The particle-size distribution (PSD) and specific surface area (SSA) of binders significantly affect the fresh and hardened characteristics of cement-based materials. An experimental investigation ...was undertaken to evaluate the influence of PSD and calculated SSA of various binary and ternary binder systems on flow characteristics, packing density, and compressive strength development of cement paste. The influence of dispersion state of the binder on packing density was evaluated using the wet packing density approach to determine the optimum water demand (OWD) needed to achieve maximum wet density. The modified Andreasen and Andersen (A&A), Rosin–Rammler (RR), and power law grading models were employed to optimize the PSD of binder system to achieve maximum packing density, while maintaining relatively low water demand. The incorporation of high-range water reducing admixture (HRWRA) is shown to decrease the OWD and increase the packing density resulting from greater degree of dispersion of the binder. The combined effect of lower OWD, greater packing density, and higher SCM reactivity results in higher compressive strength. The increase in SSA from 425 to 1600 m2/kg results in an enhancement in packing density from 0.58 to 0.72, while further increase in SSA from 1600 to 2200 m2/kg reduces the packing density from 0.72 to 0.62. Binder systems using a distribution modulus between 0.21 and 0.235 determined from the A&A model exhibited 18%–40% lower minimum water demand (MWD) to initiate flow, 8%–35% higher OWD to reach maximum wet density, and 15%–25% higher packing density compared to the binder with 100% cement. Binder systems with lower A&A distribution modulus resulted in higher relative water demand (RWD) required to increase fluidity, thus reflecting greater level of robustness. Good correlations were established between the A&A distribution modulus, SSA, RR spread factor, and power law distribution exponent.
There are many sources of urban road dust, such as soil dispersal, emissions of industrial enterprises and thermal power plants, road traffic-related processes. Chelyabinsk was selected as a typical ...Russian industrial city. This work was the first pollution study of road dust in Chelyabinsk. We examined 125 road dust samples were on the content toxic trace elements (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Sr, and Zn). The concentrations of trace elements in road dust were determined using ICP-MS. Results showed that the metal concentrations in dust were higher than the background value of local soil. The distribution curves of dust were asymmetric, had have two peaks, and showed significant unimodal distribution. The higher share of particles was in the range from 30 … 40 to 250 … 300 μm. The thoracic fraction volume (%) and concentrations of trace elements were higher near metallurgical plants. Cadmium, Сu, Mn, Ni, Sr, Pb and Zn were originated from industry and transport; electrometallurgical plant was source of Cr; Al, Co, and Fe derived from local soils and pavement erosion; As, Hg and Sb were the tracers of coal-fired power stations emission. Ingestion was a major exposure way of toxic elements in the dust. The results suggested that there was no significant potential health risk to both children and adults from exposure to any elements in road dust. The cancer risk for adults and children from exposure to As, Cd, Cr, and Pb was found to be at the acceptable or tolerable level.
The study deals with the contamination of potentially toxic trace elements (As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sb, Sr and Zn) in road dust collected from Chelyabinsk urban area.
•The high volume of the thoracic fraction was caused by industrial emissions.•Four source of trace elements were identified.•Industry has slightly affected the level of most trace elements in road dust.•Health risk of trace elements in road dust for adults and children was tolerable.
Abstract
The IC21 spherical powders with main content of Ni3Al were successfully manufactured by the high speed plasma rotating electrode process (HS-PREP). The powders particle size distribution ...fitted the mixed spraying model well. The chemical contents changes after melting were detected. The microstructure of the IC21 powders was formed by cellular crystal on the surface and dendrite inside, which was a typical PREP powder. The morphologies and properties of the irregular powders were also analyzed which indicated that the composition segregation and oxides inclusion of the electrode were the main reason for the formation. However, its proportion was less than 0.5%, which would not affect the additive manufacturing. The fundamental powder particle size distribution data for different rotating speeds was measured. The morphology and properties result show that the PREP could support qualified IC21 spherical powders with significant powder yields.
We consider the formation and evolution of axion quark nugget (AQN) dark matter particles in the early Universe. The goal of this work is to estimate the mass distribution of these objects and assess ...their ability to form and survive to the present day. We argue that this model allows a broad range of parameter space in which the AQN may account for the observed dark matter mass density, naturally explains a similarity between the "dark" and "visible" components, i.e., Ωdark ~ Ωvisible, and also offers an explanation for a number of other long-standing puzzles, such as the "primordial lithium puzzle" and "the solar corona mystery," among many other cosmological puzzles.
The soot formation characteristics in laminar premixed flames of pure n-heptane and binary mixtures of toluene and n-heptane with liquid volume ratios ranging from 0.2 to 1 were studied with the C/O ...ratio and unburned gas-mixture velocity being kept the same for all tested flames. The particle size distribution functions (PSDFs) at several selected burner-to-stagnation surface separation distances (Hp) were measured by using the burner-stabilized stagnation probe/scanning mobility particle sizer (SMPS) technique. In addition, the morphology of soot particles sampled from the probe was examined using transmission electron microscopy (TEM). From the PSDFs at different Hp and TEM images, it was observed that with the addition of toluene, soot inception occurred at lower flame heights and the primary particle size of soot aggregates was significantly reduced. A combustion kinetics model for toluene and n-heptane was used to explore the precursor chemistry. The modeling results were found to be consistent with the observations of the measured PSDFs.
Driving range and fast charge capability of electric vehicles are heavily dependent on the 3D microstructure of lithium-ion batteries (LiBs) and substantial fundamental research is required to ...optimise electrode design for specific operating conditions. Here we have developed a full microstructure-resolved 3D model using a novel X-ray nano-computed tomography (CT) dual-scan superimposition technique that captures features of the carbon-binder domain. This elucidates how LiB performance is markedly affected by microstructural heterogeneities, particularly under high rate conditions. The elongated shape and wide size distribution of the active particles not only affect the lithium-ion transport but also lead to a heterogeneous current distribution and non-uniform lithiation between particles and along the through-thickness direction. Building on these insights, we propose and compare potential graded-microstructure designs for next-generation battery electrodes. To guide manufacturing of electrode architectures, in-situ X-ray CT is shown to reliably reveal the porosity and tortuosity changes with incremental calendering steps.
The evolution of the nascent soot particle size distribution function (PSDF) was determined by mobility sizing for two series of atmospheric pressure premixed ethylene flames in the burner stabilized ...stagnation flame configuration. The first series of flames has an equivalence ratio of 1.8, corresponding to conditions just above the sooting limit. The second series has an equivalence ratio of 2.5 and is quite heavy in soot production. In each series, six flames were tested in which the cold gas velocity is varied to obtain flame temperatures ranging from 1559 to 1941 K. The temperature profiles were carefully determined and the comparison to pseudo-one dimensional simulations was satisfactory. It was found that the evolution of the PSDFs with respect to flame stoichiometry, temperature and growth time is consistent with the understanding of kinetic competition during soot formation. Finite rate kinetic limitations are observed at lower temperatures and thermodynamic reversibility occurs at higher temperatures. The observed PSDF features are highly sensitive to competition among the various processes of soot formation, from nucleation to coagulation and gas–surface reactions. The PSDFs are mostly bimodal with both nucleation and coagulation mode particles present. The evolution of the PSDF indicates a strong contribution to the mass of coagulation-mode by the nucleation-mode particles. The measured PSDFs offer comprehensive, canonical data sets useful for testing models of soot formation.
A novel stereoscopic image acquisition setup and a procedure for measuring multidimensional particle size distributions (nD PSDs) during crystallization based on image analysis are presented. Images ...of crystals in suspension passing a flow through cell are generated by two cameras which are arranged in an orthogonal manner. Particles are conveyed to the flow through cell using a sampling loop, thus allowing for online monitoring. Automated image analysis provides contour data which can be used to classify crystals into different generic particle model classes. For each type of particle size data is calculated and stored. Finally, time resolved nD PSD data can be calculated. The accuracy of this novel size measurement was confirmed by comparison to measurements obtained with a Coulter Multisizer. The non-invasive nature and repeatability of experiments are shown by monitoring populations of sodium chloride and of the β polymorph of l-glutamic acid under different conditions. Finally, crystal growth of acetaminophen during cooling crystallization is shown. In addition, a virtual test bench is used to study the measurement method in silico.
•An image based setup for measuring nD particle size distributions online is shown.•Particle classification and size calculation algorithms are introduced.•Capabilities of the setup in terms of accuracy and time resolution are demonstrated.•A virtual test bench is developed and used to investigate different image analysis effects.•The setup is tested during the growth of organic crystals.
The effects of removing non-starch components on the surface microstructure, water migration and glucose diffusion rate of highland barley starch (HBS) were systematically studied to reveal the ...models that affect the digestibility of HBS. The results of scanning electron micrographs, confocal laser scanning microscopy, polarization cross and particle size distribution showed that there were two particle size ranges in highland barley flour, large (73.99–591.90 μm) and small (<73.99 μm). Partial β-glucan and proteins form a compact and continuous matrix on the surface of HBS granules; lipids can partly be adsorbed on the surface of HBS granules, while other lipids, proteins and β-glucan are scattered around HBS granules. After the removal of non-starch components, the ratio of large particles decreased and the starch granules were more exposed, especially proteins and β-glucan. The results of low-field nuclear magnetic resonance investigation showed that the water migration rate was accelerated after the removal of β-glucan, and partial free water was transformed into weakly bound water, while the opposite effect was observed for the removal of proteins and lipids. The glucose diffusion rate in vitro was unchanged after the removal of lipids, while the removal of β-glucan significantly accelerated the diffusion of glucose in vitro. This study reveals that the effective models of HBS inhibited by non-starch components is the compact matrix mainly formed by proteins and β-glucan on the surface of HBS granules. Additionally, the rate of glucose diffusion across the small intestinal wall could be considered as one of the means of constructing slowly digestible starch.
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•The continuous matrix formed by proteins and β-glucan were found on HBS granules.•Removing β-glucan accelerated water migration and glucose release of sample gels.•Removing non-starch components decreased large particle ratio (73.99–591.90 μm).•The particle size distribution of large particles changed less during digestion.•The proteins on HBS surface still block amylase after limited gastric digestion.
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