Effect of the particle size and particle agglomeration on composite membrane performance

One of the most used methods for studying the rigidification of polymer matrices in composite membranes is differential scanning calorimetry. Glass‐transition temperatures give information about filler–polymer interaction and the rigidity of the polymer matrix. In this study, optical microscopy, mechanical property testing, and X‐ray diffraction, instead of differential scanning calorimetry, were used to study both poly(ether imide) (PEI) matrix rigidification and activated carbon–PEI interfacial adhesion. Then, the permselective properties of the mixed matrix membranes were interpreted. The change in rigidity in these composite membranes was in agreement with the decrease in the flexibility of the composite materials as the filler content increased. This fact was confirmed by the tension and elongation data and X‐ray diffraction (DRX) measurements. However, the Young's modulus value decreased as the carbon content increased. There was an increase in all of the gas permeability coefficients measured in the composites compared with that of PEI. As the particle size grew, a low particle surface area and a poor interfacial adhesion were observed. The carbon agglomerates acted as sites of stress concentration within the polymeric matrix. This decreased the intercatenary distances and limited the movement of polymer chains, which resulted in a more rigid matrix. The higher selectivity of the H₂/CH₄, H₂/CO₂ and O₂/N₂ systems observed in the composite membranes revealed that there were both a preferential sorption of certain gases in the carbon surface or carbon–polymer interface and a molecular size exclusion, which were responsible for that increment, despite the poor interfacial adhesion. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of particle size on pigments colour

The historical pigments, contrary to modern ones, are not constituted by particles having all the same size and this influences the colour of the paint layers. The hiding power and colouring power of a pigment depends, in fact, on its particle size. The aim of this study was to evaluate the influence of particle size on optical characterization of paintings in terms of reflection of light and related colour specification. Starting from the qualitative observation, we have attempted to quantify the pigments colour variations induced by grinding and then attributable to granularity. Powdered pigments of principal colours have been selected in specific particle size range by mechanical sieving. The measurements were performed both on pigment pellets and on paintings realized with binder casein. All samples were characterized by an optical and colorimetric point of view through spectrophotometric analysis and for the surface morphological observation through scanning electron microscopy. © 2016 Wiley Periodicals, Inc. Col Res Appl, 42, 236–243, 2017     

Identification of the initial particle size distribution for coal combustion simulations

Pulverized coal generally features wide particle-size distributions (PSD). How to set an initial PSD in coal combustion simulation remains an open question. To answer this, the Gaussian-quadrature theory was applied to provide a discrete reconstruction of the PSD described by Rosin-Rammler and Upper-Limit functions. From the perspective of the moments of PSD, a theoretical analysis was conducted for mass, momentum, and energy exchange terms between gas and particle phases in pulverized coal jet flame. The analysis presented that the first, the second and the third moments of PSD were the most important to capture the flame ignition behavior. The large eddy simulations showed that the proposed method with two or more particle sizes could provide good predictions of flame ignition distances. And Sauter mean diameter (D₃₂) could represent the complete PSD when predicting the ignition behavior of pulverized coal jet flame.     

Vibration sensitivity of solid explosives

The vibration sensitivity of solid explosives has been studied and is found as a function of the explosive parameters and the type of roller devices used to model various deformation conditions. A method is proposed for determining the vibration sensitivity from the probability of explosions as a function of the vibration parameters, experimental data on the sensitivity of some explosives and on the stresses in specimens are given, and a mechanism of initiating an explosion under cyclical loads is considered.Samara State Technical University, Samara 443010. Translated from Fizika Goreniya i Vzyrva, No. 1, 97–103, January–February, 1995.     

Effect of microbubbles and particle size on the particle collection in the column flotation

Particle-bubble collection characteristics from microbubble behavior in column flotation have been studied theoretically and experimentally. A flotation model taking into account particle collection has been developed by particle-bubble collision followed by the particle sliding over the bubble during which attachment may occur. Bubble size and bubble swarm velocity were measured as a function of frother dosage and superficial gas velocity to estimate the collision and collection efficiency. Separation tests were carried out to compare with theoretical particle recovery. Fly ash particles in the size range of <38, 38-75, 75-125, >125 mm were used as separation test particles. Theoretical collision and collection efficiencies were estimated by experimental data on the bubble behavior such as bubble size, gas holdup and bubble swarm velocity. Collection efficiency improved with an increase of the bubble size and particle size but decreased in the particle size up to 52 mm. Also, flotation rate constants were estimated to predict the optimum separation condition. From the theoretical results on the flotation rate constant, optimum separation condition was estimated as bubble size of 0.3-0.4 mm and superficial gas velocity of 1.5-2.0 cm/s. A decrease of bubble size improved the collection efficiency but did not improve particle recovery.     

电解质对丁二烯聚合胶乳粒径的影响

通过改变电解质的用量,研究了丁二烯聚合过程中胶乳粒径的变化规律。结果表明,无电解质条件下胶乳粒子过小,产品流动性差;0．45份电解质体系聚合转化率高,反应时间短,产品流动性好;1．25份电解质体系胶乳粒径变化分2个阶段,反应时间长,生产效率低。     

晶体粒径对碰撞成核的影响

从单个晶体运动中与结晶器内其他晶体及固体壁面碰撞过程的能量损失角度,描述了碰撞成核过程,建立了晶体粒径与成核速率的理论关系模型。结果表明,晶体的粒度对碰撞成核速率有很大的影响。并利用氯化钠晶体进行了碰撞成核实验,使用理论模型对实验结果进行拟合,进而验证了理论模型所预期的规律。指出在分析二次成核时,应充分考虑晶体粒度对成核影响的重要作用。该理论模型为实现工业结晶过程的仿真模拟提供了依据。     

Nonclassical detonation regimes of pressed and liquid explosives (Review)

Combustion, Explosion, and Shock Waves - This paper presents a review of studies of the characteristics of condensed explosives in the reaction zone of which the distribution of parameters does not...     

Synthesis and behavior of the polymer covering on a solid surface. II. Effect of the adsorbent particle size on adsorption

Adsorption of poly(5-tert-butylperoxy-5-methyl-1-hexen-3-yne-co-maleic anhydride) and poly(styrene-co-maleic anhydride) on the various ultrafine powders (TiO₂, ZnO, Al₂O₃, CaCO₃, aerosil, and quartz powder) was studied. Plateau adsorption amount per unit surface of adsorbent (a^s) decreased with the decreasing of particle size of the adsorbent. The a^s-molecular mass relationship was different for copolymers of low and high molecular mass. The fractal dimension D = 2.5 of adsorbent surface was determined if the particle radius was less than 2.5 μm. Fractal behavior was explained by aggregation of particles. Due to the aggregation the interparticle space (pore) in the area of contact of neighboring particles is inaccessible for the polymer and accessible for the solvent. The experimental isotherm with maximum was employed for estimation of the volume of inaccessible pores 2.4 cm³/g for suspension of aerosil. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 299–305, 1998     

Effect of initial particle size on grain microstructure of textured ferroelectric ceramics: A phase-field method and brush technique

A phase-field model was employed to simulate the grain microstructure evolution of the textured ceramics. Textured KSr₂Nb₅O₁₅ (KSN) ceramics were chosen as the research object and prepared by using acicular KSN particles as raw materials. A method combining the brush technique with the rolling process was proposed for the directional arrangement of the acicular particles. The effects of the initial particle length distribution and diameter on the grain growth behavior and electrical properties were investigated. It was found the influence of the initial particle length distribution on the grain growth rate mainly depended on its diameter. The use of coarse particles was beneficial to obtain a microstructure with a strongly anisotropic morphology and homogeneous grain size. The obtained KSN ceramics exhibited a high piezoelectric constant d₃₃ of 68 pC/N and Curie temperature of 120 ℃, which was closely related to the grain microstructure.     

Effect of quartz particle size on the strength of triaxial porcelain

The effect of the quartz component on strength, σ_f, and fracture toughness, K_Ic, of a triaxial porcelain was studied by varying the size distribution of the quartz particles. Both σ_f and K_Ic were found to increase and then to pass over a maximum as the quartz distribution became finer. Improvements in σ_f and K_Ic of more than a factor of 2 were achieved. The flaw size that controlled failure was shown to equal the maximum quartz particle size in the material containing the coarsest quartz component and to be a constant independent of the quartz size in the other materials. The toughness increase was attributed to microcrack toughening of the glass matrix, the microcracks being formed by thermal mismatch stresses between the quartz particles and the glass matrix on cooling from the sintering temperature.     

Effect of rigid particle size on the toughness of filled polypropylene

The role of rigid particle size in the deformation and fracture behavior of filled semicrystalline polymer was investigated with systems based on polypropylene (PP) and model rigid fillers [glass beads, Al(OH)₃]. The regularities of the influence of particle content and size on the microdeformation mechanisms and fracture toughness of the composites at low and high loading rates were found. The existence of the optimal particle size for fixed filler content promoting both maximum ultimate elongation of the composite at the tensile and maximum toughness at impact test was shown. The decrease of the toughening effect with both decreasing and increasing particle size regarding the optimal one was explained by dual role of particle size, correspondingly as either “adhesive” or “geometric” factors of fracture. The adhesive factor is due by the increase of debonding stress with the particle size decrease and the voiding difficulty resulting in the restriction of plastic flow. The geometric factor consists in the dramatic decrease of the composite strength at break if the void size exceeds the critical size of defect (for a given matrix) at which the crack initiation occurs. The analysis of the filled polymer toughness dependencies upon the particle size revealed that a capacity of rigid particles for the energy dissipation at the high loading rate depends on two factors: (i) ability of the dispersed particles to detach from matrix and to initiate the matrix local shear yielding at the vicinity of the voids and (ii) the size of the voids forming. Based on the findings it was concluded that the optimal minimal rigid particle size for the polymer toughening should answer the two main requirements: (i) to be smaller than the size of defect dangerous for polymer fracture and (ii) to have low debonding stress (essentially lower compared to the polymer matrix yield stress). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1917–1926, 2004     

Dynamics of the detonation-wave front in solid explosives

The important role of the shape of the front during detonation wave propagation in gas mixtures was substantiated by K. I. Shchelkin during construction of the theory of spinning detonation. Subsequently, a unique relationship between the curvature of the front and detonation wave parameters has been repeatedly confirmed in experiments, including for condensed high explosives (HEs). The existence of this relationship formed the basis of the theory of the dynamics of the detonation front which had been developed by the end of the 20th century. This paper presents the results of a study of detonation front propagation in cylindrical samples of a low-sensitivity HE of different diameters with one-point and plane-wave initiation. A unique relationship between the detonation velocity and the curvature of the detonation wave front has been found. Ordinary differential equations describing two-dimensional steady-state detonation front profiles for HE charges in the form of a plate, a cylinder, and a ring were derived assuming that the detonation velocity depends on the curvature of the front. It was taken into account that the boundary angle between the normal to the front and the HE edge is unique for each combination of HE and liner material. It was found that the same detonation front profile corresponds to several combinations of liner material and the determining size of the charge (plate thickness, radius of the cylinder or the inner radius of the ring). A comparison of experimental front profiles near the edges of HE charges for these combinations provides data on the dependence of detonation velocity on the curvature of the front at low velocities corresponding to shock-induced detonation regimes. Analysis of previously obtained data for detonating ring charges of low-sensitivity HEs shows that as the detonation velocity decreases, the total front curvature tends to a limit of about 0.05 mm⁻¹, i.e., of the order of the inverse critical diameter. The limit of the front curvature allows predicting the critical detonation diameter.     

Effect of zirconia particle size on the properties of alumina-spinel castables

The industrial application of alumina-spinel refractory castables has crucial requirements on the service performance. Thus, the effects of different sized desilicated zirconia particles on the castables microstructure, thermal-mechanical properties and high temperature elastic modulus have been investigated. The zirconia particle sizes were varied from 1000 µm to 2.5 µm (d₅₀). It was observed that the finer (below 88 µm) zirconia particles were beneficial to improve the cold modulus of rupture (CMOR) and the hot modulus of rupture (HMOR), but could not effectively enhance the thermal shock resistance. Fine zirconia particles can homogeneously disperse in the matrix and significantly promote the sintering process. Accompanied with the phase transformation of zirconia, both the high density of matrix cracks and the strong ceramic bonding (between the coarse grains and the matrix) were found in the refractory castables, which was responsible for an increase of CMOR. However, the binding characteristic could also give rise to the high stored elastic energy that was adverse to the thermal shock resistance, and the excessive amount of preexisting matrix cracks could induce more microdamage during the thermal shock. Additionally, it was proposed that the second-phase dispersion reinforcement and the highly ceramics bonding resulted in the superior HMOR when introducing fine ZrO₂ particles.     

Effect of particle size on the rheology of Athabasca clay suspensions

The success of the separation process conventionally used in Alberta for oil sands extraction is highly influenced by the rheology of the oil sands slurry. In the gravity separation vessel, high slurry viscosities can hinder the rise of aerated bitumen and reduce the efficiency of the recovery process. In this study, the effect of particle size on the viscosity of oil sands slurries is investigated. Solids from mature fine tails (MFT) obtained from tailings pond were fractionated into three fractions of different particle size distributions and their rheological properties were studied. The solids in each fraction were characterized by XRD analysis which showed the presence of different types of clays in each fraction. For the rheological measurements, dispersions of the three fractions were prepared in the supernatant water decanted from centrifuged MFT to maintain the solution chemistry of the solids. Suspensions of each fraction showed a non‐Newtonian shear thinning behaviour as well as yield stress that is characteristic of structure formation within the suspensions. For all solids fractions, increasing solids concentration led to higher viscosities and higher yield stress values. Viscoelastic properties of the suspensions showed stronger solid‐like behaviour at higher particle concentrations. Among the three fractions numbered from 1 to 3, solids in fraction 3 were coated with organic matters, exhibiting the highest suspension viscosities. Also for fraction 3, higher gelling potency was observed at much lower weight fractions of solids as compared to the other fractions.