Platy Particles Research Articles

Experimental insights into laser diffraction particle sizing of fine‐grained sediments for use in palaeoceanography

AbstractGrain‐size measurements of fine‐grained sediments based on laser diffraction may contain spurious information due to the over‐estimation of the size and proportion of platy particles. Consequently, some regard the use of laser diffraction particle sizing in palaeoceanography inappropriate. Here, it is shown experimentally that such concerns are not warranted. Laser diffraction particle sizing is known to be fast, precise and allows for detailed particle sizing over a broad size range; it is therefore potentially a very powerful technique if the complications associated with it can be overcome. As most sediments are mixtures of different components transported by different mechanisms, inferences of past environmental parameters require decomposition of the grain‐size record in question. Useful decomposition can only be performed if changes in the contribution of the components are registered predictably by the measuring device. This study reports on mixing experiments which show that the Fritsch A22 laser diffraction particle sizer does indeed register small changes in the contribution of the mixing components in a predictable way. Mixing proportions estimated from the measurements do, however, differ from the initial mixing proportions, but these can be converted with only small errors. Application of the conversion equations to a North Atlantic grain‐size record that showed consistent slowdown of deep‐ocean circulation in response to millennial scale ice‐rafting events during the last glacial does not quantitatively affect the original inferences. Laser diffraction particle sizing of fine‐grained sediments therefore yields reproducible and useful data for palaeoceanographic reconstructions.

Study of Natural Halloysite from the Dragon Mine, Utah (USA)

AbstractA natural sample from the Dragon Mine, Tintic District, Silver City, Utah (USA), has been characterised. It contains a mixture of halloysite and alunite. The former shows the characteristic tubularly shaped particles while the latter is found to crystallise in platy particles. The crystal structure of halloysite is stable up to 400–450 °C and before decomposition some crystallisation is observed. Amorphisation is observed with further increasing the annealing temperature. However, the halloysite particles conserve the original morphology (tubes) up to 900 °C. The size distribution of the tubes is found to be quite broad. This is argued to be responsible for the poor measured surface area.

Facile synthesis of Zn-Al layered double hydroxide from aqueous suspension of zinc oxide and aluminum hydroxide

Zn-Al layered double hydroxide containing benzenesulfonate was successfully synthesized by the hydrothermal reactions of aqueous suspension of zinc oxide and aluminum hydroxide in the presence of benzene sulfonic acid. The products were characterized by the sharp X-ray diffraction profile and platy particle morphology. The present very simple (hydrothermal reaction of the aqueous mixture) synthesis is applicable to a series of layered double hydroxides with different compositions and structures.

Mn-oxides and sequestration of heavy metals in a suburban catchment basin of the Chesapeake Bay watershed

The Chesapeake Bay is greatly impacted by numerous pollutants including heavy metals and understanding the controls on the distribution of heavy metals in the watershed is critical to mitigation and remediation efforts in controlling this type of pollution. Clasts from a stormwater catchment basin draining a subdivision near George Mason University, Fairfax VA (38°50.090°N 78°19.204°W) were investigated using X-ray diffraction (XRD), Scanning electron microcopy (SEM) and energy dispersive spectroscopy (EDS) to determine the nature of Mn-oxide coatings and relationship to bound heavy metals. Mn-oxides are poorly crystalline and occur as subhedral to anhedral platy particles and more rarely as euhedral plates. Micronodules are a commonly observed texture. Chemical compositions of coatings are variable with average major constituent concentrations being Mn (33.38 wt%), Fe (11.88 wt%), Si (7.33 wt%), Al (5.03 wt%), and Ba (0.90 wt%). Heavy metals are found in the coatings with Zn being most prevalent, occurring in approximately 58% of analyses with an average concentration of (0.66 wt%). Minor amounts of Co, Ni, Pb, and Cl are observed. Heavy metals and Cl are interpreted as being derived from road pollution. Mn-oxides can serve as a sequestration mechanism for pollution but may also release heavy metals. Field and laboratory observations indicate Mn-oxides occurring on the surface of the clasts can be mechanically mobilized. This is a mechanism for transporting heavy metals into the Chesapeake Bay watershed. Deicing agents may serve as a mechanism to release heavy metals through cation exchange and increased ionic strength. This is the first detailed mineralogical investigation of Mn-oxides and the roles they may play in pollution in the Chesapeake Bay.

Morphology control of anisotropic BaTiO 3 and BaTiOF 4 using organic–inorganic interaction

We proposed a novel concept for morphology control of barium titanate precursor to fabricate platy particles. Organic molecules play an essential role in the crystallization of BaTiOF 4 to synthesize multi-needle particles, polyhedron particles or platy particles in an aqueous solution. Precursors were successfully transformed to barium titanate single phase by annealing. Platy barium titanate precursor particles are expected for future multilayer ceramic capacitors.

Synthesis of Au Nanoparticles in the Interlayer Space of a Layered Titanate Intercalated with 2-Aminoethanethiol

Abstract The intercalation compound of a layered titanate with 2-aminoethanethiol was synthesized to prepare and support Au nanoparticles with morphology replicated by two-dimensional nanospace. The morphology of the formed Au nanoparticles was revealed to be plate, and the thickness and diameter of the platy particles varied with the added amount of Au source; less than 0.7 nm and ca. 6.8 nm, less than 0.9 nm and ca. 6.5 nm, and less than 0.9–1.0 nm and ca. 5.7 nm at molar Au/SH ratios of 0.5, 1.5, and 2.0 respectively. Platy Au nanoparticle-supported layered titanate (Au/SH ratio of 0.5) was thermally stable up to 180 °C in air and 160 °C in helium, respectively.

Modeling the effect of pigment morphology on the dynamic compression of coating layers using DEM

In the present paper, discrete element method (DEM) was employed to investigate the effect of pigment morphology on packing dynamics and compressive behavior of paper coating layers in calendering process. Spherical, platy, and needle-like particles, representing GCC, delaminated clay, and aragonite PCC pigments, were considered in this study. For each particle shape, the compression of coating structures formed by mono-sized and poly-dispersed pigments were modeled. Stress–strain behavior of the coating layers and in-plane and out-of-plane movements of the pigment particles during the compression were computed under the same maximum compressive stress. Simulation results revealed that the in-plane movements of the pigment particles during compression in the calender nip were small in magnitude (<0.35 μm). These findings help to better understand the smoothening phenomena of coating structures during the calendering process.

Morphological Characteristics of (K, Na)-Rectorite from Zhongxiang Rectorite Deposit, Hubei, Central China

The morphological characteristics of the Zhongxiang () rectorite have been studied using X-ray diffraction (XRD), electron probe micro-analyzer (EPMA), scanning electron microscopy (SEM), atomic force microscope (AFM), and high-resolution transmission electron microscopy (HRTEM). The structural formula of the Zhongxiang rectorite is: (Na0.45K0.32Ca0.37Mg0.08)(Al3.78Fe0.11Ti0.10)[(Si6.22Al1.78)O20](OH)4nH2O. It should be confined to a regular interstratification of (K, Na)-mica and Ca-montmorillonite. SEM observations show that Zhongxiang rectorite occurs as platy and fold-shaped crystals, and mainly as extremely thin plates with thickness ranging from 0.4 to 0.05 μm and a smooth (001) surface. There are well-developed polygonal steps on the surfaces of some thick crystals, suggesting a layer-by-layer growth mechanism. AFM observations show a series of steps with a height of 2 nm on the platy particles, suggesting the stacking of 20 nm fundamental particles. Club-like or fiber-shaped halloysite is included in the platy crystals with their elongated dimension paralleling (001) of the platy crystals or crossing the (001) surface of the platy rectorite, indicating multi-stage crystallization and involvement of hydrothermal fluids. The Zhongxiang rectorite was generated by both layer-by-layer growth mechanism and dissolution and crystallization growth mechanism with multistages.

Synthesis of Ni-rich 1:1 phyllosilicates

AbstractRapid dissolution of partly amorphized kaolinite in the systems kaolinite + NiCl2, kaolinite + Ni(OH)2, and kaolinite + NiCl2 + Ni(OH)2, at a temperature of 200°C and at pH between 5.3 and 7.4, leads to the precipitation of Ni-poor kaolinite, Ni-rich kaolinite and Al-Ni-serpentine. Identification of the phases was carried out using a combination of X-ray diffraction and transmission/analytical electron microscopy. Ni-bearing kaolinite shows variable morphologies in the systems studied: stacks of kaolinite with relatively small Ni contents and fine-grained curved particles of Ni-rich kaolinite dominate in the Cl-bearing system; spherical particles with a disordered structure and relatively uniform Ni contents (in the order of 0.15 atoms per formula unit (a.p.f.u.)) and platy particles of Al-Ni-serpentine characterize the products formed in the Ni(OH)2-richest systems. The presence of Ni(OH)2 in the systems (with and without Cl) favors the dissolution process as well as rapid precipitation of spherical particles, and the formation of serpentine. A difference from Mg systems studied previously is a well defined phase intermediate in composition between kaolinite and serpentine which originated in the Ni-bearing systems. Increasing Ni content is clearly reflected in the parallel increase in the b cell parameter of kaolinite. The average composition of the coexisting Al-Ni-serpentine is: (Al1.24Ti0.01Fe0.02Ni1.31) (Si1.58Al0.42)O5(OH,Cl)2.

PREPARATION AND THERMAL DECOMPOSITION OF CO(II)-MAGADIITE INTERCALATION COMPOUNDS

The intercalation of cobalt ions (Co(II)) into the interlayer space of a layered silicate, magadiite, was conducted by ion exchange reactions between magadiite and aqueous solution of cobalt(II) chloride. Thermal treatment of the Co(II)-mgadiites in air at 1000°C resulted in the transformation to cristobalite with retaining the platy particle morphology of the original magadiite.

Micaceous Sands: Microscale Mechanisms and Macroscale Response

The presence of mica changes the mechanical behavior of sandy soils. In this study, micro- and macroscale tests are used to explore the unique packing characteristics that develop in mixtures made of round and platy particles, and the effects that mica exerts on small, medium, and large strain parameters. Mixtures are prepared with different mica contents and various mica-to-sand size ratios, Lmica∕Dsand. Results provide a comprehensive characterization of mixtures made of spherical and platy particles. Mica plates change sand packing through pore filling, bridging, ordering, and mica–mica interaction; bridging prevails and leads to open fabrics when Lmica∕Dsand≥1. As the mica content increases in mixtures with Lmica∕Dsand≥1, the shear-wave velocity decreases and it becomes more sensitive to the state of stress; the constraint modulus decreases; and the peak and residual friction angles decrease. Remixing during disordered granular flow prevents mica alignment and diminishes the otherwise weakening effect of mica on large-strain strength.

Preparation of hexagonal platy particles of nanoporous silica using hydrotalcite as morphology template

Hexagonal platy composite particles with a hydrotalcite core and a nanoporous silica shell with a thickness of ca. 100 nm were synthesized by the reaction of a Mg–Al hydrotalcite with a homogeneous aqueous solution containing tetraethoxysilane, hexadecyltrimethylammonium chloride, ammonia and methanol at 3 °C. The calcination of the products at 500 °C in air led to the composite particle with a Mg/Al mixed oxide core and a nanoporous silica shell. Hexagonal platy particles of nanoporous silica with a pore diameter of 2.3 nm and BET surface area of 700 m 2 (g of silica) −1 were obtained by removing the Mg/Al mixed oxide core.

Hydrothermal Synthesis of Mg-Rich and Mg-Ni-Rich Kaolinite

AbstractMg-rich kaolinite and Mg+Ni-rich kaolinite have been synthesized in hydrothermal experiments (200 and 400°C) from poorly crystalline kaolinite and Mg- and Mg+Ni-bearing solutions. Al-rich serpentine and Al-rich chlorite were obtained as sub-products of the reactions. The formation of these phases occurred through a dissolution-precipitation mechanism that led to spherical kaolinite after short reaction times. A morphological evolution towards platy particles and stacks occurred at increasing run times.Identification of the several phases was carried out using a combination of X-ray diffraction and transmission/analytical electron microscopy. Analytical data indicate that the Mg content in kaolinite increased as a function of the reaction time and temperature, reaching up to 0.46 atoms per half formula unit (a.p.h.f.u.). The measured (Mg+Ni) content reached up to 0.56 a.p.h.f.u.. Both the gradual increase of the b-cell parameter of kaolinite at increasing Mg contents and the presence of new bands on the FTIR spectra of the synthesized kaolinite point to a Mg-for-Al replacement in the octahedral sheet rather than to the presence of serpentine-like layers interstratified in the kaolinite structure.

Controlled Particle Size and Size Distribution of Co–Al Layered Double Hydroxide via the Hydrothermal Urea Method in Aqueous Alcohols

Abstract Hexagonal platy particles of CoII and AlIII layered double hydroxide were precipitated from homogeneous solutions via urea hydrolysis under hydrothermal conditions. The particle sizes and size distribution were successfully controlled by adding alcohols to the starting mixture.

The undrained response of sands with additions of particles of various shapes and sizes

As a natural deposit, sand is rarely found clean—that is, without fractions of silt or clay. The engineering behaviour of two different host sand gradations mixed with additions of particles of various shapes and sizes is compared with that of clean sand. Anisotropically consolidated specimens are sheared in triaxial compression and extension at their ‘loosest’ initial state resulting from the same depositional method, namely air pluviation. Additive materials at contents less than 2·5% by weight can dramatically change the undrained behaviour of the host sand. The addition of rotund particles (e.g. silt) should be distinguished from that of flat or platy particles of different size (e.g. kaolin, silt or sand-size mica). The importance of shape and location of additives in modifying the sand structure is not reflected in measures such as void ratio. Mixtures of both sands with silt-size mica exhibit the most unstable response, although these had the lowest values of void or granular void ratio. The undrained response of each sand mixed with different amounts of sand-size mica is also presented. An increase in mica content usually leads to more stable behaviour at contents above a certain threshold, depending on the grading of the sand. The shear response of the sands and most mixtures is much weaker and more contractive in triaxial extension than in triaxial compression. High anisotropy is also indicated by the stiffness measurements at small strains in both loading directions.

Preparation of Large Platy Particles of Co-Al Layered Double Hydroxides

AbstractCobalt (II) and Al (III) layered double hydroxides were precipitated from homogeneous solutions using urea hydrolysis under hydrothermal conditions. The particle sizes were controlled successfully by changing the reaction temperature and period. It was found that larger particles formed by reactions at lower temperatures over longer reaction periods because the slow urea hydrolysis at lower temperatures suppresses the formation of nuclei in the solution. When the reaction was conducted at 60°C for 100 days, particles &gt;40 µm wide were obtained.

Synthesis and silica coating of calcia-doped ceria/mica nanocomposite by seeded polymerization technique

Calcia-doped ceria is of potential interest as an ultraviolet (UV) radiation blocking material in personal care products because of the excellent UV light absorption property and low catalytic ability for the oxidation of organic materials superior to undoped ceria. In order to reduce the oxidation catalytic activity further, calcia-doped ceria was coated with amorphous silica by means of seeded polymerization technique. Generally, nanoparticles of inorganic materials do not provide a good coverage for human skin because of the agglomeration of the particles. The platy particles are required to enhance the covering ability of inorganic materials. This can be accomplished by synthesis of calcia-doped ceria/mica nanocomposite with subsequent silica coating to control catalytic activity of calcia-doped ceria. Calcia-doped ceria/mica nanocomposite was prepared by soft solution chemical method followed by silica coating via seeded polymerization technique. Silica coated calcia-doped ceria/mica nanocomposite was characterized by X-ray diffraction, SEM, TEM, XPS and FT-IR.

Particle size control of plate-like lepidocrocite-related potassium lithium titanate through optimization of synthesis parameters

Platy particles are required to enhance the covering ability of inorganic UV-shielding materials. A plate-like lepidocrocite-type potassium lithium titanate, K 0.8Li 0.266Ti 1.734O 4 represents a proper candidate as a support for inorganic UV-shielding materials. Optimization of preparation conditions of lepidocrocite-type potassium lithium titanate, K 0.8Li 0.266Ti 1.734O 4, is required to obtain medium-size plate-like titanate of 5–50 μm in diameter that provide good coverage of inorganic UV-shielding materials for the human skin. A plate-like lepidocrocite-type potassium lithium titanate, K 0.8Li 0.266Ti 1.734O 4, was synthesized by calcing K 2CO 3, Li 2CO 3 and TiO 2 mixtures in the presence of KMoO 4 flux. The influences of firing temperature, time, weight ratio of flux to raw materials and Li content were investigated. The plate-like potassium lithium titanate, K 0.8Li 0.266Ti 1.734O 4, with ca. 20 μm in diameter, was obtained with flux/raw materials weight ratio of 50:50 at 1000 °C for 2 h.

Detrital ooids of Holocene age in glaciomarine Champlain Sea sediments, Gatineau, Quebec, Canada

Detrital ooids, from 0.1 to 0.5 mm diameter, almost completely dominate two 0.3 m thick layers between one and two metres depth at a site in clay-size-rich, isostatically uplifted, glaciomarine, Champlain Sea sediments north of Gatineau, Quebec. The ooids, composed of layers of tangentially oriented, platy particles, are physical aggregations of glacially ground, rock flour with the identical mineral suite that constitutes the regional Champlain Sea sediments. The ooids are not cemented and there is no evidence of diagenetic formation of minerals. A hydrodynamic "hail-stone" model, which requires a somewhat turbulent sedimentary environment within the water column, probably created by wind–wave action that kept ooid nuclei in suspension while the flocculating effect of brackish to marine conditions induced particle accretion onto their surface, is proposed for their formation.

A Peculiar Morphology of Gibbsite and Nordstrandite Co-Crystallized in the Presence of Tartrate in a Strongly Alkaline Environment

AbstractThe nature and morphology of Al(OH)3 polymorphs obtained by precipitating Al and tartrate at pH 12.0 and at a tartrate/Al molar ratio (R) of 0.1 were studied by X-ray diffraction, transmission electron microscopy and electron diffraction. Co-crystallization of unusually long (up to 18 µm) ‘stick-shaped’ gibbsite with platy particles of both nordstrandite, mainly, and bayerite was observed. Face-to-face associations of plates nucleated perpendicularly on the gibbsite surfaces parallel to the c axis produced peculiar elongated ‘brush’ -shaped particles. In a strongly alkaline environment the inhibiting effect of tartrate on Al(OH)3 polymorph formation is reduced and production of co-crystallized phases with structural crystallographic similarities can be observed.