Nucleation Stage Research Articles

Change in the Kinetic Regime of Aggregation of Yeast Alcohol Dehydrogenase in the Presence of 2-Hydroxypropyl-β-cyclodextrin.

Chemical chaperones are low-molecular-weight compounds that suppress protein aggregation. They can influence different stages of the aggregation process-the stage of protein denaturation, the nucleation stage and the stage of aggregate growth-and this may lead to a change in the aggregation kinetic regime. Here, the possibility of changing the kinetic regime in the presence of a chemical chaperone 2-hydroxypropyl-β-cyclodextrin (2-HP-β-CD) was investigated for a test system based on the thermally induced aggregation of yeast alcohol dehydrogenase (yADH) at 56 °C. According to differential scanning calorimetry data, 2-HP-β-CD did not affect the stage of the protein molecule unfolding. Dynamic light scattering data indicated changes in the aggregation kinetics of yADH during the nucleation and aggregate growth stages in the presence of the chaperone. The analysis of kinetic curves showed that the order of aggregation with respect to protein (nc), calculated for the stage of aggregate growth, changed from nc = 1 to nc = 2 with the addition of 100 mM 2-HP-β-CD. The mechanism of 2-HP-β-CD action on the yADH thermal aggregation leading to a change in its kinetic regime of aggregation is discussed.

Analysis of phase transformation thermodynamics and kinetics and its relationship to structure-mechanical properties in a medium-Mn high strength steel

The difference in transformation mechanisms between the normal and reverse phase transformation in medium Mn steel was revealed using thermodynamic and kinetic analysis. The results indicate that the austenite formation during the reverse phase transformation is a fast reaction, significant amount of 46.9 vol% retained austenite is obtained after subjected partial reversion at 650 °C × 1 h. At the nucleation stage, the lath-like structure, dislocations, martensitic packet boundaries, and grain boundaries provide high-density nucleation sites for austenite formation. The critical temperature of austenite formation is reduced by the enrichment of Mn and C. However, no ferrite transformation occurred during the normal phase transformation (650 °C × 6 h isothermal treatment and subsequent furnace-cooling process). At the nucleation stage, the undersaturated Mn and C in the prior austenite grain interior provide insufficient concentration fluctuation, leading to a low nucleation rate. At the phase growth stage, the atomic mobility of Mn and C in the parent austenite (control the ferrite growth) is 1/69 and 1/282 than that in ferrite (control the austenite growth) at 650 °C. The differences in nucleation site density, driving force, and element diffusion rate lead to significant variations in phase transformation behaviors. The excellent mechanical property with the product of strength and elongation (PSE) exceeding 20 GPa % is achieved via the sustained transformation-induced plasticity (TRIP) effect by metastable retained austenite over a large strain range.

Fabrication of ultrafine cerium oxide nanoparticles as an aqueous colloidal solution with single-molecular dispersant via shear agitation reactor or one-pot hydrolysis

Herein, ultrafine CeO2 nanoparticles are synthesized using monomolecular amino acids as dispersants. Monomolecular amino acids are suitable dispersants for the dispersion of nanoparticles with a diameter of 1 nm. Batch-type room-temperature hydrolysis (RTH) synthetic method, which takes advantage of the low decomposition pH of Ce (IV) nitrate, and a shear agitation (SA) reactor, which is highly versatile for multicomponent systems of colloidal synthesis, are used. After adding glycine, ultrafine CeO2 colloids of sizes 1.1 and 1.2 nm are obtained via the batch-type RTH synthesis method and SA reactor, respectively. The smallest CeO2 colloid size is 0.7 nm, which earned at the close concentration of the saturation of glycine using the batch-type RTH method. Because RTH can slowly hydrolyze Ce (IV) nitrate over several hours, we were able to observe the initial stage of nucleation (0.7 nm), which passes instantaneously in the SA reactor. Furthermore, glycine was found to be particularly effective in stabilizing the surface of cerium oxide due to its high adsorption capacity. Therefore, cerium oxide, which is amorphous in the synthesis stage, remained amorphous up to 100 °C due to glycine adsorption, neutralized the colloidal dispersion to form precipitates, and crystallized at room temperature after glycine was removed by washing treatment, resulting in a fluorite structure with a crystallite diameter of 1.5 nm. This crystallite diameter is maintained after heat treatment at 200 °C for 30 min.

Polyaniline Films Fabricated by Pre‐Nucleation Electrodeposition Method with High Electrochemical Activity: Parameter Optimization and Analysis

AbstractElectrochromic polyaniline (PANI) films with high electrochemical performance have been intensively pursued for their potential applications in various fields. Here, the growth process of the PANI films synthesized by the pre‐nucleation electrodeposition method is analyzed and the optimal parameters with highest electrochemical activity are obtained. The PANI film fabricated under high current density of 10 mA cm−2 and impact time of 0.2 s shows the best electrochemical performance. It has a maximum active charge of 22.3 mC cm−2. The optimum electrochemical performance is attributed to the loose and porous structure. The PANI films fabricated under the optimal parameters also show the flattest structure and the smooth surface. It concludes a universal evaluation basis of the optimal conditions for the pre‐nucleation method. That is, in the nucleation stage, the potential curve shall peak rapidly and then fall slowly to the valley without any upward growth; when entering into the low current density growth stage, the potential shall fall rapidly to a certain value and grow at that potential smoothly. This work evokes a deeper understanding and controlling of the growth process of polymers.

Unveiling Solid Electrolyte Interphase Formation at the Molecular Level: Computational Insights into Bare Li-Metal Anode and Li6PS5-xSexCl Argyrodite Solid Electrolyte.

The development of high-energy-dense, sustainable all-solid-state batteries faces a major challenge in achieving compatibility between the anode and electrolyte. A promising solution lies in the use of highly ion-conductive solid electrolytes, such as those from the argyrodite family. Previous studies have shown that the ionic conductivity of the argyrodite Li6PS5Cl can be significantly enhanced by partially substituting S with Se. However, there remains a lack of fundamental knowledge regarding the effect of doping on the interfacial stability. In this study, we employ long-scale ab initio molecular dynamics simulations, which allowed us to gain unprecedented insights into the process of solid electrolyte interface (SEI) formation. The study focuses on the stage of nucleation of crystalline products, enabling us to investigate in silico the SEI formation process of Se-substituted Li6PS5Cl. Our results demonstrate that kinetic factors play a crucial role in this process. Importantly, we discovered that selective anionic substitution can accelerate the formation of a stable interface, thus potentially resolving anode-electrolyte compatibility issues.

Deposition freezing, pore condensation freezing and adsorption: three processes, one description?

Abstract. Heterogeneous ice nucleation impacts the hydrological cycle and climate through affecting cloud microphysical state and radiative properties. Despite decades of research, a quantitative description and understanding of heterogeneous ice nucleation remains elusive. Parameterizations are either fully empirical or heavily rely on classical nucleation theory (CNT), which does not consider molecular-level properties of the ice-nucleating particles – which can alter ice nucleation rates by orders of magnitude through impacting pre-critical stages of ice nucleation. The adsorption nucleation theory (ANT) of heterogeneous droplet nucleation has the potential to remedy this fundamental limitation and provide quantitative expressions in particular for heterogeneous freezing in the deposition mode (the existence of which has even been questioned recently). In this paper we use molecular simulations to understand the mechanism of deposition freezing and compare it with pore condensation freezing and adsorption. Based on the results of our case study, we put forward the plausibility of extending the ANT framework to ice nucleation (using black carbon as a case study) based on the following findings: (i) the quasi-liquid layer at the free surface of the adsorbed droplet remains practically intact throughout the entire adsorption and freezing process; therefore, the attachment of further water vapor to the growing ice particles occurs through a disordered phase, similar to liquid water adsorption. (ii) The interaction energies that determine the input parameters of ANT (the parameters of the adsorption isotherm) are not strongly impacted by the phase state of the adsorbed phase. Thus, not only is the extension of ANT to the treatment of ice nucleation possible, but the input parameters are also potentially transferable across phase states of the nucleating phase at least for the case of the graphite/water model system.

EFFECT OF THE SUBSTRATE MATERIAL ON THE KINETICS OF SILICON ELECTROREDUCTION IN THE KCl–CsCl–K<sub>2</sub>SiF<sub>6</sub> MELT

Due to the possibility of controlling composition and morphology, one of the promising methods for obtaining silicon and its materials is the electrolysis of molten salts. However, this requires data on the influence of various factors on the kinetics of silicon electrodeposition. In this work, an effect of the cathode substrate material on the kinetics of electroreduction of silicon ions in a low-fluoride melt (wt %) 57KCl–43CsCl with the addition of 2.8 wt % K2SiF6 at a temperature of 730°C was studied by cyclic voltammetry and chronoamperometry. Interacting and indifferent materials for silicon were chosen as substrates: glassy carbon, silver, and nickel. On the glassy carbon electrode, the electroreduction of silicon ions proceeds in the potential region more negative than –0.05 V, on the silver electrode, more negative than 0.05 V, and on the nickel electrode, more negative than 0.40 V relative to the potential of the silicon quasi-reference electrode. For all the studied substrates, a cathode process is observed, which is not electrochemically reversible. In this case, according to chronoamperometry measurements, the stage of nucleation of a new phase at the cathode does not affect the kinetics of the process under study. Presumably, in the case of glassy carbon and silver, irreversibility can be caused by a delayed discharge, while silicon electrodeposition on a nickel electrode is accompanied by the formation of nickel silicides. From the voltammetric and chronoamperometric dependences, the diffusion coefficient of silicon ions to the glassy carbon electrode was estimated, the values of which were 1.5 · 10–5 and 1.2 · 10–5 cm2/s, respectively.

RAFT emulsion polymerization of methyl methacrylate mediated by protonated poly(2‐(dimethylamino)ethyl methacrylate) macromolecular chain transfer agent: A mechanism study

AbstractSurfactant‐free reversible addition‐fragmentation transfer (RAFT)‐mediated emulsion polymerization has been used in the synthesis of latex particles. Although this method has been developed for some time, some detailed mechanisms are not clear. Herein, RAFT emulsion polymerization of methyl methacrylate (MMA) mediated by protonated poly(2‐(dimethylamino)ethyl methacrylate) (H+‐PDMAEMA) macromolecular chain transfer agent (macro‐CTA) is studied. The effects of the molar ratios of MMA/macro‐CTA and initiator/macro‐CTA, and the macro‐CTA chain length on the emulsion polymerizations are investigated. At the nucleation stage, H+‐PDMAEMA‐CTA is chain extended with MMA dissolved in aqueous phase; and when the length of PMMA block is above a critical length, the formed amphiphilic block copolymer (BCP) chains self‐assemble into micellar particles. The nucleation time in the emulsion polymerization is strongly dependent on the chain length of H+‐PDMAEMA‐CTA, and the molar ratio of free radical initiator/macro‐CTA. The emulsion polymerization rate is in direct proportion to the molar ratio of free radical initiator/macro‐CTA. The size and the size distribution of the latex particles can be tuned through control of the macro‐CTA chain length and MMA/macro‐CTA molar ratio. Monodispersed latex particles can be synthesized under proper conditions. It is expected that well‐defined latex particles with a variety of hydrophilic polymers (or biomacromolecules) on the surfaces can be synthesized by this approach.

Horizontally Aligned Zn Crystals Deposition with 1T VSe2 Functional Layer for Dendrite-Free Zn Metal Anodes

To fulfill the high requirement for high-energy-density storage, Zn ions batteries (ZIBs) has been garnering great scientific attention and considered the promising candidate due to the moderate redox potential, high safety and reasonable cost. However, the problem of the inferior reversibility and limited-service period owing to the issues of side reactions and Zn dendrites hinder its application. In our study, the hexagonal 1T VSe2, owns metallic appearance, was used as the zincophilic film to replace the conventional metal and graphene-based matrix for hexagonal closest packed (HCP) typed Zn metal electrodeposition in ZIBs. Our experimental results discovers that 1T VSe2/Zn anode is beneficial to regulating Zn crystal morphology from randomly oriented to horizontally (002)-oriented plate-like. Combining with computational modelling, the early stage of Zn nucleation and morphological evolution is investigated from atomistic to meso scale. VSe2 substrate exhibits higher adsorption energy (-0.54 eV) with Zn, contrasting with graphene (-0.38 eV) and pure Zn (-0.48 eV) based on the density functional theory (DFT) calculations. And classical molecular dynamic (MD) simulations reveal the plate-like Zn electrodeposits undergo a reorientation transition with a higher fraction of the (002) facet due to the rapid adatom diffusion coefficient, which effectively prohibits the dendrite formation. The symmetric cell with modified electrodes shows an ultra-stable cyclic life with 50 mV overpotential up to 2500 cycles in the condition of 1 mA cm-2 and 1 mAh cm-2.

A Molecular Dynamics Study of Nucleation and Grain Growth of Novel Al-15Mg<sub>2</sub>Si-4.5Si Composite during Rapid Cooling Based Semi Solid Slurry Preparation

Owing to their several attractive features such as high hardness, high elastic modulus, light weight, high strength to weight ratio, high thermal conductivity, and high temperature strength, composites from Al-Mg2Si family offers promise towards deployment in several industries such as automobile, aerospace, marine, defence and electronic. The present molecular dynamics (employing LAMMPS) based simulation study is one of the first attempt to investigate the nucleation and grain growth mechanisms of Mg2Si phase at atomic level in case of novel Al-15Mg2Si-4.5Si composite, during semi-solid processing. Modified embedded atom method (MEAM) potential has been used to study the atomic interactions in the composite. Reaching the melt state at 1000 K, the temperature of the system is first decreased from 1000 K to 853 K and then the system is held at 853 K for 100 ps. The simulations are performed with three different cooling rates. With lowering of temperature, randomly distributed Mg and Si atoms form atomic clusters at arbitrary locations within the system, which is the nucleation stage for Mg2Si phase formation. Cluster size, radial distribution function has been used to investigate the structural evolution of Mg-Si clusters. Cooling rate significantly influences the grain size as well as the grain growth kinetics. The information about the thermodynamic state of the system has been revealed by extracting the values of internal energy, enthalpy, specific heat. during the slurry preparation and isothermal holding stages. The growth mechanism of Mg2Si nucleus has been characterized from the temporal variation of (Mg + Si) atoms taking part in the cluster formation. Power-law variation is observed in the cooling stage whereas a linear variation is observed in the isothermal stage.

Phase State, Surface Tension, Water Activity, and Accommodation Coefficient of Water-Organic Clusters Near the Critical Size for Atmospheric New Particle Formation.

Interactions between water and organic molecules in sub-4 nm clusters play a significant role in the formation and growth of secondary organic aerosol (SOA) particles. However, a complete understanding of the relevant water microphysics has not yet been achieved due to challenges in the experimental characterization of soft nuclei. Here, we use molecular dynamics simulations to study the phase-mixing states, surface tension, water activity, and water accommodation coefficient of organic-water clusters representative of freshly nucleated SOA particles. Our results reveal large deviations from the behavior expected based on continuum theories. In particular, the phase-mixing state has a strong dependence on cluster size; surface tension displays a minimum at a specific organic-water mass ratio (morg/mw ∼ 4.5 in this study) corresponding to a minimum inhibition of droplet nucleation associated with the Kelvin effect; and the water accommodation coefficient increases by a factor of 2 with nanocluster hygroscopic growth, in agreement with recent experimental studies. Overall, our results yield parametric relations for water microphysical properties in sub-4 nm clusters and provide insight into the role of water in the initial stages of SOA nucleation and growth.

Building block effect induces horizontally oriented bottom Zn(002) deposition for a highly stable zinc anode

The practical application of zinc anodes for rechargeable aqueous zinc-ion batteries is hindered to uncontrollable dendritic zinc deposition and side reactions. And the deposition of zinc is like building blocks layer by layer, typically considered as nucleation, growth and evolution driven by electric field. Yet the important role of the bottommost deposits is generally ignored. Here, we developed a highly self-adaptable polydimethylsiloxane (PDMS)/montmorillonite (MMT) film to regulate the process of zinc deposition sustainably. In the nucleation and growth stages of zinc, the two-step regulation of the building block effect benefits from the adsorption of oxygen-containing sites on PDMS and fast zinc ion nanochannels in the negatively charged interlayer of MMT to achieve targeted-capture of zinc ions and ordered-deposition, thus inducing horizontally oriented Zn(002) deposition in the initial nucleation layer and providing a flat deposition site for the subsequently deposited metal. In the evolutionary stage of Zn, the PDMS/MMT (PMZn) interfacial layer can achieve a conformal contact with the anode due to the high dynamic adaptability and self-healing of the micro-crosslinking of Si-O-Si and B-O bonds. Consequently, PMZn@Cu||Zn offers higher coulombic efficiency(CE) (99.77%) and the PMZn@Zn anodes exhibit an ultra-long cycle life of 2000 h, more than 10 times that of bare zinc anodes. The stability of the high capacity of PMZn@Zn||MnO2 full cells far exceeds that of Zn||MnO2. This strategy provides an effective approach to develop a stable Zn metal anode for aqueous rechargeable Zn batteries.

Stability of Single Gold Atoms on Defective and Doped Diamond Surfaces.

Polycrystalline boron-doped diamond (BDD) is widely used as a working electrode material in electrochemistry, and its properties, such as its stability, make it an appealing support material for nanostructures in electrocatalytic applications. Recent experiments have shown that electrodeposition can lead to the creation of stable small nanoclusters and even single gold adatoms on the BDD surfaces. We investigate the adsorption energy and kinetic stability of single gold atoms adsorbed onto an atomistic model of BDD surfaces by using density functional theory. The surface model is constructed using hybrid quantum mechanics/molecular mechanics embedding techniques and is based on an oxygen-terminated diamond (110) surface. We use the hybrid quantum mechanics/molecular mechanics method to assess the ability of different density functional approximations to predict the adsorption structure, energy, and barrier for diffusion on pristine and defective surfaces. We find that surface defects (vacancies and surface dopants) strongly anchor adatoms on vacancy sites. We further investigated the thermal stability of gold adatoms, which reveals high barriers associated with lateral diffusion away from the vacancy site. The result provides an explanation for the high stability of experimentally imaged single gold adatoms on BDD and a starting point to investigate the early stages of nucleation during metal surface deposition.

Membrane flux response technology for early warning of initial surface scaling in membrane distillation

Membrane distillation (MD) is a promising green separation technology for the treatment of high salinity wastewater attributed to excellent salt rejection, which is significant in relevant environmental and chemical engineering application. However, membrane scaling is an inevitable issue during long-term membrane distillation process. Thus, we developed a membrane flux response technology with data processing method to in-situ monitor the membrane scaling according to the reduction of permeate flux. By real-time analyzing the derivative of deviation between theoretical and experimental fluxes, early warning of initial membrane surface scaling was observed at initial nucleation stage. Besides, such timely detection was also achieved under different temperatures and flow velocities of feed solution, even for the poor light transmittance aqueous solution (such as NiSO4 and CoSO4 solution), which exhibited wide application potential on diverse high salinity wastewater systems. In addition, the metastable zone width of salt solution within MD system was obtained for the efficient operation design. To sum up, membrane flux response technology provides an early warning at imminent membrane scaling, which will maintain the great separation effect for a fresh feed solution after a facile cleaning by pure water, indicating the extension of device lifetime.

NUCLEATION AND CRYSTALS GROWTH IN THE VOLUME OF GLASS Li2O–Al2O3–SiO2 SYSTEM

By the Marotta et al method, temperature of 670 ?C at a holding time of 2 hours provides the maximum rate of nucleation the crystalline phase of ?-eucryptite-like solid solutions was found. The activation energy of nucleation and the Avrami parameter were measured by the DSC method, allowing to estimate the crystallization characteristics. The gradient crystallization method has established the temperature range of heat treatment, within which it is possible to obtain a transparent glass-ceramic. The refinement of regime the nucleation stage made it possible to reduce the time of the second stage crystallization required for the complete formation of the transparent glass-ceramic structure. Varying the holding time at a temperature of 710 ?C makes it possible to smoothly change the CTE in the range of ?(3…+41)?10–7 K?1 in the temperature range from ?120 to +500 ?C.

Homogeneous Phase Distribution in Q-2D Perovskites via Co-Assembly of Spacer Cations for Efficient Light-Emitting Diodes.

Quasi-2D (Q-2D) perovskites are promising candidates to apply in light-emitting diodes (LEDs). However, delicate control on crystallization kinetics is needed to suppress severe phase segregation. Here, the crystallization kinetics of Q-2D perovskites are investigated via in situ absorbance spectroscopy and for the first time find the multiphase distribution is governed by the arrangement, rather than diffusion, of spacer cations at the nucleation stage, which associate with its assembling ability determined by molecular configuration. A "co-assembly" strategy is conceived by combining co-cations with different configuration characteristics, where bulky cations disturb the assembling between slender cations and lead-bromide sheet, contributing to homogeneous emitting phase with effective passivation. Correspondingly, in the phenylethylammonium (PEA+ )-based Q-2D perovskites (<n>=3), homogeneous phase distribution is achieved by incorporating co-cation triphenylmethaneammonium (TPMA+ ), the branching terminals of which suppress cations assembling into low-n phases and afford adequate cations as passivating ligands. Therefore, the champion external quantum efficiency of the LED device reaches 23.9%, which is among the highest performance of green Q-2D perovskite LEDs. This work reveals that the arrangement of spacer cations determines the crystallization kinetics in Q-2D perovskites, providing further guidance on the molecular design and phase modulation of Q-2D perovskites.

Shed light on new growth pattern in rapid solidified Ta metal: MD simulation, DFT calculation and CALYPSO search

Aiming at the micro-structures of rapid solidified Ta system under cooling rate of 1×1010 K/s, the lowest-energy and meta-stable geometric structure of Tan (n = 19–30) clusters are systematically investigated via MD simulation, DFT calculation and CALYPSO search. It is revealed that the ground-state geometric structure of free Ta clusters plays a significant role in determining its solidified atomic structures and evolution laws in the early stage of nucleation. We explained why the hexagonal close packed (hcp) atomic clusters (Ta22) dominate the solid state of Ta when cooled at a rate of 1 × 1010 K/s. And found that the coexistence of slightly distorted icosahedral (Ta13) and hcp clusters (Ta22) at 300 K is due to the high energy stability of free Ta26–C2v (B) cluster. The larger size of Ta clusters with a perfect closed-shell geometric structure plays a key role in energetic effects, as demonstrated by their thermodynamic stability in terms of binding energy. Additionally, electronic structure stability is achieved when there are fewer electrons on the Fermi level (N(EF)), resulting in Ta atomic clusters that exhibit higher energetic stability and lower chemical activity. Our analysis of the interaction between different atoms in Ta clusters revealed that stronger electronic interactions of central(c)-central(c) and central(c)-shell(s) atoms contribute to the higher energy and chemical stability. Finally, we provide insights into understanding the growth patterns of nucleation in liquid metals through an examination of geometric and electronic structures of free Ta cluster.

Nucleation of Co and Ru Precursors on Silicon with Different Surface Terminations: Impact on Nucleation Delay.

Early transition metals ruthenium (Ru) and cobalt (Co) are of high interest as replacements for Cu in next-generation interconnects. Plasma-enhanced atomic layer deposition (PE-ALD) is used to deposit metal thin films in high-aspect-ratio structures of vias and trenches in nanoelectronic devices. At the initial stage of deposition, the surface reactions between the precursors and the starting substrate are vital to understand the nucleation of the film and optimize the deposition process by minimizing the so-called nucleation delay in which film growth is only observed after tens to hundreds of ALD cycles. The reported nucleation delay of Ru ranges from 10 ALD cycles to 500 ALD cycles, and the growth-per-cycle (GPC) varies from report to report. No systematic studies on nucleation delay of Co PE-ALD are found in the literature. In this study, we use first principles density functional theory (DFT) simulations to investigate the reactions between precursors RuCp2 and CoCp2 with Si substrates that have different surface terminations to reveal the atomic-scale reaction mechanism at the initial stages of metal nucleation. The substrates include (1) H:Si(100), (2) NHx-terminated Si(100), and (3) H:SiNx/Si(100). The ligand exchange reaction via H transfer to form CpH on H:Si(100), NHx-terminated Si(100), and H:SiNx/Si(100) surfaces is simulated and shows that pretreatment with N2/H2 plasma to yield an NHx-terminated Si surface from H:Si(100) can promote the ligand exchange reaction to eliminate the Cp ligand for CoCp2. Our DFT results show that the surface reactivity of CoCp2 is highly dependent on substrate surface terminations, which explains why the reported nucleation delay and GPC vary from report to report. This difference in reactivity at different surface terminations may be useful for selective deposition. For Ru deposition, RuCp2 is not a useful precursor, showing highly endothermic ligand elimination reactions on all studied terminations.

Nucleation and Crystallization of Ferrous Phosphate Hydrate via an Amorphous Intermediate.

The fundamental processes of nucleation and crystallization are widely observed in systems relevant to material synthesis and biomineralization; yet most often, their mechanism remains unclear. In this study, we unravel the discrete stages of nucleation and crystallization of Fe3(PO4)2·8H2O (vivianite). We experimentally monitored the formation and transformation from ions to solid products by employing correlated, time-resolved in situ and ex situ approaches. We show that vivianite crystallization occurs in distinct stages via a transient amorphous precursor phase. The metastable amorphous ferrous phosphate (AFEP) intermediate could be isolated and stabilized. We resolved the differences in bonding environments, structure, and symmetric changes of the Fe site during the transformation of AFEP to crystalline vivianite through synchrotron X-ray absorption spectroscopy at the Fe K-edge. This intermediate AFEP phase has a lower water content and less distorted local symmetry, compared to the crystalline end product vivianite. Our combined results indicate that a nonclassical, hydration-induced nucleation and transformation driven by the incorporation and rearrangement of water molecules and ions (Fe2+ and PO43-) within the AFEP is the dominating mechanism of vivianite formation at moderately high to low vivianite supersaturations (saturation index ≤ 10.19). We offer fundamental insights into the aqueous, amorphous-to-crystalline transformations in the Fe2+-PO4 system and highlight the different attributes of the AFEP, compared to its crystalline counterpart.

Effect of TiO2 on the occurrence and distribution of chromium in stainless‐steel slag glass ceramics

AbstractStainless steel slag waste can be used to prepare value‐added glass ceramics, which can fix potentially toxic Cr from the slag within the crystalline phase. The occurrence and distribution of Cr during the preparation of glass ceramics has a great influence on the final Cr fixation effect. In this study, the effects of the TiO2 content on the occurrence and distribution of Cr during the nucleation and crystallization steps and on the final properties of the glass ceramics were systematically studied. In the nucleation stage, with increasing TiO2 content, the Cr distributed in the spinel containing chromium nuclei first increases and then decreases. In the crystallization stage, Diopside crystal phase nucleates and grows with spinel containing chromium nanocrystals as heterogeneous nuclei. X‐ray photoelectron spectroscopy analysis showed that the chromium distributed in the diopside crystals first increased and then slightly decreased as the TiO2 content increased. The optimal TiO2 content is 3.4 wt.%, which resulted in 97 wt.% of the total Cr being fixed in the diopside crystalline phase (with a very low Cr leaching concentration of 0.009 mg/L), and a high compressive strength of the final glass ceramic of 267.4 MPa, and a Vickers hardness of 1211.8 HV. The research results provide theoretical and technical support for strengthening Cr fixation to enable harmless and high‐value utilization of stainless steel slag for fabricating glass ceramics.