Stages Of Crystallization Research Articles

Prolonged Trachyte Storage and Unusual Remobilization at Piton de la Fournaise, La Réunion Island, Indian Ocean: Li, O, Sr, Nd, Pb and Th Isotope Study

Abstract La Réunion Island includes two major volcanic systems. About 0·5 Myr ago, Piton des Neiges volcano declined, while Piton de la Fournaise volcano grew on its flank. Since then the Piton de la Fournaise shield volcano has produced homogeneous lavas with chemical compositions transitional between alkali and tholeiitic basalts. In April 2007, the volcano emitted a very small volume of trachytic pumice during its largest historical eruption. We conducted a comprehensive petrological and geochemical study of the pumice to understand the occurrence of such silicic melt in the feeding system of this highly active basaltic volcano. Isotopes of Sr, Nd, Pb and O, together with trace elements, indicate that the trachyte is genetically related to the La Réunion mantle plume and derives from crystallization of a typical basalt. The trachyte chemistry records a long and complex history of differentiation and outgassing. The extensive depletion of moderately volatile elements (F, Cl, B, Cs, Cu, Li) and less volatile uranium is consistent with exsolution of dense fluids at depths of several kilometres. Lithium isotopes point to closed-system degassing during the very late stages of crystallization. U-series isotopes and radiogenic 208Pb*/206Pb* constrain the age of U loss to between 0·4 and 2·1 Ma. This age is as old as or older than the Piton de la Fournaise shield edifice. The 2007 trachyte could thus be a liquid remnant of an extinct volcano, such as Piton des Neiges or Les Alizés (Piton de la Fournaise proto-volcano). It could also result from partial melting of an old syenite intrusion or remobilization of interstitial melts not fully solidified. Thermal modelling indicates that the sustained heat flux from hot basaltic magmas rising from the mantle can maintain temperatures above 800 °C in the central feeding system, and prevent total solidification of magmas trapped in this hot core.

Migration distribution and recovery of rare earth elements in the nitrophosphate process of fertilizer production

This work aimed to investigate the migration distribution and recovery of rare earth elements (REEs) of phosphate concentrate in the nitrophosphate process of fertilizer production. The nitrophosphate process was divided into three main stages, namely, acidolysis, frozen crystallization, and ammonia neutralization, to detect REE migration and distribution. By controlling the acidolysis stage parameters (55% HNO3; temperature, 60 °C; acid-to-phosphate concentrate ratio, 1.25; acidolysis time, 120 min), the leaching efficiency of REEs reached (95.4 ± 0.7)%. In the frozen crystallization stage, the crystallization temperature mainly affected the transition and distribution of REEs in the acidolysis liquid. By controlling the frozen crystallization temperature at −2 °C and time at 120 min, (4.49 ± 0.03)% of REEs co-precipitated with Ca(NO3)2·4H2O into the solid phase, and the majority of REEs stayed in the crystalline mother liquor. In the ammonia neutralization stage, the value of pH mainly influenced the extraction efficiency of REEs. By controlling the ammonia neutralization stage parameters (pH, 1.7; neutralization temperature, 60 °C; neutralization time, 180 min), the extraction efficiency of REEs in the crystalline mother liquor reached (87.6 ± 0.7)%. The ammonia neutralized precipitates were characterized by scanning electron microscopy, energy dispersive spectrum, X-ray diffraction, and X-ray photoelectron spectroscopy to verify the presence and forms of REEs. Finally, the HSC6.0 software was used to analyze the thermodynamic reaction process of phosphate concentrate decomposition with nitric acid and ammonia neutralization stage. Results showed that REEs in the form of REEH2PO42+, REENO32+, and REE3+ diffused into the mixed acid solution in the acidolysis and frozen crystallization stages, and REEs were precipitated in the form of REEPO4·nH2O, REEnCam(PO4)(3n+2m)/3, and REEF3 in the ammonia neutralization stage.

Direct Visualization of the Earliest Stages of Crystallization.

Investigating the earliest stages of crystallization requires the transmission electron microscope (TEM) and is particularly challenging for materials which can be affected by the electron beam. Typically, when imaging at magnifications high enough to observe local crystallinity, the electron beam's current density must be high to produce adequate image contrast. Yet, minimizing the electron dose is necessary to reduce the changes caused by the beam. With the advent of a sensitive, high-speed, direct-detection camera for a TEM that is corrected for spherical aberration, it is possible to probe the early stages of crystallization at the atomic scale. High-quality images with low contrast can now be analyzed using new computing methods. In the present paper, this approach is illustrated for crystallization in a Ge2Sb2Te5 (GST-225) phase-change material which can undergo particularly rapid phase transformations and is sensitive to the electron beam. A thin (20 nm) film of GST-225 has been directly imaged in the TEM and the low-dose images processed using Python scripting to extract details of the nanoscale nuclei. Quantitative analysis of the processed images in a video sequence also allows the growth of such nuclei to be followed.

Features of the Geological Structure and Genesis of the Tebinbulak Deposit (Ridge Sultan-Uvais)

In this article, we want to draw attention to the hysteron-magmatic origin of titanium-magnetite ores of the Tibinbulak gabbro-peridotite complex located in the northwestern part of the Sultan-Uvais ridge. Which is the only outlet of the Phanerozoic foundation between the mountain structures of the Urals and the Southern Tien Shan. The article examines the characteristic features of petrochemical and structural features of ore minerals (ilmenite, magnetite) and the main rock-forming minerals of the gabbro-peridotite complex (peridotite, pyroxenite, tebinnite, pyroxene hornblendite and plagioclase) with clarification of the structural relationships. It was found that magnetite mineralization of the Tebinbulak intrusion was superimposed on ultrabasic rocks in the final stages of crystallization of the latter. Prolonged auto-metasomatic transformations led to the enlargement of magnetite crystals in places subject to decay. In this case, aggregates of spinel - hercynite with sphene rims were formed. Simultaneously with the formation of sphene, ilmenite crystals appeared in the form of radiant needle-shaped aggregates. In this case, the primary crystals of magnetite lost their faces and became shapeless. Relatively large precipitates of titano-magnetite formed at this stage with the filling of cracks in the rock and interstices between minerals. Based on the data presented, we note that the titano-magnetite ores of the Tebinbulak deposit arose in the late magmatic (hysteron-geneous) setting of auto-metamorphic replacement of the main carriers of iron and titanium pyroxene and plagioclase with hornblende. Also, the studied geochemical composition of ores damages that the titano-magnetite ores of the Tebinbulak deposit are a complex raw material, from which not only iron but also vanadium concentrate can be extracted.

Properties of magnesium potassium phosphate cement-expanded perlite composites applied as fire resistance coating

Cement-based composites have been a commonly used fire resistance material. As a new cement, magnesium potassium phosphate cement (MKPC) has been a popular and important research object due to its various excellent properties including heat resistant. However, only limited studies have been conducted on its application as fire-resistant coating. In this paper, the thermal properties of MKPC blended with/without expanded perlite (EP) under fire exposure were investigated. Two types of EP with open-pore and closed-pore structures were used, and each type of EP contained two different sized particles including 212–270 μm and 270–550 μm. The fluidity and setting time of MKPC-EP composites and adhesive strength between MKPC-EP composites coating and plywood were measured. The fire resistance properties of MKPC-EP composites were studied, including loss of weight (LOW), generated cracks, phase changes, thermal analysis, residual adhesive strength, and microstructure changes. The obtained results were intended to reveal the feasibility of MKPC-EP composites applied as coating to protect the substrate against exposure to fire. The addition of EP decreased the fluidity, extended the setting time, and enhanced the adhesive strength before and after fire test. LOW and accumulative lengths of visible cracks after fire exposure reduced for certain formula and are dependent on the pore structures, sizes and dosage of EP. X-ray diffraction (XRD) investigation and thermal analysis-infrared spectroscopy reveal MgKPO4⋅6H2O decomposed to MgKPO4⋅H2O by losing crystal water stage by stage during elevating temperature. Scanning electron microscopic (SEM) observations show that EP refined the MgKPO4⋅6H2O, and, after exposure to flame, the MKPC-EP exhibited a much denser microstructure with interconnecting MgKPO4·H2O of radiative flakes, when compared to the MKPC paste.

The effect of the type of component crystal lattice on nanocrystal formation in Co-based amorphous alloys

The structure of Co-based amorphous alloys (Co-Fe-B-Si-M system, where M = Ni, Nb, or Mn) after initial stage of crystallization was studied. In Co67Fe5Nb8B20 alloy, the formation of a new metastable phase has been detected and its structure has been determined. The dependence of the type of the crystal lattice of nanocrystals being formed on the structure of an alloying component (Ni, Nb, or Mn) and their solubility in the main alloy component was discovered. The dependence observed agrees with the assumption of heterogeneous nanocrystal nucleation on ordered regions in the amorphous phase, which have the same short-range order as the crystalline phase being formed.

Crystallization behavior of two Al-Ni-Co-Gd amorphous alloys with selected Ni/Co ratios

Metallic ribbons of Al86NixCoyGd6 composition with different ratio of nickel and cobalt, (x/y = 1 and 3), were produced by standard planar flow casting method in amorphous state. Phase transformation follows upon heat treatment in 5 crystallization stages. Detailed microstructural characterizations (e. g. scanning electron diffraction experiments) were carried out to explain unusual phenomenon shown in x-ray diffraction data, calorimetric and complementary resistometry measurements bound to the second transformation stage. The observed phenomenon was proven to be connected to a observed reordering on the sub-nanometer scale without previous chemical rearrangement forming from amorphous matrix surrounding fcc-Al(Ni) nanocrystals, appearing as a second and single transformation step. Kinetics of crystallization was studied by differential scanning calorimetry and further monitored by electrical resistivity measurements. The transformation sequence up to 850 K is explained by X-ray diffraction and supported with detailed scanning transmission electron microscopy and energy dispersive spectroscopy observations.

Fast Optical Reflectance Measurements during Spin Coating and Annealing of Organic–Inorganic Perovskite Precursor Solutions

In article number 2000479, Jörg Rappich and co-workers address early stages of film formation and crystallization of organic lead triiodide perovskites by employing in-situ high-speed spectral reflectance measurements. The time scale ranges from 0.2 milliseconds to seconds. Data were taken during spincoating and subsequent low-temperature annealing. The measurements enable the investigation of changes in the solution of the spin-coating process. The evaporation of the solvent during spin-coating results in the spontaneous crystallization of the perovskite layer. During the subsequent annealing process, the diffuse reflectance measured with high sensitivity provides insight into the transformation and crystallization process of the precursor layer to the final perovskite layer.

Understanding Substrate-Guided Assembly in van der Waals Epitaxy by in Situ Laser Crystallization within a Transmission Electron Microscope.

Understanding the bottom-up synthesis of atomically thin two-dimensional (2D) crystals and heterostructures is important for the development of new processing strategies to assemble 2D heterostructures with desired functional properties. Here, we utilize in situ laser-heating within a transmission electron microscope (TEM) to understand the stages of crystallization and coalescence of amorphous precursors deposited by pulsed laser deposition (PLD) as they are guided by 2D crystalline substrates into van der Waals (vdW) epitaxial heterostructures. Amorphous clusters of tungsten selenide were deposited by PLD at room temperature onto graphene or MoSe2 monolayer crystals that were suspended on TEM grids. The precursors were then stepwise evolved into 2D heterostructures with pulsed laser heating treatments within the TEM. The lattice-matching provided by the MoSe2 substrate is shown to guide the formation of large-domain, heteroepitaxial vdW WSe2/MoSe2 bilayers both during the crystallization process via direct templating and after crystallization by assisting the coalescence of nanosized domains through nonclassical particle attachment processes including domain rotation and grain boundary migration. The favorable energetics for domain rotation induced by lattice matching with the substrate were understood from first-principles calculations. These in situ TEM studies of pulsed laser-driven nonequilibrium crystallization phenomena represent a transformational tool for the rapid exploration of synthesis and processing pathways that may occur on extremely different length and time scales and lend insight into the growth of 2D crystals by PLD and laser crystallization.

Compositional Variations of Spinels from Ultramafic Lamprophyres of the Chadobets Complex (Siberian Craton, Russia)

Ultramafic lamprophyres (UMLs) are mantle rocks that provide important information about the composition of specific carbonate–silicate alkaline melts in the mantle as well as the processes contributing to their origin. Minerals of the spinel group typically occur in UMLs and have a unique “genetic memory.” Investigations of the spinel minerals from the UMLs of the Chadobets complex show the physicochemical and thermodynamic features of the alkaline rocks’ crystallization. The spinels of these UMLs have four stages of crystallization. The first spinel xenocrysts were found only in damtjernite pipes, formed from mantle peridotite, and were captured during the rising of the primary melt to the surface. The next stages of the spinel composition evolution are related to the high-chromium spinel crystallization, which changed to a high-alumina composition. The composition then changed to magnesian ulvöspinel–magnetites with strong decreases in the Al and Cr amounts caused by the release of carbon dioxide, rapid temperature changes, and crystallization of the main primary groundmass minerals such as phlogopite and carbonates. Melt inclusion analyses showed the predominance of aluminosilicate (phlogopite, clinopyroxene, and/or albite) and carbonate (calcite and dolomite) daughter phases in the inclusions that are consistent with the chemical evolution of the Cr-spinel trend. The further evolution of the spinels from magnesian ulvöspinel–magnetite to Ti-magnetite is accompanied by the formation of atoll structures caused by resorption of the spinel minerals.

Manipulating Crystallization Kinetics of Conjugated Polymers in Nonfullerene Photovoltaic Blends toward Refined Morphologies and Higher Performances

The introduction of solvent additives has become a general approach in optimizing the active layer morphology in organic photovoltaics (OPV) to achieve high power conversion efficiency. It is of general interest to understand the mechanism of how additives optimize the thin-film nanostructure formation such as crystallization kinetics and phase separation. In the current manuscript, state-of-the-art nonfullerene bulk heterojunction blends, PM6:IT-4F mixture, are used in a slot-die coating experiment. The 1,8-octanedithiol (DIO)-aided fabrication leads to a significant increase in the power conversion efficiency (PCE) from 10.11 to 12.67%. Exciton dissociation and carrier transport have also been improved, largely associated with morphology improvement. Time-resolved crystallization kinetics during PM6:IT-4F film formation under different processing conditions was studied by in situ grazing-incidence wide-angle X-ray scattering (GIWAXS), in which a detailed polymer fibril morphology formation was seen. The Johnson–Mehl–Avrami–Kolmogorov (JMAK) crystallization analysis affords insights that the addition of the DIO additive in a small amount would not only increase the nucleation rate during the nucleation and growth stage but also introduce secondary fibril crystal perfection via burst nucleation-mediated crystallization to a grain boundary-induced crystallization stage change. These observations can be of general interest to the OPV community in manipulating the printed solar cell morphology and efficiency toward the commercial application.

Sodium recovery from crystallization waste of Bayer liquor in alumina beneficiation

AbstractThe residue generated in the crystallization stage of the Bayer process to obtain alumina may be used for sodium recovery. The addition of calcium hydroxide (Ca(OH)2) to the residues of the Bayer process may become an alternative study for recovering the caustic soda (NaOH) inserted in the process, so the objective of this work is to utilize the causticization technique in a real residue obtained from the crystallization step of the Bayer liquor. The residue characterized presented 13% Al, so this indicated that there were losses of this element in the Bayer process. Also, the presence of Na2C2O4, Na2CO3, and NaAlO2 were observed. The total sodium recovery was 87%, and the best condition for causticization to occur was in the use of a 1:1 molar ratio (Na2C2O4 and Ca(OH)2), during 6 h of reaction, and at 80°C, with the conversion of 96% of the organic carbons present in the solution. The causticization was effective in separating sodium from residue in the removal of oxalates, organics, and aluminium, and it provided a reaction that separated oxalates and carbonates that are harmful to the aluminium obtaining process.

Carboniferous high‐P metamorphism and deformation in the Belledonne Massif (Western Alps)

AbstractThe age and P–T conditions of Variscan high‐P(HP) metamorphism in the Palaeozoic basement of the western Alps remain poorly constrained, but is nevertheless crucial to build a consistent tectonic scenario for the southeastern domain of the Variscan Belt. We report here the results of a structural, petrological, thermobarometric, and geochronological investigation of an eclogite‐bearing unit exposed in the northeastern part of the Belledonne Massif (France). This unit is mostly composed of metasediments that are locally migmatized and contain decametre‐ to hectometre‐scale lenses of orthogneiss and amphibolites. SIMS U–Pb dating of magmatic zircon cores in two retrogressed ecogites yields ages at 456 ± 4 Ma and 448 ± 6 Ma, which are interpreted to date the emplacement of the magmatic protoliths. The peak pressure stage in the retrogressed eclogites is estimated to be >1.4 GPa at 690–740°C, and was followed by decompression from 1.4 to ca. 1.0 GPa at 700–800°C. By contrast, the investigated migmatitic metasediment does not present any trace of HP metamorphism, but instead preserves prograde evolution from sub‐solidus conditions (ca. 0.8–1.1 GPa and 600–700°C) to supra‐solidus conditions (1.1–1.4 GPa and 700–780°C). A later stage of retrogression below ca. 0.5–0.8 GPa and 570–610°C is recorded in both lithologies, and is taken to indicate cooling and exhumation to upper crustal levels. Metamorphism was roughly coeval in the retrogressed eclogites and in the migmatitic metasediment. Metamorphic zircon rims yield U–Pb dates scattering between 340 and 310 Ma in both lithologies. In the migmatitic metasediment, a distinct younger age at 306 ± 3 Ma is interpreted to represent late stages of melt crystallization. In the retrogressed eclogites, zircon zoning and chemical composition (Th/U and REE) indicate initial crystallization of the rims during the HP stage followed by protracted growth during decompression to granulitic/amphibolitic conditions. Rutile U–Pb dating in one eclogite sample yields an age of 340 ± 11 Ma similar to the oldest zircon ages and is interpreted to approximate the age of the peak pressure metamorphism. Retrogression in the amphibolite facies is correlated with the development of a penetrative, N30° subvertical mylonitic S2 foliation. Regionally, this deformation occurs in a dextral transpressive corridor interpreted to represent a crustal‐scale shear zone active during the mid‐late Carboniferous. We therefore suggest that this structure has driven the exhumation of eclogites from the lower crust and their mixing with mid‐crustal felsic lithologies devoid of HP assemblages.

Uranium incorporation in fluorite and exploration of U–Pb dating

Abstract. The age of ore deposits constitutes a decisive element in understanding their formation. Deciphering their precise chronology may be a challenge in the absence of mineral phases that can be dated by conventional geochronometers. Fluorite is very common either as the major or accessory mineral in a wide variety of ores and may provide information regarding the origin and timing of mineralizing fluid flows. In this contribution, we explore U–Pb dating on fluorite crystals from the world-class carbonate strata-bound fluorite ore of Pierre-Perthuis in Burgundy (Morvan massif, France). The uranium distribution within fluorite is mapped using induced fission-track and synchrotron radiation X-ray fluorescence nano-imaging, showing that higher U content is measured in an overgrowth of fluorite (Flog) as a discrete band. Preservation of a micrometer-thick zonation in U, associated with other substituted elements such as Sr, Y, Fe and Zr, implies that neither solid-state diffusion nor dissolution–recrystallization occurred. These U-bearing external fluorite overgrowths contain solid inclusions of about 30 µm globular pyrite crystals with a mean δ34S of −23.6 ± 0.4 ‰V-CDT. We propose that the U incorporation in the fluorite lattice results from the development of a redox front during bacterial sulfate reduction. Flog generation sampled and analyzed by laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS) on four different crystals provides identical U–Pb ages within the limits of analytical uncertainty. Considered altogether, these four crystals yield an age estimate of 40.0 ± 1.7 Ma, not corrected for matrix-related elemental fractionation. Our results show that fluorite LA-ICP-MS U–Pb geochronology has potential for dating distinct crystal growth stages, although further research should be conducted to evaluate its accuracy.

Unveiling the mechanism of phase and morphology selections during the devitrification of Al-Sm amorphous ribbon

The complex interplay between energetic and kinetic factors that governs the phase and morphology selections can originate at the earliest stage of crystallization in the amorphous parent phases. Because of the extreme difficulties in capturing the microscopic nucleation process, a detailed picture of how initial disordered structures affect the transformation pathway remains unclear. Here, we report the experimental observation of widely varying phase selection and grain size evolution during the devitrification of a homogeneous melt-spun glassy ribbon. Two different crystalline phases $\ensuremath{\theta}\text{\ensuremath{-}}{\mathrm{Al}}_{5}\mathrm{Sm}$ and $\ensuremath{\varepsilon}\text{\ensuremath{-}}{\mathrm{Al}}_{60}{\mathrm{Sm}}_{11}$ are found to form in the different regions of the same metallic glass (MG) ribbon during the devitrification. The grain size of the $\ensuremath{\varepsilon}\text{\ensuremath{-}}{\mathrm{Al}}_{60}{\mathrm{Sm}}_{11}$ phase shows a strong spatial heterogeneity. The coarse-grained $\ensuremath{\varepsilon}\text{\ensuremath{-}}{\mathrm{Al}}_{60}{\mathrm{Sm}}_{11}$ phase coupled with the small volume fraction of the $\ensuremath{\theta}\text{\ensuremath{-}}{\mathrm{Al}}_{5}\mathrm{Sm}$ phase is preferably formed close to the wheel side of the melt-spun ribbon. Combining experimental characterization and computational simulations, we show that phase selection and microstructure evolution can be traced back to different types and populations of atomic clusters that serve as precursors for the nucleation of different crystalline phases. Inhomogeneous cooling rates cause different structure orders across the glass sample during the quenching process. Our findings provide direct insight into the effect of structural order on the crystallization pathways during the devitrification of MG. It also opens an avenue to study the detailed nucleation process at the atomic level using the MG as a platform and suggests the opportunity of microstructure and property design via controlling the cooling process.

Monitoring Crystallization Processes in Confined Porous Materials by Dynamic Nuclear Polarization Solid-State Nuclear Magnetic Resonance.

Establishing mechanistic understanding of crystallization processes at the molecular level is challenging, as it requires both the detection of transient solid phases and monitoring the evolution of both liquid and solid phases as a function of time. Here, we demonstrate the application of dynamic nuclear polarization (DNP) enhanced NMR spectroscopy to study crystallization under nanoscopic confinement, revealing a viable approach to interrogate different stages of crystallization processes. We focus on crystallization of glycine within the nanometric pores (7–8 nm) of a tailored mesoporous SBA-15 silica material with wall-embedded TEMPO radicals. The results show that the early stages of crystallization, characterized by the transition from the solution phase to the first crystalline phase, are straightforwardly observed using this experimental strategy. Importantly, the NMR sensitivity enhancement provided by DNP allows the detection of intermediate phases that would not be observable using standard solid-state NMR experiments. Our results also show that the metastable β polymorph of glycine, which has only transient existence under bulk crystallization conditions, remains trapped within the pores of the mesoporous SBA-15 silica material for more than 200 days.

Room-temperature synthesis of various allotropes of carbon nanostructures (graphene, graphene polyhedra, carbon nanotubes and nano-onions, n-diamond nanocrystals) with aid of ultrasonic shock using ethanol and potassium hydroxide

The exploration of the synthesis methods of sp2 and sp3 carbon nanomaterials under ambient conditions is very meaningful towards their industrial applications. The existing bottom-up synthesis methods usually need high temperature or high pressure conditions. We report a facile and environmentally-friendly approach enabling the synthesis of almost all types of known carbon nanostructures at room temperature and under atmosphere pressure. They include both sp3-structured n-diamond (not cubic diamond) nanocrystals and sp2-structured graphene, defective multiwalled carbon nanotubes, defective carbon nano-onions as well as graphene polyhedra. The reaction of ethanol and potassium hydroxide at ambient conditions yields n-diamond nanocrystals. To synthesize the sp2 carbon nanomaterials, the assistance of the ultrasonic shock at the early stage of crystallization is necessary to ensure the formation of the carbon ring nucleation seeds. The synthetic yields of n-diamond nanocrystals, graphene polyhedra, defective carbon nano-onions, and graphene are estimated to be 0.37%, 0.30%, 0.04%, and 0.01% (carbon mass ratio), respectively, and all of them have good crystallinity. These results improve our understanding of the low-temperature crystal growth process of the carbon nanostructures.

Formation of bcc nanocrystals in Co-based amorphous alloys

The crystallization of amorphous alloys of Co-Fe-B-(Ti, Nb) system was studied by differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. It was determined that the alloying of amorphous alloys of Co-Fe-B system with elements having a bcc lattice promotes the formation of a metastable phase with this lattice during crystallization. Nanocrystal size and the fraction of the phase with a bcc lattice depend on the concentration of alloying components. When the concentration of bcc components increases, nanocrystal size decreases. When Nb (an element with a bcc lattice) is replaced by Ti (an element with an hcp lattice), the fraction of the bcc phase decreases, and multiphase crystallization (simultaneous formation of several crystalline phases) occurs. In Co56Fe16B20Ti8 alloy, the first crystallization stage consists of two steps. During the seemingly simultaneous formation of several crystalline phases, first a small quantity of the bcc phase and then Co23B6 and fcc-Cо crystals are formed sequentially. All the results obtained indicate heterogeneous nanocrystal formation with the nucleation on structurally related ordered regions (on ordered clusters which consist of alloy components with the structure related to the crystallizing phase).

Effects of high hydrostatic pressure on microstructure, physicochemical properties and in vitro digestibility of oat starch/β‐glucan mixtures

AbstractOats do not contain gluten protein, and oat dough structure is formed mainly through the hydrogen bonding of starch and β‐glucan. As a non‐thermal processing technology, high hydrostatic pressure (HHP) is mainly used to modify starch and protein in food processing. This study investigated the effects of HHP treatment on the morphological, structural, thermal, pasting and in vitro digestion properties of oat starch/β‐glucan mixtures. Results showed that β‐glucan interconnects with amylose through hydrogen bonding and has a protective effect on the crystalline region of oat starch. Effect of HHP treatment on the crystal structure of mixture system goes through crystal structure perfection stage, crystallisation disintegration and gelatinisation stage. After 300–400 MPa treatment, the changes in particle surface were not obvious, the phase transition temperature, the ΔHgel and the PT of mixtures increased, while the particle size, viscosity and BD values decreased. After 500–600 MPa treatment, mixtures were completely gelatinised, most of the particles swelled and deformed, the particle size increased significantly. The principal component analysis results show that the complexes were distributed in the same region with similar properties after the 300–400 MPa and 500–600 MPa treatments, respectively.

Atomic Mechanisms of Nanocrystallization via Cluster-Clouds in Solution Studied by Liquid-Phase Scanning Transmission Electron Microscopy.

The formation of nanocrystals is at the heart of various scientific disciplines, but the atomic mechanisms underlying the early stages of crystallization from supersaturated solutions are still rather unclear. Here, we used in situ liquid-phase scanning transmission electron microscopy to study at the atomic level the very early stages of gold nanocrystal growth, and the evolution of its crystallinity. We found that the nucleation is initiated by the formation of poorly crystalline nanoparticles. These are transformed into monocrystals via nanocrystallization governed by a complex process of multiple out-and-in exchanges of matter between a crystalline-core and a disordered-shell, referred to as the cluster-cloud. Our observations at the crystal/cluster-cloud interface during growth demonstrate that the initially formed nanocrystals expel the poorly crystallized phases as nanoclusters into the cluster-cloud, then readsorb it by two distinct pathways, namely, by (i) monomer attachments and (ii) nanocluster coalescence. This growth process eventually leads to the formation of monocrystalline nanoparticles.