Milled Particles Research Articles

Effect of ball size on steady state of aluminum powder and efficiency of impacts during milling

The concept of steady state milling time was examined for ball milling of aluminum powder. Four different set-ups of balls were used while the mill speed and charge ratio were kept fixed. Different criteria (morphology of particles, average particle size, deviation from the average particle size, lattice imperfections and change in crystallographic orientation) were used to study structural evolution of the milled particles and to compare the steady state time for the different milling conditions. Results showed that different criteria may not determine the same steady state time, however, all criteria were consistent in comparing efficiency of the different milling conditions. Moreover, it was found that at a given mill speed and ball to powder ratio (i.e. at a given consumed energy), a change in balls size and filling ratio of vials can improve milling efficiency. Finally, the effect of energy of each impact and the collective energy of all impacts were discussed.

Drug loading and release studies for milled silk particles of different sizes

Milled silk particles with volume median particle size (d(0.5)) of 7μm and 281nm as well as silk snippets were used for loading of model drugs Orange G, Azophloxine, Rhodamine B, and Crystal Violet. Loading and release of these chemicals depended on the size of silk particles, pH, and the structure and properties of model drugs. Both types of silk particles reached equilibrium loading in less than 10min due to high surface area whereas silk fibres needed more than 2–3days to reach equilibrium, depending on the drug type. The uptake rate in fibres could be improved by increasing temperature. Both fibres and particles could slowly release the drugs over many days at 37°C without a significant initial burst. As particle size decreased, the amount of model drug release also decreased. The release of drugs by the silk fibres was quicker than the silk particles.

Coercivity of Nd-Fe-B-type Fine Particles Prepared from Different Precursor Materials

Fine Nd-Fe-B-type particles were prepared by ball milling of different types of Nd-Fe-B precursor materials, such as die-upset magnet, HDDR-treated material, and sintered magnets. Coercivity dependence on the grain and particle size of the powder was investigated. Coercivity of the milled particles was reduced as the particle size decreased, and the extent of coercivity loss was dependent upon the precursor material. Coercivity loss in the finely milled particles was attributed to the surface oxidation. The extent of coercivity loss in the fine particles was closely linked to grain size of the precursor materials. Coercivity loss was more profound for the fine particles with larger grain size. Contrary to the fine particles from the sintered magnets with larger grain size the fine particles (~10 ㎛) from the die-upset magnet and HDDR-treated material with much finer grain size still retained high coercivity (＞ 10 kOe for die-upset magnet, ＞ 4 kOe for HDDR-treated material).

Dissolution Model of Ball Milled Rice Straw Particles in 1-Ethyl-3-Methyl Imidazolium Acetate at Elevated Temperature

In Asia, rice straw residue left in fields after harvest is often burned which causes air pollution or anaerobically digested in the rice patty moist soil to yield methane a greenhouse gas. Effective and efficient process strategies are needed to convert straw into fuels and feedstock’s which do not harm the environment. As a result, this study was undertaken to liquefy Japanese rice straw (RS) an abundant agricultural residue into a liquid after pre-treatment by ball-milling at various temperatures and develop a bioprocess model. Specifically, RS was ball milled into 75-100 μm size particles at temperatures of 60°C, 25°C, and -196°C (cryogenically) and dissolved by heating in 1-ethyl-3- methylimidazolium acetate [Emim][OAc] at different temperatures between 120° 140° and 160°C to understand the interactions between the process parameters. The milled RS powder particles were characterized by FTIR, XRD, BET analyzer and dissolution follow using optical microscopy. The particle dissolution was analyzed by measuring the particle light intensity ratio and particle cross-sectional area as a function of heating time. Higher milling temperature leads to amorphization of the RS cellulose accelerating dissolution. Measurement of the particle light intensity ratio was used to estimate the rice straw particles dissolution endpoint. A particle dissolution model indicated that ball milling temperature and [Emim][OAc] heating temperature strongly interacts influencing the dissolution time. To dissolve RS in [Emim][OAc] quickly, it important to reduce the crystallinity of the cellulose and increase the particle surface area by milling at higher temperature. It is believed this model would have applications to other biomass dissolution processes.

Influence of metal coating on sorghum milling process subjected to three body abrasion

The decline in feedstock quality related to corrugation wear, in milling machine rollers, is a significant factor in milling operation performance. The coating of materials exposed to such loading is a new technique which may assist in preserving the equipment performance. In the current study, mild steel rollers were coated with an epoxy matrix to investigate the influence of the coating on milling performance. Sorghum seeds were selected for milling under different rotational speed rollers with different gaps between the rollers. The milling performance was based on the number of milled particles, production rate (kg/h) and power consumption (kJ/kg). Scanning electron microscopy illustrated better cutting of sorghum particles for the epoxy coated rollers. In addition, statistical analysis shows that coating rollers with the epoxy matrix exhibited significant increases in the number of particles and in power consumption, and a reduction in production rate compared with uncoated rollers.

Investigation of the milling capabilities of the F10 Fine Grind mill using Box-Behnken designs

Size reduction or milling of the active is often the first processing step in the design of a dosage form. The ability of a mill to convert coarse crystals into the target size and size distribution efficiently is highly desirable as the quality of the final pharmaceutical product after processing is often still dependent on the dimensional attributes of its component constituents. The F10 Fine Grind mill is a mechanical impact mill designed to produce unimodal mid-size particles by utilizing a single-pass two-stage size reduction process for fine grinding of raw materials needed in secondary processing. Box–Behnken designs were used to investigate the effects of various mill variables (impeller, blower and feeder speeds and screen aperture size) on the milling of coarse crystals. Response variables included the particle size parameters (D10, D50and D90), span and milling rate. Milled particles in the size range of 5–200μm, with D50 ranging from 15 to 60μm, were produced. The impeller and feeder speeds were the most critical factors influencing the particle size and milling rate, respectively. Size distributions of milled particles were better described by their goodness-of-fit to a log-normal distribution (i.e. unimodality) rather than span. Milled particles with symmetrical unimodal distributions were obtained when the screen aperture size was close to the median diameter of coarse particles employed. The capacity for high throughput milling of particles to a mid-size range, which is intermediate between conventional mechanical impact mills and air jet mills, was demonstrated in the F10 mill. Prediction models from the Box–Behnken designs will aid in providing a better guide to the milling process and milled product characteristics.

Growth and characterization of the oxide scales and core/shell nanowires on Ti-6Al-4 V particles during thermal oxidation

Nanowires were grown on as-received and milled particles of Ti-6Al-4V (Ti64) alloy under an optimum condition of 750°C in an Ar atmosphere containing ~15ppm of oxygen. The as-grown nanowires and the underneath oxide scales developed on Ti64 particles were characterized by X-ray diffractometry (XRD), field emission scanning electron microscopy (FESEM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) equipped with energy dispersive X-ray spectroscope (EDS). Results revealed the formation of oxide scales consisting of double layers on the surface of Ti64 particles. The outer oxide scale was a mixture of Al2O3 and TiO2 whereas the inner oxide scale was solely TiO2. An unoxidized core was present inside depending on the size of the Ti64 particles at the initial state. The thickness of the outer oxide scale was also dependent on the size of the Ti64 particles. The nanowires grew in the outward direction from the outer oxide scale during thermal oxidation. The as-grown nanowires had fine and thick dimensions. Both types of nanowires had a core-shell structure where the core was made of TiO2 and the shell was Al2O3. It was seen that both residual and induced stress played a role for the growth of nanowires on Ti64 particles during thermal oxidation.

PARTICLE SIZE-DEPENDENT PULVERIZATION OF B4C AND GENERATION OF B4C/STS NANOPARTICLES USED FOR NEUTRON ABSORBING COMPOSITES

Pulverization of two different sized micro-B4C particles (∼10 μm and ∼150 μm) was investigated using a STS based high energy ball milling system. Shapes, generation of the impurities, and reduction of the particle size dependent on milling time and initial particle size were investigated using various analytic tools including SEM-EDX, XRD, and ICP-MS. Most of impurity was produced during the early stage of milling, and impurity content became independent on the milling time after the saturation. The degree of particle size reduction was also dependent on the initial B4C size. It was found that the STS nanoparticles produced from milling is strongly bounded with the B4C particles forming the B4C/STS composite particles that can be used as a neutron absorbing nanocomposite. Based on the morphological evolution of the milled particles, a schematic pulverization model for the B4C particles was constructed.

Magnetic Evolution of PrCo5 Nanoflakes Obtained by Surfactant-Assisted Ball Milling

In this work, PrCo 5 nanoflakes were obtained by a top-down approach using surfactant-assisted high-energy ball mill (SABM) technique. The coarse alloy powders were subjected to SABM employing oleic acid as surfactant and heptane as milling medium. The surfactant led to the dispersion of the crashed particles by suppressing the effects of re-welding and agglomeration during milling. The structural and magnetic characteristics of the milled particles proved to be functions of milling conditions. X-ray diffraction and magnetic investigations demonstrated that the nanoflakes were crystallographically anisotropic with [001] out of plane texture. The coercivity, i H c, of the milled particles showed enhancement versus milling time, and an optimum room temperature value of ∼ 7.4 kOe was obtained after 5 h of milling. TEM observations revealed that majority of the milled nanostructures exhibited aspherical, flake-type morphology.

A Study of Preparation and Characterization of Nano-Sized SiC Powder Using High Energy Ball Milling

This study investigated the preparation of nanosized crystalline SiC powders from micro sized Silicon Carbide powder at room temperature through high energy ball milling. Silicon carbide was milled with hardened steel balls and ball milling media under identical conditions of ball mass to powder mass ratio 10:1 and target milling times of 60 h. The sample was taken out after every 20 hours of milling and it was characterized for its crystalline size, lattice strain, and percentage of crystalline by using X-Ray Diffractometer (XRD). It was found that for the 60 hours The size, shape and texture of the fresh as well as nanostructured Silicon carbide powder were studied using Scanning Electron Microscopy (SEM). The raw Silicon carbide powder particles were mostly angular in shape. The shape of the 60h milled particles is irregular and the surface morphology is rough.

In-Situ Agglomeration and De-agglomeration by Milling of Nano-Engineered Lubricant Particulate Composites for Cold Spray Deposition

Nano-engineered self-lubricating particles comprised of hexagonal-boron-nitride powder (hBN) encapsulated in nickel have been developed for cold spray coating of aluminum components. The nickel encapsulant consists of several nano-sized layers, which are deposited on the hBN particles by electroless plating. In the cold spray deposition, the nickel becomes the matrix in which hBN acts as the lubricant. The coating demonstrated a very promising performance by reducing the coefficient of friction by almost 50% and increasing the wear resistance more than tenfold. The coatings also exhibited higher bond strength, which was directly related to the hardenability of the particles. During the encapsulation process, the hBN particles agglomerate and form large clusters. De-agglomeration has been studied through low- and high-energy ball milling to create more uniform and consistent particle sizes and to improve the cold spray deposition efficiency. The unmilled and milled particles were characterized with Scanning Electron Microscopy, Energy-Dispersive X-Ray Spectroscopy, BET, and hardness tests. It was found that in low-energy ball milling, the clusters were compacted to a noticeable extent. However, the high-energy ball milling resulted in breakup of agglomerations and destroyed the nickel encapsulant.

Dynamic image based shape analysis of hard and lignite coal particles ground by laboratory ball and gyro mills

A new real-time 3D dynamic image analysis system was used to measure the particle shapes of different type of coal samples (lignite and hard coals) ground by different mills (ball and gyro mills). Shape factors such as circularity, ellipse aspect ratio (EAR), bounding rectangle aspect ratio (BRAR) and Feret aspect ratio (FAR) described the results. At least 6400 particles were measured for each mill product indicating the accuracy of the results achieved with 99% statistical significance. Although experiments were performed on different ranked coal samples, there is a clear difference in the particle shapes generated by the grinding methods tested. Results indicated that the ball mill ground particles had the highest aspect ratios (EAR, BRAR, and FAR) with the lowest circularity. However, the gyro mill produced particles with highest circularity along with the lowest aspect ratios. Thus ball milled particles had the highest elongated particles with the lowest rounded particles. On the other hand, gyro mill products included the highest rounded particles and the lowest elongated particles. This relative difference in shape was attributed to the difference in grinding action involved in the ball and gyro mills. Results will find applications in various coal characterization, preparation, and utilization processes.

Electromagnetic and microwave absorbing properties of raw and milled FeSiCr particles

FeSiCr alloy (Fe: 90%, Si: 7.9%, and Cr: 2.1%) with pre-milled flaky shape was re-milled in a planetary ball-mill for 30 h. The complex permittivity (ε′−jε″) and permeability (μ′−jμ″) are measured by using the transmission/reflection method for two different aspect ratios of flake-shaped FeSiCr/epoxy composites for 30%, 40%, and 50% weight ratios. Dielectric loss tangent and magnetic loss tangent of re-milled FeSiCr powder show larger electromagnetic wave energy dissipation than those of the raw flaky FeSiCr powder. For 30 wt. % of FeSiCr/epoxy absorbers with 2 mm thickness, the calculated reflection loss reaches −25 dB at 13.0 GHz for raw flaky powder, −40 dB at 11.4 GHz for the re-milled FeSiCr powder with higher aspect ratios.

Physicochemical properties of ball milled boron particles: Dry vs. wet ball milling process

Physicochemical properties of both dry and wet milled boron particles with sub-micron sizes were investigated. Milling process was performed in N2 atmosphere and the mass ratio of tungsten carbide ball and boron was fixed at 20:1. It was found that the size distribution of boron particles grinded under dry milling condition was much broader than that under wet milling condition, and the size reduction rate in the dry process was faster than that in the wet process. Dry milled boron particles showed rougher surface morphology and more agglomerated particles, compared to wet milled boron particles. On the basis of X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and FT-IR results, it was confirmed that the initial oxide layer on the surface of boron particles was removed in the wet milling process, and BOC bond was newly formed on the surface of boron. On the other hand, XRD results showed that crystalline boron oxide layer was formed on the surface of dry milled boron particles. In addition, appropriate cleaning cycles and drying time for wet milled boron particles were suggested on the basis of FT-IR data.

Influência da granulometria da matéria-prima na expansão de extrusados de milho

Na produção de extrusados de milho, a indústria usualmente emprega o grits, que consiste no milho limpo, degerminado e moído em granulometria média. Entretanto, visando à redução dos custos de produção, fabricantes de snacks extrusados de milho vêm utilizando o fubá em substituição ao grits, devido ao menor custo apresentado por este. O objetivo deste trabalho foi verificar a influência da granulometria do milho sobre o índice de expansão dos snacks, sua textura e aceitação sensorial. Para isso, foram utilizadas três diferentes granulometrias do milho moído, sendo: grits, fubá mimoso e fubá mimoso fino. O índice de expansão radial foi analisado pela razão entre o diâmetro médio do snack e o diâmetro da matriz utilizada, a textura foi analisada em texturômetro, modelo Texture Analyser TA-XT Plus (Stable Micro Systens). A partir dos resultados obtidos, houve a confirmação da influência da granulometria nos parâmetros físicos, entretanto, não ocorreu alteração na aceitação do produto, indicando, desta forma, ser viável a substituição do grits pelo fubá na produção de snacks sob o ponto de vista do produto final.

Origin of radical coercivity reduction in fine Nd-Fe-B-type hydrogenation, disproportionation, desorption, recombination particles and its recovery

Coercivity variation of fine Nd-Fe-B-type particles prepared by ball milling of HDDR (hydrogenation, disproportionation, desorption, recombination)-treated Nd-Fe-B-type material was investigated using a HDDR-treated Nd12.5Fe80.6B6.4Ga0.3Nb0.2 material, and it was compared with that of fine particles prepared by mechanical milling of sintered Nd10Pr2.5Fe80.4B6Ga1Cu0.1 magnet. Coercivity of the fine particles prepared from the HDDR-treated Nd-Fe-B-type material was radically reduced as particle size decreased. In order to determine the major cause for the radical coercivity reduction, surface oxidation, structural damage (micro-strain), and crystallographic change (lattice shrinkage due to residual hydrogen desorption) in the milled fine particles were examined. The major contributory factor for the observed radical coercivity reduction was surface oxidation. Chemical etching proved an effective means for the recovery of the reduced coercivity in the milled fine particles prepared from the HDDR-treated Nd-Fe-B-type material. In contrast to fine particles prepared from sintered Nd-Fe-B-type magnet, the fine particles prepared from the HDDR-treated material could have reasonably high coercivity even as a very fine powder.

Microstructural Studies of (Ba<sub>0.7</sub>Sr<sub>0.3</sub>Fe<sub>12</sub>O<sub>19</sub>)<sub>1-x</sub> - (Ba<sub>0.7</sub>Sr<sub>0.3</sub>TiO<sub>3</sub>)<sub>x </sub>with x = 0.2, x = 0.5 and x = 0.8 Composite System by Mechanical Alloying Process

In this paper, we report our investigation on material structure analysis of (Ba0.7Sr0.3Fe12O19)1-x-(Ba0.7Sr0.3TiO3)x with x = 0.2, x = 0.5 and x = 0.8 composite system prepared by a mechanical alloying process to promote feroic properties. It is shown that the x-ray diffraction patterns of each composition for the composite materials are the same. It consisted of the mixture for the two phases. The average of particle size for each respective phase in the composite materials was found initially increased, up to 18-20 μm after mechanically milled for 40 hours, then start to decreased to a smaller size ~ 8-10 μm after 80 hrs milling time. However, a plot of particle size against the milling time for each composite phase shown a trend of further reduction in the mean particle sizes. In addition, the x-ray traces of dense pellet samples after sintering the milled powders at a temperature of 1100 °C showed broadened diffracted peaks pattern due to fine crystallites in the samples. Results of mean crystallite size determination of respective phases in the composite samples showed the same trend, a decrease with milling time toward values about 10 nm at 80 hrs milling time. Hence, sintering to the milled particles has promoted the formation of nanocrystal containing particles. When compared between the mean particle size and mean crystallite size of respective phase in the composite samples, the mean crystallite size for magnetic phase (B7S3F) was found more than 100 times smaller than the mean particle size of composite particles. However, finer mean crystallite sizes were found in the ferroelectric phase (B7S3T) in which the mean was about 200 times smaller than the mean particle size.

Effect of particle size on the composition of lignin derived oligomers obtained by fast pyrolysis of beech wood

The effect of particle size on the yield and composition of lignin derived oligomers (also known as pyrolytic lignin (PL)) was studied in a fluidized bed reactor. Milled beech wood particles of sizes between 0.3 and 0.55 and cylinders of 3–14mm were pyrolyzed at 500°C. The lignin oligomers were isolated from bio-oil and analyzed using several analytical techniques (TG, Py-GC/MS, and 1H NMR). The yield of PL fraction decreased half when particle size raised from 0.3 to 3mm. DTG analysis of the PL showed higher loss rates between 200 and 600°C as particle size increased from 0.55 to 3–4mm. Py-GC/MS results suggested a dramatic decrease of methoxylated phenols (in line with the 1H NMR studies) and the loss of ether bonds when the particle size was increased from milled small particles of 0.3mm to cylinders with a diameter between 3 and 5mm. In general, most chemical changes and changes in PL yield occur between the milled particles (composed mainly of the cell wall) and cylinders with original wood structure. Comparing the milled particles to the cylinders with equal length (equal vapor outflow distance) but varied diameter, the effect on the yield of PL seems to be mainly due to the impact of thermally ejected oligomers on internal cell walls of biomass particles (mass transfer limitations).

Structure and characteristics of milled silk particles

This study examined the structure, thermal property, and ion adsorption of silk particles. The particles were prepared by attritor–bead mill combination, using alkaline (pH10) charge repulsion and surfactant steric repulsion methods. Both methods produced particles with a dominant β-sheet structure, similar to the silk fibre. There was no significant difference in the decomposition temperatures for either the silk fibre or the micro/nano silk particles. An important finding from this study is clear evidence of reduction of amorphous content during the final stage of powdering using the bead mill. As a result, despite reduction in β-sheet crystallites with the progressive milling, the relative β-sheet content actually increased during this process. However, intermolecular forces between the β-sheets reduced significantly and hence the XRD results showed significant reduction in crystallinity in nano silk particles but crystal forming segments remained with β-sheet conformations after milling. The structural change influenced the ion-adsorption property where particle-size reduction resulted in a significant increase in both the rate and volume of HCrO4− adsorption.

Numerical Modeling of CFD model Applied to a Hammer Mill

A numerical model was used to predict and improve the flow characteristics in a hammer mill. For this purpose a CFD (computational fluid dynamics) model was built. SST and LES turbulence models was tested in order to improve the model. For the simulation of the sieve effect a porous domain was used. The pressure, velocity of fluid and also the turbulence areas were analyzed. The physical properties of the milled particles and the grinding process parameters are greatly affected by the fluid flow in the hammer mill and because of this, by understanding how the fluid flow takes place inside it can lead to a improved design.