Polydisperse Powder Mixtures: Effect of Particle Size and Shape on Mixture Stability

ABSTRACT

The effect of the shape and size of the components on the stability of mixtures was evaluated in binary mixtures of drug and carrier. Aspirin was used as model drug; spray-dried lactose and microcrystalline cellulose were used as carriers. The coefficient of variation (CV) of the drug in the mixture at various time intervals during mixing was used as a measure of homogeneity. The stability of mixtures was assessed under conditions that were conducive to segregation—in this case, prolonged mixing. The pattern of change in CV with time was analyzed in terms of convective, shear, and diffusive mixing stages. The variation resulting from a change in the shape of the carriers was smaller than that resulting from size differences. The segregation rate constant, calculated on the assumption of a first-order mixing process, was found to be larger in mixtures having components of different shape than in mixtures having components of similar shape. In mixtures of micronized drug and carrier, the pattern of change in the CV of drug with mixing time was attributed to the distribution of agglomerates of micronized drug during convective mixing, followed by shearing of agglomerates and, finally, the distribution of the primary particles during diffusive mixing. Mixtures of non-cohesive powders of similar size and shape behaved like random mixtures of non-interacting components.     

The effect of particle morphology on the physical stability of pharmaceutical powder mixtures: the effect of surface roughness of the carrier on the stability of ordered mixtures

The effect of particle morphology of the components on the physical stability of ordered mixtures was determined for a model system comprised of a mixture of micronized aspirin and a monodisperse carrier. Spray-dried lactose, crystallized lactose, microcrystalline cellulose, and dextrate were used as carriers. The surface texture of the carriers was quantified in terms of the ratio of the perimeter of the particles to that of an idealized shape at a constant magnification. Mixtures containing highly textured carriers segregated to a lesser extent than those containing smoother textured carriers. This was postulated to be due to the presence of a higher concentration of surface asperities on the coarse carriers that can constitute potentially strong adhesion sites for the fine component because of their higher energy relative to adjacent areas on the surface. The effect of the addition of a ternary component, magnesium stearate, on the stability of the above mixtures was studied. The observed differences in the segregation response were attributed to electrostatic charge effects.     

Development of particle size and shape measuring system for machine-made sand

Abstract

In recent years, the use of machine-made sand has gradually increased. Simultaneous monitoring of the particle size and shape of machine-made sand during its production is vital. Here, a machine-made sand size measuring methods were developed using vibration dispersion and high-speed video imaging and subsequently evaluated. Moreover, a software system for particle size and shape identification of machine-made sand was also developed using image processing algorithms. Experiment studies on this system were conducted, and the results show that the measurement results of particle size between the vibration screening method and imaging method are different. The measurement results of particle size obtained from the imaging method were affected by the degree of dispersion and particle shape of the machine-made sand. The particle shape parameter of the machine-made sand was modified to compensate for the measurement results of particle size. After compensation for measurement results of the sand size by the imaging method, the cumulative curve of the particle size distribution was in agreement with that obtained from the vibratory sieve method; the measurement error of sand size is less than 3%. Based on sphericity characterization of the particles, the particle shape measurement using the imaging method was accurate. Thus, the particle size and shape measuring system based on imaging method met the monitoring requirements for machine-made sand.     

Predicting porosity of binary mixtures made out of irregular nonspherical particles: Application to natural sediments

Predicting porosity or packing density of sediments made of coarse and fine components of arbitrary geometry is critical to many science and engineering applications. Well-established analytical models for packing of spheres express porosity of the binary mixture as a function of fine-to-coarse particle size ratio. Nevertheless, the applicability of such models to natural granular materials is limited given the nonspherical and irregular nature of the particles whose packing depends on both particle size and shape. The objective of this study is to develop a model that predicts the porosity of binary mixtures made up of irregular nonspherical particles. We modified a previously developed linear sphere-packing model so that it takes into account the effect of both the particle size and shape. As an input, the modified model uses the coarse-to-fine particles specific surface area ratio instead of using the particle size ratio required by the sphere-packing model. We tested the modified model by predicting the porosities of a binary mixture composed of coarse and fine calcite aggregates. We further validate the model by using published data on the porosity of binary mixtures made of synthesized, cubical and cylindrical particles. Our model predictions show good agreement with the measured porosity.     

Effect of particle shape on raceway size and pressure drop in a blast furnace: Experimental,numerical and theoretical analyses

Experiments and simulations are conducted to explore the changing laws of blast furnace (BF) raceway morphology and pressure drop with cylindrical particles. Experimental data show that there are five typical stages for the pressure drop during the raceway formation. The closer the aspect ratio (Ar) of the particle to 1, the bigger the raceway size and the wider the particle moving band will be. When the raceway is in stable stage, the pressure drop can be ascribed to the cooperative action of the bed height, inlet gas velocity and Ar. Numerical results reveal that the formation of large raceway for sphere-like particles is due to the small drag and contact forces. The contact forces in the prolate particle system are very large and thus result in a small raceway. Finally, the influence of particle shape is employed to improve a raceway size predictive correlation which can increase the average calculational accuracy by 3.4%.     

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.     

Influence of particle size on the distributions of liposomes to atherosclerotic lesions in mice

In order to confirm the efficacy of liposomes as a drug carrier for atherosclerotic therapy, the influence of particle size on the distribution of liposomes to atherosclerotic lesions in mice was investigated. In brief, liposomes of three different particle sizes (500, 200, and 70 nm) were prepared, and the uptake of liposomes by the macrophages and foam cells in vitro and the biodistributions of liposomes administered intravenously to atherogenic mice in vivo were examined. The uptake by the macrophages and foam cells increased with the increase in particle size. Although the elimination rate from the blood circulation and the hepatic and splenic distribution increased with the increase in particle size in atherogenic mice, the aortic distribution was independent of the particle size. The aortic distribution of 200 nm liposomes was the highest in comparison with the other sizes. Surprisingly, the aortic distribution of liposomes in vivo did not correspond with the uptake by macrophages and foam cells in vitro. These results suggest that there is an optimal size for the distribution of liposomes to atherosclerotic lesions.     

Influence of water pressure and apex angle on prediction of particle size for atomization of copper powder

Water atomization can be used to produce wide range of particle size, shape and particle size distribution of metal powder efficiently by varying operating variables which include design parameters, process parameters and thermophysical properties of metal and water. Liquid copper was water atomized in a laboratory fabricated atomizer. Few experiments were conducted to produce copper powder by varying water jet pressure. In the present work, mathematical model was formulated to propose a relationship between particle size of copper powder and operating variables. Proposed mathematical model is developed to predict particle size affected by different parameters and validated with experimental results. 3-D surface response was analyzed by varying water pressure and apex angle.     

Characteristics and in vitro biological assessment of (Ti, O, N)/Ti composite coating formed on NiTi shape memory alloy

In this investigation, plasma immersion ion implantation and deposition (PIIID) was used to fabricate a (Ti, O, N)/Ti coating on NiTi shape memory alloy (SMA) to improve its long-term biocompatibility and wear resistance. The surface morphology, composition and roughness of uncoated and coated NiTi SMA samples were examined. Energy dispersive X-ray elemental mapping of cross-sections of (Ti, O, N)/Ti coated NiTi SMA revealed that Ni was depleted from the surface of coated samples. No Ni was detected by X-ray photoelectron spectroscopy on the surface of coated samples. Furthermore, three-point bending tests showed that the composite coating could undergo large deformation without cracking or delamination. After 1 day cell culture, SaOS-2 cells on coated samples spread better than those on uncoated NiTi SMA samples. The proliferation of SaOS-2 cells on coated samples was significantly higher at day 3 and day 7 of cell culture.     

Effect of solvents quality on determination of particle size and polydispersity of nanoparticles

Nanotechnology is of great interest to researchers and industrialists and nanocolloidal carrier systems for drug delivery have been studied in great detail, but while much research has been carried out on the preparation of nanoparticles using a variety of techniques employing various solvents, no attention has been given to the quality of solvents used in the process of nanoparticles characterization. The present investigation aimed to study the effect of solvents quality on the chitosan nanoparticles characterization for average particle size (Z) and polydispersity index (P.I.). Particle size distribution study showed that the number of particles contributed by solvents significantly affects both the Z and P.I. of the nanoparticulate suspensions leading to ambiguous results. While the Z decreases upon dilution with organic solvents, the phosphate buffer and water causes a net increase in Z because of the introduction of larger extraneous nanoparticles. The P.I. was found to increase with dilution because of the differences in the size of the polymeric nanoparticles and the nanoparticles introduced by the solvent upon dilution. The study thus recommends use of the highest quality of solvents in nanoparticles manufacturing and characterization process to avoid the generation of erroneous results.     

The effect of nano-sized stainless steel powder addition on mechanical and physical properties of micropowder injection molded part

Micropowder injection molding (μPIM) is a new technology that has potential in the mass production of microcomponents. A bulk material of nanoparticles possesses completely different properties from those of large-sized particles. The main objective of this study is to study the effects of nano-sized powder addition on the μPIM process of powder-polymer mixtures for the fabrication of miniature parts. The binder systems consist of polyethylene glycol (PEG), polymethyl methacrylate (PMMA), and stearic acid (SA) with different powder loading blended with powders. The results indicate that increasing the nanopowder content to 30 wt.% increased the powder loading and decreased the injection and sintering temperatures. The sintered parts had densities of 96% of the theoretical value. High physical and mechanical properties of the sintered specimen were achieved with the 30 wt.% nano-sized powder sintered at 1200 °C at a heating rate of 5 °C/min under vacuum atmosphere. A significant reduction of the surface roughness of the sintered parts using the nano–microhybrid powder (S_a = 0.365 μm) was observed compared with the sintered parts with only micropowder (S_a = 1.002 μm). Using nanopowders, the hardness also increased from 182 HV to 221 HV with a linear shrinkage of approximately 9%, which is less than that of the micropowders (18%).     

Fluidization of lactose carrier powders through normally directed airflow: The effect of recirculation and particle size

This study investigates the fluidization of lactose carriers from a powder bed subjected to a normal force in a channel flow using high-speed imaging, particle image velocimetry (PIV), and high-speed, long-distance microscopy (HS-LDM). Pharmaceutical lactose carriers (LH200 and SV010) with different cohesiveness and fines percentages were examined in this study. Airflow velocities in the range of 1.4 m/s and 7m/s were tested, corresponding to flow rates ranging from 20 to 100 L/min. The use of HS-LDM in tandem with PIV has enabled measurement of the slip factor between particles and conveying airflow as well as metrics that help to identify dose homogeneity as a function of location in the channel flow. The results indicate a lower slip ratio and a larger change in powder particle size bands percentages along with channel height in the region near the powder bed, because of flow recirculation and higher velocity fluctuation observed in that region.     

Experimental and computational study of the effect of the system size on rough surfaces formed by sedimenting particles in quasi-two-dimensions

The roughness exponent of surfaces obtained by dispersing silica spheres through a viscous fluid in a quasi-two-dimensional cell is examined using experimental and computational methods. The cell consists of two glass plates separated by a gap which is comparable in size to the diameter of the beads. We have studied the effect of changing the gap between the plates to a limit of about twice the diameter of the beads. If a conventional scaling analysis is performed, the roughness exponent is found to be robust against changes in the gap between the plates. The surfaces formed have two roughness exponents in two length scales, which have a crossover length of about 1 cm.; however, the computational results do not show the same crossover behavior. The single exponent obtained from the simulations stays between the two roughness exponents obtained in the experiments.     

Effect of specimen size and shape on compressive strength of concrete containing fly ash: Application of genetic programming for design

The use of fly ash as a mineral admixture in the manufacture of concrete has received considerable attention in recent years. For this reason, several experimental studies are carried out by using fly ash at different proportions replacement of cement in concrete. In the present study, the models are developed in genetic programming for predicting the compressive strength values of cube (100 and 150 mm) and cylinder (100 × 200 and 150 × 300 mm) concrete containing fly ash at different proportions. The experimental data of different mixtures are obtained by searching 36 different literatures to predict these models. In the set of the models, the age of specimen, cement, water, sand, aggregate, superplasticizers, fly ash and CaO are entered as input parameters, while the compressive strength values of concrete containing fly ash are used as output parameter. The training, testing and validation set results of the explicit formulations obtained by the genetic programming models show that artificial intelligent methods have strong potential and can be applied for the prediction of the compressive strength of concrete containing fly ash with different specimen size and shape.     

Natural diatomite particles: Size-, dose- and shape- dependent cytotoxicity and reinforcing effect on injectable bone cement

Natural diatomite(DT) is the ancient deposit of diatom skeleton with many regular pores of 50–200 nm and also an abundant source of biogenic silica. Although silica is considered biologically safe and there is an increasing interest of using natural diatomite for biomedical applications, the toxicity information about natural diatomite is still missing. Here, cytotoxicity of natural diatomite on osteoblasts and fibroblasts were compared to hydroxyapatite and the relationships between cytotoxicity and diatomite sizes, dose, geometry or impurity were systematically investigated. Cell adhesion and interaction with diatomite particles were also fluorescently observed. The results clearly suggested a size-, dose-and shape-dependent cytotoxicity of natural diatomite. Disk-shaped diatomite particles with average size of30 um in diameter revealed the least toxicity, while the diatomite particles with irregular shapes and sizes less than 10 um were remarkably toxic. Diatomite particles with proper sizes were then selected to investigate the reinforcing effect on injectable calcium phosphate bone cement. Results showed that diatomite significantly improved the compressive strength of bone cement but did not alter the injectability of the cement. This work provided important biocompatibility information of natural diatomite and demonstrated the feasibility of using selected diatomite as bone implant material.     

Bonded particle modeling of grain size effect on tensile and compressive strengths of rock under static and dynamic loading

The effect of grain (particle) size on the strength is an interesting subject in the rock engineering. Some investigations about the impact of particle size on static strength of rock have been conducted and reported in the literature. However, this issue has not received enough attention when high loading rates are involved. In this work, by utilizing the CA3 bonded particle - finite element computer program, the combined influence of loading rate and particle size on the compressive and tensile strengths of rock is examined. The bonded particle model is used to simulate the crack initiation and failure of the rock specimen and the finite element is utilized to model the elastic bars in the Split Hopkinson Pressure Bar (SHPB) apparatus employed for the dynamic testing. Specimens with four different particle sizes were prepared. The results suggest that the particle size does not affect the rock strength under static and dynamic loading. However, the particle size modifies the nominal tensile strength of the notched Brazilian specimens. For the intact Brazilian specimens under high stress rates, the particle size contributes to the tensile strength and this contribution can be justified based on the principles of fracture mechanics. The theoretical reason for these observations is derived for a 3D bonded particle system and discussed.     

Influence of pile shape and pile interaction on the crushable behavior of granular materials around driven piles: DEM analyses

This study presents an analysis and a visualization of the effect that the pile shape has on the penetration resistance of driven piles in crushable granular materials. Discrete Element Method (DEM) simulations of single piles with different shapes (flat tip, open pile, triangular tip) being driven into a previously compacted uniform crushable soil are presented. The results from the DEM simulations showed that the shape of the driven piles has a significant influence on the development of penetration resistance and particle crushing. This study also presents the penetration resistance and particle crushing results when a second flat tip pile was driven in a region near a pre-existing single flat tip pile. It was found that considerable high crushing was induced by the second pile. The second pile induced crushing not only on the particles surrounding itself but also on the particles surrounding the pre-existing pile, showing that particle crushing around a driven pile not only takes place when the pre-existing pile is being driven, but it also occurs during the installation of a second pile, in a region closely located to the first one.     

Effect of the particle size on the thermal stability of nanostructured aluminum powder: dislocation density and second-phase particles controlling the grain growth

A nanostructured aluminum powder was obtained using cryogenic mechanical milling. The powder produced after 25 h of milling showed a broad particle size distribution, ranging between a few microns up to about 150 μm. Five different granulometric classes were selected and for each of these, structural and microstructural features, as well as the thermal stability were investigated using ex situ X-ray diffraction and transmission electron microscopy. There is a direct correlation between particle size and crystallite size. Grain growth tendency was found strongly dependent to the initial grain size with noticeable changes on the thermal stability for the five granulometric classes considered. Particularly the quantity of nitrogen content measured (after degassing) in each of the five granulometric classes increases with decreasing the particles size. This might justify why the calculated drag stress exerted by segregated impurities, second-phase particles and pores is effectively higher for small particles. This approach can give a methodology to modulate the microstructure of bulk nanostructured/ultrafine metals just selecting different combination in terms of particle size.     

Tableting of Eudragit RS and propranolol hydrochloride solid dispersion: effect of particle size, compaction force, and plasticizer addition on drug release

The application of a solid dispersion (SD) system of propranolol HCl and Eudragit RS was evaluated in the preparation of prolonged release tablets. The effects of SD size fraction, compaction force, and inclusion of plasticizers [namely diethylphtalate (DEP) and triethylcitrate (TEC)] on crushing strengths of matrices and release profile of drug were also investigated. The results showed that when compressed as a tablet, the SD system was more efficient in prolonging drug release than physical mixture. This effect was due to formation of much harder tablets of the SD system (crushing strength 8.5 kg) compared with those of physical mixtures (crushing strength 2.7 kg). All matrices of the SD system showed release rate patterns that were best described by the Higuchi equation. It was also shown that the rate of drug release decreased from 19.8% to 9.13% min^- 1/2 as the SD size fraction decreased from 300-350 to 125-250 µm. However, further reduction of size fraction did not significantly affect tablet crushing strength and drug release rate. Increase in compaction force from 5 to 30 kN increased the crushing strength of matrices from 2.9 to 13.6 kg. However, the rate of drug release remained nearly unchanged beyond compaction pressure of 10 kN, indicating that crushing strength of matrices in the range of 8.5-13.6 kg did not affect drug release rate. The addition of 5% or 10% of either plasticizer (DEP or TEC) led to an increase in crushing strength of matrices and more retardation of drug release. This effect was more pronounced for higher concentrations of plasticizers. This effect was probably due to more plastic deformation of matrices under the compaction force, which helped matrices to retain their shape throughout the dissolution test.     

Quantitative evaluation of effects of shape and size of artificially introduced alumina particles on the fatigue strength of 1.5Ni---Cr---Mo (En24) steel

In order to investigate the effects of non-metallic inclusion on the fatigue strength of high-strength steels, in 1963 W.E. Duckworth and E. Ineson conducted fatigue tests using specimens that contained artificially added spherical and angular alumina particles of various controlled sizes. Although the fatigue tests were carried out under the same nominal stresses in rotating-bending and tension-compression tests the fatigue lives of specimens showed a large scatter. They reported in some detail typical complicated aspects of the effects of non-metallic inclusions on the fatigue strength.

In the present study the authors have reanalysed these complicated fatigue data using the prediction equation that was proposed by Murakami et al for the quantitative evaluation of the effects of small defects on fatigue strength. The geometrical parameter that controls the scatter of the fatigue strength is the square root of the projection area √ area and not the shape of the inclusions, whether they are spherical or angular. It is shown from the data from the failed specimens that the fatigue strength of materials containing inclusions larger than a critical size can be predicted by the Vickers hardness (Hv) of the matrix and √ area of the inclusion regardless of the shape.