Intergrowth Of Crystals Research Articles

Zeolitic Imidazolate Framework/Graphene Oxide Hybrid Nanosheets as Seeds for the Growth of Ultrathin Molecular Sieving Membranes.

A defect-free zeolitic imidazolate framework-8 (ZIF-8)/graphene oxide (GO) membrane with a thickness of 100 nm was prepared using two-dimensional (2D) ZIF-8/GO hybrid nanosheets as seeds. Hybrid nanosheets with a suitable amount of ZIF-8 nanocrystals were essential for producing a uniform seeding layer that facilitates fast crystal intergrowth during membrane formation. Moreover, the seeding layer acts as a barrier between two different synthesis solutions, and self-limits crystal growth and effectively eliminates defects during the contra-diffusion process. The resulting ultrathin membranes show excellent molecular sieving gas separation properties, such as with a high CO2 /N2 selectivity of 7.0. This 2D nano-hybrid seeding strategy can be readily extended to the fabrication of other defect-free and ultrathin MOF or zeolite molecular sieving membranes for a wide range of separation applications.

Fabrication of a highly b-oriented MFI-type zeolite film-modified electrode with molecular sieving properties by Langmuir–Blodgett method

A novel highly compact and b-oriented MFI-type zeolite monolayer was obtained by assembling sec-butanol-modified rounded-coffin-shaped silicalite-1 microcrystals by Langmuir–Blodgett (LB) method. The LB monolayer was subsequently tested as a seed layer for the secondary growth of uniformly b-oriented and defect-free MFI zeolite films on stainless steel substrates and platinum electrodes. Three different methods were evaluated for identifying a suitable synthesis route to suppress the undesired a-oriented twin growth during the synthesis of MFI films. The crystal intergrowth and orientation of the MFI films were characterized by scanning electron microscopy and X-ray diffraction (XRD). The crystallographic preferred orientation indices and preferred orientation coverage values calculated using the XRD data were used to quantitatively determine the preferred orientation and surface coverage of the prepared zeolite films. The experimental results confirm that the low tetrapropylammonium hydroxide (TPAOH) method is the most effective route to suppress the undesired a-oriented twin growth, when the highly b-oriented LB monolayer was used as the seed layer for the secondary growth of the b-oriented MFI film. The highly b-oriented MFI-type zeolite film-modified electrodes were further tested as the working electrodes in electrochemical experiments. Cyclic voltammetry experimental results confirmed that the b-oriented MFI films fabricated at low TPAOH concentration were defect free and possessed a distinct molecular sieving property after calcination. The LB method, a highly reproducible and controllable method for the organization of zeolite crystals, can be further applied as an effective platform for the promotion and development of zeolite-modified electrodes as selective sensors.

Crystal Geometry Mechanism of Intergrowth of Spinel and Manganese Sulfide into a Complex Nonmetallic Inclusion

Acrystal geometry mechanism of intergrowth of crystals of MgAl2O4 spinel and MnS manganese sulfide into a single complex inclusion with anion fcc skeleton is suggested. The deformation of the edges of the polyhedrons during the intergrowth is limited to 10%. The structure of the intermediate layer is shown to be represented by a face union of triangulated polyhedrons the vertexes of which are occupied with oxygen and sulfur ions.

Structure solution and refinement of stacking-faulted NiCl(OH)

Two samples of pure NiCl(OH) were produced by hydrothermal synthesis and characterized by chemical analysis, IR spectroscopy, high-resolution laboratory X-ray powder diffraction and scanning electron microscopy. Layers composed of edge-sharing distorted NiCl6x(OH)6−6xoctahedra were identified as the main building blocks of the crystal structure. NiCl(OH) is isostructural to CoOOH and crystallizes in space groupR\overline{{3}}m[a= 3.2606 (1),c= 17.0062 (9) Å]. Each sample exhibits faults in the stacking pattern of the layers. Crystal intergrowth of (AγB)(BαC)(CβA) and (AγB)(AγB) [C6 like, β-Ni(OH)2related] stacked layers was identified as the main feature of the microstructure of NiCl(OH) byDIFFaXsimulations. A recursion routine for creating distinct stacking patterns of rigid-body-like layers in real space with distinct faults (global optimization) and a Rietveld-compatible approach (local optimization) was realized and implemented in a macro for the programTOPASfor the first time. This routine enables a recursive creation of supercells containing (AγB)(BαC)(CβA), (AγB)(AγB) and (CβA)(BαC)(AγB) stacking patterns, according to user-defined transition probabilities. Hence it is an enhancement of the few previously published Rietveld-compatible approaches. This routine was applied successfully to create and adapt a detailed microstructure model to the measured data of two stacking-faulted NiCl(OH) samples. The obtained microstructure models were supported by high-resolution scanning electron microscopy images.

Crystal Habits of Itraconazole Microcrystals: Unusual Isomorphic Intergrowths Induced via Tuning Recrystallization Conditions.

The external appearance of a crystal of active pharmaceutical ingredient (API), usually referred to as a crystal habit, has a substantial impact on the API's physicochemical and physiochemical properties and, subsequently, its pharmaceutical performance. In this work, we investigate the role of different parameters of antisolvent crystallization impacting on the itraconazole (ITR) crystal habit and how this crystal habit manipulation, including crystal intergrowth, can affect crystal interactions with water molecules. Three distinct isomorphic crystal habits of ITR, a twinned blade-shaped (CHtw), a plate-shaped (CHpl), and a flat sheet-shaped with dendritic ends (CHsh), were obtained by controlling crystallization conditions. A liquid-liquid crystalline phase separation was observed as an intermediate stage preceding crystal growth. The March-Dollase parameter was used as a quantitative description of the preferred orientation, where CHsh exhibited the highest preferred orientation. The three crystal habits were evaluated for their wettability and water vapor distribution, at 37 °C, using the Young-Nelson fitting model. CHtw crystals sorbed a statistically significantly higher amount of water than CHpl and CHsh, which was attributed to the presence of crystal defects due to the twinning boundary. On the other hand, the amount of water adsorbed on the surface of CHpl and CHsh crystals was comparable and it was about twice that adsorbed on CHtw crystals. This was related to the abundance of hydrophilic chemical functionalities on the (010) facet of CHpl and CHsh as supported by the full interaction map carried out using Mercury software. This study expands investigations of the impact of crystal habit manipulation on API's functional properties beyond the well-known solubility improvement approaches.

Rare Metal Chemistry, Microstructures, and Mineralogy of Coal Ash from Thermal Power Plants of Korea

Chemical and mineralogical properties of coal ash samples from the nine thermal power plants of Korea were investigated to acquire basic data for estimating the potential of rare metal recovery. Chemical compositions of coal ash were consistent with those of average shale and foreign coal ashes. However, there were small differences between the metal contents of domestic anthracitic and imported bituminous coal ashes. Unburned coal particles were much abundant in the ash of domestic anthracitic coal. Chalcophile elements were relatively enriched in the fly ash compared to bottom ash. Silicate glass was the major component of coal ash with minor minerals such as quartz, illite (muscovite), mullite, magnetite, lime, and anhydrite. Al and Si were the major components of the glass with varying contents of Ca, Fe, K, and Mg. Glass occurred in a form of porous sphere and irregular pumace-like grain often fused with iron oxide spheres or other glass grains. Iron oxide spheres were fine intergrowth of fast-grown iron oxide crystals in the matrix of silicate glass. Chemical, microstructural, and mineralogical properties would guide successful rare metal recovery from coal ash.

Structure and stability of BaTiSi₂O₇.

Due to their optical, photo-luminescence (PL), and afterglow properties, barium titanosilicates are compounds of great interest for functional materials and light-emitting devices. Among them, BaTiSi2O7 (BTS2) is certainly one of the most intriguing; it displays peculiar properties (e.g. PL orange emission) whose exhaustive explanation has been hampered to date by the lack of a structure model. In this work, BTS2 and the related compound BaTiSi4O11 (BTS4) were synthesized through conventional solid-state reaction methods. BTS2 invariably shows complex twinning patterns. Thus, its structure solution and Rietveld structure refinement were attempted using synchrotron powder diffraction. BTS2 was found to be an intergrowth of monoclinic and triclinic crystals. The monoclinic phase has the space group P21/n and unit cell a = 7.9836 (3), b = 10.0084 (4), c = 7.4795 (3) Å, and β = 100.321 (3)°, whereas the triclinic phase has the space group P\bar 1 and unit cell a = 7.99385 (4), b = 10.01017 (5), c = 7.47514 (3) Å, α = 90.084 (8), β = 100.368 (8) and γ = 89.937 (9)°. These lattices can be seen as a distortion of that of tetragonal synthetic β-BaVSi2O7 with Ti in place of V. The structure models obtained from this study confirm the presence of fivefold coordinated Ti atoms in a distorted pyramidal configuration. The proposed solution supports existing theories for the explanation of the PL orange colour in BTS2.

Studies on the Dual-Templating Function of TBA for the Formation of ZSM-11 Intergrowth Morphology

Hierarchically structured ZSM-11 microspheres with an intergrowth morphology have been hydrothermally synthesized using only one organic templating molecule (TBABr). An investigation of the effects of the structure-directing agent on the zeolite particle morphology and textural properties was performed. It was found that the template tetraalkylammonium ions TBA+ (or TPA+) not only were located in the channel intersections of ZSM-11 (or ZSM-5), but were also attached to the external surface of the precursors, which prevented these precursors from further condensation. Finally, a morphology of numerous nanocrystals inserting into each other was formed, and the voids among these intergrowth crystals endowed these materials with mesoporosity.

Mechanical resilience and cementitious processes in Imperial Roman architectural mortar.

The pyroclastic aggregate concrete of Trajan's Markets (110 CE), now Museo Fori Imperiali in Rome, has absorbed energy from seismic ground shaking and long-term foundation settlement for nearly two millenia while remaining largely intact at the structural scale. The scientific basis of this exceptional service record is explored through computed tomography of fracture surfaces and synchroton X-ray microdiffraction analyses of a reproduction of the standardized hydrated lime-volcanic ash mortar that binds decimeter-sized tuff and brick aggregate in the conglomeratic concrete. The mortar reproduction gains fracture toughness over 180 d through progressive coalescence of calcium-aluminum-silicate-hydrate (C-A-S-H) cementing binder with Ca/(Si+Al) ≈ 0.8-0.9 and crystallization of strätlingite and siliceous hydrogarnet (katoite) at ≥ 90 d, after pozzolanic consumption of hydrated lime was complete. Platey strätlingite crystals toughen interfacial zones along scoria perimeters and impede macroscale propagation of crack segments. In the 1,900-y-old mortar, C-A-S-H has low Ca/(Si+Al) ≈ 0.45-0.75. Dense clusters of 2- to 30-µm strätlingite plates further reinforce interfacial zones, the weakest link of modern cement-based concrete, and the cementitious matrix. These crystals formed during long-term autogeneous reaction of dissolved calcite from lime and the alkali-rich scoriae groundmass, clay mineral (halloysite), and zeolite (phillipsite and chabazite) surface textures from the Pozzolane Rosse pyroclastic flow, erupted from the nearby Alban Hills volcano. The clast-supported conglomeratic fabric of the concrete presents further resistance to fracture propagation at the structural scale.

Aspects of the Mechanism of Nucleation and Intergrowth of Gibbsite Crystals on Sodium Oxalate Surfaces in Concentrated Alkaline Solutions

To mimic the process of gibbsite nucleation on sodium oxalate crystals and their intergrowth in alumina Bayer process, such a coprecipitation process has been broken down into three distinct stages and studied by in situ AFM and ex situ SEM under static conditions. In the first stage, a solution saturated in aluminate and supersaturated in oxalate has been used for investigating the oxalate growth on its {110} face, which is controlled by a layer-by-layer mechanism. In the second stage, in a solution saturated in oxalate and supersaturated in aluminate, gibbsite secondary nucleation was preferred along macrosteps of sodium oxalate {110} faces and appeared as two-dimensional (2D) islands with pisolitic shapes. There does not appear to be a preferred epitaxial relationship at the heterointerface between gibbsite crystals and sodium oxalate substrates, indicating that the magnitude of the surface free energy for nucleation is greater than that associated with strain energy caused by lattice mismatch. In the third stage following gibbsite secondary nucleation, in a solution saturated in aluminate and supersaturated in oxalate, the inclusion of gibbsite crystallites into the bulk of sodium oxalate crystals through step growth on {110} faces of sodium oxalate was observed.

Dirac fermions and superconductivity in the homologous structures(AgxPb1−xSe)5(Bi2Se3)3m(m=1,2)

A newly discovered topological insulator (TI) $({\mathrm{Ag}}_{x}{\mathrm{Pb}}_{1\ensuremath{-}x}\mathrm{Se}{)}_{5}({\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}{)}_{3m}$ ($m=2$) has a band gap of 0.5 eV, the largest value reported in topological insulators. We present a magnetotransport study of the Dirac electrons of this compound in the quantum diffusion regime. Two-dimensional weak antilocalization due to the destructive interference of the Dirac electrons was observed. The phase coherence length of the Dirac electrons is independent of doping and disorder levels. This provides an indication of the backscattering immunity under the protection of time reversal invariance of the TI. We further report that the homologous compound $({\mathrm{Ag}}_{x}{\mathrm{Pb}}_{1\ensuremath{-}x}\mathrm{Se}{)}_{5}({\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}{)}_{3m}$ ($m=1$) is a superconductor with a transition temperature ${T}_{C}=1.7$ K. The related structures of these two phases allow lateral intergrowth of crystals to occur naturally, offering a potential platform to observe the Majorana fermion state at the boundary of two intergrown crystals.

Microporous crystalline silicoaluminophosphates: Effect of synthesis conditions on the physicochemical and catalytic properties in the reaction of methanol to C2-C4 olefins conversion

Effect of the synthesis parameters (reaction mixture composition, crystallization temperature and duration) on the physicochemical and catalytic properties of microporous crystalline silicoaluminophosphates (SAPOs) has been studied. Methods for the directional control of phase composition, degree of crystallinity, morphology and size of SAPO crystals crystallized from colloidal silicoaluminophosphate sols stabilized in tetraethylammoniun hydroxide solution as a template have been developed. It has been determined that the use of more severe synthesis conditions (increase in temperature and duration of crystallization) leads to the formation of larger crystals and a growth in the concentration of medium strength sites in the samples, which causes a rapid deactivation of the samples in the reaction of methanol conversion to C2-C4 olefins. Crystallization under milder conditions (a decrease in pH and temperature) promotes the acid formation of CHA/AEI intergrowth crystals exhibited a high and steady performance in the methanol conversion for more than 8 h at a total yield of olefins of 95 wt %.

Sticking behavior of iron ore–coal pellets and its inhibition

Most previous studies on iron ore–coal pellets (ICPs) have focused on their reduction, but studies on their sticking behavior have not been reported. The sticking behavior of iron ore–coal pellets (ICPs) at high temperatures under a load of 0.1MPa was studied. Temperature was determined to be an important factor that affects the sticking behavior: the sticking increased with increasing temperature; the sticking index was 89.28% at 1373K but only 4.78% at 1223K. The sticking mechanism results from the intergrowth of metallic iron and ferrous oxide crystals between pellet boundaries. High-melting-point materials formed by the combination of MgO and FexOy, can effectively prevent this intergrowth of iron, and the addition of a dolomite powder coating reduces the sticking index from about 90% to about 10%. The addition of limestone and iron ore powder was not found to have any beneficial effect of sticking inhibition.

Non-Destructive Investigation of a Scalenohedral Hematite Pendant from Bahrain,c.1800bc

A scalenohedral hematite pendant (presumably a pseudomorph after a calcite crystal), excavated on Bahrain (ancient Dilmun) in the Persian Gulf from layers dated to c.1800 bc, was investigated using X-ray computed microtomography. The internal porosity was studied in 3D, showing a preferential concentration of small pores in the central part, where carbonate remnants might still be present, and larger, flattened, elongated voids in the subsurface portion. Part of the scalenohedron can be described as an intergrowth of platy hematite crystals. Microtomography also yielded data on pore-size distribution. Considerations are given to the genetic model and the provenance of the hematite pendant.

Influence of Gelatin Hydrogel Porosity on the Crystallization of CaCO3

We investigated the influence of the porosity of the growth medium on the crystallization of calcium carbonate in hydrogels with different gelatin solid contents (2.5, 5, and 10 wt %). In all experiments, the precipitate consisted of calcite with occasional occurrences of some vaterite and aragonite. The calcite grew as compact radial intergrowths of crystals that show rhombohedral external faces. The crystal surfaces consist of identical 1–10 μm sized rhombohedral sub-blocks. Electron backscatter diffraction (EBSD) uncovered the radial intergrowth structure of the aggregates. EBSD also documented the internal microscale mosaicity and mesocrystal-like constitution of the gel-grown calcite. Raman spectroscopy and thermogravimetric analysis confirmed the presence of gelatin within the crystals. It reached up to ∼2 mass % in the calcite-gelatin composites that formed in hydrogels with 10 wt % gelatin content. Calcite morphology and mosaicity varied with the gelatin content of the hydrogel, such that an incre...

Influence of Si species on intergrowth and anisotropic crystal growth of silicalite-1

Silicalite-1 crystals were hydrothermally synthesized from silica gels prepared under different conditions. The influence of the state of Si species in the silica gels and the concentrations of silicate ions and a template agent in the reaction sols on crystal growth of silicalite-1 was examined. The use of silica gels with a high degree of condensation of Si species resulted in the intergrowth of silicalite-1 crystals, whereas a low degree of condensation of Si species led to coffin-shaped crystals. Thus, the degree of condensation of Si species had significant influence on the intergrowth of silicalite-1 crystals. Moreover, at a low silicate concentration, silicalite-1 crystals elongated along the c-axis were obtained. With increasing silicate concentration in the reaction sols, the aspect ratio of silicalite-1 decreased. Furthermore, with decreasing the amount of N(C3H7) 4 + used as a template agent, the silicalite-1 crystals became larger isotropically. Thus, the growth direction of silicalite-1 crystals was dependent on silicate ion concentration in the reaction sols, but not on N(C3H7) 4 + concentration.

Synthesis of Continuous and Dense TAPO-5 Molecular Sieve Membranes by Steam-assisted Gel Conversion Method

TAPO-5 molecular sieve membranes were synthesized by using steam-assisted gel conversion method. The as-synthesized TAPO-5 membranes were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), as well as UV-visible diffuse reflectance spectroscope (UV-Vis). Results were compared with those by conven- tional hydrothermal crystallization method. The influences of the aging conditions and crystallization time on the sur- face morphology, coverage and denseness of the membrane together with the crystalline structure of molecular sieve crystals were investigated. By using steam-assisted gel conversion method, continuous and dense TAPO-5 molecular sieve membranes could be fabricated on porous -Al2O3 substrates after crystallization for 48 h because the pre-aged solid gel were favorable to the incorporation of Ti atoms into the tetrahedral framework and the intergrowth of TAPO-5 crystals.

Combined silica sources to prepare preferentially oriented silicalite-1 layers on various supports

Direct in-situ hydrothermal synthesis was optimized via combination of monomeric (TEOS) and colloidal (TOSIL) silica sources to prepare preferentially b-oriented high silica MFI zeolite (silicalite-1) layers on different supports using conventional heating. Crystallographic Preferred Orientation (CPO) indices and our created Preferred Orientation Coverage (POC) values were used to determine preferred orientation and its surface coverage. Particle size distribution of precursor species was measured with Dynamic Light Scattering technique. Crystal intergrowth and zeolite phase purity were checked with Scanning Electron Microscope and X-ray diffraction. Solid and (a+b)-oriented self-supported silicalite-1 layers were synthesized on mercury surface at static and vibration conditions. Additional self-assembled and oriented silicalite-1 layers floating in bulk solution were prepared from solutions with enhanced silica content. Preferentially b-oriented silicalite-1 layers were prepared on silicon wafer and polished non-porous stainless steel. Partial b-orientation was achieved for polished porous stainless steel supports. Remarkably intergrown and b-oriented silicalite-1 layers were synthesized on porous stainless steel covered by TiO2 layer that was impregnated with tetrabutylorthotitanate acting as a coupling agent and/or surface charge modifier.

Kinetics and Mechanism of Spontaneous Crystallization of Potassium Nitrate from Its Supersaturated Aqueous Potassium Nitrate from Its Supersaturated Aqueous Solutions

Kinetics of spontaneous crystallization of potassium nitrate from its supersaturated aqueous solutions has been studied simultaneously by electrical conductance and optical transmittance methods. It was found that spontaneous crystallization of potassium nitrate was accompanied by aggregation of crystals. Growth of salt crystals was in the kinetic mode of the growth process, and was described by the equation of the first order regarding supersaturation of solution. The mechanism of aggregation and intergrowth of crystals during bulk crystallization via formation of nucleus-bridges between crystals found earlier for several salts was confirmed. Specific surface energy of potassium nitrate was evaluated on the basis of the above mechanism of aggregation and intergrowth of crystals. The established value of the specific surface energy was reasonable and agreed satisfactorily with the available literature data. Examination of crystal deposit after completion of crystallization allowed detecting crystal agglomerates of freakish and irregular forms, which may be considered as the direct confirmation of the above mechanism of intergrowth of crystals. Kinetics of crystallization, aggregation and size distribution of salt crystals after completion of crystallization have been satisfactory described by the earlier proposed model of the crystallization process. An excellent agreement was established between the experimental data on potassium nitrate solubility in aqueous solutions found in the present work and those available in the literature.

One step in situ synthesis of supported zeolitic imidazolate framework ZIF-8 membranes: Role of sodium formate

Zeolitic imidazolate frameworks (ZIFs), a sub-class of metal–organic frameworks (MOFs), are noted for their remarkable thermal and chemical stability, tunable microporous channels, and tailorable physical/chemical properties. When synthesized as films, they hold great potentials for gas sensing, catalytic membrane reactor, and gas separation membrane applications. Here, we report one step in situ synthesis of ZIF-8 membranes on unmodified porous α-alumina supports in the presence of sodium formate. In this in situ method, sodium formate plays a critical role for formation of well-intergrown continuous ZIF-8 membranes. Sodium formate was found to enhance the heterogeneous nucleation of ZIF-8 crystals on alumina supports as well as to promote intergrowth of ZIF-8 crystals. It was confirmed that sodium formate reacts with zinc source to form zinc oxide layers on α-alumina supports, which in turn promote heterogeneous nucleation. ZIF-8 membranes show molecular sieving behavior, favoring smaller molecules. It was found that sodium formate promotes heterogeneous nucleation in other ZIF systems as well, leading to continuous films of ZIF-7, Zn(Im)2 (ZIF-61 analog), ZIF-90, and SIM-1.