Morphologies Of Microcrystals Research Articles

Thermal conductivity enhancement of epoxy by a 3D Si3N4 crystal rod/grain skeleton fabricating from photovoltaic silicon waste

Silicon nitride (Si3N4) is one of the preferred fillers for the preparation of high thermal conductivity polymer composites because of its intrinsic high thermal conductivity and good electrical insulation. To maximize the thermal conductivity enhancement effect of the fillers in the composites, it is necessary to pre-construct a three-dimensional (3D) thermally conductive filler network. Herein, surfactant foaming was applied to pre-construct a 3D Si-containing framework from photovoltaic silicon waste (PSW), which was subsequently transformed into a porous skeleton consisting of Si3N4 rods and grains by in-situ nitridation reaction sintering. And finally, thermal conductive Si3N4/epoxy (EP) composites were fabricated after infiltrating EP into the network skeleton. When the filler content of Si3N4 was 41.00 vol%, the obtained Si3N4/EP composite showed the highest thermal conductivity of 2.99 W·m-1·K-1, which was 13.95 times higher than that of pure EP. Tests on running CPU and heating table showed that the Si3N4/EP substrate had excellent heat dissipation performance compared to the pure EP substrate. The 3D continuous network formed by "bridging" between two different morphologies of Si3N4 microcrystals contributed to providing effective multi-directional heat transfer paths and thereby improving the thermal conductivity of the composites. Overall, the low cost of raw silicon source originating from industrial waste as well as the simple and practical construction of heat-conducting filler network demonstrate the promising application of the Si3N4/EP composites fabricated in our work.

2D Self-Assembly of Large-Sized Inorganic Nanosheets Leading to Enhanced Power Factors in Earth-Abundant Cu3SbSe4-Based Flexible Hybrid Films.

Fabrication of large-sized inorganic nanosheets is an efficient strategy to promote carrier transportation in flexible thermoelectric (TE) films. Herein, we report the self-assembly of large-sized Cu3SbSe4 nanosheets by using a Se nanowire template via wet chemical synthesis and then vacuum-assisted filter these plate-like microcrystals on nylon to prepare Cu3SbSe4 flexible thermoelectric (TE) hybrid films. SEM reveals that the as-synthesized Cu3SbSe4 powders by using Se nanowires as selenium sources presented 2D plate-like micron structures uniformly and tightly self-assembled by acute triangle-like nanoparticles. Furthermore, XPS evidences that extra Sb vacancies are generated in the unit cell of Cu3SbSe4 crystals synthesized by using the Se NW template, resulting in the shrinkage of the unit cell and the narrowing interplanar spacing, which are characterized by XRD and TEM. As a result, both carrier concentration and carrier mobility have been significantly improved. The high carrier concentration is proved to originate from the extra carriers induced by Sb vacancies, and the high carrier mobility of the film is mainly ascribed to its continuous grain boundaries in the plate-like microcrystal morphology. The large-sized nanosheet Cu3SbSe4/nylon hybrid film (CSS MPs) exhibits a high power factor (PF) of 235.45 μW m-1 K-2 at 400 K, which is 4.23 times higher than that of the Cu3SbSe4/nylon hybrid film (CSS NPs) where Cu3SbSe4 crystals are synthesized by using raw Se particles. This work reveals a novel approach to prepare plate-like Se-based semiconductors, which requires both high carrier concentration and high carrier mobility.

Facile regulation of cuprous oxide microcrystal morphology and planes for visible light photocatalytic degradation

Cuprous oxide (Cu2O) microcrystal is an excellent material for absorbing visible light and photo-catalyzing various water pollutants. The photocatalytic performance of Cu2O crystal mainly depends on its morphology and exposure surface. In this study, Cu2O crystals have been successfully fabricated at room temperature. Morphology and the proportion of exposed crystal faces are regulated by a simple method with hydrazine hydrate as the reducing agent. The experimental results unveiled that high dosage of hydrazine hydrate tends to produce crystals with spherical and low (111) plane ratios, while low dosage of hydrazine hydrate provides an excellent condition for the formation of octahedral microcrystal with high proportion of (111) planes. The photocatalytic degradation efficiency of methylene blue (MB) in visible light increased with the proportion of (111) planes. Analysis shows that the better crystallinity and conductivity of the octahedron structure improved the utilization rate of photogenerated carriers, while the unsaturated Cu on the (111) planes as the active site promotes the decomposition of the pollutants.

Evolution of calcite microcrystal morphology during experimental dissolution

ABSTRACTPhanerozoic limestones are composed of low-Mg calcite microcrystals (i.e., micrite) that typically measure between 1 and 9 μm in diameter. These microcrystals, which host most of the microporosity in subsurface reservoirs, are characterized by a variety of microtextures. Despite the overwhelming consensus that calcite microcrystals are diagenetic, the origin of the various textures is widely debated. The most commonly reported texture is characterized by polyhedral and rounded calcite microcrystals, which are interpreted to form via partial dissolution of rhombic microcrystals during burial diagenesis. A proposed implication of this model is that dissolution during burial is responsible for significant porosity generation. This claim has been previously criticized based on mass-balance considerations and geochemical constrains. To explicitly test the dissolution model, a series of laboratory experiments were conducted whereby various types of calcites composed of rhombic and polyhedral microcrystals were partially dissolved under a constant degree of undersaturation, both near and far-from-equilibrium.Our results indicate that calcite crystals dissolved under far-from-equilibrium conditions develop rounded edges and corners, inter-crystal gulfs (narrow grooves or channels between adjacent crystals), and a few etch pits on crystal faces—observations consistent with the burial-dissolution hypothesis. Crystals dissolved under near-equilibrium conditions, in contrast, retain sharp edges and corners and develop ledges and pits—suggesting that dissolution occurs more selectively at high-energy sites. These observations support the longstanding understanding that far-from-equilibrium dissolution is transport-controlled, and near-equilibrium dissolution is surface-controlled. Our results also show that while the rhombic calcite crystals may develop rounded edges and corners when dissolved under far-from-equilibrium conditions the crystals themselves do not become spherical. By contrast, polyhedral crystals not only develop rounded edges and corners when dissolved under far-from-equilibrium conditions but become nearly spherical with continued dissolution. Collectively, these observations suggest that rounded calcite microcrystals more likely form from a precursor exhibiting an equant polyhedral texture, rather than from a euhedral rhombic precursor as previously proposed. Lastly, the observation that calcite crystals developed rounded edges and corners and inter-crystal gulfs after only 5% dissolution indicates that the presence of such features in natural limestones need not imply that significant porosity generation has occurred.

Recognizing and understanding silica-polymorph microcrystals in ceramic glazes

Different methods have been historically used to identify silica-polymorph microcrystals in various contexts. However, in the existing literature there is a substantial lack of correlation between local probe analytical data and the corresponding images showing crystal morphologies. Here we demonstrate that such correlation is attainable through an approach based on the characterization of samples prepared as polished thin sections combining optical microscope images with local probe techniques (synchrotron through-the-substrate X-ray microdiffraction and confocal micro-Raman). We report the characterization of different morphologies of silica microcrystals embedded in lead glazes from glazed pottery produced in Jouques (France) in the mid-19th century. Among the eight identified morphologies, are worthy of note cristobalite-coated quartz, paramorphic quartz after cristobalite, cristobalite-tridymite intergrowths or cristobalite twinned crystals. Elusive tridymite has been identified and mapped using μ-Raman and locates predominantly at the borders of some morphologies suggesting a growth front of tridymite that turns to cristobalite.

Experimental stabilization of carbonate sediments to calcite: Insights into the depositional and diagenetic controls on calcite microcrystal texture

Aragonite and high-magnesium calcite are abundant constituents of modern shallow marine carbonate sediments, but are rare in ancient carbonate rocks. Because these minerals are metastable, they tend to stabilize to microcrystalline calcite which is ubiquitous in most Phanerozoic marine and lacustrine limestones. Calcite microcrystals exhibit a range of textures that have been classified in terms of crystal size, morphology, and contact geometry. These textures have the potential to reveal information about the precursor sediments as well as the diagenetic conditions of stabilization, and thus may serve as a proxy for paleoenvironmental conditions. However, despite their ubiquity and importance, the origin of these textures is controversial. Hypotheses regarding the origin of calcite microcrystal textures typically involve inferences regarding the precursor depositional sediments, diagenetic conditions of stabilization, or diagenetic processes. Here, hundreds of laboratory experiments were conducted in which metastable carbonate sediments were stabilized to calcite. The goal of these experiments was to investigate the depositional and diagenetic controls on calcite microcrystal textures. The depositional variables investigated were precursor mineralogy, type, and size, and the diagenetic variables were temperature, fluid chemical composition, and fluid:solid ratio. Our results show that experimental stabilization of carbonate sediments produces calcite with a wide variety of textures depending on the various depositional and diagenetic parameters. These textures are remarkably similar to those commonly observed in the rock record. Calcite microcrystal morphology is controlled by fluid chemistry, fluid:solid ratio, and reactant type. Calcite microcrystal size is controlled by temperature, fluid chemistry, fluid:solid ratio, and reactant size. The degree to which calcite microcrystals are fitted together is controlled by reactant size and reactant microstructure. Our findings challenge most of the existing hypotheses regarding the origin of calcite microcrystal textures. We specifically show that textures that have been interpreted to indicate late diagenetic processes such as dissolution and cementation, may be the result of the early diagenetic processes of stabilization.

Pulsed electric fields induce modulation of protein liquid-liquid phase separation.

The time-resolved dynamic assembly and the structures of protein liquid dense clusters (LDCs) were analyzed under pulsed electric fields (EFs) applying complementary polarized and depolarized dynamic light scattering (DLS/DDLS), optical microscopy, and transmission electron microscopy (TEM). We discovered that pulsed EFs substantially affected overall morphologies and spatial distributions of protein LDCs and microcrystals, and affected the phase diagrams of LDC formation, including enabling protein solutions to overcome the diffusive flux energy barrier to phase separate. Data obtained from DLS/DDLS and TEM showed that LDCs appeared as precursors of protein crystal nuclei, followed by the formation of ordered structures within LDCs applying a pulsed EF. Experimental results of circular dichroism spectroscopy provided evidence that the protein secondary structure content is changing under EFs, which may consequently modulate protein-protein interactions, and the morphology, dimensions, and internal structure of LDCs. Data and results obtained unveil options to modulate the phase diagram of crystallization, and physical morphologies of protein LDCs and microcrystals by irradiating sample suspensions with pulsed EFs.

A multi-technique study of altered granitic rock from the Krunkelbach Valley uranium deposit, Southern Germany.

Herein, a multi-technique study was performed to reveal the elemental speciation and microphase composition in altered granitic rock collected from the Krunkelbach Valley uranium (U) deposit area near an abandoned U mine, Black Forest, Southern Germany. The former Krunkelbach U mine with 1–2 km surrounding area represents a unique natural analogue site with the rich accumulation of secondary U minerals suitable for radionuclide migration studies from a spent nuclear fuel (SNF) repository. Based on a micro-technique analysis using several synchrotron-based techniques such as X-ray fluorescence analysis, X-ray absorption spectroscopy, powder X-ray diffraction and laboratory-based scanning electron microscopy and Raman spectroscopy, the complex mineral assemblage was identified. While on the surface of granite, heavily altered metazeunerite–metatorbernite (Cu(UO2)2(AsO4)2−x(PO4)x·8H2O) microcrystals were found together with diluted coatings similar to cuprosklodowskite (Cu(UO2)2(SiO3OH)2·6H2O), in the cavities of the rock predominantly well-preserved microcrystals close to metatorbernite (Cu(UO2)2(PO4)2·8H2O) were identified. The Cu(UO2)2(AsO4)2−x(PO4)x·8H2O species exhibit uneven morphology and varies in its elemental composition, depending on the microcrystal part ranging from well-preserved to heavily altered on a scale of ∼200 μm. The microcrystal phase alteration could be presumably attributed to the microcrystal morphology, variations in chemical composition, and geochemical conditions at the site. The occurrence of uranyl-arsenate-phosphate and uranyl-silicate mineralisation on the surface of the same rock indicates the signatures of different geochemical conditions that took place after the oxidative weathering of the primary U- and arsenic (As)-bearing ores. The relevance of uranyl minerals to SNF storage and the potential role of uranyl-arsenate mineral species in the mobilization of U and As into the environment is discussed.

Realization of superior electrochemical performances for ZnMoO4 anode material through the construction strategy of 3D flower-like single crystalline

3D flower-like single crystalline ZnMoO4 microcrystals have been constructed via a facile one-step hydrothermal process. The influences of reaction time and reaction temperature on phase purities and morphologies of ZnMoO4 microcrystals have been investigated in detail. The results illustrate that 3D flower-like single crystalline ZnMoO4 microcrystals with mesoporous architecture can be obtained after being hydrothermal treated at 150 °C for 12 h, which can enhance the stability of structure and facilitate the diffusion of lithium ions. When applied as lithium-ion batteries anode materials, they can deliver a high discharge capacity of 514.9 mAh g−1 at a current rate of 1 C after 500 cycles with nearly 92% capacity retention based on the discharge capacity of 2nd cycle. Most importantly, they also present superior electrochemical performances even at high rates (the capacities of 316.2 and 216.9 mAh g−1 even after 2000 cycles at very large current rate of 5 and 10 C, respectively). The electrochemical results further confirm that 3D flower-like single crystalline ZnMoO4 microcrystals possess high capacity, good rate capability and superior cyclic stability. Our work may provide an effective and facile strategy to control the microstructures and boost the electrochemical performances for transition metal molybdate electrode materials.

Hierarchical MFI Zeolites with a Single-Crystalline Sponge-Like Mesostructure.

Single-crystalline sponge-like MFI mesoporous zeolites (SSMZs) have been synthesized by using bolaform surfactants with an axial chiral binaphthyl core in the hydrophobic tail and triquaternary ammonium head groups, as bifunctional organic structure-directing agents (OSDAs). By changing the length of alkyl chain between a triquaternary ammonium head group and a binaphthyl group from 4 to 10 carbons, SSMZs with high specific surface area (382-434 m2 g-1 ), abundant micropore-mesopore connectivity, and uniform mesopore diameter (4-10 nm) were obtained. OSDAs with an alkyl chain length of 11 and 12 carbons led to the formation of nanorod-constructed mesoporous MFI zeolites. A geometrical matching between the cylindrical arrangement of the binaphthyl groups and the zeolitic framework is speculated to be the key factor for the formation of mesoporous zeolites. The SSMZ zeolites, with abundant mesopores beneficial for the diffusion of reactants, exhibited significantly higher catalytic efficiencies than those of the conventional ZSM-5 with a microcrystal morphology (≈1.5 μm).

Shape-Controlled Micro-Crystals of Chain-Like Zn(II) Coordination Polymer [Zn(NIA)EDA]∝ and Its Catalytic Performance

Abstract In this study, a new Zn coordination polymer (Zn-CP), hereafter, 1Zn, was successfully assembled in a solvothermal system, exhibiting one-dimensional extended chains. 1Zn morphologies were controlled by temperature and surfactants. In addition, the catalytic performance of 1Zn microsized CP was investigated. Knoevenagel condensation after 4 h afforded a conversion of 86%, and a conversion greater than 96% was obtained for 4-chlorobenzaldehyde and 4-bromobenzaldehyde because of their electron-withdrawing ligands. In addition, excellent selectivity was achieved for the degradation (64% conversion) of malachite green in aqueous solution. The microcrystal morphology affected the conversion, and a relative catalytic mechanism was proposed. The developed strategy of shape-controlled assembled CPs will certainly enhance new potential applications of micro-CPs.

Conformational Effect of Polymorphic Terfluorene on Photophysics, Crystal Morphologies, and Lasing Behaviors

Molecular conformation is an important factor in flexible organic molecules and deeply influences their physical and chemical properties. Here, a model fluorene trimer, 2,2′:7′,2″-ter(9,9-dimethylfluorene) (TDMeF), was designed and synthesized to investigate the effect of conformational diversity of oligofluorene on the morphologies of microcrystals and photophysical properties. Single crystal X-ray diffraction analysis indicates that TDMeF has four polymorphs with different molecular conformations, and crystalline polymorphism is first observed in oligofluorenes. Moreover, the slight change in molecular conformation leads to form different crystal morphologies, namely, ribbon and rodlike microcrystals, in virtue of different intermolecular interactions. Finally, although both microcrystals display deep blue lasing behaviors, the rodlike microcrystal shows a threshold of 114 W/cm2, which is twice times lower than that of the ribbon-like one due to the effect of molecular orientation and optical microcavity.

Spectral management and energy‐transfer mechanism of Eu3+‐doped β‐NaGdF4:Yb3+,Er3+ microcrystals

Abstractβ‐NaGdF4:Yb3+,Er3+ upconversion (UC) microcrystals were prepared by a facile hydrothermal process with the assistance of ethylene diamine tertraacetic acid (EDTA). The β‐NaGdF4 UC microcrystal morphology was controlled by changing the doses of EDTA and NaF. Uniform hexagonal structure can be obtained at the 2 mmol EDTA and 9‐10 mmol NaF. The UC emissions of β‐NaGdF4:Yb3+,Er3+ microcrystals were tuned by the variation of Eu3+ doping level (0%‐5%), where the red/green intensity ratio decreased with the Eu3+ concentration increase. It was found on the base of rate equations that with the Eu3+ doping, the energy back transfer process 2H11/2/4S3/2 (Er3+) → 4I13/2 (Er3+) decreased. In addition, an energy‐transfer process from 4F7/2 (Er3+) to 5D1 (Eu3+) and a cross relaxation process of 7H9/2 (Er3+) + 5D0 (Eu3+) → 4F7/2 (Er3+) + 5D2 (Eu3+) were proposed and verified by rate equations, which dominated the energy‐transfer mechanism between Er3+ and Eu3+, resulted in the spectra tuning of β‐NaGdF4:Yb3+,Er3+. The results suggested that the color tuning of β‐NaGdF4:Yb3+,Er3+,Eu3+ UC microcrystals would have potential applications in such fields as flat‐panel displays, solid‐state lasers, and photovoltaics.

Honeycomb layered oxide Na3Ni2SbO6 for high performance pseudocapacitor

Abstract In this study, Na3Ni2SbO6 was synthesized by simple solid state method and its electrochemical behaviour was examined as a supercapacitor electrode for the first time. Na3Cu2SbO6 was also synthesized by the same preparation method in order to compare with the Na3Ni2SbO6. The structure and morphology of the samples were characterized by XRD, XPS and SEM analysis. The results shows O3-type honeycomb layered Na3Ni2SbO6 with microcrystal morphology. Electrochemical properties were characterized by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy. The results showed that the specific capacitance of the Na3Ni2SbO6 and Na3Cu2SbO6 electrodes were 397 F/g and 50 F/g at the current density of 0.5 A/g respectively. The high pseudocapacitive nature of Na3Ni2SbO6 can be attributed to reversible redox reaction of Ni(II)/Ni(III).

Direct imaging of defect formation in strained organic flexible electronics by Scanning Kelvin Probe Microscopy.

The development of new materials and devices for flexible electronics depends crucially on the understanding of how strain affects electronic material properties at the nano-scale. Scanning Kelvin-Probe Microscopy (SKPM) is a unique technique for nanoelectronic investigations as it combines non-invasive measurement of surface topography and surface electrical potential. Here we show that SKPM in non-contact mode is feasible on deformed flexible samples and allows to identify strain induced electronic defects. As an example we apply the technique to investigate the strain response of organic thin film transistors containing TIPS-pentacene patterned on polymer foils. Controlled surface strain is induced in the semiconducting layer by bending the transistor substrate. The amount of local strain is quantified by a mathematical model describing the bending mechanics. We find that the step-wise reduction of device performance at critical bending radii is caused by the formation of nano-cracks in the microcrystal morphology of the TIPS-pentacene film. The cracks are easily identified due to the abrupt variation in SKPM surface potential caused by a local increase in resistance. Importantly, the strong surface adhesion of microcrystals to the elastic dielectric allows to maintain a conductive path also after fracture thus providing the opportunity to attenuate strain effects.

Incorporation of various alcohol substituents to a metalloporphyrin platform for dramatic changes in morphologies of microcrystals

Micro crystals with various morphologies have been successfully grown from readily accessible molecular platform [10,20-bis(2,6-dibutoxyphenyl)porphyrin]Sn(OH)2. Simple synthetic alteration makes this platform into various molecular building blocks using its axial coordination sites which trigger additional interactions and allow various crystal packing arrangements. We have demonstrated how apparently small modifications to building blocks can initiate significant changes in the morphologies and molecular packings of the corresponding solid state-state materials.

Anion-controlled morphologies and photophysical features of organic microcrystals by solid-phase anion exchange reactions

Anions play key roles in controlling the morphologies of organic microcrystals fabricated by simple and green solid-phase anion exchange reactions.

Nanosuspensions Containing Oridonin/HP-β-Cyclodextrin Inclusion Complexes for Oral Bioavailability Enhancement via Improved Dissolution and Permeability.

Chemotherapy via oral route of anticancer drugs offers much convenience and compliance to patients. However, oral chemotherapy has been challenged by limited absorption due to poor drug solubility and intestinal efflux. In this study, we aimed to develop a nanosuspension formulation of oridonin (Odn) using its cyclodextrin inclusion complexes to enhance oral bioavailability. Nanosuspensions containing Odn/2 hydroxypropyl-β-cyclodextrin inclusion complexes (Odn-CICs) were prepared by a solvent evaporation followed by wet media milling technique. The nanosuspensions were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and dissolution. The resulting nanosuspensions were approximately 313.8 nm in particle size and presented a microcrystal morphology. Nanosuspensions loading Odn-CICs dramatically enhanced the dissolution of Odn. Further, the intestinal effective permeability of Odn was markedly enhanced in the presence of 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) and poloxamer. Bioavailability studies showed that nanosuspensions with Odn-CICs can significantly promote the oral absorption of Odn with a relative bioavailability of 213.99% (Odn suspensions as reference). Odn itself possesses a moderate permeability and marginal intestinal metabolism. Thus, the enhanced bioavailability for Odn-CIC nanosuspensions can be attributed to improved dissolution and permeability by interaction with absorptive epithelia and anti-drug efflux. Nanosuspensions prepared from inclusion complexes may be a promising approach for the oral delivery of anticancer agents.

Morphology and Piezoelectric Properties of Diphenylalanine Microcrystals Grown from Methanol-Water Solution

Morphology and piezoelectric properties of diphenylalanine microcrystals grown by drying the droplet of methanol and water mixture in various proportions have been studied. We have found that the increase of water concentration leads to the significant change of the microcrystal morphology from flat dendrite structures to elongated microcrystals: microtubes and microrods. The effect was attributed to increasing of the drying time. The morphology of the dendrite structures was revealed and empirical dependence of the dendrite thickness on diameter was found. Finally, the piezoelectric activity of the microtubes was demonstrated using the piezoresponse force microscopy.

Controlled synthesis of different morphologies of TiB2 microcrystals by aluminum melt reaction method

TiB2 microcrystals with different morphologies, including hexagonal plate-like, tower-like and dendritic, were fabricated by aluminum melt reaction method in this study. The growth mechanisms of these microcrystals are also discussed based on the fundamental crystal growth theories. It is found that the growth of TiB2 is controlled by two-dimensional nucleation in aluminum melt. If the atomic concentration, reaction rate and atomic diffusion rate in the melt are high, TiB2 microcrystals exhibit hierarchical tower-like and dendritic morphologies. Otherwise, the single crystal of hexagonal plate-like morphology is obtained. The growth of the hierarchical TiB2 microcrystals is controlled by two steps, intermittent two-dimensional nucleation and continuous lateral spreading of layers on the growth faces.