Effects Of Particle Dispersion Research Articles

Extraordinary Electromagnetic Waves in Weakly Relativistic Degenerate Spin-1/2 Magnetized Quantum Plasmas**Supported by the National Natural Science Foundation of China under Grant Nos 11705043, 11547137 and 11605036, the Innovation Training Project for College Students in Anhui Province under Grant No 2017CXCYS222, the Doctoral Production & Learning & Research Special Fund of Hefei University of Technology under Grant No XC2015JZBZ25, and the

By using the relativistic quantum magnetohydrodynamic model, the extraordinary electromagnetic waves in magnetized quantum plasmas are investigated with the effects of particle dispersion associated with the quantum Bohm potential effects, the electron spin-1/2 effects, and the relativistic degenerate pressure effects. The electrons are treated as a quantum and magnetized species, while the ions are classical ones. The new general dispersion relations are derived and analyzed in some interesting special cases. Quantum effects are shown to affect the dispersion relations of the extraordinary electromagnetic waves. It is also shown that the relativistic degenerate pressure effects significantly modify the dispersive properties of the extraordinary electromagnetic waves. The present investigation should be useful for understanding the collective interactions in dense astrophysical bodies, such as the atmosphere of neutron stars and the interior of massive white dwarfs.

Effects of particle dispersion and slurry preparation protocol on electrochemical performance of capacitive flowable electrodes

In this study, the effects of dispersion time and mixing methodology on electrochemical performance of flowable carbon electrodes have been investigated. Specifically, 20 different cases have been tested by systematically changing the mixing time (1.5, 3, 4.5, 8, 15 min), the mixing methodology (stir-bar vs. high-speed shear mixing), and the electrode composition (activated carbon (AC) only and AC with multi-walled carbon nanotube slurries). Each case was subjected to direct current conductivity and cyclic voltammetry measurements to identify the contribution of studied parameters on the dispersion and electrochemical performance. Results indicate that up to 60% difference in conductivity can be observed by changing mixing time and methodology for the same electrode composition. Additionally, capacity differences up to 90% within the same slurry composition have been noticed by slightly changing the electrode preparation protocol. Such major discrepancy in electrochemical performance with minimal changes in the electrode preparation highlights the significance of the degree of particle dispersion in these systems and the necessity for establishing an optimal slurry preparation protocol to achieve the best performance for a selected composition and application. This study provides insights into potential effects of electrode preparation methods and degree of dispersion of active materials on the electrochemical performance of capacitive flowable electrodes.

Effects of particle dispersion on the properties of suspension-sprayed coatings

Effects of particle dispersion on the properties of suspension-sprayed coatings

Elliptically polarized electromagnetic waves in a magnetized quantum electron-positron plasma with effects of exchange-correlation

The dispersion properties of elliptically polarized electromagnetic waves in a magnetized electron-positron-pair (EP-pair) plasma are studied with the effects of particle dispersion associated with the Bohm potential, the Fermi degenerate pressure, and the exchange-correlation force. Two possible modes of the extraordinary or X wave, modified by these quantum effects, are identified and their propagation characteristics are investigated numerically. It is shown that the upper-hybrid frequency and the cutoff and resonance frequencies are no longer constants but are dispersive due to these quantum effects. It is found that the particle dispersion and the exchange-correlation force can have different dominating roles on each other depending on whether the X waves are of short or long wavelengths (in comparison with the Fermi Debye length). The present investigation should be useful for understanding the collective behaviors of EP plasma oscillations and the propagation of extraordinary waves in magnetized dense EP-pair plasmas.

Thermomechanical Properties of Bimodal Brush Modified Nanoparticle Composites

The enthalpic incompatibility of organic polymer matrices and high surface energy inorganic nanoparticles often leads to phase separation in polymer nanocomposites (PNC) precluding the realization of anticipated property enhancements. The grafting of polymer chains to nanoparticles holds promise as a means for controlling dispersion. A single population of polymer chains with tunable graft density (σ) and molecular weight (N) is observed to have antithetical enthalpic and entropic effects on interface compatibility. We report the use of bimodal polymer brushes with fundamentally decoupled enthalpic and entropic parameters. Bimodal polystyrene brushes were grafted from 15 nm colloidal silica nanoparticles by a previously reported consecutive RAFT (reversible addition–fragmentation chain transfer) polymerization technique. The combination of a high graft density short brush and a low graft density long brush was found to cause improved nanoparticle dispersion in a polystyrene matrix when compared to single populations of long and short brushes of corresponding graft densities and molecular weights. A new quantitative model was developed to understand these results and was found capable of predicting dispersions in grafted nanoparticle composites in the allophobic dewetting regime. The bimodal-brush-graft particles were also found to be remarkably well dispersed in an entropically unfavorable higher molecular weight matrix. This facilitated a study of the role of matrix–brush entanglement on the thermomechanical properties of PNCs, isolated from the effects of particle dispersion. The best enhancements in glassy properties resulted from improved matrix–brush entanglement, attained by lowering the long chain graft density and increasing the long chain to matrix molecular weight ratio.

Tropical biomass burning smoke plume size, shape, reflectance, and age based on 2001–2009 MISR imagery of Borneo

Abstract. Land clearing for crops, plantations and grazing results in anthropogenic burning of tropical forests and peatlands in Indonesia, where images of fire-generated aerosol plumes have been captured by the Multi-angle Imaging SpectroRadiometer (MISR) since 2001. Here we analyze the size, shape, optical properties, and age of distinct fire-generated plumes in Borneo from 2001–2009. The local MISR overpass at 10:30 a.m. misses the afternoon peak of Borneo fire emissions, and may preferentially sample longer plumes from persistent fires burning overnight. Typically the smoke flows with the prevailing southeasterly surface winds at 3–4 m s−1, and forms ovoid plumes whose mean length, height, and cross-plume width are 41 km, 708 m, and 27% of the plume length, respectively. 50% of these plumes have length between 24 and 50 km, height between 523 and 993 m and width between 18% and 30% of plume length. Length and cross-plume width are lognormally distributed, while height follows a normal distribution. Borneo smoke plume heights are similar to previously reported plume heights, yet Borneo plumes are on average nearly three times longer than previously studied plumes. This could be due to sampling or to more persistent fires and greater fuel loads in peatlands than in other tropical forests. Plume area (median 169 km2, with 25th and 75th percentiles at 99 km2 and 304 km2, respectively) varies exponentially with length, though for most plumes a linear relation provides a good approximation. The MISR-estimated plume optical properties involve greater uncertainties than the geometric properties, and show patterns consistent with smoke aging. Optical depth increases by 15–25% in the down-plume direction, consistent with hygroscopic growth and nucleation overwhelming the effects of particle dispersion. Both particle single-scattering albedo and top-of-atmosphere reflectance peak about halfway down-plume, at values about 3% and 10% greater than at the origin, respectively. The initially oblong plumes become brighter and more circular with time, increasingly resembling smoke clouds. Wind speed does not explain a significant fraction of the variation in plume geometry. We provide a parameterization of plume shape that can help atmospheric models estimate the effects of plumes on weather, climate, and air quality. Plume age, the age of smoke furthest down-plume, is lognormally distributed with a median of 2.8 h (25th and 75th percentiles at 1.3 h and 4.0 h), different from the median ages reported in other studies. Intercomparison of our results with previous studies shows that the shape, height, optical depth, and lifetime characteristics reported for tropical biomass burning plumes on three continents are dissimilar and distinct from the same characteristics of non-tropical wildfire plumes.

Multiple strengthening mechanisms of cold-sprayed cBNp/NiCrAl composite coating

The cBNp/NiCrAl composite coating with 40 vol.% cBN was deposited by cold spray using a mechanically alloyed composite powder. The microstructure of the as-sprayed coating was characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that cBN particles in the size ranges of both nanometers and submicrometers were uniformly dispersed in NiCrAl alloy matrix. The XRD and TEM results revealed that the phase and nanocrystalline structures of the NiCrAl matrix were completely retained from the powder to coating during cold spraying. The hardness test results show that the dense composite coating exhibited an increased Vickers hardness of 1175 Hv compared with 280 Hv of the annealed NiCrAl matrix phase. The high hardness of the composite coating is attributed to the strengthening effects of particle dispersion, work hardening and crystal refinement. The contributions of the individual strengthening mechanisms, including particles dispersion, work hardening and crystal refinement, to hardness were theoretically estimated. The estimated hardness of the composite coating agreed well with the tested value. The work hardening strengthening is the most significant mechanism followed by crystal refinement effect and dispersion strengthening.

Effects of particle dispersion on the measurement of semi-conductor photocatalytic activity

Milling changes the particle size distribution of TiO 2 suspensions and this is reflected in the changed optical characteristics. Typically, the visible transmission is increased, as large TiO 2 agglomerates are broken down, and the UV absorption is increased. It has been shown that the rates of dye decolouration, alcohol oxidation, and carboxylic acid degradation are all changed by milling. For all the TiO 2's tested (anatase and rutile, surface areas from ∼8 to 140 m 2 g −1) photocatalytic oxidation of propan-2-ol is reduced by milling. It is suggested that this is a consequence of the I 0.5 dependence of reaction rate on UV intensity. This argument was supported by demonstrating that the rate of salicylic acid degradation (which also exhibits I 0.5 dependence), is reduced by milling. By contrast there was no significant decrease in the rate of degradation of dichloroacetate (which exhibits I 1 dependence). Fourfold changes in the rate of salicylic acid degradation were induced when the same catalyst was milled for increasing times. This implies that two catalysts which differ in activity by a factor of four may do so because of differences in their dispersion rather than because they have different intrinsic activities. It is also shown the relative performance of two catalysts which differ in their surface properties changes when they are milled. However, the relative activities of a series of iron doped catalysts with no deliberate differences in surface properties were not changed by milling.

Effects of particle dispersion on photocatalysis probed by the effect of platinum on dichloroacetic acid oxidation by P25 and nanoparticulate rutile

Oxidation of dichloracetic acid (DCA) by two titanium dioxide catalysts (P25 and a nanoparticulate rutile (NR)) was measured at pH 3 and the results compared with parallel measurements on the same TiO2s modified by deposition of platinum.Although the platinum loading corresponded to less than one platinum crystallite for each TiO2 crystal, platinization significantly increased photocatalytic activity – 30-fold in the case of NR, high area rutile. This has been attributed, by ourselves [7] and others, e.g. [9], to the increased efficiency of hole-generation as a consequence of electron trapping by the platinum.Each catalyst was then milled, and UV–vis transmission spectra were used to show that milling improved the catalyst dispersion. Milling unplatinized TiO2 caused either insignificant decreases (P25) or increased activity (NR). This contrasts with the previously reported [16] significant decrease in activity for propan-2-ol oxidation. The difference is attributed to a different dependence on UV intensity of DCA degradation and propan-2-ol oxidation. DCA oxidation rate increased linearly with UV intensity, I, whereas propan-2-ol oxidation varies as I0.5.However, milling did decrease significantly the rate of DCA oxidation by both of the platinized catalysts, especially by the platinized rutile. It is suggested that most of the UV is absorbed by TiO2 crystals that have no platinum, but that in poorly dispersed TiO2, UV-generated electrons may be transported along a chain of TiO2 crystals to a platinized TiO2 at which they are trapped. This is analogous to the antenna model postulated by Bahnemann and co-workers [15]. It is proposed that milling breaks down the antennae. Consequently electron transport is disrupted and the effectiveness of electron trapping by platinum is reduced and the measured photoactivity decreases.

Effects of Particle-Dispersion on the Strength of an Alumina Fiber-Reinforced Aluminum Alloy Matrix Composite

Aluminum alloy matrix hybrid composites, in which alumina particles were dispersed among continuous alumina fibers, were fabricated by squeeze casting, and the influence of temperature and the effects of the particle-dispersion on the strength of the composites were then investigated. The particle-dispersion among the fibers minimized preform contraction and fiber-to-fiber contact due to the melt infiltration during the squeeze casting. The tensile strength, 0.2% proof stress and elastic modulus of the composites in the longitudinal direction increased with increasing the fiber volume fraction, retaining nearly the same values up to 623 K. These values of the hybrid composite were larger than those of the particle-free composite at every temperature. This is because the fibers were distributed uniformly owing to the particles that prevented the fiber-to-fiber contact, leading to the reduction of stress concentration at the points of direct fiber contact, and stress transmission between the fiber and the matrix becomes easy. At every temperature, the transverse tensile strength and proof stress of the particle-free composite was lower than that of the unreinforced alloy, because the fracture was initiated at the fiber-to-fiber contact point and the cracks propagated mainly along the fiber-matrix interface. In contrast, the strength of the hybrid composite was close to that of the unreinforced alloy even at high-temperature, because the cracks propagated mainly throughout the matrix owing to the uniform distribution of the fibers and the strong fiber-matrix bond.

A General Deterministic Treatment of Derivatives in Particle Methods

A unified approach to approximating spatial derivatives in particle methods using integral operators is presented. The approach is an extension of particle strength exchange, originally developed for treating the Laplacian in advection–diffusion problems. Kernels of high order of accuracy are constructed that can be used to approximate derivatives of any degree. A new treatment for computing derivatives near the edge of particle coverage is introduced, using “one-sided” integrals that only look for information where it is available. The use of these integral approximations in wave propagation applications is considered and their error is analyzed in this context using Fourier methods. Finally, simple tests are performed to demonstrate the characteristics of the treatment, including an assessment of the effects of particle dispersion, and their results are discussed.

Crystallization of amorphous metal matrix composites

Crystallization characteristics of WC-amorphous-Pd 77.5Cu 6Si 16.5 metal matrix composites are studied by differential scanning calorimetry and transmission electron microscopy. The activation energy E c of crystallization of non-preannealed amorphous Pd 77.5Cu 6Si 16.5 is 3.4 eV. This is greater than those of preannealed amorphous alloys, but less than those of WC-amorphous-metal matrix composites which have been preannealed at 330°C for various annealing times. All non-preannealed amorphous alloys yield an Avrami exponent n = 1.7, however, alternative values of n were obtained for WC-containing composites preannealed at 330°C for various annealing periods. In these composites n increases with increasing volume fraction of WC, approaching n = 3.6. It is found that the crystallization progress faster in WC-dispersed composite than in non-dispersed amorphous Pd 77.5Cu 6Si 16.5 alloy. This information strongly suggests that the effects of particle dispersion and increasing short-range ordering in an amorphous structure lead to different nucleation and growth mechanisms.

Prediction of the near-burner flow and combustion in swirling pulverized-coal flames

An existing theoretical model for flow and combustion in swirling pulverized-coal flames is extended to include a stochastic simulation of particle dispersion and a more refined phenomenological model of coal devolatilization. The model is applied to predict the flow and combustion in the near-burner (ignition) zone of medium- and high-volatile bituminous-coal flames. The quality of the predictions is assessed by comparison with detailed measurements of flow pattern, gas temperature and gas composition. In general, the agreement between predictions and measurements is quite good. The predictions are more sensitive to the volatile yield than the kinetics of devolatilization, and relatively insensitive to the kinetics of char combustion. The effects of particle dispersion are significant for the medium-volatile-coal flame.

Effects of particle dispersion and circulation systems on classification performance

To classify fine powders with particles smaller than 1 μm in diameter, air classifier design must take three factors into consideration: dispersion of feed powders, air flow uniformity in the classification zone, and recovery of fine particles adhering to the coarse fraction. The effects on the classification performance of a centrifugal air classifier using a dispersion nozzle for particle dispersion and a circulation mechanism using channel air jets for the recovery of fine particles are discussed. By using a dispersion nozzle, the classification sharpness index was improved below 0.8 (D p/D p50) and the fine fraction yield was improved by 64% without changing size distribution. The circulation mechanism using channel air improved classification performance by 58% of the classification sharpness index and 65% of the fine fraction yield, although the particle size distribution of the fine fraction became 0.1 μm coarser than that without channel air.