Phase Transition Process Research Articles

<i>In vitro</i> synthesis and microscopic structural change of fetuin-A/calcium phosphate composite nanoparticles during phase transition process

<i>In vitro</i> synthesis and microscopic structural change of fetuin-A/calcium phosphate composite nanoparticles during phase transition process

Experimental and first-principles novel insights of atomic collapsed structure and composition-driven ω-precipitates

A complex ω phase transition is often observed in titanium alloys; nevertheless, the underlying knowledge of ω-embrittlement are not yet fully understood and require deeper insight. In this study, the ωT and ωH phases, as well as their interfacial structures, have been systematically investigated to examine compositional partitioning and to estimate Z values. A combination of aberration-corrected HAADF-S/TEM advanced characterization techniques, together with first-principles density functional theory calculations were performed under various heat treatment conditions. The results revealed that the low-temperature ageing process suppresses ω-assisted secondary α precipitations at ωT/β interfaces, whereas high-temperature ageing process promotes ω-assisted secondary α precipitations at ωH/β interface, due to relatively higher concentrations of Mo and Al contents. The interfacial energies (γ{ωβ}) between β and ω phases increase with decreasing local compositions of Mo and Al, suggesting increased stability of the ω phase and decreased stability of the β phase. Furthermore, the formation energies of β and ω phases were computed with Mo content at different Al composition, results indicate that the ω phase transition process is affected by the reduced Al content. The observations of this work provide deeper understanding of the ω phase transition mechanism in titanium alloys.

Heat transfer analysis and melting behavior of nano composite phase change materials (NCPCMs) in a reverse flow solar air heater

This paper presents a CFD investigation on heat transfer analysis and melting behavior of Nanocomposite Phase Change Materials (NCPCMs) in a Reverse Flow Solar Air Heater (RFSAH). Semicircular tubes filled with PCM are embedded on the top surface of the absorber plate. The study was conducted with three different nanoparticles (CuO, Al2O3, Fe3O4) based NCPCMs at three concentrations of 0.1, 0.2, and 0.3 % by weight. The constant geometrical parameters such as pitch ratio (P/e = 6), height ratio (e/Dh=0.1571), and Reynolds number (Re = 5000) is considered for this study. A 2-D transient numerical analysis using the RNG k-ε turbulence model is performed for the melting behavior of NCPCMs inside the semicylindrical tubes. The incorporation of nanoparticles into the base PCM enhances thermal conductivity but reduces the latent heat of NCPCMs. Thus, it is observed that NCPCMs have a faster melting rate. The CuO based NCPCM shows a more quick and uniform phase transition compared to the Fe3O4, and Al2O3 based NCPCMs and reached their peak value at a higher mass fraction of 0.3. Furthermore, the heat transfer and melting fraction improves with increasing in mass fraction of nanoparticles. The phase transition process of CuO based NCPCM is approximately 1.9 times, and 1.01 times, 1.03 times faster as compared to the base PCM, and Fe3O4, Al2O3 based NCPCMs respectively.

The influence of the design features of the fuel injector atomizer on the process of diesel fuel injection

Abstract. Problem. Increasing the demands for the technical and economic characteristics and the resource of modern augmented diesel engines requires finding ways and approaches to improve their design and systems, in particular, their fuel supply system. Changing the design parameters of the fuel injector atomizer allows to influence the conditions of fuel injection, its atomization in the combustion chamber, and the efficiency of the engine. The number and mutual arrangement of the nozzle holes of the fuel injector atomizer and their diameter are chosen by manufacturers based on the design features of the engine, in particular, the configuration of the combustion chamber and the conditions for filling the cylinder with fresh air. Goal. The purpose of the work was to carry out comparative numerical modelling to assess the influence of the number and diameter of the nozzle holes of the fuel injector atomizer on the diesel fuel injection process. Methodology. The problem is considered in a three-dimensional non-stationary setting. For numerical modelling, the geometry of the flow part of the fuel injector atomizer was formed, taking into account its design features (standard and modernized versions). The standard version has 7 nozzle holes with a diameter of 0.25 mm (evenly arranged relative to the axis of the atomizer, and the modernized version has 4 holes with a diameter of 0.3 mm in the standard place, evenly arranged relative to the axis of the atomizer and, additionally, 4 holes with a diameter of 0.2 mm from above (in the area of the closing cone) evenly arranged relative to the axis of the atomizer, but with a rotation around the axis of the atomizer by 45 degrees relative to the lower holes. To describe the process of the diesel fuel flow in the flow part of the fuel injector atomizer, the k - ε turbulence model is used, and to describe the process of phase transition from a liquid state to a vapour state – a mixture model is used. Results. The obtained results showed that the use of two rows of nozzle holes of different diameters for the atomizer of the fuel injector of the transport diesel engine allows to effectively organize the fuel injection process. For the atomizer nozzle of the modernized design, the volumetric fuel consumption is 30% for the upper holes and 70% for the lower ones. Originality. The scientific novelty of the work lies in determining the influence of the number and diameter of the nozzle holes of the fuel injector nozzle on the conditions of diesel fuel injection, taking into account cavitation effects. Practical value. The total area of the nozzle holes in the modernized version was increased by 20%, which makes it possible to increase the cycle supply of diesel fuel. It is especially important when using new types of fuel with a lower paraffin content and, accordingly, lower caloric content

Giant electro-optic response in transparent rhombohedral ferroelectric Sm-PIN-PMN-PT crystal based on domain engineering

The relaxor ferroelectric crystal Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT), located near the morphotropic phase boundary (MPB), exhibits exceptionally high piezoelectric and electro-optic (EO) responses. Nevertheless, lower optical transparency and phase transition temperature of PMN-PT limit its optical applications. The ternary system Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) holds promise in addressing these challenges with a higher Curie temperature. Additionally, specific ferroelectric domain polarization techniques can eliminate domain scattering, substantially enhancing the transparency of the crystal. In this study, we explore the optical properties of Sm-doped PIN-PMN-PT. We achieve a 2R domain-engineered state by polarizing along the (110) direction of the crystal. The high transparency allows us to extract an effective EO coefficient of up to 431.5 pm/V from the Sm-PIN-PMN-PT crystal at the telecommunications wavelength. Second-harmonic generation (SHG) probing verified the domain-engineered state in Sm-PIN-PMN-PT. The temperature-dependent SHG reveals the ferroelectric phase transition process, laying the groundwork for studying the stability of the EO response. The Sm-PIN-PMN-PT crystal exhibits an exceptionally high EO coefficient, which is crucial for the development of enhanced EO devices with high integration and low driving voltages.

Passive domestic air-conditioning using PCM modules

Passive cooling systems have garnered much attention in recent years as a sustainable and cost-effective method of regulating indoor temperatures. Phase change materials (PCM) are a promising technology for such systems, as they can store and release large amounts of thermal energy during the phase transition process while maintaining the temperature in a very specific range. In this study, we investigated the performance of a passive cooling system using PCM modules and evaluated the effect of different variables on its cooling efficiency. Several tests were conducted, varying the ambient temperature, number of plates, and PCM type to determine the optimal conditions for the system. A PCM with a melting temperature of around 22 °C was used and was compared to ice. While ice showed a larger cooling effect, the advantage of the PCM emerged with elevated ambient temperatures. Compared to ice, and due to the smaller the temperature difference ΔT between the PCM melting temperature and the ambient temperature, the cooling effect of the PCM, lasted for a significantly longer time. Moreover, increasing the number of plates proved to elongate the cooling effect, due to increasing the overall thermal storage capacity of the system. Overall, our findings suggest that a passive cooling system using PCM technology can be an effective solution for regulating indoor temperatures. However, careful consideration must be given to the choice of PCM type and melting temperature, as well as the number of plates in the system, to optimize its performance.

Liquid crystal droplets formation and stabilization during phase transition process

Abstract The study of phase transition processes in liquid crystals (LCs) remains challenging. Most thermotropic LCs exhibit a narrow temperature range and a rapid phase transition from the isotropic (ISO) to the nematic (N) phase, which make it difficult to capture and manipulate the phase transition process. In this study, we observed the evolution of small droplets during the ISO–N phase transition in ferroelectric nematic (NF) LC RM734. After doping with metal nanoparticles (NPs), the temperature range of the phase transition broadened, and the droplets formed during the phase transition remained stable, with their diameter increasing linearly with temperature. In addition, droplets doped with NPs can be well controlled by an external electric field. This discovery not only aids in understanding the fundamental mechanisms of LC phase transitions but also provides a simple alternative method for preparing droplets, which is potentially valuable for applications in optoelectronic devices and sensors.

Controllable phase transition process of polycrystalline diamond surface for low friction via suppressing oxygen involved tribochemical reactions

The diamond inner wall of drawing die is crucial for the precise formation of ultra-fine wires during the drawing process. Unexpectedly, when drawing soft metal wire, a significant wear occurs on hard-phase diamond surface, resulting in increased friction at the drawing interface, which leads to the wire cross-section distortion, uneven wire diameter, surface scratches and burrs. In this study, the interface interaction and friction products between diamond and iron were investigated, focusing on the primary factors influencing diamond phase transitions by adjusting friction atmosphere. Whether in air or nitrogen, the friction coefficient (CoF) decreases with the increase of load, but CoF value is relatively lower in nitrogen environment. The friction curve of diamond against iron stabilized after an initial downward trend, reaching a minimum CoF of 0.08 in nitrogen under a load of 15 N. The friction mechanism is explained through material transfer, friction products, phase transition, tribolayer formation, and interfaces interactions. It is speculated that in nitrogen, even if a small amount of oxide forms on iron surface, iron remains in contact with diamond, generating a large amount of iron carbide and inducing the graphitization of diamond, which would act as a lubricating role. In contrast, in air, oxygen atoms continuously interact with iron, forming a dense oxide film at the friction interface, which prevents carbon from continuous contacting iron atoms and limits the formation of iron carbide. Overall, the discovery provides new insights into the interaction between metals and diamonds, and offers theoretical guidance for the drawing of iron wires.

Non-limited vibrational effect on shock-induced phase transitions of condensed fluid in hard-sphere model

The essence of fluid phase transition is the jump of physical properties distinctly induced by shock waves in the hard-sphere model. Due to the strong impact of the wave, the internal freedoms of molecules are stimulated, releasing tremendous energy that commonly triggers the phase transition. Conversely, typical thermal and dynamic jumps can be described by the Rankine–Hugoniot conditions based on the Euler equation. In the theoretical simulation, the initial density and rotational freedoms of molecules are directly regarded as the primary factors to affect processes of phase transition. However, the influence of vibrational freedom in molecules has not been discussed yet. As the increasing temperature can gradually excite the affection of vibrational freedom, it is unwise to assume that the temperature element is constant in the theory. What would be a suitable model that accurately reflects the relationship between temperature and affection from vibrational freedom? The non-limited model has been courageously attempted with the temperature range from T0 to 6T0 (T0 is unperturbed temperature). We have found that the vibrational freedom can have a great effect on properties during phase transition processes.

Light/electro-thermal conversion of carbonized sweet potato 3D grid-supported PEG shape-stable phase change materials for thermal management applications

Phase change materials (PCMs) are functional energy-storage materials that achieve reversible heat storage and release through phase transition processes. They have extensive applications in the thermal management and solar energy industries. However, their low electrical and thermal conductivities and poor stability often fail to meet application requirements. In this study, we utilised an abundant biomass-derived carbon source, sweet potatoes, to prepare a three-dimensional network of carbon aerogels. By simply vacuum-impregnating polyethylene glycol (PEG), the PCM was embedded in the carbon aerogel. The obtained PEG/carbon aerogel composite material exhibited high enthalpy (158.1 J/g) and good thermal and shape stability. They also demonstrated efficient photothermal (88.47 %) and electrothermal conversion (94.02 %). This research has significant potential for applications in solar energy storage and utilisation, building energy storage, space–ground thermal energy storage, and electronic device thermal management. This study provides a novel approach for the preparation and photothermal applications of bio-based PCMs.

Topological equivalence and phase transition rate in holographic thermodynamics of regularized Maxwell theory

Utilizing the holographic dictionary from the proposal that treats Newton’s constant as a thermodynamic variable, we establish a thermodynamic topological equivalence between the AdS black holes in the bulk and the thermal states in the dual CFT. The findings further reveal that the thermodynamic topological characteristics of the RegMax AdS black holes are strongly influenced by the characteristic parameter of the regularized Maxwell theory. Additionally, we investigate the phase transition between low and high entropy thermal states within a canonical ensemble in the dual CFT. Our observations indicate that the phase transition behavior of the thermal states mirrors that of the black holes. By modeling the phase transition process as a stochastic process, we are able to calculate the rates of phase transition between the thermal states. This result enhances our understanding of the dominant processes involved in the phase transition of the thermal states in the dual CFT.

Unveiling Intercalation Chemistry via Interference-Free Characterization Toward Advanced Aqueous Zinc/Vanadium Pentoxide Batteries.

Aqueous Zn/V2O5 batteries are featured for high safety, low cost, and environmental compatibility. However, complex electrode components in real batteries impede the fundamental understanding of phase transition processes and intercalation chemistry. Here, model batteries based on V2O5 film electrodes which show similar electrochemical behaviors as the real ones are built. Advanced surface science characterizations of the film electrodes allow to identify intercalation trajectories of Zn2+, H2O, and H+ during V2O5 phase transition processes. Protons serve as the vanguard of intercalated species, facilitating the subsequent intercalation of Zn2+ and H2O. The increase of capacity in the activation process is mainly due to the transition from V2O5 to more active V2O5·nH2O structure caused by the partial irreversible deintercalation of H2O rather than the increase of active sites induced by the grain refinement of electrode materials. Eventually, accumulation of Zn species within the oxide electrode results in the formation of inactive (Zn3(OH)2V2O7·2H2O) structure. The established intercalation chemistry helps to design high-performance electrode materials.

Microstructural characterization of Stellite 6 alloy processed by electron beam melting

Stellite 6 alloy was subjected to electron beam melting (EBM) processing in this study. The main phases in the alloy are α-Co, ε-Co, M23C6 (M = Cr, Co, W, etc.), and M7C3 (M = Cr, Co, W, etc.) carbides. The microstructure of the EBM-processed Stellite 6 alloy comprises grains of relatively uniform sizes, with an average grain size of 11.1 μm. There is a relatively minor internal strain within the alloy. The majority of grains exhibit low intragranular misorientations, approximately around 0.5°, while a minority of grains display relatively larger intragranular misorientations, around 2.8°. The dominant {100} texture was developed in the build direction because of the fast growth of the <100> direction for a cubic crystal structure during solidification. The vertically aligned columnar grains contribute to the development of the <100> texture along the build direction. The elongated direction of columnar grains was parallel to the temperature gradient direction. This competitive growth direction at the solid-liquid interface results in slight tilts in the pole figures. The eutectic carbide phases are uniformly distributed along the grain boundaries. The cube–cube orientation relationships between the matrix and M23C6 carbide phase were identified as [001]α//[111]M23C6. The low stacking fault energy of the Stellite 6 alloy resulted in the formation of a high density of stacking faults within the grains. The interactions between stacking faults of different orientations were observed. Primary M7C3 carbides were found to transform into secondary M23C6 carbides, with a phase transition process observed where secondary carbides M23C6 surrounded primary carbides M7C3.

Multi-hole liquid CO2 flashing jet: A novel method for achieving trade-off between impact region and impact force through phase transition

A novel multi-hole liquid CO2 flashing jet for coalbed methane exploitation is proposed, which undergoes phase transition during the injection of superheated CO2. The thermal stress generated during the phase-transition process is beneficial for rock fragmentation. Different types of nozzles were compared, and a conical convergent nozzle was selected owing to its wider jets. The proposed jet interaction criteria based on the fuel were examined using CO2, and discrepancies due to the internal phase transition and stronger cooling effects were observed. Nozzles with larger drilling angles were found to be more prone to transition from cone-shaped to jet-shaped morphologies. Coal-breaking experiments were also performed, and three distinct coal-breaking patterns induced by multi-hole flashing CO2 jets were identified. The effects of thermal stress on rock-breaking were evaluated using a beam-scanning electron microscope and wave velocity measurement with a piezoelectric accelerometer. Thermal cracks induced by matrix contraction were identified, indicating the potential to enhance breakage efficiency. The results indicate that the trade-off between the impact region and impact force should be carefully adjusted to achieve the desired coal-breaking performance. This study provides a potential method to utilize CO2, as well as some guidance for the issues that must be addressed in energy exploration using CO2.

Data-driven clustering learning modeling for semiconductor silicon single crystal growth process based on fuzzy C-means and DBN

The optimal operation of the semiconductor silicon single crystal (SSC) growth in an industrial single crystal furnace is contingent upon the precise measurement of both the crystal diameter and melt temperature. The Czochralski (CZ) silicon single crystal growth process (CZ-SSCGP) is a phase transition process from solid to liquid that takes place in a high-temperature, enclosed furnace designed for single crystal growth. The direct measurement of crystal diameter and melt temperature using sensors can pose a challenge due to the physical limitations of the furnace. This study introduces a novel approach for modeling clustering based on data that integrate fuzzy C-means (FCM) and deep belief network (DBN) techniques. The proposed method aims to estimate the online crystal diameter and melt temperature. The objective of this approach is to efficiently and precisely derive the CZ-SSCGP model. In order to address the negative impact of nonequilibrium properties of data on the model, it is advisable to employ FCM to produce numerous subsets of data that exhibit comparable operating conditions. This is especially important because data change over time and are different in different working situations. In order to enhance the precision of the fitting process for crystal diameter and melt temperature, we amalgamate the output outcomes of DBN that have been constructed for each individual subset. It is imperative to address the nonlinear and time-varying features manifested by the engineering data. Industrial data are utilized for conducting diverse data experiments and comparative analyses. The process takes into account the data’s susceptibility to contamination by outliers. The findings suggest that the method put forth exhibits superior precision and enhanced resilience in predicting crystal diameter and melt temperature compared to alternative modeling approaches.

Synergistic Effect of Laser, Water Vapor, and Electron-Beam on the Degradation of Quasi-Two-Dimensional Ruddlesden-Popper Perovskite Flakes.

Understanding the effects of laser light, water vapor, and energetic electron irradiation on the intrinsic properties of perovskites is important in the development of perovskite-based solar cells. Various phase transition and degradation processes have been reported when these agents interact with perovskites separately. However, detailed studies of their synergistic effects are still missing. In this work, the synergistic effect of three factors (exposure to laser light, water vapor, and e-beam) on the optical and physical properties of two-dimensional (2D) Ruddlesden-Popper (RP) perovskite flakes [(BA)2(MA)2Pb3Br10] has been investigated in an environmental cell. When the perovskite flakes were subjected to moderate laser irradiation in a humid environment after prior e-beam irradiation, the photoluminescence (PL) peak centered at 480 nm vanished, while a new PL peak centered at 525 nm emerged, grew, and then quenched. This indicates the degradation process of the 2D RP perovskite was a phase transition to a three-dimensional (3D) perovskite [MAPbBr3] followed by the degradation of 3D perovskite. The spatial distribution of the 525 nm PL signal shows that this phase-transition process spreads across the flake to the area as far as ∼40 μm from the laser spot. Without humidity, the phase transition happened in the laser-irritated area but did not spread, which suggests that moisture enhanced the ion migration from the laser-scanned area to the rest of the flake and accelerated the phase transition in the nearby area. Experiments with no prior e-beam irradiation show that e-beam irradiation is the key to activating the 2D-3D phase transition. Therefore, when the three factors work synergistically, a conversion from the 2D RP perovskite into the 3D perovskite is not localized and propagates through the perovskite. These findings contribute to our understanding of the complex interactions between external stimuli and perovskite materials, thereby advancing the development of efficient and stable perovskite-based solar cells.

Three-dimensional solidification modeling of various materials using the lattice Boltzmann method with an explicit enthalpy equation.

Based on the mesoscopic scale, the lattice Boltzmann method (LBM) with an enthalpy-based model represented in the form of distribution functions is widely used in the liquid-solid phase transition process of energy storage materials due to its direct and relatively accurate characterization of the presence of latent heat of solidification. However, since the enthalpy distribution function itself contains the physical properties of the material, these properties are transferred along with the enthalpy distribution function during the streaming process. This leads to deviations between the enthalpy-based model when simulating the phase transition process of different materials mixed and the actual process. To address this issue, in this paper, we construct an enthalpy-based model for different types of materials. For multiple materials, various forms of enthalpy distribution functions are employed. This method still uses the form of enthalpy distribution functions for collisions and streaming processes among the same type of substance, while for heat transfer between different materials, it avoids the direct transfer of enthalpy distribution functions and instead applies a source term to the enthalpy distribution functions, characterizing the heat transfer between different materials through the energy change before and after mixing based on the temperature. To verify the accuracy of the method proposed in this paper, a detailed solidification model for two different materials is constructed using the example of water droplets solidifying in air, and the results are compared with experimental outcomes. The results of the simulation show that the model constructed in this paper is largely in line with the actual process.

Shocks in the warm neutral medium

Context. Atomic and molecular line emissions from shocks may provide valuable information on the injection of mechanical energy into the interstellar medium (ISM), the generation of turbulence, and the processes of phase transition between the warm neutral medium (WNM) and the cold neutral medium (CNM). Aims. In this series of papers, we investigate the properties of shocks propagating in the WNM. Our objective is to identify the tracers of these shocks, use them to interpret ancillary observations of the local diffuse matter, and provide predictions for future observations. Methods. Shocks propagating in the WNM are studied using the Paris-Durham shock code, a multi-fluid model built to follow the thermodynamical and chemical structures of shock waves at steady-state in a plane-parallel geometry. The code, designed to take into account the impact of an external radiation field, is updated to treat self-irradiated shocks at intermediate (30 &lt; VS &lt; 100 km s−1) and high velocity (VS ⩾ 100 km s−1), which emit ultraviolet (UV), extreme-ultraviolet (EUV), and X-ray photons. The couplings between the photons generated by the shock, the radiative precursor, and the shock structure are computed self-consistently using an exact radiative-transfer algorithm for line emission. The resulting code is explored over a wide range of parameters (0.1 ⩽ nH ⩽ 2 cm−3, 10 ⩽ VS ⩽ 500 km s−1, and 0.1 ⩽ B ⩽ 10 μG), which covers the typical conditions of the WNM in the solar neighborhood. Results. The explored physical conditions lead to the existence of a diversity of stationary magnetohydrodynamic solutions, including J-type, CJ-type, and C-type shocks. These shocks are found to naturally induce phase transition between the WNM and the CNM, provided that the postshock thermal pressure is higher than the maximum pressure of the WNM and that the maximum density allowed by magnetic compression is greater than the minimum density of the CNM. The input flux of mechanical energy is primarily reprocessed into line emissions from the X-ray to the submillimeter domain. Intermediate- and high-velocity shocks are found to generate a UV radiation field that scales as VS3 for VS &lt; 100 km s−1 and as VS2 at higher velocities, and an X-ray radiation field that scales as VS3 for VS ⩾ 100 km s−1. Both radiation fields may extend over large distances in the preshock depending on the density of the surrounding medium and the hardness of the X-ray field, which is solely driven by the shock velocity. Conclusions. This first paper presents the thermochemical trajectories of shocks in the WNM and their associated spectra. It corresponds to a new milestone in the development of the Paris-Durham shock code and a stepping stone for the analysis of observations that will be carried out in forthcoming works.

The Relation between Soil Moisture Phase Transitions and Soil Pore Structure under Freeze–Thaw Cycling

The process of soil moisture phase transitions (SMPT) under freeze–thaw cycling is considered a key factor driving changes in soil pore structure. However, there is still no consensus on which indicators related to SMPT affect the soil pore structure. The objectives of this study were to compare SMPT and soil pore characteristics under freeze–thaw cycling, and to analyze the inherent relationship between them as affected by different bulk densities. Hence, we employed thermal pulse time-domain reflection technology (T-TDR) and X-ray CT scanning technology (X-CT) to quantitatively study the process of SMPT and pore characteristics of soil core samples (60 mm diameter, 100 mm height) repacked with three different bulk density levels: 1.10 g·cm−3 (NC), 1.30 g·cm−3 (LC) and their combination (1.10 g·cm−3 for upper half, 1.30 g·cm−3 for lower half, SC) under freeze–thaw cycling. Our results showed that compared with NC, the porosity of LC’s 0–5 cm soil column decreased by 0.070 cm3·cm−3, the imaged porosity (ϕ&gt;60μm) decreased by 0.034 cm3·cm−3, and the maximum soil ice content (MIC) decreased by 0.030 cm3·cm−3. The pores within the range of 200−300 mm (ϕ2) and 300–400 mm (ϕ3) contribute the most significantly to ϕ&gt;60μm (50–60%). Soil initial moisture content (IMC) and MIC explained 50.1% of the change in ϕ2, and the bulk density explained 49.3% of the change in ϕ3. During the melting process, higher moisture content promotes the thaw collapse of soil particles, resulting in a decrease in ϕ&gt;60μm. The mean pore radius of the limiting layer (MRLL) and the hydraulic radius (HR) show that changes in bulk density from 1.10 g·cm−3 to 1.30 g·cm−3 do not have significant differences. Our results show the relationship between SMPT and pore structure change during freeze–thaw cycles as affected by initial soil bulk density and moisture condition.

Phase transition of Fe-containing phase in naturally cooled and water-quenched copper slags during high-temperature treatment

Iron (Fe) accounts for the highest-content of valuable metal recoverable from copper slag, which is most effectively recycled using pyrometallurgical high-temperature treatment. It is believed that the roasting temperature significantly affects the physical structure of copper slag. Therefore, this paper used thermogravimetry-differential scanning calorimetry (TG-DTG-DSC), X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), vibrating sample magnetometry (VSM), and scanning electron microscopy (SEM) to examine the Fe phase transformation in water-quenched copper slag (WQCS) and naturally cooled copper slag (NCCS) after high-temperature treatment (700–1100 °C). The main Fe-containing phases in the WQCS were represented by fayalite (Fe2SiO4) and magnetite (Fe3O4). As the temperature increased, the Fe2SiO4 underwent oxidative decomposition and re-formation, with a phase transition law of Fe2SiO4→Fe2O3+Fe3O4→FeSiO3+Fe2SiO4, while that of the Fe3O4 was Fe3O4→Fe2O3→Fe3O4. The phase transition processes were more complex in the NCCS, where the main Fe-containing phases were Fe2SiO4, Fe3O4 and chalcopyrite (CuFeS2). The oxidative decomposition temperatures of the Fe2SiO4 ranged from 700 °C to 850 °C. As the temperature increased, the phase transition law of Fe3O4 was Fe3O4→Fe2O3→Fe3O4→Fe2O3. Lastly, at 700 °C, the CuFeS2 began to oxidize and decompose, with a phase transition law of CuFeS2→FeS + Fe2O3→Fe3O4.