Stages Of Crystal Growth Research Articles

Crystallization and phase transition of tobermorite synthesized by hydrothermal reaction from dicalcium silicate

AbstractIn this paper, tobermorite was hydrothermally synthesized from the dicalcium silicate (C2S) in sodium silicate solution, and the crystallization and phase transition process were investigated in detail using XRD, Raman spectra, and SEM. The tobermorite is difficult to synthesize when the temperature is lower than 160°C because it gets converted into xonotlite (without Na2O) or pectolite (with Na2O) when the temperature is higher than 180°C. The crystallization process of tobermorite shows “S” trend with the increase in time, which can be divided into three stages: the nucleation stage, rapid crystal growth stage, and perfect crystal forming stage. During the crystallization, 90% of the crystallization of tobermorite is completed in the stage of rapid crystal growth. Raman spectra and SEM analysis show that with the increase in hydrothermal time, the C2S of monomer (Q0) is first converted into the calcium silicate hydrate of sheet (Q2 and Q3), and then continues to convert into tobermorite of chain (Q2).

Blocking of dislocation propagation by faceted solid liquid interface during Ge crystal growth by the low thermal gradient Czochralski technique

• Study of initial stage of Ge crystal growth by Low Thermal Gradient Cz technique. • Ge crystal growth in 〈1 1 1〉 with faceted interface blocks dislocation propagation. • Ge crystal growth in 〈1 0 0〉 with rounded interface provides low dislocation density. The initial stage of germanium crystal growth by the low thermal gradient Czochralski technique of pulling from the melt (LTG CZ) has been studied in a series of experiments, in which the processes have been interrupted after pulling 6 mm in dia., 70–80 mm in length crystal rod and then up to 20 mm long a cone part. The axial gradients estimated from computer modelling were 2–2.5 K/cm. Crystals pulled in 〈1 1 1〉 direction with totally faceted interface were dislocation-free if facet formation was not disturbed. Crystals pulled along 〈1 0 0〉 under identical conditions, had rounded interface due to thermal roughens of (1 0 0) faces. In that case, the dislocation density was low, but not below ~10 2 cm −2 .

Hydration kinetics and properties of cement blended with mechanically activated gold mine tailings

In this study, the hydration kinetics and properties of cement blended with raw and mechanically activated gold mine tailings were investigated. The results showed that the activity index of the activated tailings was 82.88%, and it is feasible to prepare blend cement from mechanically activated tailings. The Krstulovic–Dabic model could well simulate the hydration process of the paste sample blended with activated tailings, but not suitable for the paste blended with raw tailings. The addition of the activated tailings in cement reduced the hydration heat, prolonged the nucleation and crystal growth stage, and shorten the interactions at phase boundaries reaction stage. The mechanically activated gold mine tailings could react with Ca(OH)2 to form hydration products due to the pozzolanic reaction. The present experimental research provided a theoretical basis for utilizing gold mine tailings in cement as pozzolan, which would be environmentally friendly and cost-effective.

2D Monte Carlo Simulation of Patchy Particles Association and Protein Crystal Polymorph Selection

Typically, protein crystals inherit the polymorphic form selected by nuclei arising in the solution. However, a transition of a polymorphic form may also occur at a later crystal growth stage. Unfortunately, due to the molecular-scale processes involved, the earliest stages of protein crystal nucleation and polymorph selection remain poorly understood. This paper attempts to elucidate the polymorph selection and crystal growth process in proteins (and colloidal crystals) using 2D Monte Carlo simulations and a computational model with short-range attraction for ‘protein-like’ patchy particles (PPs) of a specific patch geometry, bond width and strength. A relatively narrow temperature range is established whereby parts of the PPs monomers arrange initially in a rapidly growing unstable rhombohedral lattice (Rh). Stable trimers form simultaneously from the monomers remaining in the solution and monomers released from the Rh lattice. These trimers serve as building blocks of a more stable Kagome trihexagonal lattice (TriHex), which appears after a prolonged simulation time. The step-by-step scenario of this polymorphic transition and the specific role of PPs’ geometric and interaction anisotropies are discussed in detail.

Diffusion-controlled and concentric growth zoning revealed by phosphorous in olivine from rapidly ascending kimberlite magma, Benfontein, South Africa

Olivine chemistry has been widely used to track the petrogenesis of mafic and ultramafic magmas from their mantle source to eruption at the surface. A major challenge in these studies is deciphering crystal growth versus diffusion controlled zoning. Here we report a multi-element approach using high-precision electron microprobe techniques to evaluate crystal growth versus diffusion in kimberlitic olivine from the Benfontein kimberlite, South Africa. These results have implications for both the petrogenesis of kimberlite magmas and the understanding of crystal growth and diffusion-based zoning in igneous olivine in general.The Benfontein olivine contain multiple phosphorous (P)-rich and P-poor zones. Core zones are characterized by homogenous low-P (<78 ppm) concentrations, consistent with xenocrystic origins. Gradational changes in Fo, Ni, Cr and other minor/trace elements at core-margins are similarly characterized by constant low-P concentrations that are indistinguishable from the central regions of the core. Olivine P-maps effectively outline the original xenocryst core, whereas gradational margins are interpreted as diffusion controlled zones related to early-stage equilibration of xenocrystic olivine with proto-/kimberlite melt.Multiple P-poor (100–150 ppm) and P-rich (200–450 ppm) concentric, oscillatory zones with inclusions of kimberlitic oxide phases are observed surrounding the low-P xenocrystic cores. Oxide phases change from chromite in the inner zones to ilmenite in the intermediate zones to magnetite-rich spinel in the outer zones of the olivine. The P-zoning corresponds with changes in Fo content implying that stages of crystal growth was preserved by both fast and slow diffusing elements rather than diffusion processes. Elements compatible with olivine (±chromite) crystallization (i.e., Ni and Cr) display a constant decrease across all zones, suggesting that magma mixing is unlikely a controlling process for P-zoning. We interpret P-rich zones to result from stages of solute trapping related of rapid disequilibrium growth driven by extrinsic factors such as changes in pressure-temperature during kimberlite evolution. In contrast, P-poor zones represent stages of equilibrium crystal growth. The outer olivine zones are characterized by an increase in Fo contents up to Fo96, and in conjunction with a change to more Fe3+-rich oxides, suggest late stage increase in fO2.Correlated Fo and P changes in the Benfontein olivine suggest that major element zonation represents an example where crystal growth-induced Fo zoning has been preserved in olivine. Furthermore, P-rich olivine zones preserve evidence for concentric growth rather than common dendritic structures seen in other occurrences. These results have implications for understanding the effect of magma dynamics and changes in pressure-temperature-fO2 conditions on olivine growth in igneous rocks.

Hydrothermally-grown nanostructured anatase TiO2 coatings tailored for photocatalytic and antibacterial properties

Low-temperature solution growth of TiO2 films provides unique surface functionalities for base materials that may not survive high processing temperatures. It involves multiple stages of crystal growth at various length scales. Having a fundamental understanding of the mechanisms involved in those stages is essential to obtain desirable functional performances. In this study, we prepared diverse anatase microstructures via a hydrothermal method, all of which start from homogeneous nucleation of the nanoparticles when precursor solution reaches above a critical saturation point. Depending on pH, concentration, temperature and ionic species of precursor solution, however, these primary nanoparticles evolve into different shapes of secondary nanostructures via aggregation of nanoparticles. Thin films of anatase TiO2 consisting of those secondary nanostructures, which have a [001]-texture with (004) surfaces exposed, exhibited the strongest photocatalytic as well as antibacterial properties.

Secondary phase formation by liquid immiscibility in Ca3Ta(Ga1−xAlx)3Si2O14 melt

The origin of secondary phase formation in Ca3Ta(Ga1−xAlx)3Si2O14 (CTGAS) single crystal growth from its melt is still controversial. Here we demonstrate that liquid immiscibility in bulk CTGAS melt is responsible for the secondary phase formation by examining other possible candidates, eutectic reaction and incongruent melting. The former and the latter possibilities were denied by the fact that the secondary phase formed even in the early stage of CTGAS single crystal growth using the micro-pulling down (µ-PD) method and that the differential thermal analysis (DTA) demonstrated the congruency of the CTGAS. We analyzed compositions of the secondary phases and the matrix in solidified CTGAS melt varying the ratio of Al to Ga in Ga site and temperature. The electron probe micro-analyzer (EPMA) analysis revealed that three kinds of phases, the ratios of which are equal, existed in the solidified melt and their populations varied depending on the ratio of Al to Ga. We demonstrate that the same ratio of Al to Ga between these three phases regardless of their population can be explained only by the presence of liquid immiscibility in CTGAS melt during growth.

The kinetics, thermodynamics and mineral crystallography of CaCO3 precipitation by dissolved organic matter and salinity

Calcium carbonate (CaCO3) precipitation is an important geochemical process. In the estuary zone and some arid shallow lakes, DOM (dissolved organic matter) and salinity are two frequent changing factors that may affect CaCO3 precipitation. The joint effect of DOM and salinity on CaCO3 precipitation kinetics and thermodynamics are still unclear. In this study, effects of DOM on CaCO3 precipitation process at 0.5‰ and 70‰ salinity were investigated by QCM (Quartz Crystal Microbalance) technique, real-time pH measurement and single-injection nanoliter ITC (isothermal titration calorimetry). The mineral crystallography was analyzed by SEM-EDS. Both DOM and salinity had inhibitory effect on CaCO3 precipitation. DOM had more pronounced inhibitory effect on CaCO3 precipitation at lower salinity. Regardless of DOM, 70‰ salinity inhibited CaCO3 precipitation >0.5‰ salinity. The CaCO3 precipitation kinetics followed the first-order kinetic model and the adhesion kinetics of the instantaneous nucleation and crystal growth stage could be well described by the exponential function. CaCO3 precipitation was an endothermic process and high salinity strongly hindered CaCO3 precipitation. The effect of DOM on the absorbed heat was significant at 0.5‰ salinity. At 70‰ salinity, regardless of the effect of DOM, CaCO3 precipitation rate was greatly slowed down because it needed much more heat. CaCO3 minerals were dominated by rhombohedral calcite while CaCO3 minerals were mainly shaped as spherical vaterite at 0.5‰ salinity and rhombohedral calcite at 70‰ salinity. The crystal phase changed during CaCO3 precipitation at 0.5‰ salinity. In conclusion, the presence of DOM had substantial impact on the micrograph of the CaCO3 minerals. The percentage of flawed crystals with rough surface increased significantly with increased DOM concentration.

Effect of nano-SiO2 with different particle size on the hydration kinetics of cement

Effect of nano-SiO2(NS) with the sizes of 15nm and 50nm on the hydration heat of cement mortar was measured and its behavior in the hydration kinetics of NS was analyzed based on the Krstulovic-Dabic model. Results showed that NS could improve the value and shorten the occurrence time of hydration exothermic peak. Moreover, NS was helpful to increase the hydration degree and hydration rate in nucleation and crystal growth (NG) stage, while it may shorten the duration time of phase boundary reaction (I) stage and decrease the hydration rate in diffusion reaction (D) stage. Compare to 50nm NS, 15nm NS accelerated hydration rate in early period more effectively, promoted hydration into D stage earlier and inhibited diffusion reaction in late period more obviously. A hydration model was proposed to interpret the difference in hydration process of cement with and without NS.

Preparation and Characterization of Fe3O4 Magnetic Nanofluid in Vegetable Oil

This paper reports the synthesis of Fe3O4 nanoparticles with a hydrophobic surface functionalized with oleic acid through a simple and efficient route in air atmosphere and by co-precipitation. The hydrophobic surfactant agent was added in the magnetic crystal growth stage. Magnetic nanofluid was obtained by ultrasonic dispersion of magnetic nanoparticles in a carrier liquid � vegetable oil. The sample as powder has been characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM), and Vibrating Sample Magnetometry (VSM) at room temperature. The magnetic nanofluid in vegetal oil was investigated by determining the stability of the nanoparticles in the vegetable oil through UV-Vis spectrometry method, the magnetic properties through Vibrating Sample Magnetometry (VSM) method at room temperature, and thermal conductivity as function of magnetic nanoparticles volume concentration and of temperature.

Superstructure of a Metal-Organic Framework Derived from Microdroplet Flow Reaction: An Intermediate State of Crystallization by Particle Attachment.

Understanding the crystallization pathway is of fundamental importance in controlling structures and functionalities for metal-organic frameworks (MOFs), but only few studies have been reported on the mechanism of crystallization for MOFs to date. Here, by using a microdroplet flow (MF) reaction technique, we successfully revealed the different status of HKUST-1 during its crystal growth process. The morphologies and structures of crystals at different stages were recorded and characterized by scanning electron microscopy, transmission electron microscopy, and small-angle X-ray diffraction. Experimental observations clearly demonstrate a process of crystallization by particle attachment (CPA) for crystal growth of HKUST-1 under MF conditions. The superstructure of HKUST-1, which is assembled from oriented attachment of nanosized particles of HKUST-1, is observed at early stage of crystal growth. This type of superstructure gradually transforms to true single crystals through a ripening effect upon increasing residence time, accompanied by increase in dimensions of crystals. Thus, the superstructure is the intermediate state during crystallization and acts as the bridge between disordered reactants and highly ordered single crystals. Based on these findings, the crystal growth of HKUST-1 in MF reaction can be elucidated as a process involving three steps: the generation of nanosized primary particles, the following assembly of the primary particles into a superstructure, and the ripening of superstructure into a crystal. Furthermore, the superstructure of HKUST-1 shows superior performance for CO2 and CH4 adsorptions. The CPA mechanism in the crystallization of HKUST-1 demonstrated in this work is in clear contrast to the monomer-by-monomer addition mechanism in classic models of crystal growth. This mechanism could have important reference meaning for understanding the crystal growth mechanism of other type of MOFs or other special morphologies.

Interfacial structures of spinel crystals with borosilicate nuclear waste glasses from molecular dynamics simulations

AbstractSpinel crystal formation presents a critical issue and glass formulation in nuclear waste glass processing. In this paper, the interfacial structures of the model borosilicate nuclear waste glasses, the international simple glass (ISG), with two types of spinel crystals, namely the MgAl2O4 and NiFe2O4, were studied using classical molecular dynamics simulations with effective partial charge potentials and recently developed composition‐dependent boron‐related parameters. The simulation results revealed the structural features of the borosilicate nuclear waste glasses and their interfaces with the two types of spinel crystals. It was found that there exist notable structural changes of glasses close to the interfacial region, affected by the adjacent crystal structures, terms of preferential segregation and ordering of cations, as well as ctaion coordination numbers. Specifically, the fraction of fourfold coordinated boron (B3) in glass near the interface decreases as compared to the bulk glass. In addition, the amount of fourfold coordinated Al decreases while fivefold Al increases in the glass region close to the glass‐crystal interface, which suggests indication of initial stage of crystal growth as Al adopts higher (sixfold) coordination like in the crystal as compared to majority of fourfold coordination in the glass. These interfacial structure changes obtained from MD simulations provide evidence of the influence of the precipitated crystals on the surrounding melt and glass and the initial stage of crystal growth.

Simulation of the Reactivity of Energy Materials in the Technosphere

Methods are proposed for regulating the reactivity of energetic materials that circulate in the technosphere and are not rarely the cause of fires and explosions, both during storage and during transportation. As man-made factors that influence the stability of these materials magnetic and temperature fields and mechanical effects were used. The magnetic field (in the range from 0.01 T to 0.3 T) was used to intensify chemical processes, both at the stage of crystal growth (by the example of silver azide) and together with mechanical action (from 105 Pa to 107 Pa) in the finished crystals. The action of the magnetic field and mechanical stress leads to the stimulation of microplasticity and macroplasticity processes, which are accompanied by a slow decomposition of the samples and subsequent destruction. It was established experimentally that a slight change in storage temperature, as compared to room temperature, accelerates the aging process of samples (range of positive temperatures up to + 30°C), or leads to loss of plasticity (range of negative temperatures down to -20°C) resulting in loss of performance and in loss of useful properties of energy materials.

Effects of seed crystal size on growth of gem-diamond single crystal

In the paper, under 5.6 GPa and 1250−1450 ℃, the Ib-ype diamond single crystals chosen as the seed crystals with different sizes, are synthesized in a cubic anvil at high pressure and high temperature. High-purity Fe-Ni-Co solvents are chosen as the catalysts. High-purity graphite powder (99.99%, purity) is selected as the carbon source. Hexahedral abrasive grade high-quality diamonds of 0.8 mm, 1.5 mm or 2.2 mm in diameter are chosen as seed crystals. The effects of seed crystal size on the growth of gem-diamond single crystal are studied in detail. Firstly, the influence of the change of seed size on the cracking of diamond single crystal is investigated. The crystal growth law of increasing the probability of cracking crystal with larger seed crystal is obtained. It can be attributed to the following two points. i) The residual cross section at the separation of the main crystal from the larger seed crystal is too large, thus reducing the overall compressive strength of the crystal. ii) The growth rate of the diamond crystal synthesized by larger seed crystal is too fast, which leads to the increase of impurities and defects and the decrease of compressive strength of the crystal. The decrease of crystal compressive strength leads to cracks in diamond crystals during cooling and depressurizing. Secondly, in the growth time of 25 hours, the relationships between the growth time and the limit growth rate of the diamond single crystals synthesized by choosing three sizes of seed crystals are investigated. The results show that the high-quality single crystal synthesis efficiency can be improved and the synthesis period can be shortened by selecting large seed crystals. This is because the size of the seed crystal becomes larger at each stage of crystal growth, resulting in the enhancement of the ability of diamond single crystal to receive carbon, so that high-quality diamond single crystals can be grown at a faster growth rate. Thirdly, with the help of scanning electron microscope or optical microscope, we calibrate the surface morphologies of diamond single crystals grown with different-size seed crystals. Using the seed crystals of 0.8 mm, 1.5 mm or 2.2 mm in diameter, high-quality diamond single crystals with smooth surfaces can be synthesized. However, with the increase of seed crystal in size, the surface flatness of the grown crystals tends to decrease and the possibility with which surface defects occur and string inclusions increase. The growth rate of high-quality diamond single crystals grown with larger seed crystals must be strictly controlled. Finally, the N impurity content values of diamond single crystals grown with different seed crystals in size are characterized by Fourier transform infrared measurement. The results show that the N impurity content of the crystal increases with the diamond growing rapidly by selecting larger seed crystal.

Understanding the Roles of Oiling-out on Crystallization of β-Alanine: Unusual Behavior in Metastable Zone Width and Surface Nucleation during Growth Stage

Oiling-out crystallization of β-alanine was conducted in water–ethanol solvent mixtures, and the roles of oiling-out on the crystallization of β-alanine were investigated during the crystal nucleation and growth stages, respectively. Nucleation metastable zone width broadened with an increase of saturation temperature when oiling-out occurred, contrary to that observed in absence of oiling-out. This observed phenomenon could be explained by the solvent composition change in the nucleation phase (dense oil droplets) under different temperatures. In the crystal growth stage, the size of oil droplets could be controlled by varying agitation speeds. The resulting crystals were lumpy with bulges on specific surfaces when the agitation speed exceeded a certain level. It was supposed to be that the absorption of oil droplets on the crystal surfaces during growth stage led to the surface nucleation, and then the bulges formed consequently. Such performance was never revealed in normal single-phase crystallization...

Isothermal and non-isothermal crystallization kinetics of composites of poly(propylene) and MWCNTs

The isothermal and non-isothermal crystallization behaviour of composites of a poly(propylene) (PP) and multi-walled carbon nanotubes (MWCNTs) were investigated using Differential Scanning Calorimetry (DSC). An Avrami analysis was used to study the isothermal crystallization kinetics of unfilled PP and composites of PP with MWCNT loadings up to 2 (w/w). The value of the Avrami exponent (n) was greater than 2 for all samples, confirming the primary stage of crystal growth is a three-dimensional phenomenon. The activation energy (ΔE), determined using an Arrhenius type expression, for the isothermal crystallization of PP increased from 87 kJ for unfilled PP to 228 kJ on incorporation of 2 (w/w) MWCNTs to PP. An attempt was made to model the non-isothermal crystallization kinetics of composites of PP and MWCNTs using a range of mathematical models, including the Jeziorny extended Avrami equation, Ozawa equation, Caze and Chuah average Avrami exponents, and a combined Avrami/Ozawa approach. The Jeziorny extended Avrami approach confirmed that the non-isothermal crystallization of MWCNT filled PP is clearly a two-stage process. Fitting of the Ozawa model was shown to be not valid and both the Caze and Chuah average Avrami approaches were ineffective as neither took in to account the effects of secondary crystallization. Only the combined Avrami/Ozawa method successfully modelled the two-stage crystallization of composites of PP and MWCNTs. The activation energy (ΔE) for the non-isothermal crystallization of PP on addition of MWCNTs increased with increasing MWCNT content, up to as high as 726 kJ.

Local ordering and interfacial structure between spinel crystal and aluminosilicate glasses from molecular dynamics simulations

AbstractMolecular dynamics simulations were performed to investigate the interfaces of soda magnesia aluminosilicate glass and MgAl2O4 spinel crystals. The glass structures were first generated and characterized. It was found that the glass‐forming network consists of fourfold coordinated [SiO4] and [AlO4] tetrahedra connected through corner sharing with Na+ and Ca2+ acting as modifiers or charge compensators. The glass and crystal interfaces were then constructed on low energy spinel surfaces with special measures to ensure two natural interfaces. The interfacial structures were characterized by z‐density profile, pair distribution function and coordination number analysis. The results show that there exist local ordering on the glass side and preferential adsorption of specific cation near the interface. Cation coordination analyses showed that aluminum ions changed from mainly fourfold coordination in the glass to five and sixfold coordination near the interface suggesting a gradual change in structural role of aluminum from the glass to the crystal. The ordering and segregation of cations, as well as change in aluminum coordination, at the glass/crystal interface strongly suggest that the ordered crystal structure influence the atom distribution and local structure of the adjacent glasses and this ordering can be the initial stage of nucleation or crystal growth.

Morphology Control of CdSe Nanoparticles via Two-Step Segmented Microreactors

Morphology control of CdSe nanoparticles was essential for their potential applications. Different shapes of CdSe nanoparticles could be synthesized in flask reactors. However, there were few researches using microreactors to control the morphologies of CdSe nanoparticles. In this article, a microfluidic approach was developed to synthesize anisotropic CdSe nanoparticles. The nucleation stage (or seed preparation stage) and crystal growth stage were separated, and PFPE was used to form segmented microreactors for the growth stage. The influence of different conditions, such as nucleation temperatures, crystal seeds concentration, the overall ratio of Cd to Se, and monomer concentration for growth stage, on the shape control of CdSe nanoparticles was studied. Branched shape CdSe nanoparticles with high monodispersity were obtained.

Quantitative Design of Seed Load Based on model identification of nucleation and crystal growth stages without transmittance data

How to quantitatively design the loading time and amount of seed is a critical problem in the seeded crystallization process. In this study, correlations for different moment of crystal size distribution (CSD) function were established by subsection induction. By using the established different moment of CSD function, a new algorithm for kinetic model that can estimate the nucleation and growth kinetic parameters was proposed. Compared with kinetic model based on the conventional moments method, the new algorithm has a great significance since the overall heat transfer coefficient U is no longer necessary in the entire calculation. Using experimental data from literature, kinetic parameters of crystallization of KNO3 aqueous solution and xylene solution were estimated by the new algorithm, which are in good accordance with those fitting with moments method. This agreement shows the feasibility of the new algorithm. Finally, since it is difficult to measure transmittance data r of some systems, a criterion K that can identify nucleation and crystal growth stages without transmittance data was established. By means of the K curve of para-xylene (PX) and vitamin C, which is based on kinetic simulation results from the new algorithm and different moment of CSD function established by subsection induction, the single step seed load and two steps seed load were designed, respectively.

Crystal Size Distribution Resulting from the Time Dependence of Crystal Nucleation

AbstractMost of the experimental studies show that new‐phase nucleation runs over prolonged time periods rather than instantaneously. After crystals nucleate, they start growing immediately. Therefore, the earlier a crystal nucleates, the larger it grows. This instigates a definite crystal size distribution (CSD). The resulting (from the initial crystal growth during the nucleation stage) CSD is calculated from the logistic time dependence of crystal number density. Having the shape of an ogee curve, CSD remains practically unchanged during the following crystal growth stage until the onset of Ostwald ripening. Only earlier born (and hence larger) crystals survive during the Ostwald ripening; the smallest crystals, which are the last born species, are dissolved. As far as the logistic dependence of crystal nuclei number density vs. nucleation time explains small molecule and protein crystallization, the calculated CSD should also describe crystallization of both small and large bio‐molecules.