Kinetics Of Phase Formation Research Articles

Concurrent Operando Neutron Imaging and Diffraction Analysis Revealing Spatial Lithiation Phase Evolution in an Ultra‐Thick Graphite Electrode

AbstractEnergy‐efficient, safe, and reliable Li‐ion batteries (LIBs) are required for a wide range of applications. The introduction of ultra‐thick graphite anodes, desired for high energy densities, meets limitations in internal electrode transport properties, leading to detrimental consequences. Yet, there is a lack of experimental tools capable of providing a complete view of local processes. Here, a multi‐modal operando measurement approach is introduced, enabling quantitative spatio‐temporal observations of Li concentrations and intercalation phases in ultra‐thick graphite electrodes. Neutron imaging and diffraction concurrently provide correlated multiscale information from the scale of the cell down to the crystallographic scale. In particular, the evolving formation of the solid electrolyte interphase (SEI), observation of gradients in total lithium content, as well as in the formation of ordered LixC6 phases and trapped lithium are mapped throughout the first charge–discharge cycle of the cell. Different lithiation stages co‐exist during charging and discharging; delayed lithiation and delithiation processes are observed in central regions of the electrode, while the SEI formation, potential plating, and dead lithium are predominantly found closer to the interface with the separator. The study emphasizes the potential to investigate Li‐ion diffusion and the kinetics of lithiation phase formation in thick electrodes.

Outstanding electrocatalytic activity and corrosion property of NiCr nanoparticle alloys electrodeposited from a choline chloride/urea deep eutectic solvent

Nickel-chromium alloys are known for their superior corrosion resistance, wear resistance, and hardness, making them a topic of significant interest. This study explores the electrodeposition of Ni-Cr alloys onto a glassy carbon electrode from a choline chloride/urea deep eutectic solvent. Electrochemical techniques, including cyclic voltammetry and chronoamperometry, were utilized to explore the deposition process. Voltametric analysis revealed that Ni-Cr alloys could be electrodeposited from the reline DES through a single potential step. The analysis of current density transients indicated that the electrocrystallization of Ni-Cr follows a three-dimensional (3D) nucleation and diffusion-controlled mechanism on the bimetallic growing surface. Additionally, the presence of the Ni(II) component was found to significantly enhance the kinetics of Ni-Cr phase formation, facilitating rapid deposition from the eutectic mixture. Surface characterization techniques, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) mapping, and X-ray diffraction (XRD), confirmed the uniform distribution of elements, the formation of the Ni-Cr phase, and its crystalline structure. The high quality of nickel-chromium alloys obtained from DES highlights their potential applications in various engineering fields, particularly in surface coating and metal protection.

Thermodynamic stability and component heterogeneity of CO2/N2 mixed hydrates: Implications for hydrate-based CO2 capture and sequestration

Injecting CO2/N2 into marine sediments to form gas hydrates for CO2 storage is an emerging Carbon Capture and Storage (CCS) technology, holds the potential to significantly reduce the costs of CCS while simultaneously enhancing environmental persistence. However, there is currently a lack of comprehensive investigation into the critical parameters and stability evaluations of CO2/N2 mixed hydrates (Mix-H) formation. This study delves into the impact of gas-liquid ratios, pressure–temperature gradients, and hydrate formation degree on the phase equilibrium, formation kinetics, and thermodynamic stability of Mix-H. Experimental findings elucidate the excess water significantly enhances CO2 dissolution, increasing the thermodynamic barrier for Mix-H formation. Consequently, this leads to weakened kinetics and reduced total CO2 composition within the Mix-H (54.2%–96.4%). Raman spectroscopy confirmed varying heterogeneous compositions and thermodynamic stability of hydrate crystals within the bulk Mix-H. The heterogeneity is quantitatively assessed using a novel test – stepwise depressurization, which revealed increased heterogeneity with decreasing initial pressure–temperature as well as increasing gas-liquid ratios and hydrate formation degree. The heterogeneity of Mix-H significantly impacts the CO2 capture efficiency and long–term stability of CO2 sequestration under environmental disturbances. The results also pave the way for evaluating the performance of mixed hydrate applications in hydrate–based chemical engineering and CCS technology.

Probing Interfacial Degradation in Solid-State Batteries Using Machine Learning Force Fields

Solid-state batteries (SSBs) are next-generation energy storage technologies with improved safety and potentially higher energy densities compared to conventional Li-ion batteries, which is enabled by using fast ion-conducting solid electrolytes (SEs). However, practical applications of SSBs are hindered by the electro-chemo-mechanical instabilities at interfaces within the SEs (grain boundaries (GBs)) and between SEs and the electrodes, which deteriorates Li transport and the chemical and mechanical integrity of the cell. To mitigate, fundamental understanding of the intrinsic physico-chemical properties at interfaces is required. To this end, we directly probe atomic structures of the interfaces and GBs by performing large-scale atomistic simulations, enabled by validated machine-learning force fields (MLFFs) and resolve the structure-property relationship at complex interfaces that governs Li-ion transport and stability of SSBs.In this talk, we will discuss the characteristics of garnet Li7La3Zr2O12 (LLZO) SE/LiCoO2 (LCO) cathode interfaces as well as the internal interfaces within the LLZO (GBs). It is observed from our simulations that the propensities for interfacial degradation strongly depend on the surface chemistry of LLZO and LCO. Doping LLZO is found to have a segregation effect at the LLZL GBs, here we will discuss its implication towards secondary phase formation and Li transport kinetics. At last, we will address the impact of interfaces on micro-crack propagation behavior in the LLZO-LCO system. In summary, our results reveal how atomic details of the dynamically evolving interfaces dictate the performance of SSBs, and provide guidance for processing and interface design to achieve desired performance .This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract number DEAC52-07NA27344. Authors acknowledge funding support from the Vehicle Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy and computational resource support from the Innovative and Novel Computational Impact on Theory and Experiment (INCITE) program. This research used resources of the Argonne Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC02-06CH11357.

High Temperature Fatigue of Additively Manufactured Inconel 718: A Short Review

Abstract With the increasing interest in adopting additively manufactured (AM) IN718 for high-temperature applications, driven by the design and manufacturing flexibility offered by AM technologies, understanding its fatigue performance is crucial before full-scale adoption. This paper reviews the recent literature on the high-temperature fatigue behavior of AM IN718. The review focuses on two primary stages of fatigue damage: fatigue crack initiation and fatigue crack growth. Notably, most existing studies have concentrated on fatigue crack initiation, and thus, this review emphasizes this aspect. In the fatigue crack initiation stage, discrepancies in low cycle fatigue (LCF) and high cycle fatigue (HCF) life performances are observed in the literature. Some studies have shown that the average room temperature (RT) fatigue life of AM IN718 is superior or comparable to that at high temperatures in the LCF regime. Conversely, in the HCF regime, high-temperature fatigue life is sometimes found to be superior to that at room temperature. However, other studies indicate no clear trend regarding the effect of temperature on HCF life. Although various mechanisms have been proposed to either improve or degrade fatigue performance across the LCF, HCF, and very high cycle fatigue (VHCF) regimes, the underlying reasons for the distinct behaviors in these regimes remain unclear. Competing mechanisms, such as surface oxide formation and thermally driven dislocations glide, can potentially enhance or reduce fatigue life. However, the interaction and control of these mechanisms over the fatigue strength of AM IN718 are not yet fully understood. Systematic studies are required to elucidate their roles in high-temperature fatigue. Microstructural investigations have suggested that controlling the formation and precipitation of deleterious secondary phases is crucial for tailoring the high-temperature fatigue strength of AM IN718. Therefore, it is imperative to design heat treatment protocols informed by a comprehensive understanding of phase formation kinetics to improve the high-temperature fatigue performance of AM IN718 compared to their traditionally manufactured (TM) counterparts. This is particularly important for IN718 parts manufactured using directed energy deposition technology, which currently lacks standardized heat treatment procedures. The review also identifies open research areas and provides recommendations for future work to address these gaps.

Kinetics of diffusion and phase formation in a solid-state reaction in Al/Au thin films

The kinetics of diffusion and formation of Al-Au intermetallic compounds in a solid-state reaction between layers of aluminum and gold has been studied by the method of in situ electron diffraction. The phase sequence in the solid-state reaction in Al/Au thin films is found to depend on the atomic ratio of aluminum and gold at the initial state. Specifically, with the atomic ratio being Al:Au=2:1, one observes the formation sequence: Al3Au8→AlAu2→Al2Au, while with the ratio Al:Au=1:4, the sequence is Al3Au8→AlAu4. The observed change in the sequence is explained using the theoretical model of EHF (Effective Heat of Formation). The kinetic parameters of the diffusion of gold through the layer of reaction products in the Al/Au thin films have been determined, including the apparent activation energy of the diffusion Ea=1.17 eV and pre-exponential factor D0=120 cm2/s. Based on the data obtained by in situ electron diffraction, the kinetic parameters of the phase formation have been estimated by the Kissinger-Akahira-Sunose method. In addition, the kinetic parameters of the formation of the Al-Au intermetallic compounds have been determined (apparent activation energy Ea, pre-exponential factor A) in the solid-state reaction in the Al/Au thin films, namely, Ea = 0.77 eV, log(A, s−1) = 9 for Al3Au8; Ea = 1.08 eV, log(A, s−1) = 13 for AlAu2; Ea = 1.13 eV, log(A, s−1) = 13 for Al2Au; and Ea = 1.35 eV, log(A, s−1) = 16 for the phase AlAu4. The kinetic parameters of the formation of the AlAu4 phase have been estimated for the first time.

Influence of the Synthesis Process on the Physical Property Characteristics of BiFeO3 Ceramics Prepared by Flux-based Molten Salt and Solid-state Reaction Route: A Comparative Study

This work reports the influence of the solid-state reaction (SSR) and molten-salt synthesis (MSS) routes on the physical properties of the multiferroic BiFeO3 (BFO) compound exploited for capacitors and memory devices. Rietveld refinement reveals that the MSS-derived BFO ceramics have exhibited a pure-phase distorted rhombohedral perovskite structure at low temperatures (650 °C) compared to the SSR method. The FE-SEM illustrates the uniform distribution of spherical-shaped BFO grains. By altering the fabrication route, the calculated bandgap values of BFO were tuned within the range of (2.14 ± 0.02) to (2.05 ± 0.02) eV based on Tauc’s plot. The suppression of oxygen vacancies led to better dielectric characteristics at higher frequencies in the MSS-prepared BFO nanoceramics. Also, the MSS-derived BFO ceramics possessed a typical canted-AFM loop with a higher MR value of ∼2.73×10−2 emu g−1. These observations suggest that fabrication techniques have a decisive effect on the phase formation kinetics and multiferroic properties of BFO ceramics.

Accessing forbidden phases

Abstract Thanks to the development of quantum mechanics-based crystal structure prediction methods in the past decade, numerous new compounds with low temperature thermodynamic stability, mainly binary intermetallic compounds, have been predicted. Differing from conventional alloy materials, the synthesis of these low temperature stable compounds may be impossible relying on traditional thermal activation methods since thermally activated atomic diffusion at low temperatures is so slow that phase formation may require cosmic-scale time. Strikingly, it has been shown that some special experimental methods can successfully synthesize low temperature stable compounds by introducing a large number of vacancies and defects into the material to enable atomic rearrangement and simultaneously increasing the phase transformation driving force to accelerate the reaction kinetics. This review summarizes the predictions of compounds that have not been experimentally reported to be stable at low temperatures and provides some experimental approaches that can be used for future synthesis. We describe the basic thermodynamics and kinetics of phase formation, show how compound formation is constrained at low temperatures, and illustrate that the formation of some compounds is nearly impossible without enhanced kinetics.

Interacting fronts in a prototypical, two-dimensional model of entropy-stabilized reactive phase formation

Solid-state reactions proceeding from an initial microstructure enable the synthesis of complex materials in a wide variety of applications. However, despite the importance of such reactions in materials’ processing, the connection between an initial, reactant microstructure and the ensuing transformation kinetics has been relatively little studied. In this work, we employ computer simulation of a reaction–diffusion model and a quantitative analysis of the associated kinetic equations to examine the propagation and interaction of evolving fronts in a prototypical system transforming via a solid-state reaction. It is found that the interaction between fronts dictates transformation kinetics. We then use our results to describe the kinetics of phase formation in the Co–Ti–O system, which contains the entropy-stabilized line compound cobalt dititanate, CoTi2O5. This system is of particular interest as it has been shown that the solid-state synthesis may be exploited to produce single-crystal cobalt dititanate.

Sigma phase kinetics in DSS filler metals: A comparison of sigma phase formation in the as-welded microstructure of super duplex stainless steel and hyper duplex stainless steel

This study investigates and compares the kinetics of sigma phase formation in established Super Duplex Stainless Steel (SDSS) and recently developed Hyper Duplex Stainless Steel (HDSS) filler metal wires. Experimental sigma phase time-temperature-transformation (TTT) maps were developed, revealing nearly equivalent interface area/volume, resulting in similar sigma phase kinetics for 1% volume despite the higher Cr and Mo content in HDSS. However, the growth rate to 5% and 10% sigma phase volumes was slightly higher in HDSS. The sigma phase kinetics in both SDSS and HDSS were analyzed using the exponential Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach based on experimental TTT data. Linearized plots from the JMAK calculations showed a transition in kinetics mechanism from eutectoid decomposition and interface-controlled growth to a diffusion-controlled growth stage in both materials. The higher volumes and morphologies of the sigma phase were found to be diffusion-dependent, mainly occurring during the second kinetics stage. The influence of HDSS's higher Cr and Mo content on the growth rate was observed for these higher volumes. For applications within the 1% sigma phase limit, both wires exhibited equivalent susceptibility to sigma phase formation, regardless of the higher alloying in HDSS.

In-situ XRD investigation of [formula omitted] phase precipitation kinetics during isothermal holding in a hyper duplex stainless steel

The precipitation kinetics and formation mechanisms of σ phase during isothermal holding of a hyper duplex stainless steel in the temperature range from 750 °C to 1025 °C were studied by means of in-situ high energy X-ray diffraction experiments. Rietveld analysis of the data determined the nose temperature as 900 °C where a σ phase fraction of 1 wt% is attained after 15 s. The measurements revealed a distinct change from initial interface controlled nucleation of σ phase to a later stage of diffusion controlled growth during holding at 1000 °C after the σ phase fraction reaches half its final value. At lower holding temperatures the change from interface control to diffusion control happens more gradual and at later stages of the transformation. At these lower temperatures σ phase precipitation is accompanied by the formation of secondary austenite. Changes in σ phase formation mechanisms and kinetics were correlated with variations in the morphology of the precipitates through SEM analysis of quenched samples. Isothermal holding at 1000∘C and 1025 °C as well as above the solvus temperature of σ phase at 1120 °C leads to local fluctuations of austenite and ferrite phase fractions and the concomitant movement of austenite/ferrite phase boundaries even when no overall change in the phase fractions occurs.

On the stability of Ti(Mn,Al)2 C14 Laves phase in an intermetallic Ti–42Al–5Mn alloy

In order to facilitate a more widespread use of intermetallic γ-TiAl based alloys in the aircraft and automotive sector, recent research focuses on the development of low-cost titanium aluminides. The strong β-stabilizing effect as well as the increased ductility upon Mn addition renders this alloying element a promising candidate to fully or partially substitute other, more expensive, alloying elements such as Mo, Ta and Nb. Mn-containing γ-TiAl based alloys, however, are prone to the formation of the undesired, brittle Ti(Mn,Al)2 C14 Laves phase during long-term exposure at the targeted service temperatures, which can deteriorate the ductility at ambient temperatures. In this study, the transformation kinetics as well as the chemical and thermal existence range of the C14 Laves phase in the low-cost Ti–42Al–5Mn (at.%) alloy were investigated by complementary experimental and computational approaches. In situ and ex situ high-energy X-ray diffraction in combination with microstructural investigations were used to study the occurrence and transformation kinetics of possible Laves phase formation in the course of annealing treatments. The chemical stability range of the C14 Laves phase was addressed by chemical analysis in conjunction with complementary ab initio modeling. Using these combined approaches, the critical local Mn concentration of ∼16 at.% for Laves phase formation within lamellar α2 and ∼17 at.% within βo in the Ti–42Al–5Mn alloy was determined. These results should be critically considered for future design of advanced low-cost γ-TiAl based alloys.

Sigma phase formation kinetics in hyper duplex stainless steel welding filler metal

Sigma phase formation kinetics in hyper duplex stainless steel welding filler metal

Advanced pre-combustion CO2 capture by clathrate hydrate formation with water-to-gas molar ratio optimization

Capturing CO2 from exhaust gases by formation of clathrate hydrates, which consist mainly of water (∼85 %), is highly promising owing to the mild operating conditions, economic feasibility, and environment-friendliness. Although tremendous efforts have been made, hydrate-based CO2 capture has not yet been realized primarily due to insufficient CO2 uptake kinetics and separation efficiency. To overcome these, the effect of the water-to-gas molar ratio (W/G ratio), which was not previously considered important despite its significance, on clathrate hydrate-based pre-combustion capture was investigated. Changes in phase equilibrium temperatures for structure Ⅰ CO2/H2 and structure Ⅱ CO2/H2/tetrahydrofuran (THF) hydrates with the W/G ratio were characterized to establish suitable operation temperature and pressure conditions. In addition, a novel strategy utilizing the residual liquid water to capture extra CO2 in structure Ⅰ hydrates was demonstrated. Contrary to the general premise, limiting the THF concentration was found to be effective in preventing unfavorable H2 capture, thus dramatically improving the separation efficiency. Through a comprehensive evaluation in terms of hydrate phase equilibria, formation kinetics, and separation efficiency, 3 mol% THF + high W/G ratio was derived as the optimal condition. The present findings demonstrate that the effect of the W/G ratio and its combined effects with other parameters on phase equilibria, formation kinetics, and separation efficiency should be emphasized to achieve an advanced pre-combustion capture using clathrate hydrates toward carbon neutrality.

Transformation of mineral matter during pyrolysis, gasification and combustion of biosolid chars

During thermochemical processing of biosolids in sewage sludge, different forms of phosphorus-containing compounds are generated in biosolid chars (biochars). This study examines the effects of biochar processing conditions on the mineral compounds produced during the pyrolysis, gasification, and combustion of biosolids, and the major determinants of phase formation kinetics. Our results show identified phase transformations through experiments in a laboratory tube furnace followed by X-ray diffraction analysis (XRD). Additionally, a synchrotron powder diffraction study was conducted to verify XRD results of the laboratory processed samples and to observe in situ phase transformations in biochars. It was found that under a neutral atmosphere, crystalline oxide phases are formed at lower temperatures and much faster than iron phosphide, while gasification and combustion conditions led to the formation of crystalline phases in phosphate forms. These forms of phosphorus compounds in by-products of biosolids thermochemical treatment can be used as agricultural fertilizers.

Influence of Oxygen on the Kinetics of Omega and Alpha Phase Formation in Beta Ti–V

A detailed understanding of the kinetics of phase formation in beta -stabilised titanium is of decisive importance for the applicability of these materials. However, the complex nature and long timescales of the various transformations, calls for specialized measurement techniques. In this work high-stability isothermal laser dilatometry is used to study the temporal volume changes associated with the various phase formation processes. Distinctly different behaviours between samples of Ti–21 at. pct V with different solute oxygen content could be detected and quantified. Temperature regimes for both diffusionless and diffusion-assisted isothermal omega -formation as well as for omega -to-alpha -transformation were determined. Low oxygen contents promote the diffusionless omega -formation mechanism, but retard the diffusion-assisted one as well as the omega -to-alpha -transformation process. The results confirm recent findings of a clear distinction between the diffusionless and diffusion-assisted isothermal omega formation modes. Modelling of the omega -phase formation applying Austin–Rickett kinetics revealed the temperature-dependent formation rates, on the basis of which the isothermal TTT-diagrams were developed which reflect the strong influence of the oxygen content.

Phase formation kinetics during heat treatments of Inconel 718 deposits based on cold metal transfer-based wire arc additive manufacturing

In this study, various heat treatments were conducted on Inconel 718 (IN718) products deposited by wire arc additive manufacturing (WAAM) to investigate the formation kinetics of phases at microstructural locations. The formation kinetics of the secondary phases precipitated by heat-treating of WAAM products differ from those of wrought or cast products because of the heat that accumulates during layer-by-layer deposition. Therefore, the secondary phases in the heat-treated WAAM products differ from those in conventional products according to the microstructural locations, e.g., the dendritic region, interdendritic region, and grain boundaries. To investigate such phase differences, a 100-layer IN718 wall was deposited using cold metal transfer (CMT)-based WAAM and then heat-treated under various conditions. In each heat-treated specimen, the δ, γ’, and γ” phases were identified by microstructural analyses. Based on the results, time–temperature–transformation diagrams were constructed for each microstructural location, which confirmed that the secondary phases were precipitated faster in the interdendritic region and at grain boundaries than those in the dendritic region. In addition, the applicability of single-aging, which can be used to satisfy the desired mechanical properties in less time with less processing, was evaluated by the hardness and tensile tests in the WAAM products.

Silicic Acid Polymerization and SiO2 Nanoparticle Growth in Hydrothermal Solution.

The approach of numerical simulation of orthosilicic acid OSA polymerization and SiO2 nanoparticle formation in hydrothermal solution have been developed based on the model of the homogeneous stage of nucleation and the subsequent growth of particles. The influence of surface tension on the interface of SiO2–water, the rate of molecular deposition, and Zeldovich factor Z were evaluated. Temperature dependence on time, pH, initial OSA concentration, and ionic strength are the main parameters that determine the kinetics of colloid phase formation, the final average size of SiO2 nanoparticles, and the particle size distribution and its polydispersity index. The results of the numerical simulation were verified with experimental data on OSA polymerization and measurement of nanoparticles sizes using the method of dynamic light scattering in a wide range of temperatures of 20–180 °C, pH = 3–9, SiO2 content Ct of 300–1400 mg/kg, and ionic strength Is of 0.0001–0.42 mol/kg. The results obtained can be used in the technology of hydrothermal synthesis of sols, gels, and nanopowders to regulate the kinetics of OSA polymerization and SiO2 nanoparticle growth, particle size distribution, morphology, and structure of products.

Reaction kinetics in the system Y2O3/Al2O3 – Use of an external electric field to control the product phase formation in a system forming multiple product phases

This study investigates the influence of an external electric field on the kinetics of a heterogeneous solid state reaction between Al2O3 and Y2O3. The reaction couples were prepared by means of pulsed laser deposition (PLD) by growing Y2O3 films on single crystalline alumina substrates with an (0001) orientation. The solid state reaction was performed at a temperature of 1400° (1673 K). Utilising attached platinum electrodes, an electric field of 350 V/mm was applied. The superposed field led to an ionic current through the reacting sample and modifies the individual growth kinetics of the three product phases/layers, Y3Al5O12 (YAG), YAlO3 (YAP) and Y4Al2O9 (YAM) The cross-sections of the reacted samples were characterised by means of SEM and XRD. Depending on the direction of the ionic current, the kinetics of the YAP phase formation in particular was strongly influenced. The general kinetics of a solid state reaction forming multiple product phases was analysed using linear transport theory. The effect of an electric field for controlling the product phase formation to prefer or to kinetically suppress the formation of a distinct phase is demonstrated.

Prospects for anisotropic superfluidity in a Fermi gas of dysprosium

The possibility of obtaining superfluid phases for a Fermi gas of dysprosium with a magnetic dipole – dipole interaction is discussed. The obstacles and possible solutions are shown. The required phases are similar to the A1 phase and the polar β phase in 3He. It is expected that in dysprosium, the macroscopic properties of the phase will be determined by the symmetry of the pair interactions. It is assumed to observe the kinetics of phase formation and spontaneous choice between two energy-degenerate phases with different projections of the orbital angular momentum.