Primary Particle Size Distribution Research Articles

Effect of Lithium Content on Spinel Phase Evolution in Lithium-Rich Layered Oxides LixNi0.25Co0.10Mn0.65O(3.4+x)/2 (0.8 ≤ x ≤ 1.6) for Li-Ion Batteries

Lithium-rich oxides LixNi0.25Co0.10Mn0.65O(3.4+x)/2 (x=1.6, 1.4, 1.2, 1.0, 0.8) were synthesized and characterized for their structural, morphological, and performance as cathode materials in Li-ion batteries. The baseline composition x=1.4 had been previously determined as having the best electrochemical performance due to its small primary particle size and homogeneous distribution of nano-domains consisting of (C2/m) and (R3¯m) phases. In this study, the Rietveld refinement results indicate the presence of two phases at high lithium levels (x=1.6 and 1.4): Li2MnO3 (C2/m) and Li M O2 ( M = Ni, Co, Mn) (R3¯m); the latter contains Ni2+ and Ni3+. At low lithium levels (x=1.2, 1.0, and 0.8) an additional spinel phase Li M 2O4 (Fd3¯m) emerges, which is known to affect the electrochemical performance of the oxide. Structural analysis reveals that the spinel phase contains mixed transition metals Ni, Co, and Mn as [Li+,Co2+][Ni2+,Co3+,Mn4+]2O4. A low lithium level is found to induce primary particle growth, as well as Co and Ni segregation within the secondary particles. These results are expected to contribute to material optimization and commercialization of lithium-rich oxide cathodes.

Coagulation of Agglomerates Consisting of Polydisperse Primary Particles.

The ballistic agglomeration of polydisperse particles is investigated by an event-driven (ED) method and compared to the coagulation of spherical particles and agglomerates consisting of monodisperse primary particles (PPs). It is shown for the first time to our knowledge that increasing the width or polydispersity of the PP size distribution initially accelerates the coagulation rate of their agglomerates but delays the attainment of their asymptotic fractal-like structure and self-preserving size distribution (SPSD) without altering them, provided that sufficiently large numbers of PPs are employed. For example, the standard asymptotic mass fractal dimension, Df, of 1.91 is attained when clusters are formed containing, on average, about 15 monodisperse PPs, consistent with fractal theory and the literature. In contrast, when polydisperse PPs with a geometric standard deviation of 3 are employed, about 500 PPs are needed to attain that Df. Even though the same asymptotic Df and mass-mobility exponent, Dfm, are attained regardless of PP polydispersity, the asymptotic prefactors or lacunarities of Df and Dfm increase with PP polydispersity. For monodisperse PPs, the average agglomerate radius of gyration, rg, becomes larger than the mobility radius, rm, when agglomerates consist of more than 15 PPs. Increasing PP polydispersity increases that number of PPs similarly to the above for the attainment of the asymptotic Df or Dfm. The agglomeration kinetics are quantified by the overall collision frequency function. When the SPSD is attained, the collision frequency is independent of PP polydispersity. Accounting for the SPSD polydispersity in the overall agglomerate collision frequency is in good agreement with that frequency from detailed ED simulations once the SPSD is reached. Most importantly, the coagulation of agglomerates is described well by a monodisperse model for agglomerate and PP sizes, whereas the detailed agglomerate size distribution can be obtained by scaling the average agglomerate size to the SPSD.

Role of Alternative Fuels on Particulate Matter (PM) Characteristics and Influence of the Diesel Oxidation Catalyst.

The influence of a platinum:palladium (Pt:Pd)-based diesel oxidation catalyst (DOC) on the engine-out particulate matter (PM) emissions morphology and structure from the combustion of alternative fuels (including alcohol-diesel blends and rapeseed oil methyl ester (RME) biodiesel) was studied. PM size distribution was measured using a scanning mobility particulate spectrometer (SMPS), and the PM morphology and microstructure (including size distribution, fractal geometry, and number of primary particles) was obtained using high-resolution transmission electron microscopy (TEM). It is concluded that the DOC does not modify the size or the microstructural parameters of the primary particulates that make up the soot agglomerates. The PM reduction seen in the DOC is due to the trapping effect, and oxidation of the PM's volatile components. The DOC performance in reducing gaseous (e.g., carbon monoxide (CO) and unburnt hydrocarbons (HCs)) and PM emissions at low exhaust temperatures was improved from the combustion of alternative fuels due to the reduced level of engine-out pollutants.

Direct fractionation of spray-dried polymeric microparticles by inertial impaction

The current study describes a convenient method for a direct size classification of spray-dried powders, which is of general interest for diverse applications in drug delivery. Accordingly, the time-consuming “trial-and-error” approach to identify critical formulation and process parameters influencing the final product specifications is replaced by a final fractionation step of the dried particles by inertial impaction.When employing the “original” vibrational spray-dryer (i.e., Nano Spray-Dryer B-90, Büchi) it was evident that both the liquid feed characteristics (e.g., concentration of dissolved solids) and process parameters (e.g., nozzle type and spray-rate) significantly affected the particle size and size distribution of generated sildenafil-loaded poly(lactide-co-glycolide) microparticles (particle size: ~4–~11μm; particle size distribution (span): ~1.3–~2.2). The said formulations showed prolonged in vitro drug release properties with mean dissolution times (MDTs) ranging between ~4 and ~14h. By contrast, replacing the electrostatic particle collector of the vibrational spray-dryer by a Next Generation Impactor enabled a direct size classification of spray-dried microparticles according to their aerodynamic behavior. Formulations collected from the individual impactor stages exhibited a defined particle size (i.e., stages I, II, III and IV with 7.8, 4.5, 3.0 and 2.1μm, respectively) and were significantly narrowly distributed (span: ≤1.2) than the non-fractionated controls. Likewise, fractionated formulations were characterized by a sustained sildenafil in vitro release behavior (MDT: ~1.5–~7h).Overall, regardless of the primary particle size and size distribution of spray-dried powders, desired size characteristics can be achieved by a terminal size classification by inertial impaction. Hence, the described approach provides spray-dried products meeting the specific requirements of the intended application (e.g., prolonged drug delivery to the lungs).

Impact of Lubricating Oil on Morphology of Particles from a Diesel Engine

Abstract This study focuses on the impact of lubricating oil on morphology of diesel particles by experimental works. A four cylinder diesel engine was used for generating particles. Neat diesel and oil-dosed fuel were burned, and samples were collected by thermophretic sampling system. Samples were analyzed by transmission electron microscopy (TEM) technique, and size distributions of primary particles, fractal dimension information of aggregates, and aggregate size were studied. Results show that oil-related primary particles are larger than fuel related under low engine load, while the influence of oil is subtle under high load condition. Lubricating oil influences the fractal geometry differently depends on load conditions. Loose structure was observed under low load, however, more compact one appeared under high load. Statistical results indicate that aggregates from oil-dosed fuel have larger gyration diameter compare with neat diesel aggregates, which may be caused by the organic fractions in oil-related particles. Overall, the various combustion ratio under different conditions is responsible for the influence of oil on particle morphology.

Rapid analysis of titanium dioxide nanoparticles in sunscreens using single particle inductively coupled plasma–mass spectrometry

Titanium dioxide (TiO2) particles in the nanometer (nm) size range are widely used in commercial sunscreens. Single particle inductively coupled plasma–mass spectrometry (SP-ICP–MS) is an emerging methodology for nanoparticle (NP) characterization and quantification. In this study, a rapid SP-ICP–MS method was developed to simultaneously determine the primary particle size, size distribution, particle concentration (particles/mL), and mass content (weight percent) of TiO2 NPs in commercial sunscreens. Quality control data indicated that the developed method was capable of accurately measuring TiO2 particle size in sunscreen matrix. Four types of commercial sunscreens containing different amounts of TiO2 were analyzed, and the primary particle sizes detected varied from 32nm to 40nm in the different sunscreens tested. TiO2 existed as TiO2 particles in the tested sunscreens. The TiO2 mass contents in these sunscreens were also determined by a novel standard addition-SP-ICP–MS method, using a 40nm TiO2 NP as the NP standard. Although the measured TiO2 mass content was close to that determined by acid digestion and the manufacturer-claimed content, improvement in accuracy is needed and can be achieved if better-matched NP standards available. The standard addition-SP-ICP–MS method offers a promising alternative for determining the TiO2 NP mass content in sunscreen, in lieu of using the laborious, time-consuming, and costly acid digestion-ICP–MS method. The major advantages of SP-ICP–MS analysis are easy sample preparation, high throughput, and informative results (particle size information and total TiO2 mass content).

Statistical investigation of agglomerate breakage based on combined stochastic microstructure modeling and DEM simulations

The internal microstructure of agglomerates has a great influence on their stability and breakage characteristics. Therefore, to optimize production processes and to improve characteristics of the final product, it is very important to understand dependencies between structural and mechanical properties of agglomerates. In this paper, we discuss usage of the discrete element method (DEM) for understanding the breakage behavior of spherical agglomerates under uniaxial compression depending on their microstructure. A flexible stochastic model has been developed to generate agglomerates with various types of microstructures. As an example, we investigate the effect of the primary particle size distribution on agglomerate strength and breakage behavior. In particular, the size distribution of primary particles is specified by a mixing of two fixed particle sizes. The model construction ensures that the size and mass of agglomerates as well as primary particles and binder content remain constant in all experiments. From the obtained results it can be seen that the breakage behavior of agglomerates is influenced in different ways. Breakage energy and the maximum force applied before the primary break depend on the mixing ratio and the variability inside the microstructure. On the other hand, the size of fragments is very similar for all mixing ratios.

The Cyclops for pulmonary delivery of aminoglycosides; a new member of the Twincer™ family

Patients infected with pathogenic bacteria have to be treated with antibiotics. When the infection is in the lungs, as for instance in cystic fibrosis, bronchiectasis and tuberculosis, inhaled antibiotics have certain advantages over systemically administered antibiotics. In this study, it is shown that re-designing the Twincer™ high dose disposable inhaler into a device named Cyclops enables effective dispersion of up to 50mg of pure spray dried tobramycin. This proves that spray dried tobramycin powders in the preferred size range for inhalation can be administered without applying complex particle engineering techniques and/or using excipients. Only some coarse sweeper crystals added separately are desired to minimise the inhaler losses to less than 20% at 4kPa. The fine particle fractions <5μm of the aerosol obtained from the Cyclops closely resemble the primary particle size distribution of the spray dried tobramycin powder. Moreover, without any further optimisation the Cyclops performs good with other spray dried aminoglycosides such as kanamycin and amikacin too. Therefore, the results of this study show that with an appropriate inhaler design, adapted to the physico-chemical properties of a particular drug or drug class, excellent dispersion can be achieved for high doses of pure (spray dried) drug.

Design, Characterization, and Aerosol Dispersion Performance Modeling of Advanced Co-Spray Dried Antibiotics with Mannitol as Respirable Microparticles/Nanoparticles for Targeted Pulmonary Delivery as Dry Powder Inhalers

Dry powder inhalation aerosols of antibiotic drugs (a first-line aminoglycoside, tobramycin, and a first-line macrolide, azithromycin) and a sugar alcohol mucolytic agent (mannitol) as co-spray dried (co-SD) particles at various molar ratios of drug:mannitol were successfully produced by organic solution advanced co-spray drying from dilute solute concentration. These microparticulate/nanoparticulate aerosols consisting of various antibiotic drug:mannitol molar ratios were rationally designed with a narrow and unimodal primary particle size distribution, spherical particle shape, relatively smooth particle surface, and very low residual water content to minimize the interparticulate interactions and enhance in vitro aerosolization. These microparticulate/nanoparticulate inhalation powders were high-performing aerosols as reflected in the aerosol dispersion performance parameters of emitted dose, fine particle fraction (FPF), respirable fraction (RF), and mass median aerodynamic diameter (MMAD). The glass transition temperature (Tg) values were significantly above room temperature, which indicated that the co-SD powders were all in the amorphous glassy state. The Tg values for co-SD tobramycin:mannitol powders were significantly lower than those for co-SD azithromycin:mannitol powders. The interplay between aerosol dispersion performance parameters and Tg was modeled where higher Tg values (i.e., more ordered glass) were correlated with higher values in FPF and RF and lower values in MMAD.

Primary Particle Size Distribution Measurement of Nanomaterials by Using TEM

Primary Particle Size Distribution Measurement of Nanomaterials by Using TEM

Automated Determination of Aggregate Primary Particle Size Distribution by TEM Image Analysis: Application to Soot

In many applications, nanoparticles appear to be in an aggregated form. Thus, a complete description of their morphology involves an analysis of their size at different scales, from the aggregate size to the primary particle size. In this study, we present an automated method for the determination of the primary particle size distribution. It is based on an image-processing algorithm operating Euclidian distance mapping leading to a function that contains information about aggregates morphology. This algorithm is first applied to virtual aggregates with point contact between spheres, generated by diffusion limited cluster aggregation code. It shows that obtained functions can be used to retrieve the parameters of the primary particle diameter size distribution. However, it also demonstrates that overlapping or necking effects between primary spheres can have an impact on the shape of the function. The analysis is also performed on real soot images generated by ethylene diffusion flame and civil aviation e...

In vitro evaluation of the DP-4M PennCentury™ insufflator

Dry powder formulations for inhalation have to be screened in animal studies for therapeutic efficacy and safety aspects and both are significantly affected by the dose and the particle size distribution (PSD) of the aerosol that is given. One of the most frequently used apparatus for pulmonary delivery of dry powder formulations in mice studies is the PennCentury™ DP-4M Dry Powder Insufflator. To make researchers of future preclinical animal studies with the DP-4M insufflator aware of the pitfalls regarding the conclusions to be drawn from their data, we investigated the dispersion behaviour by the DP-4M insufflator using two to three different powder preparation techniques for four different compounds. The primary PSDs of the different formulations were determined in duplicate by laser diffraction analysis. To measure the PSDs of the aerosols obtained with the DP-4M insufflator, the same diffractometer was used in combination with an in-house constructed adapter for the insufflator. The dispersion efficiency and delivered dose were highly affected by the amount of air available for dispersion; the 200μL of air recommended for the type of insufflator used was insufficient for adequate dispersion. In contrast, the weighed dose did not have a profound effect on the dispersion behaviour and the delivered dose of the DP-4M insufflator. Also the physico-chemical powder properties and the applied particle preparation technique influenced the amount and PSD of the delivered aerosol only to a limited extend, with a few exceptions. We advise researchers to investigate the dispersion efficiency and delivered dose from the DP-4M insufflator with the formulation under investigation prior to in vivo studies and it may be necessary to optimise the formulation for administration to mice.

Dynamic light scattering-based method to determine primary particle size of iron oxide nanoparticles in simulated gastrointestinal fluid

Simple dynamic light scattering (DLS)-based methodologies were developed to determine primary particle size distribution of iron oxide particles in simulated gastrointestinal fluid. Iron oxide particles, which easily agglomerate in aqueous media, were converted into dispersed particles by modification of surface charge using citric acid and sodium citrate. After the modification, zeta-potential value decreased to −40mV at pH 7. Mean particle diameters in suspensions of iron oxide nano- and microparticles stabilized by the mixture of citric acid and sodium citrate were dramatically decreased to 166 and 358nm, respectively, which were close to the particle size distributions observed in the micrographs. In simulated gastrointestinal fluid, both iron oxide nano- and microparticles were heavily agglomerated with particle diameters of almost 2600 and 5200nm, respectively, due to charge shielding on the citrate-modified surface by ions in the media. For determining primary particle size distribution by using DLS-based approach, the iron oxide particles incubated in the simulated gastrointestinal fluid were converted to monodisperse particles by altering the pH to 7 and electrolyte elimination. The simple DLS-based methodologies are well suited to determine primary particle size distribution of mineral nanoparticles at various physical, chemical, and biological conditions.

Modification of the mechanical granule properties via internal structure

Disadvantageous mechanical properties of ceramic granules for die pressing applications, such as too high compression strength or too low ductility, may cause imperfections within the resulting component structure. To avoid these inhomogeneities, the granules have to show optimized mechanical properties.The correlation between internal structure parameters and resulting mechanical properties of ceramic granules was investigated systematically by spray-drying of varied α-Al2O3 suspensions. Nine granule samples with different internal structures were produced. The mechanical properties were characterized using a compression test of single granules. Internal granule structures were quantified using image analysis techniques. To detect structure parameters responsible for changed mechanical granule properties, the internal structure parameters were divided in micro- and macrostructure parameters and their influence on resulting mechanical properties was studied individually.The variation of additive type or amount overlaid the effect of changed internal granule structure parameters on the resulting granule compression strength and strain. If the additive type and amount were kept constant and suspension parameters like solid content, primary particle size, particle surface charge or width of the primary particle size distribution were modified, a clear influence of changed internal granule structure parameters on the resulting mechanical granule properties were measured.Increased shell thickness (macrostructure) and reduced microporosity (microstructure) caused a granule strength increase. The effects of micro- and macrostructure parameters on mechanical granule properties can be added up. For the investigated samples a dominant influence of the microstructure on the resulting mechanical properties compared to the macrostructure effect was found.

Polymeric controlled release inhalable powder produced by vibrational spray-drying: One-step preparation and in vitro lung deposition

Innovative polymeric controlled release inhalable dry powders containing dexamethasone were developed for the treatment of pulmonary diseases. Powders were prepared in one step by vibrational atomization spray-drying using an organic solution containing dexamethasone, poly(ε-caprolactone) and a surfactant. The characteristics of the powders were monitored considering the drug content, morphological features, mean particle size, drug-polymer-surfactant compatibility and physical state. In vitro dexamethasone release was studied applying the dialysis bag method. The dose uniformity of the powders, their aerodynamic properties and the in vitro lung deposition were evaluated using a Dosage Unit Sampling Apparatus and Andersen Cascade Impactor. The powders had a high yield (65–80%), drug content between 170 and 880mg·g−1 and high encapsulation rate (93–97%). All formulations had spherical particles with a rough surface and the primary mean particle size was around 1.00μm. The formulation prepared with the lowest amount of polymer led to a more symmetric primary particle size distribution and an efficient deagglomeration behavior. The powders exhibited dexamethasone crystallinity and no interaction between the drug and other excipients was evidenced. Dexamethasone release from the powders followed the biexponential model. The lowest drug:polymer ratio led to the best controlled release of the drug. Furthermore, the powders showed dose uniformity close to 100%, a mass median aerodynamic diameter lower than 5μm and fine particle fraction between 59% and 62%. These polymeric particles (as powders) can be recommended as a platform for the production of new controlled release systems for pulmonary administration.

Optimizing the primary particle size distributions of pressurized metered dose inhalers by using inkjet spray drying for targeting desired regions of the lungs

Conventional suspension pressurized metered dose inhalers (pMDIs) suffer not only from delivering small amounts of a drug to the lungs, but also the inhaled dose scatters all over the lung regions. This results in much less of the desired dose being delivered to regions of the lungs. This study aimed to improve the aerosol performance of suspension pMDIs by producing primary particles with narrow size distributions. Inkjet spray drying was used to produce respirable particles of salbutamol sulfate. The Next Generation Impactor (NGI) was used to determine the aerosol particle size distribution and fine particle fraction (FPF). Furthermore, oropharyngeal models were used with the NGI to compare the aerosol performances of a pMDI with monodisperse primary particles and a conventional pMDI. Monodisperse primary particles in pMDIs showed significantly narrower aerosol particle size distributions than pMDIs containing polydisperse primary particles. Monodisperse pMDIs showed aerosol deposition on a single stage of the NGI as high as 41.75 ± 5.76%, while this was 29.37 ± 6.79% for a polydisperse pMDI. Narrow size distribution was crucial to achieve a high FPF (49.31 ± 8.16%) for primary particles greater than 2 µm. Only small polydisperse primary particles with sizes such as 0.65 ± 0.28 µm achieved a high FPF with (68.94 ± 6.22%) or without (53.95 ± 4.59%) a spacer. Oropharyngeal models also indicated a narrower aerosol particle size distribution for a pMDI containing monodisperse primary particles compared to a conventional pMDI. It is concluded that, pMDIs formulated with monodisperse primary particles show higher FPFs that may target desired regions of the lungs more effectively than polydisperse pMDIs.

Agglomerates and aggregates of nanoparticles made in the gas phase

Gas-phase (aerosol) technology is used widely in manufacture of various nanostructured commodities at tons/hour today. So it is quite promising for synthesis of sophisticated nanoparticles motivating basic and applied research. Frequently such nanoparticles are made as clusters of primary particles (PPs) by chemical reaction, aerosol coagulation, sintering, surface growth and even fragmentation. When PPs are bonded by strong chemical forces, they are termed aggregates. As such they are sought in catalysis, lightguide preform manufacture and, most importantly, as components in electronic devices (sensors, batteries). When PPs and aggregates are held together by rather weak, physical forces, they form agglomerates. These are attractive in nanocomposites and fluid suspensions (paints, nanofluids, bioimaging). Such clusters may have also distinct health effects, beyond those of equivalent spherical particles.Agglomerates and aggregates are characterized by microscopy, electromagnetic scattering and mass mobility measurements in terms of their volume-equivalent radius, radius of gyration and/or mobility radii in the free molecular and continuum regimes along with the corresponding power laws (fractal dimension, Df). Coagulation and sintering largely determine nanoparticle structure. Coagulation of PPs leads to agglomerates of Df=1.78 and 1.91 in the continuum and free-molecular regimes, respectively. The coagulation rate of agglomerates is higher than that of volume-equivalent spheres in the free molecular regime. Agglomerates attain also a self-preserving size distribution by coagulation facilitating process design for their manufacture. Mesoscale simulations elucidate the sintering (or coalescence) of agglomerates to aggregates and narrowing of their PP size distribution. Once agglomerates start to sinter, they follow a power law to aggregates and eventually to compact (spherical) particles, regardless of composition and initial PP size distribution. Aggregate properties are in-between those of the initial agglomerate and the fully coalesced sphere. Finally the stability of agglomerates under ultrasonication, stretching, fluid dispersion, impaction and capillary condensation is highlighted.

Bimodal size distribution of primary particles in the plasma of welding fume: Coalescence of nuclei

Nucleation and growth of the nuclei in the thermal plasma of the ionized metal vapors of welding fume are studied. The coalescence of liquid droplets formed by the vapors' nucleation is calculated. There is a high flow rate of condensable atoms from the gas phase into the condensed phase caused by the nucleation and association of nuclei with the aggregated droplets. The fast association of the nuclei with aggregated droplets leads to a decrease in the condensable vapor supersaturation and to the termination of nucleation and start of the bimodal coalescence. As a result, in the beginning of phase transition, there is bimodal size distribution of the primary particles: the small-size primary particles formed by association between the nuclei (intramodal coalescence only), and the primary large-size particles formed by association between the aggregated droplets and the nuclei (intramodal and intermodal coalescence).

Population Balance-Monte Carlo Simulation for Gas-to-Particle Synthesis of Nanoparticles

The process simulation of nanoparticle synthesis via the gas-phase method is essential to understanding the detailed dynamic evolution of nanoparticles within a very short time period under high temperature. The task is, however, very challengeable up to now as the conversion of the gaseous precursor to the end-use nanoparticle is a complex physicochemical process involving nucleation of the particulate phase, agglomeration between particles and sintering under industrial production conditions. In this article, we extended the differentially weighted Monte Carlo method for population balance to simulate the dynamic evolution of titania (TiO2) nanoparticles synthesized by gas-to-particle conversion in a single aerosol reactor, considering simultaneous nucleation, agglomeration, and sintering. The simulated size distribution of TiO2 agglomerate and primary particles produced by the thermal decomposition of titanium tetraisoproxide agreed well with the experimental data. In the simulation, the fast population balance-Monte Carlo method was utilized to accelerate the process simulation on a desktop PC. Results were obtained up to 178 times faster than that of a normal Monte Carlo method. The inhomogeneous internal structure of primary particles was considered through solving population balance of polydisperse primary particles within agglomerate. It was found the polydisperse model could predict the primary particle size distribution better. Simulation results revealed a complex competition relation among nucleation, agglomeration and sintering. Copyright 2013 American Association for Aerosol Research

Integrated Population Balance Model Development and Validation of a Granulation Process

This study is concerned with the development of an integrated three-dimensional population balance model (PBM) that describes the combined effect of key granulation mechanisms that occur during the course of a granulation process. Results demonstrate the importance of simulating the different mechanisms within a population balance model framework to elucidate realistic granulation dynamics. The incorporation of liquid addition in the model also aids in demarcating the dynamics in different regimes such as premixing, granulation (during liquid addition) and wet massing (after liquid addition). For the first time, the effect of primary particle size distributions and mode of binder addition on key granule properties was studied using an integrated PBM. Experimental data confirms the validity of the overall model as compared to traditional models in the literature that do not integrate the different granulation mechanisms.