Growth Of Needle Crystals Research Articles

A comprehensive micro-nano investigative approach to study the development of aluminosilicate gel in binary blends of lithium slag geopolymer

This study extensively investigates the formation of aluminosilicate gel in binary blends of lithium slag geopolymer (LSG) containing fly ash and silica fume. A comprehensive analysis of the aluminosilicate gel was performed at the micro-nano scale, employing techniques such as mineralogical, crystallographic, micromorphological, and micromechanical analysis. C-(N)-A-S-H and N-(C)-A-S-H gels were found between Si/Al ratios of 2.41–3.04 and 3.88 to 4.33, respectively. Fly ash incorporated LSG at 45% alkaline activator yielded the highest average nano-indented modulus of 22.54 GPa. Statistical Gaussian deconvolution was employed to categorize mineral phases in nano-indentation of LSG, revealing substantial distinctions indicated by the low p-values. Carbonation in silica fume incorporated LSG was affirmed by selected area electron diffraction (SAED) patterns of calcite crystallites. The microstructure of LSG containing fly ash was stiffened by the growth of needle crystals of hydroxy-sodalite and aluminosilicate gel. Thus, the formation of C-(N)-A-S-H gel and hydroxy-sodalite governs the strength development of LSG binary blends.

Scaling laws for two-dimensional dendritic crystal growth in a narrow channel.

We investigate analytically and computationally the dynamics of two-dimensional needle crystal growth from the melt in a narrow channel. Our analytical theory predicts that, in the low supersaturation limit, the growth velocity V decreases in time t as a power law V∼t^{-2/3}, which we validate by phase-field and dendritic-needle-network simulations. Simulations further reveal that, above a critical channel width Λ≈5l_{D}, where l_{D} is the diffusion length, needle crystals grow with a constant V<V_{s}, where V_{s} is the free-growth needle crystal velocity, and approaches V_{s} in the limit Λ≫l_{D}.

The Modeling of growth process on the surface of crystal

The article is devoted to modelling the growth of thin films on the surfaces of crystals having a similar crystal structure with a small parameter of mismatch of the lattice of substances from which the film and the crystal substrate are formed. A review of modelling methods based on both analytical expressions and computational methods is made. A number of methods for modelling the most typical processes: surface formation in the form of pyramidal formations (so-called needle crystals), two-dimensional with initial islands of growth and three-dimensional uneven growth processes. To model the process of growth of needle crystals, it is proposed to use a method based on Gaussian statistics of surface height increments. The model of three-dimensional growth of the crystal surface, which uses the iterative algorithm of Foss, and which makes it possible to investigate the processes of stepped, uneven growth of crystals, is also considered. In contrast to stepwise growth, a model of submonolayer growth of a film based on the Monte Carlo method is considered. For submonolayer growth of the film, pseudo-random sequences are used, which simulate the initial arrangement of the nuclei of the nucleus of the next layer on the crystal surface. The computational characteristics of this method are determined, namely the dependence of the number of iterations on the initial surface filling coefficient.

Molten salt synthesis of neodynium oxyfluoride in various fluoride media with different fluoride ion activities

Neodymium oxyfluoride has received much attention in the fields of anionic solid electrolytes, luminescent, catalytic and magnetic materials because of its structure combined advantages of rare-earth cations with F– and O2– anions. In this work, neodynium oxyfluoride was synthesized by the reaction between neodymium oxide and four fluoride media with different fluoride ion activities. The synthesis processes in molten LiF–CaF2–NdF3, LiF–NdF3, NaF–CaF2-NdF3 and NaF–KF–NdF3 are observed in situ by a confocal scanning laser microscope. The expansion of neodymium oxide particle is observed in the LiF–CaF2–NdF3, LiF–NdF3, and NaF–KF–NdF3 melts, and the growth of needle crystals on neodymium oxide particle is clearly observed in molten NaF–CaF2–NdF3. Based on scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses of products, neodynium oxyfluoride was successfully synthesized in the four fluoride media. The neodynium oxyfluoride generated in the LiF–CaF2–NdF3, LiF–NdF3, and NaF–KF–NdF3 melts is a tetragonal structure. However, in molten NaF–CaF2–NdF3, neodynium oxyfluoride with a rhombohedral structure is formed. It is suggested that the substitution of Na(I) and Ca(II) for Nd(III) can transform NdOF from tetragonal structure to rhombohedral structure. The growth rate of needle crystals generated in molten NaF–CaF2–NdF3 was calculated based on the result of a confocal scanning laser microscope, and it is found that the reaction kinetics of crystal formation is zero-order reaction. The effect of fluoride media on the structure and morphology of formed NdOF were evaluated by XRD, X-ray photoelectron spectroscopy (XPS) and SEM. The neodymium oxyfluoride prepared in the fluoride media with high fluoride ion activity has low binding energy of F 1s. The ratio of adsorbed oxygen to lattice oxygen for neodymium oxyfluoride prepared in molten LiF-NdF3 is larger than those in the other three fluoride media, so it can have better catalytic performance.

Factors Controlling Persistent Needle Crystal Growth: The Importance of Dominant One-Dimensional Secondary Bonding, Stacked Structures, and van der Waals Contact.

Needle crystals can cause filtering and handling problems in industrial settings, and the factors leading to a needle crystal morphology have been investigated. The crystal growth of the amide and methyl, ethyl, isopropyl, and t-butyl esters of diflunisal have been examined, and needle growth has been observed for all except the t-butyl ester. Their crystal structures show that the t-butyl ester is the only structure that does not contain molecular stacking. A second polymorph of a persistent needle forming phenylsulfonamide with a block like habit has been isolated. The structure analysis has been extended to known needle forming systems from the literature. The intermolecular interactions in needle forming structures have been analyzed using the PIXEL program, and the properties driving needle crystal growth were found to include a 1D motif with interaction energy greater than −30 kJ/mol, at least 50% vdW contact between the motif neighbors, and a filled unit cell which is a monolayer. Crystal structures are classified into persistent and controllable needle formers. Needle growth in the latter class can be controlled by choice of solvent. The factors shown here to be drivers of needle growth will help in the design of processes for the production of less problematic crystal products.

Image Analytical Approach for Needle-Shaped Crystal Counting and Length Estimation

Estimation of nucleation and crystal growth rates from microscopic information is of critical importance. This can be an especially challenging task if needle growth of crystals is observed. To address this challenge, an image analytical method for counting of needle-shaped crystals and estimating their length is presented. Since the current algorithm has a number of parameters that need to be optimized, a combination of simulation of needle crystal growth and Design of Experiments was applied to identify the optimal parameter settings for the algorithm. The algorithm was validated for its accuracy in different scenarios of simulated needle crystallization, and subsequently, the algorithm was applied to study the influence of additive on antisolvent crystallization. The developed algorithm is robust for quantifying heavily intersecting needle crystals in optical microscopy images, and has the potential for being applied for real-time crystallization monitoring and control.

Well-posedness of a needle crystal growth problem with anisotropic surface tension

We study an initial value problem for two-dimensional needle crystal growth with anisotropic surface tension. The initial value problem is derived from the so called one-sided model based on complex variables method. We then obtain the existence and uniqueness of local solution in Sobolev spaces for the needle crystal problem with arbitrary initial interface. Furthermore, we obtain that, on average in time, the solution gains derivative of smoothness in spatial variable compared to the initial data. The continuous dependence on the initial data of the solution map is also established.

Inherent features in the growth of perylene crystals on an oil substrate

Inherent growth features for molecular crystals have been discovered by vapor-phase deposition of perylene molecules onto a liquid film. We have observed a unidirectional anisotropy in the growth of needle crystals, which indicates different accommodation probabilities at opposite steps. This observation shows that the extended and generally anisotropic molecular shape will introduce important steric effects on crystal growth which are absent from inorganic crystal growth. We have also observed a creased growth morphology for square crystals. Step interactions have been proposed as the possible mechanism of the creased growth.

Studies on the kinetics process of tetra-needle-like ZnO whisker growth

The equilibrium gas controlling method was applied to prepare tetra-needle-like zinc oxide whiskers (T-ZnO) using metallic zinc as the main raw material. The kinetic processes of the generation of T-ZnO were divided into two first-order procedures, the formation of a central part and the growth of needle-like crystals of the whisker. The control of the two processes was realized by the adjusting oxidation rate. The reaction ratios of nuclei formation and needle crystal growth were calculated as 0.3 and 1.08 min −1, respectively, from which the weight proportion of needles to nuclei was deduced as 1:20.

Unidirectional anisotropies in perylene crystal growth on a liquid surface

Growth of perylene crystals by vapor phase deposition on a liquid substrate is observed by video microscopy. For a range of perylene molecule concentrations in the oil film a regime of unidirectional needle crystal growth is discovered. For even higher concentrations a switch in the preferential growth direction is found. Both growth anisotropies are linked to the loss of inversion symmetry in the growth environment, causing unidirectional anisotropies in the growth kinetics. Similar anisotropies can be expected for organic thin film growth on solid substrates.

Rigorous results in selection of steady needle crystals

This paper concerns the existence of solutions to a steady needle crystal growth problem in a one-sided model. We rigorously prove that for small nonzero anisotropy γ, analytic symmetric needle crystal solutions exist in the limit of surface tension ε 2 if only if the stokes constant S for a relatively simple nonlinear differential equation is zero. This Stokes constant S depends on the parameter β=2 9/7 γε −8/7 and earlier numerical calculations by a number of investigators have shown this to be zero for a discrete set of values of β. It is also proven that for γ=0, there can be no symmetric needle crystal solution in the considered space. The methodology consists of two steps. First, the original problem is reduced to a weak half-strip problem for any γ in a compact set of [0,1) by relaxation of the symmetry condition. The weak problem is shown to have a unique solution in the function space considered for any γ∈[0, γ m ] for some γ m >0. When a symmetry is invoked, the weak problem is shown equivalent to the original needle crystal problem. Next, by considering the behavior of the solution in neighborhood of an appropriate complex turning point for γ∈(0, γ m ], we extract an exponentially small term in ε as ε→0 + that generally violates the symmetric condition. We prove that the symmetry condition is satisfied for small ε when the parameter β is constrained appropriately.

NONEXISTENCE OF MONOTONIC SOLUTIONS OF SOME THIRD-ORDER ODE RELEVANT TO THE KURAMOTO-SIVASHINSKY EQUATION

We study the third-order ordinary differential equations (ODEs) which are relevant to the steady state of the Kuramoto-Sivashinsky equation, and/or to a model of dendritic growth of needle crystals. We show that there is no monotonic solution for certain range of parameter.

A note on the nonexistence of monotonic steady solutions of the Kuramoto-Sivashinsky equation

We present a simple proof of the nonexistence of monotonic solutions derived from the Kuramoto-Sivashinsky equation. Although our method restricts the range of parameters, it has the advantage of applicability to other equations, which includes a model of dendritic growth of needle crystals.

NONEXISTENCE OF MONOTONIC SOLUTIONS OF SOME THIRD-ORDER ODE RELEVANT TO THE KURAMOTO-SIVASHINSKY EQUATION

We study the third-order ordinary differential equations (ODEs) which are relevant to the steady state of the Kuramoto-Sivashinsky equation, and/or to a model of dendritic growth of needle crystals. We show that there is no monotonic solution for certain range of parameter.

Heat diffusion anisotropy in dendritic growth:: phase field simulations and experiments in liquid crystals

An anisotropic heat diffusion coefficient is introduced in order to study some interfacial growth phenomena. This anisotropy has been incorporated in a phase field model which has been studied numerically to reproduce some fundamental solidification situations (needle crystal growth) as well as the dynamics of a nematic–smectic- B interface. As a general result, we find that dendrites grow faster in the lower heat diffusion direction. Simulation results are compared with experiments with remarkable qualitative agreement.

Needle crystal growth during tungsten oxide reduction

Professional education and training in powder metallurgy (PM) has undergone significant expansion in North America in recent years, in parallel with the growth of the industry. Joseph M. Capus outlines the main developments and indicates what is available at the various levels and different types of institutions.

Regular perturbation expansion solution for steady nonclassical needle crystal growth

The present paper is concerned with the steady, dendrite growth from a pure melt with arbitrary undercooling parameter (−1< T ∞<0). We formulated and discussed the so-called steady nonclassical needle crystal growth problem, described the regular perturbation expansion (RPE) solution in terms of the small surface tension parameter ε 2 and also carried out extensive computation for their numerical results.

Three-dimensional dendritic growth

The entire solution for three-dimensional (3D) dendritic growth of needle crystals is described analytically. Its construction involves the existing 3D selection theory for the tip of the dendrite [Ben Amar and Brener, Phys. Rev. Lett. 71 (1993) 589] plus matching of the tail to this tip. Both intermediate and final asymptotics of the tail shape are given. This shape, which deviates strongly from an Ivantsov paraboloid, is in qualitative agreement with experimental observations. We consider the time-dependent behavior of side-branching deformations, taking into account the actual non-axisymmetric shape of the needle crystal. It is found that the amplitude of the deformation grows faster than for the axisymmetric paraboloid shape of the needle. We argue that this effect can resolve the puzzle that experimentally observed side branches have much larger amplitudes than can be explained by thermal noise in the framework of the axisymmetric approach. The coarsening behavior of side branches in the non-linear regime is discussed briefly.

Growth of mineral crystals in turkey tendon collagen fibers.

Bone and several other vertebrate mineralized tissues are formed by the organized growth of crystals of carbonated apatite within a matrix of type 1 collagen fibers. The development of this process in isolated fibrils of young turkey leg tendons has been studied by transmission electron microscopy. Collagen banding, presumably due to ion concentration, precedes the appearance of any crystals. The smallest crystals observed are short needles in bands near the surface of the fibrils. Longer needles, up to the length of the collagen gap regions, were also seen, and, evidently at a later stage, single crystal belts extending partly or wholly through the fibrils. Finally, in mature tendon crystal platelets, seemingly derived from the cracking of belts, extend partly into the collagen overlap zone. In the least mineralized tendon, extrafibrillar mineral-containing vesicles have occasionally been observed adjacent to regions of radiating needle crystal growth in the fibrils, and, more commonly, smaller particles adjacent to bands of very small needles.

Stabilization of needle-crystals by the Gibbs-Thomson effect

We develop a scheme based on pseudo-differential operators to analyze the propagation of excitations in inhomogeneous extended systems. This method is used in a very specific situation, however we think that it has some generality and should apply to various other problems of current interest. We study the well known two-dimensionalsymmetric model of solidification introduced by Langer and Turski. Assuming the existence of Ivantsov-like steady-state solutions, we calculate their excitation spectrum. We show that there are no unstable propagating modes if the Gibbs-Thomson effect is taken into account. This proves that the growth of needle-crystals is stable with respect to side-branching.