Decreasing Particle Diameter Research Articles

The H1 Nuclear Magnetic Resonance Spin-Lattice Relaxation Rate of Some Hydrated Synthetic and Natural Sands

The hydrogen nuclear magnetic resonance (NMR) spin-lattice relaxation rate [Formula: see text] of three fully hydrated natural sands was measured and compared to that for a fully hydrated synthetic sand as a function of applied magnetic field and particle diameter [Formula: see text]. [Formula: see text] values increased with decreasing particle diameter for both natural and synthetic sands. The increase in [Formula: see text] became greater with decreasing magnetic field strength. The field dependent [Formula: see text] data allowed the prediction of [Formula: see text] at the Earth’s magnetic field [Formula: see text]. Measurable [Formula: see text] differences were observed between the three natural sands, as well as the natural and a synthetic sand. The difference in [Formula: see text] of the natural sands can not be attributed to the geometric characteristics of the grains, as these were identical within experimental error. The [Formula: see text] differences can be attributed to trace paramagnetic impurities in the grains which influence the surface relaxation component of [Formula: see text]. These results show that it is unwise to predict aquifer characteristics based on [Formula: see text] values from nuclear magnetic resonance sounding without knowledge of the paramagnetic impurities in the sand grains. Furthermore, the results emphasize that laboratory measurements of [Formula: see text] should be performed at [Formula: see text].

Penetration of nanoparticles through fibrous filters perforated with defined pinholes

This paper presents experimental data for penetration of nanoparticles in the 4–30 nm size range through fibreglass filters perforated with defined pinholes at 5 and 15 cm/s. Results show that, when the filter is damaged, penetration increases with decreasing particle diameter. This lower performance is more significant for filters with high airflow resistance. A model explaining the experimental data has been designed based on balanced, laminar airflow inside the pinhole; these conditions were confirmed by detailed study. The experimental points agreed very closely with this model.

Fate and Effects of CeO2 Nanoparticles in Aquatic Ecotoxicity Tests

Cerium dioxide nanoparticles (CeO2 NPs) are increasingly being used as a catalyst in the automotive industry. Consequently, increasing amounts of CeO2 NPs are expected to enter the environment where their fate in and potential impacts are unknown. In this paper we describe the fate and effects of CeO2 NPs of three different sizes (14, 20, and 29 nm) in aquatic toxicity tests. In each standard test medium (pH 7.4) the CeO2 nanoparticles aggregated (mean aggregate size approximately 400 nm). Four test organisms covering three different trophic levels were investigated, i.e., the unicellular green alga Pseudokirchneriella subcapitata, two crustaceans: Daphnia magna and Thamnocephalus platyurus, and embryos of Danio rerio. No acute toxicity was observed for the two crustaceans and D. rerio embryos, up to test concentrations of 1000, 5000, and 200 mg/L, respectively. In contrast, significant chronic toxicity to P. subcapitata with 10% effect concentrations (EC10s) between 2.6 and 5.4 mg/L was observed. Food shortage resulted in chronic toxicity to D. magna, for wich EC10s of > or = 8.8 and < or = 20.0 mg/L were established. Chronic toxicity was found to increase with decreasing nominal particle diameter and the difference in toxicity could be explained by the difference in surface area. Using the data set, PNEC(aquatic)S > or = 0.052 and < or = 0.108 mg/L were derived. Further experiments were performed to explain the observed toxicity to the most sensitive organism, i.e., P. subcapitata. Toxicity could not be related to a direct effect of dissolved Ce or CeO2 NP uptake or adsorption, nor to an indirect effect of nutrient depletion (by sorption to NPs) or physical light restriction (through shading by the NPs). However, observed clustering of NPs around algal cells may locally cause a direct or indirect effect.

Catalytic Nitrate and Nitrite Reduction with Pd−Cu/PVP Colloids in Water: Composition, Structure, and Reactivity Correlations

A set of bimetallic Pd−Cu/PVP (PVP = poly(N-vinylpyrrolidone)) colloids, with copper proportions ranging from 0 to 50 atom %, has been examined as catalysts in a batch reactor with flowing hydrogen for the reduction of aqueous nitrate and/or nitrite. The encapsulated Pd−Cu nanoparticles were characterized by powder XRD, TEM, EDX, and IR of adsorbed CO. A significant decrease in average particle diameter and changes in the Pd−Cu crystallinity occurred above ca. 30% copper content, and this transition corresponded with a significant increase in observed nitrate reduction rates. The strong dependence on composition suggests that specific Cun ensembles on the surface of the Pd−Cu nanoparticles are needed for effective nitrate-to-nitrite conversion. In contrast, nitrite reduction rates were only minimally enhanced by the presence of copper. Increasing pH had little effect on the nitrate reduction rates, but it strongly inhibited the rate of nitrite reduction. The requisite protonation of a palladium−nitrite su...

電気泳動法により構造制御された固体電解質の作製

Improvement of proton conductivity of solid electrolyte films needs to form three-dimensional proton conduction routes by controlling the pore size and the pore structure between particles in particle films. A particle assemble method using electrophoretic deposition technique is useful for speedy and mass production assembly. In the electrophoretic deposition method, structure of particle array can be controlled by the electric field.As a result, the proton conductivity of the film showed a higher value for the regularly-arranged particle film and it is increased with a decrease in particle diameter. The proton conductivity of the film with the particles of diameter 50nm had the highest value. The particle film with the well-controlled structure may enable the fuel cell to be operated in the middle temperature range.

Thermal stability of size-selected arrays of gold nanoparticles on () sapphire – A thermal desorption spectroscopy study

Abstract Exploiting the self-organization of spherical gold salt loaded inverse micelles formed from diblock copolymer poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) in toluene, arrays of Au nanoparticles were prepared exhibiting narrow size as well as interparticle distance distributions. Starting with such Au nanoparticles (average particle diameters ranging between 1 nm and 5 nm) deposited on top of ( 1 1 2 ¯ 0 )-oriented sapphire substrates, thermal desorption spectroscopy (TDS) experiments were performed up to a maximum temperature of 1473 K at a standard rate of 5 K/s in order to test for size dependent vapor pressures as expected from Kelvin’s equation. Opposite to the expected increase of the vapor pressure for decreasing particle diameters, a split desorption behavior is observed with two peaks. Analyzing the data according to the Polanyi–Wigner equation, from the peak at lower temperature a desorption energy and attempt frequency close to bulk Au is extracted while the peak at higher temperature delivers significantly larger values for both properties. The latter observation is attributed to a substrate–nanoparticle interaction, which becomes dominant for decreasing particle diameters.

Water uptake coefficients and deliquescence of NaCl nanoparticles at atmospheric relative humidities from molecular dynamics simulations

Deliquescence properties of sodium chloride are size dependent for particles smaller than 100 nm. Molecular dynamics (MD) simulations are used to determine deliquescence relative humidity (DRH) for particles in this size range by modeling idealized particles in contact with humid air. Constant humidity conditions are simulated by inclusion of a liquid reservoir of NaCl solution in contact with the vapor phase, which acts as a source of water molecules as uptake by the nanoparticle proceeds. DRH is bounded between the minimum humidity at which sustained water accumulation is observed at the particle surface and the maximum humidity at which water accumulation is not observed. Complete formation of a liquid layer is not observed due to computational limitations. The DRH determined increases with decreasing particle diameter, rising to between 91% and 93% for a 2.2 nm particle and between 81% and 85% for an 11 nm particle, higher than the 75% expected for particles larger than 100 nm. The simulated size dependence of DRH agrees well with predictions from bulk thermodynamic models and appears to converge with measurements for sizes larger than 10 nm. Complete deliquescence of nanoparticles in the 2-11 nm size range requires between 1 and 100 mus, exceeding the available computational resources for this study. Water uptake coefficients are near 0.1 with a negligible contribution from diffusion effects. Planar uptake coefficients decrease from 0.41 to 0.09 with increasing fractional water coverage from 0.002 to 1, showing a linear dependence on the logarithm of the coverage fraction with a slope of -0.08+/-0.01 (representing the effect of solvation). Particle uptake coefficients increase from 0.13 at 11 nm to 0.65 at 2.2 nm, showing a linear dependence on the logarithm of the edge fraction (which is a function of diameter) with a slope of 0.74+/-0.04 (representing larger edge effects in smaller particles).

Primary submicron marine aerosol dominated by insoluble organic colloids and aggregates

The chemical properties of sea‐spray aerosol particles produced by artificially generated bubbles using oceanic waters were investigated during a phytoplankton bloom in the North Atlantic. Spray particles exhibited a progressive increase in the organic matter (OM) content from 3 ± 0.4% up to 77 ± 5% with decreasing particle diameter from 8 to 0.125 μm. Submicron OM was almost entirely water insoluble (WIOM) and consisted of colloids and aggregates exuded by phytoplankton. Our observations indicate that size dependent transfer of sea water organic material to primary marine particles is mainly controlled by the solubility and surface tension properties of marine OM. The pattern of WIOM and sea‐salt content in the different size intervals observed in bubble bursting experiments is similar to that measured in atmospheric marine aerosol samples collected during periods of high biological activity. The results point to a WIOM/sea‐salt fingerprint associated with submicron primary marine aerosol production in biologically rich waters.

Transesterification of Canola Oil to Fatty Acid Methyl Ester (FAME) in a Continuous Flow Liquid−Liquid Packed Bed Reactor

Experiments were performed to study the mass-transfer limitations during the acid-catalyzed transesterification reaction of triglyceride (TG) with methanol (MeOH) to fatty acid methyl ester (FAME or biodiesel). The experiments were carried out as both agitated two- and single-phase reactions in an empty pipe and a packed bed reactor. The TG conversion rate increased with an increase in total superficial velocity and a decrease in packing particle diameter for the two-phase reactions. The TG conversion rate did not increase significantly with the reaction temperature for the two-phase reactions, whereas for the single-phase reactions, the TG conversion rate increased significantly as the reaction temperature increased. The rate constant at two-phase conditions (largest velocity, smallest packing particle size, and maximum pressure gradient) was comparable to that obtained at single-phase conditions, indicating that the mass-transfer limitations for two-phase experiments can be effectively overcome using a ...

Filtration Performance of NIOSH-Approved N95 and P100 Filtering Facepiece Respirators Against 4 to 30 Nanometer-Size Nanoparticles

This study investigated the filtration performance of NIOSH-approved N95 and P100 filtering facepiece respirators (FFR) against six different monodisperse silver aerosol particles in the range of 4–30 nm diameter. A particle test system was developed and standardized for measuring the penetration of monodisperse silver particles. For respirator testing, five models of N95 and two models of P100 filtering facepiece respirators were challenged with monodisperse silver aerosol particles of 4, 8, 12, 16, 20, and 30 nm at 85 L/min flow rate and percentage penetrations were measured. Consistent with single-fiber filtration theory, N95 and P100 respirators challenged with silver monodisperse particles showed a decrease in percentage penetration with a decrease in particle diameter down to 4 nm. Penetrations less than 1 particle/30 min for 4–8 nm particles for one P100 respirator model, and 4–12 nm particles for the other P100 model, were observed. Experiments were also carried out with larger than 20 nm monodisperse NaCl particles using a TSI 3160 Fractional Efficiency Tester. NaCl aerosol penetration levels of 20 nm and 30 nm (overlapping sizes) particles were compared with silver aerosols of the same sizes by a three-way ANOVA analysis. A significant (p < 0.001) difference between NaCl and silver aerosol penetration levels was obtained after adjusting for particle sizes and manufacturers. A significant (p = 0.001) interaction with manufacturers indicated the difference in NaCl, and silver aerosol penetrations were not the same across manufacturers. The two aerosols had the same effect across 20 nm and 30 nm sizes as shown by the absence of any significant (p = 0.163) interaction with particle sizes. In the case of P100 FFRs, a significant (p < 0.001) difference between NaCl and silver aerosol (20 nm and 30 nm) penetrations was observed for both respirator models tested. The filtration data for 4–30 nm monodisperse particles supports previous studies that indicate NIOSH-approved air-purifying respirators provide expected levels of filtration protection against nanoparticles.

Experimental and numerical study of convection heat transfer of CO 2 at supercritical pressures in vertical porous tubes

Convection heat transfer of CO 2 at supercritical pressures in vertical sintered porous tubes with particle diameters of 0.1–0.12 mm and 0.2–0.28 mm was investigated experimentally and numerically. The study investigated the influence of the inlet fluid temperature, mass flow rate, pressure, particle diameter, heat flux, flow direction and buoyancy on convection heat transfer in porous tubes. The results show that the inlet temperature, pressure, mass flow rate, particle diameter and heat flux all strongly influence the convection heat transfer at supercritical pressures. When the inlet temperature is much larger than the pseudocritical temperature, T pc, the local heat transfer coefficients in porous tubes are much less than when the inlet temperature is less than T pc. For T 0 < T pc and wall temperatures not much larger than T pc, the local heat transfer coefficients have a maximum for both upward flow and downward flow along the porous tube when the fluid bulk temperatures are near T pc. Buoyancy caused the different variations in the local heat transfer coefficients along the porous tube for upward and downward flows. The results also show that the heat transfer coefficients increase as the particle diameter decrease. The numerical simulations were performed using the local thermal equilibrium model with consideration of the effects of variable porosity, thermal dispersion and area-of-contact stagnant effective thermal conductivity. The experimental and numerical results for the friction factor of CO 2 at supercritical pressures flowing in sintered porous tubes at constant temperature (without heating) corresponded very well with the known correlation. However, the predicted results for the friction factor of CO 2 at supercritical pressures flowing in the heated sintered porous tube differ from those measured in the experiments both for upward and downward flows. The calculated wall temperatures corresponded well with the measured wall temperatures.

Effect of closed-couple gas atomization pressure on the performances of Al-20Sn-1Cu powders

Al-20Sn-1Cu powders were prepared by gas atomization in an argon atmosphere with atomizing pressures of 1.1 and 1.6 MPa. The characteristics of the powders are determined by means of dry sieving, scanning electron microscopy (SEM), optical microscopy (OM), and X-ray diffractometry (XRD). The results show that the powders exhibit a bimodal size distribution and a higher gas pressure results in a broad size distribution. All particles in both cases are spherical or nearly spherical and satellites form on the surface of coarse particles. Dendritic and cellular structures coexist in the particle. With decreasing particle diameter, the secondary dendrite arm spacing (SDAS) decreases and the cooling rate increases. The particles processed under high gas atomization pressure (1.6 MPa) exhibit a lower SDAS value and a higher cooling rate than those of the same size under low gas atomization pressure (1.1 MPa). The XRD results show that the Sn content increases with decreasing particle size.

Sintering of titanium dioxide nanoparticles: a comparison between molecular dynamics and phenomenological modeling

Molecular dynamics simulations were used to determine the melting points of anatase and rutile nanoparticles. The melting points decrease with decrease in particle diameter and are in reasonable agreement with the empirical formula derived by Buffat and Borel. The phenomenological model of Koch and Friedlander is unable to predict the temperature rise during initial stages of sintering with acceptable accuracy. It is argued that the Koch and Friedlander assumption of linear surface reduction rate upon sintering may be inadequate for the time scales under consideration. A theoretical model using direct area measurement from molecular dynamics simulations and a single adjustable parameter is able to predict temperature rise during initial stages of sintering within acceptable error limits.

Investigation on the Release Characteristics of Light Hydrocarbon during Pulverized Coal Pyrolysis

In this paper, different coals were respectively heated up in a tube furnace by program temperature control under the reburning condition. The pyrolytic components of light hydrocarbon were analyzed using the gas-chromatographic technique, which shows that, under the same pyrolytic condition, the pyrolytic content of light hydrocarbon obviously decreases with the increase of the coal carbonized degree and the peak temperature value of light hydrocarbon released decreases with the decrease of the coal particle diameter. The main component of pyrolytic gas is CH4, and other contents are less, such as C2(C2H4, C2H6), C3(C3H6, C3H8), and C4H10. When coals are pyrolyzed, there is a critical particle size (dc) for each coal types. If d > dc, the total amount of light hydrocarbon increases, with the particle size decreasing. Conversely, if d ≤ dc, it tends to be saturated with the particle size decreasing.

Effect of morphology of carbon black fillers on the tribological properties of fibrillated PTFE

The tribological properties of fibrillated PTFE filled with 12 kinds of carbon black were studied using ring-on-disk tribometer. The effects of the average particle diameter, the nitrogen surface area and the DBP absorption of carbon black on the friction coefficient and the specific wear rate were studied. The carbon blacks used in this experiment were categorized into small carbon blacks ( d ≤ 25 nm) and large carbon blacks ( d ≥ 38 nm). The 10 mass% of carbon black was the best concentration for the highest wear resistance. The PTFE composites filled with the large carbon blacks showed lower friction coefficient than that of the pure PTFE. The friction coefficient decreased linearly with the decrease of the nitrogen surface area and with the decrease of the g-factor or the product of the nitrogen surface area and the average particle diameter. The specific wear rate of the PTFE composites decreased with the decrease of the average particle diameter and with the decrease of the product of the average particle diameter and friction coefficient. These results mean the wear reducing action of carbon black is to make it difficult to extract the PTFE fibre from the composite by getting caught in the carbon black and the large fillers promote the inter-winding between the fibre and the carbon black on a large degree, and result in high wear rate.

Computational Simulation on Optimization of Micro/Nano Particle-Laden Micro Jet by Electrostatic Acceleration

In-flight behavior of micro-nano particles and the interaction between shock wave and particles in a supersonic jet which impinges onto the substrate in a micro space are clarified in detail by computational simulation. The optimal particle diameter for maximum impinging particle velocity exists. Particles smaller than the optimal diameter are decelerated drastically prior to the impact on the cavity as a result of unavoidable particle-shock interaction. The larger deceleration through shockwave is observed with decrease in particle diameter. The particle less than 100 nm cannot penetrate the shockwave and carried by wall jet without impinging on the tooth cavity. The electrostatic force in the vicinity of tooth cavity acts effectively for the acceleration of submicron particles even in the presence of unavoidable shockwave in micro space.

Large-Eddy Simulation of Particle Diffusion in a Particle-laden Swirling Jet

Three-dimensional large-eddy simulation (LES) is applied to a particle-laden swirling jet, and the effect of swirl on particle diffusion is investigated. The trajectories of all particles are individually pursued with a Lagrangian method. The particles with different diameters are uniformly injected into the non-swirling and swirling flows with different Swirling numbers. The result shows that the trajectories of the particles with different diameters are quite different. The smaller particles have the peak of the particle number densities at central axis, and diffuse across swirling jet. On the other hand, the larger particles at the exit of the nozzle migrate outward by the centrifugal force, but the particles gradually migrate inward with the axial distance increases. The inward movement of the particle in the downstream region is dominated by turbulent motions, which transport the particles inward near central axis. Furthermore, above behavior is shifted upstream with the particle diameter decrease because the smaller particles are easily transferred by smaller inward fluid motions existing in the wide range of the swirling jet.

Preparation of HPMC–EA–DMAEMA nanosized latex

Nanosized copolymer latex of hydroxypropylmethylcellulose (HPMC) grafted with ethyl acrylate (EA) and dimethylaminoethyl methacrylate (DMAEMA) has been prepared by acidifying submicron-sized latex particles synthesized by soap-free emulsion graft copolymerization using potassium persulfate (KPS) as initiator. The effects on the diameter of the latex particles of different conditions, for example concentration of DMAEMA, amount of HPMC, and ratio of HCl to DMAEMA for acidification, were investigated. It was found that increasing the mole ratio of HCl to DMAEMA to 1.0 and increasing the DMAEMA content both resulted in a decrease in particle diameter, whereas increasing the amount of HPMC resulted in larger particle sizes. Measurement by dynamic light scattering (DLS) revealed the diameter of the latex particles was >200 nm before acidification and <100 nm after acidification. Evidence of grafting was obtained by use of Fourier transform infrared (FTIR) spectroscopy. Transmission electron microscopy (TEM) was used to characterize the morphology of the copolymer particles before and after acidification.

A comparison of two nano-sized particle air filtration tests in the diameter range of 10 to 400 nanometers

Two different air filter test methodologies are discussed and compared for challenges in the nano-sized particle range of 10–400 nm. Included in the discussion are test procedure development, factors affecting variability and comparisons between results from the tests. One test system which gives a discrete penetration for a given particle size is the TSI 8160 Automated Filter tester (updated and commercially available now as the TSI 3160) manufactured by the TSI, Inc., Shoreview, MN. Another filter test system was developed utilizing a Scanning Mobility Particle Sizer (SMPS) to sample the particle size distributions downstream and upstream of an air filter to obtain a continuous percent filter penetration versus particle size curve. Filtration test results are shown for fiberglass filter paper of intermediate filtration efficiency. Test variables affecting the results of the TSI 8160 for NaCl and dioctyl phthalate (DOP) particles are discussed, including condensation particle counter stability and the sizing of the selected particle challenges. Filter testing using a TSI 3936 SMPS sampling upstream and downstream of a filter is also shown with a discussion of test variables and the need for proper SMPS volume purging and filter penetration correction procedure. For both tests, the penetration versus particle size curves for the filter media studied follow the theoretical Brownian capture model of decreasing penetration with decreasing particle diameter down to 10 nm with no deviation. From these findings, the authors can say with reasonable confidence that there is no evidence of particle thermal rebound in the size range.

Quantum size effect of valence band plasmon energies in Si and SnOx nanoparticles

Spherical Si and SnOx nanoparticles in the size range between 3 and 30nm have been synthesized by microwave induced decomposition of silane and gas phase condensation, respectively. They are deposited on thin metal films and investigated by electron microscopy, Auger electron, and electron energy loss spectroscopy. An analysis of the surface composition and stoichiometry reveals that the Si particles are covered with a native oxide of less than 1nm. The energy loss spectra show features corresponding to electronic excitations in the nanoparticles due to valence band plasmons, interband transitions, and core-level ionizations. The plasmon energies are found to increase with decreasing particle diameter d as d−1.17 for Si and d−0.83 for SnOx. These energy shifts are related to the change of the dielectric band gap energy of the semiconductor due to quantum size effects.