Hexagonal Prism Shape Research Articles

Study of ZnO nanoparticle-doped dental adhesives on enamels with fluorosis: Electron microscopy, elemental composition and shear bond strength analysis.

This study aimed to evaluate dental adhesives containing different concentrations of zinc oxide nanoparticles (ZnO-NPs) for their use in the treatment of dental fluorosis, observe the interaction of the adhesive on healthy enamel surfaces and with mild and moderate fluorosis, measure the adhesive strength and fluorosis, and determine the phosphorus (P) and calcium (Ca) content on these surfaces, as a reference for the potential use of this adhesive with ZnO-NPs for dental fluorosis treatment. Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) were used to characterise the ZnO-NPs and analyse the weight percentages of P and Ca in the enamel using X-ray energy dispersive spectroscopy (EDS) and the adhesive strength using a universal mechanical testing machine. FESEM characterisation revealed that the ZnO-NPs were less than 100nm in size, with quasi-spherical and hexagonal prism shapes. The synthesis of the ZnO-NPs was confirmed by TEM, revealing their hexagonal crystalline structure. The adhesive strength by the universal mechanical testing machine showed that the adhesive with a 3% wt. concentration of ZnO-NPs was better in the three groups of teeth, showing higher adhesive strength in teeth with mild (15.15MPa) and moderate (12.76MPa) fluorosis surfaces, and was even higher than that in healthy teeth (9.65MPa). EDS analysis showed that teeth with mild and moderate fluorosis had the highest weight percentages of P and Ca, but there were no statistically significant differences compared to healthy teeth and teeth treated with adhesives. Lay description: This study focused on testing a new dental adhesive containing small particles called ZnO nanoparticles (ZnO-NPs). This study aimed to demonstrate whether this adhesive with ZnO-NPs could be useful for treating dental fluorosis by improving its adhesion to teeth. One of the first objectives was to determine whether the dental adhesive could adhere better to teeth affected by mild or moderate fluorosis than to healthy teeth by measuring whether the levels of two important elements for healthy teeth, calcium (Ca) and phosphorus (P), were affected by the adhesive. The size and shape of the small particles and teeth with mild or moderate fluorosis were observed using scanning electron microscopy. The nanoparticles were small (< 100nm) and had specific quasi-spherical and hexagonal prismatic shapes. More damage to the enamel was observed in teeth with mild or moderate fluorosis than in healthy teeth. The adhesive strength test demonstrated that the dental adhesive with 3% ZnO-NPs had the best adhesion on all healthy conditions of teeth. It was particularly effective in teeth with mild or moderate fluorosis. Finally, the evaluation of the levels of P and Ca on the enamel showed that teeth with fluorosis had higher levels of these elements, but using the dental adhesive with ZnO-NPs did not change the levels of these elements significantly because the adhesive avoided greater detachment because of greater adhesion to these surfaces. In conclusion, adding these small particles to dental adhesives could be an option for treating teeth affected by fluorosis. It stuck well and did not affect the levels of the important elements in the teeth.

Synthesis of Si3N4 powder with a controllable alpha/beta ratio by sol-gel assisted carbothermal reduction and nitridation

The controllable α/β ratio of Si3N4 powder was synthesized using tetraethyl orthosilicate (TEOS), glucose, MgCl2 and YCl3·6H2O by sol-gel assisted carbothermal reduction and nitridation (CRN). This study aimed to investigate the impact of various parameters, including a H2O/TEOS mol ratio of the sol, a C/Si mol ratio, sintering aids, and the temperature of CRN on the phase transformation of α-Si3N4. The results demonstrated that the H2O/TEOS ratio significantly influenced the relative content of α and β phase in Si3N4 by changing the morphological characteristics of SiO2. When the H2O/TEOS ratio was 100, β-Si3N4 powder with an approximate β content over 88 wt% was synthesized at 1500 °C. This remarkable phase transformation was likely facilitated by the eutectic liquid phase consisting of MgSiO3/Mg2SiO4. The SEM image revealed rod-like whiskers with a length around 1.4 μm for the β-Si3N4 grains. Due to the presence of liquid phase, the synthesis of spherical-like α-Si3N4 nano-powder with an α-phase content of 91 wt% was achieved at a lower temperature of 1450 °C, with an H2O/TEOS ratio of 15 and a C/Si ratio of 4. The size of the particles was about 70 nm due to the reduced reaction temperature. Furthermore, without the addition of any sintering aids or Si3N4 seeds, high purity α-Si3N4 with an α phase content approaching 96 wt% could be synthesized at 1500 °C, using an H2O/TEOS ratio of 15 and a C/Si ratio of 4. The resulting α-Si3N4 powder exhibited an extremely regular hexagonal prism shape with a length of approximately 2 μm.

Preparation of α-calcium sulfate hemihydrate with high mechanical strength from natural fibrous gypsum in KCl-mediated glycerol-water solution

Natural fibrous gypsum is a kind of high-quality gypsum resources, whose high-value added utilization pathway is to be transformed to α-calcium sulfate hemihydrate (α-HH), a cementitious material that can react with water to form pastes with mechanical strength. In this work, α-HH was prepared from natural fibrous gypsum in KCl mediated glycerol-water solution under mild condition. KCl played a simultaneous function on regulating the phase-transition kinetics, morphology and comprehensive strength of α-HH. Addition of low concentration of KCl prominently retarded the nucleation and growth rate of α-HH and decreased its aspect ratio due to the formation of syngenite on the side faces. While further increase of KCl concentration accelerated the nucleation and growth rate and decreased the crystal sizes. In the presence of 0.04 M KCl, the prepared α-HH presented a hexagonal prism shape with a length / width of 257.69–579.71 μm / 13.13–36.61 μm, and its dry comprehensive strength had reached 38.1 MPa that was comparable to those prepared in commercial, chloride and nitrate system. Altogether, the foreign ion-free glycerol-water solution contributed to transforming natural fibrous gypsum to α-HH with high purity and high mechanical strength.

Concept design and neutronics analysis of a heat pipe cooled nuclear reactor with CERMET fuel

Special off-grid power generations require the energy system to be reliable and compact. The heat pipe cooled reactor (HPR) is passively safe and highly modular, and is well suitable for energy demands ranging from a few kW to several MW. This study proposes a compact HPR design in which the ceramic metal composite (CERMET) fuel is used (HPR-CF). The CERMET fuel has advantages such as high temperature resistance and thermal conductivity. The fuel assembly using the CERMET fuel contains 6 heat pipes and fuel blocks with the hexagonal prism shape. The HPR-CF consists of 36 CERMET fuel assemblies containing 216 lithium heat pipes, 12 control drums, 1 safety control rod and peripheral beryllium dioxide reflector, all of which are mounted in a reactor vessel. The Monte Carlo code RMC is used to calculate the neutronics characteristics. The excess reactivity of the HPR-CF reactor is sufficient for operating at high temperature and 3MWt for over 3000 days. The power distribution and the criticality safety are calculated and discussed. The results show the neutronics availability of the HPR-CF design.

Effect of Gd3+, La3+, Lu3+ Co-Doping on the Morphology and Luminescent Properties of NaYF4:Sm3+ Phosphors

The series of luminescent NaYF4:Sm3+ nano- and microcrystalline materials co-doped by La3+, Gd3+, and Lu3+ ions were synthesized by hydrothermal method using rare earth chlorides as the precursors and citric acid as a stabilizing agent. The phase composition of synthesized compounds was studied by PXRD. All synthesized materials except ones with high La3+ content (where LaF3 is formed) have a β-NaYF4 crystalline phase. SEM images demonstrate that all particles have shape of hexagonal prisms. The type and content of doping REE significantly effect on the particle size. Upon 400 nm excitation, phosphors exhibit distinct emission peaks in visible part of the spectrum attributed to 4G5/2→6HJ transitions (J = 5/2-11/2) of Sm3+ ion. Increasing the samarium (III) content results in concentration quenching by dipole-dipole interactions, the optimum Sm3+concentration is found to be of 2%. Co-doping by non-luminescent La3+, Gd3+ and Lu3+ ions leads to an increase in emission intensity. This effect was explained from the Sm3+ local symmetry point of view.

Построение 2D-картин рентгеновской дифракции от модельных кристаллов-вискеров арсенида галлия

A set of GaAs whisker crystallites in the shape of hexagonal prism with the axis along the [111] direction have been modeled as well as constructions consisting of such prisms. For these model samples XRD patterns have been calculated. Basing on the calculated XRD pattern analysis, a fitting configuration of prismatic fragments has been built for an atomic array obtained with the help of applying molecular dynamics techniques to the initial model prismatic GaAs crystallite.

Simulating 2D-Diffraction Patterns of Model Gallium Arsenide Whisker Crystals

A set of GaAs whisker crystallites in the shape of hexagonal prism with the axisalong the [111] direction have been modeled as well as constructions consisting of such prisms. For these model samples XRD patterns have been calculated. Basing on the calculated XRD pattern analysis, a fitting configuration of prismatic fragments has been built for an atomic array obtained with the help of applying molecular dynamics techniques to the initial model prismatic GaAs crystallite. Keywords: whiskers, XRD pattern simulation, AIIIBV semiconductors, gallium arsenide.

Lanthanide-Ion-Doping Effect on the Morphology and the Structure of NaYF4:Ln3+ Nanoparticles.

Two series of β-NaYF4:Ln3+ nanoparticles (Ln = La–Nd, Sm–Lu) containing 20 at. % and 40 at. % of Ln3+ with well-defined morphology and size were synthesized via a facile citric-acid-assisted hydrothermal method using rare-earth chlorides as the precursors. The materials were composed from the particles that have a shape of uniform hexagonal prisms with an approximate size of 80–1100 nm. The mean diameter of NaYF4:Ln3+ crystals non-monotonically depended on the lanthanide atomic number and the minimum size was observed for Gd3+-doped materials. At the same time, the unit cell parameters decreased from La to Lu according to XRD data analysis. The diameter-to-length ratio increased from La to Lu in both studied series. The effect of the doping lanthanide(III) ion nature on particle size and shape was explained in terms of crystal growth dynamics. This study reports the correlation between the nanoparticle morphologies and the type and content of doping lanthanide ions. The obtained results shed light on the understanding of intrinsic factors’ effect on structural features of the nanocrystalline materials.

Molybdenum Nitride Porous Prisms with a Strong Plasmon Resonance Effect in the Visible Region for Surface-Enhanced Raman Spectroscopy

In surface-enhanced Raman spectroscopy (SERS) detection, the structure of the Raman-scattering substrate is critical to the sensitivity and stability of the detector. Herein, molybdenum nitride (MoN) porous structures with a well-defined hexagonal prism shape were synthesized via a precursor nitriding route. As a typical metallic transition-metal nitride (TMN), these molybdenum nitride porous hexagonal prisms exhibit a rare strong SPR effect in the visible region, with a resonance peak centered at 534 nm. Benefiting from the strong SPR effect and their huge surface area and porosity, these MoN porous hexagonal prisms exhibit surface-enhanced Raman scattering effects comparable to those of noble metals, with a Raman enhancement factor of 5.5 × 106. More importantly, these MoN SERS substrates exhibit ultrahigh chemical stabilities that noble metal and semiconductor substrates do not possess, which can prevent corrosion by strong acids, alkalis, and high-temperature oxidation.

Influence of the particle size on the antibacterial activity of green synthesized zinc oxide nanoparticles using Dysphania ambrosioides extract, supported by molecular docking analysis

Bacteria-associated infections have increased in recent years due to treatment resistance developed by these microorganisms. Due to the high antibacterial capacity associated with their nanometric size, nanoparticles, such as zinc oxide (ZnO), have proven to be an alternative for general medical procedures. One of the methodologies to synthesize them is green synthesis, where the most commonly used resources are plant species. Using Dysphania ambrosioides extract at various synthesis temperatures (200, 400, 600, and 800 °C), zinc oxide nanoparticles (ZnO-NPs) with average sizes ranging from 7 to 130 nm, quasi-spherical shapes, and hexagonal prism shapes were synthesized. Larger sizes were obtained by increasing the synthesis temperature. The ZnO crystalline phase was confirmed by X-ray diffraction and transmission electron microscopy. The sizes and shapes were observed by field emission scanning electron microscopy. The Zn-O bond vibration was identified by Fourier transform infrared spectroscopy. Thermogravimetry showed the stability of ZnO-NPs. The antibacterial evaluations, disk diffusion test, and minimum bactericidal concentration, demonstrated the influence of particle size. The smaller the nanoparticle size, the higher the inhibition for all pathogenic strains: Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa, and dental pathogens: Streptococcus mutans, Streptococcus sanguinis, Porphyromonas gingivalis, and Prevotella intermedia. The molecular docking study showed a favorable interaction between ZnO-NPs and some proteins in Gram-positive and Gram-negative bacteria, such as TagF in Staphylococcus epidermidis and AcrAB-TolC in Escherichia coli, which led to proposing them as possible targets of nanoparticles.

Anisotropic Crystal Growth of Layered Nickel Hydroxide along the Stacking Direction Using Amine Ligands.

Edge surfaces of two-dimensional crystals play crucial roles in their properties, such as intercalation behavior and catalytic activities; however, reports on the preparation of crystals with a high aspect ratio of thickness to lateral size, typically a prism-like crystal morphology composed of stacked layers, are scarce. We report the anisotropic crystal growth of β-Ni(OH)2 along the stacking direction using bidentate amine ligands, which act as both the base and the reservoir of Ni2+ through the formation of Ni-diamine complexes. Various characterization results of the crystal structure, composition, and crystal orientation indicate the formation of hexagonal prisms of β-Ni(OH)2 with an unusually high aspect ratio of the thickness to the lateral size higher than 1. A systematic investigation focusing on the molar ratio of amine ligands to Ni2+, the concentration of Ni-diamine complexes, and stability constants of the complexes revealed that anisotropic growth was promoted when the supersaturation was relatively high and was maintained constant for a long time. We clarified the role of amine ligands in controlling supersaturation through the controlled release of metal ions from stable complexes. β-Co(OH)2 with a hexagonal prism shape was prepared using this protocol. This study provides valuable indications for developing synthetic chemistry for various layered compounds to achieve a controlled aspect ratio.

Demand-oriented construction of Mo3S13-LDH: A versatile scavenger for highly selective and efficient removal of toxic Ag(I), Hg(II), As(III), and Cr(VI) from water

Inspired by the classic ion-exchange reaction, a single phase material of Mg0.66Al0.34(OH)2(Mo3S13)0.03(NO3)0.14(CO3)0.07·H2O (Mo3S13-LDH) was masterly constructed by intercalating Mo3S132− into the MgAl-LDH gallery. Prepared Mo3S13-LDH displays excellent binding affinity and high selectivity for Ag(I) and Hg(II) in a mixed solution, in which an apparent selectivity order of Hg(II) > Ag(I) ≫ Pb(II), Cu(II), Ni(II), Co(II), Cd(II), and Mn(II) is observed. Enormous capture capacities (qmAg = 446.4 mg/g, qmHg = 354.6 mg/g) and fast equilibration time (within 60 min) place Mo3S13-LDH in the upper ranks of materials for such removal. For oxoanions, As(III) (HAsO32−) and Cr(VI) (CrO42−) can be specifically trapped by Mo3S13-LDH with comparable loading ability (qmAs = 61.8 mg/g, qmCr = 90.6 mg/g) in the coexistence of multiple interfering anions. Notably, high Hg(II) and Cr(VI) concentrations are finally reduced below the safe limit of drinking water. The excellent capture capacity of Mo3S13-LDH benefits from the rational design by following two aspects: (i) the multiple sulfur ligands in Mo3S132− groups give place to various capture modes and different affinity orders for target ions, and (ii) large-sized Mo3S132− groups widen the interlayer spacing of LDH, thereby accelerating the mass transfer process. Furthermore, the satisfactory structural stability of Mo3S13-LDH is also reflected through the unchanged hexagonal prismatic shape after adsorption. All of these highlight the great potential of Mo3S13-LDH for the application in water remediation.

GaAs/GaAsPBi core–shell nanowires grown by molecular beam epitaxy

We report on the growth, structural, and optical properties of GaAs/GaAsPBi core–shell nanowires (NWs) synthesized by molecular beam epitaxy (MBE). The structure presents advantageous optical properties, in particular, for near- and mid-infrared optical applications. Scanning electron microscopy shows that although the stems of GaAs/GaAsP and GaAs/GaAsBi core–shell NWs preserve the hexagonal prism shape, the GaAs/GaAsPBi core–shell NWs develop a quasi-three-fold orientational symmetry affected by the hexagonal prismatic core. Detailed structural analyses of a GaAs/GaAsPBi core–shell stem show that it crystallized with zincblende structure with a nominal shell composition of GaAs0.617P0.362Bi0.021. Photoluminescence of GaAs/GaAsPBi core–shell NWs shows the luminescent peak at 1.02 eV with high internal quantum efficiency at room temperature (IQERT ∼ 6%) superior to those of MBE-grown GaAs core NWs and GaAsPBi multiple quantum wells earlier reported. Energy-dispersive x-ray spectroscopy performed on the GaAs/GaAsPBi core–shell NWs yields an estimated bandgap different from the optically measured value. We attribute this discrepancy to the NW compositional fluctuations that also may explain the high IQERT.

High-pressure synthesis, crystal structure, and physical properties of NaB13C2 single crystals

A new boron-rich boride carbide of sodium, NaB13C2 single crystals have been successfully synthesized from the elements under high temperature and high pressure. The crystals are reddish black with a metallic luster and show a regular hexagonal prism shape. NaB13C2 crystallizes into an orthorhombic LiB13C2-type structure with a space group of Imma (No. 74) and the lattice constants are a = 10.9417 Å, b = 5.6756 Å, c = 8.0898 Å. The crystal structure is characterized by a covalent framework of B12 icosahedra connected by CBC chains and Na atoms located in the void of the framework. The measured and calculated Raman spectra of NaB13C2 are in good agreement and show expected oscillations of the covalent framework. The electronic band structures reveal that NaB13C2 is a wide band gap semiconductor with a band gap of 3.36 eV. As a novel wide band gap semiconductor, NaB13C2 may have potential applications in semiconductor field.

Guest-Mediated Hierarchical Self-Assembly of Dissymmetric Organic Cages to Form Supramolecular Ferroelectrics

Guest-Mediated Hierarchical Self-Assembly of Dissymmetric Organic Cages to Form Supramolecular Ferroelectrics

Offretite zeolite templated by amphiphile and its catalytic performance in microwave-assisted Knoevenagel condensation of benzaldehyde and ethyl cyanoacetate

A detailed investigation on the crystallization of offretite (OFF) zeolite templated by non-toxic cetyltrimethylammonium bromide (CTABr) is reported. Various hydrothermal synthesis conditions are prepared by systematically adjusting the synthesis variables, namely crystallization time, heating temperature and amount of reactants (SiO2, Al2O3, K2O, M2O (M = Na+, Cs+), CTABr and H2O) to investigate their effects on the crystal growth of OFF zeolite. It is shown that each variable has its profound influences on the crystallization process, which further affect the properties of final zeolite products (e.g. phase purity, morphology, crystal size). Unlike classical synthesis pathway using tetramethylammonium (TMA+) as organic template, the CTABr-templating approach successfully produces large OFF single crystals (framework Si/Al ratio = 4.11) with hexagonal prism shape (ca. 9.4 × 1.8 μm2) and smooth surface. Besides that, the OFF zeolite (81.9% conversion) also shows comparable or even higher catalytic performance than other zeolites reported in this work and other works in microwave assisted-Knoevenagel reaction of benzaldehyde and ethyl cyanoacetate, offering a sustainable and facile pathway for preparing zeolitic materials for advanced applications.

On manipulating the thermoelectric potential of p-type ZnO by nanostructuring

Throughout this work, ZnO nanoparticles were produced by a simple co-precipitation method, in which the volume of the basic solution (NaOH, 5–30 ml) was varied to understand its effect on the properties of the nanoparticles. A structural and morphological effect was observed, namely a change in reflections between 2θ=31.75°(100) and 2θ=34.4°(002) peaks. At the same time, nanoparticles changed from a hexagonal prism shape to a desert-rose stones structure for high base concentrations. The transport measurements were performed from room temperature (RT) up to 340 K. At RT, a correlation between the Seebeck coefficient and the electrical conductivity was achieved, whereas the thermal conductivity behaves distinctly. A thermal conductivity value of 0.5 W m-1 K−1 was observed, which is two orders of magnitude lower than the bulk counterpart. The behaviours of the PF and ZT also reveal the different influences of the electrons and the phonons for the different nanostructures, since the electronic phenomena predominate in the hexagonal prism structures, the phonon phenomena predominate in the desert-rose stones, due to the reduced dimension of these structures. For higher temperatures, a thermal activation model was used to determine the Activation Energy (Ea), leading to values in the hundredths of meV range, with higher values for the volumes of NaOH where a mixture of the two types of structures is observed, where the presence of different interfaces created a barrier for the carriers to pass from grain to grain.

Offretite Zeolite Single Crystals Synthesized by Amphiphile-Templating Approach.

Offretite zeolite synthesis in the presence of cetyltrimethylammonium bromide (CTABr) is reported. The offretite crystals were synthesized with a high crystallinity and hexagonal prismatic shape after only 72 h of hydrothermal treatment at 180 °C. The CTABr has dual-functions during the crystallization of offretite, viz. as structure-directing agent and as mesoporogen. The resulting offretite crystals, with a Si/Al ratio of 4.1, possess more acid sites than the conventional offretite due to their high crystallinity and hierarchical structure. The synthesized offretite is also more reactive than its conventional counterpart in the acylation of 2-methylfuran for biofuel production under non-microwave instant heating condition, giving 83.5% conversion with 100% selectivity to the desired product 2-acetyl-5-methylfuran. Hence, this amphiphile synthesis approach offers another cost-effective and alternative route for crystallizing zeolite materials that require expensive organic templates.

Thermodynamics and kinetics of REEs in CaO–SiO2–CaF2–Ce2O3 system: A theoretical basis toward sustainable utilization of REEs in REE-Bearing slag

Sustainable utilization of rare earth elements (REEs) in REE-bearing slag has recently attracted significant interest in industries and research community. However, few thermodynamic and kinetic data have been reported for REEs systems, which greatly limits the sustainable utilization of REE-bearing slag in ceramics and other fields. Therefore, the isothermal phase diagram of CaO–SiO2–CaF2–Ce2O3 system was constructed, and the phase equlibria data of REEs in REE-bearing slag were provided in this study. On this basis, the phase equilibria of the RE-phase in CaO–SiO2–CaF2–Ce2O3 system was investigated, the exact initial crystallization temperature of cefluosil (Ce9.33-xCax(SiO4)4O5-0.5xF2) in the system was 1450 K and the cefluosil crystals were in a hollow hexagonal prism shape. The isothermal crystallization and growth kinetics of cefluosil were further studied. The crystallization kinetics of cefluosil were found to be described by the Johnson-Mehl-Avrami-Kolmogoro (JMAK) equation (when χ < 1), and the growth of cefluosil in the non-equilibrium stage is controlled by the coarsening energy. In this research, the thermodynamic and kinetic data of REEs in CaO–SiO2–CaF2–Ce2O3 system are supplied, which providing the theoretical basis for sustainable utilization of REEs in REE-bearing slag.

Seedless Hydrothermal Growth of ZnO Nanorods as a Promising Route for Flexible Tactile Sensors.

Hydrothermal growth of ZnO nanorods has been widely used for the development of tactile sensors, with the aid of ZnO seed layers, favoring the growth of dense and vertically aligned nanorods. However, seed layers represent an additional fabrication step in the sensor design. In this study, a seedless hydrothermal growth of ZnO nanorods was carried out on Au-coated Si and polyimide substrates. The effects of both the Au morphology and the growth temperature on the characteristics of the nanorods were investigated, finding that smaller Au grains produced tilted rods, while larger grains provided vertical rods. Highly dense and high-aspect-ratio nanorods with hexagonal prismatic shape were obtained at 75 °C and 85 °C, while pyramid-like rods were grown when the temperature was set to 95 °C. Finite-element simulations demonstrated that prismatic rods produce higher voltage responses than the pyramid-shaped ones. A tactile sensor, with an active area of 1 cm2, was fabricated on flexible polyimide substrate and embedding the nanorods forest in a polydimethylsiloxane matrix as a separation layer between the bottom and the top Au electrodes. The prototype showed clear responses upon applied loads of 2–4 N and vibrations over frequencies in the range of 20–800 Hz.