溶液电导率法对碳酸钙结晶动力学的研究

溶液电导率法对碳酸钙结晶动力学的研究;结垢;电导率     

Crystal growth of aragonite and calcite in presence of citric acid, DTPA, EDTA and pyromellitic acid

The influence of four calcium complexing substances, i.e., citric acid (CIT), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA) and pyromellitic acid (PMA), on the crystal growth rate of the calcium carbonate polymorphs aragonite and calcite has been studied. Using a seeded constant supersaturation method supersaturation was maintained at 4 by keeping a constant pH of 8.5 through addition of sodium carbonate and calcium chloride solutions. The unique composition of each solution was calculated using chemical speciation. The growth rate was interpreted in terms of an overall growth rate. For both calcite and aragonite, the crystal growth rate is significantly reduced in the presence of the calcium complexing substances. The growth retarding effect depends on both the concentration and the polymorph. The relative crystal growth rate was correlated to the total complexing agent concentration using a Langmuir adsorption approach. Aragonite appeared fully covered for lower total concentrations than calcite. Furthermore, CIT very efficiently blocked aragonite growth contrary to what was observed for calcite. This is thought to be related to certain distinct features of the dominant aragonite crystal faces compared to the dominant calcite faces.     

Détermination des cinétiques de croissance et de dissolution du perborate de sodium tetrahydrate en lit fluidisé

The authors present the results of an experimental study on the crystallization of tetrahydrate sodium perborate in a fluidized bed. The influences of supersaturation, seed crystal size, temperature and solution velocity on the overall growth rate were examined. The overall dissolution rate determined under comparable hydrodynamical conditions for various seed crystal sizes and temperatures is also reported.The growth rate is not very sensitive to the variations in crystal size, the temperature and the hydrodynamical conditions, but it depends on the supersaturation and the presence of some soluble impurities.The comparison between growth and dissolution rates shows that under actual working conditions the diffusional mass transfer step is not the limiting step of the growth mechanism.     

The Kinetics of Analcime Synthesis in Alkaline Solution

In this study glass has been used as a starting material in order to increase the resolution of the experiment and establish the kinetics of analcimes during hydrothermal synthesis. The experimental results show that the crystal growth curves represent two‐stage linear growth. The first stage is marked by rapid crystal growth whilst the second stage indicates much slower growth. The nuclei appear before the crystals start growing. The crystal growth rate is dependent on the experimental conditions. The nucleation rate increases as the glass dissolves and reaches a maximum when the glass is completely dissolved. Thereafter, the concentration decreases with the consumption of nutrients, and both nucleation and crystal growth stops when supersaturation occurs.     

Morphology and internal structure of barium sulfate--derivation of a new growth mechanism

Particle formation is the decisive step to control crystal morphology. Besides the classical primary processes, nucleation and molecular growth, the particle size can also increase by aggregation. The special case of self-assembled aggregation leads to the formation of highly ordered particles which often possess a porous internal structure. In the experiments of these studies the particle formation of barium sulfate has been investigated. SEM analysis shows a large variety of growth forms including plate-like, star-like, and spherical particles, whereas TEM exposures reveal the porous internal structure at all investigated supersaturation levels. The pore size and the volume fraction can be influenced by changing the supersaturation ratio. By means of a fast sampling technique in combination with cryo-TEM analysis it has been shown that the particles at the early stages of growth shortly after the beginning of nucleation consist of many small nanocrystallites which have aggregated in a highly ordered manner. The diffraction pattern indicates many small-angle grain boundaries, whereas the particles at the end of the precipitation process are monocrystalline. This leads to the conclusion that barium sulfate grows according to a self-assembled aggregation mechanism followed by a fast recrystallization process.     

Experimental and computational growth morphology of two polymorphs of a yellow isoxazolone dye

We report on the crystal structures and the experimentally found and the computationally predicted growth morphologies of two polymorphs of a yellow isoxazolone dye. The stable polymorph I has a blocklike habit, and the metastable polymorph II grows as fine needles, nucleating only by heterogeneous or contact nucleation. The habits of both polymorphs depend on the supersaturation during growth. The experimental observations are compared with predictions of the attachment energy model and kinetic Monte Carlo lattice simulations in which the growth is modeled as an "atomistic process", governed by surface energetics. These Monte Carlo simulations correctly predict the shape and the dependence on supersaturation of the crystal morphology for both polymorphs: for polymorph I, a strong dependence on supersaturation is found from the simulations. For polymorph II, the order of morphological importance is reproduced correctly, as well as the needlelike morphology.     

Crystallization monitoring in supersaturated solution with a quartz crystal sensor

The degree of supersaturation is an important measure for the operation of crystallization processes, because it is directly related to the control of crystal size distribution and shape. A conventional technique utilizing solution composition and temperature has a variety of problems caused from the measurement error and the handling of analyzing samples.A monitoring system of the supersaturation using a quartz crystal sensor is proposed here, and its performance is examined applying different manipulations of coolant temperature. The experimental outcome and photographic examination indicate that the measurements of resonant frequency and resistance of the sensor can be used for the prediction of the formation and growth of solid crystal from the crystallization process. The monitoring system eliminates the intrinsic error source of the conventional system to give the improved measurement and on-line application availability.     

Materials Discovery and Crystal Growth of Zeolite A Type Zeolitic–Imidazolate Frameworks Revealed by Atomic Force Microscopy

A new zeolitic–imidazolate framework (ZIF), [Zn(imidazolate)_2?x(benzimidazolate)_x], that has the zeolite A (LTA) framework topology and contains relatively inexpensive organic linkers has been revealed using in situ atomic force microscopy. The new material was grown on the structure‐directing surface of [Zn(imidazolate)_1.5(5‐chlorobenzimidazolate)_0.5] (ZIF‐76) crystals, a metal–organic framework (MOF) that also possesses the LTA framework topology. The crystal growth processes for both [Zn(imidazolate)_2?x(benzimidazolate)_x] and ZIF‐76 were observed using in situ atomic force microscopy; it is the first time the growth process of a nanoporous material with the complex zeolite A (LTA) framework topology has been monitored temporally at the nanoscale. The results reveal the crystal growth mechanisms and possible surface terminations on the {100} and {111} facets of the materials under low supersaturation conditions. Surface growth of these structurally complex materials was found to proceed through both “birth‐and‐spread” and spiral crystal‐growth mechanisms, with the former occurring through the nucleation and spreading of metastable and stable sub‐layers reliant on the presence of non‐framework species to bridge the framework during formation. These results support the notion that the latter process may be a general mechanism of surface crystal growth applicable to numerous crystalline nanoporous materials of differing complexity and demonstrate that the methodology of seeded crystal growth can be used to discover previously unobtainable ZIFs and MOFs with desirable framework compositions.     

Infrared spectroscopic study of polytypic effects on the crystal-growth mechanism of n-hexatriacontane (n-C36H74)

The solution-crystallization mechanism was investigated for two polytypes in the M011 modification of n-hexatriacontane (n-C36H74), single-layered structure Mon, and double-layered one Orth II. The crystal growth under controlled supersaturation was followed with a micro- Fourier-transform-infrared spectrometer equipped with an optical system for oblique transmission measurements. Supersaturation dependence of growth behavior was significantly different between Mon and Orth II. Although the Mon crystal continued growing at a supersaturation of 0.27, the overgrowth of Orth II on the (001) face of the Mon crystal was confirmed at supersaturations below 0.21. Such a polytypic transformation was not observed for the Orth II crystal at any supersaturation below 0.30. The growth rate of Mon showed a quadratic dependence on supersaturation, while that of Orth II was approximately linear, suggesting spiral growth and two-dimensional-nucleation mechanisms for Mon and Orth II, respectively.     

Kinetics of the crystallization of barium chromate

Summary The kinetics of the crystallization of barium chromate have been studied conductometrically at 298 K for both spontaneous and seeded growth systems. The rate of growth follows a quadratic dependence upon the relative supersaturation which suggests a surface-controlled growth mechanism. This rate equation holds fairly well for the various supersaturation and solid/solution ratios used. The presence of seeds in the solution appears to accelerate the growth rate. Analysis of the calculated induction times in unseeded systems corroborates the surface-controlled growth mechanism. The effect of some additives on the kinetics of growth has also been studied. The retarding effect of these inhibitors is interpreted in terms of adsorption of inhibitor ions at the active crystal growth sites.Dedicated to the memory of ProfessorE. N. Rizkalla who passed away on November 29, 1993     

Time-Resolved Dynamics of Struvite Crystallization: Insights from the Macroscopic to Molecular Scale

The crystallization of magnesium ammonium phosphate hexahydrate (struvite) often occurs under conditions of fluid flow, yet the dynamics of struvite growth under these relevant environments has not been previously reported. In this study, we use a microfluidic device to evaluate the anisotropic growth of struvite crystals at variable flow rates and solution supersaturation. We show that bulk crystallization under quiescent conditions yields irreproducible data owing to the propensity of struvite to adopt defects in its crystal lattice, as well as fluctuations in pH that markedly impact crystal growth rates. Studies in microfluidic channels allow for time-resolved analysis of seeded growth along all three principle crystallographic directions and under highly controlled environments. After having first identified flow rates that differentiate diffusion and reaction limited growth regimes, we operated solely in the latter regime to extract the kinetic rates of struvite growth along the [100], [010], and [001] directions. In situ atomic force microscopy was used to obtain molecular level details of surface growth mechanisms. Our findings reveal a classical pathway of crystallization by monomer addition with the expected transition from growth by screw dislocations at low supersaturation to that of two-dimensional layer generation and spreading at high supersaturation. Collectively, these studies present a platform for assessing struvite crystallization under flow conditions and demonstrate how this approach is superior to measurements under quiescent conditions.     

The role of polycarboxylic acids in calcium phosphate mineralization

The role of two polyelectrolytes, poly-L-glutamate and poly-L-aspartate, in the growth of calcium phosphate crystal phases, has been investigated at constant supersaturation. Both molecules are strong inhibitors of HAP growth when present in the solution phase but also act as hydroxyapatite and (octacalcium phosphate)-like crystal nucleators when adsorbed on germanium surfaces. The structure of the polymers in solution is presented and various adsorption models are analyzed. A "train-loop" structure of these long, flexible chain polymers on the crystal surface is consistent with all the adsorption (experimental and theoretical), inhibition, and electrophoretic mobility results.     

Supersaturation controlled growth of MAFAPbI<Subscript>3</Subscript> perovskite film for high efficiency solar cells

Controlling the nucleation and growth of organic-inorganic hybrids perovskite is of key importance to improve the morphology and crystallinity of perovskite films. However, the growth mechanism of perovskite films based on classical crystallization theory is not fully understood. Here, we develop a supersaturation controlled strategy (SCS) to balance the nucleation and crystal growth speeds. By this strategy, we are able to find an ideal supersaturation region to realize a balance of nucleation and crystal growth, which yields highly crystallized perovskite films with micrometer-scale grains. Besides, we provide a thoughtful analysis of nucleation and growth based on the fabrication of the perovskite films. As a result, the highest photovoltaic power conversion efficiencies (PCE) of 19.70% and 20.31% are obtained for the planar and the meso-superstructured devices, respectively. This strategy sheds some light for understanding the film growth mechanism of high quality perovskite film, and it provides a facile strategy to fabricate high efficiency perovskite solar cells.     

尿素法合成高结晶度类水滑石

尿素的高温分解特性被用于控制层状化合物合成过程中的pH值。室温下尿素可与硝酸盐形成均一溶液，当其高温分解时可以保证溶液内部各点的pH值始终一致，因而可获得高结晶度的水滑石样品。利用该法可合成出Mg-Al、Zn-Al及Ni-Al类水滑石，但难以合成出Co-Al，Mn-Al及Co-Cr类水滑石，相信这与不同金属离子发生沉淀时所需的pH值有关。     

Supersaturation controlled growth of MAFAPbI_3 perovskite film for high efficiency solar cells

Controlling the nucleation and growth of organic-inorganic hybrids perovskite is of key importance to improve the morphology and crystallinity of perovskite films. However, the growth mechanism of perovskite films based on classical crystallization theory is not fully understood. Here, we develop a supersaturation controlled strategy(SCS) to balance the nucleation and crystal growth speeds. By this strategy, we are able to find an ideal supersaturation region to realize a balance of nucleation and crystal growth, which yields highly crystallized perovskite films with micrometer-scale grains. Besides, we provide a thoughtful analysis of nucleation and growth based on the fabrication of the perovskite films. As a result, the highest photovoltaic power conversion efficiencies(PCE) of 19.70% and 20.31% are obtained for the planar and the meso-superstructured devices, respectively. This strategy sheds some light for understanding the film growth mechanism of high quality perovskite film, and it provides a facile strategy to fabricate high efficiency perovskite solar cells.     

CrystalGrower: a generic computer program for Monte Carlo modelling of crystal growth

A Monte Carlo crystal growth simulation tool, CrystalGrower, is described which is able to simultaneously model both the crystal habit and nanoscopic surface topography of any crystal structure under conditions of variable supersaturation or at equilibrium. This tool has been developed in order to permit the rapid simulation of crystal surface maps generated by scanning probe microscopies in combination with overall crystal habit. As the simulation is based upon a coarse graining at the nanoscopic level features such as crystal rounding at low supersaturation or undersaturation conditions are also faithfully reproduced. CrystalGrower permits the incorporation of screw dislocations with arbitrary Burgers vectors and also the investigation of internal point defects in crystals. The effect of growth modifiers can be addressed by selective poisoning of specific growth sites. The tool is designed for those interested in understanding and controlling the outcome of crystal growth through a deeper comprehension of the key controlling experimental parameters.

Generic in silico methodology – CrystalGrower – for simulating crystal habit and nanoscopic surface topology to determine crystallisation free energies.     

An in situ atomic force microscopy study of uric acid crystal growth

Kidney stones are heterogeneous polycrystalline aggregates that can consist of several different building blocks. A significant number of human stones contain uric acid crystals as a crystalline component, though the molecular-level growth of this important biomaterial has not been previously well-characterized. In the present study, in situ atomic force microscopy (AFM) is used to investigate the real-time growth on the (100) surface of uric acid (UA) single crystals as a function of fundamental solution parameters. Layer-by-layer growth on UA (100) was found to be initiated at screw dislocation sites and to proceed via highly anisotropic rates which depend on the crystallographic direction. The smallest b-steps exhibited minimum heights corresponding to two molecular layers, while fast-moving c-steps more commonly showed monolayer heights. Growth kinetics measured under a range of flow rates, supersaturation levels, and pH values reveal linear trends in the growth kinetics, with faster growth attained in solutions with higher supersaturation and/or pH. The calculated kinetic parameters for UA growth derived from these experiments are in good agreement with the values reported for other crystal systems.     

镁铁双羟基复合金属氧化物的可控合成及晶面生长特征研究

采用成核/晶化隔离法合成镁铁双羟基复合金属氧化物MgFe-LDH,考察了Mg ∶ Fe摩尔比对MgFe-LDH晶形的影响,探讨了晶化温度及晶化时间对晶面生长选择性及晶粒尺寸的影响规律.结果表明,随Mg ∶ Fe摩尔比增大,层板阳离子排列更为规整.晶化温度对晶粒尺寸的影响显著大于晶化时间的影响.晶化温度相同,随晶化时间延长, MgFe-LDH的晶体结构趋于完整,晶粒尺寸变化不大;晶化时间相同,随晶化温度升高,晶体结构趋于完整,晶粒尺寸明显增大.所得到的MgFe-LDH沿a轴方向的晶粒尺寸对晶化温度变化的敏感程度远大于对晶化时间变化的敏感程度,但总是沿a轴方向的晶粒尺寸大于沿c轴方向的尺寸,即[110]晶面的生长速率比[002]晶面的生长速率快.     

Crystal Growth Mechanisms and Morphological Control of the Prototypical Metal–Organic Framework MOF‐5 Revealed by Atomic Force Microscopy

Crystal growth of the metal–organic framework MOF‐5 was studied by atomic force microscopy (AFM) for the first time. Growth under low supersaturation conditions was found to occur by a two‐dimensional or spiral crystal growth mechanism. Observation of developing nuclei during the former reveals growth occurs through a process of nucleation and spreading of metastable and stable sub‐layers revealing that MOFs may be considered as dense phase structures in terms of crystal growth, even though they contain sub‐layers consisting of ordered framework and disordered non‐framework components. These results also support the notion this may be a general mechanism of surface crystal growth at low supersaturation applicable to crystalline nanoporous materials. The crystal growth mechanism at the atomistic level was also seen to vary as a function of the growth solution Zn/H₂bdc ratio producing square terraces with steps parallel to the <100> direction or rhombus‐shaped terraces with steps parallel to the <110> direction when the Zn/H₂bdc ratio was >1 or about 1, respectively. The change in relative growth rates can be explained in terms of changes in the solution species concentrations and their influence on growth at different terrace growth sites. These results were successfully applied to the growth of as‐synthesized cube‐shaped crystals to increase expression of the {111} faces and to grow octahedral crystals of suitable quality to image using AFM. This modulator‐free route to control the crystal morphology of MOF‐5 crystals should be applicable to a wide variety of MOFs to achieve the desired morphological control for performance enhancement in applications.     

Cu-Ni-Mg-Al-CO3四元水滑石的合成及结构分析

以Cu(NO3)2·2H2O,Ni(NO3)2·6H2O,Mg(NO3)2·6H2O和Al(NO3)3·9H2O为原料 ，以NaOH和Na2CO3为沉淀剂，采用成核／晶化隔离法合成了Cu-Ni-Mg-Al-CO3四元 水滑石，通过XRD，FT－IR，TG－DTA，ICP等手段对样品进行测试和表征，并且对 水滑石结构的层板和层间阴离子相互作用进行分析和讨论。结果表明，控制Cu^2+ 离子与其它二价金属离子的配比，可制备晶体结构规整的M(Ⅱ）4M(Ⅲ)2(OH) 12CO3·4H2O型水滑石；Cu^2+离子的引入导致了明显的Jahn-Teller效应；且随 Mg^2+量的增加，使得这种效应更加显著，另一方面Mg^2+量的增加有利于Cu-Ni- Mg-Al-CO3四元水滑石晶体在a方向上生长，增强其热稳定性。