EP3328548B1 - Selective aerosol particle collecting method and device, according to particle size - Google Patents

Description

Technical area

The present invention relates to the field of collection and analysis of particles which may be present in suspension in an aerosol.

It relates more particularly to the production of an electrostatic device for collecting particles by electrostatic precipitation, including nanoparticles contained in aerosols.

The present invention aims to allow a collection of particles in suspension in aerosols which is simultaneous but selective according to their dimensions, the selectivity preferably aiming to collect, by separating them, particles of micron and submicron dimension, ie greater than or equal at 300 nm, and nanometric particles.

By “nanoparticle” is meant the usual definition according to ISO TS / 27687: a nano-object whose three dimensions are on the nanometric scale, that is to say a particle whose nominal diameter is less than 100 nm approximately.

State of the art

Since the 1970s, awareness of the environmental and health effects generated by aerosols has been at the origin of new technological developments in order to better assess the associated risks.

The field quickly expanded in the 1980s to include the use of aerosols in high-tech production processes, and the control of aerosol contamination in ultra-clean atmospheres.

From the 1990s, research intensified on the properties of ultrafine particles, i.e. those smaller than 100 nm, and on the effect of aerosols on the climate. The field is therefore very broad since it covers both the field of industrial hygiene, air pollution control, toxicology by inhalation, physics and chemistry of the atmosphere, and contamination by radioactive aerosols in facilities or in the environment.

More recently, the rapid development of nanotechnologies in various fields such as health, microelectronics, energy technologies or everyday consumption such as paints and cosmetics, makes it essential to continue work on the health and environmental impacts of these new materials in order to surround themselves with optimal safety conditions.

It is therefore necessary to develop methods and tools for assessing exposure to particles - and in particular to nanoparticles - of workers, consumers and the environment.

The development of methods and devices for sampling and analysis of aerosols in a wide granulometric range up to nanometric sizes is thus a crucial issue in terms of public health and prevention of associated risks.

In particular, the development of sampling devices adapted to be portable and to be attached to the unit to a work suit of a worker in the position of manufacturing nano-objects, developing or using nanomaterials could prove imperative.

Numerous devices exist for sampling and collecting particles in suspension in aerosols, for their analysis in situ or in the laboratory. They can implement a collection by filtration on fibers or on porous membranes, a collection by diffusion for the finest particles, a collection under the effect of a field of inertia forces (impactors, cyclones, centrifuges) or gravity (sedimentation chambers, elutriators) for larger particles, or a collection under the effect of a field of electric, thermal or radiative forces.

Among these devices, electrostatic ones, that is to say the operating principle of which is based on the use of an electric field, in particular an intense electric field to create a corona discharge effect (in English " corona discharge ”) are commonly used.

When an intense electric field is generated in a volume where aerosol particles are present, the latter can be electrically charged according to two separate charging mechanisms and this can occur concomitantly.

The publication [1], in particular Figure 15. 4 from page 330 of this book, shows that the mechanism of electric charge by diffusion of unipolar ions, associated with the mechanism of electric charge by field, is applicable to a large range of particle sizes, at least for particles of dimensions included between 0.01 to 10 µm. It also appears that the mechanism of electric charge by diffusion of unipolar ions is especially preponderant for the finest particles, typically nanoparticles, that is to say those of dimensions less than 100 nm. Conversely, the field charge mechanism is more efficient for large particles, that is to say particles of micron and submicron dimensions (≥ 300 nm).

For example, if we consider the electrical mobility of a particle, denoted Z, of the order of 1 cm ² /st.Vs in electrostatic unit CGS, i.e. 3.3 × 10 ^-7 m ² / Vs in SI unit, then this particle placed between two flat and parallel plates which generate an electric field E of 10 ⁵ V / m, acquires a speed W equal to the product Z ^∗ E, that is W of the order of 0.033 m / s . It is clearly demonstrated that the electrostatic force generates speeds much higher than the other fields of forces undergone by a particle, which are the fields of gravity, inertial, thermal and radiative. This advantage is exploited in the operation of commercial electrostatic purifiers, where the processes of charge by diffusion and charge by field can act jointly.

Electrically charging aerosol particles requires the presence of unipolar ions in high concentration. By far the most effective method of creating these ions in atmospheric air is corona discharge.

To produce a corona discharge, an electrostatic field must be established in a geometry which makes it non-uniform. More precisely, this high electric field (several thousand to tens of thousands of volts per centimeter in the vicinity of the discharge electrode) is induced by two electrodes arranged close to one another: a first polarized electrode or electrode of discharge, generally in the form of a wire or a point, being arranged opposite a second electrode, the latter being in the form of a counter-electrode, generally of planar or cylindrical geometry. The electric field existing between the two electrodes ionizes the volume of gas located in the inter-electrode space, and in particular a sheath or crown of ionized gas located around the discharge electrode. The charges created, by migrating to the counter-electrode, charge the particles to be separated contained in the gas. The charged particles thus created then migrate to the counter-electrode, on which they can be collected. This counter electrode is usually called the collecting electrode. Due to the level of the electric field required, it is necessary to use a discharge electrode which has a (very) small radius of curvature. The discharge electrodes encountered are therefore generally either fine points or wires of small diameter. So by a process which originates from the electrons and ions created by natural irradiation, the electrons are accelerated in the intense electric field created in the vicinity of the electrode with (very) small radius of curvature. By the high voltage imposed, if this field exceeds a critical value, an avalanche effect causes the ionization of the air in this space. This phenomenon is called crown discharge.

For example, we have shown in Figures 1A to 1E some of the most suitable electrode configurations for obtaining a crown discharge, namely respectively a tip-plane arrangement ( figure 1A ), blade-plane ( figure 1B ), background ( figure 1C ), wire-wire ( figure 1D ), wire cylinder ( figure 1E ).

For example in tip-plane configuration, if the tip is positive with respect to the plane, the electrons move quickly towards the tip while the positive ions move towards the plane, then creating a positive unipolar space. In addition, an ion wind, also called ionic wind, is established, characterized by a flow of air directed from the point towards the plane, originating from the shocks of positive ions with the surrounding neutral molecules.

Conversely, if the tip is negative with respect to the plane, the positive ions move towards the point, and the electrons move towards the plane by attaching themselves to the air molecules to form negative ions. In all cases, even if the process of creating positive or negative ions is not exactly symmetrical, the unipolar ions migrate from the tip to the plane with a large concentration of the order of 10 ⁶ to 10 ⁹ / cm ³ and, whatever the polarity, there appears an electric wind directed from the point towards the plane.

Thus, the introduction of aerosol particles into the tip-plane space makes it possible to charge them with the same polarity as the tip, according to a charging process per field. In addition, the field used to create the crown effect and the electric wind also participate in the field charge process.

For the other configurations shown in Figures 1B to 1E , the ion production and charge processes per particle field are similar in all respects.

It is on this principle that certain commercial electrostatic precipitators work which are used to collect and collect particles on a support allowing analysis.

For example, Figure 15. 9 from page 341 of the publication [1] already cited shows an arrangement allowing the deposition of aerosol particles on a grid of electron microscope, the particles being charged and precipitated in a tip-plane configuration.

Another example is illustrated in figure 10.10 from page 223 of this same publication [1] and implements the charge and precipitation technique in tip-plane geometry to collect aerosol particles on a piezoelectric crystal.

As already mentioned, the charge mechanism by diffusion of unipolar ions applies predominantly on the finest particles. This mechanism is increasingly used in the metrology of nanoparticles, in particular to determine their particle size. Indeed, many authors have studied and are still studying devices capable of conferring high electrical mobilities on the finest particles, in order to be able to select them in instruments adapted to this new field. We can cite here in particular the article [2] which lists most of the technologies developed to date, or the principle developed by the author of the publication [3], which uses a fil- cylinder, much studied more recently as indicated in publication [4], but also before (publication [5]).

We reproduced schematically in figure 2 , a charging device, also called a charger, with diffusion of unipolar ions whose geometry is of the wire-cylinder type, as illustrated in the publication [4]. The charger 10 comprises a body with symmetry of revolution 1 in two parts which hold a hollow metal cylinder 11 forming an external electrode connected to an AC power supply and a central metal wire 12 arranged along the axis of the body and connected to a power supply high voltage not shown. Around the central wire 12 is also annularly arranged a cylindrical grid 14 forming an interior electrode. The aerosol containing the particles to be charged circulates in the charger 10 from the inlet orifice 17 to the outlet orifice 18 passing through the space 15 delimited between the internal electrode 14 formed by the grid and the 'outer electrode 11 formed by the cylinder.

The operation of this charger 10 is as follows: ions are produced by the crown effect at the level of the central wire 12 and are collected by the meshed internal electrode 14 brought to a low potential, typically to ground. A part of these ions leaves this grid 14 to go towards the internal surface of the peripheral cylinder 11 due to the tension applied to the latter. The aerosol particles pass through the space 15 between grid 14 and cylinder 11 and are therefore charged by diffusion by unipolar ions leaving the grid 14. The diffusion charge mechanism operates as a function of the product N ^∗ t, where N represents the concentration of unipolar ions and t the residence time of the particles. The diffusion charge mechanism is the only one that can occur because there can be no charge mechanism per field since the electric field is very weak in space 15.

It is interesting to note that the process of charging aerosols by diffusion of unipolar ions makes it possible to confer a given number of electrical charges on a particle of given size.

This principle is also implemented in differential electric mobility analyzers (DMA) which are instruments capable of providing the particle size distribution of fine particles by counting the concentration of particles in a given class of electric mobility. Such a device is for example implemented in the patent US 8044350 B2 .

The patent application DE19650585 discloses a charger having both the characteristics of a field effect charger and a unipolar ion diffusion charger. This type of charger takes part in the charge of any type of particles whatever their size.

It appears from the study of the state of the art that no device has been proposed which simultaneously collects particles present in an aerosol and which are of different dimensions over a wide range, typically between a few nanometers and a few tens of micrometers, and to separate them according to ranges of restricted dimensions, preferably to separate the nanoparticles from the particles of micron size.

However, there is a need for such a device, in particular in order to allow the subsequent analysis of the particles collected and separated in order to know their concentration and their chemical composition sequentially as a function of their restricted range of dimensions.

The general aim of the invention is then to meet this need at least in part.

Statement of the invention :

• aspiration de l'aérosol dans un conduit depuis son orifice d'entrée jusqu'à son orifice de sortie;
• charge des particules les plus fines, en aval de l'orifice d'entrée, par diffusion d'ions unipolaires dans un espace entre une électrode sous la forme d'une grille entourant une électrode sous la forme d'un fil générant un effet couronne, et une première portion conductrice de paroi intérieure du conduit,
• génération d'un champ électrique sans effet couronne dans l'espace entre une électrode et une deuxième portion conductrice de paroi intérieure du conduit, afin de collecter par dépôt sur une première zone de collecte (Zn) des particules les plus fines chargées par le chargeur à diffusion,
• génération d'un champ électrique avec effet couronne dans l'espace entre le fil ou la pointe d'une électrode et une troisième portion conductrice de la paroi intérieure du conduit, afin de collecter par dépôt sur une deuxième zone de collecte (Zm) distincte de la première zone de collecte, les particules les plus grosses, non chargées par le chargeur à diffusion.

To do this, the invention firstly relates to a method of collecting particles which may be present in an aerosol, comprising the following steps:

• aspiration of the aerosol in a conduit from its inlet orifice to its outlet orifice;
• charge of the finest particles, downstream of the inlet, by diffusion of unipolar ions in a space between an electrode in the form of a grid surrounding an electrode in the form of a wire generating a crown effect, and a first conductive portion of the inner wall of the conduit,
• generation of an electric field without corona effect in the space between an electrode and a second conductive portion of the inner wall of the conduit, in order to collect by deposition on a first collection zone (Zn) the finest particles charged by the charger diffusion,
• generation of an electric field with corona effect in the space between the wire or the tip of an electrode and a third conductive portion of the interior wall of the conduit, in order to collect by deposition on a separate second collection zone (Zm) from the first collection area, the largest particles, not charged by the diffusion charger.

• a/ collecte de particules radioactives sur la première et/ou la deuxième zone de collecte pendant un temps t1 ;
• b/ comptage d'impulsions générées par le courant d'ionisation de l'air dans les espaces pendant un temps t2.

According to an advantageous embodiment, when the particles are radioactive, the method further comprises the following steps:

• a / collection of radioactive particles on the first and / or the second collection zone for a time t1;
• b / counting of pulses generated by the ionization current of the air in the spaces for a time t2.

According to this mode, a step of emitting an alarm can be provided in the event of a predetermined threshold value of pulses counted according to step b / being exceeded.

• un conduit comprenant un orifice d'entrée et un orifice de sortie entre lesquels l'aérosol peut circuler ;
• des moyens d'aspiration pour faire circuler l'aérosol depuis l'orifice d'entrée jusqu'à l'orifice de sortie;
• en aval de l'orifice d'entrée, un chargeur à diffusion d'ions unipolaires comprenant une électrode sous la forme d'un fil entouré par une électrode sous la forme d'une grille, le chargeur étant adapté pour charger les particules les plus fines dans l'espace séparant la grille d'une première portion conductrice de paroi intérieure du conduit, par diffusion d'ions unipolaires au travers de la grille;
• en aval du chargeur à diffusion, une électrode adaptée pour générer sans effet couronne un champ électrique dans l'espace séparant l'électrode d'une deuxième portion conductrice de paroi intérieure du conduit et ainsi collecter les particules les plus fines, préalablement chargées par le chargeur à diffusion, par dépôt sur une première zone de collecte (Zn);
• en aval du chargeur à diffusion d'ions et de la zone de collecte des nanoparticules, un chargeur par champ électrique comprenant une électrode sous la forme d'un fil ou d'une pointe adapté(e) pour générer avec effet couronne un champ électrique dans l'espace séparant le fil ou la pointe d'une troisième portion conductrice de la paroi intérieure du conduit et ainsi charger puis collecter les particules les plus grosses, par dépôt sur une deuxième zone de collecte (Zm) distincte de la première zone de collecte.

The subject of the invention is also a device for collecting particles which may be present in an aerosol, comprising:

• a conduit comprising an inlet and an outlet between which the aerosol can flow;
• suction means for circulating the aerosol from the inlet orifice to the outlet orifice;
• downstream of the inlet orifice, a unipolar ion diffusion charger comprising an electrode in the form of a wire surrounded by an electrode in the form of a grid, the charger being adapted to charge the most fines in the space separating the grid from a first conductive portion of the inner wall of the duct, by diffusion of unipolar ions through the grid;
• downstream of the diffusion charger, an electrode adapted to generate without crown effect an electric field in the space separating the electrode from a second portion conductor of the inner wall of the conduit and thus collect the finest particles, previously charged by the diffusion charger, by deposition on a first collection zone (Zn);
• downstream of the ion diffusion charger and the nanoparticle collection area, an electric field charger comprising an electrode in the form of a wire or a tip adapted to generate an electric field with crown effect in the space separating the wire or the tip of a third conductive portion of the interior wall of the conduit and thus charging and then collecting the largest particles, by deposition on a second collection zone (Zm) distinct from the first zone of collection.

Thus, the invention consists of an electrostatic collection of all the particles present in an aerosol, but with a decoupling of the mechanisms on the one hand of charge of the particles by diffusion of unipolar ions to charge then collect the finest particles , and secondly charging by electric field with corona effect to charge and collect the largest particles in a zone different from the collection zone for the finest particles.

In other words, the invention consists in electrically charging the fine particles first by diffusion of unipolar ions, then in charging the large particles by electric field and in collecting each group of particles thus charged according to their size on a adequate support.

Thus, the invention makes it possible judiciously to classify the particles according to their particle size, by depositing them in physically distinct zones.

In an advantageous embodiment, the deposition of the particles can be carried out according to concentric rings at different locations on the same flat substrate arranged orthogonally to the direction of circulation of the aerosol.

According to this mode, it is advantageously possible to take advantage of the ionic wind to induce air circulation through the device, which can make it possible to dispense with the presence of a suction pump in the device, with as subsequent advantage of a lower weight for the device and a reduction of nuisance intrinsic to a pump (vibrations, noise, ...).

The substrate (s) on which the particle deposition collection zones are defined can then be analyzed by conventional techniques of physical or physico-chemical characterization, such as optical microscopy or electronics, surface scanner, α, β, γ spectrometry if the particles are radioactive, X-ray fluorescence spectroscopy (XRF for “X-Ray Fluorescence”), X micro-fluorescence (µ-XRF), laser spectroscopy ( LIBS for “Laser-Induced Breakdown Spectroscopy”) ...

A collection device according to the invention is particularly well suited for the sampling of particles in gaseous media, in particular the air of the premises or the environment in order to know the concentration, the particle size, the composition of the particles d aerosol likely to be inhaled.

• le conduit est un cylindre creux de révolution autour d'un axe longitudinal (X);
• les moyens d'aspiration sont constitués par une pompe ;
• les première, deuxième et troisième portions conductrices de paroi sont des portions de cylindre constituant une partie du conduit;
• le chargeur par champ comprend une électrode sous la forme d'un fil en configuration fil-cylindre avec la portion de cylindre correspondante;
• le fil du chargeur à diffusion d'ions, l'électrode permettant de générer un champ électrique sans effet couronne et le fil du chargeur par champ sont des pièces distinctes et agencées successivement l'une derrière l'autre le long de l'axe (X).

According to a first embodiment:

• the conduit is a hollow cylinder of revolution about a longitudinal axis (X);
• the suction means are constituted by a pump;
• the first, second and third conductive wall portions are cylinder portions constituting a part of the conduit;
• the field charger comprises an electrode in the form of a wire in wire-cylinder configuration with the corresponding cylinder portion;
• the wire of the ion diffusion charger, the electrode making it possible to generate an electric field without crown effect and the wire of the charger by field are distinct parts and arranged successively one behind the other along the axis ( X).

• le conduit comprend un élément creux de révolution autour d'un axe longitudinal (X) et un substrat plan agencé à une extrémité de l'élément creux en étant orthogonal à l'axe (X), la distance séparant l'élément creux du substrat plan et de son support éventuel définissant les dimensions de l'orifice de sortie, le substrat plan formant un substrat de collecte définissant à la fois la première (Zn) et la deuxième zone (Zm) de collecte;
• les moyens d'aspiration sont constitués par l'orifice de sortie;
• la première portion conductrice de paroi est une portion de révolution constituant le conduit;
• les deuxième et troisième portions conductrices sont rassemblées sur le même substrat de collecte;
• le chargeur par champ comprend une électrode sous la forme d'une pointe en configuration pointe-plan avec le substrat de collecte; la pointe étant adaptée pour générer un effet couronne participant à la charge par champ des particules mais également pour créer un champ électrique favorisant la collecte des espèces préalablement chargées par le chargeur par diffusion d'ions.
• le fil du chargeur à diffusion d'ions, l'électrode et la pointe du chargeur par champ sont des portions d'une même pièce présentant une continuité électrique qui s'étend le long de l'axe (X).

According to a second embodiment:

• the conduit comprises a hollow element of revolution about a longitudinal axis (X) and a planar substrate arranged at one end of the hollow element being orthogonal to the axis (X), the distance separating the hollow element from the substrate plane and its possible support defining the dimensions of the outlet orifice, the planar substrate forming a collection substrate defining both the first (Zn) and the second collection zone (Zm);
• the suction means are constituted by the outlet orifice;
• the first conductive wall portion is a portion of revolution constituting the conduit;
• the second and third conductive portions are collected on the same collection substrate;
• the field charger comprises an electrode in the form of a point in point-plane configuration with the collection substrate; the tip being adapted to generate a crown effect participating in the charge per particle field but also to create an electric field favoring the collection of the species previously charged by the charger by ion diffusion.
• the wire of the ion diffusion charger, the electrode and the tip of the charger per field are portions of the same piece having an electrical continuity which extends along the axis (X).

The device according to this second mode can comprise plasma actuators arranged in the vicinity of the outlet.

Advantageously, the wire of the ion diffusion charger, the electrode making it possible to generate an electric field without crown effect and the wire or the tip of the charger per field are connected to a high voltage supply, preferably between 2 and 6 kV .

The grid is preferably connected to a low voltage power supply, preferably of the order of 100 V.

The first, second and third conductive portions are preferably connected to the zero potential. It is also possible to provide the first conductive portion with low voltage, typically at around 50V.

The collection device according to the invention may constitute, after prior collection, an ionization chamber and a detector of radioactive particles with an alarm function in the event of a predetermined threshold being exceeded.

The invention finally relates to the use of a device described above for collecting while separating nanoparticles in the first collection zone (Zn) and particles of micron size in the second collection zone (Zm).

The device can also be used as an ionization chamber.

An advantageous use of the device according to the invention is to evaluate the individual exposure of workers or consumers to nanoparticles.

detailed description

• les figures 1A à 1E sont des vues schématiques de différentes configurations d'électrodes pour obtenir un effet de couronne par décharge électrique;
• la figure 2 est une vue en coupe longitudinale d'un dispositif de charge, ou chargeur à diffusion d'ions unipolaires ;
• la figure 3 est une vue schématique en coupe longitudinale d'un premier exemple de dispositif de collecte de particules selon l'invention;
• la figure 4 est une vue schématique en coupe longitudinale d'un deuxième exemple de dispositif de collecte de particules selon l'invention ;
• la figure 5 est une vue montrant la simulation effectuée à l'aide d'un logiciel de calcul par éléments finis pour déterminer les lignes de champ électrique dans la partie aval du dispositif ;
• la figure 6 est une vue montrant les forces auxquelles sont soumises les particules ainsi que des exemples de trajectoires de deux types de particules dans la partie aval d'un dispositif selon l'invention;
• la figure 7 est un graphe caractérisant l'influence sur l'efficacité de collecte de la tension appliquée à l'électrode de pointe d'obtention de l'effet de couronne dans un dispositif selon la figure 4, et ce pour différentes distances entre l'électrode de pointe et le substrat de collecte conforme à l'invention (polarité négative) ;
• la figure 8 est un graphe caractérisant l'influence sur l'efficacité de collecte du débit d'aérosol dans un dispositif selon la figure 4 pour différentes distances entre l'électrode de pointe et le substrat de collecte conforme à l'invention, et différentes polarités;
• la figure 9 est une reproduction photographique d'un substrat de collecte mis en œuvre dans un dispositif selon l'invention comme illustré en figure 4, la figure 9 montrant une zone de collecte Zm de particules de taille micronique (billes de polystyrène latex de 2µm de diamètre) ;
• la figure 10 est une vue montrant la description de modèles utilisés pour effectuer une simulation à l'aide d'un logiciel de calcul par éléments finis pour déterminer les écoulements et les champs électriques qui se produisent dans un dispositif selon l'invention comme illustré en figure 4 ;
• la figure 11 est une vue issue de la simulation par le logiciel de calcul par éléments finis pour déterminer les profils de vitesse de particules ainsi que le vent ionique produit dans un dispositif selon l'invention comme illustré en figure 4;
• la figure 12 est encore une autre vue issue de la simulation par le logiciel de calcul par éléments finis qui illustre les trajectoires de particules de diamètre égal à 100nm (partie gauche de la figure) et égal à 10nm (partie droite de la figure) dans un dispositif selon l'invention comme illustré en figure 4 ;

Other advantages and characteristics will emerge more clearly on reading the detailed description, given by way of illustration and not limitation, with reference to the following figures among which:

• the Figures 1A to 1E are schematic views of different electrode configurations for obtaining a corona effect by electrical discharge;
• the figure 2 is a view in longitudinal section of a charging device, or charger with unipolar ion diffusion;
• the figure 3 is a schematic view in longitudinal section of a first example of a particle collection device according to the invention;
• the figure 4 is a schematic view in longitudinal section of a second example of a particle collection device according to the invention;
• the figure 5 is a view showing the simulation carried out using a finite element calculation software to determine the electric field lines in the downstream part of the device;
• the figure 6 is a view showing the forces to which the particles are subjected as well as examples of trajectories of two types of particles in the downstream part of a device according to the invention;
• the figure 7 is a graph characterizing the influence on the collection efficiency of the voltage applied to the tip electrode to obtain the crown effect in a device according to the figure 4 , and this for different distances between the tip electrode and the collection substrate according to the invention (negative polarity);
• the figure 8 is a graph characterizing the influence on the collection efficiency of the aerosol flow in a device according to the figure 4 for different distances between the tip electrode and the collection substrate according to the invention, and different polarities;
• the figure 9 is a photographic reproduction of a collection substrate used in a device according to the invention as illustrated in figure 4 , the figure 9 showing a collection zone Zm of particles of micron size (polystyrene latex beads 2 μm in diameter);
• the figure 10 is a view showing the description of models used to carry out a simulation using a finite element calculation software to determine the flows and the electric fields which occur in a device according to the invention as illustrated in figure 4 ;
• the figure 11 is a view resulting from the simulation by the finite element calculation software to determine the velocity profiles of particles as well as the ionic wind produced in a device according to the invention as illustrated in figure 4 ;
• the figure 12 is yet another view resulting from the simulation by the finite element calculation software which illustrates the trajectories of particles of diameter equal to 100nm (left part of the figure) and equal to 10nm (right part of the figure) in a device according to the invention as illustrated in figure 4 ;

Throughout the present application, the terms "vertical", "lower", "upper", "bottom", "high", "below", "above", "height" are to be understood by reference with respect to a collection device arranged vertically with the inlet orifice at the top as illustrated in figure 4 .

Likewise, the terms “inlet”, “outlet”, “upstream” and “downstream” are to be understood by reference with respect to the direction of the suction flow through a collection device according to the invention. Thus, the inlet orifice designates the orifice of the device through which the aerosol containing the particles is sucked in while the outlet orifice designates that through which the air flow exits.

The Figures 1A to 1E and 2 have already been commented on in the preamble. They are not detailed below.

For the sake of clarity, the same elements of the collection devices according to the two examples illustrated are designated by the same reference numerals.

We have represented in figure 3 a first example of an electrostatic device 1 according to the invention for the selective collection of particles capable of being contained in an aerosol.

Such a device according to the invention makes it possible to collect both the finest particles, such as nanoparticles and the largest particles, such as those of micronic size while separating them from one another according to their range of cut.

The collecting device 1 firstly comprises a conduit 11 which is a hollow cylinder of revolution around the longitudinal axis X and which is electrically connected to a low voltage, for example to a voltage of 50 Volt, or even to zero potential .

The collecting device 1 comprises inside the duct 11, from upstream to downstream, between its inlet orifice 17 and its outlet orifice 18, four separate stages 10, 20, 30, 40.

The first stage consists of a charger with unipolar ion diffusion 10, and is similar to that described previously in relation to the figure 2 .

The charger 10 thus comprises a central electrode which extends along the axis X in the form of a wire 12 connected to a power supply delivering a high voltage 13, adapted to thereby create a corona discharge in the vicinity of the wire 12.

It also includes a peripheral electrode in the form of a grid 14 connected to a low voltage supply 16.

The stage 20, downstream of the charger 10, comprises a central electrode which extends along the axis X in the form of a rod 22 connected to a supply supplying a medium voltage 23, adapted to create a field without crown effect electric collecting device in the space 21 separating the central electrode 22 and the wall of the conduit 11. A hollow cylinder 24 conforming to the wall of the conduit and constituting a first collecting zone Zn is arranged around the rod 22 opposite the latter this.

Stage 30, downstream of stage 20, comprises a central electrode which extends along the axis X in the form of a wire 32 connected to a high voltage supply 33, adapted to create a crown effect in the vicinity of the wire 32 and therefore an intense electric field in the space 31 separating the central wire 32 from the conduit 11. A hollow cylinder 34 conforming to the wall of the conduit and constituting a second collection zone Zm is arranged around the wire 32 opposite that -this.

The stage 40 comprises a structure 41, for example a “honeycomb” structure, adapted to avoid the appearance of a vortex in the duct 11, and downstream a suction device 42. Depending on the configurations, the collection device according to the invention can overcome structure 41.

The operation of the collection device which has just been described with reference to the figure 3 is the next.

The air containing the particles to be collected is sucked in through the inlet orifice 17 by the action of the suction device 42.

The finest particles of the aerosol are electrically charged by diffusion of unipolar ions in the space 15 separating the grid 14 from the duct 11.

These finer particles, with high electric mobility, and the other larger particles with lower electric mobility, penetrate into stage 20.

The electric field without crown effect created in the space 21 between the rod 22 and the cylinder 24 collects the finest particles on the latter by defining the first collection zone Zn.

The other, larger particles are not collected and are always present in the aerosol which enters the third stage 30.

These larger particles are then electrically charged under the corona effect near the wire 32 and the intense field prevailing in the space 31 and are collected on the inner wall of the cylinder 34 by defining the second collection zone Zm.

The purified air of both the finest particles deposited in the first collection zone Zn and the largest particles Zm is then evacuated through the outlet orifice 18 of the device.

Each of the zones Zn and Zm can then be analyzed by conventional techniques of physical or physico-chemical characterization, such as optical or electron microscopy, surface scanner, α, β, γ spectrometry if the particles are radioactive, X-ray fluorescence spectroscopy ( XRF for "X-Ray Fluoresence"), X micro-fluorescence (µ-XRF), laser-induced plasma spectroscopy (LIBS for "Laser-Induced Breakdown Spectroscopy") .... to know the particle size on the one hand finer particles and on the other hand larger particles, their concentration, their chemical composition and / or their morphology.

Advantageously, provision can be made for the collection cylinder 24 and that 34 to consist of a single piece which thus forms a single collection substrate, which can be easily removed from the conduit once the targeted collection has been carried out.

We have represented in figure 4 , another advantageous example of a collecting device 1 according to the invention making it possible to collect the particles not on one or more cylinders arranged along the flow axis of the aerosol as illustrated in figure 3 , but on the same disc-shaped substrate 6 placed on its support 5 and arranged orthogonally to the axis of symmetry of the collection device.

In addition to better compactness, the collection device illustrated in figure 4 has the advantage compared to that illustrated in figure 3 , to be able to collect all the particles on the same flat surface of substrate according to concentric rings according to their relative dimensions, the largest particles being preferably collected at the center of the surface while the finest are preferably collected at the periphery.

In addition, the collection device illustrated in figure 4 advantageously makes it possible to take advantage of the ionic wind created by the tip-plane configuration for the collection of the largest particles, and thus induce air circulation through the device in its downstream part. This air circulation can go as far as making it possible to dispense with the presence of a suction pump, which considerably lightens the collection device according to the invention and also makes it possible to reduce its nuisances (vibrations, noise, ...).

The collecting disc 6 is preferably conductive, typically made of metal, or even semiconductor. Its diameter is preferably between 10 and 25 mm, more preferably of the order of 20 mm.

The collecting device 1 has a cylindrical geometry of revolution around the longitudinal axis X and comprises an elongated hollow body 11 surrounded by an envelope 110 which may or may not be conductive and surmounted by an electrically insulating body 3 in which the electrodes are fixed and by which the power supplies are made. Alternatively, the body 11 and the casing 110 may be one and the same piece.

The conductive envelope 110, as well as the body 11 and the support 5 can be connected to zero potential by the supply terminal 2. It is also possible to use an envelope 110 and the body 11 made of insulating material thus brought to potential floating and maintain the support 5 at zero potential by an electric wire connecting it to the power supply terminal 2.

The hollow body 11 defines within it with an insulating element 4, and a collection substrate 6 and its support 5, the aerosol circulation duct from the inlet orifice 17 to the outlet orifice 18 .

• la partie pour créer l'effet couronne pour la collecte des particules les plus grosses est en configuration pointe-plan, la pointe 32 étant à distance du plan du substrat de collecte 6 agencé orthogonalement à l'axe X ;
• le fil central 12 d'effet couronne pour la diffusion d'ions unipolaires, la tige 22 permettant de générer un champ électrique sans effet couronne pour collecter les particules fines et la pointe 32 d'effet couronne pour la collecte des particules les plus grosses formant une seule et même électrode centrale aux portions 12, 22, 32 continues mais de géométrie différente.

The collection device 1 according to the figure 4 includes the same elements as that of the figure 3 as explained above but is essentially distinguished by the fact that:

• the part for creating the crown effect for collecting the largest particles is in the tip-plane configuration, the tip 32 being at a distance from the plane of the collecting substrate 6 arranged orthogonally to the axis X;
• the central corona wire 12 for the diffusion of unipolar ions, the rod 22 making it possible to generate an electric field without corona effect for collecting fine particles and the corona effect tip 32 for collecting the largest particles forming a single central electrode with portions 12, 22, 32 continuous but of different geometry.

More specifically, the unipolar ion diffusion charger consists of a portion of the central electrode in the form of a wire 12 and a grid 14 arranged around the central wire 12. The central wire 12 preferably has a diameter less than 50 µm.

In the extension of the grid 14, an insulating element 4 makes it possible judiciously to ensure both the centering and the fixing of the electrode portion in the form of a rod 22 thus electrically connected to the wire 12.

The rod 22 ends with a tapered tip 32 facing the collection disc 6. Preferably, the angle of the tip is less than 35 ° and its apex (apex) has its greatest width less than 50 μm.

The collecting device 1 can advantageously comprise in its downstream part, that is to say in the enlarged part of the aerosol circulation duct, downstream of the grid 14, plasma actuators 8 which make it possible to control the flow of the purified air from the particles in this downstream part, before its evacuation through the outlet orifice 18, as explained below.

A single high voltage supply 13, 23, 33 makes it possible to achieve both the crown effect in the vicinity of the wire 12 and in the vicinity of the tip 32. The high voltage is chosen to be preferred between 2 and 6 kV, more preferably at about 4 kV.

A low voltage supply 16, of the order of 100V, makes it possible to polarize the gate 14 to control the production of unipolar ions in the charge space by diffusion 15.

It should be noted that there is not, in this device according to the figure 4 medium voltage power supply, the electrode 22 making it possible to generate an electric field without corona effect, as such, the medium voltage field lines without corona effect for collecting the finest particles as detailed below, resulting in this case of the high voltage applied to the tip 32.

When dimensioning the device, care is taken to achieve good mechanical strength of the subassembly consisting of the central electrode with different portions 11, 12, 32, of the grid 14 and of the insulating element 4 as well as to guarantee electrical continuity all along the high voltage supply 13, 23, 33 and of the various portions 12, 22, 32 of the electrode.

Sizing is done taking care not to introduce too much shrinkage with a reduced section. This makes it possible to minimize the pressure drop of the assembly with respect to the air circulating in the annular space 15.

Thus, the operation of the collection device according to the figure 4 is similar to that of the figure 3 .

The aerosol flows from the inlet orifice 17 to the outlet orifice 18 because the suction is carried out at the level of the latter.

The finest particles are electrically charged by diffusion of unipolar ions in the annular space 15 while the largest particles are electrically charged under the action of the intense electric field in the space 31 between tip 32 generating the effect crown and collection substrate 6.

We illustrated in figure 4 , a possible embodiment of the collection device 1 which makes it possible not to use an auxiliary suction pump. Under the effect of the ionic wind created in the space 31 between the tip 32 and the collection substrate 6, a vacuum appears in the annular space 15 of charge by diffusion, which creates a circulation at the flow q in the device.

The suction can be optimized by the more or less wide opening of the outlet orifice 18, by the choice of the high voltage applied to the tip 32 as well as by the distance between the tip 32 and the plane 6.

As illustrated in figure 4 , it is possible to maintain or even amplify the circulation of purified air of the particles which takes place in the downstream part of the duct by plasma actuators 8 arranged in the vicinity of the outlet 18. These plasma actuators 8 are advantageously of the type of those used in microelectronics for cooling microcomponents. Thus, by amplifying the flow of purified air, the collection rate q which travels through the device is increased overall. In the end, a defined geometry and high voltage corresponds to a collection rate q that can be set.

We illustrated in figure 5 , the electric field lines which take place in the downstream part of the aerosol circulation duct. The field lines being perpendicular to the equipotential lines, it is possible to contain the field lines by the equipotential lines internal to the collection zones.

We can clearly see on this figure 5 that the tip 32 makes it possible to obtain a very intense electric field locally, which allows the ionization of the air and the charge of the microparticles. But moving away vertically, it decreases very quickly to a value of about 0.5 ^∗ 10 ⁶ V / m at the place where the particles pass. The device according to the invention as shown in figure 4 , dimensioned with a portion 111 of the wall of the hollow body 11 constraining the air flow going towards the outlet 18 to pass between two parallel walls between which the electric field is significantly amplified up to a value of 10 ⁶ V / m. In addition, the radius of curvature of 1 mm at the bottom of the wall of the hollow body 11 is sufficient at the critical point to avoid any breakdown problem up to 4000 V.

As illustrated in figure 6 , it is the combination of air and electrical effects applied to the particles which will define their trajectory and therefore the area of the substrate 6 in which they will be collected.

A fine particle, of high mobility, is immediately subjected to the action of the surrounding radial electric field, which results in a radial speed towards the outside w, while being transported by the aeraulic field, which results in a radial speed. inward c. The vector result, speed u thus defines the trajectory and the point of impact of this particle on the collecting disc 6.

Thus, for a plurality of fine particles of the same mobility, laminarly injected into the annular space 15, the point of impact defines an impact circumference or ring Zn on the substrate 6, taking into account the symmetry of revolution of the device.

As for the larger particles, of lower mobility, they are not charged by diffusion, arrive in the vicinity of the tip 32, are electrically charged by bombardment of the ions produced locally by the crown effect between the tip 32 and the substrate 6, and are therefore deposited on the latter in the vicinity of the axis X on impact circumferences Zm of radii which are smaller the larger their size.

The particles are therefore collected on the disc in concentric circles according to their particle size, the finest on the outside, the largest in the center.

The inventors sought to quantitatively assess the effectiveness of a collection device 1 which has just been described with reference to the figures 4 to 6 .

A first evaluation was made from air loaded with latex-polystyrene (PSL) beads of 2 μm in diameter, sold by the company ABCR under the name ABCR 210832.

This first evaluation makes it possible to illustrate the charge mechanism by field effect of the micron-sized particles in the space 31 between the tip 32 and the metallic collecting substrate 6 and their deposition on the latter.

The inventors proceeded as follows.

An aqueous suspension of PSL beads is atomized using an aerosol generator, brand TSI, model 3076, then dried by a desiccant column, brand TSI, model 3062.

The aerosol thus generated is then introduced into a chamber in which the collection device 1 is located, as illustrated in figures 4 to 6 , at a flow rate of 3.6 L / min.

The chamber is provided with an outlet orifice making it possible to avoid an overpressure since the flow rate imposed by a pump external to the collection device, in the range of 0.4 to 1.4 L / min is always lower than the flow rate of aerosol entering the room.

In this example, an imposed flow rate Q is applied to the collection device 1 to force a flow to pass from the inlet orifice 17 to that of the outlet 18 using a variable flow pump which is controlled by a flow meter.

The high voltage 13, 23, 33 applied to the central electrode 12, 22, 32 is studied for positive (+) and negative (-) polarities from 1500 V to 4000 V and this for different distances z between the end of the tip 32 and the collection substrate 6.

The figure 7 shows that for a constant flow of 1.4 L / min, the collection efficiency which results in the ratio expressed as a percentage between the number of particles leaving the device and the number of particles entering, increases when the applied voltage (in absolute value) increases. For an applied voltage between 3500 and 4000 V (in absolute value), the collection efficiency is around 90% regardless of the distance between tip 32 and plane of substrate 6, which is varied by 2.5 mm at 6.5 mm.

The figure 8 as for it indicates that overall the collection efficiency is the highest when the flow is low, which is particularly the case for a flow of 0.4 L / min. Furthermore, it is observed that for a fixed flow rate the collection efficiency is higher when the polarity used is negative and when the distance from tip to plane is large.

These evaluation examples show that the collection device according to the invention, as described in figures 4 to 6 , can be used to collect particles of micron size thanks to a field effect charging mechanism created by the tip 32 carried at high voltage with a collection efficiency greater than 95%.

We reproduced in figure 9 , the photograph of a collection substrate 6 made of copper 20 mm in diameter on which the micron particles were collected: it is clearly seen that they are deposited according to a ring Zm concentric with the axis X of the device or also of the point 32. This white crown Zm corresponds to the deposition of PSL particles of 2 μm in diameter.

The inventors also simulated the operation of the collection device according to the invention as illustrated in figures 4 to 6 and this using a finite element calculation software marketed under the name "COMSOL Multiphysics".

The collection device 1 with the same geometry as that shown in the figures 4 to 6 , can be studied under COMSOL software by looking at flows, electric fields, particle trajectories as well as the ionic wind produced.

The figure 10 is a view showing the description of models used to perform a simulation using a finite element calculation software to determine the flows and the electric fields which occur in a device according to the invention as illustrated in figure 4 .

In the geometry represented in figure 10 and corresponding to that of the device illustrated in figure 4 , the enlarged wall portion 111 is brought to the same potential as the tip 32. In the context of the invention, it goes without saying that this portion 111 can be at a potential different from the tip 32.

The figure 11 shows the simulation of the flow for a distance z between tip 32 and plane 31 of 4 mm and a voltage applied U to tip 32 and to portion 111 of + 4000 V.

The representation of the figure 11 highlights the generation of a plasma produced by corona effect under the tip 32 where the electric fields are the most high, this plasma inducing an ionic wind in the direction of the collecting disc 6. The jet thus produced flourishes on the surface of the collecting disc.

Of this figure 11 , we also note that this ionic wind in a way sucks the aerosol upstream of the tip 32 towards the charge zone 31 by field effect and therefore participates in the excellent collection efficiencies encountered for the largest particles, whose trajectories will not have been deflected by the field lines, since they are not charged in the charging zone 15 by diffusion of ions upstream.

It emerges from this figure 11 , that the portion 111 creates an aerosol circulation in the device 1 according to the invention. By calculating the average value of the speed of the input flow, using the “Comsol” finite element software and multiplying this value by the area, we obtain a flow rate of approximately 0.5 L / min, which is a value very correct to obtain collection efficiencies greater than 94%.

This has been verified experimentally on the device of the figure 4 by the use of a smoke generator. The smoke signal made it possible to show that the ionic wind did indeed create a suction flow without an external pump at the device inlet.

The inventors also traced the trajectory of the particles in the device illustrated in figure 4 for nanoparticles with a diameter of 10 nm and 100 nm and with a flow rate Q = 0.5 L / min.

The figure 12 thus represents the simulation for an applied voltage U equal to + 4000 V and for a distance z between tip 32 and plane 31 of 4 mm, of the trajectory of the particles of diameter 100 nm respectively to the left of the figure (n = 4: number of elementary charges) and of diameter 10 nm to the right of the figure (n = 1)).

It is noted by the finite element software “Comsol” that the nanoparticles are well precipitated, i.e. deposited by electrostatic precipitation.

Thus, the collection device 1 according to the invention as shown in figures 4 to 6 collects by depositing on the same support, for example a metal disc, both particles of different dimensions, according to concentric zones corresponding to well-defined particle sizes. The coarsest particles, typically particles of micron size, are collected in a central Zm collection zone while the finest particles, typically nanoparticles are collected in a peripheral annular zone Zn.

The support can then be extracted from the rest of the collection device and then analyzed by conventional techniques of physical or physico-chemical characterization (optical or electronic microscopy, surface scanner, X-ray fluorescence, LIBS spectrometry, α, β, γ spectrometry if the particles are radioactive, ....

The collection device according to the invention is particularly well suited for the sampling of particles in gaseous media, in particular the air of the premises or the environment in order to know the concentration, the particle size, the morphology and the composition. aerosol particles likely to be inhaled ... Because of its small size and its reduced electrical consumption, this device could be portable and therefore deployable on a large scale for a moderate cost.

According to an advantageous variant, it is possible to operate the collection device according to the invention as an ionization chamber. Thus, sequentially, according to a pre-established cycle, the device can operate as an aerosol collector for a time t ₁ , then as a pulse counter for a time t ₂ .

Indeed, if aerosols are previously deposited on the substrate 6 during the collection phase (time t1), then if the high voltage applied to the tip 32 is then lower than the priming voltage of the crown effect during the counting phase (time t2), an ionization of the air will be created.

The ionization current collected by the tip 32 can then be detected by an appropriate electronic system, of the type of those commonly used in conventional ionization chambers.

Applied to radioactive aerosols, such an ionization chamber can thus constitute a radioactive contamination detector with an alarm function if a predetermined threshold is exceeded. In addition, the collection substrate 6, having played its role of collecting particles according to the invention, it can be extracted to carry out further radioactive analyzes with the subsequent advantage of depositing in thin layers for a spectrometry.

Other variants and improvements can be made without departing from the scope of the invention.

The invention is not limited to the examples which have just been described; one can in particular combine together characteristics of the examples illustrated within variants not illustrated.

References cited

1. [1]: W. Hinds, "Aerosol Technology", 2nd Edition, 1999 .
2. [2]: P. Intra and N. Tippayawong, "Aerosol an Air Quality Research", 11: 187-209, 2011 ;
3. [3]: GW Hewitt, "The Charging of small Particles for Electrostatic Precipitation", AIEE Trans., 76: 300-306, 1957 ;
4. [4]: G. Biskos, K. Reavell, N. Collings, "Electrostatic Characteriation of Corona-Wire Aerosol Chargers", J. Electrostat. 63: 69-82, 2005 ;
5. [5]: DYH Pui, S. Fruin, PH McMurry, "Unipolar Diffusion Charging of Ultrafine Aerosols", Aerosol Sciences Technology 8: 173-187, 1988 ;
6. [6]: P.Bérard, "Study of the ionic wind produced by corona discharge at atmospheric pressure for aerodynamic flow control," Engineering Sciences, Ecole Centrale Paris, 2008, NNT: 2008ECAP1085, tel-01071389 ;

Claims (15)

1. A method for collecting particles likely to be present in an aerosol, comprising the following steps:

   - sucking (18, 42) the aerosol through a conduit (11) from its inlet orifice (17) to its outlet orifice (18);

   - charging the finest particles, downstream of the inlet orifice, by unipolar ion diffusion (10) in a space (15) between an electrode in the form of a gate (14) surrounding an electrode in the form of a wire (12) generating a corona effect, and a first conductive portion of the internal wall of the conduit;

   - generating an electric field without a corona effect in the space (21) between an electrode (22) and a second conductive portion (24) of the internal wall of the conduit, in order to collect the finest particles charged by the diffusion charger by deposition onto a first collection zone (Zn);

   - generating an electric field with a corona effect in the space (31) between the wire or the point of an electrode (32) and a third conductive portion (34, 6) of the internal wall of the conduit, in order to collect the biggest particles not charged by the diffusion charger by deposition onto a second collection zone (Zm) distinct from the first collection zone.
2. The method for collecting radioactive particles as claimed in claim 1, further comprising the following steps:

   a/ collecting radioactive particles on the first and/or the second collection zone during a time period t1;

   b/ counting pulses generated by the ionization current of the air in the spaces (21, 31) during a time period t2.
3. The method for collecting radioactive particles as claimed in claim 2, comprising a step of emitting an alarm in the event that a predetermined threshold value of pulses counted in step b/ is exceeded.
4. A device (1) for collecting particles likely to be present in an aerosol, comprising:

   - a conduit (11) comprising an inlet orifice (17) and an outlet orifice (18), between which the aerosol may circulate;

   - suction means (18, 42) for circulating the aerosol from the inlet orifice to the outlet orifice;

   - a unipolar ion diffusion charger (10), downstream of the inlet orifice, comprising an electrode in the form of a wire (12) surrounded by an electrode in the form of a gate (14), the charger being adapted to charge the finest particles in the space (15) separating the gate from a first conductive portion of the internal wall of the conduit by diffusing unipolar ions through the gate;

   - an electrode (22), downstream of the diffusion charger, adapted to generate an electric field without a corona effect in the space (21) separating the electrode (22) from a second conductive portion (24) of the internal wall of the conduit and to thus collect the finest particles, previously charged by the diffusion charger, by deposition onto a first collection zone (Zn);

   - an electric field charger (30), downstream of the ion diffusion charger and of the nanoparticle collection zone, comprising an electrode (32) in the form of a wire or a point adapted to generate an electric field with a corona effect in the space (31) separating the wire or the point from a third conductive portion (34, 6) of the internal wall of the conduit and to thus charge, then collect, the biggest particles by deposition onto a second collection zone (Zm) distinct from the first collection zone.
5. The collection device as claimed in claim 4, wherein:

   - the conduit (11) is a hollow cylinder of revolution about a longitudinal axis (X);

   - the suction means are formed by a pump (42);

   - the first, second and third conductive portions of the wall are cylinder portions (11, 24, 34) forming part of the conduit;

   - the field charger (30) comprises an electrode in the form of a wire (32) in a wire-cylinder configuration with the corresponding cylinder portion (34);

   - the ion diffusion charger wire (12), the electrode (22) for generating an electric field without a corona effect and the wire (32) of the field charger (30) are distinct parts and are successively arranged one behind the other along the axis (X).
6. The collection device as claimed in claim 4, wherein:

   - the conduit (11) comprises a hollow element of revolution about a longitudinal axis (X) and a flat substrate (6) arranged at one end of the hollow element orthogonal to the axis (X), the distance separating the hollow element from the flat substrate (6) and its possible support (5) defining the dimensions of the outlet orifice (18), the flat substrate forming a collection substrate defining both the first (Zn) and the second (Zm) collection zone;

   - the suction means are formed by the outlet orifice (18);

   - the first conductive portion of the wall is a portion of revolution forming the conduit;

   - the second and third conductive portions are grouped on the same collection substrate (6);

   - the field charger (30) comprises an electrode in the form of a point (32) in a point-plane configuration with the collection substrate (6), the point (32) being adapted to generate a corona effect participating in the field charging of the particles but also for creating an electric field promoting the collection of species previously charged by the ion diffusion charger (10);

   - the wire (12) of the ion diffusion charger (10), the electrode (22) and the point (32) of the field charger (30) are portions of the same part exhibiting electrical continuity that extends along the axis (X).
7. The collection device as claimed in claim 6, comprising plasma actuators (8) arranged in the vicinity of the outlet (18).
8. The collection device as claimed in one of claims 4 to 7, comprising a high-voltage power supply, preferably between 2 and 6 kV, wherein the wire (12) of the ion diffusion charger, the collection electrode rod (22) and the wire or the point (32) of the field charger (30) are connected to the high-voltage power supply,.
9. The collection device as claimed in one of claims 4 to 8, comprising a low-voltage power supply, preferably of approximately 100 V, wherein the gate (14) is connected to the low-voltage power supply.
10. The collection device as claimed in one of claims 4 to 9, the first, second and third conductive portions (11, 24; 34 or 6) being connected at zero potential.
11. The collection device as claimed in one of claims 4 to 10, forming an air ionization chamber.
12. The collection device as claimed in one of claims 4 to 11, forming a radioactive particle detector.
13. The use of a device as claimed in one of claims 4 to 12 for collecting particles while separating nanoparticles into the first collection zone (Zn) and micron-sized particles into the second collection zone (Zm).
14. The use of a device as claimed in one of claims 4 to 12 as an ionization chamber.
15. The use of a device as claimed in one of claims 4 to 12 for evaluating the individual exposure of workers or of consumers to the nanoparticles.

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