Large Particle Size Distribution Research Articles

Reaction pathways for the formation of the YBa2Cu3O7−x compound

The kinetics of the reactions that lead to the formation of YBa2Cu3O7−x was investigated starting from various powder mixtures containing different reactants as sources of Ba, Cu, and Y (BaCO3, BaO, CuO, Y2O3. Y2Cu3O5. and BaCuO2). These powders were calcined at 940 °C for various time intervals. Quantitative x-ray analysis was used to determine the relative amounts of the compounds present in the calcined powders. When BaCO3 was used as the source of barium, long calcination times were required to obtain the single phased YBa2Cu3O7−x because of the slow decomposition of BaCO3. This leads to large particles and broad particle size distributions and hence to a lower density of the sintered superconducting pellets. Procedures to attain high density superconducting material are identified on the basis of the kinetic studies. Each of them isolates the slow reaction in a first step and prepares the superconducting material via a rapid reaction in a second step. The kinetic studies reveal the reaction mechanisms that were followed in different cases.

Size distribution of large aerosol particles during AGASP-II: Absence of st. augustine eruptive particles in the Alaskan Arctic

Number distribution data for 0.1–45 μm diameter aerosol were obtained using optical counting and sizing probes flown over the Alaskan Arctic during the second Arctic Gas and Aerosol Sampling Program (AGASP-II), flights 201–203. Due to noise present in the lowest size channels of the optical probes, estimates of the H 2SO 4 component of Arctic haze were not attempted. Large particle (> 0.5 μm diameter) results are presented here. Large particle number and volume concentration were determined along with estimated mass, which was generally </ 0.1μg m −3. Lognormal fitting to > 0.3 μg m −3 mass loading sizedistributed aerosol data produced a means for comparing volume geometric median diameters (VGMD) for these higher-mass time intervals. These VGMDs showed that solid crustal particles previously observed during AGASP-II had VGMDs in the 1.2–1.6 μm range and that the shape of these fitted lognormal distributions was essentially constant. This result suggests very-long-range transport from a distant crustal source and, in conjunction with aerosol physical and chemical characterization data, argues against the presence of the Mt. Augustine eruptive particles during AGASP-II Alaskan Arctic sampling.

Magnetic properties of Ni 0.5Ag 0.5 thin films

Ni 0.5Ag 0.5 thin films were prepared by R.F. sputtering. The magnetic properties (saturation magnetization and susceptibility) was measured by means of a Faraday balance in the temperature range 170–715K. The films are made up of fine particles of pure nickel scattered in an amorphous matrix. Below 400K the films are paramagnetic and above they have a superparamagnetic behaviour. We have also shown that the large particle size distribution leads to exchange integral fluctuations.

Evaluation Of The LOWTRAN 6 Navy Maritime Aerosol Model Using 8 To 12 µm Sky Radiances

Infrared (8 to 12 µm) sky radiance measurements over the ocean near San Diego are compared with those calculated by LOWTRAN 6 using the Navy maritime aerosol model with simultaneously measured (radiosonde) meteorological parameters and atmospheric radon concentrations. For a low wind speed condition, the measured and calculated radiances agreed within 2% at the optical horizon. However, during moderate wind speed conditions, the current wind speed component of the aerosol model had to be lowered by factors near 0.05 for the calculated and measured radiances to agree. The adjusted model is then found to agree closely with published results of large particle size distribution measurements in the North Atlantic.

Combustion of coal—water slurries: Evolution of particle size distribution for coals of different rank

The effect of coal rank on pulverized coal and coal—water slurry combustion was examined in a laboratory laminar flow reactor. Two coals were used: a low-rank lignite with high mineral matter content and a high-rank bituminous coal with low mineral matter content. The evolution of the particle size distribution of these two coals in both dry and slurry form during combustion was measured with an in situ optical particle counter. Samples were also collected after different combustion durations and were examined with a scanning electron microscope. The results indicate that the coal slurry atomization process affects the particle size distribution, but inherent coal properties associated with coal rank do not significantly affect the initial and early combustion behaviour of the pulverized coal or coal—water slurry. During char oxidation, the ash constituent of the coal dominates the small particle size distribution, while the behaviour of the large particle size distribution and agglomerates depends on the coal rank.

Wide Range Aerosol Classifier: A Size Selective Sampler for Large Particles

The Wide Range Aerosol Classifier (WRAC), a sampler employing parallel impactors coupled with a large high flow rate inlet, has been designed, built, and tested for use in determining the size distribution of large particles found in ambient air. Results of laboratory and field evaluations demonstrate that the WRAC can be used successfully to determine atmospheric aerosol “total mass” and its large particle (> 10 μm aerodynamic diameter) distribution. The sampler is mobile for operation at various field locations. With properly prepared impaction surfaces, four impactors with cut points of 9.3, 18.5, 34, and 47 μm, respectively, provide sharp well-defined separation with low internal losses. Results of an initial and two follow-up independent impactor calibrations are in strong agreement, indicating good impactor precision and valid procedures by the two calibration laboratories. The WRAC size distribution mass measurements can be used to predict the “total aerosol mass” as well as size fractionated mass ...

Large Particle Size Distribution in Five U.S. Cities and the Effect on a New Ambient Participate Matter Standard (PM10)

A mobile aerosol-sampling system was used to determine the large particle ambient aerosol size distribution (up to approximately 100 μm particle diameter) in five cities across the United States: Birmingham, Alabama; Research Triangle Park, North Carolina; Philadelphia, Pennsylvania; Phoenix, Arizona; and Riverside, California. A mobile wide range aerosol classifier (WRAC) developed at the University of Florida was used. The study shows that any measurement of ambient particulate matter with a size-fractionating inlet sampler will be influenced by the ambient particle size distribution. Mass distribution measurements determined by the WRAC were compared with mass measurements obtained simultaneously using TSP Hi-Vol and 15 μm cut-size inhalable particulate network samplers. Aerosol size-classification results showed the presence of a large particle mass mode at all sites sampled. The position and magnitude of the large particle mode varied and was not a simple function of concentration. The percentage of ...

Influence of the particle size distribution of the packing material in reversed-phase high-performance liquid chromatography

The influence of a large particle size distribution of reversed-phase silica gel packing materials in high-performance liquid chromatography (HPLC) was studied. Mixtures were prepared with ROSiL-C 18-D materials with mean particle sizes of 3, 4, 5, 6, 8 and 10 μm. The efficiency of columns packed with mixtures of different compositions was measured and the usual chromatographic parameters were deduced. The conclusion is that a large particle size distribution has no influence on column efficiency if the eluting speed is kept around the optimum value. At higher solvent flow-rates there is a small negative effect. At all eluting speeds a larger particle size distribution has a negative effect on back-pressure and on separation impedance. A good practical ratio for the diameters of larger over smaller particles in a chromatographic material is about 1.5 to 2 for the ratio d p 90/ d p 10. The negative effect of fines or dust in column packing materials is stressed.

The chemistry, biology, and vertical flux of particulate matter from the upper 1500 m of the Panama Basin

Particulate matter divided into < 1-, 1- to 53-, and > 53- μm size fractions was obtained using the Large Volume in situ Filtration System (LVFS) modified to collect four samples per deployment. Samples collected to 1500 m at 0°45′N, 86°10′W were analyzed for major and minor element, organism (species assemblage and population densities), and large particle size distributions. Vertical fluxes of fecal matter, fecal pellets, Foraminifera, and diatoms were calculated from size distribution data and two settling models. Estimates of the vertical mass, organic carbon, carbonate, and opal fluxes were compared with mean particle collection rates by sediment traps deployed at 2500 m for 234 days commencing at the time of LVFS sampling. The productivity of the surface layer at this station is controlled by the north-south position of the Equatorial Front, which separates low productivity Tropical Surface Water (TSW) from a mixture of warm Subtropical Surface Water (SSW) and cool, nutrient-rich water upwelled along the Peruvian coast. At the time of LVFS sampling the front was south of the station, with the lower productivity TSW dominating the surface water. Particle distributions and fluxes indicated lower than average productivity and highly efficient zooplankton grazing. Variability in productivity at the station was indicated by weekly sea surface temperature data and was manifested by an anomalous centrate diatom maximum centered at 400 m and by the indication that the particle flux through 1500 m was 1/40th of the rates particles were collected by the sediment traps at 2500 m. The depth of the nitrite maximum corresponded to that of strongest rate of decrease of the organic carbon flux. Fluxes of particulate opal and carbonate decreased markedly in the upper water column although it was supersaturated with respect to calcite. The occurrence of fecal pellets devoid of birefringent material in the water column indicates that the carbonate dissolution was biologically mediated. Calculations indicate that the strong carbonate dissolution in the upper waters at this station is not representative of “average” ocean conditions and is probably a local or rare phenomenon.

On the variation of the size distribution of large and giant atmospheric particles as a function of the relative humidity

On the variation of the size distribution of large and giant atmospheric particles as a function of the relative humidity

On the variation of the size distribution of large and giant atmospheric particles as a function of the relative humidity

Atmospheric aerosol samples captured by a cascade impactor were examined under a microscope at different relative humidities to gain some informations on the variation of the size distribution of large and giant particles as a function of the relative humidity. The results of ten samplings are presented and discussed. DOI: 10.1111/j.2153-3490.1971.tb00587.x