Control Of Crystal Size Research Articles

Size and shape-controlled synthesis of silver nanoparticles for high-thermal conductivity nanofluids

ABSTRACTNanofluids, consisting of nanometric particles suspended in a base fluid, have become a new alternative for improving heat management technology. Silver, which is known to exhibit pretty high electrical and thermal conductivity among metals, has been selected for this research. At present, we are focused on the study of the size- and shape-controlled synthesis conditions of silver nanocrystals in polyol media. Control of crystal size and shape at the nanoscale were achieved by suitable selection of the synthesis conditions and the presence of habit-controlling agents like chloride ions. Silver nanostructures (faceted crystals, wires, rods) were remarkable monodisperse in size and their dimension could be controlled in the 30-50nm range (particles) and 24-127nm in thickness for rods or wires.

How to control the size and morphology of apatite nanocrystals in bone

Biomineralized materials are highly organized composites with hierarchical structures, in which the basic building blocks (apatite crystals) are generally in the nanometer size range to ensure optimum physical and biological functions (1). The biological mechanisms of tissue development have attracted a great deal of recent attention in fields ranging from biology and chemistry to materials science and bioengineering (2, 3). It is well known that the organic component of bone acts as an important regulator of lattice orientation, particle size, and size distribution in biomineralization processes, but the molecular recognition details at inorganic crystal interfaces are poorly understood (4). Recently, most investigations have been focused on the effects of macromolecules such as carboxylate-rich proteins on hydroxyapatite nucleation and growth because complex interactions and changes of conformation are involved (5, 6). The role of small organic molecules such as citrate was deemphasized and was assumed to be simply that of adsorption on the crystal growth steps, resulting in inhibition of crystal growth (7, 8). However, there is still much to be learned about the mechanisms of crystal size control in biological systems. New insight about the role of citrate is emerging, as illustrated by a study in PNAS (9), in which strongly bound citrate molecules were identified as playing critical roles in interfering with crystal thickening and stabilizing apatite nanocrystal sizes in bone.

Structural Evolution of Zeolitic Imidazolate Framework-8

We report the structural evolution of zeolitic imidazolate framework-8 (ZIF-8) as a function of time at room temperature. We have identified the different stages of ZIF-8 formation (nucleation, crystallization, growth, and stationary periods) and elucidated its kinetics of transformation. We hypothesize that the observed semicrystalline-to-crystalline transformation may take place via solution- and solid-mediated mechanisms, as suggested by the observed phase transformation evolution and Avrami's kinetics, respectively. A fundamental understanding of ZIF-8 structural evolution as demonstrated in this study should facilitate the preparation of functional metal-organic framework phases with controlled crystal size and extent of crystallinity.

Toward a Structure Determination Method for Biomineral-Associated Protein Using Combined Solid- State NMR and Computational Structure Prediction

Protein-biomineral interactions are paramount to materials production in biology, including the mineral phase of hard tissue. Unfortunately, the structure of biomineral-associated proteins cannot be determined by X-ray crystallography or solution nuclear magnetic resonance (NMR). Here we report a method for determining the structure of biomineral-associated proteins. The method combines solid-state NMR (ssNMR) and ssNMR-biased computational structure prediction. In addition, the algorithm is able to identify lattice geometries most compatible with ssNMR constraints, representing a quantitative, novel method for investigating crystal-face binding specificity. We use this method to determine most of the structure of human salivary statherin interacting with the mineral phase of tooth enamel. Computation and experiment converge on an ensemble of related structures and identify preferential binding at three crystal surfaces. The work represents a significant advance toward determining structure of biomineral-adsorbed protein using experimentally biased structure prediction. This method is generally applicable to proteins that can be chemically synthesized.

Synthesis of nanocrystalline hydroxyapatite from Ca(OH) 2 and H 3PO 4 assisted by ultrasonic irradiation

This work is focused on the synthesis of hydroxyapatite powders by precipitation assisted by a tip ultrasonic irradiation (UI) from Ca(OH) 2 and H 3PO 4. The effect of UI time, applied UI power during the synthesis, initial Ca 2+ concentration and ageing time of the mixture on phase composition, morphology and specific surface area of the obtained powders was analysed. Particles obtained from the precipitation method using UI or mechanical agitation were compared with a nanosized hydroxyapatite of reference in terms of crystal size, phase composition and thermal stability. This study revealed the feasibility to produce hydroxyapatite powders with controlled crystal size between 31.7 and 70.6 nm by ultrasonic assisted precipitation method. Hydroxyapatite powder with similar surface area to the reference material can be obtained adjusting experimental conditions. The used method allowed us to synthesise hydroxyapatite powders with thermal stability up to 1100 °C.

A seed surface crystallization approach for rapid synthesis of submicron ZSM-5 zeolite with controllable crystal size and morphology

A method based on seed surface crystallization (SSC) mechanism has been proposed for facile, rapid, controllable and low-cost synthesis of ZSM-5 zeolite with submicron-size and interesting core–shell structure. The crystallization process of the ZSM-5 zeolite with all sizes can be accomplished within 2.5 h. The morphology and size of zeolite ZSM-5 products can both be facilely adjustable in the domain of 270–1100 nm depending upon the characters of silicalite-1 seeds, while the thickness of aluminum-containing zeolite ZSM-5 shells can be well tuned by changing the amount of silicalite-1 seed. More interestingly, the siliceous silicalite-1 seeds within the obtained zeolite crystals could be selectively removed by alkaline treatment. By systematically tracking the crystallization process combined with mathematical analysis, the crystallization of ZSM-5 zeolites in the reaction system is revealed as SSC mechanism with a size-independent, linear growth process. Their crystal growth rate is calculated as c.a. 0.15 μm h −1 regardless of the seed size and amount.

Synthesis and characterization of chloro-sulphide glass-ceramics containing neodymium(III) ions

In this paper, we describe the preparation of Nd 3+ doped glass-ceramics in the (GeS 2) 70–(Ga 2S 3) 20–(CsCl) 10 system. Neodymium has been introduced as metallic powder or incorporated as sulphide. Appropriate heat treatments of the base-glass lead to glass-ceramics with controllable crystal sizes that are transparent in the visible and infrared spectral ranges. X-ray diffraction as well as electron diffraction techniques were used to investigate the crystallization process. Differential scanning calorimetry indicates that neodymium ions are poor nucleating agents in this glass compared to erbium ions. Luminescence measurements were also performed and point out that although the ceramization process increases significantly the luminescence efficiency, the neodymium ions are only partially incorporated in the nanocrystals.

Hyperthermic effect of magnetic nanoparticles under electromagnetic field

Magnetic nanoparticles have attracted increasingly attention due to their potential applications in many industrial fields, even extending their use in biomedical applications. In the latter contest the main features of magnetic nanoparticles are the possibility to be driven by external magnetic fields, the ability to pass through capillaries without occluding them and to absorb and convert electromagnetic radiation in to heat (Magnetic Fluid Hyperthermia). The main challenges of the current works on hyperthermia deal with the achievement of highly efficiency magnetic nanoparticles, the surface grafting with ligands able to facilitate their specific internalisation in tumour cells and the design of stealth nanocomposites able to circulate in the blood compartment for a long time. This article presents the synthesis of cobalt ferrite nanoparticles dispersed in diethylene glycol via the so called polyol strategy and the crystal size control through successive synthesis steps. Preliminary heat dissipation evaluations on the prepared samples were carried out and the question of how particles sizes affect their magnetic and hyperthermic properties was addressed as well. Furthermore we will present how surface chemistry can be modified in order to change the dispersity of the product without affecting magnetic and hyperthermic properties. .

Shear controlled crystal size definition in a low molar mass compound using a polymeric solvent

We show that close to monodisperse crystalline fibrils of dibenzylidene sorbitol can be obtained by preparation in a polymeric solvent subjected to extended shear flow.

Nanoparticles Prepared by Salt Vapor‐Solvent Vapor Cocondensation and Controlled Nucleation: Metal Sulfides (ZnS, CdS, CdSe, PbS), and Metal Halide (LiF). Size, Aggregates, Structures, Digestive Ripening, Superlattices, and Impregnations

AbstractA versatile method for the production of gram quantities of nanocrystals of metal sulfides and metal halides has been developed, based on vaporization of the bulk materials followed by controlled nucleation of the molecular vapor species in cold solvent matrices (cocondensate). This approach worked well with ZnS, CdS, CdSe, CdTe, SnS, PbS, and LiF as examples, and is applicable for a large number of semiconductors, ionic salts, as well as metals. Choice of solvent (polar or non‐polar), vaporization rate, and rate of warm‐up of the cocondensate (period of nucleation) allows some control of crystallite size, aggregate size, and surface area. Interestingly, polar solvents lead to smaller nanocrystals, but larger, less porous aggregates. Also, molar mass of the molecular species has an effect on crystallite size, with heavier molecules giving smaller crystals, apparently due to slower migration in the warming cocondensate. Studies of sintering temperature and crystal growth have shown the nanocrystals are quite thermally stable. Addition of ligands, such as thiols, followed by heating in solvent (digestive ripening) has allowed more monodisperse materials to be formed. Finally, this molecular vapor synthesis approach can be used for impregnating semiconductors (CdS, CdSe) of controlled crystal size on solid supports, such as TiO2 or SiO2.

Textural and Capacitive Characteristics of Hydrothermally Derived RuO2×xH2O Nanocrystallites: Independent Control of Crystal Size and Water Content.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Textural and Capacitive Characteristics of Hydrothermally Derived RuO2·xH2O Nanocrystallites: Independent Control of Crystal Size and Water Content

RuO2·xH2O nanoparticulates in different crystal sizes with various water contents were prepared via a hydrothermal synthesis route, successfully demonstrating the independent control of crystal size and water content of RuO2·xH2O. The crystalline and hydrous nature of hydrothermally derived RuO2·xH2O particulates not only reduces the proton diffusion resistance but also enhances the electronic conductivity for the redox transitions of active species. Novel and unique properties of hydrothermally derived RuO2·xH2O, i.e., effective inhibition of crystallite coalescence upon annealing, relatively high thermal stability, and maintenance of the original nanostructure, are attributable to the coalescence barrier of RuO2·xH2O crystallites due to the lattice energy. Maintaining/fine-tuning the original nanostructure of annealed RuO2·xH2O crystallites with high mesoporosity favors the penetration of electrolytes into the whole oxide matrix. This effect of not only reducing the proton diffusion resistance but also ...

Control of crystal size of high-silica mordenite by quenching in the course of crystallization process

An influence of quenching in the course of crystallization process of high-silica mordenite zeolite (MOR) on the crystallization rate and crystal size was investigated in detail. It was found that the crystallization rate is considerably enhanced by the quenching, and that the crystal size decreases with the quenching time. The high-silica MOR with a crystal size of 500–700 nm was easily obtained by a combination of the quenching and the addition of seed crystals. There are no differences in the thermal stability and dealumination behavior between MORs synthesized with and without quenching during crystallization.

Control of Crystal Size and Orientation in Polymer Films by Host−Guest Interactions

The unprecedented occurrence of two different kinds of uniplanar orientation by solution casting, observed for syndiotactic polystyrene (s-PS) films, has been rationalized in terms of host−guest interactions into molecular complex phases. Correlation lengths along different crystallographic directions (Dhkl), of molecular complex crystalline domains of s-PS with several different guest molecules, have been investigated by wide-angle X-ray diffraction. The chemical nature of the guest has a strong influence on the correlation length perpendicular to the ac plane (i.e., perpendicular to the layers of close-packed enantiomorphous helices) and a weak influence on the correlation lengths along a and c (chain) axes. Less and more favorable host−guest interactions lead to molecular complex domains with low and high degree of order perpendicular to the ac layers (D010 < 6 nm and D010 > 7 nm) and generate cast films with uniplanar (010) and (002) orientations, respectively.

Morphology control of the nanoporous nickel phosphate VSB-5 from large crystals to nanocrystals

The nanoporous nickel phosphate, VSB-5 has been synthesized with organic amines in various conditions. The VSB-5 was synthesized only in weakly basic conditions. Among various factors used for synthesis, the pH of the reactant mixture was shown to be a decisive factor to form the nickel phosphate VSB-5. However, a type of organic amine used as a base was important for the control of crystal size and shape. Large crystals with a size of about 200 μm in length have been obtained by using tri- n-propylamine in a highly diluted condition, whereas nanocrystals with a size of 20 nm in width and 200 nm in length have been formed in the presence of 1,6-diaminohexane.

Crystallization on Confined Engineered Surfaces: A Method to Control Crystal Size and Generate Different Polymorphs

Patterned glycine crystals nucleated on functionalized metallic square islands. This approach can be used to fabricate particles with micron dimensions and screen solid forms under different conditions. The size of the glycine crystals is controlled by the dimensions of the islands. High energy metastable beta-glycine crystallizes on small metallic islands, whereas for large islands, the polymorphic outcome becomes biased toward the alpha-form.

Crystal Growth and Critical Current Densities of Polycrystalline&amp;lt;tex&amp;gt;$rm MgB_2$&amp;lt;/tex&amp;gt;Superconductor

We have investigated crystal growth and critical current densities of MgB/sub 2/ which was synthesized using stoichiometry or excess Mg and two kinds of B grain size. Excess Mg plays a role not only to promote crystal growth but also to make crystal grains fine. During crystal growth, the critical current densities decrease, although the density remains constant, approximately. Irrespective of the starting B powder, J/sub CM/ is the highest in the sample with the smallest crystal grains and highest density of MgB/sub 2/. The effects of excess Mg creates the possibility to control crystal size of MgB/sub 2/ by adjusting the quantity of Mg.

Effluent COD Reduction via Gas Hydrate Freezing and Its Modeling

Over the past decades, the pulp and paper industry has made considerable efforts to reduce fresh water usage and minimize effluent discharges. Several effluent free BCTMP mills using traditional evaporation technology are already in operation in various parts of the world with increased load to evaporator. Paper industry initialized application of freeze concentration by using ice as a separating agent in the Louisiana-Pacific mill. Several drawbacks were discovered during their commercialization, including washing water freezing at 0°C, ice formation and plugging in the transportation pipe, difficulties with crystal size control, and high concentration of fiber fines. This process was proven to be successful in the lab and pilot scale, however, it has difficulties in the actual mill application. This work studied the possibility of concentration of pulp mill effluent through gas hydrates formation. Gas hydrates are solid solutions which gas/gases molecules are resided inside the crystal structure formed by water molecules. This process was designed to specifically address these problems associated with previous practice. A continuous gas hydrates formation unit that can perform crystallization, washing and separation functions is built. However, a batch reactor operated at constant volume and temperature were used extensively in this research. Co2 and i-C4H10 are selected to form gas hydrates. Specific problem such as possibility of formation, effectiveness of washing and final water purity were investigated. All of these data and experience can be very useful in the design of commercial unit. The reduction of effluent TSS and TDS via gas hydrate freezing are very effective to reach a level more than 99% removal. However, the reduction of COD removal is only about 60%. Through recrystallization gas hydrate experiments, the efficiency of COD removal can be improved to 80%. Therefore a gas hydrate modeling is developed to simulate multiple recrystallizsyion for predicting improved effluent COD reduction further.

Reliable and Selective Crystallization of the Metastable α-Form Glycine by Seeding

This paper describes a reliable method to selectively produce metastable α-form glycine crystals with a controlled size in batch cooling crystallization. Seeding had a large effect both on the polymorphism and the size distribution of the product crystals. In the case of sufficient seed loadings of the α-form crystals, the metastable α-form crystals were obtained selectively as a product. Simultaneously, the crystal size distribution became unimodal with no fine crystals. However, at low seed loadings, mixtures of both the metastable α- and stable γ-form crystals were obtained. The measurement of supersaturation transient suggested that the low supersaturation caused by the growth of sufficient seeds played a key role in suppressing nucleation of the metastable α- and γ-form crystals, whereas, with no seeding, only the stable γ-form crystals were obtained. The seeding technique presented here could be a general and practical method to produce metastable polymorphs with controlled crystal size.

Control of Crystal Size and Lattice Formation by Starmaker in Otolith Biomineralization

The stone-like otoliths from the ears of teleost fishes are involved in balance and hearing and consist of calcium carbonate crystallites embedded in a protein framework. We report that a previously unknown gene, starmaker, is required in zebrafish for otolith morphogenesis. Reduction of starmaker activity by injection of modified antisense oligonucleotides causes a change in the crystal lattice structure and thus a change in otolith morphology. The expression pattern of starmaker, along with the presence of the protein on the growing otolith, suggest that the expression levels of starmaker control the shape of the otoliths.