Function Of Particle Size Research Articles

Magnetization Dynamics Behavior in Y3Fe5O12 Particles

YIG particles were obtained by Pechini method with a thermal annealing between 800 and 1200 °C. The formation of the cubic YIG phase was corroborated by means of X-ray diffraction (XRD), where YIG particles have crystallite size range between 107 and 303 nm. Magnetization dynamics were studied by means of magnetization hysteresis cycles, ferromagnetic resonance, and micromagnetic simulations. Different magnetic processes were determined as particle size function, and the magnetization dynamics can be explained by different contributions, such as single domain state, magnetic vortex state, and superparamagnetic behavior, besides considering their interactions. Graphical Abstract

Simulation of settling velocity and motion of particles in drilling operation

The advancement in drilling technologies within the last two decades has allowed deep vertical drilling and long horizontal and multilateral wells. A common operational issue in drilling such long wellbores is efficient hole cleaning and transportation of the generated drill cuttings to the surface. Efficient hole cleaning is a complex problem as it involves a simultaneous analysis of cuttings characteristics, fluid rheology and the geometry of the annulus space. Simplified analytical models, supported by lab experimental observations and numerical simulations have been proposed to determine the optimum flow rate for efficient hole cleaning. These models discard the influence of some parameters due to simplified assumptions. The use of particle based numerical models presented advantages in terms of considering the interaction of the particles and more realistically modeling the coupled flow and particles’ interaction. Yet, more studies are needed to fully understand the complex nature of cuttings transportation.In this study, we first present the results of the settling velocity of a single particle in a stationary incompressible Newtonian fluid falling vertically in an infinite medium, a pipe and an annulus space. The Basset–Boussinesq–Oseen equation (BBO) analytical solution using the differential transformation method (DTM) and DTM- Padé approximations as well as the semi-analytical solution using MATLAB were used to calculate the settling velocity and track the particle motion as a function of particle size and density as well as fluid viscosity at different time. The results were compared with experimental results and the Eulerian-Lagrangian based numerical simulations conducted using MFiX software. In overall, good agreements were observed between the results of the semi-analytical, experimental and numerical simulations. However, higher orders of approximations were required in analytical models to converge the solution and yield better results, but still may show some fluctuations.The findings of single particle analysis were extended to multiple particle simulations. The downward motion of a pack of identical 3 mm spherical particles composed of 171 particles with 8gr/cc density inside a pipe and an annulus space were simulated numerically and the velocity of the pack was determined as a function of particle size and density as well as fluid viscosity. Also, the time when the lower and upper boundaries of the pack reached the bottom of the annulus were defined. The results suggest that relationships exist between the motion (i.e. the vertical location) of the single particle and the boundaries of the multiple particles’ pack. We also simulated the settlement of heterogeneous particles, i.e. two packs of 1 mm and 3 mm particles, respectively, and two packs of anhydride and sandstone particles falling simultaneously in a stationary fluid in an annulus space. Here also relationships observed between vertical motion of single particle and multiple heterogeneous packs. This result may help to better define the corresponding depth of the cuttings observed at the surface as, due to their densities and sizes, cuttings corresponding to deeper depth may reach the surface earlier, hence, defining the novelty of this research.

Raman and Brillouin scattering of spherical nanoparticles and their clusters

The inelastic light scattering of the acoustic vibration of spherical nanoparticles is reviewed. For particles much smaller than the wavelength of the exciting light (λ), with a diameter ( d ) smaller than about 20 nm, the dominant physical mechanism, called Raman, is the polarizability fluctuation due to dipole dipole or bond polarizability induced effects. Only spheroidal modes with l = 0 and l = 2 are Raman active. For particles of size comparable with λ ( d larger than about 100 nm) a different physical mechanism is dominant, the mass displacement and relative polarization associated with the vibration, as for the usual Brillouin scattering of liquid and solids. As the size increases, higher and higher l modes with higher and higher n, the index that labels the radial wavevector, become important and many dozen of peaks appear for d > 500 nm. A simple model allows to reproduce the main features of the observed spectra. A more precise agreement is obtained by a refinement that considers the interaction among the particles in a phononic crystals. The interaction produces broadening and shift of the lines and accounts for the presence of a very low frequency broad band, attributed to the density of states of the modes of the sound propagation in the crystal. The analysis of the spectra allows to obtain information on the dynamics of the single free sphere and on the strength of the interaction. By measuring the temperature-dependence of the Brillouin spectra in clusters of polystyrene nanoparticles during the sintering process, it is possible to identify the glass- transition temperature and calculate the elastic modulus of individual nanoparticles as a function of particle size and chemistry. Surface mobility is evidenced by a size dependence of the interaction among the particles and of the glass transition temperature.

MODELLING AND OPTIMIZING THE APPLICATION OF WASTE TYRE POWDER (WTP) AS OIL SORBENT, USING RESPONSE SURFACE METHODOLOGY (RSM)

The rapid growth of the automobile industry has led to the abundance and indiscriminate disposal of waste tyres which causes environmental pollution and also lead to serious health problems. The absorption of crude oil using waste tyre powder (WTP) was investigated. A three variable Box-Behnken design was used to study the effect of particle size, contact time and temperature on the oil sorption capacity of WTP. Optimization was carried out using Response Surface Methodology (RSM). A quadratic model was obtained to predict the oil sorption capacity of WTP as a function of particle size, contact time and temperature. The optimum conditions of the sorption process obtained from RSM gave a temperature of 30.19oC, contact time 59.04 mins and particle size 0.15mm. A maximum oil sorption capacity of 4.71 g/g was obtained at these optimized conditions. Also, a comparison between the oil sorption efficiency of fresh tyre powder and regenerated tyre powder subjected to the same conditions of particle size, contact time and temperature were carried out. It was shown that the oil sorption capacity of the fresh tyre powder was higher than that of regenerated tyre powder.

Arsenic geochemistry and mineralogy as a function of particle-size in naturally arsenic-enriched soils

Naturally arsenic (As) enriched agricultural soils represent a significant global human health risk. In this study, As fractionation and mineralogy were investigated in naturally As-enriched agricultural soils and their corresponding sand, silt and clay fractions. Median As increased generally in the order (mg/kg)∶ silt (280) < bulk (314) < sand (323)<clay (484). Sequential extraction showed that amorphous and well-crystalline Fe- and Al-oxide bound and residual As forms accounted 27-42% of total As. Well-crystalline Fe- and Al-oxide bound As was highest (40-42%) in silt and clay fractions, while residual As was generally greatest (41-55%) in bulk and sand fractions. The sand, silt and bulk soils released a consistently higher percentage of non-specifically sorbed As than the clay, but clay released more specifically-sorbed As. Arsenate (As(V)) was the dominant species in soil solutions, although arsenite (As(III)) was significant in a few samples. XRD analysis showed the presence of arsenolite (As2IIIO3) in soils and fractions. SEM/EDS observations revealed that scorodite (FeAsVO4·2H2O) and amorphous Fe-oxides were the main As-bearing minerals in soils and fractions, which were consistent with the geochemical analysis. Outcomes from this research highlight the significant environmental risks of naturally As-enriched soils.

Metal sorption onto nanoscale plastic debris and trojan horse effects in Daphnia magna: Role of dissolved organic matter

There is a debate on whether the Trojan horse principle is occurring for nanoscale plastic debris (NPD < 1 µm). It is realized that NPD have a high capacity to sorb environmental contaminants such as metals from the surrounding environment compared to their microplastic counterparts, which influences the sorbed contaminants’ uptake. Herein, we studied the influence of dissolved organic matter (DOM) on the time-resolved sorption of ionic silver (Ag+) onto polymeric nanomaterials, as models of NPD, as a function of particle size (300 and 600 nm) and chemical composition [polystyrene (PS) and polyethylene (PE)]. Subsequently, the toxicity of NPD and their co-occurring (adsorbed and absorbed) Ag+ on Daphnia magna was determined. Silver nitrate was mixed with 1.2 × 105 NPD particles/mL for 6 days. The extent of Ag+ sorption onto NPD after 6 days was as follows: 600 nm PS-NPD > 300 nm PS-NPD > 300 nm PE-NPD. The presence of DOM in the system increased the sorption of Ag+ onto 300 nm PS-NPD and PE-NPD, whereas DOM decreased the sorption onto 600 nm PS-NPD. Exposure to 1 mg/L NPD or 1 µg/L Ag+ was not toxic to daphnids. However, the mixture of these concentrations of PS-NPD and Ag+ induced toxicity for both sizes (300 and 600 nm). The addition of DOM (1, 10 and 50 mg/L) to the system inhibited the combined toxicity of Ag+ and NPD regardless of the size and chemical composition. Taken together, in natural conditions where the concentration of DOM is high e.g. in freshwater ecosystems, the sorption of metals onto NPD depends on the size and chemical composition of the NPD. Nevertheless, under realistic field conditions where the concentration of DOM is high, the uptake of contaminants in D. magna that is influenced by the Trojan horse principles could be negligible.

Mass flux decay timescales of volcanic particles due to aeolian processes in the Argentinian Patagonia steppe

We investigate the timescales of the horizontal mass flux decay of wind remobilised volcanic particles in Argentina, associated with the tephra-fallout deposit produced by the 2011–2012 Cordón Caulle (Chile) eruption. Particle removal processes are controlled by complex interactions of meteorological conditions, surface properties and particle depletion with time. We find that ash remobilisation follows a two-phase exponential decay with specific timescales for the initial input of fresh ash (1–74 days) and the following soil stabilisation processes (3–52 months). The characteristic timescales as a function of particle size shows two minimum values, identified for sizes around 2 and 19–37 upmum, suggesting that these size-range particles are remobilised more easily, due to the interaction between saltation and suspension-induced processes. We find that in volcanic regions, characterised by a sudden release and a subsequent depletion of particles, the availability of wind-erodible particles plays a major role due to compaction and removal of fine particles. We propose, therefore, a simple and reproducible empirical model to describe the mass flux decay of remobilised ash in a supply-limited environment. This methodology represents an innovative approach to link field measurements of multi-sized and supply-limited deposits with saltation erosion theory.

Variation of Sulfur Content in Coking Coal as Function of Its Particle Size

To understand quality of coking coal possessing different particle sizes, coal samples from Gao Yang (GY) and Shui Yu (SY) mines were systematically studied. The samples had wide particle size variations with six distinct ranges. The main emphasis was placed on analyzing sulfur and coke contents as function of particle sizes. X-ray photoelectron spectroscopy (XPS) was used to analyze sulfur content as well as its chemical state. Sulfur coordination and group geometry was analyzed by Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) was applied to characterize surface morphology. Sieving of the coal samples increased ash and sulfur contents in all fractions. Organic sulfur was mostly present as thiophene for all particle size ranges. Macromolecular structure of coal was almost the same for all samples. Changes in total sulfur content of different coal fractions were mainly caused by the variations in inorganic sulfur concentrations because organic sulfur content remained almost constant. Understanding particle size distribution in different coals is important for selecting and optimizing appropriate desulfurization methods.

Distribution of PAHs in coal ashes from the thermal power plant and fluidized bed combustion system; estimation of environmental risk of ash disposal

The comparison of fly ash generated from lignite combustion in a thermal power plant Kolubara A (Veliki Crljeni) and bottom and fly ash from coal waste combustion in a semi-industrial fluidized bed boiler (Vinča) was performed as the function of particle size. The average total concentrations of the 16 EPA priority PAHs in ash fractions are 0.49 mg kg−1 of ash (thermal power plant) and 17.48 mg kg−1 of ash (fluidized bed boiler). The sum of 3- and 4-ring PAHs accounts for more than 93% of overall PAHs concentration, and the most abundant among them is fluoranthene.The portions of PAHs groups defined based on their physico-chemical properties, as obtained from quantitative structure-activity relationship (QSAR) models included in the Vega platform, were determined. These portions, emission factors, and benzo[a]pyrene equivalence concentrations were further on used to estimate the potential environmental impact of ash disposal. The PAHs emission factors are higher compared to values in the air pollutant emission inventory guidebook of the cooperative program for monitoring and evaluation of the long-range transmission of air pollutants in Europe (EMEP/EEA). The overall emission factors of 16 PAHs for combustion of lignite and coal waste are determined to be 0.15 and 249.97 mg kg−1 of fuel, respectively. Based on the ratios of benzo[a]pyrene equivalence concentrations of each ash and correspondent fuel, the disposal of fly ash from the cyclone of fluidized bed boiler represents the highest risk to the environment among tested ashes.

Development of the Multi-Material Inspection for Closed-Loop Rapid Optimization (MICRO) Sensor for Extrusion-Based Additive Manufacturing of Metal-Polymer Composite Inks

Additive Manufacturing (AM), or 3D printing, is a powerful technology that is revolutionizing the way designers create products across many industries. AM technology is severely limited by the lack of effective methods for in situ characterization of multi-material properties and composition during printing. The ability to detect the composition of multi-material printed inks in real time is an emerging need for a wide range of manufacturing applications. In this study, dielectric properties of embedded metal microparticles in a dielectric matrix are measured and characterized as a function of particle size, shape, volume percentage and frequency. Unexpectedly, there was no observation of any percolation threshold. The impedance was found to decrease with the percentage of metal filler as expected. While particle shape seemed to have significant effect on the impedance, there was little to no correlation between particle size and impedance. The resulting data can be used to generate a calibration curve correlating metal loading with impedance or capacitance. We discuss how this data can be used for in situ sensing of local ink composition, which does not currently exist, to facilitate greater control over the resulting properties and functionality of printed materials.

Study of gas adsorption characteristics influenced by moisture content, different coal particle sizes, and gas pressures

In coal reservoirs, coal, gas, and water coexist. Different moisture conditions may cause different gas storage capacity. In this paper, a series of isothermal adsorption experiments were conducted which consider different coal particle sizes, moisture ratios, and gas adsorption pressures. The Dubinin-Astakhov isothermal model is adopted in our simulations, and some adsorption parameters such as capacity, rate constant, and energy are obtained. Our key results are as follows: (1) the isothermal gas adsorption characteristics of coal are influenced by moisture, where the adsorption capacity decreases as the moisture content increases. The characteristic energy of adsorption decreases both as a function of particle size and as the moisture content increases. (2) The transient adsorption capacity initially increases sharply with time, which later increases slowly and gradually reaches equilibrium. (3) From the viewpoint of moisture content and particle size, the gas adsorption characteristic is inhibited by increased moisture levels and larger sizes. At the same time, the surface area of a coal sample with smaller particle sizes is greater than that of a sample with larger particle sample. This is inferred from our experiments because the sites for adsorption increase for smaller size samples. Our results can be used to ascertain the adsorption mechanism between gas and moisture on coal.

A mechanistic model for the thermal conductivity of planetary regolith: 1. The effects of particle shape, composition, cohesion, and compression at depth

This paper describes a new, analytic, and mechanistic model for calculating the effective thermal conductivity (keff) of planetary regolith, or any porous granular medium consisting of solid particles and gas (or vacuum). The model computes keff as a function of the physical properties of its components (e.g., intrinsic thermal conductivities), particle size and shape, bulk porosity, pore gas density, temperature, cohesive force, and lithostatic pressure (or depth). A simplified version of the model for the case of regolith in vacuum is also presented. Model predictions are compared to laboratory measurements from previous studies for a wide range of particle properties and temperature/pressure conditions. The model is based on the Maxwell-Eucken theoretical expressions for the upper and lower bounds for keff of heterogeneous, isotropic material. These equations provide tighter bounds than the parallel and series approximations often used to estimate keff for porous media. The effect of interparticle contact is modeled using an semi-empirical parameter fsc that represents the fractional continuity of the solid phase. An expression for this parameter is proposed with a functional dependence on the relative size and number of contacts between particles. The actual size of the contacts is estimated based on Hertzian mechanics of elastic deformation including the effects of cohesive surface forces (JKR theory). An effective contact radius is determined that also takes into account the heat transfer through the pore space in the immediate vicinity of the contact based on theoretical work by Batchelor and O’Brien (1977), as well as lower limits due to plastic deformation. Particle shape is quantified in terms of its sphericity and roundness. The effects of sphericity are explicitly included in calculations of the Maxwell-Eucken bounds, the effective pore size and, along with roundness, the average local radius of curvature at the contacts. The effect of radiative heat transfer is included, as well as the dependence of gas conductivity on temperature and Knudsen number from kinetic theory. The only free parameters in the model are two constant coefficients in the hypothesized expressions for fsc and pore size which are empirically determined by least-squares fits to laboratory measurements of keff for glass beads over a wide range of particle size and pore gas pressure. Using these best-fit values for the coefficients, the model is then shown to predict values of keff which are in close agreement (σ ≤ 20%) with previous laboratory measurements for basalt and quartz powders, crushed kyanite, and Apollo lunar soil samples. A key finding of the model is that keff does depend on the instrinsic conductivity of the solid particles (and therefore on their composition and temperature) to a greater degree than indicated in previous studies, and is especially important for regolith on airless bodies. Finally, for cohesive particulates, a method is presented for estimating the porosity as a function of particle size, surface energy, density, and gravitational force.

Microstructure and ignition mechanisms of reactive aluminum–zirconium ball milled composite metal powders as a function of particle size

Al:Zr composite powders are synthesized via arrested reactive ball milling (ARM) and contain small inclusions of Zr within an Al matrix. We characterize the microstructure and ignition temperatures of the powders as a function of size using the following size ranges: 0–10, 10–32, 32–53, 53–75, and > 75 µm. We observe uniformity in density for all size ranges but the largest (> 75 µm), implying consistent elemental composition, and we observe elongation of Zr inclusions within particles of the larger three size ranges. Williamson–Hall analyses of Zr XRD patterns indicate similar Zr grain sizes across all powder size ranges and negligible residual strain and interfacial energies within the composite powders. TGA shows an increase in oxidation as particle size decreases, which we attribute to surface oxidation through comparison to an analogous Zr-rich composite powder. The onset of ZrO2 formation is compared to that of Al–Zr intermixing and intermetallic formation, and we find that the latter corresponds well to the measured ignition temperature. Unlike pure metal fuels, where ignition is governed by the onset of oxidation and ignition temperatures typically increase with particle size, these particles ignite at much lower temperatures (< 350 °C) with no dependence on size for particles less than 75 µm. Atomic intermixing and the formation of intermetallic and Zr compounds are the primary drivers for ignition in this system at slow to moderate heating rates, and we attribute the similar ignition temperatures across multiple particle sizes to the shortest diffusional intermixing distances being comparable in each size range.

An inter-comparison of size segregated carbonaceous aerosol collected by low-volume impactor in the port-cities of Venice (Italy) and Rijeka (Croatia)

Size-segregated analysis of organic and elemental carbon (EC, OC) in aerosol is essential in understanding sources and effects on the environment. However, these studies are scarce, especially in coastal areas stressed by anthropogenic emissions and with interactions between anthropogenic and natural emissions. To partially fill this lack of information, aerosol size segregated samples were taken between August 2018 and May 2019, using a MOUDI impactor. Measurements were performed in two port-cities of Northern Adriatic Sea, Venice (Italy) and Rijeka (Croatia). A thermal-optical analysis (EUSAAR2) allowed EC and OC determination in different size ranges. For Rijeka site, the water soluble organic carbon content (WSOC) was analysed. OC and EC average concentrations in Venice were 3.16 (±0.97) and 0.40 (±0.13) μg/m3; in Rijeka: 2.48 (±0.65) and 0.37 (±0.08) μg/m3. The OC size distributions were bimodal at both sites, with an accumulation mode in the size range 0.56–0.32 μm, a coarse mode in the range 5.6–3.2 μm. EC showed a bimodal distribution in Rijeka, a single fine mode in Venice. The EC/TC ratio was large in the fine mode at both sites, however, in Rijeka non-negligible values were found in the coarse fraction suggesting contributions from resuspension of carbon-loaded dust and mixing of anthropogenic particles with sea spray. The WSOC/OC analysis as function of particle size in Rijeka showed a total value of 0.51 (±0.12) with an increase in the coarse fraction likely due to contributions of water soluble carbon from sea spray and biogenic emissions.

Investigation of Rheological Behavior of Untreated and Microwave-Assisted Alkaline Pretreated Sugarcane Straw for Biofuel Production

Biomass slurries, such as those subjected to microwave-assisted alkaline (MAA) pretreatment, will become common substrates for the production of biofuels in the future. While the rheology of acid and ionic liquid pretreated biomass is known, the rheology of alkaline pretreated biomass is not yet reported; hence, the goal of this study was to establish the rheological characteristics of untreated and MAA pretreated sugarcane straw (SC). Using rotational rheometry and rheological models, the rheology of SC slurries was assessed as a function of particle size and insoluble solids concentration. In the range of 5–17% insoluble solids concentration, the slurries were consistently pseudo-plastic (n = 0.33 ± 0.02), possessed yield stress with their flow accurately described by the Casson rheological model (R2 = 0.98–0.99). The apparent viscosity and yield stress increased by two orders of magnitude with an increase in insoluble solids concentration. Essentially, MAA pretreated slurries exhibited significantly higher values of apparent viscosity and yield stress than the untreated ones, in the range of 55–80% and 21–63% for particle sizes of < 63 µm (P63) and 90–180 µm (P90), respectively. Pretreated P63 samples exhibited higher apparent viscosity and yield stress than the P90. On the other hand, for untreated samples, P63 samples had a reduced apparent viscosity than P90 samples. The results of this study definitively reveal that MAA significantly increases the shear rate dependent shear viscosity values along with the yield stress of biomass slurries. This will, therefore, serve as a benchmark for characterizing other MAA pretreated biomass slurries to guide the design of industrial-scale production equipment.

Rising and sinking intruders in dense granular flows

We computationally determine the force on single spherical intruder particles in sheared granular flows as a function of particle size, particle density, shear rate, overburden pressure, and gravitational acceleration. The force scales similarly to, but deviates from, the buoyancy force predicted by Archimedes' principle. The deviation depends only on the intruder to bed particle size ratio, but not the density ratio or flow conditions. We propose a simple force model that successfully predicts whether intruders rise or sink, knowing only the size and density ratios, for a variety of flow configurations in physical experiments.

Experimental investigation and mechanism analysis: Effect of nanoparticle size on viscosity of nanofluids

Viscosity is important for evaluating thermal properties of nanofluids and easily influenced by many factors such as solid concentration, temperature, size & shape of nanoparticle. As so far, among all of them, the effect of particle size on viscosity is still unclear. For such reason, a series of experiments were performed by dispersing two different nanoparticles (Al2O3 and ZnO) respectively into engine oil in different particle size (20–100 nm) with volume fraction ranging from 1% to 15%. For the particle size and volume fraction investigated, viscosity is found to be different functions of particle size under different background concentration of nanoparticles; In addition, ANOVA analysis provides a comprehensive data interpretation for the effect of all factors contributing to viscosity. Moreover, mechanism analysis on particle size effect, which relies on DLVO theory and SEM microstructure of the samples was made. Consequently, the dependence of particle size effect on background concentration of nanoparticles was proposed and three corresponding stages of downtrend, constant trend and uptrend (viscosity varies with the increase of particle size) were presented.

Behavior and Bio-Interactions of Anthropogenic Particles in Marine Environment for a More Realistic Ecological Risk Assessment

Due to production, usage and disposal of nano-enabled products as well as fragmentation of bulk materials, anthropogenic nanoscale particles (NPs) can enter the natural environment and through different compartments (air, soil and water) end up into the sea. With the continuous increase of production and associated emissions and discharges, they can reach concentrations able to exceed toxicity-thresholds for living species inhabiting marine coastal areas. Behavior and fate of NPs in marine waters are driven by transformation processes occurring as a function of NP intrinsic and extrinsic properties in the receiving seawaters. All those aspects have been overlooked in ecological risk assessment. This review critically reports ecotoxicity studies in which size distribution, surface charges and bio-nanointeractions have been considered for a more realistic risk assessment of NPs in marine environment. Two emerging and relevant NPs, the metal-based titanium dioxide (TiO2), and the polystyrene (PS), a proxy for nanoplastics, are reviewed and their impact on marine biota (from planktonic species to invertebrates and fish) discussed as a function of particle size and surface charges (negative vs positive) which affect their behavior and interaction with the biological material. Uptake of NPs is related to their nanoscale size, however in vivo studies clearly demonstrated that transformation (agglomerates/aggregates) occurring in both artificial and natural seawater drive to different exposure routes and biological responses at cellular and organism level. Adsorption of single particles or agglomerates onto the body surface or their internalization in feces can impair motility and affect sinking or floating behavior with consequences on population and ecological function. Particle complex dynamics in natural seawater is almost unknown although it determines the effective exposure scenarios. Based on the latest predicted environmental concentrations for TiO2 and PS NPs in the marine environment, current knowledge gaps and future research challenges encompass the comprehensive study of bio-nano interactions. As such, the analysis of NP biomolecular coronas can enable a better assessment of particle uptake and related cellular pathways leading to toxic effects. Moreover, the formation of an environmentally-derived corona (i.e. eco-corona) in seawater accounts for NP physical-chemical alterations, rebounding on interaction with living organisms and toxicity.

Burning rate and flame structure of cocrystals of CL-20 and a polycrystalline composite crystal of HMX/AP

The synthesis and development of novel energetic materials is a costly, challenging process. Rather than synthesizing new materials, cocrystallization provides the potential opportunity to achieve improved properties of existing energetic materials. This work examined the effects of cocrystallization on the deflagration of a 2:1 molar cocrystal of CL-20 and HMX as well as a 1:1 molar cocrystal of CL-20 and TNT. A hydrogen peroxide (HP) solvate of CL-20 as well as a polycrystalline composite of HMX and ammonium perchlorate (AP) were also studied. A physical mixture of each material was also tested for comparison. The burning rate of each material was measured as a function of pressure. Flame structure during self-deflagration was examined using planar laser-induced fluorescence (PLIF) of CN and OH. The burning rate of the HMX/CL-20 cocrystal and the CL-20/HP solvate closely matched that of CL-20, but the burning rate of the TNT/CL-20 cocrystal was between the burning rate of its coformers. All HMX/AP materials had a higher burning rate than either HMX or AP individually and the burning rate of a physical mixture was found to be a function of particle size. The differences in the burning rate of the physical mixtures and composite crystal of HMX/AP can be explained by changes in the flame structure observed using PLIF. Burning rates and flame structure of the cocrystals were found to closely match those of their respective physical mixtures when smaller particle sizes were used (approx. less than 100 µm). The results obtained demonstrate that the deflagration behavior of the coformers is not indicative of the deflagration behavior of the resulting physical mixture or cocrystal. However, changes in the resulting flame structure greatly affect the burning rate.

Correlation between size, shape and magnetic anisotropy of CoFe2O4 ferrite nanoparticles

The present work reports the effect of particle size and shape of CoFe2O4 (CFO) nanoparticles on magnetic properties and their use in device applications as permanent magnets at room temperature. A set of CFO samples with different particle sizes and shapes were synthesized via the polymeric method by sintering at temperatures ranging from 300 °C to 1200 °C. These materials were characterized structurally by x-ray diffraction, morphologically by scanning electron microscopy, and microstructurally by transmission electron microscopy. The morphology of these CFO samples shows size-dependent shapes like spherical, pyramidal, lamellar, octahedral and truncated octahedral shapes for the particle sizes ranging from 7 to 780 nm with increasing sintering temperature. The emergence of magnetic properties was investigated as a function of particle size and shape with a special emphasis on permanent magnet applications at low and room temperatures. The values of saturation and remanent magnetization were found to increase monotonously with a particle size up to 40 nm and from thereafter they were found to remain almost constant. The other magnetic parameters such as coercivity, squareness ratio, anisotropy constant and maximum energy product () were observed to increase up to 40 nm and then decreased thereafter as a function of particle size. The underlying mechanism responsible for the observed behavior of the magnetic parameters as a function of particle size was discussed in the light of coherent rotation, domain wall motion and shape induced demagnetization effects. The significant values of - the figure of merit of permanent magnets - observed for single domain particles (particularly, 14 nm and 21 nm) were found to have suitability in permanent magnetic technology.