Impact of solvents during wet stirred media milling of cross-linked biopolymer suspensions

The aim of this study was to examine the impact of solvents during the wet stirred media milling of cross-linked biopolymers considering breakage kinetics, physical stability of the suspensions, and microhydrodynamics. To this end, a model cross-linked biopolymer, sodium starch glycolate (SSG), was milled in acetone and water wherein SSG was non-swellable and swellable, respectively. Suspensions containing SSG particles with and without two stabilizers, i.e., hydroxypropyl cellulose and sodium dodecyl sulfate, were prepared. The temporal evolution of the SSG particle size during the milling was tracked by laser diffraction. Swelling of the SSG particles in water was independently characterized using microscopy and laser diffraction, which revealed fast swelling within a few minutes. Results also suggest that SSG particles were broken faster in water than in acetone, and stabilizers could not prevent severe aggregation in acetone. Despite the greater viscous dampening in water, water was more favorable for faster production of stable suspensions than acetone. The superior performance of aqueous milling was primarily attributed to favorable nanoparticle stabilization in water and secondarily to swelling-induced softening and coarsening of SSG particles. Hence, also being environmentally benign and safe, it is preferred over organic solvent-based milling for the preparation of cross-linked biopolymer nanosuspensions.     

Influence of particle size of the dispersoid on compressibility and sinterability of TiO2 dispersed Al 7075 alloy composites prepared by mechanical milling

Particulate TiO₂ (with varying particle size produced by mechanical milling) dispersed AA7075 composites are synthesised by short duration milling (10 min) followed by room temperature unidirectional compaction (with varying pressure) and sintering. Apparent and relative density of the alloy powder and composites are measured. The effect of reinforcement particle size on the compressibility behaviour of the composites is demonstrated. Mechanically milled (for 25 h) alloy powder shows lower relative density than coarse alloy powder. In addition, compressibility of the alloy composites decreases with decreasing particle size of the reinforcement. In contrast, the sinterability of the composites increases with decreasing dispersoid’s size due to easy filling up of finer pores and particle induced precipitation.     

On CTE of SPS consolidated SiCp/Al composites with various particle size distributions

Abstract

The coefficient of thermal expansion (CTE) of spark plasma sintering consolidated SiC_p/Al composites with various size distributions was investigated with the combination of experimental measurements and modelling analyses. The CTE of the composites decreased with increasing particle volume fraction, and large particles played a major role in the decline of CTE. The measured CTE lay between the predictions of Kerner model and Schapery lower bound, but the possible formation of percolating particle network and the influence of matrix plasticisation led to the slight deviation of the experimental values from model predictions. A CTE peak appeared for all the composites with increasing temperature to about 250–300°C due to the action of matrix plasticisation filling the microvoids in the composites. The composites with mixed particles of substantially different sizes were prone to concentrate thermal stresses on large particles, which induced an early appearance of matrix plastic deformation that can result in a comparably low CTE peak temperature.     

Image analysis algorithm and verification for on-line molecular sieve size and shape inspection

An online machine vision inspection method is proposed to implement feedback control of molecular sieve growth process in rotary drum granulation. An experimental platform, comprising of a high-resolution digital camera and an image analysis system, has been developed to confirm the validity of the method on particle size distribution (PSD) and sphericity measurements. Experiments were performed with non-uniform molecular sieve particles (1–3 mm diameter) obtained from production line. The particle images are first obtained through digital camera and are then processed by image analysis system. After separating the overlap particles and removing non-target particles of the images, the molecular sieve size and shape are computed in less than 0.9 s. The validity of the size measuring accuracy is confirmed through comparing with the results from micrometer. The experimental results show that the repetitive precision of the proposed inspection system is about ±1%, the diameter measurement error between image method and micrometer is about ±3%, single image inspection speed is around 0.9 s/frame. The proposed method is reliable to provide feedback information for control system in rotary drum granulation.     

Modeling of particle size distribution and energy consumption of wet milled maize at varying soaking period and method in the production of Ogi

Energy consumptions and particles size distribution of soaked maize grains at varying time were studied and modeled. Rosin–Rammler–Bennet (RRB) model well fitted first milling size distribution with a high coefficient of determination (R²) and low root mean square error (RSME). The milling energy of maize grains decreased significantly (p?<?0.05) with increase in soaking time. The milling energy decrease from 32 to 8.72?kWh/kg and 32.00 to 9.00?kWh/kg for maize variety E9W at 24th hour soaking conditions of 28 and 65°C, respectively. Similar observations for A4W, B2Y and C3Y at 24?h of soaking were recorded. The Work index, Kick’s and Rittinger’s constants decreased with increase in soaking time. There was significant difference (p?<?0.05) in values obtained for Bond work index, Rittinger’s and Kick’s constants; these decreased with increase in soaking time. Predicted energy consumption followed similar trend. The interaction effect between energy consumption, Moisture content, and Milling time showed a high R² (0.8767–0.99349); while the regressed model for determining energy consumption from relationship between the mass, moisture content, milling time and the ratio of the geometric diameter mean and final size of the product were also established in this work with R² ranging from 0.9355 to 0.967.     

Relationship between water distribution and shear properties of wet granules

Wet granules are utilized in various fields due to their high workability and cost performance. However, it is difficult to observe the water distribution of wet granules directly because such granules only contain extremely small amounts of water. In this study, the water distribution of wet granules was investigated using a confocal laser microscope and quantitatively analyzed using an autocorrelation function. Furthermore, the correlation length of wet granules estimated from the autocorrelation function was compared with the shear properties of the granules. Consequently, it was found that the internal friction angle of wet granules decreased as the water volume between particles increased. These results indicated that the water in wet granules works as a drag reduction agent under shear conditions.     

Effect of the milling method and particle structure on the color tone of (Cr,Fe)2O3 inorganic black masterbatch pigment

(Cr, Fe)₂O₃ pigment was milled using different techniques into the same particle sizes to investigate the influence of milling processes on its properties. The research showed that milling type resulted in significant color differences, accompanied by the pigment color changing from intense reddish-brown to dark brown. Differences in the morphology of the particles embedded in the plastic matrix led to different light scattering, which is observed as a decrease in the color saturation of the pigment. Particle size distribution (PSD) was characterized by measuring with a laser diffraction particle size analyzer. Pigments were milled down to 4 µm in all milling methods. The very small particles in the pigment affected the light scattering and the color tone. The particle size of the pigment milled by the planetary mill was D₁₀ = 0.035 μ ± 0.1. Color values of the plastic plates were measured according to CIE laboratory analysis. The pigment milled with the planetary mill was lighter, greener, and yellower (ΔL*=4.15, Da*=3.68, Db*=2.96). The pigment milled with the jet-mill was closest to the pigment color after calcination. The pigment milled with ball mill was slightly greener than the values after calcination (Da*=1).     

Preparation of submicron calcite particles by combined wet stirred media milling and ultrasonic treatment

This paper investigates the grindability of calcite powder (D₅₀ = 6.68 µm) to submicron particle sizes using stirred media mill (0.75 l) and ultrasonic generator (400 W, 24 kHz). The present study focuses directly on the comminution of calcite powder in water media by combined stirred milling and ultrasonic treatment and effects of some operational parameters such as grinding time (10–30 min), ultrasonic power (40–100% µm as amplitude settings), and solid ratio (10–30% w/w) on comminution. Experimental results have been evaluated on the basis of product size and width of particle size distribution.     

A quality-by-design study to develop Nifedipine nanosuspension: examining the relative impact of formulation variables,wet media milling process parameters and excipient variability on drug product quality attributes

Abstract

Wet milling is a multifunctional and the most common method to prepare a drug nanosuspension for improving the bioavailability of poorly water soluble drugs. A suitable way of preparing a high drug-loaded nifedipine nanosuspension using wet stirred media milling was investigated in the present study. Nifedipine, a poorly water soluble drug, was selected as a model drug to enhance its dissolution rate and oral bioavailability by preparing an appropriate crystalline nanosuspension. Process parameters, such as milling media volume, milling speed and milling time, were optimized using the one variable at a time (OVAT) approach. A similar method was used to select an appropriate polymeric stabilizer and a surfactant from different categories of polymeric stabilizers (HPC SL, HPC SSL Soluplus®, Kollidon^® VA 64 and HPMC E 15) and surfactants (Poloxamer 407, Kolliphor TPGS and Docusate sodium). A systematic optimization of critical formulation parameters (such as drug concentration, polymer concentration and surfactant concentration) was performed with the aid of the Box-Behnken design. Mean particle size, polydispersity index and zeta potential as critical quality attributes (CQAs) were selected in the design for the evaluation and optimization of the formulation and validation of the improved product. The nifedipine nanosuspension that was prepared using HPC and poloxamer 407 was found to be most stable with the lowest mean particle size as compared with the formulations prepared using other polymeric stabilizers and surfactants. The optimized formulation was further spray-dried and characterized using the Fourier Transform Infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), polarized light microscopy (PLM) and in-vitro dissolution study. Results have shown no interaction between the drug particles and stabilizers, nor a reduction in the crystallinity of drug, nor an increase in the saturation solubility and rapid in vitro dissolution as compared with pure nifedipine crystals. Thus, the current study supports the suitability of the wet stirred media milling method and a combination of HPC SSL and poloxamer 407 as stabilizers for the preparation of nifedipine nanosuspension.     

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.     

Cutter size optimisation and interference-free tool path generation for five-axis flank milling of centrifugal impellers

Strategies for cutter size optimisation and interference-free tool path generation are proposed for five-axis flank milling of centrifugal impellers. To increase the material removal rate and provide a stronger tool shank during flank milling, the cutter size is first maximised under a set of geometric constraints. The tool path is then globally optimised in accordance with the minimum zone criterion for the determined optimal cutter size. Aside from the local interference of the cutter with the design surface, the global interferences with the hub surface and the adjacent blade surface are also considered in the optimisation models. Interference is indicated by the signed distance from the sampled point on the blade surface to the tool envelope surface. This distance is calculated without constructing the envelope surface. On the basis of the differential property of the distance function, we choose a sequential linear programming method in implementing the optimisations. This approach applies to generic rotary cutters, such as cylindrical and conical tools. Simulations are conducted to obtain the optimal cutter size and generate an interference-free tool path for a practical impeller. Simultaneously, a software module that can generate tool envelope surfaces and verify geometric errors is used to validate the proposed method.     

Effects of particle size and distribution on the mechanical properties of SiC reinforced Al-Cu alloy composites

This paper studied the combined effects of particle size and distribution on the mechanical properties of the SiC particle reinforced Al-Cu alloy composites. It has been shown that small ratio between matrix/reinforcement particle sizes resulted in more uniform distribution of the SiC particles in the matrix. The SiC particles distributed more uniformly in the matrix with increasing in mixing time. It has also been shown that homogenous distribution of the SiC particles resulted in higher yield strength, ultimate tensile strength and elongation. Yield strength and ultimate tensile strength of the composite reinforced by 4.7 μm sized SiC particles are higher than those of composite reinforced by 77 μm sized SiC particles, while the elongation shows opposite trend with yield strength and ultimate tensile strength. Fracture surface observations showed that the dominant fracture mechanism of the composites with small SiC particle size (4.7 μm) is ductile fracture of the matrix, accompanied by the “pull-out” of the particles from the matrix, while the dominant fracture mechanism of the composites with large SiC particle size (77 μm) is ductile fracture of the matrix, accompanied by the SiC particle fracture.     

Application of TUSSIM with a variable Tromp curve for predicting optimal operation of multi-compartment mills with various ball size distributions

A true unsteady-state simulator (TUSSIM) for ball milling was integrated with a variable Tromp curve for classification to simulate and optimize closed-circuit, multi-compartment cement ball milling. Using representative model–operational parameters from available literature, we first investigated the system dynamics for a two-compartment mill. Then, various simulations examined the impacts of closed-circuit vs. open-circuit operation, number of compartments, and various ball size distributions. Our results suggest that integrating an air classifier into an open-circuit ball mill can increase the production rate by 15% or increase the cement-specific surface area by 13%. A single-compartment mill entails a pre-milled feed for proper operation, whereas a two-compartment mill yields a finer cement product than a three-compartment mill. Uniform mass distribution of balls led to slightly finer product than uniform surface area or number distributions, while the impact of a classifying liner was negligibly small. Finally, we identified optimal ball mixtures in a two-compartment mill using a combined global optimizer–DAE solver, which suggests 14% capacity increase with desirable cement quality. Overall, TUSSIM’s results are not only in line with limited, full-scale experimental studies and industry best practices, but also provide fundamental process insights, while enabling process optimization with tailored ball mixtures in different compartments.     

Particle size distribution control and related properties improvements of tungsten powders by fluidized bed jet milling

Fine grinding process of different particle size tungsten powders was carried out by fluidized bed jet milling. The results showed that the jet milling treatment caused deagglomeration of tungsten powders, which led to particles sufficient dispersion and narrow particle size distribution. Grinding gas pressure of 0.70 Mpa made the particles achieve high speed which promoted the particles collision contributing to particle dispersion and shape modification. For tungsten powder with particle size of 3 μm FSSS, a higher packing density with 5.54 g/cm³ was obtained, compared with the 3.71 g/cm³ of the original powder. For tungsten powder with particle size of 1 μm FSSS, the big agglomerates disappeared and the particle size distribution become narrower, while small aggregates about 2–3 μm still exist after the jet milling process. For tungsten powder with particle size of 5 μm and 10 μm FSSS, different medium diameter particle size and narrow particle size distribution of monodisperse tungsten powders can be produced by the optimized jet milling parameters. More important, the effective dispersion, favorable shape modification and precise classification have been achieved in the simple process.     

Determination of particle size distributions and the degree of dispersion in nanocomposites

Objective of this study was the investigation of measurement techniques to determine the quality of the dispersion process of nanoparticles in polymer composites. In order to prepare the matrix suspension, alumina nanoparticles were dispersed applying shear mixing techniques in a high performance laboratory kneader. The product quality in liquid state was determined by means of dynamic light scattering (DLS) and centrifugal sedimentation analysis (CSA). However, particle measurements in carrier fluids like epoxy resin are complex and challenging. Measuring values like particle size distribution and grade of homogeneousness are strongly influenced by the sample preparation and adjustments of the measuring device. Within this study the machine settings and the formulation was analysed systematically. Hereby an identification of the key parameters and an optimisation of the measuring process were possible. Additionally, the composite was cured and analysed by scanning electron microscopy (SEM). Finally all measuring techniques were evaluated and compared among each other. Thus, DLS is the fastest method to measure spherically particles in the liquid matrix, CSA allows a certain deviation from the spherical shape and SEM gives a qualitative impression of the final particle size in cured composite condition.     

Shear properties and water connectivity of wet granules at high solid content concentration

The inner liquid distribution in wet granules strongly influences their mechanical properties. In this study, we examined the shear properties (internal friction angle, cohesion, storage modulus and loss modulus) of wet granules composed of graphite particles and water, and determined their inner water connectivity using X-ray refraction contrast imaging computed tomography (CT) to elucidate their correlation. At high solid content concentration (C_SC) region (C_SC = 85 wt.%), internal friction angle of wet granules was slightly lower than that of wet granules with lower C_SC, and their cohesion becomes almost zero. Furthermore, storage modulus of wet granules at C_SC = 85 wt.% was the highest among all wet granules. The X-ray CT and scanning electron microscopy (SEM) observations revealed that the water connectivity in the wet granules was in the pendular state and graphite particles fractured under shear test at C_SC = 85 wt.%. From these results, it can be concluded that lower shear cohesion at C_SC = 85 wt.% is caused by an increase in the number of isolated liquid bridges, and particle fracture results in a decrease in the internal friction angle owing to decreasing roughness of shear plane. Furthermore, the particle fracture also resulted in the higher storage modulus at C_SC = 85 wt.% in rheological measurements.     

Particle size distribution and dislocation density determined by high resolution X-ray diffraction in nanocrystalline silicon nitride powders

Two silicon nitride powders were investigated by high resolution X-ray diffraction. The first sample was crystallized from the powder prepared by the vapour phase reaction of silicon tetrachloride and ammonia while the second was a commercial powder produced by the direct nitridation of silicon. Their particle size and dislocation density were obtained by the recently developed modified Williamson–Hall and Warren–Averbach procedures from X-ray diffraction profiles. Assuming that the particle size distribution is log-normal the size distribution function was calculated from the size parameters derived from X-ray diffraction profiles. The size distributions determined from TEM micrographs were in good correlation with the X-ray results. The area-weighted average particle size calculated from nitrogen adsorption isotherms was in good agreement with that obtained from X-rays. The powder produced by silicon nitridation has a wider size distribution with a smaller average size than the powder prepared by vapour phase reaction. The dislocation densities were found to be between about 10¹⁴ and 10¹⁵ m⁻².     

Artificial neural network analysis of the effect of matrix size and milling time on the properties of flake Al-Cu-Mg alloy particles synthesized by ball milling

In this study, the effect of matrix size and milling time on the particle size, apparent density, and specific surface area of flake Al-Cu-Mg alloy powders was investigated both by experimental and artificial neural networks model. Four different matrix sizes (28, 60, 100, and 160?µm) and five different milling times (0.5, 1, 1.5, 2, and 2.5?h) were used in the fabrication of the flake Al-Cu-Mg alloy powders. A feed forward back propagation artificial neural network (ANN) system was used to predict the properties of flake Al-Cu-Mg alloy powders. For training process, the ANN models of the flake size, apparent density, and specific surface area have the mean square error of 0.66, 0.004, and 0.01%. For testing process, it was obtained that the R² values were 0.9984, 0.9998, and 0.9932 for the flake size, apparent density, and specific surface area, respectively. The degrees of accuracy of the prediction models were 95.145, 99.705, and 94.25% for the flake size, apparent density, and specific surface area, respectively.     

Preparation of battery-grade Li2CO3 efficiently by high shear dispersion at low temperature

With the significant increase of market demand, battery-grade lithium carbonate has become an imperative research. However, it is difficult for commercially available battery-grade lithium carbonate to simultaneously meet all criteria such as dispersion, particle size, particle size distribution, and purity. Here, we proposed a flexible method to prepare battery-grade lithium carbonate with small particle size, uniform size distribution, high purity, and good dispersion by using a high shear dispersion reactor under low-temperature conditions. First, a numerical simulation model was established, and the feasibility of this proposed method was verified by computational fluid dynamics (CFD). Then, the factors of yield optimization on Li₂CO₃ were analyzed based on response surface methodology (RSM) by using a 3-level 4-factor Box-Behnken statistical design with a fixed lithium solution concentration as the input parameter. Moreover, the reaction kinetics, size distribution, crystal morphology, and purity of Li₂CO₃ were investigated. The obtained Li₂CO₃ possessed the average particle size in 5.85 μm and total particle size range from 1.56 to 12.97 μm, which both exhibited a ten-fold reduction compared with it prepared under conventional preparation conditions. Finally, the Li₂CO₃ products with 99.81% purity met the requirements of the Chinese non-ferrous metal industry standard (YS/T582-2013) for battery-grade Li₂CO₃. We anticipate that this work may shed light on developing efficient and controllable method for the preparation of battery-grade Li₂CO₃.     

Inline method of droplet and particle size distribution analysis in dilute disperse systems

In the present article a measurement method of particle size distributions (PSD) in industrial installations which use a dispersed phase of low concentration (like spray dryers or spray scrubbers) is introduced. A new type of inline-measurement system has been developed and designed to work in spray drying conditions. A standard digital camera is used to record shadows of flowing particles inside the spray drying chamber. Collected images were analyzed by a newly developed software which recognizes particles only in the focus area and eliminates several types of artifacts. The constructed prototype of the PSD inline-analyzer was installed and used to monitor large laboratory scale spray dryer. All data collected by the designed system during the spray drying experiments were compared with data measured with an offline reference system to show accuracy of the new measurement technique.