Decrease In Mean Particle Size Research Articles

Attrition of Victorian brown coal during drying in a fluidized bed

ABSTRACT Analyzing the attrition of Victorian brown coal during air and steam fluidized bed drying, the change in particle size distribution over a range of initial moisture contents (60% to 0%) and residence times (0 to 60 minutes) was determined. Dried at a temperature of 130°C with a fluidization velocity 0.55 m/s and an initial particle size of 0.5–1.2 mm, both fluidization mediums show a shift in the particle size distribution between three and four minutes of fluidization, with a decrease in mean particle size from 665 µm to around 560 µm. Using differential scanning calorimetry (DSC), the change in particle size has been attributed to the transition between bulk and non-freezable water (approximately 55% moisture loss) and can be linked to the removal of adhesion water, but not to fluidization effects. This is proved through the comparison of air fluidized bed drying, steam fluidized bed drying, and fixed bed drying—the fixed bed drying is being used to determine the particle size distribution as a function of drying. The results show the three drying methods produce similar particle size distributions, indicating that both fluidization and fluidization medium have no impact upon the particle size distribution at short residence times around ten minutes. The cumulative particle size distribution for air and steam fluidized bed dried coal has been modeled using the equation P d = A 2 + (A 1 − A 2)/(1 + (d/x 0) p ), with the resultant equations predicting the effects of moisture content on the particle size distribution. Analyzing the effect of longer residence times of 30 and 60 minutes, the particle size distribution for steam fluidized bed dried coal remains the same, while air fluidized bed dried coal has a greater proportion of smaller particles.

Dissolution and oral absorption of pranlukast nanosuspensions stabilized by hydroxypropylmethyl cellulose

The objective of this study was to investigate the effect of particle size on the dissolution and oral absorption of pranlukast microsuspensions and nanosuspensions stabilized by hydroxypropylmethyl cellulose. Four pranlukast suspensions with different mean particle sizes (0.16, 0.89, 3.13, and 18.21μm) were prepared by various top-down processes such as jet milling, high pressure homogenization, and bead milling. The dissolution rate and oral absorption of pranlukast suspensions were significantly affected by the particle size. The in vivo pharmacokinetic parameters of pranlukast suspensions were increased with decreasing mean particle size of suspensions. Especially, the AUC0→24h and Cmax values of pranlukast nanosuspension with a particle size of 0.16μm were approximately 3.5- and 6.3-fold greater, respectively, than that of pranlukast microsuspension with a particle size of 18.21μm. Therefore, the preliminary results from our study suggest that a pranlukast nanosuspension with a mean particle size of about 0.16μm may have significant potential for clinical application.

Supercritical antisolvent micronization of PVP and ibuprofen sodium towards tailored solid dispersions

The supercritical antisolvent technology is used to precipitate polyvinylpyrrolidone (PVP) particles and crystallise ibuprofen sodium (IS) crystals separately and in the form of solid dispersion together. Supercritical carbon dioxide (scCO2) is used as antisolvent. For PVP particle generation, ethanol, acetone and mixtures of ethanol and acetone are used as solvents. The initial concentration of PVP in the solution was varied between 0.5wt% and 1.5wt%, the operation pressure between 10MPa and 30MPa and the composition of ethanol/acetone solvent mixtures between 100wt% and 0wt% of ethanol at a constant temperature of 313K. Furthermore, the mean molecular weight of the polymer was varied between 40kgmol−1, 360kgmol−1 and 1300kgmol−1. An increase of the content of the poor solvent acetone in the initial solvent mixture as well as the usage of PVP with a higher molecular weight, leads to a significant decrease in mean particle size. At all the investigated parameters always fully amorphous PVP powder precipitates. For IS, only ethanol was used as the solvent, the initial IS concentration in the solution was varied between 1wt% and 3wt% and the operation pressure between 10MPa and 16MPa. A variation of these parameters leads to a manipulation of the size and the morphology of the crystallised IS crystals. Irrespective of the parameters used, always the same polymorphic form of ibuprofen sodium is produced. The solid dispersions were generated at different compositions of PVP to IS and with two different molecular weights of PVP at otherwise constant conditions. Fully amorphous solid dispersions consisting of IS and PVP together were generated at different ratios of PVP to IS.The mechanisms that control the final particle properties are discussed taking into account two different models for “ideal” and “non-ideal” solutes. Furthermore, the study of the “unconventional” SAS parameters, molecular weight and solvation power of the solvent shows that these parameters qualify to tailor polymer particle properties via SAS processing. Next to the investigation into the behaviour of both solutes separately, fully amorphous solid dispersions consisting of IS and PVP together were generated. While X-ray diffraction was used to analyze the crystalline structure of the particles, respectively, solid dispersions, their morphology was analysed using scanning electron microscopy (SEM).

Preparation and evaluation of double-walled microparticles prepared with a modified water-in-oil-in-oil-in-water (w1/o/o/w3) method

In this study, a modified water-in-oil-in-oil-in-water (w1/o/o/w3) method was developed to prepare double-walled microparticles containing ovalbumin (OVA). The microparticles were characterized with respect to their morphology, particle size, encapsulation efficiency, production yield, thermal properties and in vitro drug release. Microscopy observations clearly showed that microparticles have spherical shape and smooth surface. These microparticles were characterized to have double-walled structure, with a cavity in the centre. By using w1/o/o/w3 method, a significant decrease in mean particle size and a significant increase in encapsulation efficiency were obtained. The mean particle size and the encapsulation efficiency of double-walled microparticles were also affected by the changing amount of OVA and mass ratio of polymers. Microparticles prepared with two polymers exhibited a significantly lower initial burst release followed by sustained release compared to microparticles made from poly(d,l-lactide-co-glycolide) 50/50 only. It can be concluded that these microparticles can be a potential delivery system for therapeutic proteins.

Effect of particle size on enzymatic hydrolysis of pretreated Miscanthus

Particle size reduction is a crucial factor in transportation logistics as well as cellulosic conversion. The effect of particle size on enzymatic hydrolysis of pretreated Miscanthus x giganteus was determined. Miscanthus was ground using a hammer mill equipped with screens having 0.08, 2.0 or 6.0mm sieve openings. Particle size distribution and geometric mean diameters were determined for all samples. Ground samples were subjected to hot water, dilute acid or dilute ammonium hydroxide pretreatment. Enzyme hydrolysis was conducted on washed pretreated solids; sugar generation was used as a measure for pretreatment efficiency. Glucose and xylose concentrations were monitored using HPLC. Glucose and xylose profiles were generated and hydrolysis rates estimated. Glucose, xylose and total conversion yields were determined by comparing final sugar concentrations obtained to amounts present in pretreated biomass. Geometric mean diameters were the smallest from 0.08mm sieve screen (56μm) followed by 2.0mm (301μm) and 6.0mm (695μm) screens. An increasing trend in percent total conversion was observed with decreasing mean particle size. Across all pretreatments, biomass ground using 0.08mm screens resulted in highest total conversion. Enzyme hydrolysis of unpretreated biomass samples also resulted in increased total conversions as particle size decreased, although mean conversions (10–20%) were much lower than for pretreated biomass samples (53–94%), indicating the need for chemical pretreatments in biomass conversion.

Nylon-sputtered nanoparticles: fabrication and basic properties

Nylon-sputtered nanoparticles were prepared using a simple gas aggregation cluster source based on a planar magnetron (Haberland type) and equipped with a nylon target. Plasma polymer particles originated in an aggregation chamber and travelled to a main (deposition) chamber with a gas flow through an orifice. The deposited nanoparticles were observed to have a cauliflower-like structure. The nanoparticles were found to be nitrogen-rich with N/C ratio close to 0.5. An increase in rf power from 60 to 100 W resulted in a decrease in mean particle size from 210 to 168 nm whereas an increase in their residence time in the cluster source from 0.7 to 4.6 s resulted in an increase in the size from 73 to 231 nm.

Operational performance of inlet barrier filters for rotorcraft

AbstractThis contribution addresses the subject of engine inlet barrier filters (IBF) for rotorcraft. The purpose of an IBF is to mitigate the risk of particle ingestion by the engine, a situation that can cause irrevocable damage to key components. The risk is significantly elevated during a brownout landing, in which the rotor wake of a descending helicopter interacts with loose ground sediment, causing the generation of a dust cloud. In such a condition, an IBF successfully removes particles from the engine-bound air at the expense of a pressure drop, which grows temporally. The increase in pressure drop is caused by but not limited to an increase in incident velocity and a decrease of mean particle size; however the rate may be slowed by operating the filter at a tangential angle to the flow. The current work presents findings of a parametric study into the factors affecting particle accumulation and the consequential loss of inlet total pressure.

Effect of NaCl addition during diafiltration on the solubility, hydrophobicity, and disulfide bonds of 80% milk protein concentrate powder

We investigated the surface hydrophobicity index based on different fluorescence probes [1-anilinonaphthalene-8-sulfonic acid (ANS) and 6-propionyl-2-(N,N-dimethylamino)-naphthalene (PRODAN)], free sulfhydryl and disulfide bond contents, and particle size of 80% milk protein concentrate (MPC80) powders prepared by adding various amounts of NaCl (0, 50, 100, and 150mM) during the diafiltration process. The solubility of MPC80 powder was not strictly related to surface hydrophobicity. The MPC80 powder obtained by addition of 150mM NaCl during diafiltration had the highest solubility but also the highest ANS-based surface hydrophobicity, the lowest PRODAN-based surface hydrophobicity, and the least aggregate formation. Intermolecular disulfide bonds caused by sulfhydryl-disulfide interchange reactions and hydrophobic interactions may be responsible for the lower solubility of the control MPC80 powder. The enhanced solubility of MPC80 powder with addition of NaCl during diafiltration may result from the modified surface hydrophobicity, the reduced intermolecular disulfide bonds, and the associated decrease in mean particle size. Addition of NaCl during the diafiltration process can modify the strength of hydrophobic interactions and sulfhydryl-disulfide interchange reactions and thereby affect protein aggregation and the solubility of MPC powders.

A rotating disk electrode study of the particle size effects of Pt for the hydrogen oxidation reaction

By using a catalyst-lean thin-film RDE method, the fast kinetics of the hydrogen oxidation reaction (HOR) on highly dispersed Pt nanoparticle electrocatalysts can be determined, free from the interference of the mass transport of H(2) molecules in solution. Measurements with carbon-supported Pt nanoparticles of different sizes thus allow revealing the particle size effect of Pt for the HOR. It is shown that there is a "negative" particle size effect of Pt on the kinetics of HOR, i.e., the exchange current density j(0) decreases with the increased dispersion (i.e. decreased mean particle size). A maximum mass activity of Pt for the HOR is found at particle sizes of 3-3.5 nm. The observed particle size effect is interpreted in terms of the size dependent distribution of surface atoms on the facets and edges, which is implied by the voltammetric responses of Pt/C catalysts with differently sized Pt particles. The accompanied decrease in the HOR activity with the increase in the edge atom fraction suggests that the edge atoms on the surface of Pt nanoparticles are less active for the HOR than those on the facets.

Synthesis of citrate-stabilized hydrocolloids of hydroxyapatite through a novel two-stage method: A possible aggregates–breakdown mechanism of colloid formation

Long-term stable (>2years) hydrocolloids of hydroxyapatite (HA) were synthesized via a low-temperature (18–50°C) reaction of aqueous ammonium phosphate with calcium nitrate in the presence of citrate ions, followed by an aging process at high temperature (80–99°C) for 4h. Changing the reaction and/or aging temperature seldom yielded stable HA hydrocolloids. The as-prepared hydrocolloids were desalinated through ultrafiltration where their average particle size gradually decreased, bottomed out at 100–400μS/cm, and sharply increased in parallel with a decrease in solution conductivity. The colloid formation is most likely through a temperature-sensitive aggregates–breakdown process. During low-temperature reaction, citrate–calcium chelation bridges the growing HA particles into loose aggregates. High-temperature aging disrupts these inter-particle links and thus breaks the aggregates, imparting negative charges to the HA, forming colloidal particles stabilized by surface charge. The decrease in mean particle size during early ultrafiltration suggested that the aggregate breakdown further proceeded through desalination. In conclusion, the temperature-dependent interactions between citrate ions and calcium sites on HA particles played key roles in the synthesis and stability of the HA colloids.

Particle‐size Evaluation of Pin‐ or Ball‐mill‐ground Phenytoin Bulk Powders by Fourier‐transformed Powder Diffuse Reflectance Infrared Spectroscopy

To determine the bulk drug powder particle size in pharmaceutical preparations, the quantitative correlation between the absorption peak intensity in Fourier-transformed powder diffuse reflectance infrared (FT-IR) spectra and the particle size of phenytoin powders obtained by pin- or ball-mill grinding was investigated. Absorption peak intensity of phenytoin powders increased with decrease in mean particle size (D). The relationships between the FT-IR absorbance at 1724 cm−1 and the specific surface area (Sw) obtained by the BET N2 gas absorption method of ground samples showed straight lines, indicating that the absorbance followed equation 1: log (I0/I) = K1/D = K2Sw (1) where I0 and I are intensities of the incident and transmitted light, respectively, and K1 and K2 are constants. Both relationships obtained from the pin- or ball-mill-ground samples gave linear plots, and the slopes were not significantly different.

The Effect of Mechanical Activation of Elemental Powders on Combustion Synthesis of NbAl<sub>3</sub>

The effect of mechanical activation procedures on the combustion synthesis of NbAl3 was investigated. The activation was carried out by a two-step high energy ball milling procedure. In the first milling, aluminum and niobium were milled separately (pre-activation). The mixture of pre-activated powders was then activated in the second milling. Reaction synthesis, by simultaneous combustion mode, was conducted on compacted pellets made of powder mixtures with and without pre-activation. The thermal behavior of the compacted pellets upon heating was recorded and the main thermal combustion reaction characteristics were evaluated. The two-step procedure produced aggregates with a globular dispersion of niobium due to increased particle hardness and decreasing mean particle size during pre-activation milling. Analysis of pellet thermal behavior showed the two-step milling procedure could enhance reaction performance by increasing maximum reaction heating rate and temperature gain during reaction.

Enhancement of Wettability and Dissolution Properties of Cilostazol Using the Supercritical Antisolvent Process: Effect of Various Additives

The aim of this study was to improve wettability and dissolution rate of a poorly water-soluble drug, cilostazol, using the supercritical antisolvent (SAS) process. The solid state of particles precipitated from dichloromethane containing additives, including poloxamer 188, poloxamer 407, TPGS 1000, Gelucire 44/14 and Gelucire 50/13, in supercritical CO(2) medium were characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD), FT-IR, particle size analysis, contact angle, and dissolution. Interestingly, the morphology of SAS particles processed with TPGS 1000, Gelucire 44/14 and Gelucire 50/13 changed to plate- or leaflet-shaped. Furthermore, the particle sizes of cilostazol processed with Gelucire 44/14 and Gelucire 50/13 were increased compared to cilostazol processed without additives. Poloxamer 188 and poloxamer 407 were superior in increasing the dissolution rate due to decreased particle size, the resulting increased surface area, and improved wettability. Micronization with the supercritical antisolvent process resulted in a significant decrease in mean particle size, and wettability of cilostazol was increased by using small amounts of hydrophilic additives.

Effects of feeding increased amounts of wet corn gluten feed on dairy cow metabolism and milk production (2009)

An experiment was conducted to evaluate the effects of feeding increasing dietary amounts of wet corn gluten feed (WCGF). Eight lactating Holstein cows were housed in a tie-stall facility and fed 1 of 4 diets containing 0, 11, 23, or 34% WCGF on a dry matter basis. To maintain similar nutrient concentrations, alfalfa hay, corn silage, corn grain, soybean meal, expeller soybean meal, and mineral supplements varied across diets. Feed intake, milk production, body weight, and body condition score were monitored, and effects of WCGF inclusion rate were assessed. Increasing the level of WCGF in the diet led to increased feed intake, milk production, and body condition. Concentrations of milk components did not differ among treatments; therefore, yield of energy-corrected milk and solids-corrected milk increased as well. In contrast, increasing dietary WCGF decreased efficiency of production and also decreased ruminal pH, possibly because treatments with greater proportions of WCGF had a decreased mean particle size. As expected, the decreased ruminal pH coincided with changes in ruminal volatile fatty acid concentrations. Furthermore, the rate of fiber digestion after 24 hours decreased when more WCGF was incorporated into diets. Results indicate that adding WCGF to dairy rations can increase energy-corrected milk yield, and this increase seems to be driven, at least in part, by an increase in feed intake.

Preparation and Characterization of β-Carotene Nanodispersions Prepared by Solvent Displacement Technique

This work demonstrated the preparation of protein-stabilized beta-carotene nanodispersions using the solvent displacement technique. The emulsifying performance of sodium caseinate (SC), whey protein concentrate (WPC), whey protein isolate (WPI), and a whey protein hydrolysate (WPH, 18% degree of hydrolysis) was compared in terms of particle size and zeta-potential of the nanodispersions. SC-stabilized nanodispersions exhibited a bimodal particle size distribution: large particles (stabilized by casein micelles) with a mean particle size of 171 nm and small particles (stabilized by casein submicelles) of 13 nm. This was confirmed with transmission electron microscopy analysis. Most of the beta-carotene precipitated (87.6%) was stabilized in the small particles. On the other hand, the nanodispersions stabilized by the whey proteins were polydispersed with larger mean particle sizes. The mean particle size of WPC and WPI was 1730 and 201 nm, respectively. The SC-stabilized nanodispersion was expected to be more stable as indicated by its higher absolute zeta-potential value (-31 mV) compared to that of WPC (-15 mV) and WPI (-16 mV). Partially hydrolyzed whey protein possessed improved emulsifying properties as shown by WPH-stabilized samples. It was interesting to note that increasing the SC concentration from 0.05 to 0.5 wt % increased the particle size of beta-carotene stabilized by casein micelles, while the reverse was true for those stabilized by SC submicelles. Microfluidization at 100 MPa of SC solution dissociated the casein micelles, resulting in a decrease in mean particle size of the casein micelle-stabilized particles when the SC solution was used to prepare nanodispersions. The results from this work showed that protein-stabilized beta-carotene nanodispersions could be prepared using the solvent displacement technique.

Preparation, characterization, cytotoxicity and transfection efficiency of poly( dl-lactide-co-glycolide) and poly( dl-lactic acid) cationic nanoparticles for controlled delivery of plasmid DNA

The objective of this study was to investigate the effect of formulation parameters (i.e. polymer molecular weight and homogenization speed) on various physicochemical and biological properties of cationic nanoparticles. Cationic nanoparticles were prepared using different molecular weights of poly( dl-lactide-co-glycolide) (PLGA) and poly( dl-lactic acid) (PLA) by double emulsion solvent evaporation at two different homogenization speeds, and were characterized in terms of size, surface charge, morphology, loading efficiency, plasmid release, plasmid integrity, cytotoxicity, and transfection efficiency. Cationic surfactant, cetyltrimethylammonium bromide (CTAB), was used to provide positive charge on the surface of nanoparticles. Reporter plasmid gWIZ™ Beta-gal was loaded on the surface of nanoparticles by incubation. Use of higher homogenization speed and lower molecular weight polymer led to a decrease in mean particle size, increase in zeta potential, increase in plasmid loading efficiency, and a decrease in burst release. The nanoparticles displayed good morphology as evident from scanning electron micrographs. In vitro cytotoxicity study by MTT assay showed a low toxicity. Structural integrity of the pDNA released from nanoparticles was maintained. Transfecting human embryonic kidney (HEK293) cells with nanoparticles prepared from low molecular weight PLGA and PLA resulted in an increased expression of beta-galactosidase as compared to those prepared from high molecular weight polymer. Our results demonstrate that the PLGA and PLA cationic nanoparticles can be used to achieve prolonged release of pDNA, and the plasmid release rate and transfection efficiency are dependent on the formulation variables.

Low-temperature fabrication and characterization of porous SiC ceramics using silicone resin as binder

Commercially available silicone resin and silicon carbide (SiC) powders were adopted as the starting materials for the fabrication of porous SiC ceramics. During the heat treatment process, silicone resin experienced an organic–inorganic transformation and acted as the bonding material between SiC particles at a low temperature of 1000 °C. The mean particle size of starting SiC powders and silicone resin content can control the pore size, open porosity and fracture strength. The flexural strength of porous SiC ceramics increases with increasing silicone resin content and decreasing mean particle size of SiC powders. Larger pores can be obtained with coarser starting SiC powders and higher silicone resin content. The fracture surface of porous SiC ceramics was observed.

Particle size, grain size and γ-MgH2 effects on the desorption properties of nanocrystalline commercial magnesium hydrideprocessed by controlled mechanical milling

The hydrogen desorption properties of commercial nanocrystalline magnesium hydride (TegoMagnan® from Degussa–Goldschmidt) processed by controlled mechanical milling(CMM) are investigated. A profound effect of the powder particle sizeon the hydrogen desorption characteristics has been observed. The onset(TON) and peak hydrogen desorption temperatures measured by differential scanningcalorimetry (DSC) decrease initially slowly with decreasing mean particle size of hydride,and when the particle size reaches a certain critical threshold value, the desorptiontemperatures start decreasing more rapidly with further decrease of particle size. Thetotal drop of desorption temperature from its initial value for the as-receivedMgH2 to the value attainedfor the milled MgH2 having aparticle size of ∼500–600 nm iswithin the range 40–60 °C. The metastable γ-MgH2 hydride coexists with the stable nanocrystallineβ-MgH2 in themicrostructure of the MgH2 powders ball milled for 10 h and longer. Quantitative evidence showsthat two factors, namely the refined powder particle size and theγ-MgH2 phase residing within the powder particles, acting additively, are responsiblefor a substantial reduction of the hydrogen desorption temperature ofMgH2 hydride.

Densification and Grain Growth of Al2O3 Nanoceramics During Pressureless Sintering

α‐Al2O3 nanopowders with mean particle sizes of 10, 15, 48, and 80 nm synthesized by the doped α‐Al2O3 seed polyacrylamide gel method were used to sinter bulk Al2O3 nanoceramics. The relative density of the Al2O3 nanoceramics increases with increasing compaction pressure on the green compacts and decreasing mean particle size of the starting α‐Al2O3 nanopowders. The densification and fast grain growth of the Al2O3 nanoceramics occur in different temperature ranges. The Al2O3 nanoceramics with an average grain size of 70 nm and a relative density of 95% were obtained by a two‐step sintering method. The densification and the suppression of the grain growth are achieved by exploiting the difference in kinetics between grain‐boundary diffusion and grain‐boundary migration. The densification was realized by the slower grain‐boundary diffusion without promoting grain growth in second‐step sintering.

Effect of process parameters on production of metal powders by water jet cooled rotating disc atomisation

An experimental centrifugal atomiser was designed and constructed. The apparatus operates on the principle of atomising molten metal by pouring it onto a water jet cooled rotating disc. The disc was of a cylindrical reversed cup shape and the disc was cooled on the reverse side. The cooling water did not come into contact with the liquid metal and powders produced. Liquid metal did not stick on the disc because of effective cooling. Pure tin was used as the raw material to investigate the effects of production parameters, such as disc geometry, disc diameter, rotating speed, fin number, fin type, superheat and flowrate, of the liquid metal on the mean powder size and yield rate. Pure lead, zinc, aluminium and AA2014 alloy were also atomised to investigate the effects on metal types.The mean particle size of powders produced were in the range of 100–150 μm for tin and lead, 170–220 μm for zinc and 350–400 μm for aluminium and AA2014 alloy depending on the process parameters. The shapes of the powders were generally irregular, flaky, teardroplike and ligamental. The amount of spherical and rounded powders increased with decreasing mean particle size. A flat disc geometry with inverted triangle shaped fins gave a finer mean particle size and higher yield rate than other designs. Increasing disc rotation speed, disc diameter, superheat of liquid metal (up to 218°C) and decreasing liquid metal flowrate resulted in a finer mean particle size and a higher yield rate for tin. Discs with two fins gave a finer mean particle size and a higher yield rate.