Search

Sodium dodecyl sulfate (SDS) was employed as a sacrificial template to assist in the preparation of catalysts, which not only modulates the catalyst morphology but also inhibits the Ostwald ripening process, resulting in more active components for the activity improvement. [Display omitted] • Alloy catalyst of sodium dodecyl sulfate (SDS) sacrificial template-assisted preparation is first reported. • Morphology of NiCo-alloy can be modulated with SDS concentration. • Synergistic interaction of Ni-Co decreases the NiOOH generation potential. Designing efficient non-precious metal-based catalysts for urea oxidation reaction (UOR) is essential for achieving energy-saving hydrogen production and the treatment of wastewater containing ammonia. In this study, sodium dodecyl sulfate (SDS) is employed as a sacrificial template to synthesize NiCo alloy nanowires (NiCo(SDS)/CC), and the instinct formation mechanism is investigated. It is found that SDS can inhibit the Ostwald ripening during hydrothermal and calcination processes, which could release abundant active cobalt, thereby modulating the electronic structure to promote the catalytic reaction. Moreover, SDS as a sacrificial template can induce the deposition of metal atoms and increase the specific surface area of the catalyst, providing abundant active sites to accelerate the reaction kinetics. As expected, the NiCo(SDS)/CC exhibits good activity for both UOR and hydrogen evolution reactions (HER) and it requires only 1.31 V and −86 mV to obtain a current density of ±10 mA cm−2, respectively. This work provides a new strategy for reducing the agglomeration of transition metals to design high-performance composite catalysts for urea oxidation. [ABSTRACT FROM AUTHOR]

[Display omitted] Metal nanoparticles (MNPs) with complex structure and uniform distribution demonstrate interesting physicochemical properties and thus are widely applied. The traditional wet chemistry methods are commonly applied to construct MNPs structure, yet they still exhibit limitations in the liquid-phase environment, particularly, for synthesis of supported MNPs in one-step process. Diverse synthesis strategies have been investigated to design complex MNPs in a more efficient manner, among which the thermal treatment atmosphere induced solid-phase ion diffusion (TASID) synthesis strategy serves as an attractive strategy. This review summaries recent progresses of complex MNPs construction via TASID synthesis strategy, which realize the structure design through thermally treating the precursors under various gas atmosphere, such as oxidative, reductive, carbonaceous, and inert gas. This TASID strategy can both achieve the MNPs structure design and uniform dispersion simultaneously, demonstrating its unique properties. MNPs with diverse composition and structure, such as hollow, core@shell, yolk@shell, Janus, and multi-chamber structure, are successfully synthesized. The TASID synthesis mechanisms of galvanic replacement, Kirkendall effect, Ostwald ripening, carburization, and exsolution are elaborated in detail. The synthesis-mechanism-structure correlation of TASID is identified and the applications of these constructed MNPs are presented. This strategy could be developed into a class of synthetic methods by applying various thermal gas. [ABSTRACT FROM AUTHOR]

Nanostructuring is important for designing thermoelectrics. Yet, nanoprecipitates are thermodynamically unstable and coarsen through Ostwald ripening. Here, the Ostwald ripening of Ag2Te in PbTe and its resulting impact on thermoelectric performance is investigated. Numerous Guinier‐Preston zones and platelet Ag2Te precipitates in the sample quenched from a single‐phase region is observed. Upon annealing, these platelet precipitates grow into big lath‐shaped second phases by consuming small Ag‐rich clusters. The crystallographic orientation relationships between Ag2Te and PbTe are unraveled by scanning transmission electron microscopy and modeled by first‐principles calculations. The interfaces with low lattice mismatch determine the morphology of Ag2Te in PbTe. Atom probe tomography reveals different chemical bonding mechanisms for PbTe and Ag2Te, which are metavalent and iono‐covalent, respectively. This leads to an acoustic phonon mismatch at the precipitate‐matrix interface. Yet, the electrons are also scattered by these interfaces, resulting in poor electrical properties in the as‐quenched sample. In contrast, the annealed sample contains abundant Ag‐decorated dislocations by activating the Bardeen‐Herring source. These dislocations strongly scatter phonons while maintaining a good electron transmission, contributing to a higher thermoelectric performance. This work demonstrates the complex role of microstructure morphologies, compositions, and bonding mechanisms in thermoelectric response, providing insights into structural design for thermoelectrics. [ABSTRACT FROM AUTHOR]

Marine carbonates record geochemical information on the state of Earth's surface environment in the geological past, but recrystallization during burial can make the records difficult to interpret. Here, we report shore to basin gradients in δ44Ca values in matrix limestone and burrow dolomite across a sequence of Late Ordovician (Katian Stage) burrow-mottled carbonates in the Williston Basin, an intracratonic epeiric marine basin in North America. Both gradients are interpreted to have diagenetic origins. The gradient in limestone δ44Ca values developed in a bathymetrically controlled sediment- to fluid-buffered diagenetic system operating between the center and the edges of the basin. Two dolomitizing events formed the gradient in dolomite δ44Ca values. The sediment-buffered end of the limestone gradient preserves the δ44Ca value of the original carbonate mud (∼–1.28 ± 0.10 ‰). The fluid-buffered end of the gradient conserves the δ44Ca value of contemporaneous seawater (–0.47 ± 0.10 ‰), because: (1) pore water exchange drivers operated with greater variety and intensity in shallow water settings, (2) shallow nearshore deposits exchanged more Ca with seawater during recrystallization to diagenetic calcite than deeper offshore deposits, and (3) diagenetic calcite formed with negligible fractionation under equilibrium conditions. The gradient conserves the local value of Δ sed (–0.81 ± 0.20 ‰) despite its diagenetic origin, and the magnitude of Δ sed is consistent with primary calcite precipitation in a 'calcite sea'. Field assessment of the equilibrium Ca isotope fractionation factor between calcite and dolomite of –0.41 ± 0.17 ‰ at ambient temperature is applied to correct basin-centered dolomite for fractionation, yielding –1.62 ± 0.27 ‰, which is very different from the –0.25 ± 0.07 ‰ value of Ca in evaporatively concentrated seawater from which the dolomite originally formed. Applying the same fractionation factor to correct literature data on early diagenetic dolomite in the Great Basin, North America, yields –0.69 ± 0.22 ‰ for the δ44Ca value of seawater, which is ∼0.2 ‰ lower than 'normal marine' waters in stratigraphically equivalent deposits in the Willison Basin, and 0.44 ‰ lower than evaporatively concentrated seawater during a brief period of basin restriction and anhydrite deposition. The nearly 0.5 ‰ variation in the δ44Ca value of Katian seawater falls within the range of scatter in the brachiopod reconstruction of seawater Ca isotopes. Here, we propose that the true ocean record of secular change lies towards the bottom of the range of scatter, and that the higher values in the record reflect local Ca cycling and circulation restriction in epeiric seas. Epeiric seas cultivate the fluid-buffered diagenetic conditions required to promote Ca isotope exchange between reactive carbonate sediments and seawater through carbonate mineral dissolution/recrystallization, crystal coarsening by way of Ostwald ripening, and replacive dolomitization. It is not the apportioning of kinetically fractionated aragonite and calcite in the carbonate deposition flux that drove secular changes in global value of Δ sed between 'calcite' and 'aragonite' seas, but rather the replacement of kinetic fractionations with equilibrium fractionations during fluid-buffered diagenesis with seawater. [ABSTRACT FROM AUTHOR]

[Display omitted] • N-doped carbon-coated Si nanocomposites with yolk shell structure (YS-Si@NC-60) derived from covalent organic frameworks (COFs) were prepared by template-free method. • Through an interesting Ostwald ripening, the core–shell Si@COP TBBA is transformed into the yolk-shell Si@COF TBBA. • The well-ordered pore structure of the COFs derived N-doped carbon shell can shorten the transport path of Li+. • The YS-Si@NC-60 with yolk shell structure can not only ease the volume expansion of silicon, but also has high ICE and cycle stability. Silicon (Si) has ultra-high theoretical capacity (4200 mAh g−1) and accordingly is widely studied as anode materials for lithium-ion batteries (LIBs). However, its huge volume expansion during charging/discharging is a fatal challenge. The preparation of Si-based composite materials with yolk shell structure is the key to solving the Si volume expansion. Here, N-doped carbon-coated Si nanoparticles (SiNPs) nanocomposites (YS-Si@NC-60) with yolk shell structure derived from covalent organic frameworks (COFs) was prepared. N-doped carbon shells derived from COFs not only maintain the well-ordered nanosized pores of COFs, which facilitates the transport of Li+ to contact with internal SiNPs, but also provide more extra active sites for Li+ storage. Most importantly, the internal void can effectively alleviate the damage effect of SiNPs volume expansion. The obtained YS-Si@NC-60 as a LIBs anode show high cyclic stability and Li+ storage performances. At 0.1 A g−1, the capacity is 1446 mAh g−1 after 110 cycles, and initial coulomb efficiency is as high as 82.2 %. The excellent performance can be attributed to the unique yolk shell structure. This simple and template-free strategy provides a new idea for preparing Si-C nanocomposites with yolk shell structure. [ABSTRACT FROM AUTHOR]

Bubble solutions are of growing interest because of their various technological applications in surface cleaning, water treatment, and agriculture. However, their physicochemical properties, such as the stability and interfacial charge of bubbles, are not fully understood yet. In this study, the kinetics of radii in aqueous microbubble solutions are experimentally investigated, and the results are discussed in the context of Ostwald ripening. The obtained distributions of bubble radii scaled by mean radius and total number were found to be time-independent during the observation period. Image analysis of radii kinetics revealed that the average growth and shrinkage speed of each bubble is governed by diffusion-limited Ostwald ripening, and the kinetic coefficient calculated using the available physicochemical constants in the literature quantitatively agrees with the experimental data. Furthermore, the cube of mean radius and mean volume exhibit a linear time evolution in agreement with the Lifshitz–Slezov–Wagner (LSW) theory. The coefficients are slightly larger than those predicted using the LSW theory, which can be qualitatively explained by the effect of finite volume fraction. Finally, the slowdown and pinning of radius in the shrinkage dynamics of small microbubbles are discussed in detail. [ABSTRACT FROM AUTHOR]

Crystallization of perovskite is monitored in carbon-electrode based, low-temperature, mesoscopic perovskite solar cells. Crystallographic and morphological properties of the perovskite are examined through changes in the film thickness of carbon-electrode or the volume of perovskite precursor. It is observed that, when a relatively thin carbon-electrode or large volume of perovskite precursor is used, perovskite crystallites mainly form on the device surface, leaving the bottom part of the device un-wetted. However, if a thicker carbon-electrode or less perovskite precursor is used, crystallization could be seen in the whole porous skeleton, and relative uniform distribution of perovskite crystallites is achieved. As such, uneven crystallization is observed. Such behavior is due to solvent evaporation on the surface, which facilitates nucleation processes on the surface, while retards crystallization on the bottom due to the Ostwald ripening effect. Charge transfer/recombination processes and photo-to-electric power conversion properties are studied. As expected, uneven crystallization results in retarded charge transfer and increased risk of recombination, and poor power conversion efficiency, for example, ∼3%. In contrast, uniform crystallization accelerates charge transfer and reduces recombination risk, and increases the efficiency to higher than 11% (AM1.5G, 100 mW/cm2). [ABSTRACT FROM AUTHOR]

Ostwald ripening (OR), a classic solution theory describing molecular transfer from metastable crystal to stable one, is applied to design time‐dependent crystal hydrogels that can automatically change their mechanical properties. Using a system made from crosslinked polyacrylamide (PAM) and sodium acetate (NaAc), we demonstrate that metastable fibrous crystal networks of NaAc preferably form in PAM hydrogels via a polymer‐involving mismatch nucleation. These fibrous crystals would undergo OR and evolve into isolated bulk crystals, leading to a significant reduction in material rigidity (179 folds) and interfacial adhesion (20 folds). This transformation can be applied to program time‐dependent self‐recovery in shape and self‐delamination. Since OR is a ubiquitous, robust feature of various crystals, the approach reported here represents a new direction for designing advanced transient soft materials. [ABSTRACT FROM AUTHOR]

Ostwald ripening (OR), a classic solution theory describing molecular transfer from metastable crystal to stable one, is applied to design time‐dependent crystal hydrogels that can automatically change their mechanical properties. Using a system made from crosslinked polyacrylamide (PAM) and sodium acetate (NaAc), we demonstrate that metastable fibrous crystal networks of NaAc preferably form in PAM hydrogels via a polymer‐involving mismatch nucleation. These fibrous crystals would undergo OR and evolve into isolated bulk crystals, leading to a significant reduction in material rigidity (179 folds) and interfacial adhesion (20 folds). This transformation can be applied to program time‐dependent self‐recovery in shape and self‐delamination. Since OR is a ubiquitous, robust feature of various crystals, the approach reported here represents a new direction for designing advanced transient soft materials. [ABSTRACT FROM AUTHOR]

BaTiO 3 terrace-like nano/microstructure were synthesized via a facile solvothermal method without surfacatant or template by controlling pH value. The phase structure, morphology and properties of the samples were characterized by XRD, FT-IR, XPS, SEM, UV–vis and ESR spectrum, etc. The piezoelectric potential analysis are calculated by finite element method simulation for BaTiO 3 prepared at different pH values under ultrasonic vibration. Morphology and crystal phase transform mechanism of BaTiO 3 at different pH values are proposed, respectively. The results show that pH value has a significant effect on the phase, crystallinity, morphology, size and piezocatalytic performance of BaTiO 3. When pH value is 10, BaTiO 3 exhibits spherical shape with an average size of ∼200 nm. With the increase of pH value, the morphology transforms grape-like shape from terrace-like shape. The transformation mechanism for BaTiO 3 is proposed to be a two–step growth model: initial nucleation and ripen, an oriented attachement accompanied by Ostwald ripening. H+ ions in OH− group occupy the Ba2+ position and affect the supersaturation of Ti (OH) 6 2−, thereby blocking the migration channel of Ba2+ and changing the crystal symmetry, resulting in changes in the content of tetragonal phase. FEM simulated shows the electric potential of BaTiO 3 is dominated by their morphologies. Compared with other samples, the best piezocatalytic performance of BaTiO 3 terrace-like nano/microstructure is demonstrated at pH = 12, which is the rate constant k of 15.5 × 10−3 min−1 by degrading 93 % of RhB dye solution in 180min, and keep almost unchanged after five cycles. The attractive piezocatalytic properties are considered to benefit from BaTiO 3 terrace-like nano/microstructure, which is composed of the numerous nanounits self-assembly micrometer-scale structure. [ABSTRACT FROM AUTHOR]

A stable neem oil-based oil-in-water nanoemulsion (o/w NE) is obtained by using a series of combinations of low and high-energy methods using optimized emulsifier composition. The application of the ultrasonication (high-energy) along with the dilution (low-energy) methods was used to intensify the process. Azadirachtin (indigenous neem oil) is used as an oil phase along with a mixture of two nonionic surfactants, namely Span80 and Tween80. The o/w NE is synthesized at an optimized HLB value of 8.5. Process parameters of ultrasonication are optimized and resulted in a 25% amplitude ratio, a 0.5 pulse mode factor, and a 30 minutes of ultrasonication time. The effects of optimized parameters are studied on droplet size distribution and the stability of o/w NE. For the oil concentration of 2.5%, the droplet diameter changed from 159 to 160.9 nm for a period of 45 days. Rheological properties of NEs are also evaluated by studying the relationship between shear rate with shear stress and viscosity at different temperatures, ranging from 20 to 50 °C. All the synthesized o/w NEs showed Newtonian behavior. Hence, the o/w NEs exhibited excellent stability for 45 days in terms of its droplet size, appearance, and rheology. The proposed o/w NE could be a potential pesticide for safeguarding the crops, without affecting the useful microorganisms, in the agriculture fields. [ABSTRACT FROM AUTHOR]

Currently, wide‐color gamut perovskite light‐emitting diodes (PeLEDs) are commonly controlled through halide composition tuning. However, the formation of perovskite crystals involving different ion radii of halogens often results in structural fragility and ionic defects, leading to emission instability during operation. This study showcases a novel approach to achieving a homogeneous and low‐defect crystalline state by regulating the thermodynamic nucleation mechanism of sky‐blue perovskite, thereby enhancing emission stability. Utilizing oxygen‐plasma treatment, a highly uniform surface energy is ensured for the nickel oxide acting as a hole transport layer. This treatment not only induces homogeneous nucleation of the perovskite layer but also effectively suppresses crystal defects. Simultaneously, the uniform surface energy alleviates halide phase separation caused by Ostwald ripening. Upon optimizing the fabrication conditions for sky‐blue perovskite, the resulting PeLEDs, featuring an electroluminescent peak at 486 nm, attain a luminance of 1125.3 cd m−2 with exceptional electroluminescent stability and a T50 lifetime. Furthermore, gaining insights into the thermodynamic nucleation mechanism in mix‐halides and perovskites contributes to the advancement of research on sky‐blue PeLEDs and offers valuable perspectives for future development. [ABSTRACT FROM AUTHOR]

The physical stability of a whey protein (WP)-stabilized red palm oil (RPO) emulsion as affected by the type and concentration of WP used was evaluated by monitoring the changes in its droplet characteristics after storage and accelerated testing. Emulsions containing 30% (v/v) RPO were stabilized by WP isolate 90 (WPI), WP concentrate 80 (WPC80), or WP concentrate 76 (WPC76) at various concentrations (2.5–15% (w/v)) via emulsification employing a two-step rotor-stator homogenization combined with a phase inversion technique. Based on the results, changes in droplet characteristics did not always represent the visually observed stability of the emulsions. In this study, WPCs performed better than WPI in forming a stable RPO emulsion. Higher WP concentrations produced smaller emulsion droplet sizes with better emulsion stability when stored at varied temperatures (i.e., 30 °C, 45 °C, and 60 °C). However, when stored at 60 °C, all the emulsions produced were least stable. Based on the results, the 15% WPC76-stabilized emulsion showed the best stability. This study found that the droplet size characterization could not fully explain the stability of the emulsion, and the emulsion investigated destabilized through different dominant mechanisms when it was stored compared to when it was centrifuged. This study provides information needed for developing a stable WP-stabilized emulsion to be the RPO carrier system. [ABSTRACT FROM AUTHOR]

Self-organisation in plutonic igneous rocks has been suggested to form by a variety of mechanisms including oscillatory nucleation and growth, competitive particle growth (CPG), and preferential dissolution and reprecipitation during fluid infiltration enhanced by compaction, with driving forces including reduction of the interfacial energy budget by either Ostwald ripening or because the energy of boundaries between two grains of the same mineral is less than that between two grains of different minerals. An investigation of the Stillwater inch-scale layering shows that the CPG patterning mechanism leaves a characteristic microstructural signature preserving evidence for a highly interconnected melt in textural equilibrium and slow super- and sub-solidus cooling; such a signature is also preserved in chromite-bearing fine-scale layers in the Bushveld intrusion. The cm-scale (centimetre-scale) micro-rhythmic layering of the Skaergaard intrusion, superimposed on single modally graded layers, does not have these microstructural features. Furthermore, the energy of all relevant interphase grain boundaries in the Skaergaard gabbros is less than that of grain boundaries involving only one mineral, viscous compaction was not a significant process in the Skaergaard intrusion, and patterning by oscillatory nucleation and growth is precluded by the fact that the micro-rhythmic layering is superimposed on modally graded layers formed by sedimentation. A new patterning mechanism is proposed, operational only in intrusions in which the interstitial liquid of the crystal mush intersects a binode and splits into two immiscible conjugates. Cm-scale separation of the immiscible conjugate liquids in a compositionally graded mush, due to both gravity and capillary forces, leads to layering due to differences in their wetting properties. The positive feedback required for pattern formation is due to the two immiscible conjugates predominantly crystallising the minerals which they preferentially wet. [ABSTRACT FROM AUTHOR]

Many biomolecular condensates, including transcriptional condensates, are formed in elastic mediums. In this work, we study the nonequilibrium condensate dynamics in a chromatin-like environment modeled as a heterogeneous elastic medium. We demonstrate that the ripening process in such an elastic medium exhibits a temporal power-law scaling of the average condensate radius, depending on the local stiffness distribution and different from Ostwald ripening. Moreover, we incorporate an active process to model the dissolution of transcriptional condensates upon RNA accumulation. Intriguingly, three types of kinetics of condensate growth emerge, corresponding to constitutively expressed, transcriptional-bursting, and silenced genes. Furthermore, the simulated burst frequency decreases exponentially with the local stiffness, through which we infer a lognormal distribution of local stiffness in living cells using the transcriptome-wide distribution of burst frequency. Under the inferred stiffness distribution, the simulated distributions of bursting kinetic parameters agree reasonably well with the experimental data. Our findings reveal the interplay between biomolecular condensates and elastic mediums, yielding far-reaching implications for gene expression. [ABSTRACT FROM AUTHOR]

The gelation kinetics of agar aqueous solutions were studied by means of the viscosity flow curves using a coaxial Couette cylinder viscometer. The viscosity curves show an unusual sigmoidal trend or an exponential decay to a viscous steady state. An original theory of gelation kinetics was developed considering the coarsening of increasingly larger and more stable clusters due to Ostwald ripening and the breakup of clusters that were too large due to the instability of rotating large particles induced by the shear rate. The developed Bounded Ripening Growth model takes into account the trend of the viscosity curves by means of an autocatalytic process with negative feedback on aggregation according to the logistic kinetic equation, in which the constants  k 1 (γ)  and  k − (ν)  are governed by the surface tension and shear rate, respectively. A dimensionless equation based on the difference between the Weber number and the ratio of the inverse kinetic constant to forward constant, accounts for the behavior of the dispersed phase in equilibrium conditions or far from the hydrostatic equilibrium. [ABSTRACT FROM AUTHOR]

Carbon-based materials are one of the ideal negative electrode materials for potassium ion batteries. However, the limited active sites and sluggish diffusion ion kinetics still hinder its commercialization process. To address these problems, we design a novel carbon composite anode, by confining highly reactive short-chain sulfur molecules into nitrogen-doped hollow carbon nanospheres (termed SHC-450). The formation process involves the controlled synthesis of hollow polyaniline (PANI) nanospheres as precursors via an Ostwald ripening mechanism and subsequent sulfuration treatment. The high content of constrained short-chain sulfur molecules (20.94 wt%) and considerable N (7.15 wt%) ensure sufficient active sites for K+ storage in SHC-450. Accordingly, the SHC-450 electrode exhibits a high reversible capacity of 472.05 mAh g−1 at 0.1 A g−1 and good rate capability (172 mAh g−1 at 2 A g−1). Thermogravimetric analysis shows that SHC-450 has impressive thermal stability to withstand a high temperature of up to 640 °C. Ex situ spectroscopic characterizations reveal that the short-chain sulfur provides high capacity through reversible formation of K2S. Moreover, its special hollow structure not only provides ample space for highly active short-chain sulfur reactants but also effectively mitigates volume expansion during the sulfur conversion process. This work offers new perspectives on enhanced K+ storage performance from an interesting anode design and the space-limited domain principle. [ABSTRACT FROM AUTHOR]

Detailed multi-technique characterization of catalyst layer degradation is fundamental for improving catalyst stability and performances in Proton Exchange Membrane Fuel Cells (PEMFCs), and Small Angle X-Ray Scattering (SAXS) coupled to chemical and/or electrochemical analysis can provide important insights of processes involved in catalyst coarsening. In this extent, we present an approach to SAXS analysis able to describe all of the layers composing the Membrane Electrode Assembly (MEA): electrolyte, catalyst support, catalyst nanoparticles, and gas diffusion layers. This approach was used to compare morphological evolution of small clusters formed by catalyst nanoparticles in pristine and aged MEAs in both ex situ and in operando conditions, on a standard SAXS beamline, without exploiting the advantages of anomalous SAXS. Twin MEAs were aged with two different types of Accelerated Stress Tests (AST): one addressed to the catalyst support (s-AST) and one targeting the catalyst layer (c-AST). Limited growth of catalyst nanoparticle size was found when running s-AST, while remarkable evolution was revealed once applying c-AST. Such a difference was mainly reconducted to the disconnection of catalyst nanoparticles from the electrical paths, as supported by analysis of specific Electrochemically Active Surface Area (ECSA). In both cases, the small clusters were found becoming more compact after AST were run. [Display omitted] • An approach to investigate catalyst degradation via X-Ray scattering is presented. • The model was validated by coupling small angle scattering and electrochemistry. • The model was validated in both ex situ and in operando measurements. • Catalyst degradation was depicted depending on two different stress tests. [ABSTRACT FROM AUTHOR]

The Si 3 N 4 raw powder, sintering aids, and sintering process are the most critical factors affecting the thermal conductivity and mechanical properties of Si 3 N 4 ceramics. The impact of sintering aids content and powder characteristics on gas pressure sintered Si 3 N 4 ceramics was investigated in this study. Lower aids content facilitated phase transformation prior to densification, promoting a pronounced bimodal microstructure. Based on in-situ shrinkage behavior, liquid phase sintering of Si 3 N 4 ceramics can be divided into three stages without clear boundaries. Between 1200 and 1400 °C, higher oxygen and metallic impurities favored particle rearrangement. Between 1400 and 1800 °C, the dissolution and precipitation process was probably controlled by the α-phase ratio and particle size. Above 1800 °C, subsequent grain growth was primarily facilitated by the Ostwald ripening process, leading to a reduced densification rate. Higher oxygen content leading to greater weight loss during sintering. Higher Fe resulted in a darker color of sintered Si 3 N 4 ceramics. High α-phase content promoted the formation of a bimodal microstructure and ensured superior mechanical properties. Reduced levels of oxygen and aluminum were prerequisites for achieving high thermal conductivity. Powders prepared by silicon nitriding method were cost-effective materials for the preparation of high-performance Si 3 N 4 ceramic substrates. [ABSTRACT FROM AUTHOR]

Hydro-methanolic extracts of pericarps and seeds of 10 different Capsicum cultivars from three different species viz., Capsicum chinense, C. annuum and C. frutescens were assessed to determine metabolic variations and anti-cholinesterase, anti-malarial and anti-protein denaturation activities at four different stages of ripening, namely green unripe (GU), turning green-orange (TGO), orange ripe (OR) and red fully ripe (RFR) stages. Many of the ripening stages of the tested cultivars showed significant bioactivities in a dose-dependent manner. In addition, metabolites were identified using GC/MS. On the other hand, HPLC analysis revealed the highest capsaicin and dihydrocapsaicin content in the pericarp of GU, TGO and RFR stages of C. chinense. ß-Carotene, capsanthin and lutein contents of C. chinense were also measured using HPTLC technique. The GU and RFR stages of C. chinense contained appropriate amounts of all three carotenoids. These results may be helpful in selecting the cultivars with the best attributes. [ABSTRACT FROM AUTHOR]

Using spectral ensemble methods (DLS, optical and luminescence spectroscopy) and the transmission electron microscopy as reference method, the dynamics of selenium nanoparticles synthesis from sodium bis(2-phenylethyl)diselenophosphinate (DSePhNa) organophosphorus precursor in aqueous solution of polysaccharide matrix arabinogalactan (Ar-Gal) was studied. It was shown that the addition of hydrogen peroxide to the aqueous solution of DSePhNa initiates its oxidation with release of Se0 atoms with formation of selenium nanoparticles already by 10 s of synthesis. This stage identified by isolation of a fraction corresponding to nanoparticles in the size distribution. Full involvement of Ar-Gal macromolecules in the stabilization of formed selenium nanoparticles is completed by 8 min of the synthesis, which is accompanied by a narrowing of the size distribution of the formed nanoparticles. All basic stages of the particle formation and growth, as well as Ostwald ripening, in the case of long-term sample storage have been recorded by both TEM and the spectral ensemble methods. In the paper the most probable mechanism of selenium nanoparticle formation under the selected synthesis conditions is explained based on all the data obtained on the nature of nanoparticle size distribution. Besides, the possibility of using these spectral methods to estimate the dynamics of nanoparticle synthesis is discussed. Highlights: Spectral ensemble methods (DLS, optical and luminescence spectroscopy) can be used to evaluate the dynamics of nanoparticle synthesis in solution. The formation of nanoparticles is identified almost instantly (by 10 s of synthesis) by the separation of the small particle fraction, in the size distributions obtained from all spectral methods and confirmed by TEM. The nature (symmetry, modality) of the size distribution of Ar-Gal-stabilized SeNPs depends on the synthesis step and varies strongly over time until the completion stage of the process is reached. Prolonged storage of aqueous solution of Ar-Gal-stabilized SeNPs is characterized by non-stationary of state and is accompanied by a number of processes typical of Ostwald ripening leading also to changes in the character of disperse distribution of particles identified by all used spectral and TEM methods. [ABSTRACT FROM AUTHOR]

A lubrication model can be used to describe the dynamics of a weakly volatile viscous fluid layer on a hydrophobic substrate. Thin layers of the fluid are unstable to perturbations and break up into slowly evolving interacting droplets. A reduced-order dynamical system is derived from the lubrication model based on the nearest-neighbor droplet interactions in the weak condensation limit. Dynamics for periodic arrays of identical drops and pairwise droplet interactions are investigated, providing insights into the coarsening dynamics of a large droplet system. Weak condensation is shown to be a singular perturbation, fundamentally changing the long-time coarsening dynamics for the droplets and the overall mass of the fluid in two additional regimes of long-time dynamics. [ABSTRACT FROM AUTHOR]

Green hydrogen, produced from surplus electricity during peak production, can be injected into subsurface reservoirs and retrieved during high-demand periods. In this study, X-ray tomography was employed to examine hysteresis resulting from repeated hydrogen injection and withdrawal. An unsteady state experiment was performed to evaluate the distribution of hydrogen and brine after drainage and imbibition cycles: images of the pore-space configuration of fluids were taken immediately once injection had stopped and after waiting for a period of 16 h with no flow. A Bentheimer sandstone sample with a length of 60 mm and diameter of 12.8 mm was used, and hydrogen was injected at ambient temperature and a pore pressure of 1 MPa. The gas flow rate was decreased from 2 ml/min to 0.08 ml/min over three cycles of gas injection followed by water flooding, while the brine injection rate was kept constant. The results showed the presence of capillary pressure hysteresis and hydrogen migration through Ostwald ripening due to the diffusion of gas dissolved in the brine. These phenomena were characterized through analysis of interfacial curvature, area, connectivity and pore occupancy. The hydrogen tended to reside in the larger pore spaces, consistent with water-wet conditions. 16 h after flow had stopped, the hydrogen aggregated into larger ganglia with a single large connected ganglion dominating the volume. Moreover, the Euler characteristic decreased after 16 h, indicating an improvement in connectivity. The work implies that Ostwald ripening – mass transport of dissolved gas – leads to less hysteresis and better connectivity than would be assumed ignoring this effect, as done in assessments of hydrocarbon flow and trapping. [Display omitted] • X-ray imaging investigated pore-scale hysteresis during hydrogen storage. • Hydrogen migration by Ostwald ripening was observed. • Ostwald ripening led to better connectivity of the gas phase. • The work implies less hysteresis for hydrogen than for hydrocarbons. [ABSTRACT FROM AUTHOR]

Research efforts have been dedicated to predicting microstructural evolution during solidification processes. The main secondary arm spacing controls the mushy zone's permeability. The aim of the current work was to build a simple sub-grid model that describes the growth and coarsening of secondary side dendrite arms. The idea was to reduce the complexity of the curvature distribution with only two adjacent side arms in concurrence. The model was built and applied to the directional solidification of Al-06wt%Cu alloy in a Bridgman experiment. The model showed its effectiveness in predicting coarsening phenomena during the solidification of Al-06wt%Cu alloy. The results showed a rapid growth of both arms at an earlier stage of solidification, followed by the remelting of the smaller arm. In addition, the results are in good agreement with an available time-dependent expression which covers the growth and coarsening. Such model can be implemented as a sub-grid model in volume average models for the prediction of the evolution of the main secondary arms spacing during macroscopic solidification processes. [ABSTRACT FROM AUTHOR]

The complexity of gas pressure liquid phase sintering (GPS-LPS) of silicon nitride induces a certain savoir-faire. This highly challenging strong bond ceramic uses sintering additives of a liquid phase sintering under high temperatures close to the silicon nitride phase decomposition which requires a gas pressure. The sintering behavior encompasses various phenomena such as Ostwald ripening grain growth, phase transition, and swelling when the pore elimination approach close porosity. The aim of this study was to model such sintering behavior. In this aim, master sintering curves (MSC) were used to study the temperature and porosity dependence of the sintering model. Then, the grain growth sensitivity of the sintering model was incorporated. Finally, the swelling phenomenon responsible for transient de-densification and sintering rate limiting mechanism at final stage sintering was extracted by an inverse method. A comprehensive sintering model reproducing all the silicon nitride sintering complexity result this study. [Display omitted] • Gas pressure liquid phase sintering of silicon nitride. • Sintering kinetics analysis from optical dilatometry. • Comprehensive simulation of sintering with a sensitivity to grain growth and swelling phenomena. [ABSTRACT FROM AUTHOR]

By varying the concentration of molecules in the cytoplasm or on the membrane, cells can induce the formation of condensates and liquid droplets, similar to phase separation. Their thermodynamics, much studied, depends on the mutual interactions between microscopic constituents. Here, we focus on the kinetics and size control of 2D clusters, forming on membranes. Using molecular dynamics of patchy colloids, we model a system of two species of proteins, giving origin to specific heterotypic bonds. We find that concentrations, together with valence and bond strength, control both the size and the growth time rate of the clusters. In particular, if one species is in large excess, it gradually saturates the binding sites of the other species; the system then becomes kinetically arrested and cluster coarsening slows down or stops, thus yielding effective size selection. This phenomenology is observed both in solid and fluid clusters, which feature additional generic homotypic interactions and are reminiscent of the ones observed on biological membranes. [ABSTRACT FROM AUTHOR]

Carbon with few active sites and narrow interlayer distance as anode for potassium ion batteries (PIBs) always shows low capacity, sluggish kinetics, and low Columbic efficiency. Herein, poly(2‐aminothiazole) (P2AT) hollow nanospheres are first synthesized as a carbon source for high N, S co‐doped carbon hollow nanospheres (NS‐HCSs). The hollow P2AT nanospheres can be controllably synthesized with an Ostwald ripening process. The unique doping and structure endow the NS‐HCSs with high content of N and S dopants in carbon, mesoporous structure with enlarged interlayer distance, elevated ratio of N‐6 and N‐5 species, enhanced conductivity, abundant surface defects, and large active sites. When evaluated as an anode for PIBs, NS‐HCSs exhibit a high reversible capacity of 422 mAh g‒1 and excellent long‐term cycling performance. Using combined experiment and theoretical computation, including in situ TEM and in situ Raman, the K‐storage mechanism and dynamic evolution processes of NS‐HCSs, including low volume expansion, enhanced K‐ion adsorption, and stable composition and structure evolution during repeating potassiation/de‐potassiation processes is revealed. This quantitative design for highly durable K‐storage and large capacity in carbon can be advantageous for the rational design of anode materials of PIBs with ideal electrochemical performance. [ABSTRACT FROM AUTHOR]

Copper nanoparticle-based catalysts have been extensively applied in industry, but the nanoparticles tend to sinter into larger ones in the chemical atmospheres, which is detrimental to catalyst performance. In this work, we used dealuminated Beta zeolite to support copper nanoparticles (Cu/Beta-deAl) and showed that these particles become smaller in methanol vapor at 200°C, decreasing from ~5.6 to ~2.4 nanometers in diameter, which is opposite to the general sintering phenomenon. A reverse ripening process was discovered, whereby migratable copper sites activated by methanol were trapped by silanol nests and the copper species in the nests acted as new nucleation sites for the formation of small nanoparticles. This feature reversed the general sintering channel, resulting in robust catalysts for dimethyl oxalate hydrogenation performed with supported copper nanoparticles for use in industry. [ABSTRACT FROM AUTHOR]

In this work, Lavandula x intermedia essential oil (LEO) was encapsulated in lipid-based nanoemulsions (NanoLEO) using the solvent-displacement technique. In order to preserve the colloidal stability of the formulation, LEO was appropriately doped with the incorporation of different levels of a water-insoluble oil used as a ripening inhibitor. All the nanoemulsion samples were evaluated in terms of the impact of the water-insoluble oil on the nanoemulsion formation, physical–chemical properties, and antibacterial effectiveness against E. coli (Gram-negative) and B. cereus (Gram-positive). The presence of the inert oil added benefits to the formulations in terms of appearance, colloidal stability, and loss of volatile components. However, the antimicrobial activity of the nanoemulsions dramatically decreased with the ripening inhibitor addition, probably because it hampered the internalization of the antimicrobial components of LEO within the bacterial cell membranes, thus nullifying the delivery ability of the nanoemulsion formulation. On the contrary, the undoped NanoLEO formulation showed unaltered antibacterial activity in both E. coli and B. cereus up to 40 weeks from the preparation. [ABSTRACT FROM AUTHOR]

This paper summarizes an approach to crystal growth that was published in parts in various articles over the course of 25 years by the present author and his colleagues. Evidence for this approach, which is confirmed in detail by data in the cited publications and in the figures and equations in the supplementary material that accompanies this paper (see the Online Materials Deposit item AM-24-18851. Online Materials are free to all readers. Go online, via the table of contents or article view, and find the tab or link for supplemental materials.), comes mainly from the shapes of crystal size distributions (CSDs). Such distributions reveal the growth histories of natural minerals and synthetic compounds, histories that can be used to make geological interpretations and to guide industrial syntheses. CSDs have three fundamental shapes: log-normal, asymptotic, and Ostwald. These shapes result from different degrees of supersaturation near the time of nucleation. The first two distribution shapes form according to the Law of Proportionate Efect (LPE) at moderate supersaturation, and the latter rare distribution forms by Ostwald ripening at large supersaturation. Initially, the first two distributions have mean diameters of up to tens of nanometers and grow by surface-limited growth kinetics. The slow step in this reaction is the incorporation of nanoparticles (bits of crystal or adparticles) onto the crystal surface. As the crystals become larger, their demand for nutrients, as calculated by the LPE, increases exponentially. Then the slow step in the reaction changes to the rate of transfer of nutrients to the crystal (supply- or transport-limited growth). Crystal diameters often grow the most during this latter stage, and the initial CSD shapes that originally formed during surface-limited growth are retained and scaled up proportionately. Proportionate growth during the supply-limited stage can be simulated approximately by multiplying the diameter of each crystal in a distribution by a constant. Crystals can also grow by a constant rate law in which a constant length is added to each crystal diameter in the distribution. This rare process causes the original CSD to narrow so that its initial shape is not preserved. The growth law that prevails, either proportionate or constant, is determined by the manner in which nutrients are supplied to the crystal. Supply is by advective flow during proportionate growth, with the nutrient solution moving with respect to the crystals. Constant growth relies on the random difusion of nutrients through a quiescent solution. Proportionate growth is by far the most common growth law, and therefore, nutrient supply by difusion alone during crystal growth is uncommon. Distributions formed by Oswald ripening and those formed by other rare processes are also discussed. During Ostwald ripening, nucleation caused by mixing reactants at large supersaturation forms crystals that are extremely fine and numerous. The larger crystals grow at the expense of the finer, less stable crystals, thereby forming, on completion, the universal steady-state CSD shape predicted by the Lifshitz-Slyozov-Wagner (LSW) theory. This unique CSD shape, as well as other rare shapes, then are scaled up to larger sizes by supply limited proportionate growth. [ABSTRACT FROM AUTHOR]

The present study was performed on three versions of 7075 alloy to which Sc or Sc + Li was added. The alloys were subjected to various aging treatments. The microhardness results show that the highest value of hardness was achieved when the alloy containing Li + Sc was aged at 120 °C for 24 h whereas the minimum level was exhibited by the base alloy aged at 280 °C. The results were interpreted in terms of the size and distribution of the main hardening phase (η′(MgZn2)), and the role of the presence of Al and Cu in the used alloy. Precipitation of Al3(Sc, Zr, Ti) phase particles during solidification of the Sc-containing ingots was also discussed. The coarsening and spheroidi-zation of η-phase particles take place through the Ostwald ripening mechanism while smaller par-ticles in solution dissolve and deposit on larger particles. In Sc-containing alloys, star phase particle consists of different layers. The change in the brightness from layer to layer indicates that the Zr and Sc concentrations are varied within the star phase, since the atomic number of Zr (40) is higher than the atomic number of Sc (21). The addition of Sc, as well, leads to marked decrease in the grain size of the as-cast alloys i.e., 300 µm and 45 µm, respectively. The interaction between Li and Sc would reduce the effectiveness of the grain refining effect of Sc. The results of the refining effect of Sc were confirmed using the EBSD technique. [ABSTRACT FROM AUTHOR]

In this paper, we propose and analyze a second‐order accurate (in time) numerical scheme for the droplet liquid film coarsening model by using the scalar auxiliary variable (SAV) method, and the Fourier‐spectral method is used in space. The scheme is linear; thus, it could be solved very efficiently. Meanwhile, due to the application of SAV approach, the unconditional energy stability of the numerical scheme is also derived, without any restriction on the time step size. In addition, we also provide a rigorous error estimate that shows that our second‐order numerical scheme with Fourier‐spectral method in space converges with order OΔt2+hm$$ O\left(\Delta {t}^2+{h}^m\right) $$, where Δt$$ \Delta t $$ and h$$ h $$ are time and space step sizes, respectively. Finally, a few numerical experiments are performed, which confirms the efficiency and accuracy of the proposed scheme, including the tests of the convergence, the mass conservation and the decrease of the energy. The simulation of coarsening process with time is also observed. [ABSTRACT FROM AUTHOR]

The formation mechanism of Cd–S–Se quantum dots (QDs) with a CdS/CdSe core–shell structure within a silicate glass system was investigated by monitoring the change in the first excitonic absorption peak of CdSe, CdS, and Cd–S–Se QDs as a function of the heat‐treatment (HT) duration. When a silicate glass containing QD formation components for CdSe or CdS single‐phased QDs was heat‐treated, CdSe QDs grew via Ostwald ripening, whereas CdS QDs hardly formed within the given silicate glass matrix. When the glass, including CdO, ZnSe, and ZnS, was utilized for the synthesis of Cd–S–Se QDs within the glass matrix, Cd–S–Se QDs were successfully formed and exhibited similar growth behavior to CdSe QDs during the initial stage of HT. The structural changes in the QD‐embedded glasses during HT were also monitored by Raman spectroscopy and discussed, and a possible formation mechanism of CdSe/CdS core–shell‐structured QDs within silicate glasses is suggested. [ABSTRACT FROM AUTHOR]

Ostwald ripening of gas bubbles is a spontaneous mass transfer process that can impact the storage volume of trapped gas in the subsurface. In homogeneous porous media with identical pores, bubbles evolve toward an equilibrium state of equal pressure and volume. How the presence of two liquids impacts ripening of a bubble population is less known. We hypothesize that the equilibrium bubble sizes depend on the surrounding liquid configuration and oil/water capillary pressure. We investigate ripening of nitrogen bubbles in homogeneous porous media containing decane and water using a level set method that alternately simulates capillary-controlled displacement and mass transfer between bubbles to eradicate chemical-potential differences. We explore impacts of initial fluid distribution and oil/water capillary pressure on the bubble evolution. Ripening in three-phase scenarios in porous media stabilizes gas bubbles to sizes that depend on their surrounding liquids. Bubbles in oil decrease in size while bubbles in water increase in size with increasing oil/water capillary pressure. Bubbles in oil reach local equilibrium before the three-phase system stabilizes globally. A potential implication for field-scale gas storage is that the trapped gas fractions in oil and water vary with depth in the oil/water transition zone. • Level set approach to gas bubble ripening on three-phase fluid configurations in porous media. • Equilibrium bubble sizes in oil and water depend on oil/water capillary pressure and gas/liquid interfacial tensions. • Ripening of gas bubbles in three-phase fluid systems displays a different behaviour in porous media than in bulk liquids. • Oil/water capillary pressure impacts the equilibration time for three-phase ripening scenarios in porous media. [ABSTRACT FROM AUTHOR]

The catalytic oxidative desulfurization (ODS) technique is able to remove sulfur compounds from fuels, conducive to achieving deep desulfurization for the good of the ecological environment. Ti-based metal–organic frameworks (Ti-MOFs) possessing good affinity to organic reactants and considerable numbers of Ti active sites are promising catalysts for ODS. However, current Ti-MOFs suffer from severe diffusion limitations caused by the size mismatch between sole micropores and bulky sulfur compounds, leading to poor ODS performance. Here, a facile method of intraparticle ripening without any additive is developed to obtain hierarchically meso–microporous Ti-MIL-125 single crystals (Meso-Ti-MIL-125) for the first time. Such Meso-Ti-MIL-125 shows a BET surface area of 1401 m2 g−1 and a mesoporous volume that is 1.7 times as high as that of the conventional Ti-MIL-125. Our novel Meso-Ti-MIL-125 exhibits excellent catalytic performance in the ODS of a series of bulky thiophenic sulfur compounds, completely removing benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (DMDBT) from model fuels, which is, respectively, 2.4 times, 1.5 times, and 6.7 times higher than the removal achieved with conventional Ti-MIL-125. Such a facile synthetic strategy is envisioned to be applied in many kinds of crystalline materials, such as zeolites, for industrial production. [ABSTRACT FROM AUTHOR]

Coarsening of two-phase systems is crucial for the stability of dense particle packings such as alloys, foams, emulsions, or supersaturated solutions. Mean field theories predict an asymptotic scaling state with a broad particle size distribution. Aqueous foams are good model systems for investigations of coarsening-induced structures, because the continuous liquid as well as the dispersed gas phases are uniform and isotropic. We present coarsening experiments on wet foams, with liquid fractions up to their unjamming point and beyond, that are performed under microgravity to avoid gravitational drainage. As time elapses, a self-similar regime is reached where the normalized bubble size distribution is invariant. Unexpectedly, the distribution features an excess of small roaming bubbles, mobile within the network of jammed larger bubbles. These roaming bubbles are reminiscent of rattlers in granular materials (grains not subjected to contact forces). We identify a critical liquid fraction Ø*, above which the bubble assembly unjams and the two bubble populations merge into a single narrow distribution of bubbly liquids. Unexpectedly, Ø* is larger than the random close packing fraction of the foam Ørcp. This is because, between Ørcp and Ø*, the large bubbles remain connected due to a weak adhesion between bubbles. We present models that identify the physical mechanisms explaining our observations. We propose a new comprehensive view of the coarsening phenomenon in wet foams. Our results should be applicable to other phase-separating systems and they may also help to control the elaboration of solid foams with hierarchical structures. [ABSTRACT FROM AUTHOR]

The impact of various heat treatment procedures on microstructure, dislocation density, hardness, tensile characteristics, and impact toughness of P92 steel was examined in the current experiment. The martensitic microstructure and average microhardness of 463 HV 0.2±8 HV 0.2 of the normalized steel were prevalent. A tempering procedure was carried out at 760 °C for a range of 2 hours to 6 hours. Additionally, an X‐ray diffraction examination was carried out, and the results were used to determine the dislocation density. The normalized sample was characterized by a high dislocation density. The dislocation density was decreased by tempering of normalized samples. With an increase in tempering time, the effect of the treatment coarsened the grains, precipitates, and decreased the area fraction of precipitates. After tempering, MX, M23C6, and M7C3 types precipitates were found to have precipitated, according to energy dispersive spectroscopy and x‐ray diffraction research. The ideal tempering period was determined to be 4 hours at a tempering temperature of 760 °C based on the microstructure and mechanical characteristics. Steel that was tempered at 760 °C for 4 hours had a yield strength of 472 MPa, an ultimate tensile strength of 668.02 MPa, and an elongation of 26.05 %, respectively. [ABSTRACT FROM AUTHOR]

Mineral replacement reactions mediated by fluids are common in sedimentary basins, where they influence geochemical cycles. Phosphorous (P) pollution of soils, sediments and water bodies is currently a widespread problem. Some apatite accumulations in sediments may have formed through the interaction of P-bearing aqueous solutions with mineral surfaces that result in mineral replacement reactions. Here, we investigate the pseudomorphic replacement of anhydrite single crystals by aggregates of β-tricalcium phosphate and hydroxyapatite upon interaction with a P-bearing solution at temperatures between 120 and 200 °C. SEM imaging is used to study the texture of the aggregates. Rietveld refinement of the X-ray diffraction patterns and Raman spectra analysis of the reacted samples provide information on the kinetics of the replacement. At all temperatures β-tricalcium phosphate forms alongside hydroxyapatite at early stages of the replacement reaction. At T ≥ 180 °C, hydroxyapatite/β-tricalcium phosphate ratio rapidly increases, and hydroxyapatite is the only phase in fully replaced samples. At T < 180 °C hydroxyapatite/β-tricalcium phosphate ratio increases slowly and fully replaced samples still contain significant amounts of β-tricalcium phosphate. The progress of the replacement is facilitated by the formation of porosity. The evolution of the hydroxyapatite/β-tricalcium phosphate ratio and the crystal habit of both phases strongly influence the arrangement of this porosity. The empirical activation energy Ea (kJ/mol) of the replacement reaction is determined by the Avrami and the iso-conversion methods. Both approaches yield an Ea of ~40 kJ/mol. Anhydrite dissolution appears as the rate-limiting process and the overall kinetics of the replacement reaction is controlled by the rate diffusion of dissolved species through the porosity network. The ripening of the metastable β-tricalcium phosphate into hydroxyapatite affects the characteristics of the porosity network and further modulates the kinetics of the replacement. These results may improve the understanding of the mechanisms of P-sequestration by mineral surfaces through coupled dissolution–precipitation reactions and shed light on the origin of apatite accumulations associated to evaporitic sedimentary rocks. [ABSTRACT FROM AUTHOR]

A comparative study has been made between some cidaroid fossil spines from Lower Cretaceous of southern Spain and other contemporary ones. The modern spines are a composite material formed by calcite nanocrystals oriented with their optical axes parallel to the elongated direction, which behave as a single crystal. Transmission Petrographic Microscopy (TPM) observations of the fossil spines prove that it is a calcite single crystal, whose optical axis coincides with the direction of elongation (as in the current spines). This paper presents a crystallographic approach to propose a secondary crystallisation mechanism, specifically the Ostwald ripening process, through a structural analysis that compares the spines and the conditions observed during the fossilisation process. [ABSTRACT FROM AUTHOR]

Semiconductor oxide gas sensors have important applications in environmental protection, domestic health, and other fields. Research has shown that designing the morphology of sensitive materials can effectively improve the sensing characteristics of sensors. In this paper, by controlling the solvothermal reaction time, a unique hexagonal flower-like structure of In2O3 materials consisting of cuboid nanorods with a side length of 100–300 nm was prepared. The characterization results indicated that with the increase in reaction time, the materials exhibited significant morphological evolution. When the solvent heating time is 5 h, the flower-like structure is basically composed of hexagonal nanosheets with a thickness of several hundred nanometers and a side length of several micrometers. With the increase in reaction time, the apex angles of the nano sheets gradually become obtuse, and, finally, with the Ostwald ripening process, they become cuboid nanorods with side lengths of 100–300 nanometers, forming unique micro-flowers. Among them, the material prepared with a reaction time of 20 h has good sensing performance for NO2, exhibiting low operating temperature and detection limit, good selectivity, repeatability, and long-term stability, thus suggesting a good application prospect. [ABSTRACT FROM AUTHOR]

One key aspect of coarsening following a quench below the critical temperature is domain growth. For the non-conserved Ising model a power-law growth of domains of like spins with exponent α = 1 / 2 is predicted. Including recent work, it was not possible to clearly observe this growth law in the special case of a zero-temperature quench in the three-dimensional model. Instead a slower growth with α < 1 / 2 was reported. We attempt to clarify this discrepancy by running large-scale Monte Carlo simulations on simple-cubic lattices with linear lattice sizes up to L = 2048 employing an efficient GPU implementation. Indeed, at late times we measure domain sizes compatible with the expected growth law—but surprisingly, at still later times domains even grow superdiffusively, i.e., with α > 1 / 2 . We argue that this new problem is possibly caused by sponge-like structures emerging at early times. [ABSTRACT FROM AUTHOR]

The process of phase separation in elastic solids and viscous fluids is of fundamental importance to the stability and function of soft materials. We explore the dynamics of phase separation and domain growth in a viscoelastic material such as a polymer gel. Using analytical theory and Monte Carlo simulations, we report a domain growth regime in which the domain size increases algebraically with a ripening exponent α that depends on the viscoelastic properties of the material. For a prototypical Maxwell material, we obtain α = 1, which is markedly different from the well-known Ostwald ripening process with α = 1=3. We generalize our theory to systems with arbitrary power-law relaxation behavior and discuss our findings in the context of the longterm stability of materials as well as recent experimental results on phase separation in cross-linked networks and cytoskeleton. [ABSTRACT FROM AUTHOR]

Present study depicts the effect of isothermal holding on microstructural morphology of the cooling slope processed slurry of A380 Al alloy. Along with the primary and eutectic phase morphology, significant effect of isothermal slurry coarsening on Iron (Fe)-rich intermetallic formation is evidenced here. The study also reports the effect of adding refining (0.15 wt% Al-5Ti-1B master alloy) and modifying (0.1 wt% Al-10Sr master alloy) agents within the melt on formation sequence and percentage of Fe- and Mn-rich intermetallics within the slurry matrix. Furthermore, modified Lifshitz-Slyozov-Wagner equation is proposed here to quantify the relative influence of Ostwald ripening and coalescence, towards determining slurry microstructure, during isothermal slurry holding stage. Optimum slurry morphology, i.e. minimum size and maximum sphericity of constituent primary Al grains as well as uniform distribution of Fe, Manganese (Mn) and Copper (Cu)-rich intermetallics, is achieved for the refiner+modifier added slurry, after 7 minutes of isothermal holding. [ABSTRACT FROM AUTHOR]

Apatite is a ubiquitous phase in granite plutons and in most adjacent country rocks, thus contamination of a granite magma with wall-rock material results in two genetic types of apatite in the magma: cognate and foreign. These two textural and chemical varieties of apatite undergo textural and compositional changes to reach physical and chemical equilibrium (perfect assimilation) in the melt. Our experiments replicate the conditions in such contaminated granites. The starting materials consist of a peraluminous synthetic SiO2-Al2O3-Na2O-K2O (SANK 1.3) granite gel with A/NK of 1.3, synthetic F-apatite, synthetic Cl-apatite, and natural Durango apatite. Initial experiments in cold-seal hydrothermal pressure vessels at magmatically realistic temperatures of 750 °C and pressures of 200 MPa produced negligible reactions, even after run times of 2000 h. Instead, we used an argon-pressurized internally heated pressure vessel with a rapid-quench setup at temperatures of 1200 °C, pressure of 200 MPa, and run durations of 192 h. An advantage of this high temperature is that it exceeds the liquidus for quartz and feldspar; therefore, apatite is the only solid phase in the run products. The starting composition of each run was 90 wt% SANK 1.3 granite gel and 10 wt% crushed apatite (consisting of one, two, or three varieties), with and without 4 wt% added H2O. Run products were examined by SEM for texture and by EMPA and LA-ICP-MS for composition. The starting synthetic granite composition contains no Ca, F, Cl, or REEs thus, in every run, apatite was initially undersaturated in the melt. In all experiments, most large apatite grains consisted of anhedral shards with rounded corners, most small apatite grains were round, and a small proportion of apatite grains developed one or more crystal faces. In experiments with two or three apatite compositions, the run-product apatite grains had compositions intermediate between those of the starting-material grains, and they were homogeneous with respect to Cl, and probably F, but not with respect to REEs. The processes to reach textural equilibrium consist of dissolution until the melt is saturated in apatite, followed by Ostwald ripening to eliminate small grains and to develop crystal faces on larger ones. The processes to reach chemical equilibrium consist of dissolution of apatite, diffusion of cations (Ca, P, REE) and anions (F, Cl, OH) through the silicate melt, and solid-state diffusion in the undissolved apatite grains. The halogens approached chemical equilibrium in all experiments, but in the experiments containing Durango apatite, the REEs have not. Models involving radial diffusion into spherical apatite grains at the temperatures of the experiments show complete re-equilibration of the halogens, but changes in the REE concentrations affecting only the outer few micrometers. We conclude that the rate of chemical equilibrium for the halogens is greater than the rate of physical equilibrium for texture, which in turn is greater the rate of chemical equilibrium for REEs. We illustrate these processes with a natural example of contaminated granite from the South Mountain Batholith in Nova Scotia. Given that all granites are contaminated rocks, we propose that future petrogenetic studies focus on developing techniques for a minerals-based quantitative estimation of contamination (QEC). [ABSTRACT FROM AUTHOR]

Ostwald ripening under a temperature gradient in binary model alloys is investigated using a quantitative phase-field model. The simulations show that a cube of average radius of a second-phase particle is proportional to time, and the particle size distribution shows self-similarity in a steady state, as with a uniform temperature field. It is found that the growth rate of particles under a temperature gradient is faster than that in the isothermal case, and the steady-state particle size distribution depends on the magnitude of the temperature gradient. Furthermore, the second-phase particles migrate from low temperature regions to high temperature regions when a non-uniform temperature field is applied. The migration velocity of particles, averaged over the whole system, increases with the magnitude of the temperature gradient. On the other hand, the velocity of each particle is not relevant to particle size. Hence, the particle migration is entirely ascribed to the diffusion flux driven by the concentration gradient originating from the temperature dependence of solute solubility. [ABSTRACT FROM AUTHOR]

A 20Cr-25Ni-2.5Al alumina-forming austenitic alloy containing W and B elements was aged at 923 K for 5000 h, and the microstructure and tensile properties with different aging time were investigated. NiAl, σ and Laves were observed at grain boundaries (GBs) successively. The matrix was covered by NiAl and Laves with the extension of aging. The evolution of precipitates during aging contributed to the variation of tensile properties. Precipitation of nanosized NbC carbides within grains and σ phase at GBs led to a rapid increase in strength and a decrease in elongation for 500 h aging sample. In the later stage of aging, the coarsening of NiAl and Laves phases, as well as the reduction in dislocation density caused a decline in strength. The coarsening of precipitates upon aging time follows the Ostwald ripening theory. Due to its lower diffusion rate in austenite compared to Mo, W may accelerate the growth of Laves at GBs. Boron was mainly enriched in Laves instead of NiAl, NbC and σ phases after high temperature aging. The addition of W and B improved the precipitation strengthening of Laves, increasing the high temperature tensile strength after long term thermal aging. The difference in tensile properties between room temperature and 923 K is due to the ductile–brittle transition of NiAl. No σ phase was observed within grains even after 5000 h aging and elemental chromium particles occurred around Laves due to boron hindering the growth of σ. [ABSTRACT FROM AUTHOR]

In this work, we have studied low-energy (5 keV) nitrogen ion-induced modification of the surface of iron oxide nanoparticles. The iron oxide nanoparticles were spin-coated on a silicon substrate. The thin films of iron oxide nanoparticles were irradiated at two different ion fluences of 1 × 1016 and 3 × 1016 ions cm−2, respectively. At a fluence of 1 × 1016 ions cm−2, the nanoparticles incline to join with each other forming small clusters which can be attributable due to Ostwald ripening because of the ion-induced defects. At higher fluence of 3 × 1016 ions cm−2, large nanoclusters are formed due to coalescence. We have investigated the morphological and structural properties of both the pristine and altered surface in detail to understand the cluster formation. We anticipate that such reformed surfaces can be beneficial to enhance the surface plasmon resonance. [ABSTRACT FROM AUTHOR]

Bimetallic alloy nanomaterials are promising anode materials for potassium‐ion batteries (KIBs) due to their high electrochemical performance. The most well‐adopted fabrication method for bimetallic alloy nanomaterials is tube furnace annealing (TFA) synthesis, which can hardly satisfy the trade‐off among granularity, dispersity and grain coarsening due to mutual constraints. Herein, we report a facile, scalable and ultrafast high‐temperature radiation (HTR) method for the fabrication of a library of ultrafine bimetallic alloys with narrow size distribution (≈10–20 nm), uniform dispersion and high loading. The metal‐anchor containing heteroatoms (i.e. O and N), ultrarapid heating/cooling rate (≈103 K s−1) and super‐short heating duration (several seconds) synergistically contribute to the successful synthesis of small‐sized alloy anodes. As a proof‐of‐concept demonstration, the as‐prepared BiSb‐HTR anode shows ultrahigh stability indicated by negligible degradation after 800 cycles. The in situ X‐ray diffraction reveals the K+ storage mechanism of BiSb‐HTR. This study can shed light on the new, rapid and scalable nanomanufacturing of high‐quality bimetallic alloys toward extended applications of energy storage, energy conversion and electrocatalysis. [ABSTRACT FROM AUTHOR]