Increasing Nucleation Rate Research Articles

High magnetic field-assisted synthesis of a pine-like hyperbranched structure alpha-Fe2O3 for enhanced magnetic properties and photocatalytic activity

The effect of a high magnetic field (HMF) on the synthesis of an iron oxide hyperbranched structure was investigated for the first time. Application of an HMF corresponded to an increased nucleation rate and decreased size. Moreover, the oriented growth in secondary branches was more pronounced; the lattice spacing of the secondary structure decreases significantly. The magnetic properties (and photocatalytic performances toward Congo red) of HMF-α-Fe2O3 were improved. The coercivity increased from a value of 645 Oe to a value of 2716 Oe at 300K, and the degradation rates of Congo red improved from a value of 65% to a value of 85% after 210 min. The enhanced oriented growth, while decreasing the size, is responsible for the improved performance of HMF-α-Fe2O3. This study fills in the gap of research on hyperbranched structures under HMF and is pertinent to preparing multifunctional materials assisted by HMF.

Crystallization Kinetics of the Fe68Nb6B23Mo3 Glassy Ribbons Studied by Differential Scanning Calorimetry

Fe-based metallic glass has wide industrial application due to its unique mechanical behavior and magnetic properties. In the present work, the non-isothermal crystallization kinetics in Fe68Nb6B23Mo3 glassy alloys were investigated by differential scanning calorimeter (DSC). The results indicate that both the glass transformation and crystallization process display an obvious kinetic effect. The activation energy is calculated using Kissinger’s method and Ozawar’s method. The activation energy for Tg (glass transition temperatures), Tx (crystallization initiation temperatures) and Tp (crystallization peak temperatures) calculated from Kissinger equation, is 308 ± 4, 342 ± 5 and 310 ± 7 kJ mol−1, respectively. The activation energy for Tg, Tx and Tp calculated from Ozawa equation is 322 ± 3, 356 ± 5 and 325 ± 7 kJ mol−1, respectively. With the increase of the crystallization volume fraction x, the Avrami exponent n(x) first decreases and then increases. At the preliminary step, 0 < x < 0.25, 2.5 < n(x) < 4.0 stands for the growth from a small size with an increasing nucleation rate. When 0.25 < x < 0.71, n(x) decreases from 2.5 to 1.5, indicating that this stage is controlled by the growth of small particles with a decreasing nucleation rate.

Carbon nanotubes and (Mg10Ni)85Ce15 synergistically activate Mg-Al alloy waste for efficiently hydrolysis hydrogen generation

Hydrogen generation via Mg-Al alloy waste (MA) hydrolysis is regarded as a potential and promising strategy for portable hydrogen generators. An efficient modification method to obtain rapid kinetics and high yield for hydrolysis H2 generation needs to be further explored. At present, it is difficult to achieve rapid and high-yield hydrogen production process while maintaining high capacity. In this work, carbon nanotubes (CNTs) and (Mg10Ni)85Ce15 (MNC15) were creatively employed as additives to synergistically activate MA. Different content of additives was respectively or simultaneously employed through high energy ball milling process to investigate their synergistic effect. The results show that the simultaneous addition of MNC15 and CNTs can significantly improve the hydrolysis kinetics and hydrogen yield of MA. MA-5CNTs-10MNC15 can generate 806.6 mL·g−1 H2 with 0.92 yield at 328 K with initial 10 min. The thermodynamic behaviors of MA and activated MA were investigated in detail and the rate-controlling steps were further analysed via different hydrolysis stages. When 10 wt% CNTs added, Ea decreases from 33.6 kJ·mol−1 to 8.1 kJ·mol−1. The Ea of MA-5CNTs-10MNC15 can reach to 15.8 kJ·mol−1. The rate-controlling steps were confirmed to transform from three-dimensional interface to one dimensional-diffusion process. The synergistic activation effect was creatively explained by nucleation and growth up mechanism on the basis of the increased nucleation rate by MNC15 and enlarged growth space by CNTs. This work may provide a novel and efficient modified strategy for transforming Mg alloy waste into pure H2, which may pave way for the application of portable hydrogen generators.

An innovative annealing treatment method and its mechanism to refine deformed mixed grains of initial aged GH4169 superalloy

The deformed mixed grains of the initial aged GH4169 superalloy need to be refined by annealing treatment. However, for the isothermal annealing treatment, the deformed mixed grains can only be refined to about 10 µm because the increase of nucleation rate needs to increase the temperature while the decrease of grain growth rate requires to decrease temperature. In the paper, an innovative method including an aging treatment and a subsequent continuous-cooling recrystallization annealing treatment (CC-RAT) is proposed. This method can not only increase the nucleation rate but decrease the grain growth rate. The effects of heat treatment parameters on microstructure are investigated. Besides, the grain refinement mechanism is studied using a developed cellular automaton (CA) model. The results show that the recrystallization takes place slowly during aging, while large number of δ precipitates appear. In subsequent CC-RAT, increasing starting temperature (Ts), decreasing cooling rate (V) or ending temperature (Te) can remarkably promote recrystallization, thereby refining grain microstructure. This attributes to the increase of recrystallization nucleation rate and the effective control of grain growth rate. In the early stage of CC-RAT, δ precipitates hinder the quick growth of recrystallized grains nucleated firstly. Moreover, the increase of Ts accelerates the nucleation rate, and the decrease of V prolongs the time for nucleation. Both of them promote the rapid formation of new recrystallized nuclei, especially at δ phase boundaries. As the annealing temperature decreases, newborn grains grow slowly, and these new grains restrict the growth of grains nucleated first. Therefore, a fine and uniform microstructure with an average grain size of 5.82 µm is obtained. However, when Ts is too high or V is too low, some coarse recrystallized grains appear. Hence, the feasible process is concluded as follows: aging treatment (900 °C×12 h), followed by CC-RAT (Ts = 990–1010 °C, V=1–2 °C/min, Te=950–970 °C).

Femtosecond laser-induced photochemical synthesis of gold nanoparticles in nitrate solution

Femtosecond laser pulses are capable of ionizing water molecules through multiphoton absorption. The generated hydrated electron and hydrogen peroxide are responsible for the nucleation and growth of nanoparticles during a photochemical synthesis. The photochemical reduction kinetics follow an autocatalytic rate law, which is determined by nucleation rate k1 and growth rate k2. In this work, we investigated the effect of adding nitrate as electron scavenger on the laser-based photochemical synthesis of gold nanoparticle. The experiment results showed enhancements of both k1 and k2 with increasing nitrate concentration, indicating the formation of a large number of nuclei followed by fast growth process. TEM images and size distribution analysis confirmed the improved growth of gold nanoparticles. In the absence of scavenger, the gold nanoparticles produced were dominated by small particles with sizes <7 nm. Adding small amount of nitrate increased the mass fraction of larger particles (∼7–15 nm), thus tuning the average size of gold nanoparticles from 6.52 nm to 7.49 nm. Exceedingly high concentration of nitrate caused the formation of even larger particles, which connected to each other. While salt effects might interfere with both nucleation and growth process, generation of reducing species from electron scavenging reaction significantly contributed to the counterintuitive increase of nucleation rate. This study demonstrated the potential use of nitrate as a modifying agent for morphological control of gold nanoparticles.

Effect of stabilization and fatty acids chain length on the crystallization behavior of interesterified blends during storage

In this work, we studied the influence of fatty acid chain length and crystallization temperature on the crystallization behavior during the storage of binary blends modified by chemical interesterification. The blends were produced with soybean oil and fully hydrogenated oils from palm kernel, palm, soybean, microalgae, and crambe, evaluated separately, at a ratio of 50:50 (% w/w). The blends were crystallized by two crystalline stabilization methods. In method I, the samples were maintained at 25 °C for 24 h before the analyses. In method II, the samples were maintained at 5 °C for 24 h, followed by crystalline stabilization at 25 °C for 24 h before the analyses. The interesterification reaction caused considerable changes in the TAGs profile with increasing asymmetric TAGs. These TAGs changes promoted an increase in the crystallization induction time, a decrease in the maximum solids content, and changes in crystals morphology. The increase in the FAs chain length promoted the increased nucleation rate that influenced morphology crystals. Method II promoted a reduction in the medium diameter of crystals and the appearance of the β phase with storage time. For crystallization carried out at higher temperatures (method I), we observed that β’ was favored. Unusual polymorphic transitions were observed with storage time in samples with higher tristearin content. We identified clear correlations between the predominance of β’ phase in the interesterified blends and TAGs of S2U and SU2-type. In addition, the blends with a more diverse range of fatty acids concerning chain size also showed the β’ polymorph. β polymorph, on the other hand, was associated with symmetric TAGs, S3 and U3, and CN-54 type TAG. In this study, we used the Rietveld method to quantify the polymorphs and amorphous content in the blends before and after the randomization reaction. This approach allowed a deeper understanding of the crystalline behavior in the blends, which would be difficult to achieve by performing only a visual analysis of the X-ray diffractograms.

Tailoring the size of silver nanoparticles by controlling mixing in microreactors

Microreactors are commonly regarded by their high mass transfer rates associated to their small diameters. Although this is true, especially when compared to batch systems, mixing is frequently exclusively dominated by diffusion in single phase flow microreactors, being the fast mixing of reactants an aspect often overlooked during their design. This paper presents the first quantitative analysis of the effect of mixing of precursors on the size and distribution of metal nanoparticles synthesized in flow microreactors. Silver nanoparticles with a range of sizes are continuously synthesized by controlling mixing efficiency in rationally-designed microreactors. The particle size decreases as the mixing index increases due to an increase in nucleation rate and thus the resulting nuclei concentration. Herein, the mixing efficiencies of different 3D curved microreactors are quantitatively evaluated using accurate simulations of their concentration profiles, avoiding the so-called numerical diffusion errors using a novel method based on backward particle tracking. A method based on forward particle tracking is improved to simulate the residence time distributions (RTD) in microreactors at a reduced computational cost. Curving the reactors channels is known to lead to the formation of Dean vortices however, these well-defined rotations lead to stagnant zones. The mixing efficiency can be enhanced and the RTD narrowed by periodically changing the direction of the Dean vortices along the length of the channel. In addition, we demonstrate the effect of the configuration of the inlet streams relative to the curvature of the reactor and thus, the Dean vortices, on the resulting mixing. These results provide rational design guidelines for the design of microreactors to manipulate advection as a way of manipulating the reaction rates as demonstrated here to control nanoparticle sizes.

Influence of MnS inclusions on dynamic recrystallization and annealing twins formation during thermal deformation

The existence of MnS inclusions during thermal deformation affects the dynamic recrystallization (DRX) behavior and twinning evolution of FCC matrix. In this study, we conducted thermal compression experiments on two sets of materials which are MnS-containing and non MnS-containing specimens, respectively. The mechanism of the influence of MnS inclusions on the dynamic recrystallization behavior of the matrix is revealed. The effect of MnS inclusions on the formation of annealed twins during dynamic recrystallization is clarified from the perspective of plastic deformation of MnS inclusions. The results show that the recrystallization behavior of MnS-containing materials are dominated by DDRX, but assisted by PSN and CDRX. Due to the severe plastic deformation and inhomogeneous deformation of MnS inclusions, the uncoordinated deformation between MnS inclusions and matrix cause the unevenly distributed stress and strain at the interface which provides a higher energy storage for the formation of the twin boundaries during DRX process. According to the growth accident model, the PSN mechanism induced by MnS inclusions produces new grains containing twin boundaries in the DRX nucleation stage, leading to the increase of nucleation rate of the twin boundaries. The faster grain boundary migration velocity promotes the nucleation and progression of twins adjacent to MnS inclusions in the DRX growth stage, thereby increasing the density of twin boundaries. Finally, the evolution of annealed twinning near the MnS inclusions during dynamic recrystallization is elucidated in detail.

Effect of Gd addition on non-isothermal and isothermal crystallisation of Cu–Zr–Al bulk metallic glass

Abstract The crystallisation kinetics of (Cu46Zr46Al8)100–xGdx (x = 0, 2 and 4 at.%) bulk metallic glasses in non-isothermal and isothermal conditions were studied by differential scanning calorimetry and X-ray diffraction. X-ray diffraction analysis shows that the crystallisation product Cu10Zr7 changes to Cu10Zr7 and Cu2Gd in the presence of Gd in non-isothermal and isothermal conditions. Crystallisation activation energy was calculated using the Kissinger and Ozawa methods in non-isothermal conditions and using the Arrhenius model in isothermal conditions. The results show that Gd addition triggers an increase in the energy barrier during crystallisation. The Johnson–Mehl–Avrami model was employed to analyse the crystallisation kinetics in the isothermal condition. The Avrami exponent, n, for Cu46Zr46Al8 is more than 2.5, which demonstrates that the crystallisation is mainly governed by diffusion-controlled three-dimensional growth with increasing nucleation rate. Comparably, n for (Cu46Zr46Al8)98Gd2 and (Cu46Zr46Al8)96Gd4 is 1.5 &lt; n &lt; 2.5, which suggests that the crystallisation is mainly determined by diffusion-controlled three-dimensional growth with decreasing nucleation rate.

Introducing PbSe quantum dots and manipulating lattice strain contributing to high thermoelectric performance in polycrystalline SnSe

Here, a p-type polycrystalline SnSe integrated with PbSe quantum dots is fabricated by an in situ magnetic field-assisted hydrothermal route. The decrease of the critical nucleation free energy and increase of homogeneous nucleation rate lead to the formation of PbSe quantum dots under high magnetic field. The enhanced density of states due to PbSe quantum dots causes significantly enhanced Seebeck coefficients and power factor. A large integral area of power factor over the full temperature range is optimized. The lattice strain induced by dislocations and stacking faults shortens the phonon relaxation time, leading to an ultralow lattice thermal conductivity (0.32 W m−1 K−1 at 873 K perpendicular to the pressing direction). Consequently, these electronic and thermal effects contribute to a high ZT of ∼1.9 at 873 K and an outstanding average ZT of 0.71 in polycrystalline SnSe. The combination of introducing PbSe quantum dots functional units and manipulating lattice strain provides a new perspective for designing high performance thermoelectric devices.

Coupling magnetic-thermal field effect on precipitation kinetics of Al–Cu–Mg alloy investigated by SAXS and WAXS

The effect of a stable magnetic field (1 T) on precipitation kinetics in an Al–Cu–Mg alloy (AA2024) aged at different temperatures has been systematically studied by small angle X-ray scattering (SAXS), transmission electron microscope (TEM) and wide angle X-ray scattering (WAXS). The synchrotron SAXS and WAXS results reveal that the precipitation kinetics in different scales is facilitated by magnetic field at ageing process. Based on the WAXS findings, under the magnetic field, the precipitation of CuAl2Mg, Al7Cu2Fe and CuAl2 phases is accelerated at all ageing process, and the highest enhancement of relative intensity of them reaches 262%. Among them, at low ageing temperature (at 130 °C), the percentage of relative intensity of CuAl2Mg and Al7Cu2Fe phases between with and without magnetic field are increased by 48%–120% and 93%–257%, respectively, as compared to the values 1 of above two phases observed at other ageing temperature (at 160–240 °C). Modifications of the precipitation kinetics under magnetic field could be associated with two reasons. One is solute diffusion increase, this is attributed to the increase of solute diffusion coefficient, which results from the change of frequency factor of atom caused by magnetic field. Another is critical nucleation energy decrease and critical nucleation rate increase, which is attributed to the presence of magnetic field energy under magnetic field.

Crystallization kinetics of glass prepared with foundry slag

Iron foundry slag and hydrated lime were used in glass preparation by the melt-quenching method. The glass obtained was heat-treated using the thermal analysis technique. A crystallization kinetics study was carried out with glass powder samples using a non-isothermal method at five different heating rates by differential scanning calorimetry (DSC). Considering that few studies compare kinetic results obtained by different methods, in this work, the activation energy (Ea) of the crystallization process was obtained using the Kissinger and Augis-Bennett models for comparison purposes. The Ea results showed negligible variation in comparing the methods used, nevertheless, linear fitting of crystallization peaks was slightly better by the Augis-Bennett than the Kissinger model. The Avrami index values showed an increasing nucleation rate for two stable phases and decreasing for the metastable phase present in the glass-ceramic. Avrami indexes obtained also indicated an interface-controlled particle growth, whose scanning electron microscopy images showed different morphologies of crystalline particles in the bulk of the glass matrix.

Crystallization kinetics of Cu–Zr–Al bulk metallic glass with Nd addition

AbstractThe crystallization kinetics of (Cu48Zr48Al4)100−xNdx (x = 0, 2 at.%) bulk metallic glasses in nonisothermal and isothermal conditions were studied by differential scanning calorimetry and X‐ray diffraction (XRD). XRD analysis shows that the crystallization product Cu10Zr7 changes to Cu10Zr7 and Cu2Nd with Nd presence in nonisothermal and isothermal conditions. Crystallization activation energy was calculated in nonisothermal conditions using Kissinger and Ozawa methods and in isothermal conditions using Arrhenius model. The results show that the activation energy harbored by (Cu48Zr48Al4)98Nd2 expresses larger value compared with Cu48Zr48Al4, which indicate that the energy barrier for crystallization has enhanced along the Nd addition. The Johnson–Mehl–Avrami model was employed for analyzing the crystallization kinetics in isothermal condition. The Avrami exponent n for Cu48Zr48Al4 is more than 2.5, demonstrating that the crystallization is mainly governed by diffusion‐controlled three‐dimensional growth with increasing nucleation rate. Comparably, the Avrami exponent n for (Cu48Zr48Al4)98Nd2 is 1.5 &lt; n &lt; 2.5, suggesting that the crystallization is mainly determined by diffusion‐controlled three‐dimensional growth with decreasing nucleation rate. The evident enhancement in crystallization activation energy based on Nd addition is rationally made up of an influential factor commonly harbored on the enhanced glass forming ability for the rare‐earth comprising Cu–Zr–Al metallic glasses.

A Study of Moist Air Condensation Characteristics in a Transonic Flow System

When water vapor in moist air reaches supersaturation in a transonic flow system, non-equilibrium condensation forms a large number of droplets which may adversely affect the operation of some thermal-hydraulic equipment. For a better understanding of this non-equilibrium condensing phenomenon, a numerical model is applied to analyze moist air condensation in a transonic flow system by using the theory of nucleation and droplet growth. The Benson model is adopted to correct the liquid-plane surface tension equation for realistic results. The results show that the distributions of pressure, temperature and Mach number in moist air are significantly different from those in dry air. The dry air model exaggerates the Mach number by 19% and reduces both the pressure and the temperature by 34% at the nozzle exit as compared with the moist air model. At a Laval nozzle, for example, the nucleation rate, droplet number and condensation rate increase significantly with increasing relative humidity. The results also reveal the fact that the number of condensate droplets increases rapidly when moist air reaches 60% relative humidity. These findings provide a fundamental approach to account for the effect of condensate droplet formation on moist gas in a transonic flow system.

Effect of precursor on structural and antibacterial behaviour of hydroxyapatite/silver nanocomposites

ABSTRACT Ion substitution in hydroxyapatite (HA) lattice is a promising way to enhance its antibacterial activity and inhibit implant-related infections. In this study, HA/silver (HA/Ag) nanocomposites were synthesised through sol-gel method from two calcium (Ca) and phosphor (P) precursors. Our results showed that, by using P precursor, larger HA particles with higher crystallinity were produced, while Ca progenitor increased nucleation rate and created amorphous particles with smaller size. These findings were further confirmed by Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis. Moreover, starting with P precursors shifted the index plasmon peak of Ag to the higher wavelengths (500–550 nm), providing a higher tendency to release Ag+ ions and in vitro antibacterial activity at concentration of 800 μg/mL. As a result, this study proved that HA/Ag particles could be synthesised from P precursor with better phase structure and antibacterial activity, developed for biomedical applications especially as a biomimetic coating of bone implants.

Non-isothermal crystallization kinetics of Ge-Cu-Te thin films for phase-change memory

We investigated the crystallization kinetics of Ge-Cu-Te ternary system phase-change thin films using non-isothermal differential scanning calorimetry and estimated the kinetic triplet (activation energy, pre-exponential factor, and reaction model) by the combined application of isoconversional and model-fitting approaches at different heating rates over a range of 10–40 K/min for GeCu2Te2 thin films. The results indicate a multi-step crystallization process where the activation energy of crystallization is not constant but decreases via three recognizable stages with crystallization fraction α. The local Avrami exponents suggest that two crystallization mechanisms containing three-dimensional growth with increasing nucleation rates in the range of crystallization fraction α ≤ 0.4 and three- and two-dimensional growths at a decreasing nucleation rate over the wide range of α > 0.4 are responsible for the whole crystallization process. Furthermore, the reaction model displays dependence on the heating rates for the GeCu2Te2 thin films, where heating rates of 10–30 K/min drive a second-order reaction while a three-halve order reaction occurs for a heating rate of 40 K/min, which is different from the second-order reaction for the GeCu2Te3 thin films. Also, both GeCu2Te2 and GeCu2Te3 thin films provide better data retention capability than the Ge2Sb2Te5 thin films without sacrificing the crystallization time. The results indicate that Ge-Cu-Te ternary system thin films have great potentiality in phase-change memory applications.

Heterogeneous Nucleation of Butanol on NaCl: A Computational Study of Temperature, Humidity, Seed Charge, and Seed Size Effects.

Using a combination of quantum chemistry and cluster size distribution dynamics, we study the heterogeneous nucleation of n-butanol and water onto sodium chloride (NaCl)10 seeds at different butanol saturation ratios and relative humidities. We also investigate how the heterogeneous nucleation of butanol is affected by the seed size through comparing (NaCl)5, (NaCl)10, and (NaCl)25 seeds and by seed electrical charge through comparing (Na10Cl9)+, (NaCl)10, and (Na9Cl10)− seeds. Butanol is a common working fluid for condensation particle counters used in atmospheric aerosol studies, and NaCl seeds are frequently used for calibration purposes and as model systems, for example, sea spray aerosol. In general, our simulations reproduce the experimentally observed trends for the NaCl–BuOH–H2O system, such as the increase of nucleation rate with relative humidity and with temperature (at constant supersaturation of butanol). Our results also provide molecular-level insights into the vapor–seed interactions driving the first steps of the heterogeneous nucleation process. The main purpose of this work is to show that theoretical studies can provide molecular understanding of initial steps of heterogeneous nucleation and that it is possible to find cost-effective yet accurate-enough combinations of methods for configurational sampling and energy evaluation to successfully model heterogeneous nucleation of multicomponent systems. In the future, we anticipate that such simulations can also be extended to chemically more complex seeds.

Effect of Nb minor addition on the crystallization kinetics of Zr-Cu-Al-Ni metallic glass

The crystallization kinetics of Zr55Cu30Al10Ni5 and (Zr55Cu30Al10Ni5)98Nb2 melt-spun metallic glasses in non-isothermal and isothermal conditions were studied by differential scanning calorimetry. According to the non-isothermal and isothermal conditions, the crystallization activation energy for the Nb-containing sample is lower than the Nb-free sample, suggesting that crystallization transformation becomes easier by Nb microalloying. The time-temperature-transformation (TTT) diagrams demonstrate that the Nb minor addition delays the onset of crystallization by shifting the incubation time to longer times, but then accelerates the crystallization progress by shortening the endset time of crystallization, yielding a narrower crystallization transformation region. The Avrami exponents for both non-isothermal and isothermal conditions have larger values in Nb-containing sample, revealing increased nucleation rates in this glassy alloy. In the isothermal condition, the Avrami exponent values in both alloys are either above or below 2.5, indicating that the governing crystallization mechanism is diffusion-controlled three-dimensional growth with either decreasing or increasing nucleation rate.

Isothermal and non-isothermal crystallization kinetics of novel metalloid-bearing light rare-earth-based La64Al26Ga4C6 metallic glass with high thermal stability

The crystallization kinetics of a novel metalloid-bearing light rare-earth (RE)-based La64Al26Ga4C6 metallic glass (MG) under isothermal and non-isothermal conditions were systematically researched by Johnson-Mehl-Avrami (JMA), Arrhenius, Kissinger, Ozawa, Kissinger-Akahira-Sunose and Ozawa-Flynn-Wall approaches using differential scanning calorimeter. The present MG possesses higher thermal stability than other light RE-based MGs without metalloid. As the isothermal crystallization temperature increases, the Avrami exponent estimated by JMA equation ranges from 2.36 to 2.94, implying that the isothermal crystallization mechanism varies from a three-dimensional diffusion-governed growth with a decreasing nucleation rate to a three-dimensional diffusion-governed growth with an increasing nucleation rate. Meanwhile, the apparent activation energy determined by Kissinger and Ozawa methods for characteristic temperatures indicates that glass transition is more difficult than crystallization process. Additionally, the local Avrami exponents show various trends, implying a transformable crystallization mechanism with crystallization proceeding. Furthermore, the crystallization process becomes easier due to the decrease of local activation energy.

Time-Controlling the Latent Heat Release of Fatty Acids using Static Electric Field

Latent heat released during freezing of phase change material (PCM), which occurs at a constant temperature, can be modified using an electric field, through a process called electrofreezing. To date, the effects of the electric field on the freezing of salt solutions or salt hydrates of inorganic PCM, such as reduction of the supercooling degree, increase of nucleation rate, and reduction of the induction time due to changes in the Gibbs free energy, have been the focus. In this paper, we describe the electrofreezing of stearic acid and lauric acid of fatty acid PCM. Because common organic PCM has relatively small or even zero supercooling, the effect of the DC electric field on the time of latent heat release at a constant temperature and crystallization time was more pronounced. A comparison was also done with inorganic CaCl2⋅6H2O PCM using previously published data. We propose that the two time parameters are closely related to the electrical and thermal conductivities. Different nucleation mechanisms for fatty acids and CaCl2⋅6H2O with interactions between the crystalline sample and electric field, as well as dissimilar Joule heating effects, have been proposed. Changes in the chemical structure and thermal stability due to electric field treatment are evaluated using the Fourier-transform infrared spectra, the decomposition and melting temperatures, and the calculation of the latent heat of fusion. We also discuss the potential applications of lauric and stearic acids as phase change composites in thermoresponsive devices for high electrical to thermal energy conversion efficiencies.