# US 8,784,949 B2 · Remote non-thermal atmospheric plasma treatment of temperature sensitive particulate materials and apparatus therefore > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,784,949 B2 - Document ID: US8784949B2 - Status: Granted - Kind: B2 - Application number: 12/808,898 - Filed: 2008-12-17 - Published: 2011-02-17 - Granted: 2014-07-22 - Earliest claimed: 2007-12-20 - Assignees: Eidgenossische Technische Hochschule Zurich - Applicants: Patrick Reichen; Axel Sonnenfeld; Philipp Rudolf Von Rohr - Inventors: Patrick Reichen; Axel Sonnenfeld; Philipp Rudolf Von Rohr - Web page: https://patentgrep.com/patent/US8784949B2 ## CPC - H05H 1/42: with provisions for introducing materials into the plasma, e.g. powder or liquid {(arc stabilising or constricting arrangements H05H1/3405; coaxial protecting fluids H05H1/341)} - C23C 4/134: Plasma spraying - H05H 1/2406: {using dielectric barrier discharges, i.e. with a dielectric interposed between the electrodes} - H05H 1/2437: {Multilayer systems} - H05H 1/466: {using capacitive coupling means, e.g. electrodes} - H05H 1/47: {using corona discharges} - H05H: PLASMA TECHNIQUE (apparatus or processes specially adapted for producing X-rays H05G2/00); PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS - C23C: COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL (making metal-coated products by extrusion B21C23/22; covering with metal by connecting pre-existing layers to articles, see the relevant places, e.g. B21D39/00, B23K; metallising of glass C03C; metallising mortars, concrete, artificial stone, ceramics or natural stone C04B41/00; enamelling of, or applying a vitreous layer to, metals C23D; treating metal surfaces or coating of metals by electrolysis or electrophoresis C25D; single-crystal film growth C30B; by metallising textiles D06M11/83; decorating textiles by locally metallising D06Q1/04) ## Abstract The present invention relates to a novel process for the remote plasma surface treatment of substrate particles at atmospheric pressure. The invention is motivated by the urge to overcome major drawbacks of particle treatment in low pressure plasmas and in-situ particle treatment at atmospheric pressure. The former requires complex and mostly expensive vacuum installations and vacuum locks usually prohibiting continuous processing. Independent of the system pressure, in-situ plasma treatment causes particle charging and therefore undesirable interaction with the electric field of the discharge, which is seen to contribute to the process of reactor clogging. Additionally, the filamentary discharges modes of atmospheric pressure plasmas are inflicted with inhomogeneous surface treatment. Furthermore, short radical lifetimes at elevated pressures complicate a remote plasma treatment approach as widely used in low pressure applications. The key-element of the invention is that by reducing the dimension of the atmospheric discharge arrangement to the micrometer range, transonic flow conditions can be achieved in the discharge zone while maintaining moderate flow rates. The resulting superimposition of high drift velocity in the gas flow and the inherent diffusion movement is to prolong the displacement distance of activated species, thus making a remote plasma treatment of substrate particles feasible and economically interesting. The circumferential arrangement of e.g. micro discharge channels around the treatment zone of variable length allows a remote plasma treatment independently of the discharge mode and benefits additionally from the aerodynamic focusing of a particle-gas stream to the center, reducing reactor clogging. Furthermore, taking advantage of non-thermal discharges, there is no restriction of the concept of the outlined invention in the material properties of the particulate solids especially not with regard to the treatment of temperature sensitive materials as often encountered in polymer or pharmaceutical industries. In conclusion, atmospheric pressure plasma treatment close to ambient gas temperature as well as continuous processing is a specialty of the invention disclosed here. ## Claims ### Claim 1 A remote plasma process for the treatment of particulate materials comprising: the step of providing a process gas stream enriched by active species, in that an electrical gas discharge is applied to the process gas stream for the creation of a non-thermal plasma at atmospheric pressure in a plasma zone, the electrons generated in the plasma being used to generate said active species in the process gas stream; the step of superimposing high velocities upon the process gas stream enriched by active species in order to prolong the displacement distance of the active species and thus, enlarge an afterglow region of the said non-thermal plasma; the step of providing a carrier gas stream loaded with substrate particles; and the step of mixing of said process gas stream enriched by active species and said carrier gas stream in a treatment zone, wherein the substrate particle treatment in the treatment zone is spatially and temporally separated from the production of said active species such that the treatment zone is located in the afterglow of the non-thermal plasma or downstream of the plasma zone; wherein a homogenous, chemical reaction of the active species on the surface of the substrate particles takes place in said treatment zone; wherein in said treatment zone the particle loaded carrier gas stream, optionally loaded with additional gases or gas admixtures introduced at different stages along the treatment zone, is guided along an axis of the treatment zone, wherein said process gas stream enriched with active species is guided to the treatment zone from a direction essentially perpendicular to said axis, or in a conical direction, in a converging manner, and is guided to the treatment zone in an essentially circumferential and circularly symmetric manner in several planes perpendicular to said axis; wherein said process gas stream enriched with active species is guided to the treatment zone through a plurality of symmetrically arranged channels located in a plane perpendicular to said axis or in a conical direction, in a converging manner, a plurality of such planar arrangements of channels being arranged in several planes distanced from each other along said axis; wherein said plurality of symmetrically arranged channels comprises a stack of alternating high voltage electrodes and counter electrodes, and wherein in the interspace between the electrodes the process gas stream travels; and wherein the treatment zone is provided as one single through hole in said electrodes, the central axis of said hole in the electrodes defining said axis of the treatment zone. ### Claim 2 (depends on 1) The process according to claim 1, wherein the substrate particles remain in the treatment zone, in the form of a drum reactor or a fluidized bed reactor. ### Claim 3 (depends on 1) The process according to claim 1, wherein the active species, which are produced in the plasma zone, are transported by a process gas flow with a mean velocity in the range of 1 to 300 m/s from the plasma zone to the treatment zone. ### Claim 4 (depends on 3) The process according to claim 3, wherein the gas velocity is achieved by restricting the plasma zone to the millimeter range. ### Claim 5 (depends on 4) The process according to claim 4, wherein the gas velocity is achieved by restricting the plasma zone to the micrometer range. ### Claim 6 (depends on 5) The process according to claim 5, wherein the plasma zone is confined to at least one slot with a height in the range of 100 um-5 mm or to at least one channel with such a height and a width in the range of 100 μm-10 mm. ### Claim 7 (depends on 1) The process according to claim 1, wherein the non-thermal plasma is generated by a barrier discharge, corona discharge, and/or a micro hollow discharge. ### Claim 8 (depends on 1) The process according to claim 1, wherein the voltage for the plasma generation is DC or AC, whereas in the AC case the frequency is in the range from low frequency to the radiofrequency. ### Claim 9 (depends on 1) The process according to claim 1, wherein a mean operating pressure inside the plasma zone is in the range from 0.5 to 50 bar. ### Claim 10 (depends on 1) The process according to claim 1, wherein the particles are fed batchwise or in a continuous mode. ### Claim 11 (depends on 1) The process according to claim 1, wherein the substrate particles are periodically carried through the treatment zone. ### Claim 12 (depends on 1) The process according to claim 1, wherein the active species, which are produced in the plasma zone, are transported by a process gas flow with a mean velocity in the range of 20 to 100 m/s from the plasma zone to the treatment zone. ### Claim 13 (depends on 1) The process according to claim 1, wherein the voltage for the plasma generation is AC, with a frequency in the range of 500 Hz-27 MHz. ### Claim 14 (depends on 1) The process according to claim 1, wherein the voltage for the plasma generation AC, with a frequency in the range of 1 kHz-20 kHz. ### Claim 15 (depends on 1) The process according to claim 1, wherein the mean operating pressure inside the treatment zone is in the range from 0.1 to 10 bar. ### Claim 16 A device for carrying out a process for the treatment of particulate materials, said device comprising: a plurality of high voltage electrodes and alternating parallel counter electrodes for the generation of a non-thermal plasma at atmospheric pressure in an interspace between said electrodes, wherein a treatment zone is provided along a central axis as one single through hole in said plurality of electrodes, said treatment zone being essentially in the form of a channel along said central axis, and wherein said central axis is essentially perpendicular to planes defined by said plurality of electrodes, wherein the interspace comprises a plurality of symmetrically arranged channels located in a plane perpendicular to said central axis or in a conical direction, a plurality of such planar arrangements of channels being arranged in several planes distanced from each other along said central axis, said process for the treatment of particulate materials comprising: a step of providing a process gas stream enriched by active species, in that an electrical as discharge is applied in said interspace to the process gas stream before entering the treatment zone for the creation of a non-thermal plasma at atmospheric pressure in a plasma zone, the electrons generated in the plasma being used to generate said active species in the process gas stream; a step of superimposing high velocities upon the process gas stream enriched by active species in order to prolong the displacement distance of active species and thus, enlarge the afterglow region of the said atmospheric plasma; a step of providing a carrier gas stream loaded with substrate particles guided through said treatment zone along said central axis; and a step of mixing of said process gas stream enriched by active species and said carrier gas stream in said treatment zone, wherein the substrate particle treatment in the treatment zone is spatially and temporally separated from the production of said active species in said interspace such that the treatment zone is located in the afterglow of the non-thermal plasma or downstream of said interspace; wherein a homogenous, chemical reaction of the active species on the surface of the substrate particles takes place in said treatment zone; wherein in said treatment zone the particle loaded carrier gas stream, optionally loaded with additional gases or gas admixtures introduced at different stages along the treatment zone, is guided along said central axis, wherein said process gas stream enriched with active species is guided to the treatment zone through said interspace from a direction essentially perpendicular to said central axis, or in a conical direction, in a converging manner, and is guided to the treatment zone in an essentially circumferential and circularly symmetric manner in several planes perpendicular to said central axis; wherein said process gas stream enriched with active species is guided to the treatment zone through said plurality of symmetrically arranged channels. ### Claim 17 (depends on 16) The device according to claim 16, wherein at least one layer of dielectric material is located between the electrodes defining said channels for the process gas in the interspace. ### Claim 18 (depends on 16) The device according to claim 16, wherein the process gas stream is guided through said channels between said electrodes in the form of micro-channels, and wherein the cross-sections of said micro-channels have round, rectangular or square shape in a plane perpendicular to the flow direction. ### Claim 19 (depends on 16) The device according to claim 16, wherein said plurality of high voltage electrodes and alternating parallel counter electrodes comprises a stack of at least three, essentially circular alternating electrodes. ### Claim 20 (depends on 19) The device according to claim 19, wherein an annular circumferential duct is provided by means of which the process gas stream is introduced in a radial direction into at least two of the interspaces between the electrodes. ### Claim 21 (depends on 16) The device according to claim 16, wherein the device comprises a stack of alternating high voltage electrodes and counter electrodes, and wherein in said interspace between the electrodes the process gas stream travels, in each plane in a multitude of symmetrically arranged converging channels, in at least eight channels per plane, wherein the height in the direction of said axis of the process gas pathway is in the range of 100 μm to-1 mm. ### Claim 22 (depends on 16) The device according to claim 16, wherein said treatment zone is provided as one single through hole along a central axis in the electrodes, wherein said through hole is arranged vertically. ### Claim 23 (depends on 16) The device according to claim 16, wherein at least one layer of dielectric material is located between the electrodes defining the flow path of the process gas, wherein the dielectric material is a polymer material, an epoxy resin, a glass or a ceramic, and is used as dielectric layers and/or an insulating casting. ### Claim 24 (depends on 16) The device according to claim 16, wherein the process gas stream is guided through said channels in the form of micro-channels between said electrodes, and wherein the cross-sections of said micro-channels have round, rectangular or square shape in a plane perpendicular to the flow direction, wherein the height of the channels is in the range from 10 μm to 10 mm, and/or a wherein the width of the channels is in the range from 1 μm to essentially the full extent of the surface enclosing the treatment zone. ### Claim 25 (depends on 16) The device according to claim 16, wherein said plurality of high voltage electrodes and alternating parallel counter electrodes comprises a stack of at least nine essentially circular alternating electrodes and wherein an annular circumferential duct is provided by means of which the process gas stream is introduced in a radial direction into at least one of the interspaces between the electrodes. ### Claim 26 (depends on 16) The device according to claim 16, wherein the treatment zone is provided as one single through hole in the electrodes, wherein the central axis of this hole in the plurality of electrodes defines said central axis of the treatment zone, wherein this through hole is arranged vertically.