Large Particle Aggregates Research Articles

Experimental Studies of the Effects of Anode Composition and Process Parameters on Anode Slime Adhesion and Cathode Copper Purity by Performing Copper Electrorefining in a Pilot-Scale Cell

Copper electrorefining tests were conducted in a pilot-scale cell under commercial tankhouse environment to study the effects of anode compositions, current density, cathode blank width, and flow rate on anode slime behavior and cathode copper purity. Three different types of anodes (high, mid, and low impurity levels) were used in the tests and were analyzed under SEM/EDS. The harvested copper cathodes were weighed and analyzed for impurities concentrations using DC Arc. The adhered slimes and released slimes were collected, weighed, and analyzed for compositions using ICP. It was shown that the lead-to-arsenic ratio in the anodes affects the sintering and coalescence of slime particles. High current density condition can improve anode slime adhesion and cathode purity by intensifying slime particles’ coalescence and dissolving part of the particles. Wide cathode blanks can raise the anodic current densities significantly and result in massive release of large slime particle aggregates, which are not likely to contaminate the cathode copper. Low flow rate can cause anode passivation and increase local temperatures in front of the anode, which leads to very intense sintering and coalescence of slime particles. The results and analyses of the tests present potential solutions for industrial copper electrorefining process.

In vitro synthesis of cellulose microfibrils by a membrane protein from protoplasts of the non-vascular plant Physcomitrella patens

Plant cellulose synthases (CesAs) form a family of membrane proteins that are associated with hexagonal structures in the plasma membrane called CesA complexes (CSCs). It has been difficult to purify plant CesA proteins for biochemical and structural studies. We describe CesA activity in a membrane protein preparation isolated from protoplasts of Physcomitrella patens overexpressing haemagglutinin (HA)-tagged PpCesA5. Incubating the membrane preparation with UDP-glucose predominantly produced cellulose. Negative-stain EM revealed microfibrils. Cellulase bound to and degraded these microfibrils. Vibrational sum frequency generation (SFG) spectroscopic analysis detected the presence of crystalline cellulose in the microfibrils. Putative CesA proteins were frequently observed attached to the microfibril ends. Combined cross-linking and gradient centrifugation showed bundles of cellulose microfibrils with larger particle aggregates, possibly CSCs. These results suggest that P. patens is a useful model system for biochemical and structural characterization of plant CSCs and their components.

Preparation of Aluminum Nanoparticles Using Bipolar Pulsed Electrical Discharge in Water

Al nanoparticles were synthesized in liquid phase plasma using Al chloride as the precursor. CTAB was used as the surfactant to obtain well dispersed particles. When the surfactant was not added, large aggregated particles were generated. With increasing CTAB dosage, the size of the Al particles decreased and the degree of dispersion of the particles increased. At the initial stage of plasma discharge, dendrite shaped particles were produced. As discharge time evolved, however, particle size decreased and the particle morphology also changed into spherical shape. The solution pH decreased with increasing plasma discharge time.

DEPENDENCE OF ENDOCYTOSIS CAUSED BY DEPLETION EFFECTS ON THE ASPECT RATIO OF COLLOIDAL PARTICLE

In colloidal suspensions containing large and small particles, a peculiar attractive force caused by entropy appears, this force can cause aggregation of large particles. With the concentration of small particles increasing, the large particles can be endocytosed by vesicle. A continuum model is developed to investigate the equilibrium mechanics between a biomembrane and an enveloped colloidal particle with different aspect ratios. The results show that the endocytosis of colloidal particle depends on the aspect ratio of colloidal particle. For a spherical colloidal particle (aspect ratio is zero), the entropy provides sufficient favorable energy to drive its engulfment; however, at a high aspect ratio, the entropy is not sufficient to overcome the resistance from the biomembrane and causes endocytosis.

Investigation of microstructure in hot-pressed Nb–23Ti–15Al alloy

Microstructure of hot-pressed Nb–23Ti–15Al alloy has been systematically investigated, with emphasis on the characterization of Ti(O, C) phase. The microstructure and composition of Nb–23Ti–15Al alloy were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA). The results indicate the presence of β, δ and Ti(O, C) phases in the alloy. The β phase exhibits as large irregular blocks, while the δ phase presents as small equiaxed particles linked together around β blocks. Ordering of β phase is shown by related selected area electronic diffraction (SAED) patterns and dark-field micrograph. The Ti(O, C), a solid-solution of TiO or TiC, is characterized for the first time in Nb–Ti–Al alloy. The Ti(O, C) has a face-centered cubic (FCC) structure and a moderate lattice parameter between that of TiO and TiC. Two different morphologies of Ti(O, C) are observed in the alloy: large cobblestone-like aggregated particles and small dispersive particles. The formation of Ti(O, C) phase can potentially increase high-temperature strength of Nb–Ti–Al alloy.

Effect of Li4Ti5O12 Particle Size on the Performance of Lithium Ion Battery Electrodes at High C-Rates and Low Temperatures

Two different Li4Ti5O12 materials were investigated: smaller primary particle size forming large secondary particle aggregates (LTO-SP, surface area 22 m2/g) and larger primary particle size with less secondary particle aggregates (LTO-LP, surface area 7 m2/g). Both samples were synthesized using the same high temperature solid state synthesis but different end processing, resulting in the same crystalline structure but different particle morphology. At 0.1C measured discharge capacities were close to the theoretical capacity of Li4Ti5O12 (175 mAh/g), and similar capacities were obtained at low C-rates and room temperature for both LTO-SP and LTO-LP. However, higher capacities were obtained with LTO-SP at high C-rates and −20 °C indicating beneficial effect of small particle size and large surface area. Shapes of the charge/discharge curves were different for LTO-SP and LTO-LP, and this is attributed to the large surface area of LTO-SP which affects the electrochemical performance because of different reaction potentials at surface sites versus bulk.

Bond–slip behaviour between self-compacting concrete and carbon-fibre-reinforced polymer sheets

The bond–slip behaviour between self-compacting concrete (SCC) and carbon-fibre-reinforced polymer (CFRP) sheets was investigated using double shear pull-off concrete specimens. Concrete blocks of size 150 × 150 × 100 mm were made from two aggregate types (limestone and basalt), two aggregate gradations (12 mm and 19 mm) and three water-to-cement (w/c) ratios (0·30, 0·35 and 0·40). CFRP sheets were attached to the concrete specimens using three different bond widths (50, 100 and 150 mm) and four bond lengths (60, 80, 100 and 120 mm). The ends of the CFRP sheets were adhered to the concrete specimens at two parallel sides using a special epoxy; the middle was left free for the wrapping of an aluminium cylinder of 100 mm diameter before pull-off testing. The obtained results and literature data were employed in the development of a statistical model to estimate the ultimate shear strength and slippage between CFRP sheets and SCC. The results showed that the effect of aggregate type is insignificant, although the basalt aggregate samples showed higher bond strength and corresponding slippage than the limestone samples. The trend behaviour of the bond–slip curves for double shear pull-off specimens showed no noticeable difference between SCC mixtures made from two different aggregate gradations, but the resulting values showed a slight increase in bond strength and slippage for the concrete specimens made from the larger aggregate particles. Water-to-cement ratio was found to have a significant effect on bond strength and corresponding slippage: bond strength and slippage increased with a reduction in w/c ratio. There was a noticeable decrease in bond stress and a noticeable increase in corresponding slippage for increasing bond length and bond width. The statistical model developed shows an excellent fit to the data used, as indicated by high coefficients of determination.

Estimation of the yield stress and distribution of large aggregates from slump flow test of self-compacting concrete mixes using smooth particle hydrodynamics simulation

A wide range of normal strength self-compacting concrete (SCC) mixes with a maximum aggregate size (g) of 20 mm ranging in compressive strength from 30 to 80 MPa were prepared in the laboratory, and the times t500 and tstop of each mix were recorded in the slump flow test. The entire cone flow test was then simulated from the moment the cone was lifted until the mix stopped to flow using the three-dimensional mesh-less smoothed particle hydrodynamics computational approach, treating the SCC mix as a non-Newtonian Bingham fluid. This numerical simulation had two aims. First, to investigate whether the yield stress τy of the mix could be accurately estimated from the measured t500 and tstop times knowing the plastic viscosity of the mix. The latter was estimated by a micromechanical procedure. Second, to compare the distribution of coarse aggregate particles larger than or equal to 8 mm in the cone spread after it stopped to flow as revealed by the numerical simulation with the distribution of the aggregate particles of the corresponding sizes in the cut sections of the cured test cone spread. The large coarse aggregate particles in the size ranges (8 ≤ g < 12, 12 ≤ g < 16, 16 ≤ g < 20 and g ≥ 20 mm) of the test SCC mixes were color coded with non-toxic non-water soluble paints so that the outlines of the aggregate particles could be clearly distinguished in the cut sections of the hardened cone spread and compared with the numerical simulations. It is shown that both aims of the investigations were successfully attained.

Phase-controlled synthesis of α-NiS nanoparticles confined in carbon nanorods for high performance supercapacitors.

A facile and phase-controlled synthesis of α-NiS nanoparticles (NPs) embedded in carbon nanorods (CRs) is reported by in-situ sulfurating the preformed Ni/CRs. The nanopore confinement by the carbon matrix is essential for the formation of α-NiS and preventing its transition to β-phase, which is in strong contrast to large aggregated β-NiS particles grown freely without the confinement of CRs. When used as electrochemical electrode, the hybrid electrochemical charge storage of the ultrasmall α-NiS nanoparticels dispersed in CRs is benefit for the high capacitor (1092, 946, 835, 740 F g−1 at current densities of 1, 2, 5, 10 A g−1, respectively.). While the high electrochemical stability (approximately 100% retention of specific capacitance after 2000 charge/discharge cycles) is attributed to the supercapacitor-battery electrode, which makes synergistic effect of capacitor (CRs) and battery (NiS NPs) components rather than a merely additive composite. This work not only suggests a general approach for phase-controlled synthesis of nickel sulfide but also opens the door to the rational design and fabrication of novel nickel-based/carbon hybrid supercapacitor-battery electrode materials.

Research on the Evaluation Method of Water Stability for Large Size Aggregate Particle Asphalt Mixture

Aiming at the deficiency of the current asphalt mixture test procedures using the traditional Marshall compaction molding test specimens method to evaluate water stability of asphalt mixture, large size aggregate particle asphalt mixture water stability test method, evaluation index and standard are proposed, namely the freeze-thaw cycles dynamic stability ratio index is adopted to evaluate asphalt mixture water stability, the freeze-thaw cycles dynamic stability ratio ≥ 85% is required and verified by experiment.

Particle Size Distribution of Sandstone Aggregate Influence on Recycled Aggregate Concrete Properties

Typically, the selection of large aggregate particle size is mainly determined by the thickness of structures and the thickness of protective layer. The greater the aggregate diameter is, the smaller the specific surface is, and the smaller coating materials demand will be without specific requirements. It will affect the concrete flowability directly if there are too much big size of aggregates or the particle size is too big for forming a certain stable packing skeleton structure. The strength of the large diameter recycled self-compacting rock-fill concrete is low so that the primary cause of its failure mechanism is bond failure and bond slip in aggregate. Shear failure in aggregate is not easy to happen due to the strength of the aggregate is too low. For this reason, we put forward the general selection requirements for large diameter aggregate.

Capillary-driven percolating networks in ternary blends of immiscible polymers and silica particles

We investigate the structure and rheology of a melt-blended ternary system composed of a continuous polymer phase, silica particles in the few-micron size range, and a small amount of a second immiscible polymer phase which preferentially wets the particles. The morphology of the ternary system is found to consist of a volume-spanning “pendular network” of particles bridged by menisci of the wetting polymer, as well as “capillary aggregates” which are large compact particle aggregates saturated by the wetting polymer. The ternary blends have strongly non-Newtonian melt rheology due to the pendular network. The relative extent of capillary aggregation depends on the melt-blending history, and the rheological properties can be used to track the changes in the blend structure. The pendular network is seen at a particle loading of only 10 vol.%, demonstrating that capillary bridging lowers the percolation threshold of a particle-filled polymer.

Study of the influence between magnesium ions and calcium ions on the morphology and size of coprecipitation in microemulsion

A series of inverse-microemulsion quasi-ternary system phase diagrams of CTAB + n -butanol + n -hexane + brine (MgCl2/CaCl2) is systematically drawn by adjusting the ratio of MgCl2 and CaCl2. On this basis, a microemulsion has been prepared with five different molar ratios of magnesium ions to calcium ions, and a calcium carbonate and magnesium carbonate coprecipitation product is obtained by reaction with an equimolar amount of sodium carbonate. The samples were characterised by scanning electron microscopy (SEM), a Fourier transform infrared (FTIR) spectrometer and X-ray diffraction (XRD). The SEM photographs indicated that when the content of Ca2+ was higher, some large fusiform aggregates of coprecipitation particles were formed in solution, but with the content of Mg2+ increased gradually, they eventually formed small and uniform sphere particles. The measurement results of XRD and FTIR indicated that the crystal structures of calcium carbonate in coprecipitation changed gradually from vaterite into aragonite and finally turned into being amorphous with the increasing of the proportion of magnesium ions.

Effect of Silicon Particle Size on Synthesis and Crystallinity of β-Silicon Carbide Particles

β-SiC particles were synthesized using silicon powder and carbon black at 1300°C. The effect of grinding the silicon powder raw material into smaller particles on the synthesis and crystallinity of the SiC particles was investigated. The size of the silicon particles decreased and the surface of the silicon particles increasingly oxidized into silicon oxide with increasing grinding time, thus decreasing the yield of SiC because of the higher SiO2 content in the ground silicon powder, since SiO2 transforms into SiC at a higher temperature than does silicon. Although the sizes of the silicon particles in the raw materials were different, all the synthesized SiC crystallites showed similar size. Transmission electron microscopy-energy dispersive X-ray spectroscopy analysis showed that although most of the synthesized SiC particles were smaller than 100 nm, the primary SiC particles had aggregated, and some unreacted silicon was observed inside the large aggregated SiC particles.

Photocatalytic Current Doubling-Induced Generation of Uniform Selenium and Cadmium Selenide Quantum Dots on Titanium(IV) Oxide

We have developed a current doubling-induced two step photodeposition (CD-2PD) technique for forming selenium quantum dots (QDs) and metal selenide QDs on TiO2, and proposed a reaction mechanism. Large aggregates of Se particles (∼100 nm) are generated on TiO2 from aqueous and 2-methyl-2-propanol solutions of H2SeO3 by UV-light irradiation. In contrast, highly dispersed selenium QDs are formed on TiO2 from the H2SeO3 ethanol and methanol solutions (Se/TiO2). The mean particle size increases with an increase in irradiation time (tp1) to reach 8.7 nm at tp1 = 2 h. The rates of Se photodeposition in the latter solvents are much faster than those in the latter solvents. These striking differences can be attributed to the current doubling effect of ethanol and methanol by photoelectrochemical measurements. Subsequent UV-light irradiation of Se(tp1 = 20 min)/TiO2 in ethanol and methanol solutions containing Cd2+ ions converts the Se QDs into homogeneous CdSe QDs (∼2 nm). The application of this in situ CD-2PD t...

3D modelling of the flow of self-compacting concrete with or without steel fibres. Part II: L-box test and the assessment of fibre reorientation during the flow

The three-dimensional Lagrangian particle-based smooth particle hydrodynamics method described in Part I of this two-part paper is used to simulate the flow of self-compacting concrete (SCC) with and without steel fibres in the L-box configuration. As in Part I, the simulation of the SCC mixes without fibres emphasises the distribution of large aggregate particles of different sizes throughout the flow, whereas the simulation of high strength SCC mixes which contain steel fibres is focused on the distribution of fibres and their orientation during the flow. The capabilities of this methodology are validated by comparing the simulation results with the L-box test carried out in the laboratory. A simple method is developed to assess the reorientation and distribution of short steel fibres in self-compacting concrete mixes during the flow. The reorientation of the fibres during the flow is used to estimate the fibre orientation factor (FOF) in a cross section perpendicular to the principal direction of flow. This estimation procedure involves the number of fibres cut by the section and their inclination to the cutting plane. This is useful to determine the FOF in practical image analysis on cut sections.

Bacteriochlorophyll Aggregates Self-Assembled on Functionalized Gold Nanorod Cores as Mimics of Photosynthetic Chlorosomal Antennae: A Single Molecule Study

We prepare artificial aggregates that mimic the structure and function of natural chlorosomal light harvesting complexes of green photosynthetic bacteria. Gold nanorods functionalized with hydroxyl groups and immobilized on a substrate serve as cores for the growth of bacteriochlorophyll (BChl) aggregates from a buffer solution. The BChl pigments form large self-assembled aggregate particles with sizes more than twice that of natural chlorosomes. The size is controllable by the aggregation time. The aggregates are characterized on a single-particle level by atomic force microscopy, electron microscopy, and single-molecule spectroscopy. The absorption and fluorescence spectral properties which reflect the molecular level arrangement of the BChl aggregates closely resemble those of the natural chlorosomes of the photosynthetic bacterium Chlorobaculum tepidum. On the other hand, the results of linear dichroism and circular dichroism are different from those of the chlorosomes and indicate a different mesoscopic structure for the artificial aggregates. These results emphasize the structural role played by the baseplate pigment-protein complex in natural chlorosomes.

Key structural arrangements at the C-terminus domain of CETP suggest a potential mechanism for lipid-transfer activity

The cholesteryl-ester transfer protein (CETP) promotes cholesteryl-ester and triglyceride transfer between lipoproteins. We evaluated the secondary structure stability of a series of small peptides derived from the C-terminus of CETP in a wide range of pH's and lipid mixtures, and studied their capability to carry out disorder-to-order secondary structure transitions dependent of lipids. We report that while a mixture of phosphatidylcholine/cholesteryl-esters forms large aggregated particles, the inclusion of a series of CETP carboxy-terminal peptides in a stable α-helix conformation, allows the formation of small homogeneous micelle-like structures. This phenomenon of lipid ordering was directly connected to secondary structural transitions at the C-terminus domain when lysophosphatidic acid and lysophosphatidylcholine lipids were employed. Circular dichroism, cosedimentation experiments, electron microscopy, as well as molecular dynamics simulations confirm this phenomenon. When purified CETP is studied, the same type of phenomenon occurs by promoting the reorganization of lipid from large to smaller particles. Our findings extend the emerging view for a novel mechanism of lipid transfer carried out by CETP, assigning its C-terminus domain the property to accomplish lipid ordering through secondary structure disorder-to-order transitions.

The effect of nanoparticles on the phase separation of waxy corn starch + locust bean gum or guar gum

Phase separation of mixtures of a gelatinized waxy corn starch (S) and locust bean gum (LBG) has been studied in detail at pH 7 and room temperature in the presence and absence of up to 1 wt.% silica nanoparticles (primary particle size 20 nm diameter). A range of silica particles of varying surface hydrophobicities was used, surface modified so as to have 100% (i.e., unmodified) to 65% of their surface SiOH groups remaining. In the absence of particles the S + LBG system separated via spinodal decomposition. In the presence of particles the phase separation was significantly curtailed. Confocal microscopy showed that the particles had a strong preference for the starch microdomains that formed, rather than the gum phase, whilst there was an increasing tendency for particle aggregation to occur within the starch microdomains and possibly at the W/W interface between the two phases as the particle hydrophobicity and particle concentration was increased. Measurements on starch + guar gum system showed that this behaved similarly to the S + LBG system. Measurements of the bulk rheology of the gum and starch phases in the presence and absence of the particles suggested that the inhibition of the phase separation was not due to changes in the viscoelasticity of the starch or gum microdomains themselves, but flocculation of the particles in the gum phase, possibly via the depletion mechanism. It is suggested that the formation of large aggregates of particles aids their accumulation at the W/W interface and subsequently slows down phase separation.

Influence of Beam Geometry and Aggregate Size on the Flexural Strength and Elastic Moduli of Cement-Stabilized Materials

Because of the depletion of good-quality materials, the use of cement stabilization for subbase and base layer materials often offers a feasible solution. As with all pavement materials, the design inputs must be determined, and this process requires comprehension of material engineering properties such as flexural strength and elastic moduli. Usually, four-point beam loading is preferred for flexural testing because the test simulates the stress–strain gradient as generated within a pavement layer. However, beam geometry, maximum aggregate particle size, and test configuration influence property measurements, which affect the mechanistic design input values. This study examines the influence of beam geometry and aggregate particle size used with respect to the span–depth ratio in the four-point beam test in monotonic loading. An increase in beam depth at a fixed loading span was shown to result in a decrease in flexural strength and elastic modulus but an increase in beam shear stresses. However, an increase of the span–depth ratio significantly reduced the resultant shear stresses in the beam. Additionally, the presence of large aggregate particles in a small beam generated localized zones of weakness, which significantly influenced the resultant flexural strength and elastic modulus.