Latent Heat Of Crystallization Research Articles

Form-stable Na2CO3-NaCl/mullite phase change composite with SiC enhanced thermal conductivity for high temperature thermal storage

High-temperature energy storage technologies are gaining prominence to meet the needs of concentrating solar power plants and industrial waste heat recovery. In this study a series of form-stable phase change materials are prepared by a simple and efficient cold compression sintering method. In this method, Na2CO3-NaCl will be mixed with mullite ceramic powder; simultaneously, SiC nanoparticles are introduced to improve the thermal conductivity of the material. The leakage, microstructure, chemical compatibility and thermal physical properties of the prepared composites are systematically analyzed using Fourier-transform infrared spectroscopy, X-ray powder diffraction, Scanning electron microscope, Differential Scanning Calorimetry and Thermogravimetric. The results of the study show that good chemical compatibility of the components in the composites, and the latent heat of melting of the encapsulated composites as well as the sample with added SiC are 266.97 J/g and 217.63 J/g, respectively, while the latent heat of crystallization is 197.37 J/g and 151.13 J/g, respectively. Compared to the thermal conductivity of PCMs (0.41 W/(m·K)), the thermal conductivity of the sample with 20 % SiC added is 1.83 W/(m·K), an increase of 8.7 times. Thermal cycling and reliability tests show that even after 300 cycles, good chemical compatibility is maintained between the components in composites, and the phase change properties and quality remain stable. In addition, the thermal storage cost of FSPCM-M40-S20 is 1.90 $/MJ. Therefore, we believe that the prepared Na2CO3-NaCl/mullite/SiC FSPCM has promising applications in high-temperature thermal energy storage, especially in solar power generation and industrial waste heat recovery.

Mesoscale simulations of spherulite growth during isothermal crystallization of polymer melts via an enhanced 3D phase-field model

A finite difference-based 3D phase-field model is developed to investigate the spherulite growth at the mesoscopic scale during the isothermal crystallization of polyamide (PA) 12. The model introduces a phase-field variable to distinguish the crystalline and amorphous phases of polymers. The phase-field evolution equation is coupled with the heat conduction equation that considers the latent heat of crystallization. The evolution equations introduce both the dimensionless diffusivity and latent heat that are dependent on the crystallization temperature. A high-order finite difference-based numerical framework is applied to the phase-field model. Both the qualitative simulation results of the phase-field model such as the crystal morphologies and the quantitative results including the radial crystal growth rate, degree of crystallinity, and lamellar thickness are validated against experiments. The simulation for single-crystal growth shows that a high crystallization temperature results in a large crystal with a slow radial growth rate. The simulation for multi-crystal growth shows that the crystals impinge on each other and finally fill the whole domain during crystallization, which further demonstrates the capability of the model in simulating the spherulite growth during isothermal crystallization of polymer melts.

Hexadecylamine@silica nanocapsule with excellent operational reliability for thermal energy storage

Hexadecylamine (HDA) was in situ encapsulated into SiO2 nanoshells, to obtain the HDA@SiO2 nanocapsule with excellent thermal reliability during the process of energy release/storage. Closed-pore structured HDA@SiO2 nanocapsule was successfully synthesized. The latent heats of crystallization and melting for HDA@SiO2 nanocapsule are 189.3 and 193.8 Jg−1, with the 91.2 wt% encapsulated HDA in the nanocapsule. The crystallization and melting temperatures (TC and TM) are 33.34 °C and 49.53 °C for HDA@SiO2 nanocapsule, respectively. After undergoing 200 thermal cycles, the latent heats of HDA@SiO2 nanocapsule decreased by 0.16% and 0.46% with the unchanged phase transition temperature, indicating HDA@SiO2 nanocapsule has superior operational reliability. Moreover, the thermal conductivity of HDA@SiO2 is 0.13 Wm−1K−1, an approximately 20% improvement over that of pure HDA. The temperature of degradation and evaporation of HDA@SiO2 nanocapsule was increased by more than 10 °C compared with that of bulk HDA. The HDA@SiO2 nanocapsule exploited in this work exhibits excellent operational reliability and high latent heat during the process of energy release/storage, which makes it more suitable and competitive in the recycling and utilization of thermal and solar energy.

Understanding the textures of Apollo 11 high‐Ti mare basalts: A quantitative petrographic approach

AbstractThis paper represents a comprehensive crystal size distribution (CSD) study of ilmenite and plagioclase from 12 Apollo 11 basalts from four of the five compositional groups (Groups A, B1, B2, B3, and one unclassified basalt—Group “U” basalt 10062). Ilmenite was saturated in the magma at/before eruption, resulting in subsurface growth of phenocrysts (Group B1) and many small crystals upon eruption. Plagioclase always exhibits linear CSDs representing a single cooling regime in each sample, which is interpreted as crystallizing within isolated magma pockets late in the cooling of the erupted lava flow. Latent heat of crystallization and insulating effects of crystallized phases produced slower cooling and lower plagioclase nucleation densities. Exceptions are the Group B2 and B3 basalts, indicating relatively earlier crystallization of plagioclase on the lunar surface. Our study demonstrates that textures of the Apollo 11 basalts are a product of the interplay among cooling rate, bulk composition, and nucleation density during crystallization. Group A basalts have the highest cooling rates compared to the other Apollo 11 samples (except 10072,53), and were erupted through high effusion rates producing thick flows that underwent extended cooling that induced textural coarsening in both early crystallizing ilmenite and late‐stage plagioclase. Group B1 lavas had the lowest effusion rates producing the thinnest flows. The Groups B2, B3, and U basalts are intermediate between these end members. Our approach can be used to define eruption environment, crystallization sequence, and cooling rate of samples collected on the Moon from non‐bedrock sources.

Effect of MgO Content on Heat Capacity of Synthetic BF Slag and Heat Release Behavior during Cooling Process

The differential scanning calorimetry (DSC) sapphire analysis was used to measure the specific heat capacity of the BF (BF) slag and observe the CaO-SiO2-MgO-Al2O3-TiO2 5-element slag system with the binary basicity fixed at 1.17. The specific heat capacity of the BF slag and the cooling heat distribution were obtained during the cooling process when the MgO content changing from 7% to 11%. The results showed that the heat released of BF slag was more than 1.2 GJ/ton during the cooling process from 1400 °C to 35 °C, of which the sensible heat was dominant. At MgO content of 9%, the latent heat of crystallization is maximum. The cooling and heat release law of BF slag is directly associated with the phase precipitated in slag cooling and micromorphology.

Application of 3D Balanced Growth Theory to the Formation of Bulk Amorphous Alloys

Since the emergence of amorphous alloys as a new class of materials, efficiency improvements have been made in optimizing the fabrication process, the mechanization of alloy formation, and the size of the alloys themselves. Amorphous alloys have been used in precision instruments as they possess excellent magnetic properties, corrosion resistance, wear resistance, high strength, hardness, toughness, high electrical resistivity, and electromechanical coupling properties. Because their hysteresis losses are lower than those of traditional transformer cores, the conversion efficiency of equipment has been significantly improved, thereby saving energy and protecting the environment. Hence, amorphous iron cores have replaced traditional materials. Amorphous alloys also show excellent performance as anti-corrosion and wear-resistant coatings. The process of preparing amorphous alloys starts with an amorphous alloy film obtained by evaporation deposition and then proceeds to the use of a high cooling rate ribbon spinning method to finally obtain a thin strip of an amorphous alloy. A widely used method of copper mold suction casting is then used to prepare the bulk amorphous alloy. The sizes of amorphous alloys have been continually increasing, which has resulted in increasingly serious challenges, such as cooling rate and thermal stability limitations. In addition, crystals can form at low cooling rates. The latent heat of crystallization is released when crystals are formed, which causes damage to the amorphous area so that the size of amorphous alloys is reduced. Because of these difficulties, new processes that eliminate the cooling rate gradient, such as 3D additive manufacturing, ultrasonic production, and mold design, combined with the concept of “entropy control” component design and the economic theory of “balanced development,” lead to a three-dimensional bulk amorphous alloy being proposed. The theory of balanced growth provides a new concept for the development and application of bulk amorphous alloys. This review offers a retrospective view of recent studies of amorphous alloys and provides a description of the formation of amorphous alloys and amorphous phases and the criteria required to predict the successful formation of amorphous alloys. Then, we address the problem of size limitation confronting current production methods. The three-dimensional balanced growth theory of bulk amorphous alloys was formulated from a flexible adaptation of the balanced growth theory of economics. We have confidence that the production and development of bulk amorphous alloys have a bright future.

A numerical model for the magmatic heat reservoir of the Las Tres Virgenes volcanic complex, Baja California Sur, Mexico

Numerical models of geothermal systems have achieved considerable progress when dealing with fundamental transport processes. Site-specific geothermal models however, often face the lack of sufficient field data, which leads to under constrained models. Recent field studies in the Las Tres Virgenes volcanic complex (TVVC) provide us with a sound framework to build a numerical model for the magmatic heat reservoir of the geothermal area. Here we present a conceptual model of the system from 30 ka to present based on updated structural and geochronological studies. The heat reservoir is described from Enhanced Seismic Tomography of the TVVC. New field data also allow an estimate of the radiogenic heat generation in the batholith of the study area. Latent heat of crystallization is also considered in the cooling of magmatic intrusions. The transient heat transfer equation is solved with a finite volume numerical method and a conjugate gradient algorithm. The model is calibrated using the estimated heat flow in the area from the literature. The simulation results predict slow cooling of the heat reservoir, with the maximum temperature decreasing about 9 °C in 30 ky. The temperature field within the magmatic heat reservoir overall remains between about 790 °C (8 km bsl) and 300 °C (3 km bsl), in the order of the temperatures at which magmatic processes, such as magma mixing and replenishments, have been inferred from the eruptive history. Whereas the phase ratio (solid/melt) ranges from 1, at the top, to below 0.1 at the bottom of the heat reservoir. Convective transport and explicit thermal-chemical coupling in the heat reservoir is proposed as a future expansion of this work.

Моделирование кристаллизации модифицированного наноразмерными частицами расплава при лазерной обработке поверхности металла

A 2D mathematical model is proposed for the modification of an iron-based alloy with refractory nanosized particles. Numerical simulation of the processes during the modification of the surface layer of the substrate metal using the energy of a laser pulse has been carried out. Within the framework of the proposed model, the processes of heating and melting of metal on a substrate covered with a layer of nanosized refractory particles penetrating into the molten metal, convective heat transfer in the melt, and solidification after the end of the pulse are considered. Metal melting is considered in the Stefan approximation, and when the melt is cooled, the model of heterogeneous nucleation and subsequent crystallization is used. The fluid flow is described by the Navier-Stokes equations in the Boussinesq approximation. The distribution of nanoparticles in the melt is modeled by moving markers. Based on the results of calculations, the mode of pulsed laser action is determined, in which a flow is formed for a homogeneous distribution of particles of the modifying substance in the presence of a surfactant in the metal. The volume of the solid phase formed around the nucleus determines the size of the grain structure in the solidified alloy. The liquidus temperature changes depending on the concentration of dissolved carbon in the melt. In the numerical simulation of the solidification of the surface layer of the metal, it was found that the conditions of nucleation and crystallization differ significantly in the volume of the melt. It is determined that the duration of nucleation in a supercooled melt is several tens of microseconds. The maximum number of crystallization centers occurs in areas where heat removal occurs most rapidly. With the growth of the solid phase in the melt and the release of the latent heat of crystallization, the value of supercooling decreases, the nucleation stops and the number of formed crystallization centers does not change further. The distribution of the dispersion of the crystal structure over the volume of the melted metal is estimated. It was found that as the melt cools, sequential-volume crystallization occurs.

Heat transfer and its effect on growth behaviors of crystal layers during static layer melt crystallization

The growth behaviors of crystal layers during static layer melt crystallization was studied from the perspectives of morphology structure, growth rates and temperature evolution. The temperature distributions of the melt and crystal layer were deduced. With these results, the heat transfer during crystallization was analyzed by considering the relative influences of natural convection, heat conduction in the melt and latent heat of crystallization. A model correlating growth rate with physical and experimental parameters was derived based on energy conservation. Effective thermal conductivity of crystal layers was evaluated. It was confirmed that the structure and density of the crystal layer can significantly affect the thermal conductivity. According to the temperature curves of melt, the static layer melt crystallization process in a tubular crystallizer can be divided into four stages as nucleation stage, fast growth stage, slow growth stage and steady state stage.

Experiments to understand crystallization of levitated high temperature silicate melt droplets under low vacuum conditions

We report experiments on crystallization of highly undercooled forsterite melt droplets under atmospheric and sub-atmospheric pressure conditions. Experiments have been conducted under non-contact conditions using the principles of aero-dynamic levitation. Real time dynamics of solidification, along with the transient evolution of surface textures, have been recorded using high speed camera for three cooling rates. These images have been matched with the time-tagged temperature data to understand the effect of pressure conditions and cooling rates on the crystallization dynamics. Compared to normal pressure, relatively higher levels of undercooling could be achieved under sub-atmospheric conditions. Results showed a strong dependence of surface textures on pressure conditions. For any externally employed cooling rate, relatively small length scale morphological textures were observed under sub-atmospheric conditions, in comparison to those achieved under ambient conditions. The observed trends have been explained on the basis of influence of pressure conditions on recalescence phenomenon and the rate at which latent heat of crystallization gets dissipated from the volume of the molten droplet. Sub-atmospheric experiments have also been performed to reproduce one of the classical chondrule textures, namely the rim + dendrite double structure. Possible formation conditions of this double structure have been discussed vis-à-vis those reported in the limited literature. To the best of our knowledge, the reported study is one of the first attempts to reproduce chondrules-like textures from highly undercooled forsterite melt droplets under sub-atmospheric non-contact conditions.

Thermal performance of galactitol/mannitol eutectic mixture/expanded graphite composite as phase change material for thermal energy harvesting

The eutectic mixture of galactitol and mannitol with the melting point of 157.6 °C and high latent heat of fusion (ΔHm=271.07 kJ/kg) is regarded as an ideal phase change material used in medium temperatures. However, the shortcomings of low thermal conductivity and severe supercooling restrict its application for thermal energy storage. To address these challenges, expanded graphite (EG) was introduced to obtain eutectic mixture/EG composites by vacuum impregnation method. SEM images showed that the pores of EG were filled by sugar alcohols and no chemical reaction happened during this process as confirmed by FTIR spectroscopy and XRD. The thermophysical properties of phase change material (PCM) composites were measured. The result revealed that the supercooling degree (Tsc) of PCM composites decreased more than 26.2% compared to that of the eutectic mixture. Although the ΔHm of PCM composites decreased with an increase in content of EG, most of them are higher than 200 kJ/kg. Unlikely the ΔHm of PCM composites, the latent heat of crystallization (ΔHc) first rose by 15.3% and then dropped slightly. Their thermal conductivities were greatly improved by EG, especially with a 14 wt.% EG loading producing a more than 30-fold increase. Also, the PCM composite with 14 wt.% EG loading shows great form stability and thermal reliability after 20 charging-discharging cycles. These results prove that galactitol/mannitol eutectic mixture/EG composite has a promising prospect in potential for thermal energy harvesting and thermal management systems application.

The 100 pc White Dwarf Sample in the SDSS Footprint

Abstract We present follow-up spectroscopy of 711 white dwarfs within 100 pc, and we present a detailed model atmosphere analysis of the 100 pc white dwarf sample in the Sloan Digital Sky Survey footprint. Our spectroscopic follow-up is complete for 83% of the white dwarfs hotter than 6000 K, where the atmospheric composition can be constrained reliably. We identify 1508 DA white dwarfs with pure hydrogen atmospheres. The DA mass distribution has an extremely narrow peak at 0.59 M ⊙ and reveals a shoulder from relatively massive white dwarfs with M = 0.7–0.9 M ⊙. Comparing this distribution with binary population synthesis models, we find that the contribution from single stars that form through mergers cannot explain the overabundance of massive white dwarfs. In addition, the mass distribution of cool DAs shows a near absence of M > 1 M ⊙ white dwarfs. The pile-up of 0.7–0.9 M ⊙ and the disappearance of M > 1 M ⊙ white dwarfs is consistent with the effects of core crystallization. Even though the evolutionary models predict the location of the pile-up correctly, the delay from the latent heat of crystallization by itself is insufficient to create a significant pile-up, and additional cooling delays from related effects like phase separation are necessary. We also discuss the population of infrared-faint (ultracool) white dwarfs and demonstrate for the first time the existence of a well-defined sequence in color and magnitude. Curiously, this sequence is connected to a region in the color–magnitude diagrams where the number of white dwarfs with a helium-dominated atmosphere is low. This suggests that the infrared-faint white dwarfs likely have mixed H/He atmospheres.

Melting and refreezing of zirconium observed using ultrafast x-ray diffraction

This paper studies zirconium subjected to high pressure conditions. Using x-ray diffraction, the authors observe the onset of melting at short times after shocking, and refreeze shortly thereafter. The latent heat of crystallization is found to provide the energy for the recrystallization process

Effect of Ca modification on the elemental composition, microstructure and tensile properties of Al-7Si-0.3Mg alloy

The effect of Ca addition on the elemental composition, microstructure, Brinell hardness and tensile properties of Al-7Si-0.3Mg alloy were investigated. The residual content of Ca in the alloy linearly increased with the amount of Ca added to the melt. The optimal microstructure and properties were obtained by adding 0.06wt% Ca to Al-7Si-0.3Mg alloy. The secondary dendrite arm spacing (SDAS) of the primary α phase decreased from 44.41 μm to 19.4 μm, and the eutectic Si changed from coarse plates to fine coral. The length of the Fe-rich phase (β-Al5FeSi) decreased from 30.2 μm to 3.8 um, and the Brinell hardness can reach to 66.9. The ultimate tensile strength, yield strength, and elongation of the resulting alloy increased from 159.5 MPa, 79 MPa, and 2.5% to 212 MPa, 86.5 MPa, and 4.5%, respectively. The addition of Ca can effectively refine the primary α phase and modify the eutectic Si phase, likely because Ca enrichment at the front of the solid-liquid interface led to undercooling of the alloy, reduced the growth rate of the primary α phase, and refined the grain size. Also, it could increase the latent heat of crystallization, undercooling, and the nucleation rate of eutectic Si, which was beneficial to the improvement of the morphology of eutectic Si.

Influence of the relative dimensions of the cavity on the conjugate convective heat transfer and on the shape of crystallization fronts in the method of Horizontal Directed Crystallization

The process of water crystallization in rectangular cavities is numerically studied. The liquid being studied is water having an inverse temperature dependence of the density. Calculations were carried out with a suddenly cooled vertical wall of a rectangular cavity. The initial temperature of the melt is maintained on the opposite wall. The finite element method was used to solve a system of equations for the nonstationary free convection of a melt, taking into account the dependence of the density on temperature. The heat conduction equation in the solidified substance was also solved. The problems were solved in a conjugate formulation taking into account the release of the latent heat of crystallization at the liquid-solid interface.

Effect of Re addition on the crystallization, heat treatment and structure of the Cu\u2013Ni\u2013Si-Cr alloy

For determination of the structure and properties of those alloys, the following investigations were carried out: scanning microscopy and EDS X-ray analysis. Investigations concerning the optimal chemical composition and production method of Cu–Ni–Si alloys modified by Cr and Re as well as the improved properties in comparison with traditional alloys contribute to better understanding of mechanisms influencing the improvement of mechanical properties of the newly developed alloys. Thermal analysis of the crystallization process allows for accurate calculation of latent heat of various phases developed during solidification. Based on the assumption that the latent crystallization heat is proportional to the share of various phases in the alloy, the thermo-derivative analysis also allows the calculation of the amount of crystallized phases. Calculation of the properties as mentioned earlier is based on the characteristic points determined in a derivative curve. The adequately selected chemical composition of the alloy, as well as the appropriate cooling rate and heat treatment conditions, leads to improvement of functional properties of manufactured elements. For the analysed alloys, a thermal derivative analysis was used to determine the kinetics of crystallization and the temperature of the beginning and the end of a phase and eutectic crystallization, mainly the liquidus temperature (TL) and solidus temperature (TSOL). The TSOL temperature determined on thermal derivative analysis is the upper limit of supersaturation of the tested alloys. The conductivity and microhardness of the tested alloys were also measured in the function of the chemical composition and the state (i.e., heat treatment).

Core melt temperature effects on cylindritic structures of co-injection molded polypropylene parts

The co-injection process offers the inherent flexibility to use the optimal properties of each material to reduce the material cost and part weight. The micro structural characteristic of co-injection molded isotactic polypropylene (iPP) products is given. Polarized light microscopy (PLM) is used for comparison co-injection molded products' microstructure of different locations (near gate, middle location, and core melt flow front) and different core melt temperatures. It is shown that a cylindritic layer occurs on the boundary of the skin and core components or the mold-skin melt interface at middle and far gate locations along filling direction. The relations between processing parameters and cylindritic structures formation are discussed by numerical simulated temperature field which considering the latent heat of crystallization. Furthermore, the energy per unit volume is used as a parameter to indicate the formation of cylindritic structure. It is found that the energy of cylindritic structures almost in the range of [39, 108] J/m3 under the given process parameters.

Microstructures formation, distribution of tin element and properties of CuSn10P1 alloy during controlled by melt cooling

In this paper, the CuSn10P1 alloy controlled by melt cooling stage was carried out through the enclose cooling slope channel (ECSC for short) and similar isothermal collection of crucible, meanwhile the microstructure element distribution of CuSn10P1 alloy were studied. The result shows that the liquid metal quickly cools down to the solid-liquid temperature range under the chilling effect of slit cooling channel. The primary phase rapid nucleation and growth, the distribution characteristic of the tin mass fraction of the core is lower and the outer ring is higher. The preheating crucible was used to collect the slurry which prepared by the ECSC, the latent heat of crystallization and volume temperature effect were used to carry out short-time similar isothermal treatment. With the process of similar isothermal treatment, the primary phase is aged and changes to the spherical shape, while the tin element diffuses into the primary phase from the liquid. The semi-solid slurry with the above-mentioned microstructure feature was subjected to squeeze casting to obtain shaft sleeve parts. The ultimate tensile strength and elongation of the shaft sleeve parts increased by 22% and 93%, respectively, compared with the liquid squeeze casting. This is attributed to the grain refinement and homogeneity of macroscopic concentration distribution of tin elements in CuSn10P1 alloy.

A 3D phase-field model for simulating the crystal growth of semi-crystalline polymers

In this study a 3D phase-field model, which is a generalization of the 2D phase-field model we ever presented, has been established for investigating the crystal growth of semi-crystalline polymers. By coupling a non-conserved crystal order parameter with a temperature field which is generated by latent heat of crystallization, our developed model can obtain its model parameters from real material parameters. Unlike the model of metals and small molecular compounds, this model has considered the partial crystallization property of semi-crystalline polymers. Moreover, due to the long-chain molecular structure, polymer crystallizations usually exhibit complex anisotropy and have polymorphous nature. In order to account for the various anisotropy of interfacial energy in 3D, three anisotropic functions for describing the anisotropic interfacial growth patterns are deduced phenomenologically which are based on a number of existing experimental facts. Simulation results have preliminarily demonstrated the good performance of our phase-field model in reproducing the complex and diverse morphology of semi-crystalline polymers in 3D. Several kinds of crystal patterns, which have been observed in experiments, can be reproduced.

Mineral growth in melt conduits as a mechanism for igneous layering in shallow arc plutons: mineral chemistry of Fisher Lake orbicules and comb layers (Sierra Nevada, USA)

Different processes have been proposed to explain the variety of igneous layering in plutonic rocks. To constrain the mechanisms of emplacement and crystallization of ascending magma batches in shallow plutons, we have studied comb layers and orbicules from the Fisher Lake Pluton, Northern Sierra Nevada. Through a detailed study of the mineralogy and bulk chemistry of 70 individual layers, we show that comb layers and orbicule rims show no evidence of forming through a self-organizing, oscillatory crystallization process, but represent crystallization fronts resulting from in situ crystallization and extraction of evolved melt fractions during decompression-driven crystallization, forming a plagioclase-dominated cres-cumulate at the mm- to m-scale. We propose that the crystal content of the melt and the dynamics of the magmatic system control the mechanisms responsible for vertical igneous layering in shallow reservoirs. As comb layers crystallize on wall rocks, the higher thermal gradients will increase the diversity of comb layering, expressed by inefficient melt extraction, thereby forming amphibole comb layers and trapped apatite + quartz saturated evolved melt fractions. High-An plagioclase (An90–An97.5) is a widespread phase in Fisher lake comb layers and orbicule rims. We show that a combination of cooling rate, latent heat of crystallization and pressure variations may account for high-An plagioclase in shallow melt extraction zones.