Platy Particles Research Articles

Synthesis of trace element Si and Sr codoping hydroxyapatite with non-cytotoxicity and enhanced cell proliferation and differentiation.

The main inorganic minerals in natural bones are non-stoichiometric hydroxyapatite (HA, Ca10[PO4]6[OH]2) doped with various trace elements, which may possess important biochemical effects. To investigate the functions of Sr and Si elements in human hard tissues, non-doped HA, trace Si doped HA, Si and Sr codoped HA with the concentration of natural bones are synthesized by hydrothermal method in this study. The samples are characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscope (SEM). The biological activities are evaluated via cytotoxicity study, adhesion and proliferation of osteoblast measurement, and alkaline phosphatase (ALP) assay. All the synthesized materials are HA phase, which have hierarchical structures with oriented HA nanorods assembled into the platy particles. These materials are non-cytotoxic against L929 cells line even at 400μg/ml powder suspension. The results clearly indicate that the proliferation of L929 cells increases with trace elements doping from trace Si-HA to Si+Sr-HA. The adhesion and proliferation of osteoblast measurement illustrates that proliferation of osteoblasts advances about 1.3 times for Si-HA and about 1.8 times for Si+Sr-HA compared with undoped HA. In general, Si-HA with trace Si element shows enhanced cell differentiation, and Si+Sr-HA dual-doped with Si and Sr elements presents increased biological activity compared with Si-HA.

Reconstructing fluid-flow events in Lower-Triassic sandstones of the eastern Paris Basin by elemental tracing and isotopic dating of nanometric illite crystals

Lower- to Middle-Triassic sandstones from eastern Paris Basin were buried to a maximum depth of 2500m at a paleo-temperature of about 100°C. They contain extensive amounts of authigenic platy and filamentous illite particles similar to those reported in reservoirs generally buried at 3000 to –5000m and subjected to temperatures of 120 to –150°C. To evaluate this unexpected occurrence, such sandstones were collected from drill cores between 1825 and 2000m depth, and nanometric-sized sub-fractions were separated. The illite crystals were identified by XRD, observed by SEM and TEM, analyzed for their major, trace, rare-earth elements and oxygen isotope compositions, and dated by K–Ar and Rb–Sr.Illite particles display varied growth features in the rock pore-space and on authigenic quartz and adularia that they postdate. TEM-EDS crystal-chemical in situ data show that the illite lath/fiber and platelet morphologies correspond at least to two populations with varied interlayer charges: between 0.7 and 0.9 for the former and between 0.8 and 1.0 for the latter, the Fe/Fe+Mg ratio being higher in the platelets. Except for the deeper conglomerate, the PAAS-normalized REE patterns of the illite crystals are bell-shaped, enriched in middle REEs. Ca-carbonates and Ca-phosphates were detected together with illite in the separates. These soluble components yield 87Sr/86Sr ratios that are not strictly in chemical equilibrium with the illite crystals, suggesting successive fluids flows with different chemical compositions. The K–Ar data of finer <0.05μm illite separates confirm two crystallization events at 179.4±4.5 and 149.4±2.5Ma during the Early and Late Jurassic. The slightly coarser fractions contain also earlier crystallized or detrital K-bearing minerals characterized by lower δ18O values. The δ18O of the finest authigenic illite separates tends to decrease slightly with depth, from 18.2 (±0.2) to 16.3 (±0.2)‰, suggesting different but contemporaneous crystallization conditions deeper in the section.The illite platelets and filaments crystallized in changing physical–chemical crystallization conditions induced by fluids flows through the host-rock pore system. These flow events were probably driven by repetitive rifting episodes of the North Atlantic Ocean, although located several hundreds kilometers away from eastern Paris Basin, and/or by fracturing events in the nearby basement of the Vosges Massif. Complex relationships between geodynamical events, thermal anomalies, and advective fluids confirm that remote tectonic activities can impact quiescent basins, even if located far from tectono-thermal activities, by discrete and long-distance fluid flows.

Determination of dimensions of exfoliating materials in aqueous suspensions

A method for measurement of dimensions of platy particles of exfoliating, or delaminating, materials, such as clays, in aqueous suspensions in situ is proposed. Equivalent spherical diameter (esd), measured by many common methods, depends more on the major (lateral) dimension of a particle, while it is less sensitive to changes of the particle thickness. Addition of the second method, results of which are a function of the particle diameter and thickness too, would provide more accurate determination of the particle dimensions. Previously, a combination of low-temperature nitrogen adsorption (BET) and dynamic light scattering (DLS) methods for determination of specific surface area of dry powder of platy particles and their esd in suspension was suggested. While such combination was suitable for measurement of particle size for non-exfoliating materials, it gave incorrect results for exfoliating materials, which dramatically change their surface area when dispersed in liquid. We modify this method by substituting BET method with NMR relaxometry, which allows to measure wetted surface area of the dispersed material directly in suspension. The advantages of this method are:•More accurate determination of diameter and thickness of platy, particularly exfoliating, materials directly in suspension.•Possibility of routine monitoring of particle size changes during the dispersing process.

Experimental constraints on phreatic eruption processes at Whakaari (White Island volcano)

Vigorous hydrothermal activity interspersed by sequences of phreatic and phreatomagmatic eruptions occur at Whakaari (White Island volcano), New Zealand. Here, we investigate the influence of sample type (hydrothermally altered cemented ash tuffs and unconsolidated ash/lapilli) and fragmentation mechanism (steam flashing versus gas expansion) on fragmentation and ejection velocities as well as on particle-size and shape. Our rapid decompression experiments show that fragmentation and ejection speeds of two ash tuffs, cemented by alunite and amorphous opal, increase with increasing porosity and that both are significantly enhanced in the presence of steam flashing. Ejection speeds of unconsolidated samples are higher than ejection speeds of cemented tuffs, as less energy is consumed by fragmentation. Fragmentation dominated by steam flashing results in increased fragmentation energy and a higher proportion of fine particles. Particle shape analyses before and after fragmentation reveal that both steam flashing and pure gas expansion produce platy or bladed particles from fracturing parallel to the decompression front. Neither fragmentation mechanisms nor sample type show a significant influence on the shape. Our results emphasize that, under identical pressure and temperature conditions, eruptions accompanied by the process of liquid water flashing to steam are significantly more violent than those driven simply by gas expansion. Therefore, phase changes during decompression and cementation are both important considerations for hazard assessment and modeling of eruptions in hydrothermally active environments.

Reduced humic acid nanosheets and its uses as nanofiller

Leonardite is highly oxidized form of lignite coal and contains a number of carboxyl groups around the edges of a graphene-like core. A novel approach has been developed to synthesize graphene oxide-like nanosheets in large scale utilizing leonardite as a starting material. Humic acid extracted from leonardite has been reduced by performing a high pressure catalytic hydrogenation. The reaction was carried out inside a high pressure stirred reactor at 150°C and 750psi (~5.2×106Pa). Morphology of the as-synthesized samples showed porous platy particles and EDAX analysis indicates the carbon and oxygen atomic ratios as 96:4–97:3%. The as-synthesized material has been used as nanofiller in polyurethane. The reduced humic acid–polyurethane nanocomposite showed over 250% increase of Young’s modulus. This new approach provides a low cost and scalable source for graphene oxide-like nanosheets in nanocomposite applications.

Facile One-Pot Synthesis of Oriented Pure Hydroxyapatite with Hierarchical Architecture by Topotactic Conversion

The oriented hierarchical architecture of hydroxyapatite (HA) shows excellent performance in multiple functions in human hard tissues such as bone and teeth. It is a challenge to mimic the architecture of biomineralization products. This study introduces a simple method for the hierarchical architecture of pure stoichiometric HA by a one-pot hydrothermal process without adding any organic molecules. The reaction process is researched by XRD, FT-IR, SEM, and TEM, and the HA crystal growth mechanism is discussed. The short rod-like HA nanocrystals are orderly assembled into micrometer-sized platy particles with the DCPD (CaHPO4·2H2O, brushite) shape retained. The ordered HA hierarchical architectures are achieved through topotactic transformation due to the crystal structural similarity from DCPD through DCPA (CaHPO4, monetite) to HA. It is found for the first time that the growth of HA crystals on DCPA is accompanied by orientation relationship of HA [1̅10] // DCPA [110] and HA (112) // DCPA (1̅12). The resemblance between the crystal structures promotes the direct phase transition. The results provide new insights into the formation mechanism of ordered HA hierarchical architectures and give hints for designing hierarchically assembled nanoarchitecture in synthetic work.

Particle alignment and clustering in sheared granular materials composed of platy particles.

By means of molecular dynamics simulations, we investigate the texture and local ordering in sheared packings composed of cohesionless platy particles. The morphology of large packings of platy particles in quasistatic equilibrium is complex due to the combined effects of local nematic ordering of the particles and anisotropic orientations of contacts between particles. We find that particle alignment is strongly enhanced by the degree of platyness and leads to the formation of face-connected clusters of exponentially decaying size. Interestingly, due to dynamics in continuous shearing, this ordering phenomenon emerges even in systems composed of particles of very low platyness differing only slightly from spherical shape. The number of clusters is an increasing function of platyness. However, at high platyness the proportion of face-face interactions is too low to allow for their percolation throughout the system.

A new method for determining platy particle aspect ratio: A kaolinite case study

A technique based on the detection method of particle size is presented to calculate the aspect ratio of particles with known layered silicate minerals. The principle relies on the premise that objects placed in an electric field modify the current flow of that field. The accurate volume of the testing particle is obtained from the difference of the conductivity of the particles and that of the conductive liquid. Platy particles have a disc-like shape. Therefore, the thickness and diameter of the particle can be calculated from its volume. The aspect ratio of the platy particle is successfully obtained from the results. This study uses a spherical standard sample with a diameter of 10μm and two different kaolinites that vary in the conductivity of two electrodes by the particles as they pass through the aperture tube. According to the thickness of the particle size and the diameter (width and length) of the disc the particle extracted from the raw data, and the standard particles of the particle-size analyzer (Coulter Multisizer 3), a new method of determining the aspect ratio of the disc-shaped particle is obtained.

Stress induced permeability anisotropy of Resedimented Boston Blue Clay

[1] In Resedimented Boston Blue Clay (RBBC), a low-plasticity glacio-marine illitic mudrock, the ratio of the horizontal to vertical permeability (the permeability anisotropy, rk) increases from 1.2 to 1.9 as the porosity decreases from 0.5 to 0.37 and the permeability decreases by more than 1 order of magnitude. Backscattered Scanning Electron Microscope (BSEM) images taken at formation stress levels reveal that particles rotate perpendicular to the axial loading direction by ∼22°, with larger particles rotating more significantly and achieving more uniform alignment than smaller particles. We show experimentally that preferred platy particle orientation can explain our permeability anisotropy measurements. The permeability anisotropy of mechanically compressed mudrocks is minimal, <2.5. We use a novel approach (cubic specimens) to measure the evolution of permeability anisotropy in different directions on the same specimen, unlike most other methods. Modified analytic techniques allow calculation of the permeability anisotropy for a specimen using directional constant head permeability methods. A better understanding of the evolution of permeability anisotropy during sediment burial is important for modeling subsurface transport processes, including hydrocarbon migration and contaminant transport, as well as estimating in situ conditions such as pore pressure, overpressure, and effective stress.

Morphological characteristics of fulvic acid fractions observed by atomic force microscopy

Structural studies on fulvic acids (FAs) are significantly important since they are believed to be involved in many environmentally important processes, such as adsorption and transportation of organic and inorganic pollutants. In this research, morphology characteristics of FAs were studied by atomic force microscopy (AFM). FAs that were isolated from three soil layers (A1, B and C) of the same vertical profile in a Korean pine forest were divided into four fractions (FA-1, FA-2, FA-3 and FA-4) by a sequence of successive elution processes. Most of FAs appeared as a platy particle in the AFM topographic and phase images. Among these platy particles, some have a regular shape, such as round flake and oblong flake; others have irregular structures, such as sand heaps. Particle morphologies of different FA fractions, including hydrophilic and hydrophobic FAs fractions, were similar. However, particle sizes and distributions of FA fractions from different soil layers at the same vertical profile did differ. Particle sizes of hydrophobic FAs were relevant with respect to the soil depth. They were increased with the increasing of the soil depth. FAs from C layers were more heterogeneous with respect to the A1 and B. Our results may foster a better understanding for the relevance between the morphology of FA particles with the soil layers and the soil depth.

Chemistry, morphology and structural characteristics of synthetic Al–Ni and Al–Co-lizardites

Al–Ni and Al–Co lizardites have been synthesized at hydrothermal conditions. The two phases display different morphologies: thin, dominantly curved platelets (Al–Ni); and stacks of very thin platy particles (Al–Co). The X-ray diffraction and transmission/analytical electron microscopy studies have been used to make accurate distinctions among different structural types and chemical populations. Al–Ni bearing lizardite includes a 1M polytype and probably very subordinate amounts of chlorite. Al–Co bearing lizardite includes two 1M polytypes with different cell-parameters, one of these consisting of an apparently modulated structure. Chemically, Al–Ni- and specially Al–Co lizardite consist of a mixture of two populations with tetrahedral compositions ~Si1.8Al0.2 and Si2.0. In contrast with previously described Al-rich serpentines, our serpentines are characterized by an asymmetrical Al distribution, with VIAl on the order of 1.0 atom per formula unit.

Quasistatic rheology and microstructural description of sheared granular materials composed of platy particles

This is the first paper of a series devoted to the micro-mechanical modeling of clayey soils, by means of discrete element simulations. We specifically focus here on the effect of the platy shape of particles by reducing the interactions between particles to mechanical contact forces (i.e., neither electrostatic repulsion nor van der Waals forces are taken into account). The particles are three-dimensional square plates, approximated as spheropolyhedra. Several samples composed of particles of different levels of platyness (related to the ratio of length to thickness) were numerically prepared and sheared up to large deformations. We analyzed the shear strength, packing fraction, orientation of the particles, connectivity, fabric of the interactions network, and interaction forces as functions of the platyness. We find that both the mechanical behavior and microstructure are strongly dependent on the degree of platyness. The principal underlying phenomenon is the alignment of particle faces along a particular direction. This ordering phenomenon, which emerges even for shapes that deviate only slightly from that of a sphere, enhances the ability of the packing to develop an anisotropic structure leading to large shear strength, especially as a consequence of the fabric and mobilization of friction forces. Moreover, the connectivity of the packings and their packing fraction also evolve with the platyness. In particular, the packing fraction evolves in a nonmonotonic fashion, as observed in other granular materials composed of elongated or angular particles.

Rapid Precipitation of Magnesite Microcrystals from Mg(OH)2-H2O-CO2 Slurry Enhanced by NaOH and a Heat-Aging Step (from ∼20 to 90 °C)

This study proposes a simple and novel synthesis route for rhombohedral single crystals (<2 μm) of magnesite. This synthesis can be summarized by two main sequential reactions: (1) aqueous carbonation of synthetic brucite (Mg(OH)2) by injection of CO2 in a highly alkaline medium (2 m NaOH) at ambient temperature (∼20 °C), leading to precipitation of platy-compacted aggregates of dypingite (Mg5(CO3)4(OH)2·5H2O) after 24 h, and (2) complete dypingite-to-magnesite transformation after 24 h by a simple heat-aging step from 20 to 90 °C. The dypingite-to-magnesite transformation implies the simultaneous dehydration and carbonation of a brucitic layer of dypingite coupled with instantaneous formation of magnesite crystals. In this study, the NaOH played a catalytic role; that is, it accelerated brucite carbonation by an increase in carbonate ion concentration with time and it promoted the formation of magnesite during the heat-aging step, as illustrated in the following global reaction:At laboratory scale, magnesite is typically synthesized at high temperature (>90 °C) and its synthesis requires several days or weeks depending on experimental conditions. For this reason, industrial-scale magnesite production has been limited. The proposed magnesite synthesis method, requiring only 48 h and moderate temperature, could easily be extrapolated on an industrial scale. Moreover, a simple and novel synthesis route for the production of fine platy particles of hydromagnesite is reported, with synthesis requiring only 5 h. On the basis of their chemical compositions and textural properties, there are potential applications for both minerals, for example, as a mineral filler and/or as a flame retardant.

Coupled spreading-fraction effects of polymer nano-binder on the network connectivity and tensile modulus of porous mineral coatings

A numerical model was developed that combines complex porous coating microstructures with continuum mechanics simulations. Platy (hexagonal plates) and blocky (frusta) particles were packed computationally. Polymer nano-bridges were then placed between the packed particles to establish network continuity. Slices from the 3-dimensional packings were extracted and a finite element method implemented to determine the mechanical properties. As a function of shape, high aspect ratio plates might be expected to resist load more effectively than 1:1 aspect ratio frusta. However, when the polymer fractions are high and there is low binder spread across the particle surfaces, the frustum packings exhibit higher tensile modulus values than the platy packings. These packed frusta have more stable solid state networks than higher aspect ratio platy packings and consequently resist load more effectively.

Designing polymeric films having specific metallic luster

The roles of blend composition and process parameters on the metallic luster of extruded polymer films and spray-coated samples have been investigated. The metallic luster is determined by the orientation of platy metallic particles which is determined from X-ray intensity ratio (XIR) of the (200) and (111) planes of the aluminum crystal lattice. The metallic luster is an optical property that is measured by the flop values derived from light scattering measurements. The XIR and flop are useful for monitoring the effect of changes in blend composition and process parameters. Addition of different shaped particles has a different effect on the orientation of aluminum flakes. It is shown that aluminum platy particles orient only when they are first dispersed in an appropriate dispersing polymer. A methodology is developed for matching the metallic luster of both spray-coated and extruded polymer resin formulations by coupling XIR data with the flop values. This methodology is shown to be useful for optimizing the process conditions and composition of polymeric blends containing aluminum flakes needed to achieve the required metallic appearance in polymer films and articles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The syntheses of thin layers of organosilica by the co-condensation of tetraethoxysilane and phenyltriethoxysilane in the presence of cationic surfactant

Thin layers (with the thickness of several tens of nanometers) of silica-surfactant hybrids were deposited on flat glass substrate from aqueous methanol solution of tetraethoxysilane, phenyltriethoxysilane, alkyltrimethylammonium chloride, and ammonia by the reaction at room temperature. Multilayered films were deposited on flat substrates by repeating the film preparation procedure. Due to the reproducible syntheses, the films are possible candidates as scaffold of sensor and photonic coatings. A hexagonal platy core–shell particle with a hydrotalcite core and organosilica shell was also synthesized by the reaction of hydrotalcite with aqueous methanol solution containing tetraethoxysilane, hexadecyltrimethylammonium chloride, and ammonia. A hollow hexagonal platy particle was obtained by removing the hydrotalcite from the core–shell particle by acidic leaching. The organosilica-coated particles may affect the anion exchange selectivity of hydrotalcite, and the organosilica hollow particle is possible candidate as a new class of carried due to the unique platy particle shape.

Determining the size distribution-defined aspect ratio of platy particles

Mineral particles are used in many industrial applications as fillers, in coatings, as ad- and absorbers or in catalysis. In these manifold fields the particle size and shape control the final performance and properties of the minerals. Much has been published using different techniques to describe the aspect ratio of platy particles. This study describes a simple method to calculate aspect ratios for platy particles based on particle size data and specific surface area determined by nitrogen adsorption, exemplified with three different talc grades which vary in their amount of specific surface area and geological origin, as well as with one nano-sized synthetic Laponite (Laponite® RD) to illustrate the sensitivity to input parameters and their physical interpretation. The contrast between mass/volume and number probability distribution of particle size is discussed and illustrated.

Surface Area and Porosity of Nanotubes Obtained from Kaolin Minerals of Different Structural Order

AbstractMesoporous materials with pore diameters in the range 2–50 nm forming tubular or fibrous structures are of great interest due to their unique properties. Because they are commonly used as sorbents and catalyst carriers, knowledge of their surface area and porosity is critical. A modified intercalation/deintercalation method was used to increase the efficiency of nanotube formation from kaolin-group minerals which differ in terms of their degree of structural order. Unlike previous experiments, in the procedure adopted in the present study, methanol was used instead of 1,3-butanediol for grafting reactions and octadecylamine intercalation was also performed. The samples were examined using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). The specific surface area and porosity of previously described and newly formed materials were investigated by N2 adsorption/desorption. Compared to results described earlier, the percent yield of nanotubes obtained in the present study was significantly greater only in the case of ‘Maria III’ kaolinite, which has high structural order. This increase was obtained mainly by the grafting reaction with methanol. Highly ordered stacking of kaolinite-methanol intercalates was noticed and, thus, the amine intercalation was more efficient. In particular, the use of long-chain octadecylamine significantly increased the nanotube yield. The grafting reaction with methanol procedure yielded fewer nanotubes, however, when applied to poorly ordered samples (‘Jaroszów’ kaolinite and ‘Dunino’ halloysite). In the case of the ‘Maria III’ kaolinite, the diameter of the rolled layers observed by TEM was ~30 nm and corresponded to average diameters of newly formed pores (DmN) determined using N2 adsorption/desorption, confirming that nanotubes contributed to an increase in surface area and total pore volume. In the case of ‘Jaroszów’ kaolinite and ‘Dunino’ halloysite mainly macropores (DmN &gt; 100 nm) and mesopores (20 nm &gt; DmN &gt; 40 nm) were formed. The pores were attributed to interparticle and interaggregate spaces in the stacks of platy particles and to the small relative number of nanotubes.

Multiple causes of diagenetic fabric anisotropy in weakly consolidated mud, Nankai accretionary prism, IODP Expedition 316

In the Nankai accretionary prism and its associated slope sediments early (pre-lithification) mechanical modification of mud induces preferred alignments of elongate or platy particles and the loss of intergranular porosity. Generic types of particle alignment include: 1. particles having long axes aligned in the plane of bedding, most likely as a consequence of burial compaction; 2. diverse bioturbation structures including alignments parallel to burrow walls, burrows filled with obliquely aligned phyllosilicates, and blotchy disruption of bedding; and, 3. planar deformation bands showing parallel alignments of both silt- and clay-size particles.Subtle compositional contrast between deformation bands and host rocks is consistent with loss of intergranular micropores within bands and supports the dominance of mechanical over chemical processes in their formation. Field-emission SEM imaging of Ar-ion-milled cross-sections shows that collapse of larger (>2 μm) pores, many localized at the margins of silt-size particles, reduces porosity within the bands by about 5 percent compared to the adjacent host rock. Despite the clear role of shear, evidence for particle comminution is equivocal.These observations on mechanical processes in early diagenesis provide useful context for interpretation of pore types and fabric anisotropies in mudrocks across a wide range of subsurface conditions.

Chemistry, morphology and structural characteristics of synthetic Al-lizardite

AbstractAl-lizardite has been synthesized under hydrothermal conditions (200ºC). Morphologically, Al-lizardite consists of thin platy particles ~400 Å wide and ~150 Å thick. Structurally, the X-ray diffraction patterns indicate that the 2H2 polytype is dominant, with cell parameters: a = 5.311(0.006) Å; c = 14.333 (0.013) Å and space group P63. High-resolution transmission electron microscopy images revealed, however, the presence of other polytypes and abundant stacking disorder. Chemically, Al-lizardite consists of a single population with average tetrahedral composition Si1.74Al0.26. In contrast to previously described Al-rich serpentines (amesite and Al-lizardite), this Al-lizardite is characterized by an asymmetrical Al distribution, with VIAl ≈0.70 and IVAl ≈0.25 atoms per formula unit.