Ejection Of Liquid Droplets Research Articles

Mixing gold and iron in nanoparticles by electrical discharges in liquid: A new approach

The possibility to create homogeneous nanoparticles containing iron and gold by nanosecond-pulsed discharges in liquids, without any laser assistance, is demonstrated. Thanks to a new kind of electrode where elements are coated by PVD on a silicon plate, AuFe nanoparticles, ranging from 10 to 50 nm, are synthesized. Depending on their residence time in the discharge, the structure of the homogeneous nanoparticles evolves to become a core–shell structure, either nested or not. Larger submicrometric particles (from 100 to 500 nm) are specifically formed with the present process by the ejection of liquid droplets from the molten pool created by the discharge on electrode surfaces. These larger particles are produced by solidification of a AuFe shell on a silicon core. This new mechanism can be used to create core–shell particles with a shell containing several, possibly immiscible, elements. Thermal post-treatment performed in situ in a TEM microscope shows the AuFe shell, where Au and Fe separate, turning either into a Janus structure or into a SiFe core facetted by gold pyramids.

Investigation of nanoscale and microscale structured cooling surfaces of thermal power plants

Studies were conducted of the heat exchange crisis depending on the coolant excess (which determined the underheating and flow rate), the thermal-physical properties of the heating surface, and the ejection of liquid droplets from the porous structure. A model of dynamics of vapor bubbles born on the solid surface in porous structures and the vapor-generating wall (substrate) has been developed. The model is based on cinematography with an SKS-1M speed camera. The removal of high heat flows (up to 2·106 W/m2) is provided through the joint action of capillary and mass forces with the use of intensifiers. Equations are obtained of critical heat flows through the thermohydraulic characteristics of the boiling process in woven porous structures. The research is of practical importance in the limiting state region of the steam-generating surface protected by cooling from overburning. Three mineral media (tuff, granite, marble) of Zaili and Dzungarian Alatau mountains near the city of Almaty (Kazakhstan) were considered. The method of holographic interferometry was used to study porous thermodynamic screens. The stress and deformed state of the samples was studied. Simulation of the acoustic field of the blast wave with th e thermodynamic field created by three thermal sources has shown its high efficiency. The created powerful thermal screen, due to the generation of strain and thermal stress fields, is an obstacle to the propagation of the reflected blast wave, causing the emergence and development of destructive cracks. Nanoscale and microscale structured surfaces in the form of coatings and mesh structures have been developed, which give an integrated effect of industrial meshes with natural mineral media coatings and have synergistic advantages of combining these two developments in an integrated technology of their production, expansion of critical thermal loads and management of the limiting state of porous coatings.

Characterization of Vibrating Mesh Aerosol Generators

ABSTRACT The fate of inhaled aerosol particles within the respiratory tract is determined by factors such as the particle size distribution, breathing pattern, and airway geometry. Thus, matching the aerosol therapy device to the patient is crucial to achieving a high target site dose and minimizing side effects. High output efficiency and minimal residual volume have been reported for vibrating mesh nebulizers, which generate a high percentage of particles in the respirable fraction. Using custom-made plates, this work aimed to investigate and identify the major operating parameters of these devices and their effects on the characteristics of the aerosol output. Each plate contained between 279 and 4606 tapered apertures that ranged from 3 to 12 µm in diameter and were uniformly sized per plate. To investigate the effect of coagulation during droplet generation, the distance between the apertures was varied from 75 to 450 µm. The resonance frequency of the piezoelectric element was scanned, and the aperture plates were then vibrated at a fixed frequency (100–300 kHz), causing the ejection of liquid droplets. The nebulizers were mainly evaluated using a 0.9% sodium chloride solution. A syringe pump injected the solution into the vibrating mesh plates. The aerosol output was carried, dried, and introduced into the mixing chamber by a dilution air flow of 160 L min–1. An aerosol size spectrometer was employed to measure both the number concentration and the size distribution of the output. The droplet size increased with the aperture diameter. The distance between apertures did not affect the number concentration or the size distribution of the generated droplets. The droplet size decreased as the resonance frequency increased, but the extent was less than we expected. Each mesh possessed an optimal vibration frequency, which varied according to the size and the number of the apertures, for consistently maximizing the aerosol output. The optimal feeding rate increased with the number of apertures and the applied electric current, but the aerosol size distribution remained the same. Additionally, our results using a cotton wick to deliver the solution from the reservoir to the vibrating mesh indicate that fibrous sorbent materials can potentially replace the syringe pump.

Automatic contactless injection, transportation, merging, and ejection of droplets with a multifocal point acoustic levitator.

We present an acoustic levitation system that automatically injects, transports, merges and ejects liquid droplets in mid-air. The system consists of a phased array operating at 40 kHz on top of a plane reflector. The phase array generates multiple focal points at independent positions that form standing waves between the array and the reflector. In the reflector there is an inlet for a piezoelectric droplet injector which automatically inserts liquid droplets at the lower pressure nodes of the standing waves, and a hole that serves as an outlet for ejecting the processed droplets out of the system. Simulations of the acoustic radiation potential acting on the levitating droplets are in good agreement with the experiments. High-speed footage captured the functioning of the system in four fluidic operations: injection, transport, merging and ejection of liquid droplets. Having these operations integrated reliably into a single automatic system paves the way for the adoption of mid-air acoustophoretic processing in biological, chemical and pharmaceutical applications.

Characterization and Sulfuric Acid Leaching of Ferrochrome Converter (CRC) Dust

A ferrochrome converter (CRC) is used for removal of silicon and carbon from ferrochrome in stainless steel production. The raw materials are molten ferrochrome and stainless steel scrap, and the process produces a raw material for argon-oxygen-decarburization (AOD). The zinc content prevents the utilization of CRC dust (CRCD). The objective of this work is characterization and sulfuric acid leaching of CRCD and evaluation of formation mechanisms and the effects of mineralogy and microstructure on the hydrometallurgical treatment. CRCD contains critical (Cr, fluorite) and economically important (Fe, Zn) materials. The mineralogy and microstructure of CRCD are complex. The dust has been formed by many mechanisms. Lime and ferrosilicon prove that take-off of solid particles during charging is important. Also, ejection of liquid droplets is considerable because ferrochrome and slag spheres are common. The highest Zn dissolution is 93–94% and at the same time 5–15% of Cr is leached. The existence of zincite explains the high dissolution of zinc. The encapsulation, e.g., magnesiochromite enclosed into glass, explains the low chromium dissolution. The best selectivity for Zn extraction over iron, chromium, and nickel is achieved with 0.5 M, at 30 and 60 °C with both L:S 10 and L:S 20.

Materials Erosion and Eroded Material Deposition Under Intense Plasma Action

The paper concerns experimental investigations of metallic material erosion under the plasma heat loads expected in ITER divertor during transient events such as the type I edge-localized modes and the disruptions. Primary attention is focused on the erosion due to melt layer movement and splashing. The targets of tungsten and other metals were repeatedly exposed to hydrogen plasma flow of 0.5 ms duration in the heat load range of 0.2-4.5 MJ/m2 at the TRINITI plasma gun QSPA-T. The ejection of liquid droplets was observed during plasma exposure by special recoded system and onset conditions of droplets ejection were defined. Between some of the plasma pulses the eroded surface was analyzed with profilometry and microscopy. The mass loss and exposed surface profile were measured as a function of heat load and number of pulses. Experimentally measured target thinning due to melt layer removal from the exposed area to periphery was compared with erosion due to mass loss as a result of droplets ejection and evaporation. The obtained surface profile was compared with the result of numerical calculations which based on simultaneous solving of the 2-D heat conductivity equation and hydrodynamics equations of “shallow water” approximation.

Metals and metal oxides particles produced by pulsed laser ablation under high vacuum

A pulsed KrF Excimer laser (248 nm, 15 mJ) was utilized to synthesize different particles on (111) Si substrate under vacuum \sim 10^{-6} torr using Aluminum (Al), Platinum (Pt), Tungsten (W), Molybdenum (Mo), Cadmium Oxide (CdO), and Yttrium Oxide (Y_2O_3) targets. Scanning electron microscope (SEM) was used to study particle size distribution on silicon substrate. The size of individual metal particles was found to be ranging from 71 nm to 2 \mu m whereas metal oxides particles were found in the range of 71 nm to 1.1 \mu m. The particles below 100 nm are formed by gas phase condensation of ions, atoms and molecules whereas particles greater than 100 nm size results either from the ejection of liquid droplets from the melt surface or stresses induced by laser on target surface. The advantage of particle formation due to laser ablation in high vacuum is pure particles production.

The influence of the laser ablation process on isotopic fractionation of copper in LA-MC-ICP-MS

Isotopic fractionation during in-situ analysis of copper using laser ablation (LA) MC-ICP-MS has been investigated. Results show that particles <200 nm transported in the aerosol are isotopically lighter by up to 0.7‰ compared to the larger particles. The dependence of this isotopic fractionation on the ablation time, together with isotopic effects caused in the ICP during particle vaporisation, explains the variations of isotope ratios observed during LA-MC-ICP-MS. LA-MC-ICP-MS measurements of copper isotope ratios in metallic copper typically show large systematic within-run variations of up to several permil (‰) depending on the ablation time and, correspondingly, large offsets from solution data for the same sample when compared directly. Analysis of small particles generated by vapour condensation after the laser impact, and larger particles formed by ejection of liquid droplets from the crater, show that the laser impact results in isotopic fractionation of 65Cu+/63Cu+ between different aerosol particle size fractions of up to 0.7‰. This fractionation cannot be overcome by removal of large particles from the aerosol that are not completely vaporised and ionised in the ICP source. However, separation of the large particles is shown to significantly reduce within-run fractionation, as well as improving the accuracy relative to solution data, and is therefore recommended for the analysis of copper metal. Temporal variations in the isotopic composition of particulate vapour condensate are explained by a crater effect that influences the residence time of large particles in the laser-generated plasma plume, leading to preferential vaporisation of the lighter isotopes.

The agglomeration state of nanosecond laser-generated aerosol particles entering the ICP

Fundamental understanding of aerosol formation and particle transport are important aspects of understanding and improving laser-ablation ICP-MS. To obtain more information about particles entering the ICP, laser aerosols generated under different ablation conditions were collected on membrane filters. The particles and agglomerates were then visualised using scanning electron microscope (SEM) imaging. To determine variations between different sample matrices, opaque (USGS BCR-2G) and transparent (NIST SRM 610) glass, CaF(2), and brass (MBH B26) samples were ablated using two different laser wavelengths, 193 and 266 nm. This study showed that the condensed nano-particles ( approximately 10 nm in diameter) formed by laser ablation reach the ICP as micron-sized agglomerates; this is apparent from filters which contain only a few well-separated particles and particle agglomerates. Ablation experiments on different metals and non-metals show that the structure of the agglomerates is matrix-dependent. Laser aerosols generated from silicates and metals form linear agglomerates whereas particle-agglomerates of ablated CaF(2) have cotton-like structures. Amongst other conditions, this study shows that the absorption characteristics of the sample and the laser wavelength determine the production of micron-sized spherical particles formed by liquid droplet ejection.

An experimental investigation of factors affecting arc-cathode erosion

A specially designed thermal plasma reactor system for the investigation of arc-cathode erosion has been set up. By using an OMA-spectrometer system, emission spectroscopic measurements of electron temperature and electron number density in the cathode region have been performed, together with single-colour and two-colour pyrometry of cathode temperature distributions. Observation of cathode spot behaviour has been carried out simultaneously by employing a telemicroscope and a high-speed vision system. Cathodes have been examined by SEM and EDX after arcing. For pure tungsten cathodes, the initial cathode geometry has almost no effect on the cathode spot's behaviour due to the molten state of the cathode spot. The major erosion mechanism is the ejection of liquid droplets from the cathode spot. However, the initial cathode geometry has a certain influence on the cathode's erosion for 2% thoriated tungsten cathodes. A highly non-uniform erosion pattern will occur if the cathode is overcooled, probably due to ion bombardment in the low-temperature regions of the arc-attachment spot.