Primary Crystals Research Articles

Fold Surfaces of Polymer Crystals Are Nucleation Sites: The Link between Polymer Decoration, Secondary Crystallization, and the Rigid Amorphous Fraction (RAF)

The fold surfaces of polymer crystals may become suitable nucleating sites for uncrystallized material left over during the primary crystallization process. This “nucleation by the folds surface” (NFS) ability is highlighted in the so-called polymer decoration technique in which vapors of polyethylene condense and crystallize on a cold fold surface substrate to form edge-on lamellae that reveal the folds and loops orientations in different growth sectors. In bulk materials, the primary crystallization leaves confined and uncrystallized material between lamellae. NFS, based on epitaxy-type interactions, is expected to take place in these confined and supercooled melt fractions before “true” homogeneous nucleation sets in. The insights provided help elucidate the structural features of the interlamellar layers of crystalline polymers, which overcomes the limits of global, indirect investigation techniques (e.g., differential scanning calorimetry (DSC)) used in attempts to analyze their structure in situ. The interlamellar layer is known to be divided into a rigid amorphous fraction (RAF) located in contact with the fold surfaces and a mobile amorphous fraction (MAF) at its center. The nature of the RAF─amorphous but rigid above its Tg, or crystalline─is still debated. The NFS provides a structural identity for the RAF that associates conformation disorder with stem orientation: the RAF is actually a “condis oriented” fraction. On heating, the small endotherm observed in DSC curves corresponds to its isotropization. The RAF is also a protonucleus for secondary crystallization and induces the growth of edge-on lamellae on top and in the interlamellar spaces of the primary crystals. As such, the RAF has also a layered lamellar structure. Polymer decoration, the “condis oriented” RAF, and the specific edge-on lamellar secondary crystallization are manifestations of the nucleation by the fold surfaces.

Research in the area of obtaining of activated alumina. Part 5. Various technological approaches to the process of fine grinding of high-alumina raw materials

The results of studying the process of fine grinding of α-Al2O3 in the presence of polyethylene glycol (PEG) and an antistatic composition are presented. It is shown that the main reason for the agglomeration of fine particles is the effect of the appearance of an electrostatic surface charge. The introduction of PEG prevents the appearance of a «pseudo-viscous grinding medium», removing the excess electrostatic charge on the surface of newly formed ultrafine particles, and also intensifies the process of abrasion of primary alpha-alumina crystals. The antistatic composition successfully neutralizes the surface electrical charge, but does not have the effect of a grinding aid.

Research in the area of obtaining of activated alumina. Part 4. New technological approaches to the synthesis of ultrafine α-Al2O3

The results of new integrated technological approaches to the synthesis of ultrafine α-alumina using commercially available metallurgical alumina as a raw material are presented. The influence of seven different modes of calcination of the initial γ-Al2O3 in the temperature range of 1200‒1600 °C was studied. It was revealed that the experimental modes determine the size of the primary crystals and the grindability of the firing products. It has been established that by varying the temperature regimes, it is possible to purposefully obtain both monomodal and multimodal powders. Ill. 5. Ref. 12. Tab. 1.

Generality of Evaporative Crystal Liftoff on Heated Hydrophobic Substrates

Scaling or mineral fouling occurs due to the presence of dissolved minerals in water. Scaling is problematic in numerous industrial and household plumbing applications where water is used. The current methods of scale removal often utilize harsh chemicals that are not environmentally friendly. The evaporation of a saline droplet provides a platform to study the role of the substrate in the dynamics of crystallization during scaling. In the present work, we show out-of-plane growth of crystal deposits during the evaporation of saline droplets of aqueous potassium chloride on a heated smooth and microtextured hydrophobic substrate. These out-of-plane deposits, termed as "crystal legs", are in minimal contact with the substrate and can be easily removed from the substrate. The out-of-plane evaporative crystallization of saline droplets of different initial volumes and concentrations is observed irrespective of the chemistry of the hydrophobic coating and the crystal habits investigated. We attribute this general behavior of crystal legs to the growth and stacking of smaller crystals (size ∼10 μm) between the primary crystals toward the end of evaporation. We show that the rate at which the crystal legs grow increases with an increase in the substrate temperature. A mass conservation model is applied to predict the leg growth rate, which agrees well with the experiments.

Fabrication of well-intergrown ZIF-8 films via sequential ZnO seed layer overlaying

The fabrication of well-intergrown metal–organic frameworks (MOFs) in film morphology is crucial for various applications such as gas separation and sensing, as it necessitates uniform and controlled mass transport and sorption at the internal pore surfaces. In this work, we report the growth of continuous zeolitic imidazolate framework-8 (ZIF-8) thin films via a secondary solvothermal growth method using a consecutive ZnO seed layer overlaying approach. The primary growth of ZIF-8 crystals on planar substrates occurs through heterogeneous nucleation in solution, followed by overlaying ZnO seed layers via radio frequency (RF) sputtering for secondary growth. We systematically investigate the morphology, crystallinity, and surface properties of the resulting ZIF-8 films. Our results confirm that the seed layer overlaying induces core–shell-like growth on the primary ZIF-8 crystals, promoting conformal growth and interconnection between isolated islands. These findings demonstrate a promising method for synthesizing continuous, well-intergrown MOF films with high surface coverage with various compositions and porosities for numerous applications.

Caterpillar-shaped hierarchical ZSM-5 resulted from the self-assembly of regularly primary nano-sized zeolite crystals

Caterpillar-shaped hierarchical ZSM-5 resulted from the self-assembly of regularly primary nano-sized zeolite crystals

Enhanced separation of bulk silicon from Si-Sn melt via electromagnetic directional solidification

Developing new methods for solar photovoltaic power generation is an effective way to solve future energy shortages. Solvent refining is one of the most promising methods to achieve the low-cost mass production of solar-grade Si. In this work, a novel method for separating bulk silicon from a Si-Sn melt under intensification by an electromagnetic stirring is proposed. The growth and enrichment of Si crystals were controlled by the upward and downward directional solidification of Si-50at%Sn melt at different moving rates. Compared with traditional directional solidification, electromagnetic stirring yielded a higher growth rate of Si. A lower moving rate improved the enrichment percentage of Si, and a large area of bulk Si with an enrichment percentage of up to 88.16% was obtained by performing downward directional solidification at a rate of 3 µm/s. Moreover, the downward movement improved the Si enrichment, because Si grew along the bottom and side walls of the crucible. These results provide a new scientific perspective and experimental evidence for the separation of primary Si crystals from Si-based multicomponent solvents.

High thermal stability of residual amorphous regions in metallic glasses

As a thermodynamic non-equilibrium material, metallic glasses have a spontaneous tendency to crystallize, commonly accompanied by a degradation of mechanical properties. In this work, the thermal stability of a composition Zr60Co27Al13 under both a monolithic amorphous state and symbiotic primary crystal-glass state was intensively analyzed to uncover the origination of the thermal stability. It shows that the symbiotic metallic glass is much more stable than that of the monolithic metallic glass, which can be attributed to the consumption of short-range order clusters, the relaxation in atomic dimensions, and the more homogenous elemental distribution in the residual amorphous regions. Revealing the effect of the primary crystal on the residual amorphous phase in the symbiotic state may be beneficial for developing metallic glasses with high thermal stability.

Organic–Inorganic Nanocomposites of Aspergillus terreus Extract and Its Compounds with Antimicrobial Properties

Due to its distinct, atypical features and possible applications, three-dimensional (3D) hierarchical nanoflowers have sparked considerable interest. Copper (II) ions were employed as inorganic components in this study, whereas various extracts from Aspergillus terreus and their extracted main components were used as organic components. Extracts from A. terreus and its isolated principal component molecules can first form complexes with copper ions, and these complexes subsequently become nucleation sites for primary copper phosphate crystals, showing interactions using an easy and successful self-assembly template synthesis technique. Therefore, the process results in the formation of 3D nanoflowers among the A. terreus extract and its remoted important additives in addition to copper ions, ensuing in a completely unique round flower-like shape containing loads of nanopetals under the most excellent conditions along with pH, attention of organic–inorganic additives, temperature, and the quantity of copper nitrate on nanoflower formation. Furthermore, A. terreus and its isolated major components, Cu3(PO4)2 nanoflowers, seemed to have a remarkable antibacterial effect. Our findings highlight the benefits of nanoflowers made with A. terreus and its isolated secondary metabolites of inorganic structures, which could be used in industrial biocatalysts, biosensors, and environmental chemistry.

Improvement of drug processability in a connected continuous crystallizer system using formulation additive

Continuous crystallization in the presence of polymer additives is a promising method to omit some drug formulation steps by improving the technological and also pharmacological properties of crystalline active ingredients. Accordingly, this study focuses on developing an additive-assisted continuous crystallization process using polyvinylpyrrolidone in a connected ultrasonicated plug flow crystallizer and an overflow mixed suspension mixed product removal (MSMPR) crystallizer system. We aimed to improve the flowability characteristics of small, columnar primary plug flow crystallizer-produced acetylsalicylic acid crystals as a model drug by promoting their agglomeration in MSMPR crystallizer with polyvinylpyrrolidone. The impact of the cooling antisolvent crystallization process parameters (temperature, polymer amount, total flow rate) on product quality and quantity was investigated. Finally, a spatially segmented antisolvent dosing method was also evaluated. The developed technology enabled the manufacture of purified, constant quality products in a short startup period, even with an 85% yield. We found that a higher polymer amount (7.5–14%) could facilitate agglomeration resulting in “good” flowability without altering the favorable dissolution characteristics of the primary particles.

Late Permian-Triassic sedimentary evolution of the Southern Adriatic area based on wells and cores analysis

Rock samples from two cores within the Triassic interval of the Puglia 1 well, were studied to reveal the sedimentary facies and diagenesis. The Core 1 (5.048–5.056 m deep) is characterized by laminated dolomudstones with thinly microbial laminae alternated to lenticular/tabular shaped anhydrite crystal levels, suggesting an intertidal/sabkha-type environment. The Core 2 (6.067–6.075 m deep), shows coarse-grained crystalline massive dolomite with remnants of oolites and shell fragments, suggesting a marginal shallow-water setting. Dolomitization is ubiquitous and occurred early after the deposition through the circulation of high saline dolomitizing fluids under general reducing conditions. The early-dolomitization preserved the dolomites from major burial diagenetic transformations, permitting only the ordering and the development of xenotopic textures in the dolomite crystals (aging). Primary anhydrite crystals were lately affected at least by one burial hydration-dehydration cycle, whereas fracture-filling anhydrite is a later-stage diagenetic product of circulating sulphate-rich fluids. Moreover, the integration of Puglia 1 well data with other six exploration wells and a seismic line allowed a possible reconstruction of the Permian-Triassic sedimentary evolution of the Southern Adriatic area. During Permian continental/coastal lagoon settings developed, while in the Ladinian, after a generalized subaerial exposure and an erosional phase, the extensional tectonic inputs linked to Tethys rifting brought to a relative sea-level rise and to the formation of carbonate shelves in NW-SE oriented tectonic depressions. During Carnian-early Norian a further extensional tectonic pulse coupled with a relative sea-level drop, led to the formation of NW-SE elongated intrashelf basin with a consequent enhancement of salinity and settlement of evaporative conditions. This triggered a massive evaporite deposition during the Norian, that filled the basinal areas. Lastly, in the late Norian-Rhaetian a marked relative sea-level rise, restored the connections with open-sea and shifted the evaporite deposition up to the shallowest parts of the basins that previously remained under subaerial conditions.

Synthesis of Graphene Quantum Dots Enhanced Nano Ca(OH)2 from Ammoniated CaCl2

Ca(OH)2 nanoparticles are effective materials for cultural heritage restoration, hazardous substance absorption and photocatalyst. However, many methods are complex, and the particle sizes are usually above 80-100 nm, involving mediocre efficacy for application in the stone restoration field. In this work, Nano Ca(OH)2 with diameters less than 70 nm and composited with Graphene Quantum Dots (GQDs) were successfully synthesized in aqueous media. The morphology and structure of the nanoparticles were investigated with TEM, HRTEM, XRD, Raman and FTIR. The particle size distribution and relative kinetic stability of the Ca(OH)2 in ethanol were performed using a laser particle size analyzer and spectrophotometer. Firstprinciple calculations based on the spin-polarized density functional theory (DFT) were carried out to study the reaction process and combination model. The nanoparticles, as prepared, are composed of primary hexagonal crystals and high ammoniated precursors, which have a positive effect on reducing the grain size, and interacted with the GQDs hybrid process. According to the First-principle calculations results, the energy variation of the whole reaction process and the bonding mode between Ca(OH)2 and GQDs can be understood better.

Tunable optical multistability and absorption in a hybrid optomechanical system assisted by an auxiliary cavity and quantum dot molecules

Coherent and tunable light-matter interaction in cavity quantum electrodynamics (C-QED) has attracted much attention for its fundamental importance and applications in emerging areas of quantum technologies. In this work, we propose a hybrid C-QED system comprising embedded quantum dot molecules (QDMs) in a primary photonic crystal (PhC) optomechanical cavity, which is further coupled to an auxiliary PhC cavity via a single-mode waveguide. We investigate the effect of the QDMs, mechanical oscillator, and the feedback from the auxiliary cavity on the multistability response shown by the mean intracavity photons in the primary optomechanical cavity. Tuning the various system parameters can control optical multistability. We further study the absorption spectra showing distinct characteristics of negative absorption (transparency dip), which strongly depend on mechanical resonator frequency. Thus, the proposed model is valuable for practically realizing efficient all-optical switching devices at low power and in various other quantum sensing devices.

Emission and sensing of high-frequency terahertz electric fields using a GaSe crystal.

A GaSe crystal cut along the (001) crystallographic plane is investigated for the emission and detection of high-frequency (i.e. up to ∼20 THz) electric fields. To date, a comprehensive analysis on high-frequency difference frequency generation and electro-optic sensing in GaSe has not been performed and should consider aspects such as electric field polarization orientation, symmetries inherent to the crystal structure, and the various possible generation and detection phase-matching arrangements. Herein, terahertz radiation generation is investigated for various excitation electric field polarizations as the GaSe crystal is rotated in the (001) plane. Subsequently, the crystal is rotated out-of-plane to investigate the difference frequency generation and electro-optic sampling phase-matching conditions for various arrangements. The measured terahertz radiation spectra show peak generation at the frequencies of 10, 16, and 18 THz (dependent on the GaSe crystal orientation), in agreement with the frequencies exhibiting perfect phase-matching. GaSe has the potential to emerge as the primary crystal for the emission and detection of high-frequency electric fields, such that this comprehensive analysis is necessary for the widespread adoption and practical implementation of GaSe as a high-frequency source crystal.

Uticaj termootporne obloge na parametre fazne transformacije tokom formiranja Al-8wt%Si-3wt%Cu strukture

Solidification of the aluminum alloys takes place in heat-resistant refractory materials made of either metal or oxides that are stable at high temperatures. The significantly different thermal conductivities between metals and heat-resistant oxides cause solidification with significantly different cooling rates. In this work, we formed a secondary Al-8wt%Si-3wt%Cu alloy in a stainless steel mould, a thin-walled stainless steel cup, and a thick-walled zirconium oxide cup. The course of the formation of the solidified structure was monitored by immersed thermocouples, which enabled the computer analysis of the cooling curves. The parameters on which the cooling rate had the most significant influence are the undercooling values of the formation of primary aluminum crystals, the time of the growth of primary aluminum crystals and the total solidification time from the formation of the first solid crystals to the formation of a fully solidified structure. The Al-8wt%Si-3wt%Cu aluminum alloy formed in metal mould has a smaller grain size and consequently higher tensile strength, lower macro-porosity and less rough surface than the alloy formed in refractory oxide coatings. The examined heat-resistant refractory material influenced the formation of three basic micro-constituents in the Al-8wt%Si-3wt%Cu alloy in different time intervals, which led to the formation of a different microstructure, where the decision on the choice of material for the heat-resistant refractory material depends on the profitability of the entire process, the required quality of the external surfaces and required minimum strength of the final product.

Assessment of the effect of small additions of some rare earth elements on the structure and mechanical properties of castings from hypereutectic chromium white irons

<abstract> <p>Article considers the influence of additions of rare earth elements such as Sm, La, Ce, Nd, and Y on the structure and properties of hypereutectic high-chromium white cast iron of grade G-X300CrMo27-2. To obtain an increased content of carbides in the studied cast iron samples, the carbon content was 3.75–3.9 and 4.1–4.2 wt%. The amount of rare earth elements additives added to the melt is 0.2% by weight. Data were obtained on the effect of overheating and cooling rate in the crystallization interval on the effect of rare earth additives, the structure and properties of white cast iron castings are given. According to the results of the microprobe analysis, it was shown that, under the chosen crystallization conditions, Sm, La, and Ce can form solid solutions with primary and eutectic carbides (FeCr)<sub>7</sub>C<sub>3</sub>. La and Ce form solid solutions with austenite. Nd and Y do not dissolve in iron chromium phases. All listed rare earth elements form phosphides and oxyphosphides. Experimental data are presented on the effect of rare earth elements on the size of primary (FeCr)<sub>7</sub>C<sub>3</sub> carbides and a hypothesis is proposed on the effect of rare earth elements on the crystallization process of hypereutectic chromium white cast irons. Experimental data are presented on the effect of REE additives on the microhardness of phases, hardness, strength, and resistance to abrasive wear of cast iron castings. It was found that the introduction of these additives into hypereutectic chromium white cast iron does not contribute to the modification of the structure and leads to an increase in the size of primary crystals, as well as a decrease in their mechanical properties. However, the addition of Y increases the abrasive wear resistance, but reduces the strength of castings made from such white cast iron.</p> </abstract>

X-ray computed tomography of cast metal matrix composites

The development of new cast metal matrix composites and technological processes for their production are inextricably linked with the need to improve the methods of quantitative non-destructive testing. In this work, the features of the spatial structure of cast in-situ metal matrix composites (on example of the Al – Mg2Si system) were studied using X-ray computed microtomography. The parameters of tomographic scanning were optimized to identify structural components with close ranges of radioparency. The rational selection of the scanning parameters of the samples made it possible, during the subsequent computer processing of the slice sets, to clearly identify the structural constituents of the metal matrix composites depending on the gray levels in their comparison with the characteristic morphology of the observed constituents (primary Mg2Si crystals, pseudobinary eutectic, compounds of impurity elements). The total volume of porosity in the studied samples of Al + 15 wt.% Mg2Si composites after melt thermal-rate treatment at 900 °C did not exceed 0.05 mm3, which corresponds to a porosity content in the sample of 0.13 vol.%. The presented results show the significant potential of tomography in the study of the structural and morphological characteristics of composite materials and internal defects in cast products made from them. This research was funded by the Russian Science Foundation (Project № 20-19-00687).

Conditions favorable for secondary ice production in Arctic mixed-phase clouds

Abstract. The Arctic is very susceptible to climate change and thus is warming much faster than the rest of the world. Clouds influence terrestrial and solar radiative fluxes and thereby impact the amplified Arctic warming. The partitioning of thermodynamic phases (i.e., ice crystals and water droplets) within mixed-phase clouds (MPCs) especially influences their radiative properties. However, the processes responsible for ice crystal formation remain only partially characterized. In particular, so-called secondary ice production (SIP) processes, which create supplementary ice crystals from primary ice crystals and the environmental conditions that they occur in, are poorly understood. The microphysical properties of Arctic MPCs were measured during the Ny-Ålesund AeroSol Cloud ExperimENT (NASCENT) campaign to obtain a better understanding of the atmospheric conditions favorable for the occurrence of SIP processes. To this aim, the in situ cloud microphysical properties retrieved by a holographic cloud imager mounted on a tethered balloon system were complemented by ground-based remote sensing and ice-nucleating particle measurements. During the 6 d investigated in this study, SIP occurred during about 40 % of the in-cloud measurements, and high SIP events with number concentrations larger than 10 L−1 of small pristine ice crystals occurred in 4 % of the in-cloud measurements. This demonstrates the role of SIP for Arctic MPCs. The highest concentrations of small pristine ice crystals were produced at temperatures between −5 and −3 ∘C and were related to the occurrence of supercooled large droplets freezing upon collision with ice crystals. This suggests that a large fraction of ice crystals in Arctic MPCs are produced via the droplet-shattering mechanism. From evaluating the ice crystal images, we could identify ice–ice collision as a second SIP mechanism that dominated when fragile ice crystals were observed. Moreover, SIP occurred over a large temperature range and was observed in up to 80 % of the measurements down to −24 ∘C due to the occurrence of ice–ice collisions. This emphasizes the importance of SIP at temperatures below −8 ∘C, which are currently not accounted for in most numerical weather models. Although ice-nucleating particles may be necessary for the initial freezing of water droplets, the ice crystal number concentration is frequently determined by secondary production mechanisms.

Structure and solidification of the (Fe0.75B0.15Si0.1)100-xTax (x=0–2) melts: Experiment and machine learning

Fe–B–Si system is a matrix for synthesis of new functional materials with exceptional magnetic and mechanical properties. Progress in this area is associated with the search for optimal doping conditions. This theoretical and experimental study is aimed to address the influence of Ta alloying on the structure of undercooled (Fe0.75B0.15Si0.1)100-xTax (x = 0–2) melts, their undercoolability and the processes of structure formation during solidification. Small concentration of Ta complicates standard ab initio and machine learning investigations. We developed a technique for fast and stable training of machine learning interatomic potential (MLIP) in this case and uncovered the structure of undercooled (Fe0.75B0.15Si0.1)100-xTax (х = 0–2) melts. Molecular dynamic simulations with MLIP showed that at Ta concentration of 1 at.% there is a sharp change in the chemical short-range ordering in the melt associated with a change in the interaction of Ta atoms. This effect leads to a restructuring of the cluster formation in the system. At the same time, our experimental investigation shows that melts with a Ta content of 1 at.% have the greatest tendency to undercoolability. Alloying with Ta promotes the formation of primary crystals of Fe2B, and at a concentration of more than 1.5 at.% Ta, also of FeTaB. Herewith, near 1 at.% Ta, the crystallization of the melt proceeds nontrivially: with the formation of two intermediate metastable phases Fe3B and Fe2Ta Laves phase. Also, the highest tendency to amorphization under conditions of quick quenching is exhibited by a melt with a Ta concentration of 1 at.%. The results not only provide understanding of optimal alloying of Fe–B–Si materials but also promote a machine learning method for numerical design of metallic alloys with a small dopant concentration.

Origin and diagenetic evolution of dolomites in Paleogene Shahejie Formation lacustrine organic shale of Jiyang Depression, Bohai Bay Basin, East China

The origin of dolomite in Shahejie Formation shale of Jiyang Depression in eastern China were studied by means of petrologic identification, compositional analysis by X-ray diffraction, stable carbon and oxygen isotopic composition, and trace element and rare earth element analyses. The results show that the development of dolomite is limited in the lacustrine organic rich shale of Shahejie Formation in the study area. Three kinds of dolomite minerals can be identified: primary dolomite (D1), penecontemporaneous dolomite (D2), and ankerite (Ak). D1 has the structure of primary spherical dolomite, high magnesium and high calcium, with order degree of 0.3-0.5, and is characterized by the intracrystalline corrosion and coexistence of secondary enlargement along the outer edge. D2 has the characteristics of secondary enlargement, order degree of 0.5-0.7, high magnesium, high calcium and containing a little iron and manganese elements. Ak is characterized by high order degree of 0.7-0.9, rhombic crystal, high magnesium, high calcium and high iron. The micritic calcite belongs to primary origin on the basis of the carbon and oxygen isotopic compositions and the fractionation characteristics of rare earth elements. According to the oxygen isotopic fractionation equation between paragenetic dolomite and calcite, it is calculated that the formation temperature of dolomite in the shale is between 36.76-45.83 °C, belonging to lacustrine low-temperature dolomite. Based on the maturation and growth mechanism of primary and penecontemporaneous dolomite crystals, a dolomite diagenetic sequence and the dolomitization process are proposed, which is corresponding to the diagenetic environment of Shahejie Formation shale in the study area.