Crystal Growth Shape Research Articles

Probing microscale crystallization phenomena: Transforming waste slags into riches

Metal smelting and combustion of solid fuels produce significant quantities of waste slag, leading to issues such as land occupation and environmental pollution. Understanding and controlling the microscale crystallization phenomena of these slags during thermal treatment is crucial for transforming waste slags into materials suitable for carbon capture or glass ceramics. Previous research has primarily focused on macroscopic crystallization behaviors, significantly advancing the utilization of waste slags in cement clinker production. However, macroscopic results are inadequate for precisely controlling the microscale crystallization behaviors of waste slags. Here, we employed the single hot thermocouple technique to visually explore crystal growth modes, shapes, sizes, numbers, and translational rates of the crystal growth front in a representative blast furnace slag under various isothermal temperatures. The results revealed that crystals exhibited five modes as the isothermal temperature gradually increased, including equiaxed, equiaxed & columnar, columnar, columnar & planar, and planar. Moreover, the translational rate of the crystal growth front increased from 0.011 μm·s−1 to 43.7 μm·s−1 with an increase in the isothermal temperature. Simultaneously, the number of crystals decreased from around 104 to 100 μm−2. On this basis, correlations between microscale crystallization behaviors and isothermal temperature were established to fill the current gap.

The Thermal Field Design of a 150 mm Sic Crystal Growth System by Numerical Simulation

AbstractNumerical simulation analysis, enabled by the physical vapor transport (PVT) technique, has been widely adopted to study the growth process of silicon carbide (SiC). In this study, a 2D axisymmetric model employed the finite volume method (FVM) is adopted to simulate the thermal fields and mass transfer of SiC powders with different particle sizes, thicknesses of the top thermal insulation, side wall thicknesses of the lid, and distances between the lid center and the top thermal insulation in a SiC crystal growth system. The simulation results revealed that the reduction in particle size increased the radial and axial temperature gradients in the powder region. Meanwhile, when the thickness of the top thermal insulation decreased, the axial temperature gradient inside the crucible increased significantly. Furthermore, the change in the side wall thickness of the lid significantly affected the thermal field distribution on the crystal surface and consequently affected the crystal growth shape. Finally, the variation in the distance between the lid center and the top thermal insulation has a significant influence on the axial and radial temperature gradients. Overall, these results indicate that the quality of SiC crystal growth may be improved by adjusting particle size, thermal insulation and crucible design.

Effect of surfactants on the growth and characterization of triglycine sulfate crystals

This study investigates the effect on crystal growth and physical properties of triglycine sulfate (TGS) single crystals grown in the presence of surfactants, namely the anionic surfactants sodium dodecyl sulfate (SDS) and sodium 1-decanesulfonate (S1-DS). Pure TGS as well as SDS_TGS and S1-DS_TGS single crystals have been grown from aqueous solution, using a temperature lowering technique. The use of surfactants affects both crystal growth rate and shape. Concerning the latter feature, SDS_TGS crystals show larger (010) faces (b-face) and the S1-DS_TGS crystals show an elongation in [010] direction (b-direction). All samples are monoclinic and show the same Curie temperature (49 °C) as pure TGS. The UV–Vis transmittance of the crystals is found to be decreased due to the presence of surfactants during the growth process. At room temperature, the relative permittivity of the samples is decreased from 10.5 for pure TGS to 7.5 and 5.5 for SDS_TGS and S1-DS_TGS crystals, respectively. However, all crystals show the same pyroelectric coefficient of 168 μC/(m2·K) at room temperature. With that, the pyroelectric voltage figure of merit (FOM) (pc/ (ε.ε0)) is increased from 201 kV/(m·K)for pure TGS up to 245 kV/(m·K) for SDS_TGS, and up to 317 kV/(m·K)for S1-DS_TGS. The energy harvesting figure of merit(pc2/ε·ε0) is increased from 30.37 J/(m3.K2) for pure TGS to 42.52 and 58 J/(m3.K2) for SDS_TGS and S1-DS_TGS crystals, respectively.

Early stage condensation frosting characteristics on plain and nano Al2O3-epoxy mixture-coated brass

Early stage condensation frosting on plain and nano Al2O3-epoxy mixture-coated brass were experimentally investigated. The contact angles of water on the plain and coated brass were 95.8° ± 80.8° and 135.5° ± 80.5° respectively. Surface temperature of both samples ranged from −7.4 °C ± 1.6 °C to −21.3 °C ± 0.3 °C. Dropwise condensation, crystal growth and early frost layer growth were observed. Effects of surface temperature and hydrophobicity on nucleation, crystal growth and crystal shape were examined. It is found that the critical nucleation size of the condensed droplet varies with surface hydrophobicity at different surface temperatures. The crystallization is remarkably postponed using the present coating. The crystal height does not increase until t = 1924 s ± 180 s at Tsurf = −7.4 °C ± 1.6 °C, t = 422 s ± 57 s at Tsurf = −15.0 °C ± 1.2 °C, and t = 73 s ± 12 s at Tsurf = −21.3 °C ± 0.3 °C on the coated brass, compared with t = 39 s ± 5.1 s, t = 30 s ± 2.4 s and t = 14 s ± 3.3 s respectively on the plain brass. Besides, three types of crystal shapes are captured, including the column clumping, stacked stellar plates and dendrites. A stronger dendritical pattern is built at a lower surface temperature. However, no obvious dependency of the crystal shape on the surface hydrophobicity is detected. Moreover, the crystal height growth rate is quantitatively analyzed. The maximum growth rate of crystal height, which corresponds to the moment when the sensible heat removal rate equals to the latent heat release rate, increases with decreasing surface temperature, and is achieved sooner at a lower surface temperature or on the surface with higher hydrophobicity.

Growth Velocity and Shape of TBAB Hydrate Crystals Propagating on a Cooling Surface

Growth Velocity and Shape of TBAB Hydrate Crystals Propagating on a Cooling Surface

Anisotropy in Conformation and Dynamics of a Glycolate Ion Near the Surface of a TiO2 Rutile Crystal Between Its {001} and {110} Planes: A Molecular Dynamics Study

A molecular dynamics simulation was conducted to elucidate the conformation and dynamics of a glycolate ion (CH2(OH)COO–) at the surface of a TiO2 rutile crystal. The simulation was performed for the {001} and {110} planes of the crystal. The results indicate that, for both planes, the conformation and dynamics of the ion are strongly dominated by a layered structure of water on the surface. The simulation suggests that the ion binds to the surface more stably on the {110} plane than on the {001} plane, and that the stable conformation of the ion at the surface differs between the planes: on the {110} plane the carboxyl group of the ion is preferentially oriented toward the surface, whereas on the {001} plane it is oriented toward liquid water. These simulation results are compared with the growth shapes of rutile crystals synthesized in the presence of glycolic acid, and the role of glycolate ions in controlling the morphology of rutile crystals is discussed.

Effect of bio-calcium oxide on the morphology of hydroxyapatite

A study of the Hydroxyapatite (HAp) synthesis through a hydrothermal process was carried out. Bio-Calcium oxide (CaO) obtained by heat treatment of sand dollar was used in the synthesis at different proportions to react with monetite (CaHPO3). Structural and chemical characterization of the samples was carried out using scanning electron microscopy (SEM), X-ray diffraction; Infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). In each sample were observed different morphologies such as agglomerates, hexagonal particles, epitaxial growth, and fibers. O, Ca, P, C and small amounts of Mg and Si were the main chemical components of the sharp morphologies. The hydroxyapatite, whitocklite, portlandite and calcite were the crystalline phases found in each of the samples analyzed. Two different growth shapes of HAp single crystals were found using transmission electron microscopy. The HAp single crystal with six well-defined prismatic faces was reveled to grow along side the <1 0 –1 0> crystallographic direction. The HAp single crystal with fiber morphology grew alongside c-axis. However, both morphologies of HAp single crystals present a ratio Ca/P less compared with the stoichiometric ratio (Ca/P=1.67).

Study on crystal-melt interface shape of sapphire crystal growth by the KY method

In this article, the influence of the flow field structure and temperature gradient of forefront interface on the shape of crystal-melt interface which may reflect the interface stability were analyzed through the method of numerical simulation by using CGSim software. In order to get a suitable interface shape and grow high-quality sapphire crystal, the heater arrangement should be adjusted during the KY process. The results indicate that the effect of Marangoni convection cannot be neglected at the last stage, the crystal-melt interface is governed by the flow field structure and the temperature gradient in melt at the crystal-melt interface. The phenomenon of shoulder concave appears at the stage of shoulder turning and interface inversion appears at the last stage during the crystal growth is discussed. Adjusting heater arrangement may effectively optimize the shape of crystal-melt interface.

Simulating growth morphology of urea crystals from vapour and aqueous solution

The prediction of solvent-induced urea crystal growth shape from the internal and interfacial atomic structure was investigated. A computational model was used to calculate crystal growth morphologies from vapour and aqueous solution as a function of supersaturation; predicted growth shapes agree well with experimental observations.

ChemInform Abstract: Basic Concepts in Crystal Growth

AbstractReview: 31 refs.

On the elementary processes of protein crystallization: Bond selection mechanism

The paper explores the application of bond selection mechanism (BSM) in protein crystal growth; previously, BSM was employed to explain the slow rate of protein crystal nucleation, equilibrium crystal shape and energy barrier in nucleus formation (C.N. Nanev, Prog. Cryst. Growth Charact. Mater. 59 (2013) 133–169). Now, the elementary growth processes are considered from BSM perspective and the crystal growth shape is tackled, the latter resulting from a strong directional kinetic anisotropy in step advancement rates in different crystallographic directions. The most significant surface patterns of growing protein crystals, such as two-dimensional nuclei and growth spiral shapes observed by atomic force microscopy (AFM), are also considered. The activation barrier associated with entering of a protein molecule into the kink site is evaluated and the start of the kinetic roughening is established. Crystal lattice bond energies are estimated (being well above the thermal energy, kBT) from the supersaturation dependence of 2D- into 1D-nuclei transformation.

Regime II–III transition in isotactic polybutene-1 tetragonal crystal growth

The lateral growth rate and growth shape morphology of isotactic polybutene-1 tetragonal crystals were investigated for crystallization from the melt at temperatures of 68–101 °C. The growth rate of tetragonal crystals shows supercooling dependence derived from the nucleation theory, and a regime II–III transition is observed at temperatures of 77–82.2 °C. The morphology of single crystals is rounded below temperatures of 77–85 °C, while the growth shape has a faceted morphology at a higher crystallization temperature of 100 °C. The kinetic roughening transition occurs between 77 and 85 °C. The regime II growth mode is observed above 82.2 °C and proceeds by multiple nucleation on the faceted growth front, while the regime III growth mode is observed below 77 °C and proceeds by rough surface growth on the kinetically roughened growth front. The observed regime II–III transition can therefore be explained by the morphology transition of crystal growth shape.

Effect of anisotropic surface tension on deep cellular crystal growth in directional solidification

An asymptotic solution of the concentration and interface morphology for a deep cellular crystal in directional solidification is obtained by using the matched asymptotic expansion method and multiple variable expansion method, and the effect of anisotropic surface tension on deep cellular crystal growth is studied. Results show that the anisotropic surface tension has a significant effect on the concentration and interface shape of deep cellular crystal growth in directional solidification. As the anisotropic surface tension parameter increases, the concentration near the front part of deep cellular crystal decays and the interface shrinks; when as the concentration near the root increases and the curvature of the interface near the root increases or the curvature radius decreases; and the amplitude of the deep cellular crystal increases. The concentration and interface shape of the deep cellular crystal in directional solidification can be calculated with the results obtained in this paper.

Basic concepts in crystal growth

The aim of this chapter is to reminde some fundamental concepts in Crystal Growth developed in the last century. These concern the definition of the state of non‐equilibrium, the equilibrium and growth shapes of crystals, the atomistic point of view on surface energy, the crystallochemical description of the surface in terms of bond chains and the first mechanisms unravelling the way crystals grow. We hope it can help to place in the proper scientific context the peculiar subjects of this book.

Effect of storage temperature on crystal formation rate and growth rate of calcium lactate crystals on smoked Cheddar cheeses

Previous studies have shown that storage temperature influences the formation of calcium lactate crystals on vacuum-packaged Cheddar cheese surfaces. However, the mechanisms by which crystallization is modulated by storage temperature are not completely understood. The objectives of this study were to evaluate the effect of storage temperature on smoked Cheddar cheese surfaces for (1) the number of discrete visible crystals formed per unit of cheese surface area; (2) growth rate and shape of discrete crystals (as measured by area and circularity); (3) percentage of total cheese surface area occupied by crystals. Three vacuum-packaged, random weight (~300g) retail samples of naturally smoked Cheddar cheese, produced from the same vat of cheese, were obtained from a retail source. The samples were cut parallel to the longitudinal axis at a depth of 10mm from the 2 surfaces to give six 10-mm-thick slabs, 4 of which were randomly assigned to 4 different storage temperature treatments: 1, 5, 10°C, and weekly cycling between 1 and 10°C. Samples were stored for 30wk. Following the onset of visible surface crystals, digital photographs of surfaces were taken every other week and evaluated by image analysis for number of discrete crystal regions and total surface area occupied by crystals. Specific discrete crystals were chosen and evaluated biweekly for radius, area, and circularity. The entire experiment was conducted in triplicate. The effects of cheese surface, storage temperature, and storage time on crystal number and total crystal area were evaluated by ANOVA, according to a repeated-measures design. The number of discrete crystal regions increased significantly during storage but at different rates for different temperature treatments. Total crystal area also increased significantly during storage, at rates that varied with temperature treatment. Storage temperature did not appear to have a major effect on the growth rates and shapes of the individual crystals that were chosen for analysis. The data indicated that the effect of storage temperature was complex, likely involving solubility changes, the formation of d(−) and l(+) lactic acid, and the occurrence of syneresis, which in turn affected the number of crystal formation sites and total crystal area on the cheese surface.

Effect of stoichiometry on the surface energies of {100} and {111} and the crystal shape of TiCx and TiNx

The surface energies of the {100} and {111} surfaces of TiCx and TiNx with different stoichiometries (x ≤ 1.0) were investigated using the density-functional theory, employing Perdew Wang 91 (PW91) under the generalized gradient approximation (GGA) method. The result explains the dominating effect of the TiCx and TiNx stoichiometry on their growth shapes and why TiCx and TiNx evolve from octahedron to truncated-octahedron and finally to sphere during the self-propagating high-temperature synthesis (SHS). With the increases in stoichiometry, both the {100} and {111} surface energy values decrease. However, the surface energy of the {100} surfaces decrease more quickly than that of the {111} surfaces, which means that the {100} surfaces tend to be more stable at quite high stoichiometries. In this case, the {100} surfaces gradually expose on the crystal growth shape, while the {111} surfaces gradually shrink. According to this result, through controlling the stoichiometry during the SHS, the TiCx and TiNx particles with different shapes can be obtained.

Tailor-Made Additives for Morphology Control in Molecular Bulk-Heterojunction Photovoltaics

Tailor-made additives, which are molecules that share the same molecular structure as a parent molecule with only slight structural variations, have previously been demonstrated as a useful means to control crystallization dynamics in solution. For example, tailor-made additives can be added to solutions of a crystallizing parent molecule to alter the crystal growth rate, size, and shape. We apply this strategy as a means to predictably control morphology in molecular bulk-heterojunction (BHJ) photovoltaic cells. Through the use of an asymmetric oligomer substituted with a bulky triisobutylsilyl end group, the morphology of BHJ blends can be controlled resulting in a near doubling (from 1.3 to 2.2%) in power conversion efficiency. The use of tailor-made additives provides promising opportunities for controlling crystallization dynamics, and thereby film morphologies, for many organic electronic devices such as photovoltaics and field-effect transistors.

Crystal growth and equilibrium crystal shapes of silicon in the melt

ABSTRACTThe crystal growth shape (CGS) and equilibrium crystal shape (ECS) of silicon in Si melt are observed using in situ observation. Fully faceted silicon CGSs, which are dominated by the {111} facets, are observed from the {112} and {110} orientation. Silicon CGS in three‐dimensional in Si melt is octahedral in shape, bounded by {111} facets. Silicon ECSs in the melt are obtained by the relaxation from the CGSs and exhibit the {111} facets separated by curved interface. Copyright © 2012 John Wiley & Sons, Ltd.

Effect of 6H-SiC crystal growth shapes on thermo-elastic stress in the growing crystal

The effect of 6H-SiC crystal growth shapes on the thermo-elastic stress distribution in the growing crystal was systematically investigated by using a finite element method. The thermo-elastic stress distribution in the crystal with a flat growth shape was more homogeneous than that in the crystals with concave and convex growth shapes, and the value of thermo-elasticity in the crystal with a flat growth shape was also smaller than that in the two other types of crystals. The maximum values of thermo-elastic stress appeared at interfaces between the crystal and the graphite lid. If the lid was of the same properties as 6H-SiC, the thermo-elastic stress would decrease in two orders of magnitude. Thus, to grow 6H-SiC single crystals of high quality, a transition layer of SiC formed by deposition or reaction is suggested; meanwhile the thermal field in the growth chamber should be adjusted to maintain the crystals with flat growth shapes.

Crystal and faceted dendrite growth of silicon near (1 0 0)

The crystal growth shape (CGS) and faceted dendrite growth of silicon near (100) are observed by in situ observation. The morphological transformations of the facets and curved orientations on the CGSs under different undercoolings (ΔT) are investigated, and the growth mechanism of the faceted dendrite is clarified. (110) facets with a low growth velocity and (100) curved interface with a relatively high growth velocity are observed on the crystal during the formation of silicon CGS, which shows a perfect foursquare shape dominated by (110) facets. At a relatively high ΔT, a faceted dendrite with a flat tip appears at the (110) facet of CGS. The (100) curved interface disappears with decreasing curvature. With increasing ΔT, both facet and curved interface growth velocities increase linearly, and the rate of curvature decrease increases. A two-dimensional image is developed to elucidate the growth mechanism of silicon 〈110〉 faceted dendrites near (100).