Spherical Fly Ash Particles Research Articles

Age-hardening characteristics of aluminum alloy-hollow fly ash composites

The aging characteristics of aluminum alloy A356 and an aluminum alloy A356 containing hollow spherical fly ash particles were studied using optical microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, hardness tests, and compressive tests. The variation of hardness and compressive strength as a function of aging time for the composite have been reported. Since the density of the composite is lower than that of the base alloy due to the presence of hollow particles, the composites have a higher specific strength and specific hardness compared to the matrix. Even though the hardness of the as-cast composite was higher than that of the base alloy, no significant change in the aging kinetics was observed, due to the presence of spherical fly ash particles in the matrix. Aging times of the order of 104 to 105 seconds were required to reach the peak hardness (92 HRF) and compressive strength (376 MPa) in both the A356-5 wt pct fly ash composite and the matrix alloy. The possible effects of shape and hollowness of particles, the interface between the matrix and the particles, the low modulus of the particles, and the microcracks formed on the surface of hollow fly ash particles on the kinetics of the age hardening of aluminum alloy A356 are discussed.

Heat transfer characteristics of liquid-solid suspension flow in a horizontal pipe

Particles in liquid-solid suspension flow might enhance or suppress the rate of heat transfer and turbulence depending on their size and concentration, The heat transfer characteristics of liquid-solid suspension in turbulent flow are not well understood due to the complexibility of interaction between solid particles and turbulence of the carrier fluid. In this study, the heat transfer coefficients of liquid-solid mixtures are investigated using a double pipe heat exchanger with suspension flows in the inner pipe. Experiments are carried out using spherical fly ash particles with mass median diameter ranging from 4 to 78 μm. The volume concentration of solids in the slurry ranged from 0 to 50% and Reynolds number ranged from 4,000 to 11,000. The heat transfer coefficient of liquid-solid suspension to water flow is found to increase with decreasing particle diameter. The heat transfer coefficient increases with particle volume concentration exhibiting the highest heat transfer enhancement at the 3% solid volume concentration and then gradually decreases. A correlation for heat transfer to liquid-solid flows in a horizontal pipe is presented.

Effects of fly ash on fatigue and fracture properties of hardened cement mortar

The aim of the work described in this paper was to investigate the effects of fly ash on the fatigue resistance of cement mortars. Mortar mixes were prepared with similar compressive cube strengths using a range of fly ash contents up to 25%. Samples from these mixes were tested in a double torsion facility under cyclic loading and the rates of crack growth measured, recorded and plotted against the applied stress intensities on log-log scales in V—K diagrams. At later ages the fly ash was found to increase fatigue resistance and toughness. This was thought to be due to the spherical fly ash particles having a blunting effect. At greater ages the mixes containing fly ash were slightly less resistant to fatigue crack growth. Bond between the gel and the large fly ash particles was observed to be poor, resulting in their effectively acting as flaws that were now large in relation to other flaws in the matrix which had reduced with continued hydration.

Precision and Accuracy in the Determination of Sulfur Oxides, Fluoride, and Spherical Aluminosilicate Fly Ash Particles in Project MOHAVE

The precision and accuracy of the determination of particu-late sulfate and fluoride, and gas phase SO2 and HF are estimated from the results obtained from collocated replicate samples and from collocated comparison samples for high-and low-volume filter pack and annular diffusion denuder samplers. The results of replicate analysis of collocated samples and replicate analyses of a given sample for the determination of spherical aluminosilicate fly ash particles have also been compared. Each of these species is being used in the chemical mass balance source apportionment of sulfur oxides in the Grand Canyon region as part of Project MOHAVE, and the precision and accuracy analyses given in this paper provide input to that analysis. The precision of the various measurements reported here is ±1.8 nmol/m3 and ±2.5 nmol/m3 for the determination of SO2 and sulfate, respectively, with an annular denuder. The precision is ±0.5 nmol/m3 and ±2.0 nmol/m3 for the determination of the same species with a high-volume or low-volume filter pack. The precision for the determination of the sum of HF(g) and fine particulate fluoride is ±0.3 nmol/m3. The precision for the determination of aluminosilicate fly ash particles is ±100 particles/m3. At high concentrations of the various species, reproducibility of the various measurements is ±10% to ±14% of the measured concentration. The concentrations of sulfate determined using filter pack samplers are frequently higher than those determined using diffusion denuder sampling systems. The magnitude of the difference (e.g., 2-10 nmol sulfate/m3) is small, but important relative to the precision of the data and the concentrations of particulate sul-fate present (typically 5-20 nmol sulfate/m3). The concentrations of SO2(g) determined using a high-volume cascade impactor filter pack sampler are correspondingly lower than those obtained with diffusion denuder samplers. The concentrations of SOx (SO2(g) plus particulate sulfate) determined using the two samplers during Project MOHAVE at the Spirit Mountain, NV, and Hopi Point, AZ, sampling sites were in agreement. However, for samples collected at Painted Desert, AZ, and Meadview, AZ, the concentrations of SOx and SO2(g) determined with a high-volume cascade impactor filter pack sampler were frequently lower than those determined using a diffusion denuder sampling system. These two sites had very low ambient relative humidity, an average of 25%. Possible causes of observed differences in the SO2(g) and sulfate results obtained from different types of samplers are given.

Characterization of North Sea aerosols by individual particle analyses

On aerosol and rain water samples, collected in the Southern Bight of the North Sea, single particle analyses were performed using both laser microprobe mass analysis and electron-probe X-ray microanalysis in combination with an automated image analysis system. In the aerosols collected from an air mass that had travelled from the Atlantic Ocean along the coast of North France, pure seasalt constituted the most abundant particle type, while aluminosilicates (mostly spherical fly-ash particles) amounted to about 20% and mixed seasalt/aluminosilicate, carbonaceous particles, CaSO 4 and spherical iron oxides contributed each 5–10 %. In air masses that had a longer residence time over the continent, spherical iron oxides, carbonaceous particles and ammonium sulfates together made up 70 % of the total particle load. Seasalt particles were nearly all enriched in sulfate or nitrate, but they were seen to be washed out efficiently after a rain shower. In rain water, some 40 % of the particles appeared to be spherical or irregularly shaped aluminosilicates, from fly-ash and dust dispersal, but more than 50 % consisted of SiO 2. The high relative abundance of these particles in rain water may be the result of Al leaching from fly-ash, or of more efficient scavenging by rain droplets.

Quantification of Fly Ash in Concrete by Image Analysis Techniques: a Preliminary Investigation

ABSTRACTThe fly ash present in concrete mixtures is readily identified with qualitative electron microscope techniques. Quantification of the fly ash present in samples is more difficult. Visual analysis of a representative sample volume can be accomplished in a reasonable amount of time through use of image analysis techniques.Our research efforts have focused on the development of an image analysis technique which uses particle shape and composition to quantify the fly ash present in samples. The resultant binary image is filtered to eliminate the smallest particles and pieces of particles. Shape factor analysis distinguishes spherical fly ash particles from irregularly shaped grains of unhydrated cement clinker. The volume percent of nearly spherical particles is calculated and adjusted to compare the percentage of spherical particles in the matrix of fly ash-containing specimens to the percentage in a control specimen with no fly ash.There is a 2.2-fold increase in the number of spherical particles associated with the substitution of Portland cement by 60 wt% fly ash. Proportional changes in this ratio should be observable in samples with varying amounts of fly ash. The most obvious limitation of the method is related to the requirement that one knows the percentage of high atomic number particles in the fly ash beforehand.

The Morphology and Size Distribution of Atmospheric Particles Deposited on Foliage and Inert Surfaces

Particles deposited on leaves and inert surfaces during dry periods were examined with scanning electron microscopy to determine their morphologies and size distributions. Deposited particles were classified into two general types: spherical fly ash particles released during the burning of fossil fuels, and nonspherical particles (primarily soil material) consisting of both organic and mineral matter. Size distribution data indicated that deposited particle mass was dominated by particles larger than 10 microns in diameter, despite the fact that nearly 40 percent of the over 3800 particles analyzed were less than 2 microns in diameter. Our observations lend support to the hypothesis that a small fraction of the airborne particle population is responsible for an unproportionally large fraction of the dry-deposited particle mass and that particle sedimentation may be an important dry deposition process.

Concentration, Velocity, and Particle Size Measurements in Gas-Solid Two-Phase Jets

An optical technique was developed and used to measure particle concentration profiles in dense two-phase axisymmetric jets. Gas velocity profiles of the single-phase jet were measured by a pitot probe. Particle size distribution across the jet was measured with isokinetic particle sampling probes. Schlieren photographs of shock waves in the jet were taken to study the influence of particles on shock-wave structure near the exit of the nozzle. The effect of nozzle configuration on the two-phase jet flow was also investigated. The measurements were made by seeding 1,3, and 5% by weight of 24 /xm mean diameter spherical fly ash particles into jets at Mach numbers of 0.2, 0.8, and 1.0. The particle concentration profiles showed that particles concentrate on the axis of the jet at the exit of the nozzle and the profiles are influenced by the seeding rate, the velocity of the jet, and the nozzle configuration. The particle size distribution is homogeneous in the jet. Schlieren photographs of shock waves in the jet showed that the normal shock wave near the exit of the nozzle was convexly curved with the addition of a suspension of particles in the jet.