Phase Nucleation Research Articles

In Situ Electrodeposition of Pb and Ag Applied on Fluorine Doped Tin Oxide Substrates: Comparative Experimental and Theoretical Study.

A comparison between lead and silver electrodeposition onto fluorine-doped tin oxide (FTO) electrodes from nitrate solution was investigated in this work. Chronoamperometry has been used as an in situ technique to track the dynamics of the electrodeposition during advanced nucleation phases. The experimental results are correlated with a theoretical evaluation. It has shown that they have a strong correlation with each other. After that, the obtained deposits are characterized and compared as well by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), and impedance spectroscopy. The data reflects the effect of the material under investigation on current density, deposition density, and dielectric properties. Additionally, the electrodeposition approach (a two-in-one technique) can be followed in order to make well-controlled thin films that can be used for various purposes in addition to recovering heavy metals from wastewater.

Elastic investigation for the existence of B33 phase in TiNi shape memory alloys using atomistically informed Eshelby’s ellipsoidal inclusion

The existence of the B33 phase in TiNi alloys, which was reported to be a stable phase using density functional theory calculations but not confirmed experimentally, is controversial. Using Eshelby’s ellipsoidal inclusion, which was atomistically informed by density functional theory calculations, we investigated the existence of the B33 phase in the TiNi shape memory alloy. The calculated total strains of the heterogeneously nucleated B33 phase were similar to the eigenstrains of the B19’ phase, which were also calculated using density functional theory calculations. Considering the similarity of the atomic structures of B33 and B19’, this indicates that the B33 phase was elastically suppressed and changed to the B19’ phase by the original B2 matrix. We confirmed that the elastic inhomogeneity between the B2 matrix and B33 phase plays a role in this change.

Role of Heteronucleants in Melt Crystallization of Crystalline Solid Dispersions.

Few publications exist concerning polymorphic control during melt crystallization, particularly when employing heteronucleants. Here, the influence of a polymeric thin film (polyethylene terephthalate, PET) on the crystallization from melt of the polymorphic compound acetaminophen (ACM) in polyethylene glycol (PEG) was investigated. Molten ACM-PEG at different compositions was monitored using in situ Raman spectroscopy for nucleation induction time measurements and phase identification. Furthermore, X-ray diffraction (XRD) served to analyze the preferred orientation (PO) of the pastilles (solidified melt droplets) on PET-coated and uncoated substrates. The results indicate that PET-coated substrates qualitatively accelerate the nucleation of ACM form II (ACM II) in PEG compared to uncoated glass substrates. Additionally, the occurrence of ACM II in PEG was increased by an average of 10% when crystallized on PET-coated substrates compared to uncoated substrates. Overall, these results suggest that ACM can interact through hydrogen bonding with the PET-coated substrate, leading to faster nucleation. This investigation illustrates the effect of PET-coated substrates in the selective crystallization of ACM II in PEG as crystalline solid dispersions (CSDs). Ultimately, the results suggest the implementation of polymeric heteronucleants in melt crystallization processes, specifically, in advanced polymer-based formulation processes for the enhanced polymorphic form control of pharmaceutical compounds in CSDs.

A modelling study of interfacial polyamidation

Interfacial polymerization (IP) is a fast polymerization technique that does not have stringent requirements on operating conditions or extreme monomer purity. The fast reaction kinetics, and the involvement of a complex array of several transport, reaction, and equilibrium processes, make its mathematical modelling challenging, and very few attempts have been made to model IP reaction, especially to predict the film properties. In particular, no detailed models exist for the commercially important polyamide system, in which the liberation of HCl brings in some unique complications and features.This work extends the earlier work on polyurea (Dhumal and Suresh, 2009) to the interfacial reaction of a diamine with a diacid chloride and accounts for different physicochemical processes associated with the reaction, such as ionic equilibria in the aqueous phase, external mass transfer, monomer diffusion through the film, solution thermodynamics, phase separation kinetics, and film formation. Flory–Huggins theory has been used to calculate the solubility limits of the oligomers in different solvents. A competition between nucleation and spinodal decomposition-based phase separation has been postulated to predict the film’s crystallinity.Since only the unprotonated fraction of the amine monomer takes part in the reaction, HCl evolved in of the reaction, and restricts monomer availability in the reaction zone. The present model explains the experimental observation that the reaction ceases in spite of both monomers being still available, as being due to the amine monomer being almost entirely protonated by about 33% conversion. The consequences of this on the reaction kinetics and film properties are explored.

Atomistic mechanisms of phase nucleation and propagation in a model two-dimensional system

We present a computational study on the solid–solid phase transition of a model two-dimensional system between hexagonal and square phases under pressure. The atomistic mechanism of phase nucleation and propagation are determined using solid-state Dimer and nudged elastic band (NEB) methods. The Dimer is applied to identify the saddle configurations and NEB is applied to generate the transition minimum energy path (MEP) using the outputs of Dimer. Both the atomic and cell degrees of freedom are used in saddle search, allowing us to capture the critical nuclei with relatively small supercells. It is found that the phase nucleation in the model material is triggered by the localized shear deformation that comes from the relative shift between two adjacent atomic layers. In addition to the conventional layer-by-layer phase propagation, an interesting defect-assisted low barrier propagation path is identified in the hexagonal to square phase transition. The study demonstrates the significance of using the Dimer method in exploring unknown transition paths without a priori assumption. The results of this study also shed light on phase transition mechanisms of other solid-state and colloidal systems.

Kinetic control of competing nuclei in a dimer lattice-gas model.

Nucleation is a key step in the synthesis of a new material from a solution. The well-established lattice-gas models can be used to gain insight into the basic physics of nucleation pathways involving a single nucleus type. In many situations, a solution is supersaturated with respect to more than one precipitating phase. This can generate a population of both stable and metastable nuclei on similar timescales and, hence, complex nucleation pathways involving a competition between the two. In this study, we introduce a lattice-gas model based on two types of interacting dimers representing the particles in a solution. Each type of dimer nucleates to a specific space-filling structure. Our model is tuned such that stable and metastable phases nucleate on a similar timescale. Either structure may nucleate first, with a probability sensitive to the relative rate at which a solute is replenished from their respective reservoirs. We calculate these nucleation rates via forward flux sampling and demonstrate how the resulting data can be used to infer the nucleation outcome and pathway. Possibilities include direct nucleation of the stable phase, domination of long-lived metastable crystallites, and pathways in which the stable phase nucleates only after multiple post-critical nuclei of the metastable phase have appeared.

Study of Nonisothermal Crystallization Kinetics of Unstretched and Uniaxially Stretched Electroactive PVDF Composite Films

AbstractIncorporation of graphene‐based fillers such as graphene oxide (GO) and reduced graphene oxide (rGO) into polyvinylidene fluoride (PVDF) followed by uniaxial stretching can significantly improve their electroactive phase content as well as the dielectric properties. In this study, the nonisothermal crystallization kinetics of unstretched and uniaxially stretched PVDF‐GO and PVDF‐rGO composite films are investigated through differential scanning calorimetry (DSC) at different cooling rates. Avrami‐modified Jeziorney's model is used to understand their crystallization behavior which leads to the nucleation of electroactive crystalline phases in PVDF. Avrami's exponent “n” values in the range of 2–4 are obtained for nonisothermal crystallization of PVDF in different samples which reveal both two‐ and three‐dimensional growth of spherulites in the crystalline region. Kissinger's method is used to calculate the activation energy of crystallization and the results reveal accelerated crystallization of PVDF after addition of GO and rGO fillers followed by uniaxial stretching.

Hydration, microstructure characteristics, and mechanical properties of high-ferrite Portland cement in the presence of fly ash and phosphorus slag

High-ferrite Portland cement (HFPC) has the advantages of excellent sulfate resistance, higher abrasion resistance, lower energy consumption, and lower CO2 emission, and is expected to be widely utilized in erosion environmental engineering. This paper presents evolution and kinetics of hydration process, quantity of unhydrated clinker and portlandite (CH), C–S–H structure, pore structure, and mechanical properties of HFPC in the presence of fly ash (FA) and phosphorus slag (PS). PS exhibits lower mechanical properties and hydration heat in comparison with FA at early age owing to its retarding effect. The Qmax order is: HFPC > PS > FA, where HFPC, PS25, and FA25 (25 indicates percentage replacement of HFPC, the same below) correspond to 345 J/g, 322 J/g, and 313 J/g, respectively, according to the Krstulovic-Dabic (K-D) model. The FA and PS retard the crystal nucleation and growth (NG) and phase boundary reaction (I), and I process of FA takes longer than PS. PS hinders the formation of CH and C–S–H at early age, and plenty of CH and high polymerization C–S–H are formed at a later time. The effects of FA on the enhancement of Al content of C–S–H and mean chain length (MCL), as well as the pozzolanic reaction are more significant than that of PS. FA and PS have a comparable total porosity at 90 days. FA has an excellent ability to refine the pore structure distribution, which reduces the prevalence of large pores (50–10,000 nm) by 17.92% and increases the proportion of small pores (2.5–20 nm) by 8.87% than PS, at 90 days. The quantity of C–S–H and pore size distribution affect the mechanical properties more than the CH content. The unhydrated C2S in HFPC, FA25, and PS25 are about 14.3%, 9.1%, and 22.1% at 90 days.

Definition of the induction time for CO2 and CH4 hydrate via evaluation of the heat released during the process and the gas consumption rate.

The induction period is defined as the time required to obtain a detectable quantity of hydrates during their natural or artificial production. This period includes the initial nucleation phase and part of the following massive growth phase. Several methods were thought to measure its length: the most adopted are the visual observation of the process and the direct measure of the temperature increase. However, these techniques are not always feasible and their accuracy is often low. This work deals with the definition of the induction time by considering the heat produced during the process, which is proportional to the temperature but significantly less affected by the stochastic nature of the process. In order to prove the feasibility of the process, the results were then compared with what obtained by considering the gas consumption rate to measure the induction time. The proposed method was validated for methane hydrates. The same confirmation was not possible for carbon dioxide hydrates, due to the high solubility in water of this species and the consequent overestimation of the gas consumption during the process.

A Space–Time Neural Network for Analysis of Stress Evolution Under DC Current Stressing

The electromigration (EM)-induced reliability issues in very large-scale integration (VLSI) circuits have attracted increased attention due to the continuous technology scaling. Traditional EM models often lead to overly pessimistic predictions incompatible with the shrinking design margin in future technology nodes. Motivated by the latest success of neural networks in solving differential equations in physical problems, we propose a novel mesh-free model to compute EM-induced stress evolution in VLSI circuits. The model utilizes a specifically crafted space–time physics-informed neural network (STPINN) as the solver for EM analysis. By coupling the physics-based EM analysis with dynamic temperature incorporating Joule heating and via effect, we can observe stress evolution along multisegment interconnect trees under constant, time-dependent, and space–time-dependent temperature during the void nucleation phase. The proposed STPINN method obviates the time discretization and meshing required in conventional numerical stress evolution analysis and offers significant computational savings. Numerical comparison with competing schemes demonstrates a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times $ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$52\times $ </tex-math></inline-formula> speedup with a satisfactory accuracy.

Effect of Copper on the Formation of L12 Intermetallic Phases in Al–Cu–X (X = Ti, Zr, Hf) Alloys

Transition metal trialuminides of the Al3X type of groups 4 and 5 of the periodic system have reduced density, high melting points, and corrosion resistance. Aluminides with a cubic lattice of the Al3Sc type can be used as a nucleating phase for aluminum alloys. However, low plasticity and a tetragonal lattice limit their application. In this work, we stabilized the metastable cubic lattice of Al3X-type aluminides by replacing aluminum with copper. The conditions for the formation of L12 metastable aluminides in the Al–Cu–TM (TM: Ti, Zr, Hf) alloys were studied using a wide range of copper concentrations. A high concentration of copper (hypereutectic alloys) is the one of the necessary conditions for the formation of (Al1−xCux)3Ti, (Al1−xCux)3Zr, (Al1−xCux)3Hf aluminides. With an increase in the copper concentration, the number of metastable aluminides sharply increased. The process of their formation strongly depended on the sequence of dissolution of the corresponding components in the melts. The low volume fraction of precipitated titanium aluminides was the result of insufficient supersaturation of α-Al with titanium (at the peritectic temperature) compared to that for alloys with zirconium and hafnium. Under identical synthesis conditions in the crystal lattice of metastable aluminides formed in experimental Al–Cu–Ti, Al–Cu–Zr, Al–Cu–Hf alloys, copper was found to substitute up to 8, 10, and 13 at.% of aluminum, respectively. The crystallographic and dimensional similarities of the lattices in metastable transition metal aluminides and in α-Al suggest their usefulness as modifying additions in aluminum-based alloys.

Charge modifications of graphene oxide enhance the inhibitory effect on insulin amyloid fibrillation based on electrostatic interactions

Graphene oxide (GO) is a biocompatible nanomaterial that has an inhibitory effect on insulin amyloid fibrillation. In order to enhance the inhibitory effect of GO and explore the rules of electrostatic interactions on the inhibitory effect, carboxyl group, PEI and PEG were coupled to the GO nanoplatelet surface to prepare inhibitors of different surface electrical properties. The effects of surface electrical properties of inhibitors on insulin fibrillation were investigated. The results showed that GO, carboxyl group modified GO (GO-COOH), PEI modified GO (GO-PEI), and PEG modified GO (GO-PEG) inhibited insulin fibrillation in a dose-dependent manner. Compared with GO, positive charge-modified GO-PEI and negative charge-modified GO-COOH enhanced the inhibitory effect, while uncharged polymer-modified GO-PEG weakened the inhibitory effect. The inhibitory effect of the inhibitors increased with the increase of surface charge density. The difference in inhibitory effect between GO-PEI and GO-COOH was due to the different electrostatic interactions between inhibitors and insulin, and the different inhibition mechanisms. In addition, inhibitors mainly interact with insulin during the nucleation phase to hinder insulin fibrillation. The charge modifications of graphene oxide enhanced the inhibitory effect on insulin fibrillation based on electrostatic interactions, which will provide new thoughts for the development of anti-amyloid fibrillation drugs.

Thermobarometry, vesicularity and microlite populations in pyroclastic density current deposits from the last 4500 years of activity at Galeras, Colombia

Vulcanian eruptions during the 19th and 20th Centuries at the Galeras volcano have produced small eruption columns and bomb fields around the active vent. Four pyroclastic density current (PDC) deposits from the early history of the currently active Galeras cone which have ages between 4500 and 2300 years before present have a much wider distribution. The first two (ML 1 and ML 2) were deposited from hot, dilute, pumice-rich pyroclastic density currents. Amphibole thermobarometry indicates that the magma for these eruptions tapped reservoirs between 5 and 28 km (ML 1) and 33–41 km (ML 2) below the crater. Debse, degassed magma formed a conduit plug which persisted for up to several weeks before the eruptions based on the thickness of breakdown rims around the amphibole. Amphibole-bearing pumice came from a reservoir 5–26 km below the crater and since it lacks breakdown rims it must have reached surface in <8 days. The vesicularity of the pumice indicates two phases of bubble nucleation and growth which coincides with growth of plagioclase and orthopyroxene microlites. The upper two layers (ML 3 and ML 4) are block and ash flows. ML3 shows significant hydrothermal alteration of the dense lithic clasts and has only minor vesicular scoria. The magma for the ML 3 eruption came from a reservoir 17–29 km below the crater and the presence of 20 μm thick breakdown rims on the amphibole implies that the degassing plug was stable for ∼20 days, though the degree of hydrothermal alteration of the clasts appears to require a significantly longer time. The uppermost layer (ML4) is relatively unaltered with a large proportion of pumice. Dense lithics indicate plug formation from magma that had its source at ∼17 km below the crater and remained stable during degassing for ∼20 days. The absence of amphibole from the pumice in ML 4 implies a distinct magma composition was emplaced after the plug.

Revealing the Origin of Heterogeneous Phase Transition and Deformation Behavior in Au-Ag-Cu-Based Multicomponent Alloys

Local chemical heterogeneity of highly-concentrated multicomponent alloys has drawn much attention as it can produce novel material behaviors and remarkable properties. In Au-Ag-Cu-based multicomponent alloys, phase separation and ordering have long been recognized to correlate with grain boundaries (GBs), but there is still a lack of atomic-scale understanding of the heterogeneous phase transition and how the microstructures respond to deformation. In this paper, a joint experimental and theoretical study was conducted on a medium-entropy polycrystalline model alloy, which is a representative Au-Ag-Cu-based multicomponent alloy with important applications in fields such as photocatalyst and micro-/nano-electromechanical systems. The GB regions are observed to preferentially nucleate two-phase lamellar structures, which are softer than grain interiors featuring short-range-order and modulated morphologies. First-principles calculations suggest the GB segregation of Ag and depletion of Cu are energetically favorable, consequently creating compositions that facilitate phase separation and impede ordering. Calculations of elasticity-based mechanical properties, stacking fault and surface energies reveal the GB lamellar structures are intrinsically soft with heterogeneous deformation capabilities. Furthermore, design strategies based on GB segregation engineering and tuning the dual-phase compositions are proposed to control heterogeneities. The results provide new insights into GB segregation, phase nucleation precursor and mechanical properties of noble-metal multicomponent alloys.

Precipitation Kinetic Analysis in a Maraging 350 Steel Using KJMA and Austin-Rickett Equations

Maraging steels are martensitic steels hardened by intermetallic compounds that precipitate during aging heat treatments. During aging of these steels complex phenomena involving nucleation and growth of several phases as well as changes in the precipitates, morphology and stoichiometry take place. The present work aims to study the kinetics of precipitation in a maraging 350 steel through the KJMA and Austin-Rickett (AR) equations. Analysed data were obtained from Vickers microhardness measurements carried out in samples heat-treated between 440 and 560 °C. Variation in the n-constant has been observed for both equations, indicating changes in the precipitation behavior. However, the n-constant values obtained from AR equation follow the microstructural changes observed in previous works on maraging steels. Interpretation of the n-constants using the AR equation was linked to the precipitation on dislocations at 440 °C, the growth of finite long cylinders in comparison to their separation at 480 °C, and general particle growth from small dimensions at 520, and 560 °C.

Influence of selected alloying variations on liquid metal embrittlement susceptibility of quenched and partitioned steels

In this work, the influence of selected alloying variations on Zn-assisted liquid metal embrittlement (LME) susceptibility of Zn-coated advanced high strength steels (AHSS) is investigated. Cold-rolled AHSS alloys of different carbon (C), manganese (Mn), silicon (Si), and aluminum (Al) concentrations were continuous-annealed to generate a third generation AHSS microstructure (composed of martensite and retained austenite) via quenching and partitioning. High temperature tension tests using simulated spot-weld thermomechanical cycles revealed no significant influence of C and Mn variations on the Zn-LME susceptibility of AHSS. On the other hand, Zn-LME susceptibility was strongly correlated with the Si content of AHSS. A direct comparison of the (reacted) coating microstructures of the Si-alloyed and Low-Si AHSS variants revealed that Si in the AHSS substrate suppresses Fe–Zn alloying reactions and retards the nucleation and growth of Fe-Zn intermetallic phases at the coating-substrate interface in these spot weld simulations. The suppressed intermetallic formation at elevated Si concentrations is consistent with phase equilibria considerations in the Fe-Zn-Si ternary system. In the context of Zn-assisted LME, therefore, Si is hypothesized to aggravate LME behavior by increasing the liquid Zn availability for embrittlement and promoting direct contact between liquid Zn and the AHSS steel substrate.

Formation and thermal stability of two-phase microstructures in Al-containing refractory compositionally complex alloys

ABSTRACT Phase separation into an A2+B2 two-phase microstructure in refractory compositionally complex alloys (RCCA) has been speculated as being spinodal in nature with continuous chemical distribution during the separation. However, these reactions might instead occur as precipitation by nucleation and growth. In order to unequivocally elucidate the distinct nature of phase separation sequence in RCCA from the system Ta-Mo-Ti-Cr-Al, atom probe tomography and electron microscopy techniques were utilized on samples that were annealed over multiple orders of magnitude in time. The composition 82(TaMoTi)-8Cr-10Al (at.%) was chosen, as it exhibits a two-phase microstructure, with a desired A2 matrix and embedded B2 phase. Quenching the samples from 1200°C resulted in a microstructure consisting of ordered clusters (2 nm) of distinct chemical composition. Subsequent annealing at 800°C to 1000°C leads to an increase in the volume fraction of the precipitating phase, which saturates after 10 h. Further annealing leads to the ripening of the microstructure; however, the absolute size of the precipitates stays <100 nm even after 1000 h. For the investigated conditions, the interface between matrix and precipitate can be considered sharp within the resolution of the applied techniques and no significant change in the transition of chemical composition across the interface is observed. Therefore, the phase separation mechanism is confirmed to be phase nucleation and growth in contrast to the possible spinodal decomposition, as hypothesized for other RCCA systems. The impact of precipitation and coarsening on the hardness of the alloy is discussed.

Effect of microsegregation behaviors on solidification microstructure of IC10 superalloy fabricated by directed energy deposition

Due to the solidification process and thermal history, the microstructure and properties along the deposition direction are generally inhomogeneous in components fabricated by the directed energy deposition technique. By developing a microsegregation model, this study gives an innovative understanding of the elemental segregation behavior of an as-deposited IC10 superalloy along the different heights and its influence on the microstructure. Results indicate that the γ-γ ´ eutectic-free microstructure is only obtained at the initial deposition layer, and as the deposition height increases, eutectic phases gradually appear in interdendritic regions. By taking account of the nonequilibrium solidification and dendritic tip undercooling, the new microsegregation model can well explain the segregation behavior of the alloy at different deposition heights. Compared to the back diffusion coefficient, the partition coefficient plays a major role in microsegregation behavior under rapid solidification conditions, especially for the elements with a high diffusion coefficient in solid, such as Ti and Al. Moreover, microstructure transformation is dependent on varying solidification processes due to the change in microsegregation. Limited by the heat transfer efficiency as the increased deposition heights, the temperature gradient and solidification rate decrease, which exacerbates the enrichment of Al and Ti at interdendritic regions and promotes the eutectic phase nucleation. Restricted by the diffusion rate of alloying elements, the eutectic reaction rate slows down, γ and γ ´ lamellae thickness increase, and finally the petal-like eutectic phases form.

Coordination-Controlled Electrodeposition of Palladium/Copper Thin Films onto a Pyridine-Terminated Self-Assembled Monolayer

A scheme for the electrodeposition of ultrathin bimetallic layers on top of a self-assembled monolayer (SAM) is investigated which combines the deposition of one metal (Pd) coordinated to a functionalized SAM (3-(4-pyridine-4-yl-phenyl)-propane-1-thiol, PyP3) on Au/mica with another metal (Cu) from the bulk electrolyte. The coordination-controlled electrodeposition (CCED) is a four-phase process comprising (i) Pd2+ coordination to the terminal pyridine units of the SAM, (ii) reduction of Pd and nanoparticle formation, (iii) formation of an intermixed shell of Pd and Cu, and (iv) deposition of bulk Cu. Chronoamperometry reveals a fast nucleation phase where Pd nanoparticles form within a few milliseconds and seed the Cu deposition. The Pd-Cu core-shell nature of deposited nanoparticles is confirmed by transmission electron microscopy (TEM). Harnessing the selective coordination of Pd2+ to PyP3, a one-pot procedure is further developed using electrolytes containing both Pd2+ and Cu2+ ions. Thus simplifying complexation and reduction, continuous Pd/Cu films are obtained in a multistep process as verified by scanning tunneling microscopy (STM). With a percolation threshold below 3 nm, CCED, as a SAM-controlled deposition strategy, offers an avenue for generation of ultrathin films.

Ice thermal energy storage enhancement using aligned carbon nanotubes under external magnetic field

In this work, the magnetic Multi-walled Carbon Nanotubes (MWCNTs) with the magnetization range of 27.6–55.6 emu/g were prepared. It is indicated the aligned MWCNTs are distributed along with the magnetic field direction, and their ultra-high thermal conductivity at the axial direction could be fully utilized. Furthermore, the effect of magnetic field on ice thermal energy storage using aligned MWCNTs was studied. Specifically, the solidification characteristics including nucleation and solidification phase change process under various magnetic field intensities were investigated experimentally and theoretically. The results showed the optimal magnetic field intensity exists for aligned MWCNTs Phase Change Material (PCM), at which PCM has the lowest supercooling degree, the shortest solidification phase change time, and phagocytosed MWCNTs by growing solid-liquid interface. The optimal magnetic field intensities are 150 mT, 100 mT, 75 mT, 75 mT with increased mass ratios of Fe3O4 on the wall of MWCNTs from 1:1 to 4:1, and their supercooling degree are decreased by 36.0 %, 46.5 %, 70.0 %, 65.1 % compared with pure water. For solidification phase change process, the results showed that nearly 50 % of the aligned MWCNTs PCM is solidified in 25 % of the total solidification time. It is concluded aligned MWCNTs fully exhibited nucleating agent and the heat transfer enhancement as they uniformly distributed in the PCM under optimal magnetic field intensity.