Plate-like Shape Research Articles

Simulation of self-organization processes in crystal-forming systems: Supramolecular cyclic R6 cluster precursors and self-assembly of TeO2-TEL (Tellurite) and TeO2-PAR (Paratellurite) structures

The supramolecular chemistry of oxides of sp elements (SO2, SeO2, and TeO2) is considered. The self-assembly of TeO2-TEL (Tellurite) and TeO2-PAR (Paratellurite) crystal structures is simulated. Methods of combinatorial and topological analysis (TOPOS program package) are applied which are based on constructing a basis 3D network of the structure in the form of a graph, the sites of which correspond to the positions of centroids of TeO2 molecules and the edges characterize bonds between them. The topological type of the basis 2D network in the TeO2-TEL structure corresponds to graphite (C-GRA), while in the TeO2-PAR structure the basis network corresponds to the 3D diamond network (C-DIA). A nanocluster precursor of cyclic type (R6) composed of six covalently bound TeO2 molecules (chair conformation) is established for both structures. The desymmetrization of the cyclic structure of the R6 cluster in TeO2-PAR is related to the formation of Te-Te bonds with lengths of 3.824 and 4.062 A. The symmetry and topology code of the processes of self-assembly of 3D structures from nanocluster precursors is completely reconstructed into the form “primary chain → microlayer → microframework.” In both structures R6 clusters form 2D packings with a coordination number of 6. The cluster self-assembly model explains the specific features of the morphogenesis of TeO2-TEL and TeO2-PAR (phases with low and high crystallization temperatures, respectively): platelike shape, perfect cleavage in the (110) plane, and preferred growth in the primar-chain direction [100] in the former case and growth in the direction of the primary [001] axis with the preferred formation of tetragonal prism faces (110) in the latter case.

Plate-like Na0.5Bi0.5TiO3 particles synthesized by topochemical microcrystal conversion method

Abstract In this work, plate-like Na 0.5 Bi 0.5 TiO 3 (NBT) particles were successfully synthesized from a bismuth layer-structured ferroelectric Na 0.5 Bi 4.5 Ti 4 O 15 (NBT4) precursor by a topochemical microcrystal conversion (TMC) method. Because of the high anisotropic structure, plate-like NBT4 particles were first synthesized by molten salt process. After topochemical reaction with the complementary reactants (Na 2 CO 3 ) and TiO 2 at 950 °C for 4 h in NaCl flux, the layer structure of the NBT4 particles was transformed into a simple perovskite NBT template. The resulting large NBT templates had plate-like shape, an average size of 10–15 μm and retained the morphological features of the NBT4 precursor. The large as synthesized plate-like NBT particles were utilized to fabricate textured 99.40 Na 0.5 Bi 0.5 TiO 3 -0.60BaZrO 3 (NBT-BZ) ceramics via the templated grain growth (TGG) method.

Preparation of silicon-substituted hydroxyapatite coatings on Ti–30Nb–xTa alloys using cyclic electrochemical deposition method

Silicon-substituted hydroxyapatite coatings on Ti–30Nb–xTa alloys, prepared using a cyclic electrochemical deposition method, have been investigated using a variety of surface analytical experimental methods. The silicon-substituted hydroxyapatite (Si-HA) coatings were prepared by electrolytic deposition in electrolytes containing Ca2+, PO43− and SiO32− ions. The deposited layers were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and a wettability test. Phase transformation from (α″+β) to largely β occurred with increasing Ta content in the Ti–30Nb–xTa alloys, yielding larger grain size. The morphology of the Si-HA coatings was changed by increasing the number of deposition cycles, with the initial plate-like structures changing to mixed rod-like and plate-like shapes, and finally to a rod-like structure. From the ATR-FTIR spectra, Si existed in the form of SiO44− groups in Si-HA coating layer. The lowest aqueous contact angles and best wettability were found for the Si-HA coatings prepared with 30 deposition cycles.

Solvent-regulated solvothermal synthesis and morphology-dependent gas-sensing performance of low-dimensional tungsten oxide nanocrystals

This paper reports a solvent-regulated, surfactant-free hydrothermal process at 180°C for 24h to synthesize tungsten oxide (WO3) nanocrystals with various morphologies (urchin-like, rod-like and plate-like WO3) using WCl6 as the W source and just changing the solvents (from ethanol, ethanol/water (1:1 in v/v) to water); then those WO3 nanocrystals are used as the active materials to fabricate gas sensors. The results of XRD, SEM, TEM and N2 adsorption-desorption isotherms indicate that the sample obtained in ethanol takes on a urchin-like morphology (U-WO3) with apparent diameters of 1-2 μm derived by radially aggregating WO3 nanorods (∼5nm in diameter), different from the sample obtained in the mixture of ethanol/water (1:1 in v/v), showing a rod-like morphology (R-WO3 with diameters of ∼5nm), and the product synthesized in water, showing a plate-like shape (P-WO3) with dimensions of (100–200nm)×(100–200nm)×(20–30nm). Common volatile organic compounds (acetone, methanol, methanal, ethanol and benzene) and some gases (H2, CO and H2S) are used as the target substances to evaluate the gas-sensing performance of the WO3 sensors obtained. The U-WO3 sensor is highly sensitive to acetone vapors, whereas the R-WO3 and P-WO3 sensors are highly sensitive to H2S. The morphology-dependent gas-sensing performance can be attributed to the difference in microstructures and crystalline states of the WO3 nanocrystals obtained in different solvents.

The impact of particle shape on the angle of internal friction and the implications for sediment dynamics at a steep, mixed sand–gravel beach

Abstract. The impact of particle shape on the angle of internal friction, and the resulting impact on beach sediment dynamics, is still poorly understood. In areas characterized by sediments of specific shape, particularly non-rounded particles, this can lead to large departures from the expected sediment dynamics. The steep slope (1 : 10) of the mixed sand–gravel beach at Advocate Harbour is stable in large-scale morphology over decades, despite a high tidal range of 10 m or more, and intense shore-break action during storms. The Advocate sand (d < 2 mm) was found to have an elliptic, plate-like shape (Corey Shape Index, CSI ≈ 0.2–0.6). High angles of internal friction of this material were determined using direct shear, ranging from φ ≈ 41 to 49°, while the round to angular gravel was characterized as φ = 33°. The addition of 25% of the elliptic plate-like sand-sized material to the gravel led to an immediate increase in friction angle to φ = 38°. Furthermore, re-organization of the particles occurred during shearing, characterized by a short phase of settling and compaction, followed by a pronounced strong dilatory behavior and an accompanying strong increase of resistance to shear and, thus, shear stress. Long-term shearing (24 h) using a ring shear apparatus led to destruction of the particles without re-compaction. Finally, submerged particle mobilization was simulated using a tilted tray submerged in a water-filled tank. Despite a smooth tray surface, particle motion was not initiated until reaching tray tilt angles of 31° and more, being ≥7° steeper than for motion initiation of the gravel mixtures. In conclusion, geotechnical laboratory experiments quantified the important impact of the elliptic, plate-like shape of Advocate Beach sand on the angles of internal friction of both pure sand and sand–gravel mixtures. The resulting effect on initiation of particle motion was confirmed in tilting tray experiments. This makes it a vivid example of how particle shape can contribute to the stabilization of the beach face.

Hydroxyapatite formation on biomedical Ti–Ta–Zr alloys by magnetron sputtering and electrochemical deposition

The purpose of this study was to investigate hydroxyapatite formation on Ti-25Ta-xZr titanium alloys resulting from radio-frequency magnetron sputtering and electrochemical deposition. Electrochemical deposition of hydroxyapatite (HA) was first carried out using a cyclic voltammetry (CV) method at 80°C in 5mM Ca (NO3)2+3mM NH4H2PO4. Then a physical vapor deposition (PVD) coating was obtained by a radio-frequency (RF) magnetron sputtering technique. The microstructures, phase transformations, and morphologies of the hydroxyapatite films deposited on the titanium alloys were analyzed by optical microscopy (OM), X-ray diffractometer (XRD), energy dispersive X-ray spectroscopy (EDS) and field-emission scanning electron microscopy (FE-SEM). The morphologies of electrochemically deposited HA showed plate-like shapes on the titanium alloys, and the morphologies of the RF-sputtered HA coating had the appearance droplet particles on the plate-like precipitates that had formed by electrochemical deposition. For the RF-sputtered HA coatings, the Ca/P ratio was increased, compared to that for the electrochemically deposited HA surface. Moreover, the RF-sputtered HA coating, consisting of agglomerated droplet particles on the electrochemically deposited HA surface, had better wettability compared to the bulk titanium alloy surface.

Characterization and in vitro biological evaluation of mineral/osteogenic growth peptide nanocomposites synthesized biomimetically on titanium

Nanocomposite layers of mineral/osteogenic growth peptide (OGP) were synthesized on calcium phosphate coated titanium substrates by immersing in calcium-phosphate buffer solution containing OGP. Peptide incorporated mineral was characterized by determining quantity loaded, effects on mineral morphology and structure. Also, the biological activity was investigated by cell adhesion, proliferation assay, and measurement of alkaline phosphatase (ALP) activity. X-ray photoelectron spectroscopy (XPS) and micro-bicinchoninic acid (BCA) assay revealed that OGP was successfully incorporated with mineral and the amount was increased with immersion time. Incorporated OGP changed the mineral morphology from sharp plate-like shape to more rounded one, and the octacalcium phosphate structure of the mineral was gradually transformed into apatite. With confocal microscopy to examine the incorporation of fluorescently labeled peptide, OGP was evenly distributed throughout mineral layers. Mineral/OGP nanocomposites promoted cell adhesion and proliferation, and also increased ALP activity of mesenchymal stem cells (MSCs). Results presented here indicated that the mineral/OGP nanocomposites formed on titanium substrates had the potential for applications in dental implants.

Platelike LiMPO4(M = Fe, Mn, Co, Ni) for Possible Application in Rechargeable Li Ion Batteries: Beyond Nanosize

The peculiarities of LiMPO4 (M = Fe, Mn, Co, Ni) formation with controlled platelike crystal shape using layered M(OH)2 hydroxides as templates were studied. Thin, platelike crystals of NH4MPO4·H2O with Mn, Fe, and Co were formed in aqueous solutions as intermediate products, whereas for NH4NiPO4·6H2O, particles in the form of spherulites were observed. For replacement of ammonium groups by lithium cations, a solid-state reaction between NH4MPO4·xH2O and Li2CO3 at elevated temperatures was used. The obtained LiMPO4 particles repeat completely the shape of the intermediated NH4MPO4·xH2O crystals. The surface of platelike particles represents a cellular structure and consists of agglomerated, slightly randomized crystallites of several hundred nanometers, which are oriented along the c-axis perpendicular to the plate surface. It was shown in the LiFePO4 example that the cathode materials, consisting of platelike particles and reduced graphene oxide (RGO), have the discharge capacity of 145 mAh/g in Li ion batteries after 10 cycles with 0.1C. This value can successfully compete with the best literature results reported for nanosized LiFePO4/RGO cathode materials. A possible explanation of that is discussed.

Low thermal conductivity and high thermoelectric figure of merit in p-type Sb2Te3/poly(3,4-ethylenedioxythiophene) thermoelectric composites

p-type Sb2Te3/poly(3,4-ethylenedioxythiophene) (PEDOT) thermoelectric composites are fabricated by embedding PEDOT into Sb2Te3 matrix. The grains of Sb2Te3 in the composites are found to be in micron degree and keep plate-like shapes. The measurements of thermoelectric properties show that the thermal conductivity κ of the composites is about 0.14 W m−1 K−1 in the temperature range of 300–523 K, much lower than that of Sb2Te3 compounds. The maximum of dimensionless figure of merit of the composites reaches to 1.18 at 523 K, which is the highest value for the reported Sb2Te3/organic composites. It is suggested that the plate-like Sb2Te3 grains and the embedded PEDOTs may play a significant role in decreasing the thermal conductivity. Furthermore, results of the thermal cycling between the room temperature and 523 K for 50 cycles show that the composites are stable with κ remaining a low value.

THERMAL, MICROSTRUCTURE AND DIELECTRIC BEHAVIOR OF LA-MODIFIED BISMUTH TITANATE CERAMIC

Environmentally safe and lead free La-modified bismuth titanate (BLT) was synthesized by conventional solid state reaction method. The thermal, dielectric, Microstructural behaviors of BLT ceramic have been investigated. Based on the thermal stability of BLT, samples were calcined at 750 0 C, percentage weight loss and thermal behavior was studied by TGA/DSC. The influence of La on crystal structure of BLT showed orthorhombic crystal structure. Increase of La concentration does not show a secondary phase. Among all the La-doped BLT ceramic samples, x = 0.60 exemplified good results. Dielectric permittivity of BLT is higher at x = 0.60 comparing to other, microstructure study of sintered ceramic sample showed plate-like shape with enhanced density. The results show that the La 3+ doped BLT ceramics may be used as a probe for the phase transition of the ferroelectric materials.

Phase behaviour of liquid-crystal monolayers of rod-like and plate-like particles.

Orientational and positional ordering properties of liquid crystal monolayers are examined by means of Fundamental-Measure Density Functional Theory. Particles forming the monolayer are modeled as hard parallelepipeds of square section of size σ and length L. Their shapes are controlled by the aspect ratio κ = L/σ (>1 for prolate and <1 for oblate shapes). The particle centers of mass are restricted to a flat surface and three possible and mutually perpendicular orientations (in-plane and along the layer normal) of their uniaxial axes are allowed. We find that the structure of the monolayer depends strongly on particle shape and density. In the case of rod-like shapes, particles align along the layer normal in order to achieve the lowest possible occupied area per particle. This phase is a uniaxial nematic even at very low densities. In contrast, for plate-like particles, the lowest occupied area can be achieved by random in-plane ordering in the monolayer, i.e., planar nematic ordering takes place even at vanishing densities. It is found that the random in-plane ordering is not favorable at higher densities and the system undergoes an in-plane ordering transition forming a biaxial nematic phase or crystallizes. For certain values of the aspect ratio, the uniaxial-biaxial nematic phase transition is observed for both rod-like and plate-like shapes. The stability region of the biaxial nematic phase enhances with decreasing aspect ratios for plate-like particles, while the rod-like particles exhibit a reentrant phenomenon, i.e., a sequence of uniaxial-biaxial-uniaxial nematic ordering with increasing density if the aspect ratio is larger than 21.34. In addition to this, packing fraction inversion is observed with increasing surface pressure due to the alignment along the layers normal. At very high densities the nematic phase destabilizes to a nonuniform phases (columnar, smectic, or crystalline phases) for both shapes.

Effect of Annealing on Structure and Mechanical Behavior of an AA2139 Alloy

An AA2139 alloy with a chemical composition of Al–4.35Cu-0.46%Mg–0.63Ag-0.36Mn–0.12Ti (in wt.%) and an initial grain size of about 155 μm was subjected to annealing at 430°C for 3 h followed by furnace cooling. This treatment resulted in the formation of a dispersion of coarse particles having essentially plate-like shape. The over-aged alloy exhibits lower flow stress and high ductility in comparison with initial material in the temperature interval 20-450°C. Examination of microstructural evolution during high-temperature deformation showed localization of plastic flow in vicinity of coarse particles. Over-aging leads to transition from ductile-brittle fracture to ductile and very homogeneous ductile fracture at room temperature.

The enhanced upconversion fluorescence and almost unchanged particle size of β-NaYF4:Yb3+, Er3+ nanoparticles by codoping with K+ ions

In this work, the improved upconversion (UC) intensity, the same morphology and almost unchanged particle size of β-NaYF4:Yb3+, Er3+ via codoping with low content K+ ions is reported. Hexagonal NaYF4 nanoparticles with a spherical morphology are synthesized by introducing 0–15mol% K+ ions. The morphology of the nanoparticles changed to a hexagonal plate-like shape when the K+ ion concentration continuously increased to 20mol% or more. The UC fluorescence intensities of the green and red emissions of Er3+ are gradually improved and reached a maximum when the concentration of K+ ions was 15mol%. The decay lifetimes of 4S3/2 and 4F9/2 were determined. The enhancement in UC intensity was mainly ascribed to tailoring the local crystal field around Er3+ ions. Furthermore, we tested the optimized concentration by monitoring the decay lifetime of the intermediate 4I11/2 state followed by theoretical steady-state rate equations.

Influence of heat treatment temperatures on structural and magnetic properties of Sr0.50Ca0.20La0.30Fe11.15Co0.25O19 hexagonal ferrites

M-type ferrite Sr0.50Ca0.20La0.30Fe11.15Co0.25O19 magnetic powders and magnets were prepared by a ceramic process. The phase identification of magnetic powders was performed by X-ray diffraction. At calcination temperatures ranging from 1170 to 1270°C, the phase compositions of the magnetic powders consist of M-type hexaferrites together with small amount of impurity phases such as α-Fe2O3, LaFeO3 and CoFe2O4. At calcination temperatures above 1270°C, single-phase M-type hexaferrites can be obtained. The microstructures of the magnets were investigated by field emission scanning electron microscopy. The particles appear in hexagonal plate-like shape and the particles are distributed homogeneously. The radial shrinkage of the magnets increases with the increase of calcination or sintering temperature. The magnetic properties of the magnets and magnetic powders were measured by a permanent magnetic measure equipment and a vibrating sample magnetometer, respectively. For high remanence, intrinsic coercivity, magnetic induction coercivity and maximum energy product, the optimized calcination and sintering temperatures are 1250°C and 1190°C, respectively.

Ultrafine-Grain and Isotropic Cu/SAC305/Cu Solder Interconnects Fabricated by High-Intensity Ultrasound-Assisted Solidification

With the miniaturization of portable electronic devices, the size of solder joint interconnects is decreasing to micrometer levels. These joints possess only several or even one or two grains, resulting in anisotropy and failure issues. Direct ultrasound-assisted solidification of Cu/SAC305/Cu interconnects for grain refinement and fabrication of isotropic solder joints is presented herein. These joints consist of many β-Sn grains. The average cross-sectional area of the Sn-rich phase is significantly reduced by up to 99% when compared with conventional as-reflowed samples. The ultrasonic power density exhibits a threshold value for affecting the microstructures. Below 200 W cm−2, the β-Sn grains were refined and had circular shape. The Ag3Sn phase grew in a manner similar to branched coral to sizes reaching 30 μm, or as rods aggregated together with Cu6Sn5 tube fragments. Above 200 W cm−2, the microstructures were coarsened and Ag3Sn had plate-like shape. The thickness of Cu6Sn5 intermetallic layers at the Cu/solder interfaces was reduced by more than 26%. The relationships among the ultrasonic power, nucleation rate, local temperature drop, and pressure were identified. At the highest power density of 267 W cm−2, the nucleation rate was about 4.05 × 1014 m−3 s−1, the local temperature drop was 248 K, and the local pressure was on the order of several GPa.

Development of highly sensitive mechanoluminescent sensor aiming at small strain measurement

This paper was focused on the elasticoluminescence (ELS) characteristics, especially a response to small strain (below 1000 μst), of mechanoluminescence (ML) sensor using strontium aluminate doped with small amount of europium ( SrAl 2 O 4: Eu ) synthesized by different methods. By using nitrate decomposition method as a synthetic method of SrAl 2 O 4: Eu , the response to small strain of the ML sensor was enhanced in comparison with using a conventional solid-state reaction method. Based on SEM observation and thermoluminescence (ThL) measurement, we proposed a hypothesis that the sensing characteristic of small strain affect the plate-like shape of SrAl 2 O 4: Eu grain and/or shallower carrier trap levels formed by nitrate decomposition method.

Hydrothermal fabrication of hydroxyapatite/chitosan/carbon porous scaffolds for bone tissue engineering

Porous carbon fiber felts (PCFFs) have great applications in orthopedic surgery because of the strong mechanical strength, low density, high stability, and porous structure, but they are biologically inert. To improve their biological properties, we developed, for the first time, the hydroxyapatite (HA)/chitosan/carbon porous scaffolds (HCCPs). HA/chitosan nanohybrid coatings have been fabricated on PCFFs according to the following stages: (i) deposition of chitosan/calcium phosphate precursors on PCFFs; and (ii) hydrothermal transformation of the calcium phosphate precursors in chitosan matrix into HA nanocrystals. The scanning electron microscopy images indicate that PCFFs are uniformly covered with elongated HA nanoplates and chitosan, and the macropores in PCFFs still remain. Interestingly, the calcium-deficient HA crystals exist as plate-like shapes with thickness of 10-18 nm, width of 30-40 nm, and length of 80-120 nm, which are similar to the biological apatite. The HA in HCCPs is similar to the mineral of natural bone in chemical composition, crystallinity, and morphology. As compared with PCFFs, HCCPs exhibit higher in vitro bioactivity and biocompatibility because of the presence of the HA/chitosan nanohybrid coatings. HCCPs not only promote the formation of bone-like apatite in simulated body fluid, but also improve the adhesion, spreading, and proliferation of human bone marrow stromal cells. Hence, HCCPs have great potentials as scaffold materials for bone tissue engineering and implantation.

Early subchondral bone changes in an osteoarthritis model in wild type and tgf-alpha knockout mice

Early subchondral bone changes in an osteoarthritis model in wild type and tgf-alpha knockout mice

Morphology of hydroxyapatite nanoparticles in coatings on nanotube-formed Ti–Nb–Zr alloys for dental implants

The deposition and morphology of hydroxyapatite (HA) nanoparticles on nanotube-formed Ti–Nb–Zr alloys for dental implants has been investigated utilizing electrochemical, field-emission scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy (FTIR) methods. Ti–29Nb−xZr ternary alloys with 3 and 15 wt.% Zr content were prepared by arc melting. Nanotubular oxide layers were formed on these alloys by an anodic oxidation method in 1 M H3PO4 electrolyte containing 0.8 wt.% NaF at room temperature. Hydroxyapatite coatings were deposited onto the nanotubular surfaces via an electrochemical method (pulsed current). The HA layers were well-deposited and contained features of the underlying nanotube structure; observed morphologies consisted of particles, a mixture of particles and plate-like shapes, and entirely plate-like shapes. This variation in morphology occurred with an increasing number of deposition cycles and increases in Ca and P concentrations in the electrolyte. X-ray diffraction revealed that the nanotubular coating contained the anatase form of TiO2, and FTIR indicated that the electrochemically deposited calcium phosphate layer contained HPO42−, PO43−, H2O, and OH− indicative of the HA composition.

Influence of Annealing on Mechanical Properties of Al-20Si Processed by Selective Laser Melting

The microstructure and mechanical properties of Al-20Si produced by selective laser melting (SLM) are investigated for different heat treatment conditions. As a result of the high cooling rate during processing, the as-built SLM material displays a microstructure consisting of a supersaturated Al(Si) solid solution along with heavily refined eutectic Si and Si particles. The Si particles become coarser, and the eutectic Si gradually changes its morphology from fibrous to plate-like shape with increasing annealing temperature. The microstructural variations occurring during heat treatment significantly affect the mechanical behavior of the samples. The yield and ultimate strengths decrease from 374 and 506 MPa for the as-built SLM material to 162 and 252 MPa for the sample annealed at 673 K, whereas the ductility increases from 1.6 to 8.7%. This offers the possibility to tune microstructure and corresponding properties of the Al-20Si SLM parts to meet specific requirements.