Phase Transformation Mechanism Research Articles

Solid‐Solid Phase Transformation Behavior of ϵ‐CL‐20 Induced by Typical Organic Solvents: A Theoretical and Experimental Study

AbstractThe solid‐solid phase transformation of ϵ‐CL‐20 induced by external conditions is one of the bottlenecks limiting the widespread applications of CL‐20‐based energetic materials. Herein, we report the investigation on the influence of solvent polarity on ϵ‐CL‐20 solid‐solid phase transformation behavior both theoretically and experimentally. Density functional theory (DFT) calculation was performed to evaluate the possibility of ϵ‐CL‐20 phase transformation induced by organic solvent molecules from the perspective of ϵ‐CL‐20 electronic structure and molecular structure variations. Additionally, experimental study of ϵ‐CL‐20 phase transformation induced by 1,2‐dichloroethane, ethanol, and methanol gas environment was conducted. Solvent with higher polarity was confirmed to significantly vary molecular surface electrostatic potential and molecular conformation of ϵ‐CL‐20 molecule. Furthermore, ϵ‐CL‐20 critical phase transformation temperature decreased when using inducing solvent with higher polarity. And the observed maximum phase transformation rate was the one induced by the highest polarity solvent. A four‐parameter model was established to describe the phase transformation process as a function of time based on the experimental results. Possible ϵ‐CL‐20 solid‐solid phase transformation mechanism was proposed. Hopefully, these results will be beneficial for the rational preparation and utilization of CL‐20‐based energetic materials.

Aluminium-doped vanadium nitride as cathode material for high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are increasingly favored for their environmentally friendly and impressive energy storage performance. Vanadium nitride (VN) is receiving much attention as a cathode material for AZIBs due to its high electrical conductivity and controllable structure. However, the direct use of VN in AZIBs presents challenges such as sluggish kinetics, insufficient specific capacity and limited stability. Herein, a heteroatom doping strategy is utilized to improve the electrochemical energy storage performance of the VN by incorporating aluminium (Al) via a hydrothermal process and a subsequent calcination treatment. Electrochemical characterizations indicate that the as-synthesized aluminium-doped VN (Al-doped VN) exhibits an outstanding specific capacity of 544 mAh·g−1 at 1 A g−1 and retains a high rate capacity of 275.6 mAh·g−1 at 10 A g−1. Further studies show that the Al incorporation effectively modulates the electronic configuration of the VN, which accelerates the charge transfer kinetics and thus enhances the electrochemical storage performance of VN. The phase transformation mechanism of the Al-doped VN is also investigated and the results show that the VN undergoes partial conversion into Zn3(OH)2V2O7·2H2O during the charge/discharge process.

Fabrication and characterization of foam ceramics from recycled waste concrete powder and waste glass powder

Incorporating multi-solid wastes to prepare foam ceramics has attracted widespread attention due to its excellent characteristics and environmental protection. In this study, foam ceramics were prepared by sintering method using recycled waste concrete powder (RWCP) and waste glass power (WGP) as the major material, Na2CO3 as foaming agent and borax as fluxing agent. The effect of sintering temperature on the physical properties and pore structure of foam ceramics were studied. The phase transformation and reaction mechanism were also discussed. The results reveal that when the RWCP content was 40%, the WGP content was 60% and the sintering temperature was 890 °C, the foam ceramics showed the best overall performance. The compressive strength, bulk density, water absorption and porosity were 2.39MPa, 0.83g/cm3, 8.27% and 66.68%, respectively. At this time, the pore size distribution was optimal, and mesopore occupied the vast majority. The fractal dimension of pore reached the minimum of 1.09. In addition, The XRD results showed that WGP and RWCP gradually depolymerized and reconstructed under the action of flux. Then the foam ceramics with mullite, pyroxene and wollastonite as the main phases were formed. The experimental results showed that it was feasible to prepare foam ceramics using RWCP. This study can provide a new train of thought for the reuse of RWCP.

A Review on the Partitioning of Solutes Along Dislocations and Stacking Faults in Superalloys

AbstractChemical and microstructural alterations at near-atomic scale can influence the high temperature mechanical performance of superalloys. These alterations are strongly associated with solute segregation at crystal defects, such as dislocations and stacking faults. This review provides an overview of the phenomena that occurs during deformation at elevated temperatures due to the interactions of solutes with crystal defects. These interactions are discussed based on investigations conducted by exploiting the recent technological advancements of advanced characterization methods, such as transmission electron microscopy and atom probe tomography. Insights on local phase transformation mechanisms along stacking faults are discussed providing perspectives on new alloy design concepts. Besides, various microstructural alterations controlled by the interactions of solutes with dislocations are discussed. Bringing together observations at near-atomic scale that control superalloys in the macroscopic level, we aim to bridge an atomic scale microanalysis gap. Thus, providing insights that future alloy designers, modelers, and engineers can incorporate these effects into their analyses, alloy design models and life prediction calculations.

Low-dose neutron irradiation effects on the elastoplastic deformation mechanisms of aluminum-doped gallium nitride under contact loading

The elastoplastic deformation mechanisms of irradiated aluminum (Al)-doped gallium nitride (GaN) under contact loading are investigated in this work using the nanoindentation simulations, which is of great significance for understanding the mechanical properties of the Al-doped GaN and guiding the design of durable and high-performance GaN-based devices. The mechanical behaviors of the Al-doped GaN with different doping concentrations are analyzed, including the indentation hardness, Young's modulus, elastic recovery rates, phase transformations, and stress distribution. It is found that Al doping increases their hardness, Young's modulus, and elastic recovery rates, and leads to an enlargement of the phase transformation regions, which is dominated by the high coordination number (CN) phase transformations. Furthermore, the effects of low-dose neutron irradiation on their elastoplastic deformation mechanisms are studied by triggering cascade collisions within the structure. When subjected to such irradiation, structural changes occur in the Al-doped GaN, their indentation hardness, Young's modulus, and elastic recovery rates increase remarkably, and its phase transformation mechanism is changed remarkably. The dislocation behaviors of the doped and undoped GaN are different under neutron irradiation. This study is important for capturing the mechanical stability and integrity of Al-doped GaN in an irradiation environment, as well as developing GaN-based devices with superior irradiation resistance.

Hydrogen-based mineral phase transformation mechanism investigation of pyrolusite ore

Hydrogen-based mineral phase transformation mechanism investigation of pyrolusite ore

Hollow spherical Na3.95Fe2.95V0.05(PO4)2P2O7 suppressing inactive Maricite-NaFePO4 with ultrahigh dynamics performance

sodium ion batteries are considered as excellent energy storage battery materials with the characteristic of low cost and renewability. As a critical component of sodium-ion energy storage batteries, cathode materials have attracted great attention from scientists around the world. Recently, Na4Fe3(PO4)2P2O7 (NFPP) which offer a theoretical capacity of 129 mAh g-1 has garnered widespread attention. However, the formation of inactive maricite NaFePO4 (NFP) and low capacity Na2FeP2O7 (Na2FPO) during the synthesis process restricts the capacity utilization, while poor conductivity further limits its electrochemical performance. To address these issues, here, Na3.95Fe2.95V0.05(PO4)2P2O7/C (V0.05-NFPP/C) composite material was synthesized and assembled into cell for testing. A capacity of 114 mAh g-1 was given at 0.1C and rate performance also represent 90 mAh g-1 at 10C. Vanadium-ion improves the dynamic performance by inhibiting maricite NFP and participating in electrochemical reactions. Furthermore, sodium-ion storage mechanism of V0.05-NFPP/C was revealed by ex-situ XRD patterns with the assistance of first-principles calculations, and the phase transformation mechanism during the sintering process was explored.

Determination of the β to γ Phase Transformation Mechanism in Sc- and Al-Alloyed β-Ga2O3 Crystals

Determination of the β to γ Phase Transformation Mechanism in Sc- and Al-Alloyed β-Ga₂O₃ Crystals

A deep insight of re-entrant martensitic transformation mechanism in Co2Cr(Ga,Si) shape memory alloys

Co2Cr(Ga,Si) shape memory alloys have a wide application temperature range due to the unique re-entrant martensite phase transformation (RMT) behavior. Nevertheless, the microscopic mechanism of RMT remains elusive and unsystematic. The heart of this investigation lies the comprehensive exploration of phase stability, phase transformation path, and martensite slip direction during RMT from martensite (D022-PM) to austenite (L21-FM). In this work, we systematically investigate the re-entrant martensitic transformation of Co2Cr(Ga,Si) SMAs using first-principles methods for the first time. Firstly, the density of states (DOS) calculation indicates that the stability of L21-FM is higher than D022-PM. The charge density calculation further indicates that the bonding strength between Co atoms and Cr (Si) atoms in the L21-FM phase is the highest. In addition, Fermi surface calculation further reveals that phase instability is due to the Fermi surface nesting caused by electron-phonon coupling. Moreover, the minimum energy path was calculated by the G-SSNEB method for the first time, which indicates the RMT can occur. Finally, the calculation of the elastic constants indicates that RMT is caused by the crystal plane slip of the D022-PM phase along the <110> direction. Our calculations provide the electronic-level and thermodynamic mechanism for RMT of Co2Cr(Ga,Si) alloy and shed some light on the revelation of the phase transformation mechanism.

PbSO4 decomposition kinetic and phase transformation mechanism during lead waste recycling

PbSO4 is the main component of lead paste, lead smoke and other lead-containing solid wastes. It usually matches with the primary lead concentrate to co-smelt for lead extraction, mostly in the oxidation smelting stage. The lead waste quickly experiences different temperature and atmosphere fields from feeding the furnace to the completion of the reactions. This work investigated PbSO4 decomposition kinetic and phase transformation mechanism during lead waste pyrometallurgical recycling. The results show that the activation energy of the decomposition reaction of PbSO4 at 800 ℃∼1000 ℃ in Ar atmosphere is 121.35 kJ/mol. The PbSO4 decomposition reaction in Ar and Air is a multi-step decomposition process, which may undergo PbSO4 → PbO·PbSO4 → 2PbO·PbSO4 → 4PbO·PbSO4 → PbO. PbO is not generated through direct decomposition of PbSO4. The results are expected to provide guidance for the lead wastes co-smelting process to achieve a target PbSO4 decomposition product.

Uncovering the combining V with Ni micro-addition alloying on the mechanical properties and multiphase transformation during solidification and homogenization of Al–Zn–Mg–Cu–Sc alloy

The ultimate tensile strength of the T6-aged Al–Zn–Mg–Cu–Sc alloy is improved by 24 MPa reached 667 MPa with the addition of 0.10 % V, 0.20 %Ni and decrease 0.1 %Sc. The thermodynamic and microalloying mechanisms of phase transformation during solidification and homogenization of Al–Zn–Mg–Cu–Sc–V–Ni alloy were clarified. The phase transformation model of Al3Sc (V, Ni) structure induced by V and Ni addition during homogenization was established. The calculation radius showed that coherent L12-ordered Al3Sc(V, Ni) nanoparticles were formed in the Al–Zn–Mg–Cu–Sc–V–Ni alloy, which had a small critical nucleation radius (22.0 nm). The large thermodynamic driving force and the high kinetic energy migration energy barrier of γ-Al7Cu4Ni and Al3Sc (V, Ni) phases led to the finer microstructure of grain. V element not only promoted the formation of Al21V2 phase containing Sc but also hindered the mutual diffusion of Al and (Sc, Ni) elements in the eutectic system via segregation at the α-Al/Al3Sc (V, Ni) interface, which improved the stability of the whole alloy. The edge nucleation of γ-Al7Cu4Ni phase upon its diffusion into a Sc-containing Al21V2 phase induced the formation of Al3Sc (V, Ni) structure, whereas the segregation of V and Ni further strengthened the alloy matrix.

Deformation Behavior and Microstructural Evolution of Ti–6.5Al–2Zr–1Mo–1V Alloy during Isothermal Hot Compression

In this investigation, the effects of different deformation passes—namely, single pass and multipass—on the microstructural evolution and deformation mechanisms in the Ti–6.5Al–2Zr–1Mo–1V alloy are analyzed. It is observed that following a single‐pass hot compression, the extent of lamellar α phase spheroidization enhances as the temperature increases. During multipass hot compression, there is a gradual reduction in the size and concentration of equiaxed α phase, alongside an increase in spheroidization. Dislocation density escalates to 15.88%, while the proportion of high‐angle grain boundaries (HAGBs) diminishes to 75.24%. Static recrystallization occurring during the holding process facilitates dislocation annihilation. The dynamic phase transformation mechanism manifests through interfacial permeation at the primary α phase. Strain localization at the boundaries or sub‐boundaries of the primary α phase, which exhibit minimal curvature, induces elevated shear stress, thereby promoting the shearing of the primary α phase and reducing its presence. Texture components predominantly observed are &lt;‐12‐10&gt;//Z0 and &lt;0001&gt;//Z0, transitioning from &lt;‐12‐10&gt; to &lt;0001&gt; with increasing strain.

K-Rich Spinel Interface of Air-Stable Layered Oxide Cathodes for Potassium-Ion Batteries.

Potassium-containing transition metal layered oxides (KxTmO2), although possessing high energy density and suitable operating voltage, suffer from severe hygroscopic properties due to their two dimensional (2D)layered structure. Their air sensitivity compromises structural stability during prolonged air exposure, therefore increasing the cost. The common sense for designing air-stable layered cathode materials is to avoid contact with H2Omolecules. In this study, it is surprisingly found that P3-type KxTmO2 forms an ultra-thin, potassium-rich spinel phase wrapping layer after simply water immersion, remarkedly reduces the reaction activity of the material's surface with air. Combined with Density Function Theory (DFT) calculations, this spinel phase is found to be able to effectively withstand air deterioration and preserving the crystal structure. Consequently, the water-treated material, when exposed to air, can largely maintain its good electrochemical performance, with capacity retention up to 99.15% compared to the fresh samples. Such an in situ surface phase transformation mechanism is also corroborated in other KxTmO2, underscoring its effectiveness in enhancing the air stability of P3-type layered oxides for K+ storage.

Selective extraction of Li and Mn from spent lithium-ion battery smelting slag: Insights from isomorphous replacement in minerals

Recycling the high content of valuable metal elements contained in spent lithium-ion batteries (SLIBs) has attracted significant interest. By leveraging the concept of substitution of isomorphous replacement in earth minerals, this study proposes a novel approach for the selective extraction of Li and Mn from the artificial spodumene-type lithium-rich slag comprising LiAlSi2O6 and Mn2SiO4 through two-step selective roasting process with Na2SO4 and CaCl2, respectively. The thermodynamic calculations confirmed the feasibility of selective Li extraction by Na2SO4 roasting, with the experimental results showing that over 99 % Li was preferentially extracted as LiNaSO4. In the subsequent CaCl2 roasting step for Mn recovery, the Mn2SiO4 was effectively transformed into soluble Na2MnCl4, achieving a maximum Mn extraction efficiency of 86.5 %. The leaching kinetics of the Na2SO4 roasting products were investigated, revealing that the leaching of Li was governed by diffusion and chemical reactions in line with the shrinking core model. Characterization methods such as XRD, SEM, XPS, and TG-DSC were employed to reveal the phase transformation mechanisms of Li and Mn during Na2SO4 and CaCl2 roasting, respectively. The proposed process introduces a novel paradigm for its remarkable selective recovery of Li and Mn from SLIBs smelting slag.

Tuning α precipitation via post-heat treatments in direct energy deposited metastable β Ti-5Al-5Mo-5V-3Cr alloy and its impact on mechanical properties

In this study, the strength and ductility of a direct energy deposited (DEDed) metastable β Ti-5Al-5Mo-5 V-3Cr (wt%, Ti-5553) alloy was explored by tuning the formation of various α microstructures through post-heat treatments. The microstructure of DEDed Ti-5553 with and without post-heat treatments was systematically studied using scanning electron microscopy, three-dimensional (3D) focused ion beam-scanning electron microscopy tomography, transmission electron microscopy, scanning transmission electron microscopy, and atom probe tomography. Nanoscale ω phase and O′ phase particles were observed in the as-built DEDed Ti-5553 without post-heat treatment for the first time. By altering the aging temperatures and heating rates during post-heat treatments, various microstructural evolution pathways were activated, leading to α microstructures with different sizescales, morphologies, and number densities. By fast heating and isothermal aging at 600°C for 2 hours, refined α microstructure was formed through the pseudospinodal decomposition mechanism. While slow heating (at the heating rates of 5 °C/min or 0.5 °C/min) to 600°C and isothermal aging for 2 hours, super-refined α microstructures were produced respectively, primarily via ω-assisted and O′-assisted α precipitation mechanisms. By fast heating to and isothermal aging at 700°C, fine-scaled intragranular α microstructure was formed, dramatically different in morphology and sizescale from the coarse α microstructure formed in the casted Ti-5553, which is suspected to be related to the indirect influence of nanoscale isothermal ω phase particles formed during the DED process and the excess oxygen introduced during the DED process. With fast heating to and isothermal aging at 800°C, coarse α microstructure forms through the classical nucleation and growth mechanism. Various α microstructures led to a drastic change of mechanical properties with improvements up to a 55 % increase in hardness and 92 % increase in tensile yield strength, compared with as-built DEDed Ti-5553. Our work indicates the feasibility of achieving tailored mechanical properties in DEDed metastable β-Ti alloys by tuning α microstructures through selectively activating various phase transformation mechanisms via post-heat treatments.

Liquid phase transformation mechanism of β-caryophyllonic acid initiated by hydroxyl radicals and ozone in atmosphere

β-caryophyllonic acid (BCA), as an important precursor of aqueous secondary organic aerosols (aqSOA), has adverse effects on the atmospheric environment and human health. However, the key atmospheric chemical reaction process in which BCA participates in the formation of aqueous secondary organic aerosols is still unclear. In this study, the reaction mechanism and kinetics of BCA with ·OH and O3 were investigated by quantum chemical calculations. The initiation reactions between BCA and ·OH include addition and H-abstraction reaction pathways, subsequent intermediates will also react with O2, ultimately undergo a cracking reaction to generate small molecular substances. The reaction of BCA with O3 can generate primary ozone oxides and the Criegee Intermediates oIM3, subsequent main reaction products include keto-BCA, as well as other small molecule aqSOA precursors. The entire reaction process increases the O/C ratio of aqSOA in the aqueous phase and generates products of small molecules such as 4-formylpropionic acid, which plays an important role in the formation of aqSOA. At 298K, the transformation rate constants of BCA initiated by ·OH and O3 are 1.47 × 1010 M−1 s−1 and 3.16 × 105 M−1 s−1, respectively, the atmospheric lifetimes of BCA reacting with ·OH range from 0.86 h–5.40 h, while the lifetimes of BCA reacting with O3 range from 0.44 h–10.04 years. This suggests that BCA primarily reacts with ·OH. However, under higher O3 concentrations, its ozonolysis becomes significant, promoting the formation of aqSOA. According to the risk assessment, the toxicity of most transformation products (TPs) gradually decreased, but the residual developmental toxicity could not be ignored. In this paper, the atmospheric liquid phase oxidation mechanisms of sesquiterpene unsaturated derived acid were studied from the microscopic level, which has guiding significance for the formation and transformation of aqSOA in atmosphere.

An integrated exploration from microstructure to mechanics in austenite to pearlite transformation of high carbon steel under high magnetic fields

The effects of a high magnetic field (12 T) on the microstructural evolution and mechanical properties of high carbon steel during isothermal pearlitic transformation at 720 °C were investigated. The application of a high magnetic field effectively promotes pearlitic transformation and leads to a reduction in the lamellar spacing and the geometrically necessary dislocation density (GND) as well as to a slight increase in the grain size of the pearlite, which leads to a decrease in hardness. This is because the magnetic field reduces the magnetic Gibbs energy of ferrite and cementite, resulting in an increase in the driving force of phase transformation, which shortens the pearlite maturation time and reduces the nucleation barriers of pearlite, thereby accelerating the growth rate of pearlite. In addition, the interfacial energy of ferrite/cementite was found to be increased by the magnetic field from the thermodynamic point of view, and the mechanism of action of the magnetic field -induced precipitation of cementite in the form of particles and short rods was elucidated. The present work will enhance the understanding of the mechanism of magnetic field-induced phase transformation in iron-based materials.

Continuous reduction and phase transformation mechanism of pellets in lumpy zone based on dissected hydrogen blast furnace

The continuous phase transition phenomena and mechanism of pellets in the hydrogen blast furnace is achieved by dissecting the 40m3 hydrogen blast furnace. The results of the dissection reveal that the lumpy zone extends to the bosh of the hydrogen blast furnace (HBF), while it ends at about 2/3 of the stack in traditional blast furnace. The iron oxide (FeOx) began to appear in the upper stack, while the iron started to appear in the lower stack. The reduction rate and metallization rate at the bosh are measured at 95.18% and 95.54%. The content of ferrous oxide (FeO) decreases significantly (measured at 1.73% at the bosh), resulting in an increase in the melting point of the primary slag and a deterioration of its fluidity. FeOx formed in the upper stack continuously diffuses and merges into the gangue, which affects the subsequent transformation of FeOx. FeOx shows a preference for interacting with SiO2, CaO, and MgO, directly influencing the formation of slag in the cohesive zone. These findings offer valuable insights for numerical simulation and research on hydrogen-rich operation.

Benchmark of Techniques for the Characterization of the Mechanism of Phase Transformations in Steel of Near-Peritectic Composition

This study addresses challenges in elucidating the mechanism of phase transformations occurring in steel of near-peritectic composition. The importance of using and integrating, complementary experimental techniques is emphasized. While thermal analysis tools such as Differential Scanning Calorimetry (DSC) and Differential Thermal Analysis (DTA) are vital, they offer limited insight on events occurring during cooling. Employing standard thermal analysis (DSC) alongside high-temperature microscopy, incorporating simultaneous thermal analysis within a high-temperature microscope, and concentric solidification, two of steels of near-peritectic composition were investigated. Key findings include the correlation between heating rates and completion temperatures of phase transformation in the DSC heating experiments; absence of a peritectic transition inferred from DSC cooling curves supported by visual observation, and insights into restricted austenite phase nucleation attributed to diffusional constraint and limited nucleation sites. This investigation not only contributes to understanding phase transformation behaviour in peritectic steels, but more generally provides a framework for utilizing different techniques synergistically to address complexities in the interpretation of the mechanism of phase development.

Study on the phase transformation mechanism and influencing factors of inorganic condensable particulate matter from coal-fired power plants

In this study, the concentration of inorganic ions (SO42−, NH4+, NO3− and NO2−) and morphological characteristics of condensable particulate matter (CPM) were investigated to elucidate the formation mechanism of inorganic CPM from ultra-low emission coal-fired power plants. The concentration of inorganic ions increased with the increase of H2O content and concentration of inorganic gaseous contaminants (SO2, NOX and NH3), and decrease of condensation temperature, indicating the enhancement of heterogenous reaction in the saturated flue gas. Furthermore, NOX and SO2 could undergo redox reactions, leading to an elevation in the concentration of SO42− and NO3−. Additionally, the introduction of NH3 resulted in increased concentrations of SO42−, NO3−, and NO2−, highlighting the significant role of NH3 neutralization in CPM nucleation. The condensation of SO3/sulfuric acid aerosols was enhanced under saturation conditions, and SO2 and SO3/sulfuric acid aerosols could contribute synergistically to the formation of SO42−. Moreover, morphological analysis revealed the presence of both well-aggregated solid CPM and dispersed liquid CPM, confirming the formation of inorganic CPM during fast condensation. Furthermore, the detected CPM were composed of S and O, which identified the significant role of sulfates in the inorganic CPM. These findings provide valuable insights for the control of inorganic CPM in flue gas systems.