Effect Of Crystal Morphology Research Articles

Effect of crystal morphology on cementability and micromechanical properties of calcium carbonate precipitate induced by crude soybean enzyme

Enzyme-induced carbonate precipitation (EICP) has emerged as an innovative soil stabilization technology to precipitate CaCO3 by catalyzing urea decomposition. Although extensive efforts have been made to increase the calcium carbonate content (CCC) formed in the EICP process for the better bio-cementation effect, the cementability and micromechanical properties of CaCO3 are rarely known. A study of the cementitious characteristics and micromechanical properties of CaCO3 precipitates with different mixing percentages of crystal morphology is essential for soil improvement. In the present study, ultrasonic oscillation tests and nanoindentation tests were performed to investigate the cementability and micromechanical properties of CaCO3 precipitate. The results show that the cementability and micromechanical properties of CaCO3 precipitate are related to the composition of the crystal morphology. A high content of calcite is beneficial to improve the adhesion of calcium carbonate precipitate. Calcite has better mechanical properties (elastic modulus, hardness and ductility) than vaterite, and the presence of vaterite can significantly affect the measured value of mechanical properties in nanoindentation tests. The ductility of CaCO3 precipitate induced by crude soybean urease (CSU) is higher than that of CaCO3 precipitate induced by commercially available pure enzyme, suggesting that commercially available pure enzyme can be replaced by CSU for cost-effective field-scale engineering applications. This work can provide insight into optimizing the properties of CaCO3 precipitate from the micro-scale.

Effect of Crystal Morphology on Electrochemical Performances of IRH-2 and IRH-2/PANI Composite for Supercapacitor Electrodes.

In the context of recent progress in designing metal-organic framework (MOF)-based supercapacitor electrodes, we report herein the successful growth of two different crystal morphologies of a cerium-based MOF, octahedral crystals named IRH-2-O and elongated square-bipyramidal crystals named IRH-2-ESBP (IRH = Institute de Recherche sur l'Hydrogène). The identical crystal structure of both materials was confirmed by powder X-ray diffraction (PXRD). Furthermore, scanning electron microscopy and energy-dispersive X-ray mapping analysis corroborated this fact and showed the crystal shape variation versus the surface composition of synthesized materials. Fourier transform infrared spectroscopy, UV-vis spectroscopy, and PXRD were used to confirm the purity of pristine MOFs as well as desired MOF//PANI composites. Cyclic voltammetry and electrochemical impedance spectroscopy highlighted the effect of crystal shape on the electrochemical performance of IRH-2 MOFs; the specific capacitance tripled from 43.1 F·g-1 for IRH-2-O to 125.57 F·g-1 for IRH-2-ESBP at 5 mV·s-1. The cycling stability was notably ameliorated from 7 K for IRH-2-O to 20 K for IRH-2-ESBP. Regarding the composites, the cell voltage was notably ameliorated from 1.8 to 1.95 V. However, the electrochemical performance of IRH-2/PANI composites was drastically decreased due to instability in the acidic media. To the best of our knowledge, our work is the first work that related the MOF crystal shape and the electrochemical performance.

Improving corrosion resistance of pure titanium by simple and controlled oxidation for biomedical applications

AbstractIn this study, the TiO2 passive layer was formed on a pure titanium substrate by simple oxidation in an aqueous solution of H2O2 35 wt.%. In order to determine the appropriate time for the oxidation of the pure titanium substrate, the corrosion rate of the metal in the solution of H2O2 was investigated. The electrochemical behaviour of the TiO2 passive layer on the Ti substrate was investigated in Hank's solution at 37.5°C. The results show that Tafel‐plot extrapolations from the potentiodynamic curves revealed a substantial improvement in the corrosion potentials for the TiO2 coatings. According to the theory calculation, to obtain the optimal surface roughness values, around 100 nm to 300 nm, the oxidation time in H2O2 35 wt.% solution is controlled in the range of 2‐5 hours. The results were explained by considering the effects of crystal morphology and roughness. The results indicated that the controlled oxidation‐prepared TiO2 coatings have attractive prospects for use in biomedical applications since better corrosion protection of pure Ti can be expected.

Effects of Crystal Morphology on the Hot-Carrier Dynamics in Mixed-Cation Hybrid Lead Halide Perovskites

Ultrafast pump-probe spectroscopies have proved to be an important tool for the investigation of charge carriers dynamics in perovskite materials providing crucial information on the dynamics of the excited carriers, and fundamental in the development of new devices with tailored photovoltaic properties. Fast transient absorbance spectroscopy on mixed-cation hybrid lead halide perovskite samples was used to investigate how the dimensions and the morphology of the perovskite crystals embedded in the capping (large crystals) and mesoporous (small crystals) layers affect the hot-carrier dynamics in the first hundreds of femtoseconds as a function of the excitation energy. The comparative study between samples with perovskite deposited on substrates with and without the mesoporous layer has shown how the small crystals preserve the temperature of the carriers for a longer period after the excitation than the large crystals. This study showed how the high sensitivity of the time-resolved spectroscopies in discriminating the transient response due to the different morphology of the crystals embedded in the layers of the same sample can be applied in the general characterization of materials to be used in solar cell devices and large area modules, providing further and valuable information for the optimization and enhancement of stability and efficiency in the power conversion of new perovskite-based devices.

Shape-dependent adhesion and endocytosis of hydroxyapatite nanoparticles on A7R5 aortic smooth muscle cells.

The interaction between nanohydroxyapatite (HAP) and smooth muscle cells is an important step in vascular calcification. However, the effect of the shape of HAP on adhesion and endocytosis to aortic smooth muscle cells has been rarely reported. Four different morphological HAP crystals (H-Rod, H-Needle, H-Sphere, and H-Plate) were selected to interact with rat aortic smooth muscle cells (A7R5). Fluorescence-labeled HAP was used to detect crystal adhesion and endocytosis and then pretreated with different endocytic inhibitors to explore the pathway of endocytotic crystals. The distribution of crystals inside and outside the cells and the crystal localization in lysosomes was observed through laser confocal microscopy. The effect of crystal on the cell cycle and the changes in the expression of phosphatidylserine, osteopontin, α-actin, core binding factor alpha 1, and osterix on the surface of A7R5 cells were detected. The adhesion and endocytosis of HAP on A7R5 cells were closely related to crystal shapes and ranked as follows: H-Plate > H-Sphere > H-Needle > H-Rod. H-Sphere and H-Needle were internalized into the cells mainly via the clathrin-mediated pathway, whereas H-Plate and H-Rod were internalized into the cells mainly via macropinocytosis. The endocytosed nano-HAP was mainly distributed in the cell lysosome. The adhesion and endocytosis of HAP to A7R5 cells were positively correlated with the specific surface area, and contact area of HAP and negatively correlated with the absolute value of Zeta and contact angle of HAP. This study provided insights into the effect of crystal morphology on vascular calcification and its mechanism.

Computational analysis of mesoscale thermomechanical ignition behavior of impacted LLM-105 based explosives.

LLM-105 (2,6-diamino-3,5-dinitropyrazine-1-oxide) is an insensitive high explosive crystal which has performance between that of HMX and TATB. An elastoviscoplastic dislocation model is developed for LLM-105 crystal, which accounts for the dislocation evolutions at the crystal interior and crystal wall and strain-rate dependent work hardening. Three different crystal morphology (cubic, icosahedral, rodlike) of LLM-105 based explosive computational models were constructed and subjected to an impact velocity of 200 m s−1 and 500 m s−1. Effects of crystal morphology and initial dislocation density on thermomechanical ignition behavior of LLM-105 based explosives were analyzed. Dislocation density of both crystal interiors and crystal walls in the rodlike LLM-105 based explosive increases slower than that in the cubic and icosahedral explosives. Both the volume averaged and localized stress and dislocation density are the lowest for the rodlike explosive. At the impact velocity of 500 m s−1, a temperature rise due to volumetric work, plasticity work and chemical reaction is sufficiently high to lead to the ignition of the cubic explosive, which shows that the rodlike explosive is the least sensitive among the three explosives. Moreover, with the increase of initial dislocation density, the corresponding volume averaged and localized stress and temperature increase as well. Results presented bridge the macroscale thermomechanical ignition response with the mesoscale deformation mechanisms, which is essential for better understanding the ignition mechanisms and guiding the design of LLM-105 based formulations.

Continuum modeling of twinning, amorphization, and fracture: theory and numerical simulations

A continuum mechanical theory is used to model physical mechanisms of twinning, solid-solid phase transformations, and failure by cavitation and shear fracture. Such a sequence of mechanisms has been observed in atomic simulations and/or experiments on the ceramic boron carbide. In the present modeling approach, geometric quantities such as the metric tensor and connection coefficients can depend on one or more director vectors, also called internal state vectors. After development of the general nonlinear theory, a first problem class considers simple shear deformation of a single crystal of this material. For homogeneous fields or stress-free states, algebraic systems or ordinary differential equations are obtained that can be solved by numerical iteration. Results are in general agreement with atomic simulation, without introduction of fitted parameters. The second class of problems addresses the more complex mechanics of heterogeneous deformation and stress states involved in deformation and failure of polycrystals. Finite element calculations, in which individual grains in a three-dimensional polycrystal are fully resolved, invoke a partially linearized version of the theory. Results provide new insight into effects of crystal morphology, activity or inactivity of different inelasticity mechanisms, and imposed deformation histories on strength and failure of the aggregate under compression and shear. The importance of incorporation of inelastic shear deformation in realistic models of amorphization of boron carbide is noted, as is a greater reduction in overall strength of polycrystals containing one or a few dominant flaws rather than many diffusely distributed microcracks.

Effects of crystal morphology on space charge transportation and dissipation of SiC/silicone rubber composites

The addition of silicon carbide (SiC) micro powder into silicone rubber (SiR) matrix has been found to introduce a marked nonlinear conductivity into the resulting composites, without a degradation of the insulating properties under low electric field. Owing to these properties, the SiR-based nonlinear conductive composites have a potential use as the field grading material (FGM) layer in high voltage direct current (HVDC) cable accessories, which is employed to uniform electric field and suppress charge accumulation at the interface between crosslinked polyethylene (XLPE) and accessory insulation. In this paper, the space charge transportation and dissipation behaviors of SiC/SiR composites were investigated by pulsed electro-acoustic (PEA) test, in view of the effects of SiC filler size and crystal morphology. The results indicated that with the enhancement of nonlinear conductivity, the charge transportation and dissipation processes were accelerated. Compared with α-SiC particles, the β-SiC whiskers could provide a larger nonlinear conductivity. Meanwhile, the trap level distributions of SiC/SiR composites showed that the β-SiC whiskers introduced a shallower trap level at 0.81 eV than the α-SiC particles (0.85 eV). In addition, for the α-SiC particles filled composites, with the increase of the filler size from 0.45 μm to 5.0 μm, the shallow trap density increased, and the deep trap density decreased, resulting in an enhancement of space charge dissipation.

Effects of crystal morphology, Si/Al ratio and thickness of an MTW zeolite membrane on water/2-propanol separation by pervaporation

MTW-type zeolite nanocrystal-layered membranes composed of nanocrystal and protection layers were successfully prepared by a secondary growth method under hydrothermal conditions. The separation abilities of the membranes during pervaporation were investigated by studying the separation of water from water/2-propanol solutions. Both the nanocrystal and protection layers were found to play important roles in the separation process. The crystal size and morphology of the MTW-type zeolite in the protection layer formed on the MTW nanocrystal layer could be controlled by varying the organic structure directing agent (OSDA), such that small crystals approximately 50 nm in size were obtained when using tetraethylammonium bromide as the OSDA. Membranes with nanometer-sized crystals in the protection layer exhibited 4 times higher water flux values and enhanced separation factor as compared with membranes having micrometer-sized crystals. In both layers, zeolite crystals with higher Al contents generated higher water fluxes due to their enhanced hydrophilicity. Moreover, the membranes with nanocrystal layer thicknesses of 7.5, 10, 12 and 17 μm were prepared, and the water flux through the membranes was observed to increase as the nanocrystal layer thickness was decreased.

Palladium nanocrystals supported on photo-transformed C60 nanorods: Effect of crystal morphology and electron mobility on the electrocatalytic activity towards ethanol oxidation

We report on the synthesis and decoration of high-aspect-ratio crystalline C60 nanorods (NRs) by functionalized palladium nanoparticles with an average size of 4.78±0.66nm. In their pristine form, C60 NRs suffer from partial damage in the solution-based decoration process resulting in poor crystallinity. However, by modifying the NR surface via in situ photochemical transformation in the liquid state, we are able to prepare highly stable NRs that retain their crystalline structure during the decoration process. Our method thus opens up for the synthesis of highly crystalline nanocomposite hybrids comprising Pd nanoparticles and C60 NRs. Bys measuring the electron mobility of different C60 NRs, we relate both the effect of electron mobility and crystallinity to the final electrocatalytic performance of the synthesized hybrid structures. We show that the photo-transformed C60 NRs exhibit highly advantageous properties for ethanol oxidation based on both a better crystallinity and a higher bulk conductivity. These findings give important information in the search for efficient catalyst support.

Improvement to the Corrosion Resistance of Ti-Based Implants Using Hydrothermally Synthesized Nanostructured Anatase Coatings.

The electrochemical behavior of polycrystalline TiO2 anatase coatings prepared by a one-step hydrothermal synthesis on commercially pure (CP) Ti grade 2 and a Ti13Nb13Zr alloy for bone implants was investigated in Hank’s solution at 37.5 °C. The aim was to verify to what extent the in-situ-grown anatase improved the behavior of the substrate in comparison to the bare substrates. Tafel-plot extrapolations from the potentiodynamic curves revealed a substantial improvement in the corrosion potentials for the anatase coatings. Moreover, the coatings grown on titanium also exhibited lower corrosion-current densities, indicating a longer survival of the implant. The results were explained by considering the effects of crystal morphology, coating thickness and porosity. Evidence for the existing porosity was obtained from corrosion and nano-indentation tests. The overall results indicated that the hydrothermally prepared anatase coatings, with the appropriate morphology and surface properties, have attractive prospects for use in medical devices, since better corrosion protection of the implant can be expected.

Crystal morphology-dependent graft polymerization in poly(ether ether ketone) films

The effect of crystal morphology, such as the crystallinity and lamellar structure, on the radiation-induced graft polymerization of styrenesulfonate ethyl ester (E4S) onto poly(ether ether ketone) PEEK films was evaluated. The PEEK films possessing crystallinities ranging from 11 to 32% were irradiated with 30–150 kGy, and the graft polymerization was performed in an E4S/1,4-dioxane solution at 80 °C. For the PEEK films with crystallinities between 11 and 26%, the graft polymerization proceeded and reached grafting degrees of up to 70%, whereas for those having crystallinities higher than 26%, the reaction barely proceeded. The concentration of phenoxy radicals that initiated the graft polymerization in the irradiated PEEK films was constant over the entire range of crystallinity (11–32%). On the other hand, in the small-angle X-ray scattering (SAXS) profiles, a discontinuous change in the peak intensity at Q = 0.44 nm−1, which corresponds to a lamellar spacing of 14 nm, was observed at a crystallinity of approximately 26%; namely, the PEEK films with a crystallinities greater than 26% exhibited prominent anisotropic scattering in the drawing direction. Judging from the above results, it can be concluded that the graft polymerization of styrene derivatives onto the PEEK films was affected by the formation of oriented lamellar structures that inhibited monomer diffusion into the films.

Toughening of Poly(L-Lactic Acid) by Annealing: The Effect of Crystal Morphologies and Modifications

Poly(L-lactic acid) (PLA) samples prepared by hot pressing were treated by two different processes: process a—quenching of the molten specimens in water, then annealing at high temperatures; process b—direct crystallization at high temperatures from the molten specimens. The crystal modification and morphology of PLA were investigated by differential scanning calorimetry, dynamic mechanical analysis, polarized light microscopy, and wide-angle X-ray diffraction. In the case of process a, the α′ (disordered α) crystal modification was formed at relatively low annealing temperature (T a < 100°C), while the ordered α phase was formed in the case of process a at high T a (> 100°C) and process b. Furthermore, in process a, the nucleation density of spherulites was higher and the radius of the spherulites was much smaller compared with that of the spherulites formed by process b. The effects of crystal modification and morphology on the impact behaviors of PLA were investigated by notched Izod impact testing. The macroscopic fracture toughness was discussed in terms of the microscopic structures. Finally, we suggest an alternative approach for the preparation of high-performance PLA.

A new approach to crystallographic orientation measurement for apatite fission track analysis: Effects of crystal morphology and implications for automation

Apatite fission track analysis and in particular, computer-assisted fission track recognition require the determination of crystallographic orientation, crystal morphology, cracks, fractures and inclusions. The selection of a crystal for fission track analysis has largely been based on its surface and track etching characteristics that, in conventional fission track dating, is performed by the analyst. This requires manual scanning of the entire mount for suitable grains, which is a very time-intensive process during manual fission track counting. Therefore, a computer-assisted grain characterisation system is of interest to allow for an automated pre-selection of suitable crystals. With the use of a fully automated Fabric Analyser, c-axis orientations can be measured inside an apatite crystal for each pixel with a spatial resolution of 5 μm. The results are represented in geometric quality and retardation maps consisting of the c-axis orientations for each pixel and two quality values evaluating each orientation. These maps allow the determination of the crystallography of the apatite grain as well as its outline. In addition, most of the crystal morphologies, fractures and impurities, which can influence automated fission track recognition techniques based on image analysis, are determinable using the quality maps. On the other hand, the method is not sensitive to smaller crystal cracks, high fission track densities or coating. The quantification of the crystal geometric properties by this method is a step forward to develop a fully automated fission track analysis process.

Influence of calcium phosphate crystal morphology on the adhesion, spreading, and growth of bone derived cells

In this study, rat periosteal cells and bone marrow stromal cells (BMSC) were examined when cultured on octacalcium phosphate (OCP) crystals to determine the effects of crystal morphology on their adhesion, spreading, and growth. Three type of OCP crystals with different morphology were prepared by different precipitation methods. OCPI was prepared by homogeneous precipitation; while OCPII and III were prepared by heterogeneous precipitation dripping a calcium ion containing solution into a phosphate ion solution or vice versa, respectively. The effects of crystal morphology on the attachment and spreading of cultured cells on OCP crystals were observed using SEM. The effects of crystal morphology on the growth of periosteal cell or BMSC were evaluated using the MTT assay, while OCP crystal cytotoxicity was determined by measuring lactic dehydrogenase (LDH) released from 2.12 x 10(5) cells incubated with 60 mg of the different OCPs. BMSCs and periosteal cells attached to or between the crystals of OCPI and the cell number increased over the 17 days of culture. In contrast, cell numbers could not be measured for either periosteal cells or BMSC on OCPII and III. BMSC incubated with OCPII and III showed a higher rate of LDH release, compared with the cells incubated with OCPI. This study demonstrated that the morphology of OCP crystals influenced the attachment, spreading and growth of periosteal cells and BMSC.

Measurement of three‐dimensional concentration gradients around a crystal growing from its aqueous solution using laser schlieren

AbstractSchlieren measurements of the gradients of the concentration field around a KDP crystal growing from its aqueous solution are reported. The measurement of the concentration gradient field is important for crystal growth because it controls the rate of solute transport from the bulk of the solution to the crystal surface. In the crystal vicinity, the concentration gradients have a three dimensional distribution. The concentration gradient field has been imaged using monochrome schlieren technique. Four view angles, namely 0, 45, 90 and 135° have been utilized. By interpreting the schlieren images as projection data of solute concentration gradient, the three‐dimensional concentration gradient field around the crystal has been determined using an algebraic reconstruction technique. At low supersaturation levels, the growth process is accompanied by weak fluid movement during which diffusion effects are significant. At higher levels of supersaturation and large crystal size, a well‐defined convective plume around the growing crystal is observed. Reconstruction of concentration gradients around the crystal explains the preferential growth rates of various faces of the crystal. The non‐circular shape of the crystal is seen to affect the symmetry of the distribution of concentration gradients in its vicinity. The effect of crystal morphology on the orientation of convection currents rising from the crystal surface has also been brought out on the basis of the reconstructed concentration gradients distribution in the growth chamber. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

The effect of crystal morphology and mill type on milling induced crystal disorder

Milling is a key process in the preparation of many solid dosage forms. One possible milling induced change is the production of small levels of disorder or amorphous material found predominantly at the surface of a powder, which could lead to significant chemical and physical instability. The influence of crystal habit on this change was investigated using β-succinic acid, in plate like and needle like morphologies. β-Succinic acid crystals with these habits were processed in a ball mill and a jet mill. SEM images indicated jet milled material was finer than the ball milled product. Powder X-ray diffraction of the milled powders revealed an amorphous halo at lower angles and peak broadening suggesting disorder though this could not be quantified accurately. In addition, a partial conversion during milling to the alpha form was noted. Quantitation of the alpha form in the milled powders indicated it was present at <2% (w/w). Plate and needle shaped particles had similar heats of solution pre-milling, however, all milled powders had lower heats of solution compared to the unmilled powers. The contribution of the alpha polymorph to the lower heats of solution was calculated to be insignificant. Therefore, the reduced heat of solution is attributed to a loss in crystallinity. The largest decreases were seen in the plate like morphology. These findings suggest that β-succinic acid crystals with plate like morphology are more prone to crystallinity loss on milling compared to the needle like morphology. The mill type has also been shown to influence the final crystallinity.

Effect of Crystal Morphology and Crystallinity on the Mechanical α- and β-Relaxation Processes of Short-Chain Branched Polyethylene

The temperature and the Gibbs free energy of activation of the α-relaxation in ethylene-1-octene and ethylene-1-hexene copolymers drop with decreasing crystal size which is triggered by increasing concentration of short-chain branches and/or increasing cooling rate during melt crystallization, respectively. The activation enthalpy and entropy, unexpectedly, increase with decreasing crystal size, obtained by increasing the cooling rate at constant branch concentration. Both effects can be explained by hindrance of the intracrystalline translational mobility and the restricted segment exchange between the crystalline and amorphous phases, caused by branch points accumulated at the crystal surface. The significant drop of the activation enthalpy and the temperature of β-relaxation with increasing branch-concentration point to decreasing restriction of cooperative segmental mobility by crystals. The restriction is reduced as result of decreasing crystallinity or increased crystal perfection, respectively. Thus, the distribution of the local branch concentration controls the molecular mobility of short-chain branched polyethylene expressed both in the α- and β-relaxation.

Crystal morphology of calcium aluminates hydrated for 14 days

phase [2–4]. Many researchers [5–7] have investi-gated the development of these hydrated phases byelectron microscopy. The effects of crystal morphol-ogy on the hydration characteristics and setting timehave also been studied by some workers [8–9]. Theaim of the work reported here is to investigateexactly what the crystal habit and morphology are onthe fourteenth day of hydration of calcium alumi-nates, and what their role is in the development ofcompressive strength of the hydrated samples.Calcium aluminates such as CA, CA

Effect of crystal morphology in selective catalytic reduction of nitric oxide over V 2O 5 catalysts

Structural specificity of vanadium pentoxide catalysts was investigated in the selective catalytic reduction (SCR) of nitric oxide. Catalysts were prepared by different temperature-programmed methods to obtain particles having preferential exposure of different crystal planes. Catalyst samples were characterized using the BET surface area technique, X-ray diffraction, laser Raman spectroscopy. X-ray photoelectron spectroscopy, scanning electron microscopy and 3-D imaging techniques. A steady-state fixed-bed reactor system was used for activity and selectivity measurements. Identification and quantification of reaction effluents were achieved using an analytical scheme that combined gas chromatography, chemiluminescence, gas chromatography-mass spectroscopy and wet chemistry techniques. Samples that preferentially exposed the (010) basal planes were found to promote direct oxidation of ammonia more readily than nitric oxide reduction as evidenced by the differences in nitric oxide and ammonia conversions and in nitrogen and nitrous oxide yields. The difference in catalytic activity and selectivity was related to the relative abundance of V O sites exposed on the catalyst surface and the competing reactions that are involved in SCR and direct ammonia oxidation reaction schemes.