Primary Particle Size Distribution Research Articles

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.

Over time and space changing characteristics of estuarine suspended particles in the German Weser and Elbe estuaries

Fine cohesive, suspended sediments appear in all estuarine environments in a predominately flocculated state. The transport and deposition of these flocs is influenced by their in-situ and primary particle size distribution. Especially the size of the inorganic particles influences the density and hence the settling velocity of the flocculated material. To describe both the changes in primary particle size of suspended particulate matter as well as the variability of floc sizes over time and space, the data of In-Situ Particle-Size Distributions (ISPSDs), Primary Particle Size Distributions (PPSDs) and Suspended Sediment Concentrations (SSCs) were collected. For this, Laser In-Situ Scattering and Transmissiometry (LISST) measurements as well as the water samples were collected in the German Elbe and Weser estuaries, covering seasonal variability of the SSC.The data of the ISPSDs show that the inorganic and organic Suspended Particulate Matter (SPM), as found in the Elbe and Weser estuaries, mostly appears in a flocculated state. The substrate for organic matter is mainly imported from the seaside and transported into the estuaries as indicated by an upstream decrease of the amount of fine particles. In winter, when the freshwater discharge is high, different PPSDs are found in the case of the Elbe estuary in the Turbidity Maximum Zone (TMZ) as well as in the landward and in the seaward sections close to the TMZ. In summer, the distance between the seaward and the landward section is too low to obtain an individual PPSD within the Elbe TMZ.A missing correlation between the PPSD and ISPSD shows that the inorganic constituents do not have an influence on the in-situ floc size. Although flocs aggregate and disaggregate over a tidal cycle and with changing SSC, they do not change their PPSD. The microflocs are therefore strong enough to withstand further breakage into their inorganic constituents.

Restructuring of aggregates and their primary particle size distribution during sintering

During sintering (coalescence) of aggregates of polydisperse primary particles (PPs), restructuring takes place, the average PP size increases and the PP size distribution (PPSD) narrows affecting particle performance in a number of applications. Here, aggregate sintering by viscous flow, lattice, and grain boundary diffusion is simulated by multiparticle discrete element methods focusing on PP growth dynamics and elucidating the detailed restructuring of aggregates during their coalescence. The effect of initial PPSD and sintering mechanisms on the evolution of PP polydispersity (geometric standard deviation) and surface area mean diameter are presented. Each sintering mechanism results in a distinct evolution of PPSD but quite similar growth in average PP diameter. Grain boundary diffusion has the strongest impact among all sintering mechanisms and rapidly results in the narrowest PPSD, as it has the strongest dependence on PP size. During sintering of aggregates with initially monodisperse PPs, the PPSD goes through a maximum width before narrowing again as PPs coalesce. A power law holds between projected aggregate surface area and number of PPs regardless of sintering mechanism and initial PP polydispersity. This law can be readily used in aerosol reactor design and for characterization of aggregates independent of material composition, initial PP polydispersity, and sintering mechanism. © 2013 American Institute of Chemical Engineers AIChE J, 59: 1118–1126, 2013

Primary particle size and agglomerate size effects of amorphous silica in ultra-high performance concrete

Abstract Silica fume is widely used in ultra-high performance concrete (UHPC). However, it is a by-product in the industrial silicon production and therefore far from an optimized additive. Silica fume improves the compressive strength, but its detailed reaction mechanisms in concretes with low water/cement ratios are not yet fully understood. This study focuses on the influence of primary particle sizes and sizes of agglomerates of different amorphous silicas in UHPC. As a reference system, wet-chemically synthesized silica was used with very high purity, defined particle sizes, narrow primary particle size distributions and controllable agglomerate sizes. The obtained data were compared to silica fume. The results indicate that non-agglomerated silica particles produce the highest strength after 7 d, but a clear dependence on primary particle sizes, as suggested by calculations of packing density, was not confirmed. UHPC may be improved by incorporating an ameliorated dispersion of silica e.g. through commercial silica sols.

Variations in diesel soot reactivity along the exhaust after-treatment system, based on the morphology and nanostructure of primary soot particles

The reactivity of soot at different sites of the exhaust after-treatment system of a diesel engine (upstream and downstream of the diesel oxidation catalyst (DOC), downstream of the diesel particulate filter (DPF), as well as inside the DPF) was investigated on the basis of morphology and structure of primary soot particles by high resolution transmission electron microscopy (HRTEM). The results indicate that combustion-formed soot particles are susceptible to further transformations of their morphology within the exhaust system. The same primary soot particles can possess both oxidation-promoting and oxidation-inhibiting morphological features, the particle cores being highly reactive. Most reactivity-promoting features are encountered in pre-DOC and post-DOC primary particles, suggesting that soot can be more easily oxidised before it enters the DPF. The residence time of soot in the DPF contributes to modification of its reactivity by affecting size distribution and nanostructure of primary particles. Partial NO2 oxidation and high temperatures during active regeneration modify the morphology of outer particle shells, thus rendering post-DOC and post-DPF primary soot particles less reactive in this respect. Primary soot particles that pass through the DPF and reach the atmosphere are characterised by the highest graphitisation degree and sizes larger than those entering the DPF. Complementary Near-Edge X-ray Absorption Fine Structure (NEXAFS) analyses proved not as relevant regarding soot reactivity but indicate higher chemical inhomogeneity of pre-DOC than of post-DOC and post-DPF soot and high contents of carboxyl carbon in post-DPF particles.