Effect of particle size on densification of pure magnesium during spark plasma sintering

The effect of particles size ranges (<38 μm, 75–150 μm, 270–550 μm) of atomized magnesium powders on densification mechanisms during spark plasma sintering (SPS) process was investigated. The intrinsic driving force, local pressure and current of Mg powders with different particle sizes were analyzed by theoretical calculation. The results obviously indicate that the densification of pure magnesium can be improved by the reduction of particle size, suggesting the intrinsic driving force, local pressure and current intensity are enhanced significantly by a decrease in the particle size at the same sintering conditions, which can promote shrinkage of pores, formation of the sintering neck and mass transportation in the SPS process. Not only that, rapid densification is also interpreted in term of mechanical movement of particles, Joule heating effect and plastic deformation. However, the mechanical movement of the large particles is higher than that of small particles due to high punch displacement, and plastic deformation, detected by scanning electron microscopy, plays a main role in densification for large particles in the case during the sintering. Joule heating effect is the key factor for densification of small Mg particles, and high densification degree can be obtained by sintering small particles.     

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.     

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 milling and particle size distribution on the sintering behavior and the evolution of the microstructure in sintering powder compacts

In this investigation, it was observed that the contamination arising from the milling medium has a great influence on the sintering behavior. The densification rate of the powder milled with ZrO₂ balls is largely inhibited, and the activation energy of ZrO₂-doped alumina is significantly enhanced. The possible reasons for the enhancement of the activation energy were discussed. The effects of particle size distribution of powder compacts on the microstructural evolution of alumina during sintering were proposed and discussed.     

Effect of zirconia particle size distribution on the toughness of zirconia-containing ceramics

The zirconia particles in zirconia-containing ceramics have a size distribution similar to Gaussian distribution. The spontaneously martensitic start temperature (M_s) of different particles are not the same. The larger the particle, the higher its M_s. On cooling from high temperature to a value lower than the macro M_s of the materials, the stress-induced and spontaneous transformation will happen, so that the toughness of the materials increases at first, then gradually drops to a value slightly higher than that of the matrix. The size distribution plays an important role in affecting the toughness of the materials. When the average particle size increases, the maximum toughening (K_c)_max and the temperature (T_max) at which (K_c)_max happens will all increase. The toughness at given temperature will increase at first and then drop also to a value slightly higher than that of matrix with increasing of average particle size. The stronger concentration of the size distribution, the higher (K_c)_max will be. The weaker concentration for size distribution (either the range of zirconia particle sizes becomes wider or the scale parameter of the distribution increases), the lower (K_c)_max, but the range of temperature in which the toughness is larger than certain value will become wider. Some suggestions of designing ceramics with high toughness at different temperatures are given.     

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.     

Effect of particle-size distribution on sintering

A sintering model, taking into account the effect of particle-size distribution and the effect of grain growth, has been derived. The model predicts a dependence of densification on the width of the particle-size distribution. This dependence is strongly affected by the occurrence of grain growth. Prior to the occurrence of grain growth, the model predicts that the densification rate increases and then decreases as the particle-size distribution width of the original powder increases. After grain growth occurs, the densification rate decreases as the particle-size distribution width of the starting powder increases.     

Influence of particle size and particle size distribution on MICA filled nylon 6 composite

Particulate reinforced thermoplastic composites are designed to improve the properties and to lower the overall cost of engineering plastics. In this study the effects of particle size and particle size distribution on the properties of mica filled nylon-6 was investigated. Composites of nylon-6 with varying concentrations (viz. 5 to 40 wt%) of mica were prepared by twin screw extrusion. The composite showed improved mechanical, thermal as well dielectric properties on addition of filler.     

Effect of rubber particle size on the impact tensile fracture behavior of MBS resin with a bimodal particle size distribution

We performed impact tensile fracture experiments on methylmethacrylate–butadiene–styrene (MBS) resin with small and large particles in a bimodal size distribution, and examined the effects of particle size on fracture behavior by fixing the total rubber content (28 wt%) and the small particle size (about 140 nm), and varying the size of large particles (about 490 nm or 670 nm). Dynamic load P′ and displacement δ′ of single-edge-cracked specimens were measured using a Piezo sensor and a high-speed extensometer, respectively. A P′−δ′ diagram was used to determine external work U _ex applied to the specimen, elastic energy E _e stored in the specimen, and fracture energy E _f for creating a new fracture surface A _s. Energy release rate was then estimated using G _f = E _f/A _s. Values of G _f were correlated with fracture loads and mean crack velocity v _m determined from load and time relationships. We then examined the effect of particle size on G _f and v _m, and results indicated that particle size plays an important role in changing the values of G _f and v _m.     

Influence of particle size and particle size distribution on toughening mechanisms in rubber-modified epoxies

The principal toughening mechanism of a substantially toughened, rubber-modified epoxy has again been shown to involve internal cavitation of the rubber particles and the subsequent formation of shear bands. Additional evidence supporting this sequence of events which provides a significant amount of toughness enhancement, is presented. However, in addition to this well-known mechanism, more subtle toughening mechanisms have been found in this work. Evidence for such mechanisms as crack deflection and particle bridging is shown under certain circumstances in rubber-modified epoxies. The occurrence of these toughening mechanisms appears to have a particle size dependence. Relatively large particles provide only a modest increase in fracture toughness by a particle bridging/crack deflection mechanism. In contrast, smaller particles provide a significant increase in toughness by cavitation-induced shear banding. A critical, minimum diameter for particles which act as bridging particles exists and this critical diameter appears to scale with the properties of the neat epoxy. Bimodal mixtures of epoxies containing small and large particles are also examined and no synergistic effects are observed.     

粉煤灰粒径分布对硅酸盐水泥水化性能的影响

为研究粉煤灰粒径对硅酸盐凝胶材料水化性能的影响,经球磨仪研磨得到3种不同粒径的粉煤灰,探讨其对硅酸盐水泥水化放热速率、水化放热总量、水化反应程度和粉煤灰自身水化反应程度的影响。结果表明:随粉煤灰粒径的减小,粉煤灰的水化活性明显增大,水化反应程度增大,养护龄期为7 d时,水化程度增加20.7%;粉煤灰粒径分布对硅酸盐水泥水化放热总量的影响较小,主要影响其水化放热速率、水化反应程度,养护龄期为28 d时,胶凝材料水化程度增加3%。     

Effect of particle size distribution on hydrodynamics of pneumatic conveying system based on CPFD simulation

The effect of particle size distribution on the hydrodynamics of dilute-phase pneumatic conveying system was analyzed using computational particle fluid dynamics (CPFD) simulation. The influence of a simulation parameter, i.e., correction factor of drag coefficient (k), on the hydrodynamics of pneumatic conveying system was determined via CPFD simulation. When results of simulation were compared with experimental data of previous studies, the average error of pressure drop per length predicted by the CPFD approach with the correction factor was below 4.4%. Saltation velocity and the pressure drop per unit length declined as the drag force coefficient increased. Simulation results also revealed that the pressure drop per length and the saltation velocity were decreased when the fine powder fraction in the particle size distribution was increased, although the width of particle size distribution was widened, and the standard deviation was increased. Finally, the Relative Standard Deviation (RSD) of pressure drop per length was measured and compared with median diameter (d₅₀), Sauter mean diameter, geometric mean diameter, and arithmetic mean diameter. The RSD of the Sauter mean diameter was 5.8%, approximately twice less than the RSD value of d₅₀ commonly used in pneumatic conveying.     

The effect of particle size distribution on barite reduction

The present study is a follow-up of investigation on barite reduction to barium sulfide as a function of starting particle size distribution and temperature of reaction. In this work we study the high temperature reduction process of barite from the view point of particle size distribution. Conversion-time data have been obtained using iodometry method in each isothermal condition. A modified kinetic model used to express the carbothermic reduction process. To obtain the values of activation energy and frequency factor, the same expression was selected for each sample at all temperatures. The rate of reaction is found to be related to the particle size distribution and the gasification reaction of coke which has influence on reduction process. The kinetic parameters calculated from standard analysis of isothermal kinetic data indicated that the particle size of barite controlled the reaction when it was coarser than 400 mesh both in presence and absence of catalyst.     

Liquid-phase sintering in the glass-cordierite system: particle size effect

The effect of particle sizes of glass and ceramic filler on the densification kinetics of glassfilled ceramics has been studied using borosilicate glass-cordierite as the model system. Within the particle size range investigated, the densification is found to be significantly enhanced by increasing the cordierite size, reducing the glass size and increasing the green density. These results are attributed to both the increased driving force of densification by reducing the glass particle size and the decreased glass redistribution distance by either increasing the green density of compacts or increasing the particle size ratio between the cordierite and glass powders. In addition, a large cordierite-to-glass size ratio gives a dense, uniform microstructure of sintered body as a result of forming a homogeneous close packing of the low-melting glass phase around the refractory cordierite particles.     

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 performance and particle kinetics in a centrifugal slurry pump handling multi-size particulate slurry

A significant variation in particle size distribution (PSD) is generally encountered in slurry transportation. The goal of this work is to establish the effect of variation in PSD on the centrifugal slurry pump (CSP) performance and particle kinetics. Computational fluid dynamics (CFD) modeling of a CSP with multi-size particulate slurry has been performed with a sliding mesh approach using the granular Eulerian-Eulerian model. The numerical model is validated with the experimental data of the pump performance for multi-size particulate fly ash slurry. The maximum deviations in the predicted head and efficiency compared to the measured values are of the order of ±2% and ±3.5%, respectively. Simulations with a single representative particle size for multi-size particulate slurry using median and weighted mean diameter approach are also carried out to understand the difference in performance prediction with equi-size and multi-size slurry. The predicted trend of pump performance variation with PSD is linear and non-linear with equi-size and multi-size slurries, respectively. The median and weighted mean approaches showed error in capturing the effect of variation in PSD on pump performance. The variation in PSD significantly affects the flow of particles inside the impeller and casing flow passages due to particle kinetics. Reduction in the intensity of granular pressure, maximum granular viscosity, and the head loss due to friction in impeller and casing flow passages are found with the increase in the fine size particles.     

Spectral attenuation and aerosol particle size distribution

The problem of the reconstruction of the spectrum of a dispersed system from data on its spectral attenuation is studied. The numerical algorithm for obtaining the particle size distribution by the use of the concept of regularization is thoroughly treated. The applicability of this method to the reconstruction of the particle size distribution of a typical marine aerosol is tested. A method of choosing the regularization parameter of the solution for the inverse problem based on an objective estimate of the validity of the obtained solution is proposed. Results are presented for a set of numerical experiments in which the radius interval for which the distribution function can be obtained with a satisfactory accuracy is estimated. The validity of solutions is estimated depending on the measuring spectral range for the attenuation, the radius interval, and the number and position of points within this interval. The possibility of extending the radius interval for which the distribution function can be obtained by the use of extrapolation of the distribution function tail is discussed.     

Effect of TiH2 particle size distribution on aluminum foaming using the powder metallurgy method

TiH₂ decomposes over a range of temperatures strongly influenced by diverse factors including particle size. In the present research, a systematic study of the dehydrogenation behavior of TiH₂ powder of different particle size distribution was undertaken with the aid of thermogravimetric analysis. The effect of this parameter on aluminum foaming was evaluated. It was found that when TiH₂ exceeds a critical particle size (around 50 μm), dehydrogenation occurs as a single desorption event with onset temperatures around 500 °C. The reduction of particle size, besides reducing the onset of hydrogen release, decreases the dehydrogenation rate. As a result, the first dehydrogenation event gets sharper and tends to overlap with the second with increasing particle size. The use of selected powders on foaming showed that the final foam expansion and porosity features, such as pore size, pore density, and homogeneity are largely influenced by the particle size distribution of the foaming powder. TiH₂ of the largest particle size was the most suitable for foaming pure aluminum.