Collection of submicron particles by H2 bubbles

A theoretical analysis is presented to describe the deposition of Brownian particles onto H₂ bubbles (flotation) by analogy with classical filtration theory.Experimentally, it is shown that submicron and smaller particles of MnO₂ are collected by H₂ bubbles without using the special collector or chemicals usually employed in flotation. The experimental technique for determining the total collection efficiency is described.A comparison between the theory and our experiment makes it clear that there are cases in which the simpler filtration theory is adaptable to a complicated flotation analysis. In addition, we find that the collection mechanisms of submicron particles of MnO₂ is predominantly characterized by interception and Brownian diffusion.     

Collection of hydrophilic and hydrophobic charged submicron particles by charged water droplets

An experimental system capable of measuring the collection efficiency of charged submicron particles by charged water droplets is described. Collection efficiencies are measured for both hydrophilic and hydrophobic particles to clarify the effect of wettability on collection. Excellent agreement with the theory is obtained for hydrophilic submicron particles when the Coulombic force is dominant. No significant difference in collection efficiencies between hydrophilic and hydrophobic particles is observed. It is concluded that the wettability of submicron particles has no effect on its collection by water drops when Coulombic attraction is the dominant mechanism.     

超细颗粒物增湿团聚技术研究进展

流化床内喷雾增湿可以使颗粒在不断的碰撞中发生强烈的传热传质而团聚长大。综述了颗粒物化特性、操作参数及加入团聚促进剂对颗粒团聚的影响,分析了循环流化床烟气脱硫工艺的工艺过程、床内增湿团聚机理以及综合脱除SO2以及超细颗粒物的可行性,指出增湿团聚技术可以有效提高燃煤烟气中超细颗粒物的脱除效率,有很好的应用前景。     

Vapor-phase surface modification of submicron particles

Submicron iron oxide red, TiO₂ and talc particles were chemically modified twice in the same double-cone reactor with vapor of 2,4,6,8-tetramethylcyclotetrasiloxane(TMCTS) and then 1-dodecene, 1-tetradecene or vinyl terminated poly(dimethylsiloxane). For the second modification alumina balls coated with hexachloroplatinic(IV) acid by simple impregnation of the catalyst-containing solution were used as a catalyst, reducing aggregation of the particles as well. The conversion of the second modification was even higher than that obtained in conventional liquid-phase hydrosilylation under comparable process conditions. Segregation of the particles from the ball was important for large volume modification. Under the given particle loading, the optimal ball size and catalyst concentration existed for the efficient use of catalyst. The ball catalysts were effective in four consecutive batches without any appreciable decrease in the conversion. Intermittent tumbling and the use of baffle enhanced the conversion of any gas-solid reaction such as both the first and the second modifications, minimizing simple tumbling (no mixing) and lump formation of particles.     

Swelling behavior of submicron gel particles

We prepared submicron Poly(N-isopropylacrylamide) gel particles. Their swelling behavior was investigated by a photon correlation spectroscopy (PCS) technique. The swelling behavior of submicron gel particles showed a continuous volume phase transition for various temperatures. We combined the extended Flory-Huggins model for mixing solvent and network with a modified Flory-Rehner theory for the elastic contribution. The proposed model agreed very well with swelling behaviors of both submicron gel particles and bulk gels. A continuous volume phase transition behavior of submicron gel particles was predicted successfully by the proposed model. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 109–114, 1998     

Classification of submicron Ni particles by heterocoagulation

In this work, the size classification of a mixture of submicron and micron size Ni particles dispersed in aqueous solution was investigated. The suspension of Ni particles was allowed to flow, under laminar condition, through a burette filled with an adhesion medium (i.e. substrate). The difference between zeta potentials of larger particles and adhesion medium created a base for the heterocoagulation. Thus, the larger particles move towards the medium assisted by the Saffman lift force and are attracted to its surface. The finer particles, on the other hand, flow off the burette and were collected as a separate fraction. This phenomenon was then explained by numerical simulating the particle's motion and showing that a stronger Saffman lift force will act in the direction of the substrate only for large particles, leaving the smaller ones unaffected as they sediment out.     

Finite size effects in submicron barium titanate particles

An experimental and theoretical analysis of finite size effects in submicron barium titanate particles is presented. The dielectric data show that the dielectric constant (ε = 734) of small particles (d = 20 nm) remains very similar to that of single crystals provided that the particles are grown from an amorphous phase and not mechanically crushed into powder. This shows that what has in the past been mistaken for true size effects (i.e., depolarization fields) is due to lattice strain. The X-ray data show that the Curie temperature (cubic-tetragonal transition temperature) decreases monotonically to zero degree Kelvin as particle size is reduced. However this is shown to be a simple function of lattice constant: The lattice constant expands as the particle diameter d contracts. This is similar to surface relaxation in thin films.     

荷电水雾脱除超细颗粒物的研究进展

综述了荷电水雾脱除超细颗粒物的作用机理和影响因素,分析了荷电水雾脱除燃煤电厂烟气中超细颗粒物及综合脱除其它燃煤污染物的可行性,指出利用荷电水雾对燃煤电厂烟气进行处理能够有效提高传统静电除尘器对超细颗粒物的脱除效率,并能实现燃煤污染物的联合脱除,应用前景广阔。     

Collection efficiency of sintered ceramic filters made of submicron spheres

The performance of filters made of sintered submicron alumina particles was evaluated. The filter has a high collection efficiency and high pressure drop, requiring the development of a special measuring system for its evaluation. The system consists of a polydisperse NaCl particle generator, a differential mobility analyzer (DMA), an ejector to supply aerosols for testing filters with high pressure drop, and a mixing-type condensation nucleus counter (CNC) capable of obtaining a stable reading of very low concentration particles. Penetrations as low as 10⁻⁹ can be measured in the particle diameter range of 0.02-0.14 μm. Two filters made by sintering 0.60 and 0.84 μm alumina particles were evaluated. The experimental data collected served as the basis of theoretical development. Following the single fibre theory, the filter penetration is calculated by using a single sphere as the element. Both the diffusion and interception collection mechanisms were taken into account. The resulting equation gives a general trend of efficiency curves as a function of the parameters involved, e.g. the test aerosol size, packed particle size and filtration velocity. However, it is not sufficiently accurate for providing quantitative performance results.     

Mechanical production and stabilization of submicron particles in stirred media mills

A joint research project between the Technical University of Braunschweig and the Technical University of München investigates the possibilities for the production of stable product suspensions in a particle size range smaller than 100 nm. This paper shows the experimental setup which allows the measurement of the most important electrochemical properties and the analysis of the particle size distribution of the product suspension as well as an adjustment of the pH value for stabilization during the comminution process. Results for comminution of fused corundum with different grinding media materials and grinding media sizes are shown. In addition, results showing the influence of the electrostatic stabilization on the grinding progress are presented. Further, the rheology of the product suspension is examined depending on grinding progress and suspension stability.     

Development of apparatus for electro-flotation

A new apparatus for electro-flotation has been developed by using the impeller of stirred tank as electrode(s). The principle of this apparatus reported is that the gas bubbles generated by electrolysis float the flocs while flocculation is promoted by the rotation of electrode(s). The collection efficiency of this apparatus for tap water containing blue ink of 10^?3m³/M³ in concentration has been discuss by using various electrode(s) and changing the rotation speed of the electrode(s).     

Polymerization of MMA at the surface of inorganic submicron particles

Inorganic submicron particles, such as TiO₂, were modified with titanate coupling agents. The structure and stability of some titanates, both in solution and at the particle surface, were investigated by various methods. The modified titanium dioxide was dispersed in a solution of sodium dodecylsulphate (SDS) in water. The surfactant adsorbs at the now hydrophobic particle surface, thus creating a micellelike structure with an inorganic particle in the centre. In this system an emulsion polymerization of methyl methacrylate was carried out. Product formed at the particle surface is either physically bound by entanglement or chemically bound by covalent bonding to the titanates. In this way a core-shell morphology is obtained with an inorganic core and a polymer shell. The effects of several reaction parameters on the kinetics of the polymerization were studied. The encapsulated TiO₂ particles may offer interesting prospects in those applications where good coupling between polymer matrix and inorganic particles is necessary, such as latex paints and polymer composite materials.     

Deposition of submicron particles in deep bed filtration under unfavorable surface conditions

Deterioration in the filter removal efficiency of submicron particles (λ/λ_o) under unfavorable surface conditions is affected by the number of deposited particles per filter grain. In the case of above micron particles, the deterioration of filter removal efficiency has been mainly due to the blocking effect of deposited particles and not by the number of deposited particles. Deposition of large number of submicron particles changed the surface characteristics of collectors (filter grain associated with deposited particles) and enhanced unfavorable surface conditions. Filtration experiments were conducted with monodispersed suspensions of known sizes of submicron latex particles at different ionic strengths, using glass beads as filter grains. The filtration performance was predicted by using a mathematical model, assuming a linear relationship between λ/ λ_o and Σ (i.e. λ/λ_o=1 − kΣ). For both particles, k was found to decrease andλ _o was found to increase with the increase in the ionic strength. A comparison was made of the importance of blocking effect for the filtration of submicron particles.     

Laser initiation of compositions based on PETN with submicron coal particles

This paper describes the results of experiments on laser initiation of composites based on PETN and inclusions of submicron coal particles. The thresholds and kinetic characteristics of explosion of mixed compositions based on PETN and inclusions of submicron coal particles (brown coal B and parabituminous coal P) are studied under the impact of neodymium laser (1064 nm; 12 ns), depending on the mass concentration of inclusions in the range of 0–5%. It is shown that the minimum threshold of explosive decomposition of PETN equal to 1.1 J/cm² can be achieved if the concentration of both types of inclusions is 0.5%.     

Agglomerates and granules of nanoparticles as filter media for submicron particles

An experimental study on filtration of submicron solid and liquid aerosol particles by using a filter media composed of agglomerates or granules of nanoparticles is described. Fumed silica nanoagglomerates, carbon black granules, silica shells, activated carbon granules, glass beads and nanoporous hydrophobic aerogel were among the granular filter media tested and compared to a commercially available HEPA fiber-based filter. Other than the glass beads which were used for comparison purposes, the primary particle size of the agglomerates/granules is of nanometer scale, but they agglomerate to form porous structures of about several hundreds of microns which were customized as packed (deep bed) or fluidized bed filters and challenged against submicron solid and liquid aerosols. For packed bed filters, the size of the granules has been optimized to a range of 150-500 µm with a filter thickness of about 1-3 in. and superficial gas velocities of less than 4 cm/s. Fluidized beds required granules smaller than 150 µm and the height of the bed was in the range of 15-40 cm.The customized filters and a HEPA fiber-based filter were challenged simultaneously against the same aerosol at the same superficial gas velocities. When using carbon black or aerogel granules as filter media, collection efficiencies comparable or even higher than HEPA fiber-based filters are obtained, but with the advantage of extra filtration capacity due to the deep bed configuration and the absorption of liquids into the porosity of the media. A fluidized bed filter of aerogel granules not only provides higher collection efficiency and larger capacity than a HEPA fiber-based filter when challenged against both oil mist and solid aerosols but also has an extremely low pressure drop compared to a packed bed filter and can be operated continuously with respect to removing saturated granules and adding fresh ones.     

Spark plasma sintering of TiC-based composites toughened by submicron SiC particles

TiC-based composites toughened by submicron SiC particles with improved fracture toughness were fabricated and fracture mechanism has been investigated. It has been found that the improvement in fracture toughness of TiC–SiC composites is due to both crack paths propagating through uniformly distributed SiC particles and the fracture mode transition from intergranular type to transgranular type caused by the change of residual stresses originating from the addition of SiC particles. The optimum of fracture toughness (5.2 MPa m^1/2) was achieved at 14.6 vol% SiC, whereas the toughness decreased with increasing amount of SiC beyond 30 vol%.     

Estimation of acoustic forces on submicron aerosol particles in a standing wave field

The net acoustic force acting on submicron particles suspended in a gas and exposed to a standing wave field is investigated as a function of particle size, by measuring both the aerosol number density and size distribution in a flow-through resonator. By taking into account all contributions relevant to the net force, this experimental study provides a first estimate for the acoustic radiation force in a size range where molecular effects are expected to be significant. The experiment consists of an electrostatic transducer generating a standing wave in the 50–80 kHz frequency range, with the submicron aerosol particles concentrated at pressure antinodes located across the height of a rectangular channel. A section of the flow is sampled isokinetically and analyzed using a Scanning Mobility Particle Sizer (SMPS), while the nodal patterns are visualized simultaneously using light scattering. The net acoustic force is calculated from their measured displacement along the axis of the 1D standing wave field. The component of this force resulting from radiation pressure is estimated by subtracting contributions from other forces. The results provide the first experimental estimation of the size dependence of the acoustic contrast factor for submicron aerosol particles, demonstrating the possibility of performing acoustic separation for diameters as small as 150 nm.

Copyright © 2018 American Association for Aerosol Research