Effect of the particle size ratio on the structural properties of granular mixtures with discrete particle size distribution

In this study, the discrete element method was used to examine the structural properties and geometric anisotropy of polydisperse granular packings with discrete uniform particle size distributions. Confined uniaxial compression was applied to granular mixtures with different particle size fractions. The particle size fraction (class) was defined as the fraction of the sample composed of particles with a certain size. The threshold value of number of particle size fractions (i.e., the value above which structural properties of assemblies remain constant) was determined. The effect of heterogeneity in particle size on the critical value of number of particle size fractions was investigated for packings with different ratios between diameters of the largest and smallest grains. The threshold number of particle size classes decreased from five to three as the diameter ratio between the largest and smallest grains increased. Regardless of the diameter ratio, the critical number of particle size fractions (above which the packing density and coordination number of the granular mixtures remained constant) was determined to be five. The study has also shown an increase in packing density of binary mixtures with particle size ratio increasing up to 2.5, which was followed by decrease in density of mixtures with larger particle size ratios, which has not so far been reported in the literature.     

Effects of particle size on thermal durability and microporous characteristics for sintered bodies of alumina-pillared fluorine micas

Powder compacts of alumina-pillared fluorine micas having different particle sizes were fired at various temperatures in the range of 500–800 °C. Sintered bodies of the alumina-pillared micas were obtained at 500–700 °C with retaining their pillared structure. The pillared structure collapsed at 800 °C, losing microporous characters. Specific surface area and micropore volume of the sintered bodies obtained from coarse particles are larger than those obtained from fine particles. Thermal durability of the pillared structure depends on the particle size of alumina-pillared fluorine micas, especially on the c-dimension of the host mica crystals; thermal durability of the sintered bodies obtained from coarse particles is higher than that from fine particles. The sintered bodies are machinable due to the interlocking microstructure of the flaky mica crystals.     

Effect of particle size on the performance of cross-flow microfiltration

The effects of particle size on the cake properties and the performance of cross-flow microfiltration are studied. A particulate sample with a wide size distribution range from submicron to micron is used in experiments. The probabilities of particle deposition are analyzed based on a force analysis. Since themajor forces in determining the particle deposition and packing in the filter cake are different for submicron and micron particles, the particle size plays an important role in the filtration performance. Cake properties, such as mass, porosity and average specific filtration resistance of the cake, are calculated theoretically and compared with experimental data. Except for the overestimation of the mean particle size for about 1 μm, the calculated results of the pseudo-steady filtration rate and cake properties under various operating conditions agree fairly well with the experimental data.     

纳米二氧化硅增强尼龙12选择性激光烧结成形件

使用纳米二氧化硅增强尼龙12选择性激光烧结(SLS)成形件,通过溶剂沉淀法制备SLS用纳米二氧化硅/尼龙12复合粉末材料,研究了纳米二氧化硅对SLS成形件力学性能的影响,结果表明:纳米二氧化硅以纳米尺寸均匀分散在尼龙12基体中:复合粉末的粒径比纯尼龙12的粉末小,因而有利于提高烧结速率及成形件精度;复合粉末比尼龙12的粉末具有更高的热稳定性;复合粉末烧结件的拉伸强度、拉伸模量以及冲击强度比纯尼龙12烧结件分别提高了约20.9%、39.4%和9.5%,说明纳米二氧化硅对尼龙12 SLS成形件的增强效果显著.     

颗粒粒度分布对树脂基磁致伸缩复合材料性能的影响

已有研究在Terfenol-D颗粒粒径及粒度分布对树脂基磁致伸缩复合材料性能的影响规律上存在分歧。本文中以Terfenol-D为磁致伸缩颗粒,以不饱和聚酯树脂为基体,采用5 种窄分布颗粒(30～53μm、53～150μm、150～300μm、300～450μm、450～500μm)和1种宽分布颗粒(30～500μm)制备颗粒体积分数为20 %的磁致伸缩复合材料,并测试其动静态磁致伸缩系数、磁机械耦合系数、弹性模量及抗压强度等性能参数。在窄分布颗粒制备的试样中,以53～150μm制备的复合材料的磁致伸缩性能最佳;而采用宽分布颗粒制备的试样其性能优于窄分布颗粒制备的试样。该结果表明,增大颗粒粒径同时具有积极作用与消极作用, 其对复合材料磁致伸缩性能的影响取决于哪一个居主导地位。      

Effect of particle size distribution on flowability of granulated lactose

The flowability of powders used in tableting significantly affects tablet weight and content uniformity of active pharmaceutical ingredients. Use of granulated materials instead of powdered materials can improve flowability. In this study, the effect of particle size distribution on flowability of granulated lactose was quantitatively analyzed. Three types of granulated lactose were classified into progressively narrower size fractions, and nine samples were systematically prepared. The mass median diameters were nearly constant (i.e., 130.5 ± 13.5 μm) and the geometric standard deviations ranged from 1.29 to 2.04. Two flow properties (angle of repose and compressibility) were measured. The correlations between flow properties and the particle size distributions were analyzed, and the coefficients of determination were obtained for different particle diameters and cumulative mass fractions. The optimal conditions to maximize the coefficients of determination were defined. Furthermore, static and dynamic friction properties were evaluated, and their correlations with particle size distribution were calculated.     

Nitrofurantoin: particle size and dissolution

Tablets manufactured from micronized anhydrous nitrofurantoin exhibited unsatisfactory dissolution properties, whereas excellent results were obtained with unmilled drug material having fine particle size.     

Preparation of cast aluminium alloy-mica particle composites

The optimum conditions for producing cast aluminium alloy-mica particle composites, by stirring mica particles (40 to 120 m) in molten aluminium alloys (above their liquidus temperatures), followed by casting in permanent moulds, are described. Addition of magnesium either as pieces along with mica particles on the surface of the melts or as a previously added alloying element was found to be necessary to disperse appreciable quantities (1.5 to 2 wt.%) of mica particles in the melts and retain them as uniform dispersions in castings under the conditions of present investigation. These castings can be remelted and degassed with nitrogen at least once with the retention of about 80% mica particles in the castings. Electron probe micro-analysis of these cast composites showed that magnesium added to the surface of the melt along with mica has a tendency to segregate around the mica particles, apparently improving the dispersability for mica particles in liquid aluminium alloys.The mechanical properties of the aluminium alloy-mica particle composite decrease with an increase in mica content, however, even at 2.2% the composite has a tensile strength of 14.22 kg mm^–2 with 1.1% elongation, a compression strength of 42.61 kg mm^–2, and an impact strength of 0.30 kgm cm^–2. The properties are adequate for certain bearing applications, and the aluminium-mica composite bearings were found to run under boundary lubrication, semi-dry and dry friction conditions whereas the matrix alloy (without mica) bearings seized or showed stick slip under the same conditions.     

Rubber particle size and cavitation process in high impact polystyrene blends

The rubber particle size and its volume fraction are recognised as being important factors in determining the yield and fracture behaviour of high impact polystyrene (HIPS). However, correlations between the average particle size and cavitation in the rubber with toughening efficiency have only recently been established theoretically. This work provides further evidence on how the deformation kinetics in HIPS are affected by variations in the average rubber particle size highlighting along the way the role of rubber cavitation in the process. Variations in the average particle size were achieved by melt blending different proportions of two commercial grades of HIPS that had the traditional multiple inclusion particle morphology. Tensile and impact properties of the blends were measured and correlated to morphological parameters determined by quantitative image analysis. It was found that yield and fracture behaviour in tensile and impact test were strongly dependent on the amount of sub-micron particles in the blend. At high rates, toughness drops steeply with particle size. It was proposed that stress at yield and post yield strain hardening are controlled by particle size and rubber stretching respectively. Microfracture analysis by transmission electron microscopy lent support to the arguments presented. This revised version was published online in November 2006 with corrections to the Cover Date.     

Estimation of particle size distribution from cross-sectional particle diameter on the cutting plane

To control highly functional sintered materials, it is necessary to evaluate particle size segregation within materials. In the present study, a new method for estimating particle size distribution is proposed; this method considers the occurrence probability of the cutting diameter. The proper particle size distribution in a particle bed was estimated by calculating a matrix consisting of the occurrence probability and the distribution of particle diameters measured on a cutting plane. The estimated particle size distribution was smoothed using the Phillips–Twomey method. A cavity-filling simulation was carried out to verify the validity of the proposed method using the Distinct Element Method. The particle size distribution estimated by this method correlated well with the actual particle size distribution. The effect of particle size distributions with various geometrical standard deviations on the accuracy of estimated values was also investigated. The accuracy increased as the geometric standard deviation increased, and there was an optimum particle size bin number for a specific particle distribution. It was found that a large bin number and a large number of measured particles were required to obtain a higher accuracy for narrow size distributions.     

Effect of particle size distribution on green properties during high velocity compaction

Iron powders with two different particle size distributions were compacted by high velocity compaction. The influences of particle size distribution and impact velocity on green properties, including green density, springback, tensile strength and bending strength etc., were studied with scanning electron microscopy (SEM) and a computer controlled universal testing machine. The results show that the particle size distribution and the impact velocity strongly affect its properties. Wider size distribution results in green compact with higher density and better strength. Furthermore, springback of compacts is lower produced by the powder with wider size distribution, especially for radial springback. As impact velocity increases, its green density and green strength gradually increases, but the increasing rate of density decreases gradually. No special relation is found between springback and impact velocity. In addition, the axial springback and the bending strength are higher than the radial springback and the tensile strength, respectively.     

Effect of particle size distribution on green properties during high velocity compaction

Iron powders with two different particle size distributions were compacted by high velocity compaction. The influences of particle size distribution and impact velocity on green properties, including green density, springback, tensile strength and bending strength etc., were studied with scanning electron microscopy (SEM) and a computer controlled universal testing machine. The results show that the particle size distribution and the impact velocity strongly affect its properties. Wider size distribution results in green compact with higher density and better strength. Furthermore, springback of compacts is lower produced by the powder with wider size distribution, especially for radial springback. As impact velocity increases, its green density and green strength gradually increases, but the increasing rate of density decreases gradually. No special relation is found between springback and impact velocity. In addition, the axial springback and the bending strength are higher than the radial springback and the tensile strength, respectively.     

粒度对纳米掺杂BaTiO3陶瓷结构和性能的影响

制备了纳米掺杂BaTiO3陶瓷,研究了纳米掺杂剂和BaTiO3的粒度对BaTiO3陶瓷的微观结构和介电性能的影响．结果表明,小粒度、高分散的纳米掺杂剂更易对BaTiO3颗粒实现均匀包裹,有效地抑制晶粒生长并形成更多的壳-芯晶粒,大比表面积使更多高活性的表面原子与BaTiO3发生原子输运形成传质,导致晶粒壳／芯比增大,从而提高其介电性能．纳米掺杂陶瓷的平均晶粒尺寸和四方率与BaTiO3粒度几乎成正比．随着BaTiO3粒度的减小,立方晶粒壳增大而四方晶粒芯减小,陶瓷由四方晶相向赝立方晶相转变,居里峰被显著压制,从而改善介电温度特性．同时,晶粒的壳与芯之间失配产生的内应力随之增加,使居里点向高温方向移动．     

Fracture mechanisms and particle shape formation during size reduction of a model food material

The importance of particle shape to powder properties warrants examination of the effect of size reduction on particle shape formation. In this study, a model food material (dried gelatinized starch) was comminuted in an impact breakage gun, a hammer mill (with and without a screen) and in a blender. After sieving, particle shape at selected sizes was assessed as deviation from sphericity. Generally, particle shapes were elongated at smaller size, except for those produced by unscreened hammer milling. Particle shapes were unaffected by impact velocity in the gun, but were rounded by increased milling. Fractography was used to demonstrate how elongated particles formed. During fracture, fracture fronts were disturbed by air holes in the material, creating cleavage steps. Subsequent undercutting of the steps as fracture planes spread released the elongated particles. Such particle formation mechanisms may account for anomalous size distribution results at early stages of grinding. Particle shape differences between mills and single impact breakage were ascribed to particle selection mechanisms surmised to be operating in the mill. Both material properties and the size reduction method were shown to affect particle shape, thus fracture progress in a given material should be studied if particles of specific shapes are to be produced by comminution.     

Slurry erosion of metallics,polymers, and ceramics: particle size effects

Abstract

One of the least well understood areas in the study of erosion by solid particles is the effect of particle size. Erosion is generally assumed to be independent of particle size above a critical value. However, there is evidence that this pattern is dependent on the process conditions. In the present study, the effect of particle size was investigated for different classes of materials, which included two pure metals, an alloy, a ceramic, and a polymer. The apparatus used was an impinging jet. Scanning electron microscopy was used to characterise the degradation following erosion. The results showed that the erosion rate peaked at intermediate particle sizes, for some of the materials studied. However, the particle size at which the peak occurred changed as a function of target and particle properties. Such observations were explained in terms of the combined effects of particle, target, and fluid flow parameters on the erosion mechanisms of the different materials.     

Effect of particle size ratio and contribution of particle size fractions on micromechanics of uniaxially compressed binary sphere mixtures

This paper is an extension of the recent work of Wi?cek (Granul Matter 18:42, 2016), wherein geometrical parameters of binary granular mixtures with various particle size ratio and contribution of the particle size fractions were investigated. In this study, a micromechanics of binary mixtures with various ratio of the diameter of small and large spheres and contribution of small particles was analyzed using discrete element simulations of confined uniaxial compression. The study addressed contact normal orientation distributions, global and partial contact force distributions and pressure distribution in packings of frictional spheres. Additionally, the effect of particle size ratio and contribution of particle size fractions on energy dissipation in granular mixtures was investigated. The particle size ratio in binary packings was chosen to prevent small particles from percolating through bedding. The bimodality of mixtures was found to have a strong effect on distribution of contact normal orientation and distribution of normal contact forces in binary mixtures. Stress transfer in binary packing was also determined by both, particle size ratio and volume fraction of small particles. Dissipation of energy was higher in mixtures with higher particle size ratios and decreased with increasing contribution of small spheres in system.     

Filler from crushed aggregate for concrete: Pore structure,specific surface,particle shape and size distribution

Characteristics of fine particles (0–125 μm diameter) from seven different crushed and natural sands from five different Norwegian rock types were determined. The results suggest that the same water absorption values, as determined by EN 1097-6 on coarser sand fractions, can be applied to the fines. The values of specific surface area measurements vary widely between different materials and between different measurement methods. BET measurements seem to be strongly affected by the mineralogical composition (presence of mica) and surface morphology (weathering) of the particles. Specific surface area calculated from the particle size distributions (PSD) is mainly dependent on the precision of the test methods in the size range below about 3–5 μm, because these small particles contain most of the surface area. Shape measurements by both Dynamic Image Analysis (DIA), which is a 2-D method, and X-ray microcomputed tomography (μCT), which is a 3-D method, have yielded similar relative length-to-thickness aspect ratios of the particles between different mineralogies, though with lower absolute values for DIA due to 2-D projection of 3-D quantities.     

Effects of model scale and particle size on micro-mechanical properties and failure processes of rocks—A particle mechanics approach

A numerical procedure to determine the equivalent micro-mechanical properties of intact rocks is presented using a stochastic representative elementary volume (REV) concept and a particle mechanics approach. More than 200 models were generated in square regions with side lengths varying from 1 to 10 cm, using the Monte Carlo simulation technique. Generated particle models were then used for the calculation of equivalent micro-mechanical properties. Results with a core sample of diorite from Äspö, Sweden, show that the variance of the calculated values of mechanical properties decrease significantly as the side lengths of particle models increase, reaching a REV side length about 5 cm with an acceptable variation of 5%, which is equal to the minimum diameter of rock specimen for uniaxial compressive tests suggested by ISRM. The complete stress–strain curve of the diorite rock sample was predicted under uniaxial compression, as the basis for evaluating the damage and failure processes. The unique contribution of this paper is its study on impacts of sample size and particle size distributions on mechanical behaviour of rocks when particle mechanics approaches are used.     

Effect of vibro-milling time on phase formation and particle size of nickel niobate nanopowders

A columbite-type phase of nickel niobate, NiNb₂O₆, nanopowder was synthesized by a solid-state reaction via a rapid vibro-milling technique. The effect of milling time on the phase formation and particle size of NiNb₂O₆ powder was investigated. Powder samples were characterized using DTA, XRD, SEM and laser diffraction techniques. It was found that the smallest particle size of 32 nm was achieved at 25 h of vibro-milling after which a higher degree of particle agglomeration was observed on continuation of milling to 35 h. In addition, by employing an appropriate choice of the milling time, a narrow particle size distribution curve was also observed.     

Influence of the size of micronized active pharmaceutical ingredient on the aerodynamic particle size and stability of a metered dose inhaler

Pharmaceutical inhalers are often used to treat pulmonary diseases. Only active pharmaceutical ingredient (API) particles from these inhalers that are less than approximately 5 microm are likely to reach the lung and be efficacious. This study was designed to investigate the impact of micronized API particle size on the aerodynamic particle size distribution (PSD) profile and the particle size stability of a suspension metered dose inhaler (MDI) containing propellant HFA-227 (1,1,1,2,3,3,3 heptafluoropropane) and a corticosteroid. The median API particle size ranged from 1.1 microm to 1.8 microm (97% to 70% of particles <3 microm, respectively). This study showed that increasing the particle size of the API used to manufacture a suspension MDI product increased the aerodynamic PSD of the MDI product. Furthermore, upon storage of the MDI product under temperature cycling conditions, samples containing larger-size API particles were less stable with respect to their aerodynamic PSD than those with smaller-size API particles. It was found that size-dependent particle growth and/or aggregation of the suspended API may be occurring as a result of temperature cycling. In conclusion, this study has shown that the particle size of the raw API impacts the properties and stability of the emitted aerosol spray. Based on the findings from this study, it is recommended that the API particle size be carefully controlled in order to meet specifications set for the finished MDI product.