of phase separation become stronger than the dilution of soft segments to PA6 segments during isothermal process, resulting in an increase in the microphase separation rate of TPAE‐6. Furthermore, despite microphase separation, the overall crystallization rate of TPAE‐6 decreases with rising isothermal temperature and varies with increasing soft segment content at different temperatures. Additionally, the crystallization mode of TPAE‐6 follows two‐dimensional, three‐dimensional, or a combination of both crystal growth mechanisms, accompanied by a heterogeneous nucleation mechanism.

Vertically Concentrated Quantum Wells Enabling Highly Efficient Deep‐Blue Perovskite Light‐Emitting Diodes

AbstractDeep‐blue perovskite light‐emitting diodes (PeLEDs) based on quasi‐two‐dimensional (quasi‐2D) systems exist heightened sensitivity to the domain distribution. The top‐down crystallization mode will lead to a vertical gradient distribution of quantum well (QW) structure, which is unfavorable for deep‐blue emission. Herein, a thermal gradient annealing treatment is proposed to address the polydispersity issue of vertical QWs in quasi‐2D perovskites. The formation of large‐n domains at the upper interface of the perovskite film can be effectively inhibited by introducing a low‐temperature source in the annealing process. Combined with the utilization of NaBr to inhibit the undesirable n=1 domain, a vertically concentrated QW structure is ultimately attained. As a result, the fabricated device delivers a narrow and stable deep‐blue emission at 458 nm with an impressive external quantum efficiency (EQE) of 5.82 %. Green and sky‐blue PeLEDs with remarkable EQE of 21.83 % and 17.51 % are also successfully achieved, respectively, by using the same strategy. The findings provide a universal strategy across the entire quasi‐2D perovskites, paving the way for future practical application of PeLEDs.

Vertically Concentrated Quantum Wells Enabling Highly Efficient Deep-Blue Perovskite Light-Emitting Diodes.

Deep-blue perovskite light-emitting diodes (PeLEDs) based on quasi-two-dimensional (quasi-2D) systems exist heightened sensitivity to the domain distribution. The top-down crystallization mode will lead to a vertical gradient distribution of quantum well (QW) structure, which is unfavorable for deep-blue emission. Herein, a thermal gradient annealing treatment is proposed to address the polydispersity issue of vertical QWs in quasi-2D perovskites. The formation of large-n domains at the upper interface of the perovskite film can be effectively inhibited by introducing a low-temperature source in the annealing process. Combined with the utilization of NaBr to inhibit the undesirable n=1 domain, a vertically concentrated QW structure is ultimately attained. As a result, the fabricated device delivers a narrow and stable deep-blue emission at 458 nm with an impressive external quantum efficiency (EQE) of 5.82 %. Green and sky-blue PeLEDs with remarkable EQE of 21.83 % and 17.51 % are also successfully achieved, respectively, by using the same strategy. The findings provide a universal strategy across the entire quasi-2D perovskites, paving the way for future practical application of PeLEDs.

Microstructure and mechanical properties of electron beam welded joints of GH3128 and CoCrFeNi high-entropy alloy

This study addresses the research gap in the field of fusion welding for high-entropy alloys and high-temperature alloys. The microstructure and mechanical properties of CoCrFeNi/GH3128 electron beam welded joints were investigated. Influenced by solidification rate and elemental composition, differences in grain crystallization modes and morphologies were observed on both sides of the weld, accompanied by a columnar-to-equiaxed transition in the weld center. Significant fluctuations in elemental concentrations across the weld indicated elemental segregation, with distinct segregation behaviors observed for Fe, Co, Cr, Ti, Al, W, and Mo elements between columnar and dendritic grains. XRD results revealed the presence of γ, γ', FeCrNi solid solution, and various intermetallic compounds such as Ni17W3, Cr4Ni15W, and Fe3Ni2 in the weld zone. Hardness testing showed a gradual increase in microhardness from CoCrFeNi to GH3128 within the weld. Tensile testing indicated a tensile strength of 532.5 MPa and an elongation of 40.4 %, suggesting a ductile fracture mechanism for the joint. Post-tensile testing, noticeable work hardening, tensile deformation in the weld zone, grain refinement, and increased hardness were observed, highlighting the joint's enhanced strain-hardening ability. However, the corrosion resistance of the CoCrFeNi base material decreased.

Assessing phosphorus recovery from anaerobic digestion effluent of tapioca starch processing in a pilot – scale fluidized – bed homogeneous crystallizer: Effects of operation modes

This present study aimed to investigate the effects of two crystallization operation modes, batchwise operation (BO) and continuous operation (CO), on P recovery efficiency and characteristics of precipitates in a pilot – scale fluidized – bed homogenous crystallizer, using real anaerobic digestion (AD) effluent derived from tapioca starch processing as influent. Characterization techniques, including SEM – EDX, powder XRD, profile – matching, FT – IR, and crystal size distribution (CSD) analysis, were employed to identify phase compositions. Additionally, the purity and %P content of the target product were quantified using principles of hierarchical equilibrium thermodynamics and elemental analysis. As a result, the highest P recovery efficiency was 72.5 % for BO and 83.2 % for CO at a pH of 9 and a mixing rate of 400 rpm. Phase identification results revealed that struvite formed with Ca – rich solids, such as hydroxyapatite (HAP), notably exhibited higher impurity levels originating from CO modes. Precipitates from BO modes predominantly held 65 – 75 % struvite, with %P content ranging from 7.4 to 13.1 % — surpassing that of single superphosphate fertilizer (SSP, 18 – 22 % as P2O5), resulting in a suitable process in this study. Moreover, results obtained from the cost – benefit analysis (CBA) highlighted that BO scenario had economic viability (NP +0.05 to +1.53) with an estimate production cost of 3.47 USD/kg Premoved. Hence, the findings not only indicated that real AD effluent is suitable for P recovery, yielding high – quality struvite products, but also contribute to understanding the nuanced impact of crystallization modes on recovery yields and characteristics. This insight is invaluable for optimizing the process, leading to environmental benefits through reduced P and nitrogen discharge.

Effect of manganese on the structure of CMAS slag glass–ceramics

With the acceleration of industrialization, environmental issues have received great attention from governments and societies around the world. Utilizing solid wastes containing valuable heavy metals and exploring their role and application in materials is one of the focal issues of environmental protection in recent years. In this paper, in order to explore the effect of Mn content on the crystallization of CaO-MgO-Al2O3-SiO2 glass–ceramics, glass–ceramics with different content of MnO2 were prepared by sintering method and the effect of MnO2 doping on the crystalline properties, glass stability and heavy metal fixation properties of the stainless steel slag glass–ceramics was investigated by differential scanning calorimetry (DSC), Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscope (SEM). The analysis using crystallization kinetics showed that surface crystallization dominated the whole crystallization process in the range of 0% to 10% MnO2 content. The peak glass crystallization and depolymerisation temperatures of the glass–ceramics increased gradually with increasing MnO2 content, and the main crystallization mode of the samples was one-dimensional crystallization. The main crystalline phase of the resulting glass–ceramics was transformed from diopside to spinel, with a crystallization temperature of 860℃. Heavy metals solidified in the spinel phase. This study shows that heavy metals can be effectively immobilized in glass–ceramics. In summary, the use of solid waste to prepare final products with good environmental performance provides a feasible way to utilize solid waste resources.

In situ crystallization of amorphous Sb2Se3 films at electron beam irradiation

Amorphous films of Sb2Se3 were studied for crystallization under the action of electron irradiation. Electron microscopy studies demonstrated, that phase transformation is the island polymorphous crystallization mode with the relative length δ0≈ 183 for a film with a thickness 25 nm and δ0≈ 489 for a film with a thickness 40 nm. The dependence of the fraction of the crystalline phase on time has an exponential character, described by the JMAK formula. For films of both thicknesses numerical value of Avrami exponent nearest integer = 2.

Phase-pure Ruddlesden–Popper tin halide perovskites for solar energy conversion applications

Solvophobic engineering strategy promotes the self-assembly of fluorinated cations into micelles, which changes the crystallization mode and thus leads to the formation of phase-pure Ruddlesden–Popper tin halide perovskites.

Химико-термодинамические свойства чистых и многокомпонентных растворов сахарозы

To select an optimal mode of evaporation and crystallization, sugar producers need comprehensive databases of chemical and thermodynamic properties of sucrose solutions. This article introduces refined experimental estimates of the chemical and thermodynamic properties of pure and technical multicomponent sucrose solutions. 
 The study involved a modernized ebulliometer with two circulation tubes that measured the true boiling points of concentrated and supersaturated homogeneous solutions, as well as heterogeneous crystallizing systems. The boiling points of pure and multicomponent sucrose solutions were observed for the following variables: 5–93% dry solids, 60–100% purity, 20–100 kPa.
 In this study, the sucrose solutions did not obey Raoult’s laws for ideal mixtures, while the Ramsay-Young’s equation and Dühring’s rule were approximate. The thermodynamic properties of these solutions fit in the Lewis theory of activity. The study yielded a new thermodynamic equation for the boiling point in pure and technical multicomponent sucrose solutions. The authors revealed the correlation between the constants of Ramsay-Young and Dühring and the concentration and supersaturation of sucrose solutions, as well as the change in the entropy of these solutions. The error of estimate was 2–3%. The supersaturation coefficient was measured by the ratio of the boiling points of the solution and water. 
 The authors used differential and relative ebulliometric criteria to develop some practical methods for monitoring and controlling the process of isobaric evaporative crystallization. The new method can improve the commercial mass sucrose crystallization from boiling solutions.

Controllable single phase enables superior thermal stability in Sb-Sn-S films

Sb-Sn-S thin films were prepared by magnetron sputtering, and the effects of the SnS content on the macroscopic performance and microstructure of Sb were investigated. Results show that Sb55(SnS)45 exhibited the best performance, with a crystallization temperature of 210 °C, solving the issue of spontaneous Sb crystallization. However, the thermal stability of Sb37(SnS)63 film could no longer be significantly improved. The investigated crystallization mode revealed that Sb55(SnS)45 exhibited a growth-dominated crystallization behavior, maintaining a high crystallization rate while substantially improving the thermal stability. In terms of the microstructure, high-energy Sb–S and Sb–Sn bonds were formed, breaking the originally unstable Sb–Sb bonds. In the case of Sb37(SnS)63, the internal Sb–S and Sb–Sn bonding environment reached a saturation state, and the excessive introduction of SnS resulted in the stacking arrangement of the Sb–Sn–S amorphous alloy, leading to lattice distortion. However, an appropriate amount of Sb–Sn–S amorphous alloy polymerized around the SbSn grains, limiting the grain growth and the element segregation, thereby enhancing the long-term stability of the phase-change thin film.

Structure, morphology and crystallization of isodimorphic random copolymers: Copolyesters, copolycarbonates and copolyamides

Random copolymerization is used to prepare new polymeric materials that combine the desirable properties of different homopolymers. The covalent bonds between the comonomers enable miscibility and the formation of random copolymers with specific properties tailored for various applications. The crystallization behavior of random copolymers is intricate, encompassing up to three crystallization modes, i.e., total comonomeric exclusion, isomorphism, and isodimorphism. Isomorphism and isodimorphism allow for crystallization across the entire composition range, resulting in unique and potentially advantageous properties for each composition. These characteristics have garnered significant attention, as evidenced by the multiple publications that have appeared in the last decade.This contribution reviews the progress made in several aspects of isodimorphic copolymers, including new cases and applications. The initial section focuses on the factors influencing the pseudo-eutectic position, which is crucial for understanding the crystallization behavior of these copolymers. Subsequently, advancements in determining the degree of comonomer inclusion are discussed. Another section highlights studies that have raised new questions about the concepts of isodimorphism and isomorphism, particularly their presence in blends and terpolymers. These findings have opened up new avenues for research.In the final part of this review, selected examples are presented to illustrate the relationship between structure and properties in random copolymers. Furthermore, practical applications, such as using random copolymers as hot melt adhesives, are showcased. Despite significant progress in understanding the crystallization modes in random copolymers, this contribution emphasizes that new phenomena continue to emerge, providing further opportunities for exploration and shedding light on novel applications related to these intriguing crystallization modes.

Challenging Isodimorphism Concepts: Formation of Three Crystalline Phases in Poly(hexamethylene-ran-octamethylene carbonate) Copolymers.

In this work, poly(hexamethylene-ran-octamethylene carbonate) copolycarbonates were synthesized by melt polycondensation in a wide range of compositions. The copolymers displayed some of the characteristic isodimorphic thermal behavior, such as crystallization for all the compositions and a pseudoeutectic behavior of the melting temperature (Tm) versus composition. The pseudoeutectic point was located at 33 mol % poly(octamethylene carbonate) (POC) content (i.e., corresponding to the PH67O33C copolymer). Surprisingly, the crystallinities (Xc) for a wide range of copolymer compositions were higher than those of the parent components, a phenomenon that has not been observed before in isodimorphic random copolymers. The structural characterization, performed by wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering experiments, revealed unexpected results depending on composition. On the one hand, the poly(hexamethylene carbonate) (PHC)- and POC-rich copolymers crystallize in PHC- and POC-type crystals, as expected. Moreover, upon cooling and heating, in situ WAXS experiments evidenced that these materials undergo reversible solid-solid transitions [δ-α (PHC) and δ-α-β (POC)] present in the parent components but at lower temperatures. On the other hand, a novel behavior was found for copolymers with 33-73 mol % POC (including the pseudoeutectic point), which are those with higher crystallinities than the parent components. For these copolymers, a new crystalline phase that is different from that of both homopolymers was observed. The in situ WAXS results for these copolymers confirmed that this novel phase is stable upon cooling and heating and does not show any crystallographic feature of the parent components or their solid-solid transitions. FTIR experiments confirmed this behavior, revealing that the new phase adopts a polyethylene-like chain conformation that differs from the trans-dominant ones exhibited by the parent components. This finding challenges the established concepts of isodimorphism and questions whether a combination of crystallization modes (isodimorphism and isomorphism) is possible in the same family of random copolymers just by changing the composition.

Design of Crystal Growth Dimensionality in Synthetic Wax: The Kinetics of Nonisothermal Crystallization Processes.

The demand for the development of multifunctional materials in emerging technologies has stimulated intensive research on the control of crystallization processes in numerous scientific and engineering fields. In this article, we examine the kinetics of nonisothermal melt crystallization in synthetic wax using differential scanning calorimetry (DSC) supported by polarized optical microscopy (POM) to describe crystallization modes in a multicomponent molecular system. We detected the macroscopic growth of three crystal phases and the formation of two crystal phases as a transformation from a disordered crystal mesophase into an ordered crystal. To characterize individual crystal phase formation, we examine the activation energy evaluated by isoconversional analysis and utilize the Ozawa and Mo methods to determine the kinetic details of the crystal growth from the isotropic phase. Our investigation reveals the possibility of the design of crystal growth dimensionality as three-dimensional spherulitic-like, two-dimensional rodlike, and one-dimensional needle-shaped crystal forms of shorter n-alkanes by controlling the solidification pathway of long-chain n-alkanes and the interplay of the thermodynamic and kinetic mechanisms of crystallization.

Effect of TiO<sub>2</sub> Addition and Cooling Rate on Crystallization Behavior of Separated Slag Containing Low-grade RE

With the continued exploitation and utilization of high-grade rare earth ores, it is increasingly important to extract rare earths from separated slag containing low-grade rare earth. The X-ray powder diffraction, scanning electron microscopy, electron probe micro-analyzer and confocal laser scanning microscopy were used to explore the influence of TiO2 and cooling rate on the crystallization of CaO-SiO2-TiO2-10 wt% P2O5-8 wt% Nb2O5-5 wt% CeO2-5 wt% CaF2 slag system. In this study, the britholite was precipitated selectively as the Ce-enriched phase. When TiO2 was added at less than 12 wt%, the britholite was promoted to crystallize meanwhile the Ca2Nb2O7 was suppressed. However, CaTiSiO5 inhibited the growth of britholite when the TiO2 content exceeded 15 wt%. The non-isothermal crystallization kinetics had also been investigated for the TiO2 content and cooling rate varied from 0-18 wt% and 10-40°C/min, respectively. The continuous cooling transformation diagram and the relative crystallinity of the primary crystals were also constructed. Based on the observation and measurement of crystallization process, the modified Avrami model was applied to determine the crystallization mode of britholite with 9 wt% TiO2 addition. It was constant nucleation rate and one-dimensional growth with diffusion controlled. Considering the nucleation and growth of crystals, 20–30°C/min was preferred to be the reasonable parameter during cooling stage.

Electrodialytic crystallization to enable zero liquid discharge

The management of hypersaline brines (that is, wastewater of high salinity) is a technical challenge that has received increasing attention due to their growing volume, environmental impacts and increasingly stringent regulations. Here we present electrodialytic crystallization (EDC) as a new process to achieve brine crystallization without evaporation. In an EDC process, the brine stream recirculating between an electrodialysis cell and a crystallizer remains oversaturated via continuous electromigration of ions from the feed stream across the ion exchange membranes. We first used Na2SO4 as the model salt to demonstrate the feasibility of EDC and to perform a systematic investigation of how crystallization kinetics and crystal size distribution depend on current density and crystallization mode. We then elucidated the criterion of crystallizability and showed how it depends on salt species, membrane properties and operating conditions. Lastly, we analysed the energy consumption of an EDC-reverse osmosis treatment train for achieving zero liquid discharge of a Na2SO4 brine. Overall, this study provides a proof of concept for EDC as an electric-field driven and non-evaporative crystallization process, and lays the foundation for its future technical development and optimization. Achieving zero liquid discharge is an essential step towards the sustainability of hypersaline brine treatment. A potential method to achieve zero liquid discharge on the basis of electrodialysis crystallization is now demonstrated.

Unsteady, steady, and self-oscillatory modes of the bulk continuous crystallization with mass influx and withdrawal of product crystals

Unsteady, steady, and self-oscillatory modes of the bulk continuous crystallization with mass influx and withdrawal of product crystals

Crystal growth in amorphous films of tantalum pentoxide

Amorphous films are formed on substrates at room temperature in the process of pulsed laser sputtering of Ta target in an oxygen atmosphere. Electron beam irradiation causes their crystallization with the formation of Ta2O5 crystals with hexagonal lattice. Electron microscope investigation, including “in situ” and video recording methods, revealed the following crystallization modes in different regions of the same amorphous film of Ta2O5. 1. Island polymorphous crystallization. 2. Interjacent crystallization mode. 3. Layer polymorphous crystallization mode. The presence of three different crystallization modes is explained by the phenomenon of polyamorphism in amorphous films.