基于数字图像分析的颗粒生长监测技术

为了实现滚筒造粒过程中对球形颗粒生长的精确控制,提出基于数字图像分析技术的球形颗粒尺寸在线检测方法,使用工业数码相机搭建颗粒图像采集实验平台,开发图像分析软件。结果表明,该方法对单幅图像的分析时间为0.9 s;系统对粒度检测的可重复精度约为±1%,与千分尺测量的粒度相比,误差约为±3%;该方法可用于构造造粒机的视觉反馈控制系统,以实现颗粒生长过程的闭环控制。     

Numerical studies of particle segregation in a rotating drum based on Eulerian continuum approach

Solid–solid–gas three-phase particle segregation in a half-filled rotating drum is simulated using Eulerian continuum approach coupling the kinetic theory of granular flow. A dynamic angle of repose fitting (DARF) method is proposed to determine granular kinetic viscosities of particles of six different sizes moving in the drum rotating at 10 rpm, 20 rpm or 30 rpm. The DARF granular kinetic viscosity increases and decreases with the increasing of particle size and drum rotational speed, respectively. The determined DARF granular viscosity values are used to simulate size-induced particle segregation in a rotating drum. The simulated small-particle-rich segregation structure shows a central small-particle-rich band together with two small-particle-rich side wings. The size of the wings decreases with the increasing of the drum rotational speed. The formation of radial segregation core and axial segregation bands qualitatively agree with the experimental observations.     

In-line particle sizing for real-time process control by fibre-optical spatial filtering technique (SFT)

Sizing of particles in industrial processes is of great technical interest and therefore different physical-based techniques have been developed. The objective of this study was to review the characteristics of modern sizing instruments based on a modified fibre-optical spatial filtering technique (SFT). Fibre-optical spatial filtering velocimetry was modified by fibre-optical spot scanning in order to determine simultaneously the size and the velocity of particles. Sizing in-line instruments of Parsum GmbH use these measuring principles and may be adapted to different process conditions. Particles with sizes of 50–6000 μm and velocities up to 50 m/s may be measured by the probe system IPP 70. An overview is given to real-time sizing of particles in different technical applications: fluid-bed granulation, high shear wet granulation, Wurster coating, mixing, spray drying, crystallization and milling.     

A method to predict nuclei size distributions for use in models of wet granulation

Models of granulation and agglomeration are becoming more sophisticated and accurate, but nucleation is poorly understood. Models of granulation processes typically either use simplistic nucleation assumptions; complex multi-phase simulations or deliberately focus on the final granulation stages only. Here, we validate a simple method to generate nuclei size distributions using the dimensionless spray flux parameter, for future use in granulation models in the drop controlled regime.Dimensionless spray flux describes the spray density in the spray zone, which is closely related to the Poisson distribution. A simple model to estimate the nuclei size distribution at a range of spray flux conditions was compared with data generated in a previous study. The simulations were in reasonable agreement with experimental data at low penetration time and low spray flux (Ψ_a < 0.3) but diverged when either the spray flux was >0.5. For a longer penetration time system, the simulations and experimental results agreed up to Ψ_a = 0.5. Multi-modal experimental results could not be modeled. Spray flux derived models of nuclei size distributions are useful nucleation granulation models, provided that the simulations are restricted to the drop controlled regime (Ψ_a < 0.1) and extended to higher spray fluxes with caution.     

Upgrading of low-grade gold ore samples for improved particle characterisation using Micro-CT and SEM/EDX

There is a considerable challenge in accurate characterisation of gold (Au) particles in low-grade plant ore mineral samples. This is particularly true for automated mineralogical tools such as X-ray micro-computed tomography (Micro-CT) and scanning electron microscopy (SEM), where the need for statistically meaningful numbers of particles requires many sections to be analysed. Whiles the Vertical Gas Stream (VGS) elutriator is suitable for coarse particle upgrading (i.e. >38 μm), the performance is poor for finer particles (i.e. <38 μm). Consequently, the system has been modified to Vertical Water Stream (VWS) elutriator using higher density fluid (i.e. water) to enable analysis of Au particles below 38 μm. In this work, the VGS system was used to upgrade Au particles in the ?53 + 38 μm size fraction (in rougher concentrate, rougher tailings, regrind mill discharge and regrind cyclone underflow) and the VWS system was used to upgrade Au particles in the ?38 μm size fraction of the regrind mill discharge sample. The VWS elutriator was calibrated using galena (specific gravity, S.G. of 7.58) and quartz (S.G. of 2.65) particles of <38 μm size as model minerals. From the calibration tests, partition curves as a function of particle size were generated. Using these measurements, theoretical partition curves for Au (S.G. of 19.3) have been calculated. The VWS concentrate was characterised using Micro-CT and compared with SEM coupled with energy dispersive X-ray (EDX) analysis of ?53 + 38 μm ore size fraction of the VGS concentrate of the four sample streams. The Micro-CT analysis of VWS Au concentrate showed that sufficient particles (Au) can be upgraded. SEM/EDX results indicate that regrind does not affect changes in free Au particle morphology, aspect ratio and frequency of shearing damage in the ?53 + 38 μm size fraction. Cyclone classification of the regrind mill discharge in the ?53 + 38 μm size fraction appears to perform surface cleaning by exposing obscuring silver (Ag) surfaces on Au particles in the mill discharge sample.     

Improving the recovery of low grade coarse composite particles in porphyry copper ores

The flotation behaviour of low grade, coarse composite particles for two porphyry copper ores was studied. Different grinding times were employed to obtain size distributions for the flotation feed (d₈₀) ranging from 150 to 320 μm. Copper containing particles in the fine to intermediate size ranges were recovered in the rougher flotation stage. The rougher tailing was then screened through a 75 μm laboratory sieve. The +75 μm fraction was conditioned with a longer chain collector and floated in either normal viscosity (water) or high viscosity (glycerol–water mixture) medium. The recovery of copper was analysed on an un-sized and size-by-size basis. The recovery of coarse composite copper bearing particles was found to increase in high viscosity medium, even when the liberation of copper bearing minerals was only as low as 10%. The ability to recover these types of particles may result in a reduction in energy consumption in grinding due to the ability to achieve higher overall recovery of valuable mineral at coarse particle size distribution.     

The effects of RESS parameters on the diclofenac particle size

The RESS method was used to manufacture the fine particles of diclofenac. A reduction in particle size increases the dissolution rate of the drugs in the biological fluids and enhances the bioavailability of them in body. CO2 was used as the supercritical fluid because of its mild critical temperature (31.1 °C) and pressure (7.38 MPa). In this study, effect of extraction temperature (313–333 K), extraction pressure (14–220 MPa), spraying distance (1–10 cm), nozzle length (2–15 mm) and effective nozzle diameter (450–1700 μm) were investigated.Based on the different experimental conditions, the average particle size of diclofenac was between 10.92 and 1.33 μm. The size and morphology of the micronized diclofenac particles were monitored by scanning electron microscopy (SEM). The SEM images show a successful size reduction of virgin diclofenac particles. In all the experiments, the parameters had moderate effect on the mean particle size of the diclofenac. Also, the morphology of the processed particles was change to quasi-spherical and irregular while the virgin particles of diclofenac were irregular in shape.     

Synthesis and characterization of the iron oxide magnetic particles coated with chitosan biopolymer

Magnetic particles are extremely interesting for several biomedical applications; amongst these are therapeutic applications, such as: hyperthermia and release of drugs. The use of magnetic particles to induce hyperthermia in biological tissues is an important factor in cancer therapy. The aim of this study was to prepare and characterize iron oxide magnetic particles coated with biopolymer chitosan, and also to produce ferrofluids from the magnetic particles. The iron oxide magnetic particles (IOMP) were coated with chitosan (CS) by spray-drying method using two IOMP/coating ratios (IOMP/CS = 1.6 and IOMP/CS = 4.5). The magnetic particles were characterized by way of scanning electronic microscopy and energy-dispersive X-ray. The analysis by energy-dispersive X-ray was carried out to determine the chemical composition of particles in samples. The size distribution the iron oxide magnetic particles uncoated and coated were evaluated by the laser diffraction analysis and image analysis, respectively. Amongst the prepared ferrofluids, the sample IOMP/CS = 1.6 proved to be the one that has brought about the best results in therapeutics applications, such as in hyperthermia treatment. This sample was placed within an alternating magnetic field during 40 min, it was observed that 1 °C heated in 3 min and underwent a temperature variation of 7 °C, since it varied from 25 °C to 32 °C. Considering that the experiment would be carried out at body temperature 37 °C, probably, the temperature variation would be very close to the one reported at 25 °C. In such a way, the cancerous cells would reach 44–45 °C and at such temperatures the cancer cells generally perish.     

Formation of ZnS nano- and microparticles from thiourea solutions

Effects of temperature, concentration of thiourea and reaction conditions (thermal heating and microwave irradiation) on morphological properties of ZnS particles obtained by sedimentation from 0.01, 0.1 and 1 М zinc nitrate solutions are studied. It is found that ZnS particles of two shapes are formed from thiourea solutions at a thermal heating (70–90 °С): agglomerated particles of the spherical shape with the dimensions of agglomerates 50–100 nm (particle size in agglomerates of 3–5 nm) and hexagonal columns in length up to 2 μm and diameter of 80–100 nm. At the microwave heating conditions (90 °С), irrespective of thiourea concentration formation of spherical ZnS particles with the size 0.6–1.2 μm is observed.     

Effects of the agglomerated states and the gap of coverage for admixed particles on particle-bed packing fractions

One of the techniques used to decrease the cohesive force between particles is the admixing of nano-particles. However, the optimal conditions that will produce a minimum amount of force have not been established. In this study, we investigated the effects of the agglomerated state and the gap of coverage for admixed particles on particle-bed packing fractions in uni-axial compression. The main particles were made up of 397 nm silica particles. The admixed particles included 8, 21, 62 and 104 nm silica particles. The main and admixed particles were mixed using a mortar and pestle for 5 min for various mass ratios. SEM images were used to analyse the coverage diameter and the surface coverage ratio. As a result, the packing fractions with admixed particles of 8 and 21 nm were larger than when admixed particles were not used, and these admixed particles adhered onto the surface of the main particles as agglomerates. However, packing fractions of 62 and 104 nm were almost constant and were independent of the coverage states of admixed particles. Furthermore, these admixed particles with relatively larger diameters were adhered onto the surface as single particles. From the coverage diameter and actual surface coverage ratio obtained by the SEM image, the average gaps between agglomerates of 8 and 21 nm on the main particle were calculated. When the gap approached twice the size of the coverage diameter, packing fractions of 8 and 21 nm proved to be the maximum values. However, when the gap was less than the coverage diameter, the packing fractions deteriorated.     

A novel route to cysteine capped Au–CdSe hybrid nanoparticles

We report the synthesis of cysteine Au–CdSe hybrid core–shell nanoparticles via a facile ‘green’, solution based route. The absorption spectrum of the hybrid particles displays unique excitonic features that vary from CdSe and Au. The X-ray diffraction pattern shows peaks attributed to both the parent materials. The transmission electron microscopy (TEM) images shows well aligned particles with an average size of 15 ± 3 nm. The High Resolution TEM image confirms the core/shell structure of the particles.     

Influence of duty cycle on the microstructure and microhardness of pulse electrodeposited Ni–CeO2 nanocomposite coating

The Ni–CeO₂ nanocomposite coatings have been synthesized by pulse electrodeposition technique with different duty cycles (6, 9 and 17%) from a Watts-type electrolyte containing nano-sized CeO₂ particles. The XRD results show that the (2 0 0) orientation is dominant over (1 1 1) orientation in the Ni–CeO₂ nanocomposite coatings prepared with 6 and 17% duty cycles, while the opposite is true for the sample prepared with 9% duty cycle. The maximum amount of CeO₂ (10 wt%) incorporation in the coating occurs at 9% duty cycle. The crystallite size changes from micrometer to nanometer as the duty cycle changes from 6 to 9%. The hardness increases as the duty cycle increases from 6 to 17%. However, a coating with optimum smoothness and small number of microcracks is obtained at 9% duty cycle.     

Influence of processing method on the properties of hydroxyapatite nanoparticles in the presence of different citrate ion concentrations

The objective of this study was to investigate the effect of processing methods on the formation of ultra fine hydroxyapatite (HAp) nanoparticles in the presence of citrate ions and analyze their various physical properties. The addition of the citrate ions was found to reduce the size and prevent the agglomeration of HAp particles dramatically in the high gravity (HG) method compared to precipitation method. In precipitation method, the particle size reduced from 300 ± 70 nm to 90 ± 20 nm with the addition of citrate ions. In high gravity method, the particle size decreased more significantly from 80 ± 10 nm to 13 ± 5 nm with the addition of citrate ions. Furthermore, more uniform size distribution of nanoparticles was achieved in high gravity method. X-ray diffraction of nanoparticles prepared in both method exhibited slight shift of peaks to the higher angle with the addition of citric acid, indicating the incorporation of carbonate (CO₃) content in the HAp nanoparticles irrespective of the particle size. The mechanical properties of HWMPE matrix composite reinforced with nanoparticles was examined and this nanocomposite with nanoparticles prepared in high gravity method with the addition of citrate ions showed increased mechanical strength due to the considerable reduction in the particle size and higher uniformity of the particles. In vitro cellular analyses of the nanoparticle prepared in high gravity with the addition of citrate ions also displayed the most pronounced spreading of cell growth.     

An investigation of the effect of SiC particle size on Cu–SiC composites

In this study mechanical properties of copper were enhanced by adding 1 wt.%, 2 wt.%, 3 wt.% and 5 wt.% SiC particles into the matrix. SiC particles of having 1 μm, 5 μm and 30 μm sizes were used as reinforcement. Composite samples were produced by powder metallurgy method and sintering was performed in an open atmospheric furnace at 700 °C for 2 h. Optical and SEM studies showed that the distribution of the reinforced particle was uniform. XRD analysis indicated that the dominant components in the sintered composites were Cu and SiC. Relative density and electrical conductivity of the composites decreased with increasing the amount of SiC and increased with increasing SiC particle size. Hardness of the composites increased with both amount and the particle size of SiC particles. A maximum relative density of 98% and electrical conductivity of 96% IACS were obtained for Cu–1 wt.% SiC with 30 μm particle size.     

An investigation on process of seeded granulation in a continuous drum granulator using DEM

Numerical simulation of wet granulation in a continuous granulator is carried out using Discrete Element Method (DEM) to discover the possibility of formation of seeded granules in a continuous process with the aim of reducing number of experimental trials and means of process control. Simple and scooped drum granulators are utilized to attain homogenous seeded granules in which the effects of drum rotational speed, particles surface energy, and particles size ratio are investigated. To reduce the simulation time a scale-up scheme is designed in which a dimensionless number (Cohesion number) is defined based on the work of cohesion and gravitational potential energy of the particles. Also a mathematical/numerical method along with a MATLAB code is developed by which the percentage of surface coverage of each granule is predicted precisely. The results show that use of continuous granulator for seeded granulation is promising provided that a high level of shear is considered in the granulator design, i.e. using baffles inside drum granulators is essential for producing seeded granules. It is observed that the optimum surface energy for seeded granulation in scooped granulator (used in this study) with rotational speed of 50 rpm is 3 J/m², which is close to the value predicted by the concept of Cohesion number. It is also shown that increasing the seed/fine size ratio enhances the seeded granulation both quantitatively (60% increase in seeds surface coverage) and qualitatively (more homogeneous granules).     

Microstructure and mechanical properties of 12 wt.% Cr ferritic stainless steel with Ti and Nb dual stabilization

TCS stainless steel is a 12 wt.% Cr ferritic stainless steel with 0.040 wt.% Ti and 0.096 wt.% Nb dual stabilization. This paper investigated the microstructures and mechanical properties of TCS stainless steel heated at 600–1300 °C for 10 min and followed water quenching. Results show the increasing of both tensile strength and hardness meanwhile the ductility and toughness have experienced the decreasing due to formation of martensitic phase and grain coarsening. In the unheated and heated TCS stainless steel, there are mainly two kinds of particles: Ti-rich particles in size of 2–5 μm; Nb-rich particles in size of 20–50 nm.     

Grey correlation analysis between strength of slag cement and particle fractions of slag powder

The particle size distributions of slag powder were investigated by Laser Scatter equipment. The influence of particle fractions of slag powder on the compressive strength of slag cement composed of 50% slag powder and 50% Portland cement was also studied by the method of grey correlation analysis. The results indicated that the volume fraction of particles 5–10 μm had a maximum positive effect on the mortar compressive strength of slag cement at 7 d and the volume fraction of particles 10–20 μm had a maximum positive effect on the mortar compressive strength at 28 d, whereas the volume fraction of particles larger than 20 μm had a negative effect on the mortar compressive strength at 7 and 28 d.     

Control of size and morphology in NiO particles prepared by a low-pressure spray pyrolysis

Nickel oxides (NiO) nano- and submicron particles were synthesized by a low-pressure spray pyrolysis system. Conversion of micrometer droplets into particles in the gas phase using NiO synthesis as a model was studied. Different types of precursors (aqueous Ni(NO₃)₂·6H₂O, NiCl₂, and Ni(HCO₂)₂·2H₂O) and temperatures from 400 to 900 °C have great influences on controlling the size and morphology of final particles. The results show that operation of a low-pressure system leads to substantial changes in size and morphology of particles, and that the NiO particles having size around 20 nm can be generated under a limited of conditions.     

Estimation of agglomerate size of multi-walled carbon nanotubes in fluidized beds

The objective of this study was to determine hydrodynamic characteristics of multi-walled carbon nanotubes (MWCNTs) agglomerates and examine their sizes. The bed collapsing process of MWCNTs agglomerates was found to be closer to that of Geldart group C particles than group A particles. Median diameters of MWCNTs agglomerates determined by sedimentation method at initial superficial gas velocity of 0.120 and 0.190 m/s were 157 and 221 μm, respectively. The size of these MWCNTs agglomerates in fluidization state was measured by image analysis using a high speed camera. Median diameters of these MWCNTs agglomerates in freeboard were increased from 138 to 189 μm as superficial gas velocity was increased from 0.088 to 0.190 m/s at static bed height of 0.16 m. Median diameter and size distribution determined by sedimentation method fitted well with those measured using image analysis. Results were reasonable at superficial gas velocity up to 0.190 m/s.     

Powder synthesis and properties of LiTaO3 ceramics

The LiTaO₃ powders with sub micrometer grade grain size have been synthesized successfully using a molten salt method. Lithium tantalate began to form at 400 °C reaction temperature and transformed to pure phase without residual reactants when it was processed at 500 °C for 4 h in static air. The undoped LiTaO₃ ceramics with a Curie temperature about 663 °C were obtained by pressureless sintering at 1300 °C for 3 h. The relative dielectric constant (ɛ_r) increases from 50 to 375 at temperature ranging from 30 to 663 °C and then decreases quickly as the temperature increases above 663 °C. The ceramics shows a relative dielectric constant of 49.4, a dielectric loss factor (tan δ) of 0.007, a coercive field (Ec) of 28.66 kV/cm and a remnant polarization (Pr) of 32.48 μC/cm² at room temperature.