Agglomerate Size Research Articles

Polyphenols-inspired interface modification and reduced agglomeration of solid propellants via a functionalized fluorine-containing organic substance coating layer

Interface modification of aluminum particles plays a crucial part in reducing the agglomeration during the combustion of solid propellants. In this study, the aluminum (Al) particles are pretreated with gallic acid (GA) to get Al@GA with an adhesion-favorable surface, which facilitates the further coating procedure. One new fluorine-containing organic substance is prepared, namely p-HFBA. The p-HFBA further coats the Al@GA to produce Al@GA/p-HFBA. The interface between Al@GA and the coating layer p-HFBA forms AlF bonds and induces a pre-ignition reaction with an aluminum oxide shell. Hence, the agglomerate size of propellants containing Al@GA/p-HFBA significantly decreases from 176.30 μm to 84.72 μm. The agglomerates volume is reduced by approximately 97 %. Additionally, more gaseous products investigated by TG-MS provide the Al particles with greater impetus (aerodynamic forces, Fae), enabling them to leave the burning surface and reduce the residence time. The rise in Fae and drop in adhesion force (Fad) effectively reduce the agglomeration intensity according to the skeleton layer model. This work proves that interface modification can effectively enhance the combustion performance of aluminized solid propellants.

Impact of typical land use type on the stability and content of carbon and nitrogen of soil aggregates in western Hubei

AbstractIn order to investigate the characteristics of soil structural stability and the factors influencing it under typical land use types in the karst region of western Hubei, soil samples were collected from five land use types (natural mixed forest [NF], cypress forest [CF], stone dike terrace [ST], stone dike forest [SF], and abandoned land [AL]) in Xialaoxi to analyze the particle size distribution of aggregates, structural stability, and the distribution characteristics of carbon, nitrogen, and extracellular enzyme contents. The results showed that the aggregates of NF, CF, SF, and AL were dominated by >2‐mm aggregates, while ST showed mostly 2–0.25‐mm aggregates. The mean weight diameter (EMWD) and the geometric mean diameter (EGMD) of mechanical aggregates showed a trend of CF > NF > SF > AL > ST, whereas the erodibility factor K showed an opposite trend. The total organic carbon (TOC), labile organic carbon (LOC), and total nitrogen (TN) contents of aggregates of each particle size were significantly higher in NF and CF than in ST and AL under the five land types. The content of available nitrogen (AN) was highest in NF and ST. The content of carbon and nitrogen and extracellular hydrolases (β‐glucosidase [BG], cellulose disaccharide hydrolase [CBH], β‐N‐acetyl‐aminoglucosidase [NAG], and leucine aminopeptidase [LAP]) in soil aggregates were mainly concentrated in <0.25–0.053‐mm aggregates. The variation in carbon and nitrogen abundance of each particle size agglomerate mainly originated from the LAP content of that particle size agglomerate and showed significant correlation. The partial least squares path models (PLS‐PM) showed that the main influences on the stability of soil aggregates in small watersheds were land use types, soil physical properties, carbon and nitrogen abundance, and extracellular enzyme activity. In conclusion, the structural stability of soil aggregates in Xialaoxi watershed is the result of the interaction between human disturbance and soil nutrient self‐cycling. In general, NF and CF have better soil aggregate stability and are conducive to soil carbon and nitrogen accumulation, whereas for later development and management of SF, ST, and AL sample plots, scientific cultivation means should be adopted, and attention should be paid to long‐term carbon and nitrogen accumulation and conservation.

Precise particle size control during spherical agglomeration of benzoic acid by modification of the bridging liquid phase using TWEEN 20

The interest in spherical agglomeration processes in the pharmaceutical industry is rising due to the possibility of direct tableting of Active Pharmaceutical Ingredients and enhancements in bulk powder properties translating into improved powder processability. While agglomerating needle-shaped particles into spheres offers numerous advantages, such as improved flowability, filterability, and particle density, achieving precise control over the particle size and shape of the agglomerates remains a significant challenge. More specifically, the obtained agglomerate size rarely reaches values below 500 μm, which is the desired size range for pharmaceutical applications. To address this challenge, the current research investigates the effectiveness of incorporating surfactants at varying concentrations as a means to control the particle size and shape of the resulting agglomerates. Reversed addition antisolvent crystallization experiments were performed in ethanol/water using benzoic acid as a model compound, followed by the addition of a bridging liquid (toluene), which wets and bridges the single crystals into agglomerates. To modify the interfacial tension between the two immiscible liquid phases, different concentrations of the tween 20 surfactant were used, leading to a range of interfacial tensions spanning from 0.50 to 16.38 × 10−3 N/m. Both crystallization and agglomeration processes were monitored in situ using in-process microscopy tools. The experimental results demonstrated that by adjusting the surfactant concentration and thus the corresponding interfacial tension of the bridging liquid, highly tunable agglomerate sizes were achieved, ranging from 160 μm to 4412 μm. A higher surfactant concentration is correlated with smaller agglomerates and is key to control the final agglomerate size. However, it should be noted that the introduction of surfactants in the spherical agglomeration process negatively impacted the agglomerate's strength. Nonetheless, this method remains a promising and innovative technique for controlling the final particle size during spherical agglomeration.

Ternary Dry Powder Agglomerate Inhalation Formulation of Melatonin With Air Jet Mixing to Improve In Vitro And In Vivo Performance

An improved agglomerate formulation with melatonin and fine lactose for dry powder inhalation using Turbuhaler® was developed. Co-grinding lactose with 1 % magnesium stearate prior to air jet mixing served as a key factor to improve the in vitro aerosolization and in vivo efficacy. Elevated mixing pressure facilitated the dispersion and homogenization of the cohesive mixture for even distribution of agglomerate size after spheroidization and subsequent higher emitted dose with lower variation. Magnesium stearate was employed as a tertiary component to adjust the interparticle force for better aerosolization. At optimized mixing pressure, co-grinding lactose with magnesium stearate before jet mixing displayed further improvement of fine particle fraction to 71.6 ± 3.1 %. The superior fine particle deposition efficiency contributed to rapid onset of action and a high bioavailability of 67.0 % after intratracheal administration to rats. Overall, an inhalable melatonin dry powder formulation exhibiting good aerosol property and lung deposition with clinical translation potential was developed.

Optimizing the surface modification of cohesive polyethylene powders in a vibrated plasma-spouted bed: Exploring agglomerate size impact on coarser particle addition mechanism

Ultrafine polymer powders have garnered attention owing to their superior physical properties and reactivity. Nonetheless, the cohesive nature of these powders notably impedes efficient plasma surface modification, thereby limiting potential applications. The effects of optimizing the fluidization of cohesive powders on plasma treatment within a plasma-spouted bed were investigated in a prior study, wherein surface modification was significantly improved by incorporating coarser particles and vibration. However, the optimal conditions and mechanisms by which adding coarser particles to a vibrated plasma-spouted bed contributes to this enhancement remain unelucidated. This study entailed an investigation of the influence of gas flow rate, agglomerate properties, and plasma distribution in optimizing the wettability modification of ultrafine powders. Results indicate that increased gas flow rate, coarser particle size, and quantity lead to the formation of smaller, more uniform-sized agglomerates. Furthermore, the contact angle of the treated powder demonstrated a linear decrease with the reduction of average agglomerate size within a suitable gas velocity range, suggesting that enhanced exposure of the powder surface to plasma contributes to the optimization of plasma treatment. However, high-gas velocity may trigger particle entrainment and diminish surface modification, as evidenced by the limited plasma distribution primarily at the bottom of the reactor.

Effects of agglomerate structure and operating humidity on the catalyst layer performance of PEM fuel cells

Understanding the transport mechanism in catalyst layer (CL) agglomerates is crucial to enhance Pt utilization and overall fuel cell performance. In this study, high-resolution porous agglomerates are stochastically reconstructed, and capillary condensation of water in agglomerates is directly simulated using a lattice Boltzmann pseudopotential model. On this basis, a pore-scale electrochemical model is developed to investigate the effects of agglomerate structure and operating humidity on local transport resistance and agglomerate effectiveness at different Pt loadings. The results reveal that liquid water formed above 70%RH improves the electrochemical surface area (ECSA) of agglomerates with low ionomer content. An optimum I/C of 0.4 in agglomerates is determined by balancing the activated ECSA and oxygen transport resistance. Through the comparison of local transport resistance with limiting current data, an additional oxygen dissolution resistance of 60–350 s m−1 at the pore/ionomer or ionomer/Pt interface is quantified. The lowest local transport resistance of the agglomerate is achieved at about 70%RH, while condensed water at higher humidities hampers oxygen diffusion within the agglomerate, leading to reduced Pt utilization. Agglomerate size significantly affects the local transport resistance only when excessive ionomer or liquid water severely blocks primary pores. Finally, a novel multiscale coupling strategy integrating the porous agglomerate sub-model with a continuous-scale CL model is proposed, offering innovative insights into comprehending the relationship between CL structure and the performance of proton exchange membrane fuel cells.

Structure-property relationships in the electrical conductivity of multilayer graphene sheet/epoxy nanocomposites

The relationship between the physicochemical properties of multilayer graphene sheets (GSs), their resulting state of dispersion, and the effective electrical conductivity of GS/epoxy nanocomposites is investigated. To construct such relationship, four types of GSs with dissimilar properties were physicochemically, structurally, and morphologically characterized, and correlated with the direct current and alternating current (AC) electrical responses of their polymeric nanocomposites. It was found that the most influential parameters that affect the electrical conductivity of the nanocomposites are the size and density of agglomerates formed at the mesoscale. Both parameters, in turn, are governed by the physicochemical properties of the individual GSs. At the nanostructure level, the lateral size of the GS arises as the most influential parameter, with larger GSs yielding higher conductivities and lower percolation thresholds. The carbon/oxygen ratio of the GSs also showed moderate influence. The nanocomposites showed a resistive (R)-capacitive (C) electrical response in AC, which fits to a two-element parallel RC model. Both, the power law and general effective media (GEM) models predict similar percolation thresholds, but the GEM model is more general and adequately reproduces the whole electrical curve for all filler concentrations.

Effect of PEG nanoparticle surface coating on the magnetic and structural properties of CoFe2O4/PVDF composites

This research focuses on the impact of polyethylene glycol (PEG) coating on the magnetic and structural properties of composites consisting of an electroactive polyvinylidene fluoride matrix and CoFe2O4 nanoparticles. The intrinsic piezoelectric and magnetic properties of the constituents fundamentally determine the properties of composites, but the microstructure and particle packing of the composite are equally crucial for enhancing magnetoelectric coupling. Our findings reveal that PEG coating promote a more uniform spatial distribution of particles agglomerates within the polymer matrix, which achieved by strengthening of the interfacial coupling and reducing of the filler density during the solvent casting process. Together with reduced agglomerates size from an average of 28 ± 3 μm to 17 ± 1 μm uniform spatial distribution leads to decrease of magnetic dipolar interactions from ∼ 900 Oe to ∼ 800 Oe - tendence confirmed from the first-order reversal curve (FORC) analysis. Additionally, the root mean square roughness of the composite surface decreases from 185 nm to 74 nm, indirectly confirming increased sample uniformity. Local electrical properties, measured through Piezoresponse Force Microscopy (PFM), show a substantial enhance of the local piezoelectric response by ∼ 40 %. Results can be used for the enhancing of magnetoelectric effect in biocompatible materials, utilized at low frequency.

Improved physical and structural properties of high-protein powders by fluidized-bed agglomeration.

High-protein powders (milk protein isolate (MPI) and soybean protein isolate (SPI)) were treated with maltodextrin solution (10% or 20%) or water as a binder and then subjected to fluidized-bed agglomeration. The MPI agglomerates were compared with the SPI agglomerates as a function of maltodextrin (MD) concentration. The particle size, wettability, and porosity values of SPI agglomerates were much higher than those of the raw powder when compared to the MPI agglomerates. The agglomerated protein powders with MD binder showed significantly higher solubility values than the raw powders. These tendencies were discernible in the morphological examination via SEM analysis. The dynamic modulus values of SPI agglomerates decreased with an increase in MD concentration from 10 to 20% whereas those of MPI agglomerates increased. These findings indicate that the physical, structural, and rheological properties of agglomerated high-protein powders are greatly influenced by the type of protein and the addition of MD binder.

Enhancement of material attributes of poorly compressible metformin hydrochloride through coprocessing with hydroxypropyl cellulose (HPC-L) using coprecipitation (CPT)

Coprocessing involves integration of multiple substances to improve the physical, chemical, mechanical, and biopharmaceutical properties of a material. Coprocessing is a promising technique in the pharmaceutical industry which support both drug substance and drug product processes. When active pharmaceutical ingredients (APIs) are coprocessed with excipients, it can enable direct compression and continuous manufacturing. Hydroxypropyl cellulose (HPC-L), a commonly used excipient in pharmaceutical formulations, can enhance drug stability, solubility, and bioavailability. In this study, we have employed coprecipitation (CPT) to coprocess metformin hydrochloride (MET) with HPC-L, resulting in the formation of agglomerates with improved physical attributes without any risk of polymorphic changes. Acetone/acetonitrile and heptane were used as solvent and antisolvent, respectively. Screening study revealed that the use of a rotor stator helps to control the size of metformin hydrochloride and HPC-L agglomerates (M-CPT) without negatively impacting bulk density and powder flow properties. The CPT agglomerates showed residual solvent levels within the specified ICH limits. Powder rheology results demonstrated a sixfold increase in FFC of M-CPT compared to neat MET. The compressibility, tabletability, compactability, and “In-Die” Heckel analysis data further suggested that the M-CPT agglomerates are directly compressible with no observable changes in the dissolution profile of MET. Overall, this study demonstrates application of CPT approach to tune the physical and mechanical properties, and HPC-L can be used as an excipient of choice for CPT technique to improve the compressibility and flowability of APIs.Graphical

Impact of environmental oxygen on nanoparticle formation and agglomeration in aluminum laser ablation plumes.

The role of ambient oxygen gas (O2) on molecular and nanoparticle formation and agglomeration was studied in laser ablation plumes. As a lab-scale surrogate to a high explosion detonation event, nanosecond laser ablation of an aluminum alloy (AA6061) target was performed in atmospheric pressure conditions. Optical emission spectroscopy and two mass spectrometry techniques were used to monitor the early to late stages of plasma generation to track the evolution of atoms, molecules, clusters, nanoparticles, and agglomerates. The experiments were performed under atmospheric pressure air, atmospheric pressure nitrogen, and 20% and 5% O2 (balance N2), the latter specifically with in situ mass spectrometry. Electron microscopy was performed ex situ to identify crystal structure and elemental distributions in individual nanoparticles. We find that the presence of ≈20% O2 leads to strong AlO emission, whereas in a flowing N2 environment (with trace O2), AlN and strong, unreacted Al emissions are present. In situ mass spectrometry reveals that as O2 availability increases, Al oxide cluster size increases. Nanoparticle agglomerates formed in air are found to be larger than those formed under N2 gas. High-resolution transmission electron microscopy demonstrates that Al2O3 and AlN nanoparticle agglomerates are formed in both environments; indicating that the presence of trace O2 can lead to Al2O3 nanoparticle formation. The present results highlight that the availability of O2 in the ambient gas significantly impacts spectral signatures, cluster size, and nanoparticle agglomeration behavior. These results are relevant to understanding debris formation in an explosion event, and interpreting data from forensic investigations.

INFLUENCE OF YAG CERAMIC POWDERS GRINDING CONDITIONS OF ON THE PROPERTIES OF OPTICAL CERAMICS

In this study, the changes in the morphology and degree of agglomeration of both precursor powders and ceramic YAG powders under varying grinding conditions was considered. The effect of these parameters on the optical properties and structure of the ceramics was assessed. The YAG precursor powders were obtained through chemical co-precipitation. The morphology, size of agglomerates, and crystallites was evaluated using scanning electron microscopy, laser diffraction analysis, X-ray phase analysis, and Brunauer–Emmett–Teller gas adsorption. It was found that milling the YAG precursor powders allows for a reduction in the degree of agglomeration of the ceramic powders. It was discovered that optimal modes can be achieved at a mass ratio of grinding balls to precursor powder of 6.75/1 and a ratio of the mass of the grinding medium to the mass of the precursor powder of 4.5/1. These modes provide the necessary granulometric characteristics and the highest monodispersity. Therefore, it has been demonstrated that the use of an additional milling stage for powders synthesized by chemical precipitation, along with the selection of milling modes, can improve the properties of YAG optical ceramics.

Synthesis and Properties of Rubidium Salts of Phosphotungstic Acid

The work is devoted to the study of the influence of synthesis conditions on the properties of water-insoluble rubidium salts of phosphotungstic acid (PTA). Such heteropoly compounds have a wide range of applications, including in the field of electrocatalysts and solid electrolytes for various electrochemical devices. The acid salts of PTA with high activity of acid sites on the particle surface are of particular interest. It is known that the properties of water-insoluble PTA salts strongly depend on synthesis conditions, such as the ratio of reagents, temperature, concentrations, and other parameters. The work examines the influence of the ratio and concentration of reagents on the sizes of crystallites and agglomerates, specific surface area (SSA), porosity, water content, and ionic conductivity of the synthesized PTA salts. The SSA value of the obtained samples varied in the range of 84–123 m2 g−1, and the ionic conductivity was 13–90 mS cm−1 at room temperature and 75% RH. An increase in the acid concentration and the degree of proton substitution led to an increase in SSA, accompanied by an increase in particle sizes without changing the size of crystallites. The results of the work may be useful for the development of new materials based on the obtained salts in many fields, including hydrogen energy.

Investigation of the Particle Formation Mechanism during Coprecipitation of Ni-Rich Hydroxide Precursor for Li-Ion Cathode Active Material

Industrial production of cathode active material (CAM) for lithium-ion batteries is conducted by coprecipitation of a hydroxide (NixCoyMnz(OH)2) precursor (referred to as pCAM) in a stirred tank reactor and subsequent high-temperature calcination of the pCAM with a lithium compound. The physical properties of the resulting CAM are significantly affected by the associated pCAM utilized for synthesis. For an economical manufacturing of pCAM and CAM, the pCAM particle size and sphericity during the coprecipitation reaction must be precisely controlled, requiring an in-depth understanding of the NixCoyMnz(OH)2 particle formation mechanism. Therefore, the development of the secondary particle size and morphology throughout the semi-batch coprecipitation of Ni0.8Co0.1Mn0.1(OH)2 at various stirring speeds was monitored by light scattering and SEM imaging, respectively. A two-stage particle formation mechanism was identified: In the initial seeding phase, irregular-shaped secondary particles agglomerates are formed, which in the subsequent growth phase linearly increase in size with the third root of time, governed by the growth of individual primary particles. Thereby, the degree of turbulence governs the initial agglomerate size and number formed during seeding, which dictates the growth rate and the secondary particle sphericity. Finally, the proposed particle formation mechanism is compared to mechanisms prevailing in the literature.

The synergistic triad of graphene quantum dots, polymer, and ferrites for the photodegradation of dyes in aqueous solution

This work aimed to investigate photocatalytic properties of GQDs@PEG@Mg–ZnFe2O4 nanocomposite, composed of graphene quantum dots (GQDs), polyethylene glycol (PEG), and Mg–ZnFe2O4, for the degradation of methylene blue (MB) and crystal violet (CV). This nanocomposite was synthesized using facile ultrasonics-assisted methodology. XRD analysis confirmed the formation of the spinel structure of the Mg–ZnFe2O4 in the nanocomposite, whereas the presence of GQDs and PEG was confirmed by Fourier transform infrared spectroscopy. Scanning electron microscopy (SEM) revealed a reduction in agglomeration and particle size in the ternary nanocomposite. The GQDs@PEG@Mg–ZnFe2O4 nanocomposite demonstrates a remarkable degradation efficiency of 98 % for CV and MB dyes in the presence of sunlight in 120 min, indicating its potential as an efficient photocatalyst. Vibrating sample magnetometer (VSM) analysis confirmed the superparamagnetic behavior of the GQDs@PEG@Mg–ZnFe2O4 nanocomposite which enables magnetic recovery of the photocatalyst after the degradation process. Overall, this study emphasizes the utilization of an environmentally friendly approach to effectively eliminate organic pollutants from wastewater, addressing a crucial environmental concern.

Drug loading comparison of commercial ibuprofen on magnetite nanoparticles surface by UV–Vis spectrophotometry and acid-alkali titration by a factorial design of experiments

The drug efficacy for the pathologies treatments depends on several physicochemical properties of the drug. Among these, solubility is one of the most important and is directly related to the bioavailability of the drug. Ibuprofen is a popular drug used for the treatment of different diseases. However, its dissolution rate in aqueous media is limited, which causes undesirable adverse effects on the patient. One of the possibilities to solve this challenge is loading ibuprofen on the surface of the nanoparticles for drug delivery. However, some challenges related to complicated experimental procedures, expensive chemical precursors, the techniques for ibuprofen quantification, and the loading efficiency continue to be a problem. This work reports the synthesis of magnetite nanoparticles and the straightforward loading with commercial ibuprofen in a mixed ethanol/water solution without intermediate surfactants, stabilizers, or linkers. XRD, SEM, FT-IR, Magnetometry, UV–Vis Spectrophotometry, and DLS techniques allowed for determining the samples' structure, morphology, functional groups, magnetism, and agglomerate size. A complete factorial Design of Experiments allowed for comparing the encapsulation efficiency for two exposure and centrifugation times (20 and 40 min) by UV–VIS and Acid-alkali titration. The results suggest that the magnetic separation and centrifugation (< 2000 RPM) were inappropriate for nanoparticle decantation. This produces an underestimation of the ibuprofen adsorbed by the nanoparticles. Under our experimental conditions, 20 min is enough to achieve maximum encapsulation efficiency (14%) without surfactants or binders.

Discrete element analysis of diametrical compression of annular agglomerates

The tensile strength is an important material attribute of granular products, and diametrical compression is one of the most common methods to determine the tensile strength of the agglomerate. In this study, three-dimensional diametrical compression tests of annular agglomerates with various bonding strengths, i.e. interfacial energies and internal holes, are for the first time modelled by the Discrete Element Method (DEM) with the JKR theory. The fracture patterns and tensile strengths of annular specimens are analysed and compared with those of disc specimens. It is found that annular specimens show complete tension failures with progressive fractures along the loading diameter towards the central hole, while the disc specimens show wedge-shaped shear fractures near the platens. The results also show that the tensile strengths of annular specimens are linear with the surface energy, whereas increase with the size of internal hole and then decrease with the size of internal hole. A dimensionless parameter is introduced to analyse the failure mechanism of the agglomerate. This parameter quantifies the ratio between the external force exerted by the platens and the cohesive force among bonded particles. The proposed parameter emphasises the crucial influence of the internal hole size of an annular agglomerate and bonding capacity on its tensile strength.

Extension of Geldart classification based on the magnitude of interparticle forces

The boundary between Geldart groups A and C is formulated based on the magnitude of interparticle forces (IPFs). It was postulated that the transition from group A to C happens if the interstitial gas velocity at minimum fluidization exceeds the particle terminal velocity. The proposed model led to novel equations correlating the magnitude of IPFs and the corresponding agglomerate size at this boundary to the bed voidage at minimum fluidization. The proposed boundary was validated by experimental data from literature, including those under an enhanced level of IPFs. The transition between Geldart groups A and C typically occurs when minimum fluidization voidage is 0.6–0.7, corresponding to IPFs about an order of magnitude greater than the weight of a particle and agglomerates about three times larger than the particle size. A comparison of the weight of particles at the boundary between groups A and C and between groups A and B suggests that IPFs are about an order of magnitude smaller than the weight of a particle for the latter. It was shown that, for a given material, particle diameter at the boundary between Geldart groups A and C is proportional to the cube root of interparticle forces. The variation of the boundary between groups A and C with IPFs were presented in a 3D graph.

On regularities of the formation of fractal structure on the surface of metal films of different thickness

The surface morphology of nanosized copper and nickel films on mica is studied using a scanning tunneling microscope. Altitude parameters and fractal dimension are determined for copper and nickel films of different thicknesses. The characteristic sizes of structural agglomerates for copper and nickel films are indicated depending on the thickness. The choice of the film thickness and the conditions for its production makes it possible to formulate recommendations for the development of the technology of “growing” structures with a given surface morphology.

Simplified finite element method for resistance response of graphene composites considering size distribution and agglomeration

Simplified finite element method for resistance response of graphene composites considering size distribution and agglomeration