Crystal Growth Modifier Research Articles

Crystallization of ZnO in Aqueous Precursor Solution at 90 °C

AbstractZnO crystallization from suitable aqueous precursor solutions is well known, albeit with crystal growth modifiers and high calcination temperatures. However, processing parameters such as molarity, pH, stirring, and mixing of the reacting solutions can be controlled to make the reactants react at lower activation energies (also implying lower crystal growth temperatures) to obtain the final product. The motivation behind this work is to show that by proper mixing and stirring and using appropriate molarities of the reactants, the kinetics of ZnO formation can be designed, and highly crystalline and oriented ZnO can be obtained with ease. In this work, 0.1 M zinc acetate and 8 M KOH aqueous solutions are slowly mixed while stirring and then reacted at 90 °C to obtain wurtzite crystal structured ZnO without calcination at high temperatures.

Bio-inspired mineralization of CO2 into CaCO3: Single-step carbon capture and utilization with controlled crystallization

CO2 mineralization which involves the reaction of CO2 with alkaline earth metal cations to form carbonates, is a promising pathway that could be crucial for combating global warming via long-term CO2 utilization and storage. However, due to the large abundance of natural calcium carbonate (CaCO3) and advanced milling techniques, micron-ranged CaCO3 is conventionally produced via the top-down method because it is more economically attractive than mineralization or precipitation unless particles with functional properties are generated so that a higher product value is achieved. In this study, inspired by the natural formation of nacre, which is produced naturally via controlled crystallization (using environmental CO2) in the marine environment, we produce CaCO3 particles with different morphologies via single-step CO2 capture and mineralization. We used a gas diffuser reaction setup to bubble CO2 in liquid media containing CO2 absorption promotor, water-soluble polymer, and surfactant as crystal growth modifiers, and Ca2+ to form functional CaCO3. First, different inorganic and organic CO2 absorption promoters and their combinations were investigated for their effectiveness on Ca2+ conversion to CaCO3. Ca2+ conversion and pH of the reaction system with various concentrations of CO2 absorption promoters were monitored every 5 min. Second, the effect of the polymer combined with different concentrations of surfactant on CaCO3 properties was studied. It was found that the combination of triethanolamine and ammonium hydroxide as absorption promotors results in 53.2% Ca2+ conversion into stable CaCO3 particles within 5 min of CO2 bubbling. Absorption promotors themselves could not regulate the particle shape; however, with increasing concentrations, smaller particles agglomerated to form bigger rhombohedral particles. Polymer and surfactant-mediated mineralization of CO2 produces spherical and hollow, stable calcite particles that could serve as dies, heavy metal adsorbents, supports to catalysts, functional composite fillers, etc.

Nb5+-doped SrTiO3-based glass-ceramics: Insight into crystallisation kinetics, microstructure, and dielectric properties

Nb5+-doped SrTiO3-based glass-ceramics composed of SrO–B2O3–SiO2–TiO2 were modified by Nb2O5 doping and prepared via a melt-quenching process accompanied by controlled crystallisation. The effect of the Nb2O5 concentration on the crystallisation, microstructure, and dielectric properties of the glass-ceramics was investigated. Surface analysis conducted by XPS revealed that with the addition of Nb2O5, the number of non-bridging oxygens (NBO) decreased while the number of bridging oxygens (BO) increased, increasing the interconnection of the structural units. The crystallisation activation energies of the samples tended to decrease from 376.06 kJ/mol to 271.50 kJ/mol (Kissinger model), and the crystal growth modes changed from two-dimensional to three-dimensional (Avrami indexes n: 2.38–4.23) with increasing Nb2O5 concentration. The XRD, SEM, and EDS analyses showed that the addition of Nb5+ promoted the growth of crystals (0.44–1.35 μm). The dielectric properties show that an appropriate amount of Nb2O5 greatly improves the dielectric constant of the glass-ceramics. The dielectric constant of the glass-ceramic doped with 1.5 mol% Nb2O5 is 178.1 (300 K, 1 MHz), which is approximately 6.7 times higher than that of the undoped Nb2O5-doped glass-ceramics (26.5). The introduction of Nb2O5 reduced the activation energy of glass devitrification, promoted crystal development, and improved the dielectric properties of the glass-ceramics.

Indomethacin: Effect of Diffusionless Crystal Growth on Thermal Stability during Long-Term Storage.

Differential scanning calorimetry and Raman spectroscopy were used to study the nonisothermal and isothermal crystallization behavior of amorphous indomethacin powders (with particle sizes ranging from 50 to 1000 µm) and their dependence on long-term storage conditions, either 0-100 days stored freely at laboratory ambient temperatures and humidity or placed in a desiccator at 10 °C. Whereas the γ-form polymorph always dominated, the accelerated formation of the α-form was observed in situations of heightened mobility (higher temperature and heating rate), increased amounts of mechanically induced defects, and prolonged free-surface nucleation. A complex crystallization behavior with two separated crystal growth modes (originating from either the mechanical defects or the free surface) was identified both isothermally and nonisothermally. The diffusionless glass-crystal (GC) crystal growth was found to proceed during the long-term storage at 10 °C and zero humidity, at the rate of ~100 µm of the γ-form surface crystalline layer being formed in 100 days. Storage at the laboratory temperature (still below the glass transition temperature) and humidity led only to a negligible/nondetectable GC growth for the fine indomethacin powders (particle size below ~150 µm), indicating a marked suppression of GC growth by the high density of mechanical defects under these conditions. The freely stored bulk material with no mechanical damage and a smooth surface exhibited zero traces of GC growth (as confirmed by microscopy) after >150 days of storage. The accuracy of the kinetic predictions of the indomethacin crystallization behavior was rather poor due to the combined influences of the mechanical defects, competing nucleation, and crystal growth processes of the two polymorphic phases as well as the GC growth complex dependence on the storage conditions within the vicinity of the glass transition temperature. Performing paired isothermal and nonisothermal kinetic measurements is thus highly recommended in macroscopic crystallization studies of drugs with similarly complicated crystal growth behaviors.

Application of metabolomics in urolithiasis: the discovery and usage of succinate

Urinary stone is conceptualized as a chronic metabolic disorder punctuated by symptomatic stone events. It has been shown that the occurrence of calcium oxalate monohydrate (COM) during stone formation is regulated by crystal growth modifiers. Although crystallization inhibitors have been recognized as a therapeutic modality for decades, limited progress has been made in the discovery of effective modifiers to intervene with stone disease. In this study, we have used metabolomics technologies, a powerful approach to identify biomarkers by screening the urine components of the dynamic progression in a bladder stone model. By in-depth mining and analysis of metabolomics data, we have screened five differential metabolites. Through density functional theory studies and bulk crystallization, we found that three of them (salicyluric, gentisic acid and succinate) could effectively inhibit nucleation in vitro. We thereby assessed the impact of the inhibitors with an EG-induced rat model for kidney stones. Notably, succinate, a key player in the tricarboxylic acid cycle, could decrease kidney calcium deposition and injury in the model. Transcriptomic analysis further showed that the protective effect of succinate was mainly through anti-inflammation, inhibition of cell adhesion and osteogenic differentiation. These findings indicated that succinate may provide a new therapeutic option for urinary stones.

Synthesis, characterization and crystallization kinetics of a bio-based, heat-resistance nylon 5T/10T.

The rapid consumption of fossil resources and its adverse impact on the environment require the use of bio-based materials to replace petrochemical products. In this study, we present a bio-based, heat-resistant engineering plastic, poly(pentamethylene terephthalamide) (nylon 5T). To address the issues of the narrow processing window and difficulty in melting processing of nylon 5T, we introduced more flexible decamethylene terephthalamide (10T) units to create a copolymer, nylon 5T/10T. The chemical structure was confirmed by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (13C-NMR). We investigated the influence of 10T units on the thermal performance, crystallization kinetics, crystallization activation energy, and crystal structures of the copolymers. Our results demonstrate that the crystal growth mode of nylon 5T is a two-dimensional discoid growth pattern, while nylon 5T/10T exhibits a two-dimensional discoid or three-dimensional spherical growth pattern. The melting temperature, crystallization temperature, and crystallization rate first decrease and then increase, and crystal activation energy first increases and then decreases as a function of 10T units. These effects are attributed to the combined impact of molecular chain structure and polymer crystalline region. Bio-based nylon 5T/10T shows excellent heat resistance (melting temperature > 280 °C) and a wider processing window than nylon 5T and 10T, which is a promising heat-resistant engineering plastic.

Thermal and mechanical properties of poly(lactic acid)/poly(butylene adipate-co-terephthalate)/calcium carbonate composite with single continuous morphology

Abstract Poly(lactic acid)/poly(butylene adipate-co-terephthalate) with a content ratio of 90/10, and its calcium carbonate (CaCO3) composites with nano- and micro-sized particles were prepared by melt mixing. The dependence of thermal and mechanical properties of the composites on the particle size and addition content of the CaCO3 filler was investigated. The composite containing five parts micro-sized filler (abbreviated as 90L10B5mC, similarly hereinafter) exhibited α and α′ crystallines on cooling as 90L10B without fillers. 90L10B11mC and 90L10B11n5mC exhibited only α′ crystalline, and the others exhibited no discernible crystalline. Jeziorny method showed that the crystallization mode of poly(lactic acid) chains in different composites was close, and Mo method showed that the crystal growth mode in 90L10B11n5mC was different from others. Changes in thermal and mechanical properties were attributed to the overall connection strength which was dependent on the particle size and addition content of the CaCO3 filler. From the perspective of industrialization, 90L10B5n11mC was preferred.

Nonclassical Growth of Atomically Flat Two‐Dimensional Organic Single Crystals on a Liquid Surface through Fusion

AbstractOrganic single crystals with low defect density are key functional materials for next‐generation electronics. Classical crystallization commonly results in a high density of molecular steps, which are defects that can trap charge carriers and reduce the mobility of organic semiconductors. Herein, a novel nonclassical crystallization mechanism involving nucleation, fusion, and growth is designed. The introduction of the fusion stage changes the crystal growth mode from three‐dimensional island growth to two‐dimensional layer‐by‐layer growth and leads to large‐area two‐dimensional molecular crystals with almost no molecular steps. Therefore, the average mobility is observed to improve from 1.26 to 2.07 cm2 V−1 s−1. The nonclassical crystallization mechanism paves the way for atomically flat single crystals to probe the intrinsic optoelectronic properties of organic semiconductors.

Confocal scanning laser microscopy investigation of crystallization behavior of hot blast furnace slag

The isothermal and non-isothermal crystallization behavior of blast furnace (BF) slag with varying CaO/SiO2 ratios was in-situ observed through a confocal scanning laser microscopy (CLSM). The crystallization kinetics was analyzed and precipitation of crystalline phases was discussed by theoretical analysis from FactSage 8.0 and X-ray Diffraction (XRD). The results showed that, with the increasing CaO/SiO2 ratio from 1.0 to 1.3, the crystals morphology changed first from rectangles and squares to small-size and irregular, and further to long strip shape at the cooling rate of 100 °C/min. The onset crystallization temperature in CTT diagram was higher at a larger CaO/SiO2 ratio due to the decrease of polymerization degree of the slag. For the isothermal crystallization process at 1250°C, the crystals morphology changed gradually from lamellar to long-trip or columnar, and the incubation period in TTT diagram became shorter with the increase of CaO/SiO2 ratio. Avrami index n decreased from appropriately 2.3 to 1.5, and the growth mode of crystals converted from two-dimensional to one- dimensional. XRD analysis showed that only merwinite existed in four slags at 1380°C. Akermanite and gehlenite were generated at 1350°C, and their amount first increased greatly and then decreased slightly with a continuous increase of CaO/SiO2 ratio. At the low temperature, the number of akermanite and gehlenite reduced, while that of merwinite increased obviously in the slags when CaO/SiO2 ratio was 1.2 and 1.3, indicating that increasing CaO/SiO2 ratio promoted the generation of merwinite.

Indomethacin: The Interplay between Structural Relaxation, Viscous Flow and Crystal Growth.

Non-isothermal differential scanning calorimetry (DSC) was used to study the influences of particle size (daver) and heating rate (q+) on the structural relaxation, crystal growth and decomposition kinetics of amorphous indomethacin. The structural relaxation and decomposition processes exhibited daver-independent kinetics, with the q+ dependences based on the apparent activation energies of 342 and 106 kJ·mol−1, respectively. The DSC-measured crystal growth kinetics played a dominant role in the nucleation throughout the total macroscopic amorphous-to-crystalline transformation: the change from the zero-order to the autocatalytic mechanism with increasing q+, the significant alteration of kinetics, with the storage below the glass transition temperature, and the accelerated crystallization due to mechanically induced defects. Whereas slow q+ led to the formation of the thermodynamically stable γ polymorph, fast q+ produced a significant amount of the metastable α polymorph. Mutual correlations between the macroscopic and microscopic crystal growth processes, and between the viscous flow and structural relaxation motions, were discussed based on the values of the corresponding activation energies. Notably, this approach helped us to distinguish between particular crystal growth modes in the case of the powdered indomethacin materials. Ediger’s decoupling parameter was used to quantify the relationship between the viscosity and crystal growth. The link between the cooperativity of structural domains, parameters of the Tool-Narayanaswamy-Moynihan relaxation model and microscopic crystal growth was proposed.

Controlled synthesis of Cu2O nanorods in aqueous solution using gallic acid as both reductant and crystal growth modifier

We report a solution synthesis approach for crystalline Cu2O nanorods, in which Gallic acid acts as both reductant and crystal growth modifier. The results show that Cu2O nanonrods were generated under the conditions of temperature at 80 °C, dropping rate of CuSO4 solution at 10 mL/min, pH values at 10–10.2 and initial Cu2+:GA molar ratio of (1–2):1. Compared with Cu2O cubes, Cu2O nanorods demonstrated a superior photocatalytic performance due to their rough surfaces consisting of the dominant active facets such as {111} and {211}. This study offers a promising route to make functional oxides in an environmentally friendly way.

Structural characteristics and chloride intrusion mechanism of passive film

Passive film is a natural barrier against corrosion, which forms spontaneously in alkaline solution. But as a key problem for corrosion resistance, the growth and failure process of passive film has not been clearly confirmed. In this paper, the fine structure of passive film is explored on the atomic scale, and the growth mode of crystals is demonstrated; ion channels are found in inner passive film, which explains the appearance of defect zones and concentrated attack of chloride ions in corrosion. This study will help to judge the corrosion initiation from the perspective of micro damage of passive film.

The Effect of Acidity Coefficient on the Crystallization Properties and Viscosity of Modified Blast Furnace Slag for Mineral Wool Production.

The crystallization and viscosity of modified blast furnace slag are key factors in fiber forming conditions. In this paper, the crystallization behavior of modified blast furnace slag under continuous cooling conditions was studied by differential scanning calorimetry, and its crystallization kinetics with different acidity coefficients were established. On this basis, the evolution law of the crystallization phase and the influence of crystallization on the viscosity of modified blast furnace slag with different acidity coefficients were analyzed. The results indicated that the crystallization phases of slag with acidity coefficients of 1.05 and 1.20 were, respectively, Melilite and Anorthite. During the cooling process at the acidity coefficient of 1.05, the critical rates of precipitation of Melilite and Anorthite were 50 °C/s and 20 °C/s, respectively, while they were 20 °C/s and 15 °C/s, respectively, at the acidity coefficient of 1.20. With the increase of the acidity coefficient, the crystal growth mode of slag changed from two-dimensional and three-dimensional mixed crystallization to surface nucleation and one-dimensional crystallization. The crystallization activation energy of slag with acidity coefficients of 1.05 and 1.20 were 698.14 kJ/mol and 1292.50 kJ/mol, respectively. In addition, the change trend of viscosity was related to crystal size and content.

Crystallization behavior and properties of a novel rare-earth rich BaO–SiO2–La2O3 glass-ceramic for millimeter-wave technology

In this work, a novel low permittivity and high expansion coefficient rare-earth rich BaO–SiO2–La2O3 (BSL) glass-ceramic for millimeter-wave technology was systematically investigated by the network structure, crystallization the phase transformation, microstructure and microwave dielectric properties. With the decrease of the SiO2/BaO mol ratio from 3.75 to 0.9, the crystallization activation energy (Ec) of BSL glass calculated by the Kissiger equation continued to fall from 400.65 to 316.85 kJ/mol, and the crystal growth mode of all samples judging by Avrami parameter (n) was 1-D volume crystallization, implying that the crystallization ability of the BSL glass was enhanced. The main crystal phase of BSL glass-ceramic transformed from BaSi2O5 to BaSiO3 phase, coincided with a second phase Ba4La6O(SiO4)6. And then, the relative permittivity εr of BSL glass-ceramic had increased from 7.8 to 11, while quality factor (Q × f), temperature coefficient of frequency τf, and coefficient of thermal expansion (CTE) had decreased with the decrease of SiO2/BaO ratio. By adjusting the mol ratio of SiO2/BaO, the best comprehensive properties of 20BaO–75SiO2–5La2O3 glass-ceramic could be obtained with εr = 7.8, Q × f = 21000 GHz, CTE = 12.39 × 10−6/°C (30–800 °C), which was favorable properties for microwave dielectric applications.

Front Cover: Controllable Zeolite AST Crystallization: Between Classical and Reversed Crystal Growth (Chem. Eur. J. 35/2022)

A truly reversed crystal growth mode in which the crystallization starts at the surface of a spherically amorphous aggregate and then proceeds towards its center is described. The fundamental function of the structure-directing agent (SDA) controlling the crystallization pathway has been uncovered. The crystallization pathway can be “switched” between classical and reversed crystal growth by tuning the concentration of the SDA. It follows the classical mechanism at a low ratio of SDA/framework elements, but turns to the reversed crystal growth at a high ratio. More information can be found in the Research Article by Q. Yue, M. Opanasenko and co-workers. (DOI: 10.1002/chem.202200590).

Effect of hyaluronic acid on the struvite crystallization: A structural, morphological, and thermal analysis study

The struvite crystals constitute one of the common types of urinary stones. Such stones are also referred as “infection stones” due to their tendency to cause infections in urinary tract. A considerable effort has been placed to identify natural or synthetic crystal-growth modifiers for this kind of urinary stone in literature, yet macromolecules commonly found in urine have been underexplored. In the present study, we experimentally focus on how hyaluronic acid, a protein commonly found in urine, alters the struvite crystallization in aqueous solution and in an artificial urine media. By gradually adding ammonium dihydrogen phosphate to a solution containing magnesium chloride hexahydrate, reactive crystallization is carried out in a well-mixed and thermostated vessel at 37 °C. The resulting struvite crystals are characterized structurally by XRD and FTIR as well as morphologically and in terms of their surface charge. In addition, the thermal decomposition behavior of the struvite with and without hyaluronic acid and released volatile products were simultaneously investigated using a TGA/FTIR system. The average activation energy calculated using the Friedman method was 49.2 ± 5.1 kJ/mol. The results of the kinetic and thermodynamic analyses showed that decomposition of the struvite crystals was endothermic and followed the multiple stage reaction mechanism.

Nitrogen- and Halogen-Free Multifunctional Polymer-Directed Fabrication of Aluminum-Rich Hierarchical MFI Zeolites.

Aluminum-rich hierarchical MFI-type zeolites with high acidic-site density exhibit excellent activity and selectivity in bulky molecule-involved reactions. However, it is challenging to develop a facile and environmentally benign method for fabricating them. Herein, we employ a polymer that does not contain nitrogen and halogen elements to successfully synthesize aluminum-rich hierarchical ZSM-5 zeolite with a Si/Al ratio of 8 and a significant number of mesopores comprised of oriented-assembled nanocrystals. It is demonstrated that the nitrogen- and halogen-free polymer is instrumental in the formation of the ZSM-5 zeolite by serving as a template for constructing the hierarchical micro/mesoporous structure. Moreover, this polymer also acts as a crystal growth modifier to form a single-crystalline zeolite. Notably, the resultant zeolite shows a better catalytic performance in converting waste plastic into hydrocarbons than a commercial one. Our work enables the synthesis of high-quality hierarchical zeolites without requiring quaternary ammonium templates.

Controllable Zeolite AST Crystallization: Between Classical and Reversed Crystal Growth.

Crystal growth mechanisms govern a wide range of properties of crystalline materials. Reversed crystal growth is one of the nonclassical mechanisms observed in many materials. However, the reversed crystallization starting from amorphous aggregates and the key factors driving this growth remain elusive. Here, we describe a characteristic model of reversed crystal growth representing the inner structure and crystallinity development of aggregates studied by microscopy and nano X-ray computed tomography. By adjusting the synthesis conditions, the fundamental function of the structure-directing agent, which determines the crystallization pathway, was revealed. As a result, the crystal growth mode can be "switched" from the classical route at a low ratio of SDA/framework elements to reversed growth at a high ratio. Our findings provide further insights into crystal growth control, which is crucial for improving synthesis protocols and designing various forms of crystalline materials.

Plate-like titanium silicalite-1 zeolites for green oxidation of alkenes to epoxides

Plate-like zeolites have attracted extensive attention due to their less molecular diffusion restriction. It is challenging to simultaneously control the high crystal aspect ratio and thin thickness. Here, two kinds of plate-like titanium silicalite-1 (TS-1) zeolites with crystal sizes of about 1.5 × 0.2 × 2.0 μm (a × b × c) and 0.3 × 0.06 × 0.6 μm were synthesized via assisted with crystal growth modifiers of citric acid and nitrilotriacetic acid, respectively. The 60 nm thickness was the thinnest TS-1 crystal among the reported by using crystal growth modifiers. The c/b aspect ratio of 10 was also one of the largest aspect ratios among the reported values for TS-1 crystals. Both of them displayed higher catalytic activities in 1-hexene epoxidation as compared with conventional nano-sized TS-1 catalysts.

Growth mode control of CVD-grown WS2 monolayer flakes via O2 pre-annealing for organic surfactant oxidation

Chemical vapor deposition (CVD) using liquid solution precursors is a promising method for synthesizing uniform and large-area monolayers of transition metal dichalcogenides. Organic surfactants, such as iodixanol, are crucial additives for the uniform coating of substrates with liquid solution precursors. However, during the heating process of CVD, carbons from the incompletely decomposed organic surfactant suppress crystal growth unfavorably. Here, we investigate the role of such residual carbons in the crystal growth behavior of WS2 monolayers. The crystal growth modes were precisely manipulated by residual carbon oxidation and the precursor etching rate, which was implemented by introducing O2 pre-annealing into the CVD process. Without O2 pre-annealing, flakes of limited size and multilayers were synthesized owing to the carbonization of surfactant, whereas sufficiently oxidized residual carbons via O2 pre-annealing allow for crystal growth with a large monolayer size. Moreover, the growth modes of the flakes in terms of triangles and hexagons can be systematically controlled by the O2 amount for pre-annealing because the remnant O2 compensates for the role of H2, which manipulates the etching rate of the residual W precursors on the substrate. Our results pave the way for controlling the growth modes of CVD-grown WS2 by introducing an optimized O2 pre-annealing process.