Fine Metal Particles Research Articles

Using immiscible magnetic liquids of different density as a separating medium for magnetic liquid separation

The article presents the results of a new magnetic liquid separation method study. This method differs from known methods by the presence of a bilayer separation medium in the form of immiscible ferromagnetic liquids of different density. When separating in a bilayer separation medium, the particle equilibrium condition on a plane surface, recorded according to Young's law and Neumann's rule, must be supplemented by the linear tension of a curved phase interface. A linear tension is a force and energy barrier that prevents fixing of fine particles of noble metals at the phase interface, and is the reason for their effective extraction into the heavy fraction. The magnetic liquid separation method was tested on concentrates containing platinoids. It was established that during separation in a bilayer medium, the extraction of platinoids into the heavy fraction was 25,89 %, and during separation in a water-based ferromagnetic fluid it was 19,73 %. The quality of the heavy fraction makes it possible to direct it to the hydrometallurgical process, bypassing the copper plant, which increases the extraction of precious metals by 5,0 % abs.

Calculation of the characteristics of the ignition of a metallized composite propellant using various methods for describing its thermophysical properties

The ignition of a metallized composite propellant by a local energy source of limited heat content is studied. The main characteristic of the process (ignition delay time) is calculated over a wide range of initial temperatures of the source (800–1500 K) for the actual inhomogeneous structure of the propellant with consideration of the presence of fine metal particles and for an effective heterogeneous structure with thermophysical properties calculated by formulas based on the rule of additivity of the thermophysical properties of the components. The thermal conductivity of the propellant is also calculated by approximate expressions proposed by Maxwell, Frick, Bruggeman, Meredith, Xiao, Hamilton, Cross, Behrens, Misnar, Peterson, Hermans, and Nielsen for polymeric materials containing finely dispersed inclusions with a higher thermal conductivity as compared to the polymer matrix. It is found that the expressions proposed by these authors yield values of the ignition delay time and the minimum initial temperature of the heat source required to initiate combustion that differ from those predicted by the model with account of the real heterogeneous structure by up to 75 and 15%, respectively.

Preparation and properties of gadolinium/noble metal fine particle compounds

Preparation and properties of gadolinium/noble metal fine particle compounds

Promoting hydrogen production and minimizing catalyst deactivation from the pyrolysis-catalytic steam reforming of biomass on nanosized NiZnAlOx catalysts

Hydrogen production from the thermochemical conversion of biomass was carried out with nano-sized NiZnAlOx catalysts using a two-stage fixed bed reactor system. The gases derived from the pyrolysis of wood sawdust in the first stage were catalytically steam reformed in the second stage. The NiZnAlOx catalysts were synthesized by a co-precipitation method with different Ni molar fractions (5, 10, 15, 25 and 35%) and a constant Zn:Al molar ratio of 1:4. The catalysts were characterized by a wide range of techniques, including N2 adsorption, SEM, XRD, TEM and temperature-programmed oxidation (TPO) and reduction (TPR). Fine metal particles of size around 10–11nm were obtained and the catalysts had high stability characteristics, which improved the dispersion of active centers during the reaction and promoted the performance of the catalysts. The yield of gas was increased from 49.3 to 74.8wt.%, and the volumetric concentration of hydrogen was increased from 34.7 to 48.1vol.%, when the amount of Ni loading was increased from 5 to 35%. Meanwhile, the CH4 fraction decreased from 10.2 to 0.2vol.% and the C2–C4 fraction was reduced from 2.4vol.% to 0.0vol.%. During the reaction, the crystal size of all catalysts was successfully maintained at around 10–11nm with lowered catalyst coke formation, (particularly for the 35NiZn4Al catalyst where negligible coke was found) and additionally no obvious catalyst sintering was detected. The efficient production of hydrogen from the thermochemical conversion of renewable biomass indicates that it is a promising sustainable route to generate hydrogen from biomass using the NiZnAl metal oxide catalyst prepared in this work via a two-stage reaction system.

Fine Particulate Matter in Beijing: Sources and Health Impacts

Introduction: High concentration of atmospheric fine particulate matter (PM2.5) could deteriorate air quality, reduce visibility, influence climate change, and affect human health. PM2.5 has attracted increasing attention in Beijing, China, as there are frequent haze episodes in recent years. Health impact of PM2.5 is still a great concern of the public. To better understand the health effects of PM2.5 and develop effective policies to control fine particulate pollutants, research on sources of particulate matter and its associated health effects are in urgent need. Methods: PM2.5 was collected on filters at a representative urban site in Beijing in different seasons, including haze and non-haze days. Detailed chemical composition including carbonaceous components, ions, and metals in fine particles was measured. Receptor-model based source apportionment of PM2.5 was performed to determine source contributions. The production of reactive oxygen species by fine particles was determined based on the cell-free surrogated lung fluid solution method. Results: Sources of fine particle in Beijing exhibited seasonal variations, with higher biomass burning contribution in summer and fall, and higher coal combustion contribution in winter. Secondary sources played a dominant role in most of the haze episodes. However, reactive oxygen species produced by per PM2.5 mass was much higher in clean days compared to haze days, and was found to be well correlated with trace metals such as Fe, Mn and Cu. Conclusions: Chemical characteristics and sources of PM2.5 in Beijing have clear difference between haze and non-haze days and between seasons. Correlations between chemical compositions and sources with health effects have been investigated through reactive oxygen species. The study of sources and health impacts of fine particles during severe haze episodes in Beijing is very important, which requires more research in the future.

Emission Inventory of Heavy Metals in Fine Particles Emitted from Residential Coal Burning in China

Based on a dilution sampling system and domestic burning tests, emission factors (EFs) for eleven heavy metals of V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Sb and Pb in PM2.5 from raw coal and honeycoal burning were calculated, using their contents in raw coals of different provinces. Then the total emission amounts of heavy metals from residential coals burning in 2012 were calculated and 30 km×30 km grid cell-based emission inventories were established. The results showed that the EFs of Pb, Zn, As and Cu were higher from honeycomb coal burning. They were 27.1, 16.8, 0.99 and 0.97 mg·kg-1, which were 56, 6, 10 and 2 times of those for raw coal, respectively. The total emissions of V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Sb and Pb in PM2.5 from residential coal burning in 2012 were 0.5, 30.1, 59.5, 1.1, 29.3, 20.0, 188.9, 64.9, 1.6, 3.4 and 176.7 t. Hunan, Hebei, Inner Mongolia, Henan, and Shandong held higher emission amounts, which were 12.4%, 12.3%, 10.4%, 9.9% and 9.3% of the total emissions of the whole country. Beijing, Henan, Shandong, Hunan, Jiangxi, Guizhou and Inner Mongolia were the regions with higher emission intensities and emission amounts per capita. The spatial distribution showed that the regions with higher annual emissions of Zn and Pb distributed widely, mainly in Inner Mongolia, Hebei, Beijing, Tianjin, Shandong, Henan, Gansu, Hunan and Jiangxi. The emission inventories for heavy metals in fine particles established here are important for regional air quality modeling and human health risk assessment.

SiO2 nanoparticles surface modified with polyethyleneimine-oleic acid complex as stabilizers of Ni fine particles in dense nonaqueous suspensions

SiO2 nanoparticles (NPs) surface modified with polyethyleneimine-oleic acid complex (PEI-OA) has successfully prepared in a simple manner as a stabilizer of metal (Ni) fine particles (FPs) as well as a component of Ni/SiO2 composite particles. Starting from SiO2 NPs which were collected through centrifugation of commercial SiO2 colloids, it was found that PEI-OA can effectively adsorbed on collected SiO2 NPs surface during their redispersion process in toluene with the assistance of ultrasonication. The aggregated particle size (Z-average size) in toluene could be successfully reduced to c.a. 100nm under saturated adsorption of PEI-OA. It was also found that PEI-OA-modified SiO2 NPs can effectively attach to the Ni FPs by a simple mixing process in toluene. The FE-SEM observation confirmed the adsorption of the PEI-OA-modified SiO2 NPs on the Ni FPs without forming severe NP aggregates. Owing to the attachment of the PEI-OA-modified SiO2 NPs with surfaces that are compatible to toluene and α-terpineol, the suspension stability of the Ni/SiO2 composite particles in these solvents drastically improved. The result was confirmed by the effective reduction of the sedimentation velocity of diluted suspensions as well as by the reduction of the viscosity of dense suspensions.

Structure, optical properties and thermal stability of Al2O3-WC nanocomposite ceramic spectrally selective solar absorbers

Traditional metal-dielectric composite coating has found important application in spectrally selective solar absorbers. However, fine metal particles can easily diffuse, congregate, or be oxidized at high temperature, which causes deterioration in the optical properties. In this work, we report a new spectrally selective solar absorber coating, composed of low Al2O3 ceramic volume fraction (Al2O3(L)-WC) layer, high Al2O3 ceramic volume fraction (Al2O3(H)-WC layer) and Al2O3 antireflection layer. The features of our work are: 1) compared with the metal-dielectric composites concept, Al2O3-WC nanocomposite ceramic successfully achieves the all-ceramic concept, which exhibits a high solar absorptance of 0.94 and a low thermal emittance of 0.08, 2) Al2O3 and WC act as filler material and host material, respectively, which are different from traditional concept, 3) Al2O3-WC nanocomposite ceramic solar absorber coating exhibits good thermal stability at 600 °C. In addition, the solar absorber coating is successfully modelled by a commercial optical simulation programme, the result of which agrees with the experimental results.

Enhanced catalytic activity of Ni3Al foils towards methane steam reforming by water vapor and hydrogen pretreatments

A pretreatment procedure consisting of water vapor oxidation followed by H2 reduction has been developed for enhancing the catalytic activity of as-rolled Ni3Al foils for steam reforming of methane. The catalytic activities of the as-rolled Ni3Al foils in the temperature range of 873–1023 K at a steam to carbon ratio of 1.0 were found to be significantly improved by the pretreatment procedure consisting of a water vapor oxidation at 873–923 K for 1 h followed by a H2 reduction at 873 K for 1 h. Surface characterization of the foils before and after the reactions revealed that many fine NiO particles were formed on the surface by the water vapor oxidation at 873–923 K, whereas much less NiO particles were formed by the water vapor oxidation at low temperatures (<873 K) or high temperatures (>973 K). During the subsequent H2 reduction treatment at 873 K, These NiO particles were reduced to metallic Ni. It is supposed that the enhancement in catalytic activity is attributed to the fine metallic Ni particles formed on the foil surface by the pretreatment procedure.

Influence of Fine Metal Particles on Surface Discharge Characteristics of Outdoor Insulators

Focusing on the influence of fine metal particles on the insulation characteristics of outdoor insulators, spherical micrometer-level iron powders were used to represent fine metal particles of different parameters on a polymer insulator specimen surface. Dynamic movement and lift-off behavior of fine particles, as well as the triggered surface discharges under AC voltage were investigated in a uniform electric field under different experimental conditions. The results reveal that the inception, propagation and intensity of surface discharges are significantly affected by the particle parameters, including particle size, amount and distributing characteristic. Based on the measurement of light emission during the flashover process using a high-speed camera, the process of surface discharge to flashover triggered by the fine metal particles were investigated to obtain a relationship between flashover voltage, discharge light intensity and particle parameters. It is suggested that particle size smaller than 28 µm and particle amount more than 40 mg in contact with the non-uniform distribution can cause a significant distortion and intensification of the electric field resulting in a higher risk of surface discharges leading to flashover. Such investigations can enhance the operating reliability of outdoor insulators subjected to these conditions.

Effect of Glass Transition Temperature of Stabilizing Polymer of Air-Stable Gelatin-Stabilized Copper Fine Particles during Redox Two-Step Low-Temperature Sintering Process

Abstract It has been found in this study that the glass transition temperatures can be considered as the lowest temperature for sintering metal fine particles to obtain electro-conductive metallic layers from the differential scanning calorimetry measurement of the fine particles. Gelatin-stabilized copper fine particles could be sintered to form an electrically conductive copper layer with a resistivity of 1.9 × 10−5 Ω cm at as low as 150 °C using oxidation–reduction two-step sintering.

A computer‐aided methodology for the optimization of electrostatic separation processes in recycling

The rapid growth of technological products has led to an increasing volume of waste electrical and electronic equipments (WEEE), which could represent a valuable source of critical raw materials. However, current mechanical separation processes for recycling are typically poorly operated, making it impossible to modify the process parameters as a function of the materials under treatment, thus resulting in untapped separation potentials. Corona electrostatic separation (CES) is one of the most popular processes for separating fine metal and nonmetal particles derived from WEEE. In order to optimize the process operating conditions (i.e., variables) for a given multi‐material mixture under treatment, several technological and economical criteria should be jointly considered. This translates into a complex optimization problem that can be hardly solved by a purely experimental approach. As a result, practitioners tend to assign process parameters by few experiments based on a small material sample and to keep these parameters fixed during the process life‐cycle. The use of computer experiments for parameter optimization is a mostly unexplored area in this field. In this work, a computer‐aided approach is proposed to the problem of optimizing the operational parameters in CES processes. Three metamodels, developed starting from a multi‐body simulation model of the process physics, are presented and compared by means of a numerical and simulation study. Our approach proves to be an effective framework to optimize the CES process performance. Furthermore, by comparing the predicted response surfaces of the metamodels, additional insight into the process behavior over the operating region is obtained. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Enrichment of heavy metals in fine particles of municipal solid waste incinerator (MSWI) fly ash and associated health risk

During the pretreatment and recycling processes, the re-suspended dust from municipal solid waste incinerator (MSWI) fly ash might pose a significant health risk to onsite workers due to its toxic heavy metal content. In this work, the morphological and mineralogical characteristics of fly ash in different particle sizes are presented. The concentrations of seven trace elements (Zn, Pb, Cu, Cd, Cr, Fe and Mn) in these samples were determined. The results show that volatile metals, such as Zn, Pb, Cu and Cd, were easily concentrated in the fine particles, especially in Dp2.5-1 and Dp1, with soluble and exchangeable substances as the main chemical species. The health risk assessment illustrated that the cumulative hazard indexes for non-carcinogenic metals in Dp10-5, Dp5-2.5, Dp2.5-1, and Dp1 were 1.69, 1.41, 1.78 and 2.64, respectively, which were higher than the acceptable threshold values (1.0). The cumulative carcinogenic risk was also higher than the threshold value (10−6). For the onsite workers, the relatively apparent non-carcinogenic and carcinogenic effects were from Pb and Cr, respectively. The above findings suggest that fine-grained fly ash contained a considerable amount of heavy metals and exhibited a great health risk.

Bimodal Particle Reinforcement for Wear Resistant Powder Metallurgy Steels

Reinforcement of powder metallurgy steels with fused tungsten carbide (FTC) has been shown to improve the wear resistance under certain loading conditions. A weakness is however the low hardness of the matrix, which results in selective wearing of the matrix between the carbide particles, i.e. “washing-out” effects. In the present study, in a first round fine metallic or carbidic particles were added to the iron-graphite powder mix, and the blends were die compacted and sintered in protective atmosphere. The specimens were then tested under different wear loads. It showed that also metallic powders added were transformed into carbides during sintering, thus resulting in reinforcement by fine carbides. Since Mo alloying proved to be most effective with regard to hardness and strength, specimens Fe-3%Mo-0.8%C reinforced with 20% coarse FTC (all in mass%) were sintered and tested according to ASTM G65, Continuous Impact Abrasion and dry sliding against ball bearing steel. It showed that Mo addition had quite pronounced positive effect on the G65 erosion resistance and, somewhat less, on dry sliding, while wear resistance in CIAT was less affected; the basic wear mechanisms however remained unchanged.

Effect of Seeding and pH Conditions on the Size and Shape of Au Nanoparticles in Reduction Crystallization

AbstractEfficient and simple methods for gene integration into various plants have been studied by many researchers. The particle gun method using fine metal particles is one of the most potent technologies. However, it is difficult to control the particle size distribution and shape of the metal particles and, thus, to design and create adequate particles of suitable quality for the gene‐supporting media. Here, reduction crystallization of nanometer‐ and submicron‐sized Au was investigated in order to clarify the effects of the seeding and reaction conditions on the sizes and shapes of Au particles. The seed size has an influence on the surface roughness of the Au nanoparticles. Experiments to form Au particles were also performed using pH‐controlled ascorbic acid. The pH has a great influence on the size and shape of nano/submicron Au particles and the mechanism of reduction crystallization.

Characteristics of Fine Metallic Soap Particles Using Jet-Mixing Method

Characteristics of Fine Metallic Soap Particles Using Jet-Mixing Method

Identification of the typical metal particles among haze, fog, and clear episodes in the Beijing atmosphere

For a better understanding of metal particle morphology and behaviors in China, atmospheric aerosols were sampled in the summer of 2012 in Beijing. The single-particle analysis shows various metal-bearing speciations, dominated by oxides, sulfates and nitrates. A large fraction of particles is soluble. Sources of Fe-bearing particles are mainly steel industries and oil fuel combustion, whereas Zn- and Pb-bearing particles are primarily contributed by waste incineration, besides industrial combustion. Other trace metal particles play a minor rule, and may come from diverse origins. Mineral dust and anthropogenic source like vehicles and construction activities are of less importance to metal-rich particles. Statistics of 1173 analyzed particles show that Fe-rich particles (48.5%) dominate the metal particles, followed by Zn-rich particles (34.9%) and Pb-rich particles (15.6%). Compared with the abundances among clear, haze and fog conditions, a severe metal pollution is identified in haze and fog episodes. Particle composition and elemental correlation suggest that the haze episodes are affected by the biomass burning in the southern regions, and the fog episodes by the local emission with manifold particle speciation. Our results show the heterogeneous reaction accelerated in the fog and haze episodes indicated by more zinc nitrate or zinc sulfate instead of zinc oxide or carbonate. Such information is useful in improving our knowledge of fine airborne metal particles on their morphology, speciation, and solubility, all of which will help the government introduce certain control to alleviate metal pollution.

The facile preparation of Cu–Zn–Al oxide composite catalysts with high stability and performance for the production of dimethyl ether using modified aluminum alkoxide

Modified aluminum alkoxide prepared by alcoholysis was used as an aluminum source in the complete liquid-phase technology for the preparation of slurry catalysts. The use of the modified aluminum alkoxide afforded control over the rate of the hydrolysis/condensation reactions during the preparation of the catalyst precursors, thereby generating catalysts with a fine nano-structured active metal and metallic oxide particles. Four types of Cu–Zn–Al (molar ratio is 2:1:4) catalysts were prepared using different procedures. These catalysts were tested for CO hydrogenation at 553K, 4.0MPa and H2/CO=1.0 in a kettle with a mechanical agitator. The results indicated that the activity of the catalysts was greatly dependent on the rate of the hydrolysis/condensation reactions, and the catalyst with the best catalytic performance was obtained by controlling the hydrolysis/alcoholysis rate during catalyst synthesis by pre-alcoholysis of AIP as the aluminum source, over which the CO conversion and dimethyl ether selectivity could reach 62.6% and 62.5%, respectively.

Ignition delay time in a methane—air mixture in the presence of iron particles

Ignition of a stoichiometric methane—air mixture in a piston-driven setup at temperatures of 900–1200 K and pressures of 1–1.2 MPa is experimentally studied. The experiments reveal the emergence of bright points in the duct of the facility. The measurements show that luminescence in the volume appears almost immediately after the end of the compression stage, whereas the methane—air mixture ignites only after 4–5 ms. Presumably, these bright points appear owing to ignition of fine particles. It is experimentally found that ignition of these particles reduces the ignition delay time of the gas mixture. A physicomathematical model of ignition of methane-oxygen-nitrogen/argon mixtures in the presence of fine metal particles is proposed to obtain a theoretical description of this phenomenon. This model takes into account both detailed kinetic mechanisms of chemical conversions in the reacting gas mixture and reduced kinetic mechanisms of oxidation of metal particles. Calculations by this model show that ignition of particles at low temperatures (less than 1100 K) leads to reduction of the ignition delay time of the gas mixture.

Effect of Lattice Strain on the Debye-Waller Factors on the Fine Metal Particles

Effect of Lattice Strain on the Debye-Waller Factors on the Fine Metal Particles