This study focuses on metal/polymer nanocomposite thin films made by atmospheric pressure Plasma-Enhanced Chemical Vapor Deposition. The aerosol of isopropanol-dissolved tetrachloroauric acid (HAuCl 4 :3H 2 O gold salt) is injected in a dielectric barrier discharge to synthesize plasmonic nanocomposite thin films. Argon is used as carrier gas with or without 133 ppm addition of ammonia (NH 3 ) to respectively get or not a Penning mixture. Results show that NH 3 largely influences the salt reduction and thin film properties. According to the aerosol characterization, the size distribution at the plasma entrance supports that isopropanol mainly evaporates before injection in the plasma. The salt initially dissolved in each droplet precipitates during evaporation before injection as solid nanoparticles of about 30 nm diameter with eventual traces of solvent. Then, the nanocomposite thins film are studied. Optical properties, as plasmonic resonance, are characterized by UV–visible absorption spectroscopy. The chemical composition is analyzed using X-ray photoelectron spectroscopy and Raman spectroscopy, complemented by X-ray diffraction analysis as well as chemical mapping obtained by Energy dispersive spectroscopy coupled to scanning electron microscopy (SEM) operating in Scanning Transmission Electron Microscopy mode. Additionally, the morphology of the deposits is investigated by atomic force microscopy and SEM, highlighting the influence of NH 3 gas on the film nature and therefore its role in the overall deposition process. Finally, optical emission spectroscopy of the plasma gives clue to better understand the effect of NH 3 . The overall results show that the salt nanoparticles are reduced in the plasma phase leading to non-aggregated metal Au NPs embedded in a carbon-based matrix formed by isopropanol polymerization. The presence of NH 3 in the plasma unambiguously decreases the salt reduction and affects the thin film properties, consequently changing their plasmonic response related to the size, concentration, and composition of the embedded NPs.

This study designed and tested a 30 L/min PM0.1 non-bouncing impactor (PM0.1 NBI) for ultrafine particle (UFP) mass concentration measurement. The PM0.1 NBI uses a wetted glass fiber filter with continuous water injection to maintain a clean surface, preventing particle loading and bounce effects. Lab tests showed the 30 L/min PM0.1 NBI outperformed the PM0.1 stage of NCTU micro-orifice cascade impactor (NMCI, non-rotating) with a silicon oil-coated aluminum foil substrate in collecting solid particles, as the particle collection efficiency of the latter decreased obviously with increasing particle aerodynamic diameter for particles larger than ca. 300 nm, an apparent particle bounce phenomenon. The ambient field tests showed very close UFP mass concentrations between the PM0.1 NBI sampler (the PM0.1 NBI preceded by 3 stages with 18, 10, and 2.5 & mu;m cutoff sizes) and the reference rotating 10-stages NMCI with the difference of & PLUSMN;0.5 & mu;g/m3 only. In addition, the 3 L/min PM0.1 NBI was combined with a condensation particle counter to measure the UFP number concentrations which were shown to be very close to those of the reference with the difference of & PLUSMN;5% only in the laboratory tests for loaded particle mass up to 300 & mu;g. Good agreement was also found in the field tests. Therefore, the current 3 L/min PM0.1 NBI and the future PM NBI with smaller flow rates (0.2-2.1 L/min) and larger cut-sizes (such as 0.4-0.9 & mu;m) can be used as viable UFP classifiers for improving UFP measurement accuracy both in mass concentrations and number concentrations and reducing the maintenance needs for the UFP classifiers which are important to long-term sampling and monitoring.

We have investigated the potentialities of dielectric barrier discharges (DBD) for aerosol electro-processing with a special focus on ion production and aerosol charging for deposition (filtration and materials) and aerosol measurement tools. The advantages and drawbacks of aerosol injection downstream or upstream of the discharge are compared according to the application. The main parameters that control ion production and transport are investigated based on post-discharge ion current measurements. Post-DBD aerosol chargers are compared for submicron particle size measurements based on aerosol bipolar charging and electrical mobility analysis. Finally, the principle of counterflow extraction of bipolar ion from an atmospheric pressure DBD is established from upstream measurements of positive and negative ion fluxes in air, without neither ozone (<0.1 ppmv) nor nanoparticles.

Supercritical Carbon Dioxide treatment of clean and soiled Filtering Face-Piece respirators is shown to meet mandatory requirements for safe reuse of FFP2. Preliminary tests enabled us to select optimal conditions for Supercritical Carbon Dioxide treatment of FFP2, for one hour at 343 K under 7.5 MPa, with a biocide solution. FFP2s from Paul Boye ' (R) were then tested before and after Supercritical Carbon Dioxide treatment with a soiling solution and a biological indicator (i.e. spores of GeoBacillus stearothermophilus) with respect to three objectives: (i) washing of organic deposits, (ii) sterilization (i.e. spores inactivation) and (iii) preservation of the filtration performances. The proposed Supercritical Carbon Dioxide treatment fulfils these three criterions, with effective decontamination of spores and promising washing preserving FFP2 requirements for filtration efficiency of aerosol ( 94%) with acceptable pressure drop (< 240 Pa). As a simple and low-cost one-step recycling method, Supercritical Carbon Dioxide fits to economical and sustainable development standpoints but also allows one to come back to good practices of face protective equipment use, lowering eventual shortage and tensions for most countries importing these respirators.

This article focuses on the mean charge per particle of monodisperse submicron aerosols charged by the diffusion of unipolar ions in post-corona discharge. It aims to confirm and discuss the limits of considering a single value ofN(i)center dot tto describe aerosol charging and then to present methods to control the size-charge relation. Three aerosol chargers with different mixings of ion and aerosol flows are investigated. Despite comparable ion sources with discharge currents of a few tens of mu A, the size-charge relations differ from one charger to another due to different ion-aerosol mixing conditions and subsequent differences in ion density along the particles' trajectories. Discrepancies are even more noticeable as the particle size increases. Discharge current, velocities of ion and aerosol flows and the electric field control post-discharge ion density at each point of the charging zone. The control of particle trajectory in expanding unipolar ion clouds leads to tuneable size-charge relations. Aerosol inertia and charging dynamics both depend on particle size, affect theN(i)center dot texperienced by the particle and thus the final charge of the particle. Operating conditions to reach a constant mean charge for particles larger than 200 nm are reported. Conclusions provide a basis to design aerosol chargers devoted to electric mobility selection for aerosol deposition, separation or electrical measurements, especially to overcome the limits of mobility-to-size data inversion due to the multiple charge ambiguity inherent to diffusion chargers. Copyright (c) 2020 American Association for Aerosol Research

Abstract The influence of aerosol concentration on the charge per particle is investigated in post-DC corona diffusion chargers for particle diameter between 10 nm and 1 µm. Particles are charged as they pass through the charger volume by collection of ions; the ion concentration decreases along the same path due to unipolar space charge repulsion and collection on walls. With crossflow of ions and aerosols, the final mean charge per particle decreases by up to one order of magnitude with increasing aerosol concentration from 109 to 1011 m−3. The evolution of the ion density profile along particle trajectories with aerosol concentration is shown to be due to the consumption of ions by aerosol charging and to ion dispersion by unipolar space charge repulsion including ions and charged particles. Both are investigated using a simplified 1.5 D model with axial symmetry and homogeneous mixing of ions and aerosols. It is shown that, for a given operating condition, the aerosol space charge is responsible for the modification of the spatial ion distribution and the related lower Ni × τ and charge per particle reported at higher aerosol concentration. From calculations, we define the maximal aerosol concentration to keep the mean charge per particle unaffected by aerosol space charge in the optimal case of homogeneous mixing of ion and aerosol. Finally, the comparison of different ion-aerosol mixing conditions highlights that an axial symmetry of the charger reduces the influence of aerosol space charge. This effect of aerosol concentration on the particle charge is critical for aerosol chargers devoted to electric mobility selection for size measurements or focused electro-deposition, as well as for concentration measurements as performed using emerging low cost sensors based on corona chargers. Copyright © 2021 American Association for Aerosol Research

Electrospray of Water and aqueous solutions is a simple, steady and continuous process for the production of charged droplets. Applications of this low cost spraying process, easy to scale up and environment friendly with low water consumption are first presented. This review addresses the Electro-Spray (ES) in the cone-jet mode, with focus on water ES with or without discharges in ambient air. The physical constraints to achieve steady water electrospray in ambient air are depicted to account for Electro-Hydro-Dynamic equilibrium required for the cone and jet formation on the one hand and to control electrical discharges in the gas around the liquid (with continuous corona or without any discharge) on the other hand. Operating conditions and empirical scaling laws between regulation parameters (liquid flow rate and corona current) and the properties of droplets such as the size and the charge are presented for the corona-assisted cone-jet mode of water electrospray in air. Subsequent working conditions to achieve the other steady water ES, without discharge, are then justified. The interest of this corona assisted cone-jet mode of electrospray in air for the steady production of self-dispersed unipolar water droplets (close to the Rayleigh limit) with unimodal size distribution is presented with one environmental application for filtration by bipolar-scrubbing of suspended particles from exhaust or ambient aerosols, with lab-scale efficiencies of High Efficiency Particulate Air filters.

A postplasma neutralizer for submicron particles size measurements by mobility analysis has been evaluated. Bipolar ion currents have been measured downstream a dielectric barrier discharge (DBD) to estimate the ion fluxes at the inlet of charging volume and the n(i).tau product that define the theoretical maximal concentration that can be neutralized. Charge distributions were measured versus DBD voltage, aerosol diameter and concentration for monodisperse aerosols. It is confirmed that the charge distribution of particles depends on the ratio of initial positive and negative ion currents controlled by the DBD voltage leading to a tuneable mean charge of aerosol in this post-DBD bipolar charger. As expected from Gunn's law, the mean charge and the variance are proportional to particle diameter above 50 nm and independent of the aerosol concentration. The size distributions measured with Kr-85 and post-DBD neutralizer present the same modal diameters and a maximal overestimation of the total concentration of 10%, for aerosol from 15 to 730 nm with concentrations up to 6 x 10(12) m(-3). This post-DBD bipolar charger can be used for submicron aerosol neutralization and thus for scanning mobility particle sizer size distribution measurements in air as well as in nitrogen to suppress ozone downstream DBD.

The presentation first depicts the objectives and the outlines of this special session on plasma-based aerosol processes. Recent developments of atmospheric pressure plasmas for the production of nanoparticles and coated nanoparticles by nucleation, either from cooling of expanding vapour plumes produced by plasma-surface interaction, like in spark generators (Deppert, 2012) or from injection of gaseous precursors in or downstream the plasma for reactive nucleation and subsequent coating of particles or substrates (see fig. 1). Besides, the transport of so-formed nanoparticles for deposition on surfaces as well as integration into nanocomposite thin films will also be addressed (Massines, 2012).

This paper deals with the electric and hydrodynamic confinement of negative ions in a point-to-plane corona discharge gap. Radial ion current density profiles have been measured on the earthed planar electrode, drilled in the axis of the point. The experimental setup is first validated by comparison with the Warburg's law without injected gas flow rate. The gas injected in the gap and blown from the discharge gap through the hole located at the centre of the plane affects neither the electric field close to the point nor the subsequent electric wind. However, it leads to the confinement of ions flux towards the central symmetry axis in the low electric field region up to a critical gas velocity, which for no more effect is measurable. Hence, electro hydro-dynamics confinement of ions can be achieved by limiting the outward radial expansion of ions to increase ion current densities on specific locations close to the low field planar electrode.

Nanoparticles are employed in a wide variety of applications including catalysis and functional coatings. However, the inherent instability of small metal nanoparticles at elevated temperatures limits their range of application or their processing, e.g. in the calcination of particle layers to the substrate to obtain robust coatings. While the thermal stability may be improved by a silica coating of the nanoparticles, a hampering of the accessibility of the active particle surface, e.g. for heterogeneous catalysis, has to be avoided at the same time. So far these two opposing requirements have been addressed by permeable silica coatings as a consequence of cracking under heat treatment [1] or the use of pore builders [2]. However, not all materials can withstand higher treatment temperatures and the liquid route for porous silica coatings is rather tedious and time consuming [2]. The aim of this contribution is to present a simple method to apply a defined silica coating on arbitrary core nanoparticles by mixing the aerosol particles with TEOS vapour and reactive species from a DBD plasma. Due to the reaction of the TEOS vapour with the ozone (and probably some nitric oxides) formed in the DBD plasma an intermediate species is formed which condenses on the nanoparticles. This liquid coating may reach a thickness of several 10 nm, quite independent of the core particle size (cf. Fig.1).

The plasma-based aerosol process developed for the direct coating of particles in gases with silicon oxide in a continuous chemical vapor deposition (CVD) process is presented. It is shown that non-thermal plasma filaments induced in a dielectric barrier discharge (DBD) at atmospheric pressure trigger post-DBD gas phase reactions. DBD operating conditions are first scanned to produce ozone and dinitrogen pentoxide. In the selected conditions, these plasma species react with gaseous tetraethyl orthosilicate (TEOS) precursor downstream of the DBD. The gaseous intermediates then condense on the surface of nanoparticles and self-reactions lead to homogeneous solid SiOx coatings, with thickness from nanometer to micrometer. This confirms the interest of post-DBD injection of the organo-silicon precursor to achieve stable production of actives species with subsequent controlled thickness of SiOx coatings. SiOx coatings of spherical and agglomerated metal and metal oxide nanoparticles (Pt, CuO, TiO2) are achieved. In the selected DBD operating conditions, the thickness of homogeneous nanometer sized coatings of spherical nanoparticles depends on the reaction duration and on the precursor concentration. For agglomerates, operating conditions can be tuned to cover preferentially the interparticle contact zones between primary particles, shifting the sintering of platinum agglomerates to much higher temperatures than the usual sintering temperature. Potential applications for enhanced thermal stability and tunable photoactivity of coated agglomerates are presented.

Certain types of aerosol measurements require an experimental set up including two or more routes through which the particles are made to flow alternatively. Indeed, this appears to be critical to limit uncertainties in aerosol properties determined from comparative measurements. Typical examples are the comparison of the performance of different instruments and the measurement of particle filtration efficiency. Except for the presence of the test units (e.g. the instruments or devices to be compared) it is commonly accepted that the two routes must be identical: they should contain the same type and number of tubes, valves, junctions, bends, connectors, etc. For nanometer-sized particles undergoing substantial diffusion losses, the lack of perfect symmetry between the two routes induces discrepancies in measurements performed in both lines. This article provides a general methodology to avoid or reduce the errors arising from these possible asymmetries. The method consists in making two measurements, one with the given setup, the other with an alternative set up in which the test units have been exchanged. The correct result (e.g. filtration efficiency) is the geometric mean of the results obtained with the two alternative setups. The proposed methodology may seem tedious and time consuming, but doing so, the experimental measurement is not affected neither by possible errors due to a test aerosol changing with time nor by the possible asymmetry of the line accessories (valves, T׳s, connections, etc.).

A compact, inexpensive and simple dielectric barrier discharge (DBD) design is presented with related electro-thermal properties for the production of metal nanoparticles.Nanoparticle formation and growth mechanisms are depicted from size distributions and chemical analyses of particles collected just after the 70 kHz DBD in nitrogen. At first, it is confirmed that the initial local vapor flux is produced from the spots of interaction between plasma filaments and different metal electrodes (Au, Ag, and Cu). Amorphous and crystalline pure metal primary nanoparticles with diameters below 5 nm are then produced by physical nucleation in expanding vapors jets. Finally, some small agglomerates with diameters still below 5 nm are also formed by ballistic agglomeration of a fraction of these primary particles. This happens at the end of the vapor jet expansion, as well as after the production during the transit between subsequent filaments in the DBD. The first local agglomeration step can be limited at reduced energy per filament by lowering the initial vapor flux in smaller gaps, while the second growth step depends on the transit time in the DBD. Hence, such "low" energy plasma filaments (up to a few tens of mu J) lower the initial vapor flux to control the agglomeration. DBD were thus successfully tested for the production of tailored nanoparticles with tunable size, controlled morphology of spherical agglomerates and the same composition as the metal electrode.The production per unit energy (mol J(-1)) is related to both plasma and material properties. Besides, neglecting vapor and nanoparticles losses, the mass production rate (g s(-1)) depends on the input power related to the product of the energy controlling the production per filament times the number of filaments per second, for any given material.This non-thermal plasma process presents great potentialities for nano-technologies since it is performed at atmospheric pressure and can be used to reach size-dependent properties of nano-materials, without any gaseous precursor or solvent. (C) 2014 Elsevier Ltd. All rights reserved.

To develop a “real time” aerosol sizer, a postcorona charger is studied. Aerosol charging depends mainly on N i.τ product (Ni is the ion density and τ is the charging time) and on the aerosol diameter. The time devoted to charging is shorter than 0.1 s. To compensate this short time, mean ion densities of about 10 8 cm are required. At first, geometrical and electrical parameters of the corona discharge are chosen to achieve a stable ion production and quasi-stationary ion density profiles in the charger. Then, the ion extraction to reach such post-discharge ion density is optimized. Since the mixing of ions with aerosol is critical for post-discharge ion distribution and so for N i.τ product “seen” by the aerosol, two mixing arrangements are compared. Indeed, it is confirmed that the final number of elementary charge collected by the aerosol depends on the mixing.

This study aims to develop a post-Dielectric Barrier Discharge (DBD) neutralizer for aerosol (solid or liquid particles suspended in a gas). Indeed, DBD in air, at atmospheric pressure are known to produce bipolar ions required to this application. This work focuses on ion production, extraction and losses from DBD based on measured post-discharge ions currents. It is shown that post-DBD ion currents depend on discharge electrical properties defining ion production as well as losses in the discharge and in post-discharge related to an electro-hydrodynamic competition. In a plane-to-plane DBD arrangement with wire electrodes, all the filaments have the same charge and energy within 30%. Due to losses, the post-DBD ion currents of both polarities are not proportional to the charge production, related to the time integrated charge per filament. At last, post-DBD ions densities reach the same order of magnitude than those in radioactive neutralizers proving the potentialities of post-DBD aerosol neutralization.

MonteCarlo simulations of diffusive particle trajectories, as well as Stolzenburg's model calculations, have shown that the mean mobility of the particles classified by a differential mobility analyzer (DMA) at a given applied voltage may differ from the theoretical one inferred from the Knutson-Whitby equation if the particles are withdrawn from the tails of the particle mobility distribution. In this case, the true mean mobility, defined as the mean mobility of the particles classified at the specified voltage, can be precisely measured by a second DMA operating in series with the first one (tandem DMA). However, if particles are extracted from the central part of the distribution, their mobility can be correctly measured with a single DMA. Besides showing the importance of the usage of the tandem DMA technique for accurate measurements of mobility, this article provides an analytical expression which, if the mobility distribution of the polydisperse aerosol fed to the DMA is known, allows an accurate estimation of the true (mean) mobility of the classified particles.