Onset Of Crystallization Research Articles

Non-isothermal crystallisation behaviour of a Cr–Fe–Ni–Co–Mo–Si amorphous coating

The kinetics and mechanism of crystallisation of a Cr–Fe–Ni–Co–Mo–Si amorphous coating were studied using differential scanning calorimetry, owing to its relatively complex crystallisation behaviour. The premise of the production and application of amorphous materials is to understand the crystallization process of amorphous materials. It is closely related to the thermal stability of materials. Thermal stability is an important parameter to determine the effective working limit of materials. This study provides significant guidance for obtaining amorphous materials with excellent performance by controlling the crystallisation process and predicting the crystallisation failure of the coating in service. In the non-isothermal crystallisation process, results showed that the apparent activation energy (Ex) corresponding to the temperature of the onset of crystallisation was greater than those corresponding to the glass transition (Eg) and peak crystallisation (Ep) temperatures; Ex, Eg, and Ep were calculated using the Kissinger and Ozawa methods. This finding revealed that for the amorphous coating, the nucleation process was more difficult than overcoming the energy barrier for the rearrangement of atoms and the grain growth process of crystallisation. The relational plots between the local activation energy and crystallisation volume fraction under non-isothermal conditions illustrated that the crystallisation process of the amorphous coating was initially difficult but became easy in the succeeding stages. The kinetic fragility indices calculated by the Angell’s method and DA equation were 16.75 and 16.42, respectively; the results suggested that the Cr–Fe–Ni–Co–Mo–Si amorphous coating was a ‘strong material’. Furthermore, the two kinetic fragility indices indicate the good glass forming ability and thermal stability of the Cr–Fe–Ni–Co–Mo–Si amorphous coating.

Investigation of Crystallization and Relaxation Effects in Coarse-Grained Polyethylene Systems after Uniaxial Stretching.

In this study, we investigate the thermo-mechanical relaxation and crystallization behavior of polyethylene using mesoscale molecular dynamics simulations. Our models specifically mimic constraints that occur in real-life polymer processing: After strong uniaxial stretching of the melt, we quench and release the polymer chains at different loading conditions. These conditions allow for free or hindered shrinkage, respectively. We present the shrinkage and swelling behavior as well as the crystallization kinetics over up to 600 ns simulation time. We are able to precisely evaluate how the interplay of chain length, temperature, local entanglements and orientation of chain segments influences crystallization and relaxation behavior. From our models, we determine the temperature dependent crystallization rate of polyethylene, including crystallization onset temperature.

Facile Production of Graphene/Polypropylene Composites with Enhanced Electrical and Thermal Properties through In Situ Artificial Latex Preparation

In order to obtain the unique properties of graphene-based composites, to realize homogeneous dispersion of graphene throughout the polymer matrix remains the key challenge. In this work, edge-oxidized graphene/polypropylene (EOGr/PP) composites with well-dispersed EOGr in PP matrix, synchronously exhibiting high electrical conductivity and thermal property, were simply fabricated for the first time using a novel strategy by in situ artificial PP latex preparation in the presence of EOGr based on solution-emulsification technique. The good dispersion state of EOGr in the PP matrix was demonstrated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). A blue shift in Raman G peak of the EOGr nanosheets was observed in the EOGr/PP composites, indicating the strong interactions between the EOGr nanosheets and the PP matrix. The onset crystallization and crystallization peak temperatures increased as the EOGr loading increases due to its good nucleating ability. An improved thermal stability of EOGr/PP composites was observed as evaluated by TGA. The EOGr/PP composites showed an insulator-to-conductor percolation transition in between that of 1 and 2 wt% EOGr content. Such strategy provides a very effective pathway to fabricate high-performance nonpolar polymer/graphene composites with excellent dispersion state of graphene.

The gallium isotopic composition of the Moon

In this study, we present new Ga isotope data from a suite of 28 mare basalts and lunar highland rocks. The δ71Ga values of these samples range from -0.10 to +0.66‰ (where δ71Ga is the relative difference between the 71Ga/69Ga ratio of a sample and the Ga-IPGP standard), which is an order of magnitude more heterogeneous than δ71Ga values in terrestrial magmatic rocks. The cause of this isotopic heterogeneity must be established to estimate the bulk δ71Ga value of the Moon. In general, low-Ti basalts and ferroan anorthosite suite (FAS) rocks have δ71Ga values that are lower than high-Ti basalts and KREEP-rich rocks. The observation that rocks derived from later forming LMO cumulates have higher δ71Ga values suggests that Ga isotopes are fractionated by processes that operate within the chemically evolving LMO, rather than localized degassing or volatile redistribution.Correlations between indices of plagioclase removal from the LMO (e.g. Eu/Eu*) with Ga isotope ratios suggest that a Δ71Gaplagioclase-melt of -0.3‰, (where Δ71Gaplagioclase-melt is the isotopic fractionation associated with crystallization of plagioclase from a melt), could drive the observed isotopic fractionation in high-Ti mare basalts and KREEP-rich rocks. This would be consistent with the observation that FAS rocks have δ71Ga values that are lower than mare basalts. However, the addition of KREEP-like material into the mare basalt source regions would not contribute enough Ga to perturb the isotopic composition outside of analytical uncertainty. Thus, basalts derived from early formed LMO cumulates such as those from Apollo 15, would preserve light Ga isotopic compositions despite containing modest amounts of urKREEP.We estimate that the δ71Ga value of the LMO was ∼0.14‰ prior to the onset of plagioclase crystallization and extraction. Whether this δ71Ga value is representative of the initial BSM cannot be ascertained from the current dataset. It remains plausible that the Moon accreted with a heavier Ga isotopic composition than the Earth. Alternatively, the Moon and Earth could have accreted with similar isotopic compositions (BSE = 0.00 ± 0.06‰, Kato et al., 2017) and volatile loss drove the LMO to higher δ71Ga values prior to formation of the lunar crust.

Asymptotically Justified Boundary Conditions for a Viscoelastic Two‐Phase Fiber Model

AbstractIn this work we present asymptotically justified boundary/interface conditions for a viscoelastic two‐phase fiber model with flow‐enhanced crystallization. While the model equations are well‐established in the literature, the choice of boundary conditions is still under discussion as they might cause artificial layering at the crystallization onset. We show that our conditions avoid such layering, yielding a regularly perturbed boundary value problem with either continuous or discontiunous interface.

The effect of nitrogen (III) oxide on direct synthesis of concentrated nitric acid

The effect of nitrogen (III) oxide on the process of dinitrogen tetroxide separation in a dephlegmator during preparation of a "crude mixture" (HNO3–N2O4–N2O3–NO2–NO–H2O) in the production of concentrated nitric acid by direct synthesis was studied in this work. The dependence of crystallization onset on the composition of the N2O4–N2O3 mixture and temperature was determined. The refrigerant capable of maintaining the optimal temperature of the N2O4 extraction was suggested. The absence of nitrogen (III) oxide and nitrogen (I) oxide in the autoclave acid was confirmed.

Determination of the temperature-dependent optical properties of amorphous silicon films at elevated temperatures

The temperature-dependent optical properties of PECVD deposited amorphous silicon films are determined for radiation wavelengths of 1000 nm up to 2000 nm in a temperature range of up to 1110 K. The measurements are performed at heating rates of over 2300 K/s in order to shift the onset of solid-phase crystallization of the amorphous material to temperatures above 1110 K and to make the optical properties of amorphous silicon accessible for examination. In this work, the laser-based measurement setup, the experimental procedure, the simulation methods, and the resulting material-specific data are shown.

Molecular Dynamics and Kinetics of Isothermal Cold Crystallization in the Chiral Smectogenic 3F7FPhH6 Glassformer

An investigation of the glass transition of the antiferroelectric smectic CA* phase and cold crystallization of (S)-4′-(1-methylheptylcarbonyl)biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluoro- butoxy)heptyl-1-oxy]benzoate (denoted as 3F7FPhH6) by differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy is presented. The fragility index mf = 72, classifying 3F7FPhH6 as a glassformer with intermediate fragility, was obtained from the temperature dependence of the α-process relaxation time, measured upon cooling. Duplication of the α-process was observed exclusively upon heating, before the onset of cold crystallization, and is connected with the pre-transitional effect. The presence of two crystal phases likely influences the kinetics of cold crystallization; the idea stems from a comparison with previous results for the 3F7HPhF6 and 3F7HPhH7 compounds. Additionally, the presence of the smectic Cα* sub-phase in a narrow temperature range was proved based on the differential scanning calorimetry and broadband dielectric spectroscopy results, as well as the fractal dimension analysis of the textures obtained by polarizing optical microscopy.

Long-Range Structures of Amorphous Solid Water

High-energy X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) of amorphous solid water (ASW) were studied during vapor deposition and the heating process. From the diffraction patterns, the oxygen–oxygen pair distribution functions (PDFs) were calculated up to the eighth coordination shell and an r = 23 Å. The PDF of ASW obtained both during vapor deposition at 80 K as well as the subsequent heating are consistent with that of low-density amorphous ice. The formation and temperature-induced collapse of micropores were observed in the XRD data and in the FTIR measurements, more specifically, in the OH stretch and the dangling mode. Above 140 K, ASW crystallizes into a stacking disordered ice, Isd. It is observed that the fourth, fifth, and sixth peaks in the PDF, corresponding to structural arrangements between 8 and 12 Å, are the most sensitive to the onset of crystallization.

Photocatalytic Activity of Nanocoatings Based on Mixed Oxide V-TiO2 Nanoparticles with Controlled Composition and Size

V-TiO2 photocatalyst with 0 ≤ V ≤ 20 mol% was prepared via the sol–gel method based on mixed oxide titanium–vanadium nanoparticles with size and composition control. The mixed oxide vanadium–titanium oxo-alkoxy nanonoparticles were generated in a chemical micromixing reactor, coated on glass beads via liquid colloid deposition method and underwent to an appropriate thermal treatment forming crystallized nanocoatings. X-ray diffraction, Raman, thermogravimetric and differential thermal analyses confirmed anatase crystalline structure at vanadium content ≤ 10 mol%, with the cell parameters identical to those of pure TiO2. At a higher vanadium content of ~20 mol%, the material segregation began and orthorhombic phase of V2O5 appeared. The crystallization onset temperature of V-TiO2 smoothly changed with an increase in vanadium content. The best photocatalytic performance towards methylene blue decomposition in aqueous solutions under UVA and visible light illuminations was observed in V-TiO2 nanocoatings with, respectively, 2 mol% and 10 mol% vanadium.

Effect of nanoparticle modified polyacrylamide on wax deposition, crystallization and flow behavior of light and heavy crude oils

In this article, the potential use of silica and alumina polyacrylamide to inhibit wax crystallization and deposition of real crude oils has been studied for the first time. The performance of nanocomposites on a light and heavy crude oil was evaluated using cold finger apparatus, differential scanning calorimeter (DSC), polarizing microscopy, and rheometer. Nanocomposites effectively reduce wax deposition with 79% and 70% maximum efficiency for heavy and light oil, respectively. The flowability of treated heavy oil was improved, while a less pronounced effect was observed for treated light oil. DSC measurements indicated nanocomposites to delay the wax crystallization onset of heavy oil more noticeable than light oil. Polarized microscopy showed a visible morphological change, as the introduction of nanocomposites caused regular roundly shaped and finely dispersed wax crystals for both light and heavy crude oils. The results indicate that the presence of nanocomposites delays the wax crystallization process by presenting multiple spherical nucleation templates, influencing the wax crystal interactions, and preventing the formation of stable wax networks in agreement with the percolation theory predictions. The better inhibition effect of nanocomposites for heavy oil may result from two mechanisms. First, the well-dispersed nanocomposites act as nucleation centers for wax crystals. Second, asphaltene adsorption on the nanocomposite surface may prevent the formation of the asphaltene-wax three-dimensional network and delays wax crystallization. This research indicates the possibility of using silica and alumina polyacrylamide as an effective chemical agent for the inhibition of wax deposition of crude oil.

Inhibitory effect of thyme oil as an antioxidant for waste cooking oil biodiesel crystallization

The effects of thyme oil extract as an antioxidant on crystallization properties of waste cooking oil biodiesel were investigated. The inhibitory effect was determined for ASTM D7545 standard method for biodiesel added with 1000, 2000, and 3000 ppm of additives by using oxifast device and compared with the chemical antioxidant butylated hydroxytoluene (BHT). Inhibition time data were determined by converting the oxidation stability analysis results. The crystallization temperatures (Tcr) of the samples were determined by using a Differential Scanning Calorimetry (DSC) technique. Tcr values of samples with antioxidants were decreased compared to the non-antioxidant biodiesel sample (B100). The order of antioxidant power was B100<B100T1<B100T2 = B100BHT1<B100BHT2<B100T3<B100BHT3. The solid fat content (SFC %) values were determined with different antioxidant concentrations versus different times. The minimum SFC % was determined in B100T3 and B100BHT3 in 3000 ppm antioxidant concentrations in 720 min. DSC results show that the crystallization onset temperatures for B100, B100T3, and B100BHT3 were −51.83 °C, −53.59 °C, and −54.15 °C, respectively. The kinetics of crystallization was determined and k and n values were calculated. The addition of thyme oil extract as a natural antioxidant has a positive effect on biodiesel oxidative stability for all concentrations.

Role of Co content on the microstructure and anti-corrosion performance of high-hardness AlNiYCox high entropy metallic glasses

In the present paper, the role of Co content on phase structure, thermal stability and anti-corrosion performance of melt-spun (Al1/3Ni1/3Y1/3)100-xCox (x= 5, 8, 12, 15 and 20 at.%) high entropy metallic glasses has been investigated. The microstructure and average hardness of AlNiYCox alloy ribbons were characterized and detected using a scanning electron microscope (SEM) and Vickers-type hardness tester, respectively. The corrosion behavior in 3.5 wt% NaCl solution was tested through the conventional potentiodynamic polarization curves (Tafel curves) and electrochemical impedance spectroscopy (EIS). Results suggested that all kinds of high entropy metallic glass ribbons could remain amorphous nature and the crystallization onset temperature are all above 750 K. The average hardness value of each ribbon sample is more than 530 HV0.1 as well. With the increase of Co content, the corrosion resistance begins to enhance and then lowers gradually. When the Co content increases from 5 at.% to 20 at.%, it can result in a decrease of corrosion current density from 9.546 µA/cm2 of the (Al1/3Ni1/3Y1/3)95Co5 to 0.508 µA/cm2 of the (Al1/3Ni1/3Y1/3)92Co8 and 0.741 µA/cm2 of the (Al1/3Ni1/3Y1/3)80Co20 alloy ribbons. Therefore, it is assumed that adding appropriate content of Co element into (Al1/3Ni1/3Y1/3)100-xCox alloys can enhance ability to resist corrosion in 3.5 wt% NaCl solution. The ribbons with 8 at.% Co exhibited the excellent anti-corrosion performance in this current study.

Impact of high‐intensity ultrasound on physical properties and degree of oxidation of lipase modified menhaden oil with caprylic acid and/or stearic acid

AbstractThe purpose of this research was to determine the effect of high‐intensity ultrasound (HIU) on physical properties, degree of oxidation, and oxidative stability of structured lipids (SLs). Caprylic acid (C) and stearic acid (S) were incorporated into menhaden oil using Lipozyme® 435 lipase to obtain five samples: (1) LC 20 (menhaden oil with 20% of C), (2) LC 30 (menhaden oil with 30% C), (3) LS 20 (menhaden oil with 20% S), (4) LS 30 (menhaden oil with 30% S), and (5) Blend C (menhaden oil with 16.24% C and 13.04% S). Samples were crystallized for 90 min at the following temperatures: (1) LC 20 at 15.5°C, (2) LC 30 at 17.5°C, (3) LS 20 at 24°C, (4) LS 30 at 30°C, and (5) Blend C at 18.0°C, and HIU was applied at the onset of crystallization. Physical properties, degree of oxidation, and oxidative stability were evaluated in sonicated and nonsonicated samples. All SLs had statistically higher G′ after sonication. Sonicated LS 30, LC 30, and Blend C had a higher melting enthalpy than the nonsonicated ones, while enthalpy values in sonicated LS 20 and LC 20 samples were not statistically different than the nonsonicated ones. No significant difference between sonicated and nonsonicated samples was observed in peroxide values (1.2 ± 0.1 meq/kg, p > 0.05) and in the oxidative stability index (6.3 ± 0.2 h, p > 0.05). These results showed that HIU was effective at changing physical properties without affecting the oxidation of the samples.

Thermodynamics of strain-induced crystallization in filled natural rubber under uni- and biaxial loadings, Part I: Complete energetic characterization and crystallinity evaluation

The present paper provides the first full thermo-mechanical characterization of a crystallizing filled natural rubber under uniaxial and biaxial loadings. During the mechanical tests, the temperature was measured by using infrared thermography and processed by means of the heat diffusion equation for determining the corresponding heat power density. The intrinsic dissipation due to viscosity and stress softening are evaluated under cyclic loading by the energy balance. Energy contributions to the hysteresis loop converted into heat and stored in the material are distinguished. The heat power density is also used to evaluate the strain-induced crystallinity. This analysis provides new results on the energetic behavior of filled natural rubber. Accordingly, crystallization takes place under high biaxiality levels, close to the equibiaxial loading condition, while multiaxiality influences the crystallization onset. These experimental results are used in the second part of the present paper for a physically based modeling of the complex behavior of filled natural rubbers.

Precursor nuclei on the bottom of a vibrating container: The onset of granular self-assembly crystallization

Kinetic energy is transferred through collisions to the millimeter particles that are in contact with the base of a vertically vibrated 3D container. In the early stages of a vibrational annealing process where the dimensionless acceleration is kept constant, the spontaneous appearance and disappearance of unstable clusters of ordered particles near the bottom surface of the container is observed. In later stages of this vibrational annealing process, the precursor nuclei stabilize becoming stable crystal seeds which resembles a thermal phase transition. Molecular Dynamics simulations based on these experimental observations are used to study the unstable–stable transition. The Ornstein–Zernike equation using the Percus–Yevick closure is applied to the stages before and after the observation of the stable crystal seeds in order to extract the effective potentials associated with the phase transition. Both the radial distribution function and the effective potentials show a clear correspondence of the spatial correlation as the crystallization phase begins to appear.

Low-temperature atomic layer deposition of indium oxide thin films using trimethylindium and oxygen plasma

Indium oxide (InxOy) thin films were deposited by plasma-enhanced atomic layer deposition (PEALD) using trimethylindium and oxygen plasma in a low-temperature range of 80–200 °C. The optical properties, chemical composition, crystallographic structure, and electrical characteristics of these layers were investigated by spectroscopic ellipsometry (SE), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), as well as current-voltage and capacitance-voltage measurements. The SE results yielded a nearly constant growth rate of 0.56 Å per cycle and a thickness inhomogeneity of ≤1.2% across 4-in. substrates in the temperature range of 100–150 °C. The refractive index (at 632.8 nm) was found to be 2.07 for the films deposited at 150 °C. The PEALD-InxOy layers exhibit a direct (3.3 ± 0.2 eV) and an indirect (2.8 ± 0.1 eV) bandgap with an uptrend for both with increasing substrate temperature. Based on XPS characterization, all InxOy samples are free of carbon impurities and show a temperature-dependent off-stoichiometry indicating oxygen vacancies. XRD diffraction patterns demonstrate an onset of crystallization at 150 °C. Consistent with the optical, XPS, and XRD data, the films deposited at ≥150 °C possess higher electrical conductivity. Our findings prove that a low-temperature PEALD process of InxOy is feasible and promising for a high-quality thin-film deposition without chemical impurities on thermally fragile substrates.

Improvement in thermal stability and crystallization mechanism of Sm doped Ge2Sb2Te5 thin films for phase change memory applications

The thin films of (Ge2Sb2Te5)100−xSmx(x = 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2) (Sm-GST) phase change material have been investigated employing X-ray photoelectron spectroscopy (XPS) to examine the nature of chemical bonding in as-deposited thin films of Sm-GST. The composition of as-deposited thin films of Sm-GST has been also analyzed from the peak area ratios of XPS core-level spectra and the morphology of the thin film has been studied using field emission scanning electron microscopy (FESEM). The powder samples obtained from the as-deposited thin films have been utilized for the non-isothermal differential scanning calorimetry (DSC) measurements at the constant heating rate of 10 K/min. The values of glass transition temperature (Tg), onset crystallization (Tc), peak crystallization temperature (Tp) and melting temperature (Tm) obtained from DSC curves of Sm-GST thin films have been used for the evaluation of thermal stability parameters. The activation energy for crystallization (Ec) and avrami exponent (n) for fcc and hexagonal phase of Sm-GST thin films have been evaluated using Henderson’s method and Matusita’s method. The impact of Sm doping on the thermal stability, glass-forming ability and crystallization activation energy of as-deposited thin films have been examined and its possible influence on the memory device performance has been correlated.

Water‐CaO‐Al2O3 Join Interaction: Crystallization Behavior Investigation Using the Single Hot Thermocouple Technique (SHTT)

AbstractCalcium aluminate system is widely used in several ceramic and metallurgical materials and processes such as tundish and mold slags for continuous casting process. In the case of mold powders, they play significant role during the steel solidification process and knowing its physicochemical properties is crucial in the study of slag behavior. In this context, the crystallization tendency of the mold powders plays a significant role in essential properties such as viscosity—which is fundamental to the efficiency of the casting process. In the present study, the effect of a water vapor atmosphere on the crystallization behavior of the CaO‐Al2O3 join is investigated using the single hot thermocouple technique. Distinct crystallization behaviors in presence of water vapor atmosphere are observed, according to the temperature range. Hindering of crystallization onset occurs at a temperature range above 1150 °C. For the temperature range below 1150 °C, crystallization improvement can be observed. The resulting time–transformation–temperature diagrams show the influence of temperature on the effect of water vapor upon crystallization, denoting the amphoteric nature of water.

On flow-enhanced crystallization in fiber spinning: Asymptotically justified boundary conditions for numerics of a stiff viscoelastic two-phase model

For flow-enhanced crystallization in fiber spinning, the viscoelastic two-phase fiber models by Doufas et al. (2000) and Shrikhande et al. (2006) are state of the art. However, the boundary conditions associated to the onset of crystallization are still under discussion, as their choice might cause artificial boundary layers and numerical difficulties. In this paper we show that the model class of ordinary differential equations is singularly perturbed in a small parameter belonging to the semi-crystalline relaxation time and derive asymptotically justified boundary conditions. Their effect on the overall solution behavior is restricted to a small region near the onset of crystallization. But their impact on the performance of the numerical solvers is huge, since artificial layering, ambiguities and parameter tunings are avoided. The numerics becomes fast and robust and opens the field for simulation-based process design and material optimization.