Supersaturation Of Solution Research Articles

Mechanisms of eutectic lamellar destabilization upon rapid solidification of an undercooled Ag-39.9 at.% Cu eutectic alloy

The eutectic Ag-Cu alloys exhibiting fine Ag-Cu lamellar eutectic structure formed upon rapid solidification have great potentials being used in various engineering fields. However, the desired fine primary lamellar eutectic structure (PLES) is usually replaced by a coarse anomalous eutectic structure (AES) when the undercooling prior to solidification exceeds a certain value. The forming mechanism of AES in the undercooled eutectic Ag-Cu alloy has been a controversial issue. In this work, the undercooled Ag-39.9 at.% Cu eutectic alloy is solidified under different cooling conditions by using techniques of melt fluxing and copper mold casting. The results show that the coupled eutectic growth of this alloy undergoes a transition from a slow eutectic-cellular growth (ECG) to a rapid eutectic-dendritic growth (EDG) above a undercooling of 72 K, accompanying with an abrupt change of the distribution and amount of AES in as-solidified microstructures. Two kinds of primary lamellar eutectic structures are formed by ECG and EDG during recalescence, respectively. The destabilization of PLES that causes the formation of AES is ascribed to two different mechanisms based on the microstructural examination and theoretical calculations. Below 72 K, the destabilization of PLES formed by slow ECG is caused by the mechanism of “termination migration” driven by interfacial energy. While above 72 K, the destabilization of PLES formed by rapid EDG is attributed to the unstable perturbation of interface driven by interfacial energy and solute supersaturation.

Impact of Surfactants on Polymer Maintained Nifedipine Supersaturation in Aqueous Solution.

To study the impact of different surfactants on the supersaturation of nifedipine stabilized with HPMC and PVP-VA. Different kinds of surfactants, including one cationic surfactant, two anionic surfactants, and three nonionic surfactants, were used to evaluate their impacts on the supersaturation of nifedipine stabilized with HPMC and PVP-VA. Polymer-surfactant interaction was studied by nuclear magnetic resonance (NMR) and fluorescent method. Solubility of nifedipine in solutions containing different amounts of polymers and surfactants was measured. Drug-polymer affinity was evaluated by measuring the percentage of polymer coprecipitated together with the drug from supersaturated solutions. Different polymer-surfactant combinations had different impacts on the supersaturation of nifedipine. Some combinations, such as PVP-VA/SLS and PVP-VA/NaTC under higher surfactant concentrations, showed improved drug supersaturation, due to increased drug solubility or polymer-surfactant synergy; while other combinations, such as HPMC/SLS and HPMC/Tween 20 under lower surfactant concentrations, showed reduced drug supersaturation, which could result from competitive surfactant-polymer or drug-surfactant interaction that disrupted pre-existent drug-polymer interaction. The ultimate impacts of various surfactants on polymer stabilized nifedipine supersaturation could be attributed to the interplay between different factors, including solubility enhancement of the drug, drug-polymer-surfactant interactions, and polymer-surfactant synergy.

Thermal stability and mechanical properties of Ti–22Al–25Nb alloy with different initial microstructures

Abstract In order to better understand the thermal stability and mechanical properties of the nominal Ti–22Al–25Nb alloy with different initial microstructures, microstructural evolution after long-term aging, and mechanical properties at room temperature and 650 °C of four differently heat-treated Ti–22Al–25Nb alloy were investigated. The investigation results indicated that α2 platelets formed by aging at (α2+B2) region were not as stable as previous research claimed and spontaneously decomposed into fine (O+β/B2) mixture during the annealing at 650 °C. As a result, the alloy's steady-state creep strain rate dropped dramatically at the secondary creep stage and tensile strength grew. On the contrary, long time aging exposure resulted in the connection of original dispersed lenticular O precipitation and thus degraded the ductility of all specimens. Besides, the discontinuous precipitation B2→β+O caused by supersaturation of solutes in the matrix also harmed the mechanical properties. Under the condition of 650 °C/250 MPa, the steady-state creep strain rates of the Ti–22Al–25Nb specimens show a significant dependence on their grain size. Crept samples showed that most dislocation motion was restrained in the β channels under a small strain and then extended into O phase when creep strain grew over 10%. Finally, by comparing the room temperature tensile property and creep resistance of four samples, supertransus solution and furnace cooling ensured the alloy most balanced mechanical properties among lamellar samples. The supertransus then furnace-cooled sample did not only have an excellent creep resistance but also kept a moderate room temperature elongation to failure of nearly 6%.

A readily monitored and controllable hydrothermal system for the facile, cost-effective transformation of FGD gypsum to calcium sulfate hemihydrate whiskers

The controllable transformation of flue gas desulfurization (FGD) gypsum to calcium sulfate hemihydrate (HH) whiskers under facile, readily monitored, and cost-effective hydrothermal conditions could play a vital role in the preparation of high quality HH whiskers and improve our understanding of the transformation process. This work assessed the conversion of FGD gypsum to HH whiskers in 5×10–4 mol/L H2SO4 and 1.5 wt% CuCl2 at 120 °C while determining the effects of temperature as well as H2SO4 and CuCl2 concentrations on transformation kinetics. The preparation of HH whiskers was found to involve a solution-mediated transformation from the dihydrate (DH) to the α-HH. This transition was determined to proceed via a dissolution crystallization mechanism, the rate of which was controlled by nucleation and growth of the HH whiskers. An autocatalytic kinetic model was established based on variations in the HH whiskers mole fraction over time, and this model accurately fit the experimental data with R2 = 0.990. Increasing the temperature or H2SO4 concentration accelerated the transformation by modifying the super-saturation and water activity in the reaction solution, while increasing the CuCl2 concentration had the opposite effect. The hydrothermal conditions had an important effect on the transformation from FGD gypsum to HH whiskers.

The fabrication and characteristics of hydroxyapatite film grown on titanium alloy Ti-6Al-4V by anodic treatment

To improve the growth of hydroxyapatite (HA) coating on the Ti-6Al-4V substrate, a solution containing calcium acetate (CA), calcium glycerophosphate hydrate (Ca-GP), and different concentrations of Na2SO4 as the electrolyte for anodic treatment was investigated in this study. The results found that the anodic method is suitable for Ti-6Al-4V titanium alloy to form an HA coating with the electrolyte consisting of CA, Ca-GP, and Na2SO4. These anodic oxide films display a greater rough structure on the surface of films and the addition of Na2SO4 into the electrolyte during the anodic oxidation process contributes to an increase in the atomic ratio (at%) of Ca in the anodic film. These Ca-containing films are considered bioactive and tend to dissolve into simulated body fluid (SBF) solution and then enhance the degree of the supersaturation of SBF solution with respect to the apatite. Therefore, increasing the concentration of Na2SO4 increases the growth of HA following immersion into SBF. In addition, prior to immersion into SBF solution, the contact angle measurement using an SBF droplet was also investigated for HA growth. The results indicate that when the contact angle of anodic surface is larger, the formation time of HA coating is shorter and it will easily grow a thicker HA.

Combination of MRI and SEM to Assess Changes in the Chemical Properties and Permeability of Porous Media due to Barite Precipitation

The understanding of the dissolution and precipitation of minerals and its impact on the transport of fluids in porous media is essential for various subsurface applications, including shale gas production using hydraulic fracturing (“fracking”), CO2 sequestration, or geothermal energy extraction. In this work, we conducted a flow through column experiment to investigate the effect of barite precipitation following the dissolution of celestine and consequential permeability changes. These processes were assessed by a combination of 3D non-invasive magnetic resonance imaging, scanning electron microscopy, and conventional permeability measurements. The formation of barite overgrowths on the surface of celestine manifested in a reduced transverse relaxation time due to its higher magnetic susceptibility compared to the original celestine. Two empirical nuclear magnetic resonance (NMR) porosity–permeability relations could successfully predict the observed changes in permeability by the change in the transverse relaxation times and porosity. Based on the observation that the advancement of the reaction front follows the square root of time, and micro-continuum reactive transport modelling of the solid/fluid interface, it can be inferred that the mineral overgrowth is porous and allows the diffusion of solutes, thus affecting the mineral reactivity in the system. Our current investigation indicates that the porosity of the newly formed precipitate and consequently its diffusion properties depend on the supersaturation in solution that prevails during precipitation.

Overcoming salt crystallization with ionic hydrogel for accelerating solar evaporation

A new hydrogel-based solar evaporator was prepared by a convenient one-step cross-linking method. Sodium alginate and PEDOT:PSS composite hydrogels were used as the functional layer to realize photothermal conversion and in situ heating for the generation of the solar steam. The evaporation rate of the evaporator was as high as 1.23 kg/m2h, and the removal rate of various ions in simulated seawater was higher than 99.8%, showing excellent application stability. It was also found that the salt crystallization phenomenon could be effectively overcome in the process of solar desalination. Based on the swelling ability and super hydrophilic three dimensional pores of the ionic hydrogel, the evaporator exhibited stable self-driven water-drawing ability to form a hydration layer in an effort to suppress the supersaturation of the salt solution at the evaporation interface. PEDOT component realized in situ heating of the hydration layer near the evaporation interface for enhancing the utilization of thermal energy. The purpose of this paper is to provide references for the practical desalination application using a new hydrogel-based solar evaporator.

A novel architecture for achieving high drug loading in amorphous spray dried dispersion tablets

Although Amorphous Solid Dispersions (ASDs) effectively increase bioavailability, tablet mass can be high due to the large fraction of excipients needed to stabilize the amorphous drug in the solid state, extend drug supersaturation in solution and achieve robust manufacturability. The aim of this work was to reduce tablet mass of an ASD tablet comprising a low glass transition temperature (Tg), rapidly crystallizing drug without compromising these key attributes.In this approach, erlotinib (Tg = 42 °C, Tm/Tg = 1.4 K/K) was spray dried with the high Tg polymer poly(methyl methacrylate-co-methacrylic acid) (Eudragit® L100, Evonik) (Tg = 187 °C) to facilitate high drug loading while maintaining physical stability. Hydroxypropyl methylcellulose acetate succinate (HPMCAS) (AQOAT® HF, Shin-Etsu) was granulated with the ASD to extend supersaturation in solution. For comparison, a benchmark ASD was spray dried at a lower drug loading with HPMCAS-H (Tg = 119 °C).This High Loaded Dosage Form (HLDF) approach reduced tablet mass by 40%, demonstrated similar physical stability and in vitro performance as the benchmark and exhibited excellent downstream manufacturability. Strategically combining two different polymers in a tablet to maintain physical stability and sustain supersaturation in solution can decrease tablet mass of some low Tg, rapidly crystallizing amorphous drugs.

Development of Precipitation Hardening Parameters for High Strength Alloy AA 7068.

The mechanical properties after age hardening heat treatment and the kinetics of related phase transformations of high strength AlZnMgCu alloy AA 7068 were investigated. The experimental work includes differential scanning calorimetry (DSC), differential fast scanning calorimetry (DFSC), sophisticated differential dilatometry (DIL), scanning electron microscopy (SEM), as well as hardness and tensile tests. For the kinetic analysis of quench induced precipitation by dilatometry new metrological methods and evaluation procedures were established. Using DSC, dissolution behaviour during heating to solution annealing temperature was investigated. These experiments allowed for identification of the appropriate temperature and duration for the solution heat treatment. Continuous cooling experiments in DSC, DFSC, and DIL determined the kinetics of quench induced precipitation. DSC and DIL revealed several overlapping precipitation reactions. The critical cooling rate for a complete supersaturation of the solid solution has been identified to be 600 to 800 K/s. At slightly subcritical cooling rates quench induced precipitation results in a direct hardening effect resulting in a technological critical cooling rate of about 100 K/s, i.e., the hardness after ageing reaches a saturation level for cooling rates faster than 100 K/s. Maximum yield strength of above 600 MPa and tensile strength of up to 650 MPa were attained.

Chemical Stability-Sensitive Osteoconductive Performance of Octacalcium Phosphate Bone Substitute in an Ovariectomized Rat Tibia Defect.

The purpose of this study was to investigate whether the chemical condition of osteoporotic serum affects the chemical stability of octacalcium phosphate (OCP) and its osteoconductive property. The in vitro chemical dissolution in osteoporotic ovariectomized (OVX)-simulated conditions was analyzed. OCP and its composite form with gelatin (OCP/Gel), containing specific amounts of OCP (either 17% or 44% by weight), were used as experimental materials. The degrees of supersaturation (DS) of the OVX-simulated buffer solutions, containing distinct inorganic phosphate (Pi) ion concentrations, after immersing OCP or OCP/Gel, were determined. The rod-shaped OCP/Gel was then implanted into the OVX and Sham rat tibia defects, exhibiting a similar shape and size, and assessed at 4, 8, and 12 weeks. Increasing Pi concentration in OVX-simulated buffer solution increased the DS, with respect to OCP, upon the introduction of OCP and 44% OCP/Gel, but decreased the DS to a slightly saturated condition with 17% OCP/Gel, indicating that increasing the OCP in the Gel matrix tends to inhibit the hydrolysis of OCP into hydroxyapatite (HA). Histomorphometric analyses of bone formation and the appearance of osteoblasts and osteoclast-like cells, together with OCP resorption, confirmed that while 44% OCP/Gel showed higher bone formation than 17% OCP/Gel at intramedullary bone defect sites in Sham rat tibia, both OCP/Gels tended to enhance cortical bone formation in the OVX group, concomitant with the higher resorption of OCP within 17% OCP/Gel. The appearance of osteoclast-like cells in the OVX group increased as the OCP dose decreased from 44% to 17% in the Gel matrix, with an approximately 4 times higher bone formation rate, 8-12 weeks after the implantation. Additional in vitro assays showed that bone marrow mesenchymal stem cells isolated from OVX and wild-type (WT) rats treated with OCP had similar proliferation and differentiation rates, up to 21 days. These results show that OCP can enhance cortical bone repair even in osteoporotic bone if suitable thermodynamic metastable dissolution conditions are provided in relation to the mass of OCP.

Time-Resolved Dynamics of Struvite Crystallization: Insights from the Macroscopic to Molecular Scale.

The crystallization of magnesium ammonium phosphate hexahydrate (struvite) often occurs under conditions of fluid flow, yet the dynamics of struvite growth under these relevant environments has not been previously reported. In this study, we use a microfluidic device to evaluate the anisotropic growth of struvite crystals at variable flow rates and solution supersaturation. We show that bulk crystallization under quiescent conditions yields irreproducible data owing to the propensity of struvite to adopt defects in its crystal lattice, as well as fluctuations in pH that markedly impact crystal growth rates. Studies in microfluidic channels allow for time-resolved analysis of seeded growth along all three principle crystallographic directions and under highly controlled environments. After having first identified flow rates that differentiate diffusion and reaction limited growth regimes, we operated solely in the latter regime to extract the kinetic rates of struvite growth along the [100], [010], and [001] directions. In situ atomic force microscopy was used to obtain molecular level details of surface growth mechanisms. Our findings reveal a classical pathway of crystallization by monomer addition with the expected transition from growth by screw dislocations at low supersaturation to that of two-dimensional layer generation and spreading at high supersaturation. Collectively, these studies present a platform for assessing struvite crystallization under flow conditions and demonstrate how this approach is superior to measurements under quiescent conditions.

Modeling remelting induced destabilization of lamellar eutectic structure in an undercooled Ni-18.7 at.% Sn eutectic alloy

Achieving a high melt undercooling (ΔT) is expected as an effective strategy to significantly reduce lamellar spacing of bulk eutectic alloys. However, the undercooled eutectic alloys usually exhibit coarse anomalous eutectic structure (AES) when ΔT exceeds a certain value. In our recent work (Scripta Materialia, 177 (2020) 123–127), we showed that in an undercooled Ni-18.7 at.% Sn eutectic alloy the remelting induced destabilization of primary lamellar eutectic structure (PLES) during the post-recalescence period can lead to the formation of the AES using high-temperature laser scanning confocal microscopy technique. In this work, an analytical model within the framework of interface stability analyses is established to quantitatively describe the destabilization of PLES during the post-recalescence period. The model calculations show good agreement with the experimental results. The analyses based on the derived model indicate that the destabilization of PLES is driven by solute supersaturation and capillary force. The former amplifies the interface perturbation of the eutectic lamellae and initiates the destabilization, while the latter dominates the subsequent morphological transition process. We further showed that our model is consistent with the reported experimental results of other undercooled eutectic alloys.

On the Effect of Secondary Nucleation on Deracemization through Temperature Cycles

Herein, the pivotal role of secondary nucleation in a crystallization-enhanced deracemization process is reported. During this process, complete and rapid deracemization of chiral conglomerate crystals of an isoindolinone is attained through fast microwave-assisted temperature cycling. A parametric study of the main factors that affect the occurrence of secondary nucleation in this process, namely agitation rate, suspension density, and solute supersaturation, confirms that an enhanced stereoselective secondary nucleation rate maximizes the deracemization rate. Analysis of the system during a single temperature cycle showed that, although stereoselective particle production during the crystallization stage leads to enantiomeric enrichment, undesired kinetic dissolution of smaller particles of the preferred enantiomer occurs during the dissolution step. Therefore, secondary nucleation is crucial for the enhancement of deracemization through temperature cycles and as such should be considered in further design and optimization of this process, as well as in other temperature cycling processes commonly applied in particle engineering.

Evolution of microstructure and properties of novel aluminum‑lithium alloy with different roll casting process parameters during twin-roll casting

Twin-roll casting (TRC) process combines continuous casting and rolling deformation into one process, which compensates for the solidification shrinkage of liquid metal in the roll-casting region and solves the defects caused by the addition of lithium in aluminum alloy, such as shrinkage porosity and shrinkage cavity in aluminum‑lithium alloy ingots produced by traditional casting technique. In this work, the evolution of microstructure and properties of AA2099 aluminum‑lithium alloy sheets fabricated with different cast-rolling speeds during TRC process was investigated in detail. The quantitative relationship between the degree of central macro-segregation and micro-segregation of the TRC slabs as well as secondary dendrite arm spacing (SDAS) and the number of non-equilibrium eutectic phase with different cast-rolling speeds was revealed. The cooling rate increases gradually with the increase of cast-rolling speeds, the dendrites will be refined and the degree of central macro-segregation relieves dramatically, and the number of non-equilibrium eutectic phases decreases significantly at relatively higher cooling rate during TRC. In addition, more alloying elements will be captured and dissolved in the α-Al matrix in a faster cooling rate, and the solid solution supersaturation of solute elements in alloys is significantly enhanced. Hence the mechanical properties of the sheets have been improved remarkably.

Influence of quench rate on multi-stage ageing of AA6014 alloy

The influence of quench rate after solution heat treatment on the microstructure in the as-quenched state and subsequent ageing kinetics of alloy AA6014 was investigated by means of transmission electron microscopy, positron annihilation lifetime spectroscopy and hardness measurements. Various ageing temperatures and stages were taken into consideration. Consistent with previous studies, we found that solute and vacancy supersaturation decrease during slow quenching due to precipitation and annihilation, respectively. Additionally, we observed cluster formation during cooling below 200 °C. As for the influence on ageing behaviour we observe different behaviour for high and low ageing temperature: Artificial ageing is more affected than pre-ageing and natural secondary ageing. The detrimental effect of natural ageing on paint-bake hardening also depends on the quench rate. Possible interpretations are associated with cluster formation during natural ageing and also during quenching. The influence of pre-ageing at different temperatures on subsequent ageing kinetics is similar for slower industrial-type quenching and for fast quenching, thus allowing to apply the findings from idealised quenching conditions to situations closer to real application.

Estimation of the Growth and Dissolution Kinetics of Ammonium Bicarbonate in Aqueous Ammonia Solutions from Batch Crystallization Experiments. 2. The Effect of Sulfate Impurity

In this study, we estimated the growth kinetics of ammonium bicarbonate crystallized from aqueous ammonia solutions containing an impurity in the form of ammonium sulfate. The evolution of the ammonium bicarbonate concentration of seeded desupersaturation experiments, estimated by ATR-FTIR measurements, has therefore been fitted to a population balance model that accounts for the real speciation of the system in the computation of the solution supersaturation. Furthermore, non-idealities of the liquid phase have been considered through the extended-UNIQUAC model. In this work, it has been found that the presence of sulfate ions in solution leads to a progressive decrease in the ammonium bicarbonate crystal growth rates as the concentration of the sulfate ions increases. A competitive adsorption model based on a Langmuir-type isotherm in which the sulfate ions represent the impurity in the system has been found to describe the experimental data rather well. Moreover, the analysis of the ammonium bicarbonat...

Effects of solution supersaturation on barite precipitation in porous media and consequences on permeability: Experiments and modelling

The understanding of porosity evolution in porous media due to mineral reactions and its impact on the transport of fluids and solutes is important, as this is a key factor in the long-term behaviour of underground engineered systems. The implementation of such coupled processes into numerical codes requires a mechanistic understanding of the relevant precipitation/dissolution processes in porous media and model validation with quantitative experiments. In this context, we conducted a series of flow-through column experiments to investigate the effect of supersaturation on barite precipitation mechanisms (e.g. nucleation) and consequential permeability changes. These experiments were modelled using the reactive transport code OpenGeoSys-GEM. Although the Kozeny-Carman equation is widely applied in numerical models describing porosity and permeability changes due to mineral dissolution and precipitation, it distinctively underestimated the permeability changes observed in the experiments. Instead, a porosity-permeability relationship involving a critical porosity at which the permeability decreases significantly had to be considered in the model. Post-mortem characterization (Scanning Electron Microscopy) highlighted the importance of including pore-scale information on passivation processes in order to get a better match between experimental and simulated results.

Study of nucleation and growth processes of ettringite in diluted conditions

Ettringite is a key compound of cementitious materials, formed during hydration that influences the rheological behavior of the cement paste. Despite its importance, ettringite formation has been poorly studied. In this work, nucleation and growth processes of ettringite were separately investigated. Ettringite nucleation was described using the Classical Nucleation Theory and an interfacial crystal-solution energy was determined. After the initial primary homogeneous nucleation, when the surface of already formed crystals was still low, the precipitation rate was shown to depend almost exclusively on the solution supersaturation. When the surface of crystals in suspension was getting bigger, a secondary nucleation responsible for an increase of ettringite needle diameter was observed. The precipitation rate became surface dependent and increased significantly. Results of this work show that nucleation of ettringite is easy as it requires few energy and that after primary nucleation precipitation occurs rapidly via secondary nucleation and growth.

A comparative study on the nucleation, growth, and agglomeration kinetics of potassium dihydrogen phosphate crystal in circulating fluidized‐bed crystallizer

AbstractThe crystallization in a fluidized‐bed crystallizer has recently received increasing interest for separation and purification of crystals. Past investigations on potassium dihydrogen phosphate (KDP) crystallization mainly focused on process efficiency and thermodynamics and less on kinetics. In this paper, the fluidized crystallization technology is used to investigate a KDP crystallization process. The mechanisms involved in crystal formation have been explored by observation of a continuous withdrawal of a suspension containing target crystals having certain size distribution. The crystallization process of KDP is researched to investigate the key parameters (suspension density [MT], solution supersaturation [ΔC], and fluid shear force [expressed by circulation flow rate; Re]) influencing crystal growth, nucleation, and agglomeration process. Three proposed crystallization kinetic models about crystals growth, nucleation, and agglomeration rates are developed and validated against data from the fluidized‐bed crystallizer. Taking advantage of multivariate nonlinear regression analysis, crystallization kinetic parameters are obtained by adopting the kinetic model in fluidized‐bed crystallization process. The comparative research of three crystallization kinetic rates is also studied. The results indicated that the parameters given by the kinetic mathematics model fit well with the experimental data. The error rate between the experimental and calculated value is also controlled within a reasonable range.

Study on the influence of hydro-thermal-salt-mechanical interaction in saturated frozen sulfate saline soil based on crystallization kinetics

The freezing of saturated saline soil is a dynamic hydro-thermal-salt-mechanical (THSM) interacting process. One-side freezing experiment of saturated sulfate saline soil in an open system with no-pressure water supplement is carried out. The coupling mechanism of water and salt migration and the soil deformation in the freezing process has been investigated by the one-side freezing experiment. Based on the crystallization kinetics theory, a hydro-thermal-salt-mechanical coupled mathematical model for saturated frozen sulfate saline soil with the effect of phase change is proposed. Moreover, the influence of solute on the physical and mechanical properties of soil during the freezing process is considered. To solve the nonlinear equations, the finite element algorithm is applied to solve the general form of governing equations. Finally, numerical simulation is implemented with the assistance of COMSOL. Validation of the model is illustrated by comparisons between the simulation and experimental results. From this study, it is found that, (1) the phenomenon of macroscopic crystallization can be well illustrated by the microscopic crystallization kinetics theory on the basis of the concepts of the water activity and the solution supersaturation. (2) The pore pressure due to the effect of phase change is main driving force for water and salt migration as well as the deformation of porous medium. It is concluded that the positive pore pressure is the main factor for soil deformation, and the negative pore pressure is the driving force for water migrates to the frozen zone. (3) Salt migrates with water and is rejected into the unfrozen water in the process of ice formation, and the rate of salt rejection gradually increases with the decrease of cooling rate. Therefore, salt crystals with layer distribution are formed in the frozen zone during the freezing process, and the largest salt crystals distribution zone is formed near the freezing front due to the effect of solute diffusion. (4) The calculated results are well agreement with the experimental data, demonstrating that the proposed hydro-thermal-salt-mechanical coupling model can well clarify the mechanism of heat and mass transfer in saturated frozen sulfate saline soil, and predict the deformation due to the effects of frost heave and salt expansion.