Particle Layer Thickness Research Articles

Relaxation of adsorbed layer thickness and electrophoresis of polystyrene latex particles after overshooting of polyelectrolytes with different charge density

Temporal change of hydrodynamic layer thickness (δH) and electrophoretic mobility (EPM) of polystyrene sulfate latex (PSL) particles adsorbed by oppositely charged polyelectrolytes were monitored herein to clarify the relaxation behavior after overshooting. Two linear polyelectrolytes with nominal molecular weight of 5 million differing in chain charge density, σ = 100 % (PTMA5M) and σ = 4 % (PTMC5M), and PSL particles of different diameters were used in the experiment. With the former polyelectrolyte, a remarkably thick layer that is formed at the incubation decays with the time scale of several tens of minutes and the EPM remains constant. The value of δH decreases with the increase of particle size, whereas with the latter polyelectrolyte, the initial value of δH is several times smaller than that of the former. There is a case wherein the EPM decreases with time, although δH remains constant. The initial δH is independent of the particle size. Ascribing the reason for the relaxation phenomena to desorption of overshot polyelectrolytes attached with meta-stable conformation in the initial stage, we have obtained an approximate picture of the conformational change for the chain of different charge density.

Numerical study on the attenuation effect on the blast wave of encircling a high explosive with granular media

This study explored the practicality of a two-phase flow model for granular media in elucidating the attenuation mechanism of the blast wave. To validate the model, the numerical data were compared with the results of the previous experiments in terms of the interaction between the planar shock wave and particle layer, dispersal of steel particles saturated with a liquid explosive after the detonation of the explosive, and attenuation effect of the particle layer on the blast wave. Results of the validation confirmed good agreement and consistency between both data. Next, the attenuation effect on the blast wave created by a spherical pentolite by encircling the high explosive with a particle layer of sand was investigated, where the main parameter for comparison was the particle layer thickness. Here, a thicker particle layer further attenuated the blast wave, whereas a thinner one was accelerated to a velocity exceeding the sound speed of air, which generates a secondary shock wave ahead of the particle layer and behind the incident shock wave. When the secondary shock wave was coupled with the incident shock wave, the blast wave strength was locally recovered. To quantitatively comprehend the attenuation mechanism of the particle layer on the blast wave, the total energy transfer between the particle layer and air was computed. Results revealed a strong correlation between the blast wave strength and the amount of energy transferred between the particle layer and air and to the flow structures generated by the particle motion.

Theoretical model of optical transmission and reflection characteristics of dusty PV modules

Modeling radiative transfer on a dusty photovoltaic (PV) module is a complicated problem. In this work, an improved optical light pathway model was established based on a three-layer system (dust particles–cover glass–solar cell); this system models radiative transfer by considering absorption, reflection, and transmission. Transmittance and reflectance formulae based on the light transmission and reflection pathway were obtained. Optical experiments were conducted for incident light with a spectral range of 0.30–0.7 μm to verify the improved model. The results show that when the thickness of the particle layer was larger than the sum of the minimum and maximum diameters, the theoretical spectral transmittance and reflectance agree well with the experimental data. The relative errors of spectrum transmittance and reflectance were 1.17–16.79% and 4.17–11.68%, respectively. Spectral transmittance through the composite layers was very low, and the dust particle composition and layer thickness had strong inhibiting effects on the transmission of incident light.

Thermal Transport in Nanoparticle Packings Under Laser Irradiation

Abstract Nanoparticle heating due to laser irradiation is of great interest in electronic, aerospace, and biomedical applications. This paper presents a coupled electromagnetic-heat transfer model to predict the temperature distribution of multilayer copper nanoparticle packings on a glass substrate. It is shown that heat transfer within the nanoparticle packing is dominated by the interfacial thermal conductance between particles when the interfacial thermal conductance constant, GIC, is greater than 20 MW/m2K, but that for lower GIC values, thermal conduction through the air around the nanoparticles can also play a role in the overall heat transfer within the nanoparticle system. The coupled model is used to simulate heat transfer in a copper nanoparticle packing used in a typical microscale selective laser sintering (μ-SLS) process with an experimentally measured particle size distribution and layer thickness. The simulations predict that the nanoparticles will reach a temperature of 730 ± 3 K for a laser irradiation of 2.6 kW/cm2 and 1304 ± 23 K for a laser irradiation of 6 kW/cm2. These results are in good agreement with the experimentally observed laser-induced sintering and melting thresholds for copper nanoparticle packing on glass substrates.

Energy estimation of the interaction of a roller vibratory classifier’s blade with crushed rock mass for solving design problems

The roller vibratory classifier is equipped with an impact device for implementing vibro-shock mode, which improves the classification efficiency, especially of viscous and wet materials. The new device is a disk nozzle with blades, which are made like petals of wearresistant polymer. The immersion of a petal at a given depth in a crushed rock mass is investigated experimentally. Theoretical studies includes pair correlation and regression analysis methods. It is obtained that an increase in humidity promotes penetration and leads to a decrease in the energy necessary for impact, whereas an increase in particle size and layer thickness leads to its increase. Analysis of regression equations makes it possible to establish the percentage ratio of influencing factors. The article presents mathematical models of impact energy from variable factors for the initial moisture content of the material, including separately for small classes (-2.5 + 1) mm and further, with variation of all three parameters in the range: layer thickness – 20-40 mm, particle size 1-10 mm, humidity – up to 9 %. The obtained correlation dependencies and regression models are necessary for improving the existing and designing new blade-type roller vibratory classifiers.

Cold-state experimental study on discharge characteristics of solid particles in a gravity driven moving bed solar receiver

A small-scale multi-tube experimental system was established to pretest the workability of a gravity driven moving bed solar receiver with its absorbing section containing an insert in each tube. Discharge characteristics of solid particles with various particle sizes range from 149 μm to 1359 μm in mean diameter are studied at ambient temperature. In multi-tube experiments, the discharge rate in each tube is almost uniform. In single-tube experiments, the packed height in the particle dispenser exhibits negligible influence on the mass flow rate. Three models have been set up to predict the mass flow rate in the without-insert case of particle flow experiments. Among them, Model-3 is shown to obtain the minimum mean error of 1.54% compared with the experimental results, and proved that the influence of particle size and orifice diameter on the gas-solid slip velocity should be considered. Effect of the insert on particle flow characteristics was also investigated. The added insert in the tubes is proved to increase the mass flow rate of the finest particles. However, for particles coarser than 642 μm in mean diameter, this effect is insignificant and the mass flow rate in with-insert case is consistent with predicted results by Beveloo equation and Model-3. Besides, the experimental results of particles finer than 297 μm in with-insert case are larger than predicted results by Model-3 and less than that by Beveloo equation. It is noteworthy that two types of flow instability are observed with specific experimental variables, indicates that particle layer thickness, particle size and orifice diameter are relevant parameters to affect the granular flow state. Hence, optimizing structural parameters and selecting suitable size of particles are necessary to avoid flow instability in this type of solid particle solar receiver.

Study on electric field distribution in cylindrical metal silo considering particle segregation

The cylindrical metal silo plays an important role in the industry for storing the product, while the undesired of electrostatic charge on the dielectric powder leads to dangerous electrostatic discharge and threatening human safety and causing a great economic loss. The aim of the study was to investigate the effect of the particle segregation on the electric field in the silo base on the electric field simulation. Three parameters were studied: large particle layer thickness fraction, small particle space charge density (ρS) and large particle space charge density (ρL). The effect of the particle segregation on the electric field in the silo was evaluated through comparing the electric field in the segregation case to that in the uniform case. The results showed that the particle segregation significantly affected the electric field in the silo. The space charge density of the small particle mainly influenced the electric field in the small particle layer, while that of the large particle had a significant effect on the electric field in the large particle layer. The particle segregation not only could increase the electric field strength but also could decrease the electric field, which was dependent on the relative magnitude of the large (|ρL|) and small (|ρS|) particle space charge density. Additionally, the relative growth rate (absolute value) of the maximum electric field strength increased with the increase of |ρL-ρS|.

Characterization of soot deposition and oxidation process on catalytic diesel particulate filter with ash loading through an optimized visualized method

The purpose of study is to investigate the structure of soot layer and evolutionary mechanisms of its deposition/regeneration process when applying five ash loadings in CDPF. The mechanisms can be used to reveal the principle of dual-layer filtration technology and lay the proper foundation for making advanced regeneration strategies to save energy and improve efficiency. The characterization of soot layer structure was analyzed by 2-D laser displacement sensor, pressure sensor and scanning electron microscope (SEM). The deposition process could be divided into four stages. The shift value of particle layer thickness to start the last stage was about 20 µm. With the ash amounts increasing, the initial pressure drops increased from 1260 Pa to 4550 Pa and the time-consuming in the first three deposition stages reduced from 250 s to 0 s. The mechanism of 2 g/L ash condition was similar to the dual-layer technology. The regeneration process could be divided into three stages. The irregular soot layer scallops were found in the middle of the 2nd regeneration stage. The “back diffusion” of micro-concentration oxygen molecules caused by catalyst could reduce the beginning temperature from 525 °C to 500 °C. With the ash amounts increasing from 0 g/L to 8 g/L, the duration time of II-regeneration stage gradually reduced from 3000 s to 0 s. The ash particles could act as oxygen carrier and have a catalytic effect on soot layer. The ash layer could absorb more thermal energy and have higher heat storage capacity.

Modification of photocatalyst morphology by ball milling and its impact on the physicochemical properties of wet coated layers

Mixtures of polymeric siloxane binder and titania were subjected to ball milling for variable time. After milling, they were spin-coated and inkjet printed onto soda-lime glass plates producing a titania-polysiloxane hybrid layers which were converted into titania-amorphous silica hybrid layers by thermal curing. Various experimental methods indicated that the ball milling process induced significant changes in the textural properties of the layer forming material. While some material properties and layer parameters show monotonous systematic decrease with milling time (particle size, surface roughness, layer thickness and haze), others show a maximum (specific surface area, photocurrent density). Thus by a careful control of the milling process we can adjust and optimize the performance of both powder and immobilized photocatalysts.

A viscosity prediction model for cement paste with nano-SiO2 particles

The workability of cement paste with nano-SiO2 (NS) particles depends on NS dosage and water to cement ratio (W/C). To characterize the workability of cement paste with hydrophilic NS particles, the viscosity of cement paste with different NS dosages and W/C is studied. An original viscosity prediction model is proposed to predict the minimum apparent viscosity of cement pastes with different NS dosages and W/C. In this viscosity prediction model, cement paste with NS can be taken as a suspension, i.e. cement particles is suspended in NS suspension. Therefore, the viscosity of cement paste with NS is composed of the viscosity of NS suspension and the relative viscosity of pure cement paste. The viscosity prediction models for NS suspension and pure cement paste are built up, respectively. The limitation of the viscosity prediction model of cement paste with NS is also discussed. Results show the proposed viscosity prediction model has high accuracy in predicting the viscosity of cement pastes with hydrophilic NS when NS volume fraction in NS suspension is less than 5.5%. The adsorbed water layer thickness of NS particles can be also calculated by the proposed model, and it is well in agreement with the mixing state results of NS suspension.

Novel technique for measurement of coating layer thickness of fine and porous particles using focused ion beam

A novel technique for the measurement of the coating layer thickness of fine particles was developed in this work based on cross-sectioning of micrometre-sized single coated particles using focused ion beam (FIB) milling. This technique was tested on two batches of aerogel particles coated with thin coatings in a spouted bed. The FIB milling procedure consisted of two steps. First, the desired part of the coated particle was removed using a high ion beam current. The resulting cross-sectioned area was then polished using a lower ion beam current to make the cross-section clearly visible. The FIB milling process was controlled with simultaneous scanning electron microscopy (SEM). Afterwards, the coating layer thickness was evaluated using the SEM images.The coating layer was successfully applied on the porous aerogel microparticles in the spouted bed. The coating uniformity of the highly porous particles increased with increasing sprayed coating solution amount, with up to 91% of the particle pores being covered. The FIB-cross-sectioning technique using an ion beam of 2.50nA for the first milling and 0.43nA for polishing of the surface resulted in successful generation of cross-sections of representative particles with a visible particle core and coating layer. A coating layer thickness of approximately 700nm was achieved on particles with sizes of below 45μm.

Electrochemical Investigation of Stainless Steel Cladded Carbon Steel Manufactured Via Powder Bed Selective Laser Melting

This study aims to investigate the electrochemical and corrosion properties of 316L-stainless steel cladded carbon steel manufactured using powder bed the selective laser melting (PB-SLM) technique in various environments. The PB-SLM technique involves localized melting of a thin layer of 316L-SS powder bed with Yb - fiber laser. Main parameters of the PB-SLM process such as particle size, particle size distribution, laser power, laser-scanning speed and layer thickness were selected to optimize the density of the cladded layer and the quality of metallurgical bond to the substrate. Using the optimized process parameters, carbon steel substrates were cladded with stainless steel of various thicknesses. Several mechanical and microscopic tests (viz. nano-indentation, X-ray diffraction, Scanning electron microscopy) were performed to characterize both the bulk properties of the stainless steel layer and the interface between the cladding and the substrate. Electrochemical and corrosion properties were tested via. open-circuit potential monitoring, electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP) in electrolytes with acidic to alkaline pH range and with increasing levels of chloride, simulating different application conditions. Scanning vibrating electrode technique was employed to study the galvanic corrosion properties of the stainless steel and carbon steel at the clad-substrate interface.

Image analysis estimation of iron ore particle segregation in epoxy blocks

The phenomenon of particle segregation during epoxy block preparation for characterisation studies by optical or SEM microscopy, and its potential detrimental effect on the results of such characterisation, is well known. However, the absence of a proper study showing the possible scale of errors caused by it, and the existing belief that in certain circumstances the effect can be neglected, result in the continuing practice where important characterisation is performed using traditional horizontally sectioned epoxy blocks.This article presents the results of optical image analysis of the particle segregation effect during epoxy block preparation for different size fractions of iron ore fines using the CSIRO Mineral4/Recognition4 software. The differences in mineral abundances and liberation characteristics for different horizontal layers of vertical sections of epoxy blocks were analysed. Also the effects of particle layer thickness, epoxy block mixing techniques and the relative ratio of the iron ore sample to the epoxy during initial specimen preparation were investigated and discussed.The work performed shows that the difference between layers in the epoxy block due to density segregation can be unacceptably high for iron ore samples and, similarly, to any ore samples with significant density differences between particles of different texture. The traditional block preparation technique, with its random selection of the analysed horizontal layer, can therefore result in large errors in estimation of mineral abundances, mineral liberation and textural classification characteristics. It is suggested that vertical sections of epoxy blocks are used for image analysis where significant density difference between particles is suspected.

Groundborne vibration attenuation by particulate dampers to reduce building vibration at sonic frequencies

Particulate medium can act as efficient damper for building vibrations. Mechanical properties of particulate material and their size distributions determine their vibration absorption characteristics. Unconsolidated particulate damper of uniform size is shown to have bandpass filter behavior for mechanical vibrations that are transmitted through them. The dampers absorption spectrum also shows bandgap structure where mechanical vibration in each frequency range is strongly absorbed. We use samples of uniform size spherical particulates that are subjected to mechanical vibrations in the audible frequency range to determine their absorption characteristics as a function of particle size, frequency, intensity, and direction of propagation. The effects of particle sizes and layer thickness on vibration absorption are determined. The goal is to determine the required absorption characteristics as a function of particle size distribution, that is required to mitigate building vibrations.

Critical evaluation of the pulsed selective laser melting process when fabricating Ti64 parts using a range of particle size distributions

Selective Laser Melting (SLM) is a metal additive manufacturing process where parts are fabricated from metal powder based on CAD data. Selection of the best process parameters for the pulsed SLM processes is a fundamental problem due to the increased number of parameters that have a direct impact on the melt pool compared to the continuous SLM processes. In previous studies, volumetric energy density or scan speed have been used as control variables for applied energy. In this paper, the process parameters (laser power, exposure time, point distance and hatching distance) were considered individually, in addition to particle size distribution and layer thickness. The Taguchi experimental design method was used to determine and optimise the effect of the selected input parameters. The effect of exposure time and its correlation with layer thickness and particle size distribution was then investigated. The results show the best combination of process parameters which can provide fully or near fully dense parts. The results also show the minimum exposure time that can be used with different powder types and layer thicknesses. The paper concludes with a study which shows the part location has a significant impact on sample quality.

Critical rubber layer thickness of core-shell particles with a rigid core and a soft shell for toughening of epoxy resins without loss of elastic modulus and strength

Core-shell particles with a rigid silica core and a poly(butyl acrylate) (PBA) rubber shell are used to toughen epoxy resins without loss of elastic modulus and tensile strength. Both the diameter of silica core (D) and thickness of PBA shell (Ts) of silica-PBA core-shell particles are accurately controlled by sol-gel synthesis and seed emulsion polymerization process, respectively. From the results of notched Izod impact tests, a brittle-ductile transition of these epoxy/silica-PBA composites occurs when the rubber shell thickness (Ts) exceeds a critical value (Tsbd). It is found that Tsbd increases with increasing D which implies a critical rubber content (10 wt%) in the core-shell particles or a critical Ts/D ratio (0.0375), above which all composites transit from brittle to ductile failure. The composite elastic modulus decreases with increasing Ts. However, the critical thickness values of Tsm and Tss, below which composite modulus and tensile strength, respectively, are equal to or higher than the corresponding epoxy matrix values, are both larger than Tsbd. These results prove that brittle polymers can be toughened without loss of elastic modulus and tensile strength. However, the critical surface-to-surface inter-particle distance (Lc) is controlled by both properties of the core-shell particles and polymer matrix. When the rubber shell thickness Ts > Tsbd, Lc is increased when D is decreased. But when Ts < Tsbd, the brittle-to-ductile transition cannot occur, even when Lc is less than 100 nm.

Comparative study on the defects of kaolinite from America, Brazil and China applied for paper coating: XRD and refinement by Rietveld method

Three kaolinite samples applied for paper coating were collected from America (KA), Brazil (KB), and China (KC), respectively. Parameters such as average bond length of Si-O and Al-O (l(Si-O) and l(Al-O)), tetrahedral rotation angles (α), changes of tetrahedral flattening angles (τ) and octahedral flattening angles (ψ) comparative to ideal angle, particle layer thickness (T) and basal z corrugation (Δz) were analyzed by XRD and Rietveld method. The experimental results indicated that Δz KA > Δz KC > Δz KB. KB has a regular structure and KA has a disorder structure, αKA > αKC > αKB, ΔτKA > ΔτKC > ΔτKB, and ΔψKA> ΔψKB >ΔψKC. KA has unstable tetrahedron and octahedron. KB and KC have stable tetrahedron and octahedron, respectively. In the process of manufacture, kaolinite structure may be broken from places with unstable tetrahedron and octahedron. l(Si-O)KA > l(Si-O)KB > l(Si-O)KC and l(Al-O)KA > l(Al-O)KC > l(Al-O)KB. What only considered is the effect of bond length, KA may be most easily broken in the manufacture. Compared with bond lengths of KA and KB, Si-O, and Al-O of KB and KC may be easily broken, respectively. T KA < T KC < T KB. KB should be delaminated to finer particles, or it would hinder its dispersibility.

Radiative heat transfers of Carreau fluid flow over a stretching sheet with fluid particle suspension and temperature jump

Abstract The current study is to deliberate the flow and heat transfer of a Carreau fluid over a stretching sheet with fluid particle suspension. The temperature jump is also taken into account. The standard nonlinear system is resolved numerically via Runge-Kutta based shooting scheme. Role of substantial parameters on flow fields as well as on the fiction factor and heat transportation rates are determined and conferred in depth through graphs. It’s found that the velocity profile decreases and temperature profile increases, with an increasing the values of Weissenberg parameter. Further, the higher thermal slip parameter reduces the thermal boundary layer thickness. The thermal boundary layer thickness of fluid and dust particles decreases with the rise in Prandtl number.

Surfactant and graphite powder–assisted electrical discharge machining of titanium alloy

Surfactant and graphite powder–assisted electrical discharge machining was proposed and experiments were performed on titanium alloy in this investigation. Analysis was carried out to observe changes in dielectric fluid behaviour, material removal rate, surface roughness, recast layer thickness, surface topography and energy-dispersive X-ray spectroscopy. It was found out that the addition of surfactant to dielectric fluid (electrical discharge machining oil + graphite powder) improved the material removal rate and surface roughness. It was noticed to have reduced the recast layer thickness and agglomeration of graphite and sediment particles. Biface material migrations between the electrode and the workpiece surface were identified, and migration behaviour was powerfully inhibited by the mixing of surfactant. Surfactant added into dielectric fluid played an important role in the discharge gap, which increased the conductivity, and suspended debris particles in dielectric fluid reduced the abnormal discharge conditions of the machine and improved the overall machining efficiency.

Experimental Study on the Influence of DPF Micropore Structure and Particle Property on Its Filtration Process

A single layer filtration system was developed to investigate the filtration and regeneration performance of diesel particle filter (DPF). The particle layer thickness was directly measured online to analyze the different filtration stages. The influence of particle property on particle layer stage performance was also investigated. The results indicate that the filtration velocity can greatly affect the deep bed filtration stage, and the deposited particle layer can be compressed even in very low filtration velocity and higher filtration velocity trends to form denser particle layer. Optimizing the pore structure can effectively shorten the deep bed filtration stage and reduce the pressure drop eventually. An empirical function was proposed to relate the pore structure and the initial increment rate of pressure drop, which presented that reducing the pore size distribution range (3σ) can result in low DPF filtration pressure drop. The filtration stage could be further divided into four stages, and the value of particle layer thickness ranging within 15~20 μm has been found to be critical number for the shift from the transient stage to the cake filtration stage. Particle with large primary diameter and BET surface was beneficial to form loose particle layer.