Regular Crystals Research Articles

Preparation of Regular Cement Hydration Crystals and Ordered Microstructures by Doping GON and an Investigation into Its Compressive and Flexural Strengths

In this work, we found that by controlling the size of the graphene oxide nanosheets (GON) at 5–140 nm, 5–260 nm and 5–410 nm, respectively, we could prepare regular shaped cement hydration crystals with the shape of nano-needle-like, flower-like, and polyhedron-like crystals, respectively. Together, these crystals formed an ordered structure of cement composites on both the micro and macro levels, and the compressive and flexural strengths of the cement composites obviously increased when compared to the control samples. Our results indicated that the smallest structural unit of regular crystals was the nano-polyhedron-like crystals, which consisted of AFt, AFm, CH, and crystallization C–S–H, and could assemble into regular needle-like crystals, flower-like crystals, and polyhedron-like crystals, as well as an ordered structure on the micro and macro levels. Most of the C-S-H was transferred into a monoclinic system crystals and the remainder played the role of an adhesive in the forming process of regular crystals and structure. The cracks and holes in the cement composites disappeared by the self-repairing effect of the growing hydration crystal. The results indicate that ordered structural cement composites with defect-free structures and high strength can be prepared using GON with a suitable size range.

Significance of Crystal Morphology Controlling in Semiconductor-Based Photocatalysis: A Case Study on BiVO4 Photocatalyst

Precise control of the morphology and crystalline structure of semiconductor-based photocatalyst is crucial for improving the efficiency of solar energy conversion system. In this work, taking BiVO4 semiconductor photocatalyst as an example, we investigated the formation process for the regular decahedron BiVO4 crystals prepared by a convenient hydrothermal method and found that the synthesis is undergoing a dissolution–recrystallization process, concomitantly, the phase was transformed from tetragonal zircon type to monoclinic sheelite-type. By controlling the kinetics of crystal growth for BiVO4 through regulating acidity of the reaction solution, we rationally tune the morphology of monoclinic BiVO4 from regular decahedron crystals to short rod-like particles, particularly precisely modulate the proportion of {010}/{011} facets for the decahedron BiVO4. By tuning the crystalline phase and morphologies of BiVO4 crystal, we found that the photocatalytic water oxidation activity for the well-defined BiVO4...

Comparative Morphological and Crystallographic Analysis of Electrochemically- and Chemically-Produced Silver Powder Particles

Silver powders chemically synthesized by reduction with hydrazine and those produced by electrolysis from the basic (nitrate) and complex (ammonium) electrolytes were examined by X-ray diffraction (XRD) and scanning electron microscopic (SEM) analysis of the produced particles. Morphologies of the obtained particles were very different at the macro level. The needle-like dendrites, as well as the mixture of irregular and regular crystals, were formed from the nitrate electrolyte, while the highly-branched pine-like dendrites with clearly noticeable spherical grains were formed from the ammonium electrolyte. The agglomerates of spherical grains were formed by reduction with hydrazine. In the particles obtained from the nitrate electrolyte, Ag crystallites were strongly oriented in the (111) plane. Although morphologies of Ag particles were very different at the macro level, the similarity at the micro level was observed between chemically-synthesized particles and those obtained by electrolysis from the ammonium electrolyte. Both types of particles were constructed from the spherical grains. This similarity at the micro level was accompanied by the similar XRD patterns, which were very close to the Ag standard with a random orientation of Ag crystallites. For the first time, morphologies of powder particles were correlated with their crystal structure.

Effect of sintering temperature rise from 870 to 920 °C on physicomechanical and biological quality of nano-hydroxyapatite: An explorative multi-phase experimental in vitro/vivo study

Hydroxyapatite (HA) is a proper scaffold for bone repair, however, it is not of excellent mechanical properties. Most previous studies on the effect of temperature increases were in vitro and had assessed merely improvements of HA's physicomechanical quality. This in vitro/vivo study investigated the effect of temperature increases from 870 to 920°C on physicomechanical and biological quality of Nano-HA. Forty experimentally produced HA disks sintered at 870 to 920°C were prepared (n=20×2). Disks were subjected to Vickers microindentation test (1 disk from each group divided into 4 quarters), Fourier transform infrared spectroscopy (1 disk), X-ray diffraction (XRD) [1 disk together with non-sintered HA], field emission scanning electron microscopy (FSEM, 1 disk from each group together with non-sintered HA), cell seeding and SEM assessment (2 disks), MTT assay over 4 different time periods (16 quadrants of 4 disks from each group), 6 one-thirds of 2 disks from each group for immunocytochemical (ICC) assay, and 8 disks from each group [as well as non-sintered HA] for the animal study (implantation in 4 sockets in 8 rabbits [32 specimens], histomorphometry, and computerized tomography) over two time periods. Quantitative data were analyzed statistically (α=0.05). Vickers microhardness increased from 63.7±11.9 in the 870 group to 153.4±104.7 in the 920 group (P=0.057). XRD indicated more regular crystal patterns in sintered groups compared to non-sintered nanoHA. FSEM showed larger crystals in the 920 group compared to 870 and non-sintered nanoHA. Expression of osteocalcin, osteonectin, and RUNX2 genes were more visible in ICC samples of the 920HA group. In MTT, cell numbers increased in all groups significantly (P=0.000), with no between-group differences (P>0.3). In rabbit experiments, the extent of ‘newly formed bone’ increased significantly over time (two-way ANOVA, P=0.000), reaching 39.5%, 46.4%, and 77.5% in the groups non-sintered HA, 870, and 920, respectively. The 920°C-sintered nanoHA induced the highest bone formation (P=0.000). Increasing the temperature of nanoHA sintering from 870 to 920°C can improve its physicomechanical properties and bone formation potential.

Controlling Nucleation and Growth of Metal Halide Perovskite Thin Films for High-Efficiency Perovskite Solar Cells.

Metal halide perovskite thin films can be crystallized via a broad range of solution-based routes. However, the quality of the final films is strongly dependent upon small changes in solution composition and processing parameters. Here, this study demonstrates that a fractional substitution of PbCl2 with PbI2 in the 3CH3 NH3 I:PbCl2 mixed-halide starting solution has a profound influence upon the ensuing thin-film crystallization. The presence of PbI2 in the precursor induces a uniform distribution of regular quadrilateral-shaped CH3 NH3 PbI3 perovskite crystals in as-cast films, which subsequently grow to form pinhole-free perovskite films with highly crystalline domains. With this new formulation of 3CH3 NH3 I:0.98PbCl2 :0.02PbI2 , this study achieves a 19.1% current-voltage measured power conversion efficiency and a 17.2% stabilized power output in regular planar heterojunction solar cells.

Effects of coagulation conditions on structure and properties of cellulose-based fibers from aqueous NaOH solvent

Hydroxyethyl cellulose (HEC) fibers with low degree of substitution were prepared by wet spinning of solutions in 8wt% NaOH solvent, and H2SO4/Na2SO4/ZnSO4 solution was chosen as coagulants. The influence of coagulation temperature and H2SO4 concentration on structure and mechanical properties of resultant HEC fibers was examined by synchrotron X-ray measurements, scanning electron microscope and tensile tests. The results were analyzed from the perspective of coagulation kinetics by determining coagulation rate and mass transfer rate difference. It is shown that the increase of either coagulation temperature or H2SO4 concentration would accelerate the diffusion and coagulation process. The lowest coagulation temperature of 20°C or moderate H2SO4 concentration around 10–15wt%, which provided a gentle solidification process, favored the development of regular crystal and oriented structure, uniform and dense inner structure as well as cross sections closer to circular, resulting in HEC fibers with better tensile properties.

Influence of surface-modified Mo back contact on post-selenized Cu(In,Ga)Se2 thin films

In this work, the influences of surface-modified Mo back contacts on the morphology of Cu layers and quality of Cu(In,Ga)Se2 (CIGS) thin films are investigated. One method of sputtering treatment to modify the Mo surface effectively improved the adhesion between the Cu and Mo layers. However, Cu layers electrodeposited on the various modified Mo surfaces created different morphological structures, which impacted the CIGS thin films. First, an alloyed Cu-In-Ga film based on the Cu layer of smooth structure would experience homogeneous element diffusion compared to the Cu layer of the rugged structure. Second, the CIGS film based on the smooth Cu-covered substrate exhibited a uniform surface profile with regular crystals, while the CIGS film based on a rugged one exhibited an uneven surface profile with several irregular crystals. Additionally, the smooth Cu-covered substrate reduced the adverse phase separation of CuInSe2 and CuGaSe2 more effectively.

Evolução Microestrutural da Fase Amorfa na Liga Co72Nb24B4

<p>A evolução estrutural da fase amorfa na composição Co72Nb24B4 foi processadas por fundição em forno a à arco e caracterizadas por difração de raios-x (DRX), microscopia eletrônica de varredura (MEV) e espectroscopia de energia dispersiva (EDS). A evolução da microestrutura amorfa leva a criação de um grupo de materiais com propriedades altamente desejáveis, com alta resistência mecânica, dureza e resistência à abrasão e à corrosão. Além disso, a formação de quantidade considerável de fase amorfa e a sua transformação parcial de fases cristalinas durante o processo de fusão no forno à arco foram revelados . Verificou-se igualmente que, na fundição ocorre mudanças de morfologia de pó entre a fase amorfa e cristalina, facilitando o surgimento de fases intermetálicas com lamelas,pequenos cristais regulares a base de óxidos e o seu tamanho aumenta inicialmente.</p>

Effects of Silicon Particle Size on the Morphology of Rod-Like Si<sub>3</sub>N<sub>4 </sub>Crystals Prepared by SHS Method

Silicon nitride whiskers or rod-like crystals have a wide range application due to its excellent mechanical properties and high temperature performance. Two different silicon powders with different size (mesh 200 and mesh 300, respectively) were chosen to prepare rod-like Si3N4 crystals by SHS method and the effects of silicon particle size on the morphology of rod-like Si3N4 crystals were investigated. The results indicate that rod-like Si3N4 crystals could be formed with either kind of silicon powders when no more than 9wt% extra Y2O3 was introduced, which could effectively promote the growth of rod-like Si3N4 crystals. The residual free silicon was detected when using coarse silicon powders, while the silicon could be reacted completely with nitrogen gas when using fine silicon powders. The morphology of samples with coarse Si powders as starting materials is more uniform and regular than that of fine Si powders samples. Fine silicon powders are not ideal candidates for forming uniform and regular rod-like Si3N4 crystals.

Methamphetamine use among gay and bisexual men in Australia: Trends in recent and regular use from the Gay Community Periodic Surveys

BackgroundGay and bisexual men typically report high rates of illicit drug use, including methamphetamine use. This paper aimed to analyse trends in crystal methamphetamine (‘crystal’) and powder methamphetamine (‘speed’) use among gay and bisexual men in Australia, and characterise the sociodemographic, drug use, and sexual risk practices of men who reported crystal use. MethodsThe Gay Community Periodic Surveys, routinely conducted behavioural surveillance surveys of gay men in Australia, were analysed to examine trends in recent crystal and speed use during 2005–14 (any use in the previous 6 months), and trends in regular crystal and speed use during 2007–14 (at least monthly use in the previous 6 months). Covariates of recent and regular crystal use were analysed using 2014 data. ResultsSpeed use declined from 25.0% to 10.2% during 2005–14 (p-trend <.001), while regular speed use declined from 7.0% to 2.3% during 2007–14 (p-trend <.001). Any crystal use declined from 15.6% to 11.4% during 2005–14 (p-trend <.001) and increased during 2010–14 (from 9.6% in 2010; p-trend <.001). Regular crystal use declined from 6.1% to 4.0% during 2007–14 (p-trend <.001) and remained stable during 2010–14 (3.9% in 2010; p-trend=.64). Participants who reported regular crystal use were more likely than men who used crystal less frequently to have used gamma-hydroxybutyrate, used party drugs for sex, and to have injected drugs in the previous 6 months. High rates of crystal use and injecting were reported among HIV-positive participants. ConclusionRates of both crystal and speed use, despite fluctuations, were consistently high throughout the study period. The high rates of crystal use and associations with potentially risky sexual practices indicate that gay and bisexual men should be a particular focus for targeted harm reduction and combined harm reduction and sexual health services.

Giant gain enhancement in photonic crystals with a degenerate band edge

We propose a new approach leading to giant gain enhancement. It is based on unconventional slow-wave resonance associated with a degenerate band edge (DBE) in the dispersion diagram for a special class of photonic crystals supporting four modes at each frequency. We show that the gain enhancement in a Fabry-P\'erot cavity (FPC) when operating at the DBE is several orders of magnitude stronger when compared to a cavity of the same length made of a standard photonic crystal with a regular band edge (RBE). The giant gain condition is explained by a significant increase in the photon lifetime and in the local density of states. We have demonstrated the existence of DBE operated special cavities that provide for superior gain conditions for solid-state lasers, quantum cascade lasers, traveling wave tubes, and distributed solid-state amplifiers. We also report the possibility to achieve low-threshold lasing in FPC with DBE compared to RBE-based lasers.

Solvent effects on nucleation of disodium guanosine 5′-monophosphate in anti-solvent/water mixtures

The influence of the solvent on the nucleation of disodium guanosine 5′-monophosphate (GMPNa2) in eight methanol (ethanol)–water mixtures and at three supersaturation levels at 293.15 K was investigated. The interfacial free energy, the critical size for nucleation, and the number of molecules were calculated using equations re-derived from the classical nucleation theory. GMPNa2 nucleation involves not only a primary nucleation process but also the conversion from a homogeneous to a heterogeneous process. The transformation experiment indicated that the nucleation of GMPNa2 follows the two-step model. A surface entropy factor (fb) was proposed to relate the solvent composition and interfacial free energy in order to explain the solvent effects on the nucleation process. Although the fb values can be used to judge the crystal growth mode, nucleation and growth cannot be separated, since pure primary nucleation does not occur for this compound. The fb values clearly increased with increasing solvent content and decreasing supersaturation. For the homogeneous process in a methanol–water system, regular crystals can be formed only when fb > 5, regardless of the supersaturation, as was observed for solvent contents of 40 mol% and 30 mol% (S = 1.83 and 1.70, respectively). These results can help select a suitable solvent system and its composition during anti-solvent crystallization.

Infrared spectra of thin CO2 crystal at 7–77 K: the band shape in the ν313CO2 absorption region

The IR spectra of reflection from a mirror covered with thin CO2 crystal layers are obtained in the temperature interval T=7–77K. The spectra in the ν3 and ν2 regions of the 12CO2 and 13CO2 molecules and their dependence on temperature and the layer thickness are discussed. The complex shape of the ν3 band in the region of 13CO2 absorption is explained by the resonance dipole–dipole interaction between two 13CO2 molecules located in the first or second coordination sphere of each other in the regular crystal.

Structure dependent hydrogen induced etching features of graphene crystals

H2 induced etching of graphene is of significant interest to understand graphene growth process as well as to fabricate nanoribbons and various other structures. Here, we demonstrate the structure dependent H2 induced etching behavior of graphene crystals. We synthesized graphene crystals on electro-polished Cu foil by an atmospheric pressure chemical vapor deposition process, where some of the crystals showed hexagonal shaped snowflake-dendritic morphology. Significant differences in H2 induced etching behavior were observed for the snowflake-dendritic and regular graphene crystals by annealing in a gas mixture of H2 and Ar. The regular graphene crystals were etched anisotropically creating hexagonal holes with pronounced edges, while etching of all the dendritic crystals occurred from the branches of lobs creating symmetrical fractal structures. The etching behavior provides important clue of graphene nucleation and growth as well as their selective etching to fabricate well-defined structures for nanoelectronics.

Microwave intensified synthesis of regular shaped sodium bisulfate crystal

Microwave was employed to prepare sodium bisulfate crystal using equimolar quantities of sulfuric acid and sodium sulfate. The effects of microwave on heating behavior and water content changes were studied by monitoring the temperature and weight. To embody the positive effect of microwave on dehydrating speed and crystal transformation, thermal conductive heating was compared. The phase transformation and micro morphology of the product were characterized by X-ray diffraction and scanning electron microscopy. It was observed that crystallization with lower water content obtained higher percentage of sodium bisulfate. Microwave can significantly speed up dehydration and the dehydrating efficiency increase over the output power. According to the phase transformation process, a possible mechanism for H+-dependent sodium bisulfate crystallization is proposed. Moreover, regular crystal with greater size was obtained under microwave irradiation. The specific phenomenon may be ascribed to the oriented attachment of hydrogen sulfate in alternating electromagnetic field.

Investigation of nucleation kinetics and crystal defects of HMX

The nucleation kinetics of HMX (cyclotetramethylene tetranitramine, C4H8N8O8) in γ‐butyrolactone was studied in cooling process by induction time method. The laser scattering method was used to measure the solubility data and metastable region of HMX in γ‐butyrolactone. The induction time was measured over a range of supersaturation at different temperatures. Then, the nucleation mechanism of HMX in γ‐butyrolactone was investigated by analysis the relationships between induction time and supersaturation. The results indicated homogeneous nucleation dominated at high supersaturation of S &gt;1.35, while the heterogeneous nucleation dominated at low supersaturation of S &lt; 1.35. The values of interfacial tension at different final temperatures were calculated to indicate the ability of HMX to be crystallized. The growth mechanism of HMX was investigated by the data fitting applying different growth mechanism models and identified as two‐dimensional nucleation‐mediated (2D) growth. Finally, the effects of supersaturation and temperature on the crystal defects were analyzed based on the nucleation kinetics. When the temperature is below 303.15K, homogeneous nucleation dominated the nucleation process at higher supersaturation. Fine HMX crystals with more defects were produced. On the contrary, heterogeneous nucleation mechanism dominated at lower supersaturation. large regular HMX crystals with fewer defects were formed when the temperature is above 318.15K.

High-Resolution Solid-State NMR Characterization of Morphology in Annealed Polylactic Acid

Single-pulse 13C NMR spectra and spin-lattice relaxation times T1(1H), detected indirectly via 13C carbons, and T1(13C) were measured at 31°C for virgin pelletized and annealed polylactic acid (PLA) samples using the magic-angle spinning technique. The structural relaxation resulting in more regular crystals with narrower conformation distribution and increase in the lamellae thickness and crystallinity brought about by annealing at 100°C was deduced from the narrowing of the 13C NMR lines and proton spin-lattice relaxation times T1(1H). The spin-lattice relaxation times T1(13C) related to the respective carbons of the α-polymorph of PLA are also discussed in the study.

Corrosion Behavior of V2AlC and Cr2AlC Materials in Acidic Media

This work involves the manufacturing of MAX phase materials including V2AlC and Cr2AlC using powder metallurgy as a new class of materials which characterized by regular crystals in lattice. Corrosion behavior of these materials was investigated by Potentiostat to estimate corrosion resistance and compared with the most resistant material represented by SS 316L. The experiments were carried out in 0.01N of HCl and 0.01N H2SO4 at four temperatures in the range of 303-333K. Polarization resistance values which calculated by Stern-Geary equation indicate that the MAX phase materials have more resistance than SS 316L. Optical microscopy results for corroded surfaces were confirming the resistivity of MAX phase materials.

Solvent-aided layer crystallization—Case study glycerol–water

Solid-layer melt crystallization with an additional assisting liquid medium, just like an extraction solvent, is introduced. A case study of the purification of glycerol from mixtures containing 1–10wt% water and the use of 1-butanol as additional solvent assisting to control crystallization kinetics is presented. Cold finger experiments were carried out. It was found that in regular melt crystallization without the use of 1-butanol, water concentration could be reduced to 30–80wt% in comparison to the residual melt at growth rates between 4×10−8 and 1.4×10−7m/s, with lower growth rates resulting in lower water concentrations. No post-treatment like sweating or washing was applied. The dependence between purification success and growth rate could not be changed by initial water content or duration of the experiment and only little by agitation of the melt. The use of 1-butanol allowed an improvement of the process in terms of higher product purities and higher growth rates. Distribution coefficients improved by a factor of 2–4 without a loss in the growth rate or growth rates could be increased by a factor 5 without harming the separation quality. The influence of 1-butanol on the crystallization in comparison to that of water is further investigated. An understanding of how to use additional assisting solvents to control crystallization kinetics and to improve the separation is interesting for the purification of other components, especially high-viscous ones such as tocopherols or phytosterols as well.

Design of industrial crystallization of interferon gamma: Phase diagrams and solubility curves

Phase diagrams and solubility curves for engineering of crystallization for interferon gamma have been developed by small scale precipitation and crystallization experiments. A scale up was carried out to proof the accuracy and the suitability of the created phase diagram with sodium sulfate for bulk crystallization. To provide nucleation and a high yield the operating point was chosen at a protein concentration of 6mg/mL and a sodium sulfate concentration of 25% [w/v]. Crystallization was completed within 5h with a yield of>95%. The double logarithmic plot of crystallized fraction versus time yielded in an overall kinetic crystallization constant of 5.79×10−2min−1. Regular cubic crystals can be observed which contradicts the low Avrami coefficient. The Avrami coefficient of 1 is interpreted that nucleation takes place throughout the entire crystallization process and larger crystals are formed by Ostwald ripening instead of growth out of the liquid phase. The established process with its conditions is suited for industrial protein crystallization.