Device for treating a gas phase by plasma and associated method

Abstract

Device for treating a gas phase by plasma and associated method The invention relates to a device (1) for treating a gas phase (2) comprising at least one assembly (11) of electrodes comprising an injection electrode and an electrode connected to a ground (12) of the device (1), separated by a separator material, the assembly (11) being configured so that, under the application of an electrical voltage, a plasma (3) is generated between the injection electrode and the electrode connected to the ground, the separator material having an electrically insulating behavior when the separator material is subjected to a voltage lower than a threshold voltage, called "starting voltage", and an electrically conductive behavior allowing the passage of a current when the separator material is subjected to a voltage greater than or equal to the starting voltage.This allows access to two plasma generation regimes to improve the treatment of the gas phase (2). Figure for abstract: Fig.1.

Description

Title of the invention: Device for treating a gas phase by plasma and associated method Technical field

[0001] The present invention relates to the field of devices for non-thermal plasma treatment of a gas phase. It finds particularly advantageous application in the field of air treatment, for example indoor air, and / or pollutant emissions, and / or olfactory nuisances. STATE OF THE ART

[0002] It is known that volatile organic compounds (VOCs) have harmful effects on health, for example irritation of the eyes and mucous membranes, respiratory tract, heart and nervous system disorders, headaches, and nausea. Some VOCs are even recognized as carcinogenic, and / or toxic for reproduction or mutagenic (so-called "CMR" compounds for Carcinogenic-Mutagenic-Reprotoxic),

[0003] The risks posed by VOCs have led to numerous regulations, resulting in a complex set of measures to meet the standards. These standards aim to reduce VOCs, odors, and ensure satisfactory biological air quality.

[0004] Beyond VOCs, other harmful species can have adverse effects on health, the environment or olfactory comfort. This is the case for microorganisms such as bacteria, viruses, fungi and / or their spores.

[0005] There is therefore a need for the development of a system for depollution / decontamination of gaseous phases likely to include harmful species such as indoor air or polluting discharges from human activity, for example from industry.

[0006] In recent years, the indoor air purification market has grown with the marketing of equipment displaying indoor air purification properties in the form of stand-alone devices, as well as construction and decoration materials highlighting depolluting properties. There is no certification of indoor air purification devices, and some of them can lead to the formation of compounds potentially more harmful than the VOCs initially present.

[0007] Today, for this field, filtration is the most used technique. HEPA filters stop suspended matter, including organic matter. These, fixed on the filters or having sedimented in the conduits of the filtration systems, are however a preferred place of growth of microorganisms. In addition, viruses nanometric size are not captured by these filters.

[0008] Non-thermal plasma technology (so-called "cold" plasma) has many advantages: it is an electrical and non-chemical technology, without consumables, non-selective, compact and modular (capable of treating flow rates ranging from a few cm3 / h to tens of thousands of m3 / h). Cold plasma treatments are effective on a multitude of pollutants, VOCs but also microorganisms. Indeed, cold plasma destroys the DNA of these microorganisms without distinction of size and is therefore effective on these pathogenic elements. It should be noted that this technology is very suitable for highly diluted pollution (low concentrations of pollutants) which makes it a technology of choice for the treatment of odors (low concentrations but high nuisances).

[0009] Conventional cold plasma treatments, for example generated by dielectric barrier discharge (abbreviated DBD), are energy-intensive and generate harmful compounds such as ozone, by-products of degradation of the treated pollutants.

[0010] Document US 2005 / 0118079 A1 describes a device for gas purification, using surface electrodes comprising photocatalysts in order to improve the efficiency of a non-thermal plasma. However, ANSES (French National Agency for Food, Environmental and Occupational Health and Safety) in France advises against the use of physicochemical air treatments, because their effectiveness, particularly against viruses, has not been proven. Following sometimes incomplete degradation of pollutants, they can also negatively impact indoor air quality by the formation of compounds that are potentially dangerous to health, including CMR chemical agents.

[0011] An object of the present invention is therefore to propose a device improving the treatment of a gaseous phase by plasma, in particular by cold plasma, and in particular that of air.

[0012] Other objects, features and advantages of the present invention will become apparent from a consideration of the following description and accompanying drawings. It is understood that other advantages may be incorporated. SUMMARY

[0013] To achieve this objective, according to one aspect, a device for treating a gas phase is provided comprising at least one assembly of electrodes comprising at least one so-called injection electrode and at least one other electrode connected to the ground of the device, separated by a material called "separator material", the assembly being configured so that, under the application of an electrical voltage, a plasma is generated between the at least one injection electrode and the at least one electrode connected to the ground.

[0014] The separator material exhibits electrically insulating behavior when it is subjected to an electrical voltage lower than a threshold voltage, called “breakthrough voltage”, and an electrically conductive behavior allowing the passage of a current when the separator material is subjected to an electrical voltage greater than or equal to the breakthrough voltage.

[0015] The separator material thus allows access to two plasma generation regimes: a homogeneous regime (electrical discharges generated when the material behaves as an insulator) and an erratic regime, also called an energetic regime (electrical discharges generated when the material behaves as an insulator), which corresponds to an energetic multi-filamentary regime. These two regimes can appear simultaneously or successively.

[0016] The erratic regime does not exist in conventional DBD devices. This regime, together with the homogeneous regime, makes it possible to perfect the cold plasma treatment by improving the degradation of the treated compounds and to limit the residual harmful degradation by-products. This also makes it possible to degrade a wider range of pollutants than with a conventional DBD device.

[0017] The synergy between these two regimes allows for more efficient electrical discharges, which improves the efficiency and speed of gas phase treatment. The device can thus be made more compact and of simplified design.

[0018] The treatment of the gas phase is thus improved by the joint application of these two plasma regimes on the gas phase flowing in the device. In addition, the use of catalyst is avoided, which simplifies the device as well as its maintenance.

[0019] Furthermore, during the development of the invention, it was demonstrated that this type of separator material made it possible to lower the value of the electrical voltage to be applied to generate the plasma. The cost, particularly the energy cost, of treating a gas phase is thus reduced. The safety of use of the device is also improved.

[0020] Another aspect relates to a method of treating a gas phase using the device according to the first aspect, and comprising: - the introduction of the gas phase into at least one electrode assembly, - applying an electrical voltage to the assembly so as to generate a plasma between the at least one injection electrode and the at least one electrode connected to ground to treat the gas phase.

[0021] The method has the effects and advantages described in relation to the device according to the first aspect.

[0022] In addition, since plasma discharges are more efficient, the treatment time of the gas phase can be reduced compared to treatment by a DBD device. conventional. This is particularly advantageous for the elimination of viruses, which generally requires more energy (and more time) than that of VOCs. BRIEF DESCRIPTION OF THE FIGURES

[0023] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0024] [Fig.l] [Fig.l] represents an overall view of the device and its operating principle, according to an exemplary embodiment.

[0025] [Fig.2] [Fig.2] represents a diagram of the electrical circuit for studying the com electrical behavior of the separating material, according to an example.

[0026] [Fig.3] [Fig.3] schematically represents the electrical behaviors of the separator material according to several exemplary embodiments, in comparison with an insulator of a DBD device.

[0027] [Fig.4][Fig.5][Fig.6] Figures 4 to 6 represent different geometries of electrodes in an assembly, according to several exemplary embodiments.

[0028] [Fig.7][Fig.8A][Fig.8B][Fig.9] Figures 7 to 9 represent different arrangements of assemblies, according to several examples of realization.

[0029] [Fig.l0A][Fig.l0B] Figures 10A and 10B represent two graphs showing the percentage of degradation of VOCs, respectively ethylene and isopropanol, as a function of the voltage applied to an assembly to generate the cold plasma, in comparison with two assemblies of DBD devices of the state of the art.

[0030] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. In particular the relative dimensions between the VOCs, the electrodes and the device are not representative of reality. DETAILED DESCRIPTION

[0031] Before commencing a detailed review of embodiments of the invention, optional features are set out below which may optionally be used in combination or alternatively.

[0032] According to one example, the breakdown voltage is between 1 kV and 10 kV, preferably between 3 kV and 6 kV. These breakdown voltage parameters are taken for a 50 Hz AC type signal and for a tip / tip electrode geometry on the surface of the separator material, for a gap between 5 and 15 mm.

[0033] According to one example, the separator material is chosen from the group consisting of: a semiconductor material, for example a semiconductor ceramic, a semiconductor polymer, a composite material comprising conductive particles or semiconductors dispersed in a matrix. However, it must have the dielectric properties with an insulator / conductor transition for the selected operating voltage range. The insulating phase also has the charge trapping / detrapping characteristics required to enable the energy regime.

[0034] According to one example, the separator material being a composite material comprising conductive or semiconductive particles dispersed in an insulating matrix, the insulating matrix is ​​based on or made of a material chosen from the group consisting of a polymer and a ceramic, and the conductive or semiconductive particles are based on or made of a material chosen from the group consisting of a metal, an intermetallic, a metal alloy, a ceramic.

[0035] According to one example, the separator material has no porosity. According to an alternative embodiment, the separator material has a non-zero average porosity and preferably greater than or equal to 10%. Preferably, this porosity is between 10% and 30%. This porosity in the material has the advantage of improving the performance of the device. This porosity is open, pores being present on the external face of the material and therefore in contact with the medium surrounding the material.

[0036] [According to one example, the material is a semiconducting ceramic, comprising a microstructure comprising: - 5 to 40% by volume of a particulate conductive phase, - 60 to 95% by volume of a particulate insulating phase, the particle size of the conductive phase being between 5 nm and 11 pm, 65 to 80% of the conductive particles having an average diameter of less than 1 pm and 20 to 35% of the conductive particles having an average diameter of between 1 and 11 pm; - and the distance between two neighboring conductive phase particles being between 30 Angstroms and 5 pm.

[0037] According to one example, the material constituting the conductive phase is chosen from the group consisting of MoSi2, TiB2, TiN, Ni3Si, HfB2, ZrB2.

[0038] According to one example, the particle size of the insulating phase is between 0.3 and 3 μm.

[0039] According to one example, the material constituting the insulating phase is chosen from AI2O3, mullite, Si3N4.

[0040] According to one example, the ceramic comprises 15 to 25% by volume of MoSi2, and preferably 21 to 24% by volume of MoSi2.

[0041] According to one example, the conductive phase based on MoSi2 particles further comprises between 0% and 2% by weight of carbon.

[0042] According to one example, the surface of the semiconductor ceramic is vitrified.

[0043] According to one example, the conductive phase based on MoSi2 particles further comprises 1% by weight of an element selected from Al, Ta, Ti, Zr, Y and B.

[0044] According to one example, the ceramic further comprises 0.1 to 0.9% by weight of lanthanide compound.

[0045] According to one example, the voltage applied to generate the plasma has a non-zero value less than 10 kV and preferably 6 kV.

[0046] According to one example, the injection electrode has, on at least a portion of the assembly, a tip configuration also referred to as a tip electrode. The tip configuration of the injection electrode promotes electrical discharges in the erratic regime, in synergy with the nature of the separator material as well as the electrical signal and the geometry of the electrodes.

[0047] According to one example, the device is more particularly configured to make the homogeneous and erratic discharge regimes coexist temporally or spatially during the generation of the plasma.

[0048] According to one example, the separator material has a cylindrical shape extending in a main extension direction of the assembly, and: on a first portion of the assembly, the electrode connected to ground and the injection electrode together form a coaxial structure on either side of the separator material, around the main extension direction of the assembly, on a second portion of the assembly, distinct from the first portion, the electrode connected to the ground extends coaxially to the main extension direction of the assembly around the separator material, and the injection electrode has a tip configuration arranged in an interior volume defined by the separator material.

[0049] In the first portion, the plasma is generated in the homogeneous regime. In the second portion, the plasma is generated mainly in the erratic regime. The assembly thus has two treatment zones in which the two regimes coexist and are spatially separated. The gas phase thus passes through the first portion and the second portion to be treated successively by discharges according to the two regimes, in order to maximize the degradation of the compounds to be treated.

[0050] According to one example, the first portion is arranged upstream of the second portion, according to the direction of circulation of the gas phase in the assembly.

[0051] According to one example, the first portion and the second portion are separated by an intermediate portion, the assembly being configured so that under the application of the electrical voltage, a plasma is generated only in the first and second portions. The intermediate portion makes it possible to increase the spatial separation between the first and second portions. Thus, the by-products generated by the treatment plasma in one of these portions, and preferably in the first portion, can react with each other before the treatment is finalized in the other portion, preferably the second portion.

[0052] Depending on the volume constraint associated with the device, it is also possible to provide that the first and second portions are directly juxtaposed, in order to limit the size of the device.

[0053] According to one example, the separator material has a first face and a second face opposite the first face, the injection electrode and the grounded electrode are arranged on the first face of the separator material, the injection electrode and the grounded electrode being arranged at a distance from each other. The assembly can thus have a planar geometry, the electrodes being arranged on the same face of the separator material. This geometry allows the generation of plasma discharges according to the two homogeneous and erratic regimes. These two regimes can coexist spatially. The assembly thus has a treatment zone in which the two regimes coexist and follow each other temporally. The gas phase thus passes through the treatment zone and is successively treated by discharges according to the two regimes, in order to maximize the degradation of the compounds to be treated.

[0054] According to one example, on the second face of the separator material, at least one injection electrode and at least one grounded electrode are further arranged at a distance from each other. The planar geometry of the assembly thus makes it possible to functionalize the two faces of the separator material by the electrodes. The compactness of the device is further improved.

[0055] According to one example, the injection electrode and the grounded electrode each have a facing tip configuration between the injection electrode and the grounded electrode. This makes it possible to promote a surface discharge rather than a volume discharge.

[0056] According to one example, the grounded electrode has a first face comprising at least one opening leaving the separator material visible, at least one injection electrode being arranged in the at least one opening and extending from the separator material in an oblique direction, preferably perpendicular, to the first face of the grounded electrode. This geometry can be described as a “tip / surface plane”. An advantage of this geometry is to promote the quantity of plasma generated.

[0057] According to one example, the assembly is connected to a power supply module configured to power the assembly with a pulsed electrical voltage signal. The pulsed signal makes it possible to apply a pulsed voltage to generate the plasma. This type of current is compatible with all assembly geometries.

[0058] According to one example, the assembly is connected to a power module configured to power the assembly with an alternating voltage signal. An alternating signal is cheaper and easier to implement in use. The design of the device is therefore simplified and its cost reduced. For this, it is preferable that the electrodes are arranged on the same face of the separator material.

[0059] According to one example, the device comprises a plurality of assemblies stacked in at least one direction perpendicular to a main extension direction of the assembly. The plurality of assemblies makes it possible to increase the quantity of the gas phase treated, while reducing the dead volume between the assemblies to increase the compactness of the device.

[0060] According to one example, the voltage applied to generate the plasma has a non-zero value less than 10 kV, between 3 and 6 kV. The voltage applied to generate the plasma is thus reduced compared to that generally used in DBD devices, typically greater than or equal to 20 kV.

[0061] According to one example, in the device, the gas phase is at atmospheric pressure.

[0062] In the remainder of the description, the term “on” does not necessarily mean “di directly on”. Thus, when we indicate that a part or organ A is supported “on” a part or organ B, this does not mean that the parts or organs A and B are necessarily in direct contact with each other. These parts or organs A and B can be either in direct contact or be supported on each other through one or more other parts. The same applies to other expressions such as, for example, “A acts on B”, which can mean that “A acts directly on B” or that “A acts on B through one or more other parts”.

[0063] In the detailed description which follows, use may be made of terms such as "horizontal", "vertical", "longitudinal", "transverse", "upper", "lower", "top", "bottom", "front", "rear", "inside", "outside". These terms must be interpreted relatively in relation to the normal position of use of the device, and more particularly the direction of circulation of the gas phase in the device and the assembly. For example, the notion of "longitudinal" corresponds to the main direction of extension of the assembly, a direction which is substantially parallel to the direction of circulation of the gas phase in the assembly.

[0064] A reference will also be used whose longitudinal or rear / front direction corresponds to the x axis, the transverse or right / left direction corresponds to the y axis and the vertical or down / up direction corresponds to the z axis.

[0065] The device 1 for treating a gas phase 2 is now described according to several exemplary embodiments with reference to the figures.

[0066] As illustrated in [Fig.l], the device 1 is configured such that a gas phase 2 to be treated flows into the device 1. The gas phase 2 may comprise suspended species 20, and in particular polluting species, for example VOCs, and / or microorganisms such as bacteria, fungi and / or their spores, viruses, particles. In order to degrade these species 20, the device 1 comprises a body 10 through which the gaseous phase 2 circulates. For this, the device may comprise a suction module 14 of the gaseous phase 2, for example a fan. The device 1 therefore comprises an air circulation circuit from an inlet of the body 10 to an outlet of the body 10, not shown in the figures.

[0067] The device 1 comprises at least one assembly 11 of electrodes. Each assembly 11 comprises at least one injection electrode 110 and at least one electrode 111 connected to the ground 12 of the device 1, hereinafter referred to as the grounded electrode 111, as illustrated by FIGS. 4 to 6 described in more detail later. The assembly 11 is configured so that, under the application of an electrical voltage, a plasma is generated between the injection electrode 110 and the grounded electrode 111. This voltage may be more particularly applied by a power supply module 13 connected to the electrodes 110, 111. The power supply module 13 may be configured to supply the device 1, and more particularly the assembly 11, with an electrical current, allowing the application of this voltage.

[0068] During its circulation in the device 1, the gaseous phase 2 comprising the species 20 to be treated circulates in the assembly 11. The plasma 3 generated in the assembly acts on the species 20 causing their degradation. The gaseous phase 2' at the outlet of the device 1 can thus be considered as depolluted or decontaminated, that is to say the quantity of species 20 is at least reduced, preferably the species 20 are eliminated.

[0069] The injection electrode 110 and the grounded electrode 111 are separated by a separator material 112. In conventional DBD devices, this separator material 112 is an electrical insulator. In the device 1, the separator material 112 exhibits electrically insulating behavior when it is subjected to a certain electrical voltage lower than a threshold voltage, hereinafter designated the trigger voltage Vo. When the separator material 112 is subjected to an electrical voltage greater than or equal to the trigger voltage Vo, it exhibits electrically conductive behavior allowing the passage of an electric current.

[0070] This separator material 112 therefore has a non-linear electrical resistance (the U / I ratio is not constant). Below the trigger voltage Vo, it has a high impedance and therefore a very low leakage current, and preferably a zero leakage current. Above the trigger voltage Vo, the material 112 has a lower impedance and allows the passage of a higher leakage current. In other words, beyond the trigger voltage Vo, the impedance of the separator material 112 drops to allow electrical conduction in the form of a leakage current. When the voltage returns to a level below the trigger voltage, the impedance increases again to return to its initial value. The transition can be abrupt when switching from insulator / conductor behaviors but also from insulator / low leakage current / conductor behaviors. The wider the transition zone (i.e., voltage range), the more the weakly mixed homogeneous regime exists.

[0071] It is therefore understood that the separating material 112 can pass from one behavior to the other and vice versa depending on the applied voltage, unlike an insulator which is destroyed beyond its breakdown voltage and which can no longer regain insulating behavior when the voltage drops.

[0072] These electrical behaviors of the separator material 112 can be observed thanks to the assembly 4 illustrated in [Fig.2], in which a power source 40 supplies an electrical circuit connected to the separator material 112. The electrical circuit comprises a voltmeter 41 connected in shunt to the separator material 112 and an ammeter 42 connected in series to the circuit. It is thus possible to measure the voltage across the separator material 112 and the intensity of the current passing through it. In this assembly 4, the material 112 can be held between two electrodes (for example two solid brass discs) by a system of springs and coated with conductive paste for better electrical contact. [Fig.3] is a graph representing the intensity (I) of the current 5 as a function of the voltage 6 (V) across the separator material, for an insulator 7 and for three examples of separator material 112a, 112b, 112c.

[0073] At the breakdown voltage, the insulator 7 is destroyed and no longer exhibits insulating behavior. When they are subjected to a voltage greater than the breakdown voltage Vo, the separator materials 112a, 112b, 112c change from an insulating behavior where the current I is very low, or even zero, to a more conductive behavior in which the current I increases with the voltage across the terminals of the material, a leakage current then being measurable. This increase can be sudden or more or less gradual as illustrated by the three curves 112a, 112b, 112c. The shape of this increase can influence the nature of the different non-thermal plasma regimes generated during the use of the device 1, among a homogeneous regime, a mixed regime or an erratic regime (also called an energetic regime).

[0074] The starting voltage may be between 1 kV and 10 kV, preferably between 3 kV and 6 kV. This type of value allows efficient and controlled operation, in combination with a 50 Hz AC type signal, an electroceramic material and a surface type geometry.

[0075] Generally speaking, a person skilled in the art will know how to adapt the value of the trigger voltage according to the nature of the signal, the nature of the material and the geometry for the intended application.

[0076] The geometry defines in particular the shape of the electrodes, the placement of the electrodes relative to the separator material, the inter-electrode gap, the stacking or arrangement of the cells.

[0077] The person skilled in the art will be able to adapt the variable parameters without any difficulty to obtain the desired effect. In particular, he will be able to adapt the nature of the signal (for example for a pulsed signal: its shape, its rising edge, its duration, its value), its frequency, the geometry and the placement of the electrodes (in particular the distance also referred to as the inter-electrode "gap"). Naturally, the reactor will also be sized in relation to the desired end use in terms of flow rate.

[0078] Thanks to these electrical behaviors of the separator material 112, when an electrical voltage is applied to the assembly 11, a cold plasma can be obtained by charges according to two main regimes: the homogeneous surface regime by discharge in the insulating behavior or an energetic multifilamentary volume regime by discharge in the conductive behavior, or even a mixed regime.

[0079] The energy regime is not accessible with insulators in conventional DBD devices. This regime makes it possible, in synergy with the homogeneous regime, to improve the degradation of species 20 and to extend the number of species 20 that can be treated by plasma. For example, certain VOCs are more efficiently degraded by a plasma in a homogeneous regime, such as for example sulfides, aromatic compounds, and halogenated VOCs. The treatment of VOCs in a plasma in a homogeneous regime can further generate ozone and / or harmful reaction by-products.

[0080] During the development of the invention, it was observed that a complementary treatment to a homogeneous plasma 3 by a plasma 3 in an energetic regime makes it possible to limit, and preferably to eliminate, the residual ozone as well as the reaction by-products as well as to obtain a better selectivity in CO2. This complementary treatment also makes it possible to degrade molecules which would not have been degraded by a plasma 3 discharge in a homogeneous regime, too low in energy, and in particular ketones or even acids.

[0081] Furthermore, the minimum voltage to be applied to generate a plasma 3 is lowered compared to a conventional DBD device thanks to the separator material 112. The discharges are also more efficient, which makes it possible to reduce the degradation time of the species 20.

[0082] Furthermore, the coexistence of plasma discharges 3 in homogeneous regime and plasma discharges 3 in energetic regime allows an aggregation of the particles possibly present in gas phase 2, in the manner of an electrostatic filter. It is therefore possible to trap the particles at the outlet of the device 1, for example by adding a filter. The deposits inside the device 1 are reduced, which limits the fouling of assembly 11 and / or the risk of short circuit.

[0083] The device 1 can be used in a method for treating a gaseous phase 2. This gaseous phase 2 can be indoor air, for example inside a building, or else an industrial waste gaseous phase.

[0084] The gaseous phase 2 can be introduced into the assembly 11, for example by suction through the suction module 14. The suction module is sized in relation to the treatment capacity of the device, which is itself sized according to the need for treatment of the gaseous phase. For example, for the treatment of the air in a 30 m2 room, a flow rate of 250 Nm3 / h is desirable.

[0085] The electrical voltage can be applied to the assembly 11 to generate a plasma 3 between the injection electrode 110 and the grounded electrode 111 to treat the gas phase 2. The voltage applied to generate the plasma 3 can have a non-zero value of less than 10 kV, for example between 3 and 6 kV.

[0086] According to one example, the gas phase 2 is introduced continuously into the device 1. The plasma treatment 3 can also be carried out continuously. Alternatively, it can be provided that the plasma treatment is carried out discontinuously or non-constantly. For example, it can be provided that the activation of the treatment and / or its flow rate are controlled according to the pollution of the gas phase to be treated. For this, it is possible to provide sensors arranged to measure a parameter relating to the pollution or contamination of the gas phase. The control is a function of these measurements. Thus, according to this control, the volume of gas phase 2 sucked in can then be treated by successive volumes.

[0087] Particular examples of separator material

[0088] The separator material 112 is now described according to several exemplary embodiments.

[0089] The separator material 112 can be chosen from: - a semiconductor material, for example a semiconductor ceramic, such as for example SiC, ZnO or GaN, - a semiconductor polymer, - a composite material comprising conductive or semi-conductive particles dispersed in an insulating matrix.

[0090] The composite material may, in one example, comprise conductive or semiconductive particles dispersed in an insulating matrix. The insulating matrix may be based on or made of a polymer or a ceramic, for example. The conductive or semiconductive particles may be based on or made of a metal, a metal alloy, or a ceramic. For example, the composite material may be a polymer / metal, polymer / ceramic, a cermet (ceramic / metal), or ceramic / intermetallic.

[0091] The separator material may have a certain porosity. This porosity in the material has the advantage of improving the performance of the device. This porosity is preferably greater than or equal to 10%. Preferably this porosity is between 10% and 30%.

[0092] It is also possible to provide for the porosity to be zero or low.

[0093] In the following, a particular example is described without limitation, in which the separator material 112 is a composite semiconductor ceramic, composed of an insulating phase and a conductive phase.

[0094] The operating mechanism of current semiconductor ceramics based on Sialon and SiC is based on the intrinsic properties of one of the constituents of the ceramic (surface conduction of the SiC added to open porosity).

[0095] The composite ceramic is formed from a conductive phase included in an insulating matrix. This makes it possible to obtain a globally semiconducting material with a microstructure of the same type as Sialon and SiC-based semiconducting ceramics (grain boundaries, defects, etc.) and optimal thermomechanical properties.

[0096] The priming process then no longer depends on the intrinsic properties of one of the constituents and the microstructure of the surface, but on the material in its global approach.

[0097] In order for the injected charges not to be conducted through the volume of the ceramic, the implantation of the charges must take place at a speed greater than the conduction speed translated by the relaxation time which characterizes the return to equilibrium after interruption of the field.

[0098] In the presence of conductive grains surrounded by insulating grain boundaries, the charges are trapped on the surface of the grains, thus inducing a curvature of the valence and conduction bands with the formation of a double Schottky barrier. The grain boundaries are in fact comparable to two back-to-back Schottky diodes. Since trapping induces a space charge, there is therefore a field gradient followed by a relaxation of this space charge, this relaxation depending on the carrier transit time and the thickness of the insulator. The greater the thickness of the insulator, the greater the relaxation time and the higher the "breakdown" (in fact conduction) voltage.

[0099] Conduction in the ceramic according to this example is controlled by several mechanisms: - first of all, at the ceramic interfaces: the Schottky emission (the increase in electronic emission when the applied electric field increases is due to the decrease in the extraction work), which determines the quality of the injection and which is strongly correlated with the quality of the contacts and the field emission; - then, in the mass of the ceramic: the Poole-Frenkel effect (trapping / detrapping) and the hopping effect (conduction by jump).

[0100] The Fowler-Nordheim tunneling effect and space charge also participate in conduction both at interfaces and in the bulk.

[0101] The constraint is now carried by the capacity of the material to resist severe environmental constraints.

[0102] The materials that can be considered for the conductive phase can be GaN, MoSi2, HfB2, TiB2, ZrB2 or even TiN.

[0103] Properties of these materials are given in the following table.

[0104] [Tables 1] GaN MoSi2 HfB2 TiB2 ZrB2 TiN Vickers Hardness (MPa) / MOHS 1 8700-920 0 3000 2300 2300 Thermal Conductivity (W.m'.K1) 1.3 90 Coefficient of Thermal Expansion 106 K1) 3.17 6.8 5-7 7.8 5.9 8-8.5 Resistivity (Q.cm) 2.106 2.2.105 105 7.106 6.106 50.106 Melting Temperature (°C) 2500 2020 3380 3225 3245 2950

[0105] Molybdenum disilicide (MoSi2) can be an advantageous material for producing the conductive phase due to its intrinsic qualities but also due to its ability to resist oxidation.

[0106] The advantages induced by the use of a MoSi2 base for the conductive phase are that MoSi2 has a high melting temperature (2030°C), that MoSi2 has a high resistance to oxidation up to 1600°C, that MoSi2 has a high thermal conductivity 50 WMK, and that MoSi2 is thermodynamically stable.

[0107] When two phases of different electrical conductivities are mixed, the resulting compound is likely to have a very wide range of conductivity values. The conductive grains of MoSi2 behave as connections between capacitors whose dielectric is formed by TAI2O3.

[0108] Near the critical region, only a few percolating beam paths remain, the role of capacitors thus becoming very important. With a microstructure having large alumina "packets" which are the capacitors governing the conduction mechanism, and which are too large to allow the passage of charges by tunneling, the charges remain trapped in the alumina and conduction remains very limited.

[0109] Conversely, when the conductive particles are small and above all well dispersed, the percolation threshold is lowered and there is instantaneous conduction as soon as a voltage is applied, the inter-particle distance having been greatly reduced.

[0110] Two micro structures of the same compositions can thus present com completely different behaviors depending on the arrangement of the two phases and it is therefore necessary to have a compromise between the two extreme cases where the MoSi2 grains percolate and that where none are in contact.

[0111] Therefore, the micro structure according to the invention is a homogeneous distribution of the MoSi2 particles in the alumina matrix (by particle we mean grain or cluster of grains from 15 nm to 5 qm), this in order to allow the passage of charges by tunnel effect, to compensate for the tearing off of too large MoSi2 particles which would cause a break in the conduction process by distant percolation and to obtain satisfactory mechanical properties.

[0112] The presence of a "conductive particle size gradient" within the insulating matrix makes it possible to obtain the expected overall electrical effect (totally insulating then conductive behavior of the material). The particle size distribution is done, for example, according to the following diagram: - “small particles”: average diameter less than 240 nm (19.5 to 24% of particles of the conductive phase); - “medium particles”: average diameter of 240 nm to 1 pm (45.5 to 56% of particles of the conductive phase); - “large particles”: average diameter of 1 pm to 11 pm (20 to 35% of particles of the conductive phase).

[0113] In order not to obtain a conductive material as soon as the voltage is applied, it is preferable, for the same conductor / insulator ratio, to limit the passage of charges (no contact, no uniformly small inter-particle distances); this is why this particle size gradient is important.

[0114] In order to delay conduction, large particles are used, few in number and far from each other.

[0115] The probability of tunnel transfer decreases with the interparticle distance; when large particles are present, it is preferable to compensate for these distances by defects in the inter-particle zone or by the presence of small particles which ensure conduction always without contact but by tunnel effect made easier by the smaller inter-particle distances.

[0116] The medium particles are of "intermediate" use, they ensure conduction once it is established (and can play the role of either the large particles or the small ones depending on where they are located) and allow the material to be homogenized.

[0117] The expected microstructure is therefore grains as well as agglomerates of MoSi2 grains (of controlled sizes) distributed uniformly in the matrix.

[0118] It will be noted that, when the alumina grain size is reduced, the number of grain boundaries is increased and thus the number of trapping regions is extended, with conduction increasing; the size of the alumina grains is therefore also a factor to be controlled.

[0119] We therefore propose a semi-conductor ceramic comprising: - 5 to 40% by volume of a particulate conductive phase, preferably MoSi2 particle base; - 60 to 95% by volume of a particulate insulating phase, the particle size of the conductive phase being between 5 nm and 10 qm, and the distance between two neighboring particles of conductive phase being between 0.1 and 10 qm.

[0120] Preferably, a semi-conductor ceramic is proposed comprising: - 10 to 30% by volume of a conductive phase based on MoSi2 particles, - 70 to 90% by volume of a particulate insulating phase, the particle size of MoSi2 being between 15 nm and 5 qm, and the distance between two neighboring particles of MoSi2 being between 0.1 and 6 qm. In the context of the present invention, the term “particle” means a grain or an aggregate / cluster of grains.

[0121] The measurement method used to measure the size of MoSi2 particles includes scanning electron microscope observation of the fracture facies of broken samples. The images are then reprocessed using ESIVISION AnalySIS 3.2 software. The average diameter of the MoSi2 particle is obtained.

[0122] Advantageously, the semiconductor ceramic may comprise 15 to 25% by volume of MoSi2 and preferably 21 to 24% by volume of MoSi2.

[0123] According to the present invention, a “conductive phase based on MoSi2 particles” is understood to be essentially consisting of these particles. However, it may include other constituents such as carbon, boron or different metals.

[0124] Preferably, the conductive phase according to the invention comprises more than 90% of MoSi2 particles, more preferably more than 95%, even more preferably- potentially more than 97% MoSi2.

[0125] In an alternative embodiment of the ceramic according to the invention, the conductive phase in MoSi2 comprises between 0.1% and 3% by mass (of the total mass of insulating phase + conductive phase) of a simple element (C, B, etc.) or of a rare earth. An advantage of the introduction of carbon (boron or rare earth) is to improve the mechanical properties of the conductive phase in MoSi2.

[0126] The insulating phase can be made from AI2O3, Si3N4, mullite (2 SiO2, 3 AI2O3), or even ALON.

[0127] Properties of these materials are given in the following table.

[0128] [Tables2] AI2O3 Si3N4 mullite ALON Mohs / Vickers hardness (MPa) 9 1580 7.5 Thermal conductivity (W.m'.K1) 26-35 15-43 3-5 2.5 Coefficient of thermal expansion 106 K1) 6.7-9 3 5-6 2-3 Resistivity (Q.cm) 1014 1012-1015 1010-1013 1011-1014 Melting temperature (°C) 2050 1900 1880 1470

[0129] In one embodiment of the ceramic according to the invention, the insulating phase of the ceramic is made from Si3N4. Indeed, this material has greater hardness, greater thermal conductivity and greater resistivity than AI2O3, mullite and ALON.

[0130] In another embodiment of the ceramic according to the invention, the insulating phase is made from AI2O3.

[0131] Indeed, alumina (AI2O3) has a high electrical resistivity, excellent resistance to aging at temperatures above 1400°C and good resistance to chemical attacks. Furthermore, an advantage of a composite of MoSi2 and AI2O3 for the conductive and insulating phases of the ceramic is that these two materials have similar expansion coefficients, so as to reduce the thermal stresses between these two materials. Advantageously, the particle size of the insulating phase can be between 0.3 and 3 pm.

[0132] The measurement method used to measure the particle size of the insulating phase includes observation of the fracture surface of broken samples using a scanning electron microscope. The images are then reprocessed using ESIVISION AnalySIS 3.2 software. The average particle diameter of the insulating phase is obtained.

[0133] The separator material may have a certain porosity. This porosity is an open porosity, the pores being accessible from the external face of the material. This porosity in the material has the advantage of improving the performance of the device. This porosity is preferably greater than or equal to 10%. Preferably this porosity is between 10% and 30%. It is also possible to provide for the porosity to be zero or low.

[0134] This porosity value depends on the technique used to produce the ceramic. For example, if natural sintering is used to produce the ceramic, the average porosity is less than or equal to 10%. If hot press sintering (HP) is used, the average porosity of the ceramic is less than or equal to 2%. Finally, if current-assisted sintering (SPS) is used, the average porosity of the ceramic is less than or equal to 3%. All of these sintering techniques will be described in more detail below.

[0135] However, in the event that the ceramic comprises open porosities, the surface of the semiconductor ceramic can be vitrified. This makes it possible to minimize the so-called "Pest" phenomenon which can lead to the disintegration of the semiconductor ceramic. Vitrification of the surface of the semiconductor ceramic therefore makes it possible to improve the strength of the ceramic.

[0136] According to a variant making it possible to minimize the Pest phenomenon, the conductive phase in MoSi2 can comprise 1% by weight of an element chosen from Al, Ta, Ti, Zr, Y and B. Advantageously, the semiconductor ceramic according to the invention can also comprise 0.1 to 0.9% by weight of lanthanide compound (for example La2O3, or La2B6). A lanthanide (La2O3, LaB6) is a material promoting electronic emission. Thus, its addition, in small quantity, in the semiconductor ceramic makes it possible to reinforce the thermo-emission of the semiconductor ceramic.

[0137] A method of manufacturing the semiconductor ceramic according to this example is now described.

[0138] In order to solve the reliability problems over time of electroconductive ceramics, it is important to develop a material under optimal conditions, to control its microstructure in order to obtain the desired properties. The electrical characteristics depend on the volume percentage of conductive phase and the type of micro structure developed after sintering.

[0139] The production process, the most important parameters of which determine the microstructure and thus the physical characteristics of the sintered samples, is in fact the crucial phase. These parameters concern in particular: the nature of the powders the proportions of the insulating and conductive phases the quantity and composition of the additives the deagglomeration processes the shaping technique the sintering conditions.

[0140] The method of manufacturing a semiconductor ceramic comprises the following steps: preparation of a homogeneous suspension of a conductive phase, for example based on MoSi2 particles, to obtain a first slip, preparation of a homogeneous suspension of a particulate insulating phase to obtain a second slip, mixing the first and second slips to obtain a mixture of the two phases in the desired proportions (i.e. the first slip representing 5 to 40% by volume of the mixture and the second slip representing 60 to 95% by volume of the mixture), drying and sieving the composition; sintering the composition to obtain a ceramic in which the particle size of the conductive phase is between 5 nm and 10 qm, and the distance between two neighboring particles of conductive phase is between 30 Å and 5 qm.

[0141] As described previously, the conductive phase may be selected from the group consisting of MoSi2, TiB2, TiN.

[0142] Furthermore, the insulating phase can be based on alumina AI2O3 or mullite, Si3N4. To prepare the first slip, the conductive phase of MoSi2 is mixed with water with a pH between 8 and 10.

[0143] This makes it possible to improve the homogeneity of the microstructure. To prepare the second slip, the insulating phase is mixed with water of pH equal to 10 containing a dispersant, advantageously a surfactant polymer of the ammonium polymethacrylate type such as DARVAN® C marketed by VANDERBILT. This dispersant makes it possible to avoid the agglomeration of the alumina particles AI2O3II and is advantageously introduced at a level of 0.1% by weight.

[0144] The two slips are then mixed to obtain a mixture of the two phases. The intimate mixing of the two slips is carried out using a turner or ball mill. Grinding time is between 5 and 24 hours.

[0145] The mixture is then dried in an oven for 48 hours. In order to avoid differential sedimentation of the two types of particles, rapid drying by ROTOVAP can be considered. The powder thus obtained is ground in a mortar; then placed with glass beads (diameter 10 mm) in a 250 pm mesh sieve of an electric sieve, the powder passed to 250 pm is poured into a 100 pm mesh sieve containing alumina beads (diameter 3 mm).

[0146] The composite powder thus collected and roughly granulated is ready to be shaped and then sintered. The shaping step is optional. Its implementation depends on the sintering technology used. The shaping step transforms the material into a green product having the controlled size, shape and surface area and the particular density and microstructure. Careful control of the density and microstructure of a green ceramic is necessary to obtain the performance of the final product because the defects introduced by the shaping process are generally not removable by sintering.

[0147] A smooth and even surface is normally desirable and may be essential for some products. The strength must be sufficient to carry out the operations following shaping. Product reproducibility is very important for industrial production. The size and density of the green part must be controlled to maintain a constant shrinkage factor between the green and sintered part.

[0148] For the shaping step, the so-called compaction or dry compaction technology can be used.

[0149] Compaction is a process of shaping powder or granulated material enclosed in a rigid or flexible mold.

[0150] Dry compaction is a widely used process due to its reproducibility and its ability to produce large format parts of various shapes that do not exhibit shrinkage during drying. It preferably comprises the following steps: - (1) filling the matrix; - (2) compaction and shaping; - (3) ejection of the part; - (4) densification.

[0151] The composition is then sintered. Unlike ceramic firing, sintering does not, in principle, involve a bonding of the particles by a glassy phase. The coherence and densification of the pressed powders occur as a result of transformations affecting the surface of the particles and leading to solid-solid interfaces called grain boundaries. The sintering conditions determine the microstructure and therefore the properties of the final material.

[0152] Advantageously, different technologies can be used for sintering the com position. For example, in one embodiment of the method, the sintering is natural sintering. In another embodiment, the sintering is hot press sintering. In yet another embodiment, the sintering is current-assisted sintering (SPS).

[0153] For the implementation of sintering by hot press, the press furnace used is of the Goliath type (Stein Heurtey Physitherm) combining a press (maximum load 20 tonnes) and a graphite resistance furnace (maximum temperature 2200°C) the use of which requires an inert atmosphere or a high vacuum.

[0154] Temperature control is provided by a 5 / 26% tungsten / rhenium thermocouple placed near the resistor and by a bichromatic pyrometer (IRCON®) which measures the actual temperature at the surface of the tool. Hot press (HP) sintering allows 37 mm pellets to be obtained. It does not require any shaping of the pellets.

[0155] Optimal densification of the ceramic is obtained for a temperature between 1600°C and 1700°C (and preferably equal to 1650°C) and a load of 45 MPa. The temperature allowing the best densification / microstructure compromise favorable to the expected electrical behavior to be obtained is 1500°C.

[0156] For the implementation of natural sintering, the same furnace is used as that used for hot pressing. Simply, in this case the samples are placed after the shaping step in a graphite crucible, and are not subjected to a load during sintering.

[0157] In order to limit gas exchanges with the outside, the preformed pellets are placed in an alumina crucible for "bogue cooking", i.e. the use of loose powder of the same nature as the pellets and coating them in order to avoid any contact with the atmosphere of the furnace. Current-assisted sintering (SPS, abbreviated from the English Spark Plasma Sintering) can also be carried out, as described previously. Current-assisted sintering (SPS) makes it possible to densify materials while retaining the characteristics of the initial powders and to densify difficult materials.

[0158] Current-assisted sintering (SPS) is a process similar to conventional hot pressing. The precursors (metals, ceramics, polymers and their composites, etc.) are introduced into a chamber (made of graphite) allowing uniaxial pressure to be applied during sintering.

[0159] The major difference in this method is that the heat source is not external. An electric current (direct - pulsed direct - or alternating) passes through the conductive pressing enclosure and also in appropriate cases through the sample.

[0160] Thus, the enclosure itself acts as a heating source which allows to achieve high heating rates (up to 600 °C / min and more) and good heat transfer to the sample. Sintered objects of very high compactness can be obtained for lower temperatures (a few hundred degrees lower) and especially significantly shorter sintering times (a few minutes) than for conventional methods. Current-assisted sintering (SPS) is an extremely promising technique for improving the shaping of existing materials.

[0161] Densification is increased by the use of a pulsed current or field.

[0162] Particular examples of assemblies 11

[0163] The assembly 11 is now described in more detail according to several exemplary embodiments, with reference to FIGS. 4 to 6.

[0164] Conventional assembly geometries 11 used in DBD devices can be used for device 1 with separator material 112.

[0165] Particular geometries have further been developed. According to one example, at least the injection electrode 110 has, on at least a portion of the assembly 11, a pointed configuration. An electrode with a "point configuration" is understood to mean a configuration in which the electrode forms one or more peak structures, the point-shaped or equivalently peak-shaped end of these structures being arranged opposite the other electrode, for example the grounded electrode 111. By "point" or "peak", it is not necessarily implied that the end is conical; it may be sharp and planar. For example, the electrode may have a brush structure, the ends of the brush being arranged opposite the other electrode, as illustrated in [Fig. 4]. According to another example, the electrode may extend in a main extension direction between two point-shaped ends, as illustrated in [Fig. 5].In another example, the electrode may be in the form of a rod, the ends of the rod forming the pointed structures described above. The pointed configuration of an electrode promotes plasma discharges in the erratic regime, in synergy with the nature of the separator material 112. .

[0166] A first geometry is described with reference to [Fig.4], according to an exemplary embodiment. The assembly 11 extends in a main extension direction x substantially parallel to the flow direction of the gas phase 2 in the assembly 11. The separator material 112 may have a cylindrical shape centered on the main extension direction x, and separate the injection electrode 110 and the electrode connected to the ground 111. By "cylindrical", it is meant that the cross-section of the separator material 112 may have a substantially circular, elliptical or ovoid shape.

[0167] The assembly 11 may have a first portion 11a and a second portion 11b, these portions being distinct from one another. Preferably, the first portion 1 la is located upstream of the second portion 11b according to the direction of flow of the gas phase 2 in the assembly 11.

[0168] In the first portion 11a, the grounded electrode 111 and the injection electrode 110 may together form a coaxial structure centered around the main extension direction x, on either side of the cylindrical separator material 112. Note that the injection electrode 110 may be arranged inside the cylinder formed by the separator material 112, the grounded electrode 111 then being arranged outside the cylinder, or vice versa. This first portion 11a promotes plasma discharges 3 in the homogeneous regime.

[0169] In the second portion 11b, the grounded electrode may extend coaxially to the main extension direction x around the separator material 112. The grounded electrode 111 is then preferably arranged outside the separator material 112. The separator material 112 may delimit an interior volume 1120. The injection electrode 110 may be arranged in this interior volume 1120. The injection electrode 110 has a tip configuration in this volume. For example, the injection electrode 110 may have a brush structure whose tip ends are arranged opposite the separator material 112 and the grounded electrode 111. Preferably, the tip ends are arranged radially opposite the separator material 112, around the main extension direction x. This second portion 11b promotes the generation of plasma discharges in the energy regime.

[0170] In the first and second portions 11a, 11b, the electrode connected to the ground 111 may be in the form of a grid or a plate. In the first portion 11a, the injection electrode 110 may be in the form of a spiral.

[0171] The two portions 11a, 11b being distinct, it is understood that two treatment zones are thus formed: - a first zone in which plasma discharges 3 in homogeneous regime are favored, - a second zone in which plasma discharges 3 in energy regime are favored.

[0172] This geometry is particularly suitable for the degradation of certain VOCs, such as sulfides, which are better degraded by a homogeneous plasma in the first zone. These zones are spatially distinct. Preferably, the gas phase 2 flows into the first zone then into the second zone to be successively treated by a homogeneous plasma then an energetic plasma.

[0173] As illustrated in [Fig.4], the portions 11a, 11b may be separated by an intermediate portion 11e. Preferably, no plasma is generated in the intermediate portion 11e. This intermediate portion 11e serves as a buffer between the generating zones. plasma generation 3. The species generated in the first zone can thus react with each other to continue their degradation before entering the second zone. In particular, the ozone can react with the reaction by-products or the species 20 which have not been degraded in the first zone for their degradation.

[0174] Naturally, the person skilled in the art will know how to adapt the geometry and dimensions according to the final application, and in particular according to the contact time of the plasma with the targeted species, the nature of the targeted species, the flow rate or the volume, etc.

[0175] A second geometry and a third geometry are now described with reference to Figures 5 and 6 respectively. In these two geometries, the separator material 112 has a first face 11a and a second face 112b. The electrodes 110, 111 are arranged on the same face of the separator material 112, at a distance from each other. Electrodes 110, 111 may be arranged on each of the faces of the separator material 112. Thus, the compactness of the device 1 is improved.

[0176] For example, the injection electrode 110 may have a pointed configuration opposite the electrode connected to the ground 111. These geometries allow the generation of plasma discharges according to the two homogeneous and energetic regimes. These two regimes may in particular coexist spatially. The assembly thus has a treatment zone in which the two regimes coexist and follow each other temporally. In these two geometries, the plasma discharge energetic regime 3 may be predominant.

[0177] In the second geometry, the injection electrode 110 and the grounded electrode 111 each have a pointed configuration facing each other. For example, each electrode 110, 111 may extend in a main extension direction, for example the y direction, between two pointed ends. The electrodes 110, 111 are arranged such that at least one end of each injection electrode 110 faces one end of a grounded electrode 111.

[0178] The assembly 11 may comprise several injection electrodes 110 and several grounded electrodes 111. The injection electrodes 110 may be arranged in one or more rows in a direction substantially parallel to the direction x of flow of the gas phase 2 in the assembly 11. The grounded electrodes 111 may also be arranged in one or more rows in a direction substantially parallel to the direction x of flow of the gas phase 2 in the assembly 11. A row of injection electrodes 110 may be spaced by a distance d from a row of grounded electrodes 111. The distance d may be chosen so as to favor a particular plasma discharge regime. This is particularly the case when the assembly 11 is powered by a pulsed signal, as described in more detail later. The distance d is for example between 3 and 25 mm, preferably between 10 and 15 mm.

[0179] In the third geometry, the separator material 112 may be at least partly covered by the grounded electrode 111. The grounded electrode 111 then has an upper face 111a comprising openings 1110 leaving the separator material 112 visible. The injection electrode 110 may extend from the opening 1110. The injection electrode 110 preferably extends from a first face 112a of the separator material 112, being in contact with the latter. The injection electrode 110 may extend in an oblique direction, and preferably perpendicular, to the first face 11a of the grounded electrode 111.

[0180] According to one example, the grounded electrode 111 has several openings 1110, and an injection electrode 110 is arranged at each opening 1110.

[0181] The injection electrode 110 may be in the form of a rod, a first end of which is mounted on, preferably directly on, the separator material 112. The second end of the injection electrode 110 may be connected, preferably directly, to the power supply module 13.

[0182] In each of the geometries described, the injection electrode 110 may be connected directly or via another element, such as another injection electrode 110 or a conductive element, to the power supply module 13.

[0183] For each of the geometries described, the power supply module 13 configured to power the assembly 11 can power it with a pulsed electric current. This pulsed electric current comprises phases of application of the current interspersed with phases during which no current is applied. The electrical signal powering the assembly 11 is therefore discontinuous. The voltage applied to the assembly is thus pulsed and may be positive or negative. A phase of application of the current, preferably each phase of application of the current, may have a duration less than or equal to 1 ps, for example substantially equal to 500 ns. A pulsed electric current has the advantage of being able to more easily modulate the nature of the plasma discharge regime obtained.

[0184] For the second and third geometries, the power supply module 13 can power the assembly 11 with an alternating electric current (abbreviated AC). An AC power supply requires that the electrodes 110, 111 be arranged on the same face of the separator material 112. This type of power supply is less expensive and simpler to implement, which simplifies the design of the device 1 and reduces its cost. An AC electrical signal also makes it possible to further lower the voltage to be applied to obtain a plasma discharge. For example, the AC electrical signal has a frequency of 50 Hz. As an example, a plasma has been obtained with an AC signal. from 50 Hz to only 3 kV (compared to 20 kV for conventional DBD devices), with an interelectrode distance of 10 to 15 mm for the second geometry.

[0185] Note that it may be provided that the device 1 is configured so as to be supplied with both pulsed current and alternating current. This may in particular make it easier to spatially separate one or more plasma discharge zones in a homogeneous regime and one or more plasma discharge zones in an energetic regime. For this, the device 1 may comprise several assemblies 11, a portion of these assemblies 11 being supplied with pulsed current and the other portion being supplied with alternating current. Alternatively or in addition, for an assembly 11, and in particular for the second and third geometries, a portion of the injection electrodes 110 may be supplied with pulsed current and the other portion may be supplied with alternating current.

[0186] The device 1 preferably comprises several assemblies 11. These assemblies can be stacked so as to maximize the number of assemblies 11 and reduce the total volume of the device 1, in order to minimize its bulk. For this, the assemblies 11 can be stacked in a direction perpendicular to their main direction of extension x, for example the z direction or the y direction, or in two directions y, z perpendicular to the x direction. As illustrated in FIGS. 7, 8A and 8B, the assemblies of planar geometry can be stacked for example in the z direction. The device 1 can thus have a rectangular shape as illustrated in [Fig.7], or cylindrical as illustrated in [Fig.8A] and 8B. As illustrated in [Fig.9], the assemblies of cylindrical geometry can be stacked in the y and z directions to form a compact stack.

[0187] The device 1 may comprise assemblies 11 of different geometries, depending on the size, the flow rate of gas phase 2 to be treated, and / or the type of pollution to be treated.

[0188] Examples of VOC treatments

[0189] As an example, the degradation of two VOCs was measured with an assembly 11 having a conventional tip / plane geometry, therefore in volume, with a distance between electrodes of 4 mm. The applied signal is a positive pulsed square signal. The separator material 112 is a semi-conducting ceramic according to the particular example described previously. These measurements were compared with an assembly of a conventional DBD reactor comprising either an alumina separator material 7a or a glass separator material 7b. These graphs represent the percentage of destruction 8 of the VOC as a function of the voltage applied to generate the plasma (V in kV). In [Fig.lOA], the gas phase 2 comprises ethylene at an initial concentration of 500 ppm. In [Fig.lOB], the gas phase 2 comprises isopropanol at an initial concentration of 500 ppm. In both cases, the VOCs are degraded at a lower voltage than that required to generate the plasma for conventional DBD device assemblies. In addition, higher degradation percentages are achieved for both VOCs for assembly 11 including the semiconductor ceramic.

[0190] The assembly 11 described above was tested on many other VOCs, for example, a gas phase containing 3000 ppm of a mixture of 32 sulfur compounds was treated, which represents a very high concentration. A total VOC degradation rate of 75% was achieved.

[0191] In view of the above description, it appears clearly that the invention proposes a device improving the treatment of a gaseous phase by plasma, and in particular air.

[0192] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention. The present invention is not limited to the examples previously described. Many other variant embodiments are possible, for example by combining features previously described, without departing from the scope of the invention. In addition, the features described in relation to one aspect of the invention may be combined with another aspect of the invention. In particular, the device may comprise any feature allowing the implementation of a step of the method and the method may comprise any step resulting from the implementation of a feature of the device.

Claims

Claims

1. Device (1) for treating a gaseous phase (2) comprising at least one assembly (11) of electrodes comprising at least one so-called injection electrode (110) and at least one electrode (111) connected to a ground (12) of the device (1), separated by a material called "separating material" (112), the assembly (11) being configured so that, under the application of an electrical voltage, a plasma (3) is generated between the at least one injection electrode (110) and the at least one electrode connected to the ground (111), and in which the separator material (112) has an electrically insulating behavior when the separator material (112) is subjected to an electrical voltage lower than a threshold voltage, called "starting voltage", and an electrically conductive behavior allowing the passage of a current when the separator material (112) is subjected to an electrical voltage greater than or equal to the voltage priming,and characterized in that the separator material (112) is a composite material comprising conductive or semiconductive particles dispersed in an insulating matrix, the insulating matrix being based on or made of a material selected from the group consisting of a polymer and a ceramic, and the conductive or semiconductive particles being based on or made of a material selected from the group consisting of a metal, an intermetallic, a metal alloy, a ceramic.,

2. Device (1) according to the preceding claim, in which the injection electrode (110) has, on at least a portion of the assembly (11), a pointed configuration.

3. Device (1) according to the preceding claim, in which the separator material (112) has a cylindrical shape extending in a main extension direction (x) of the assembly (11), and: • on a first portion (11a) of the assembly (11), the grounded electrode (111) and the injection electrode (110) together form a coaxial structure on either side of the separator material (112), around the main extension direction (x) of the assembly (11), • on a second portion (11b) of the assembly (11), distinct from the first portion (11a), the grounded electrode (111) extends coaxially with the main extension direction (x) of the assembly (11) around the separator material (112), and the injection electrode (110) has a tip configuration disposed in an interior volume (1120) defined by the separator material (112).

4. Device (1) according to the preceding claim, wherein the first portion (11a) and the second portion (11b) are separated by an intermediate portion (11c), the assembly (11) being configured so that under the application of the electrical voltage, a plasma (3) is generated only in the first (11a) and second (11b) portions.

5. Device (1) according to claim 2, wherein the separator material (112) has a first face (112a) and a second face (112b) opposite the first face (112a), the injection electrode (110) and the grounded electrode (111) are arranged on the first face (112a) of the separator material (112), the injection electrode (110) and the grounded electrode (111) being arranged at a distance from each other.

6. Device (1) according to the preceding claim, in which, on the second face (112b) of the separator material, at least one injection electrode (110) and at least one electrode connected to ground (111) are further arranged at a distance from each other.

7. Device (1) according to any one of the two preceding claims, in which the injection electrode (110) and the grounded electrode (111) each have a facing point configuration between the injection electrode (110) and the grounded electrode (111).

8. Device (1) according to either of Claims 5 and 6, in which the grounded electrode (111) has a first face (111a) comprising at least one opening (1110) leaving the separator material (112) visible, at least one injection electrode (110) being arranged in the at least one opening (1110) and extending from the separator material (112) in a direction oblique to the first face (111a) of the grounded electrode (111).

9. Device (1) according to any one of the preceding claims, wherein the assembly (11) is connected to a power supply module (13) configured to power the assembly (11) with a pulsed electrical signal.

10. Device (1) according to any one of claims 5 to 8, wherein the assembly (11) is connected to a power supply module (13) configured to power the assembly (11) with an alternating electrical signal.

11. Device (1) according to any one of the preceding claims, in which the separator material (112) has a non-zero average porosity and preferably greater than or equal to 10%, and preferably between 10% and 30%.

12. Device (1) according to any one of the preceding claims, comprising a plurality of assemblies (11) stacked in at least one direction perpendicular to a main extension direction (x) of the assembly (11).

13. Method for treating a gaseous phase (2) using the device (1) according to any one of the preceding claims, and comprising: • introducing the gaseous phase (2) into the at least one assembly (11) of electrodes, • applying an electrical voltage to the assembly (11) so as to generate a plasma between the at least one injection electrode (110) and the at least one electrode connected to ground (111) to treat the gaseous phase (2).

14. Method according to the preceding claim, in which the voltage applied to generate the plasma has a non-zero value of less than 10 kV and preferably 6 kV.

15. A method according to any one of the two preceding claims, wherein, in the device (1), the gas phase (2) is at atmospheric pressure.

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