Method for generating an atmospheric plasma jet and atmospheric plasma minitorch device

Abstract

A method and a device for generating a plasma in atmospheric-pressure, low-temperature conditions are described herein. The device described for the generation of the plasma comprises a first pair of electrodes, each of which separated by a dielectric layer and externally positioned with respect to a tubular duct where the gas flows, and a second pair of electrodes, also in this case each of which separated by a dielectric layer and externally positioned with respect to said tubular duct where the same gas flows downstream with respect to the first pair with respect to the direction of the flow. A high-frequency excitation is applied to the first pair of electrodes while a Radio-Frequency excitation is applied to the second pair of electrodes. The plasma generated in this manner emerges from the gas flow at the outlet of the transport duct. The high-frequency excitation can be applied in pulse trains and the Radio-Frequency generator is substantially activated in said pulse trains for the purpose of limiting the thermal load on the treated substrate. Chemical precursors and reagents can be added to the plasma as vapors or aerosols by means of a central transport duct coaxial with the tubular duct for the gas.

Claims

1. Method for generating an atmospheric plasma jet which comprises: flowing a process gas that advances in a flow direction (202, 402, 502) through a tubular duct (201, 401, 501) made of dielectric material with an inlet section and an outlet section (207, 410) at atmospheric pressure; positioning a first pair of coaxial electrodes (203-204, 307-308, 404-405, 503-504) and a second pair of coaxial electrodes (205-206, 309-310, 406-407, 505-506) in contact with the external surface of said tubular duet (201, 401, 501); said first pair of electrodes (203-204, 307-308, 404-405, 503-504) being placed in position upstream of said second pair of electrodes (205-206, 309-310, 406-407, 505-506) in relation to the flow direction of said process gas in said tubular duct (202, 402, 502) and being connected to a high-frequency generator (208, 301); said second pair of electrodes (205-206, 309-310, 406-407, 505-506) being connected to a Radio-Frequency generator (209, 303); said high-frequency generator (208, 301) generating a filamentary plasma within said tubular duct (201, 401, 501), said filamentary plasma extending at least to said second pair of electrodes (205-206, 309-310, 406-407, 505-506); said Radio-Frequency generator (209, 303) generating a second RF plasma; flowing out said RF plasma and said filamentary plasma to outside the tubular duct (201, 401, 501) through said outlet section (207, 410), such plasmas at the outlet comprising at least one neutral gas at the outlet having temperature not higher than about 100 C.

2. Method according to claim 1, wherein during the generation of said RF plasma, by said Radio-Frequency generator (209, 303), said high-frequency generator (208, 301) is substantially always operative for generating said filamentary plasma.

3. Method according to claim 1, wherein the process gas, introduced into said tubular duct (201, 401, 501) through the inlet section thereof, comprises at least one from among the following substances: helium, hydrogen, oxygen, nitrogen, argon, air, neon, carbon oxide, hydrocarbons.

4. Method according to claim 3, wherein the process gas, introduced into said tubular duct (201, 401, 501) through the inlet section thereof, comprises a mixture containing at least one noble gas and at least one reactive gas.

5. Method according to claim 1, wherein the high-frequency generator (208, 301) generates pulse trains and the Radio-Frequency generator (209, 303) is substantially exclusively active in said pulse trains.

6. Method according to claim 5, wherein the Radio-Frequency generator (209, 303) operates in the frequency range comprised between 1 and 30 MHz.

7. Method according to claim 5, wherein the pulsed high-frequency generator (208, 301) operates in the frequency range comprised between 1 and 100 kHz; wherein the pulse duration is up to 20 ms with a duty cycle in the range comprised between 10 and 98%.

8. Atmospheric plasma minitorch device characterized in that it comprises: a tubular duct (201, 401, 501) made of dielectric material with an inlet section and an outlet section (207, 410) at atmospheric pressure; at least one supply source connected to the inlet section of said tubular duct (201, 401, 501) and arranged for introducing said process gas into said tubular duct (201, 401, 501); a first pair of coaxial electrodes (203-204, 307-308, 404-405, 503-504) and a second pair of coaxial electrodes (205-206, 309-310, 406-407, 505-506) in contact with the external surface of said tubular duct (201, 401, 501); said first pair of electrodes (203-204, 307-308, 404-405, 503-504) being placed in position upstream of said second pair of electrodes (205-206, 309-310, 406-407, 505-606) in relation to the flow direction of said process gas in said tubular duct (202, 402, 502) and being connected to a high-frequency generator (208, 301); said second pair of electrodes (205-206, 309-310, 406-407, 505-506) being connected to a Radio-Frequency generator; said high-frequency generator (208, 301) being arranged for generating a filamentary plasma within said tubular duct (201, 401, 501), said filamentary plasma extending at least to said second pair of electrodes (205-206, 309-310, 406-407, 505-506) and exiting from said tubular duct (201, 401, 501) through said outlet section; said Radio-Frequency generator (209, 303) being arranged for generating a RF plasma which exits from said tubular duct (201, 401, 501) through said outlet section (207, 410); said filamentary plasma and said RF plasma exiting from said tubular duct (201, 401, 501) comprising at least one neutral gas at the outlet having temperature not higher than about 100 C.

9. Atmospheric plasma minitorch device according to claim 8, characterized in that it comprises control means connected to said high-frequency generator (208, 301) and to said Radio-Frequency generator (209, 303) and arranged for controlling said high-frequency generator (208, 301) between a first non-operative state and a first operative state, in which said high-frequency generator (208, 301) generates said filamentary plasma; said control means being arranged for controlling said Radio-Frequency generator (209, 303) between a second non-operative state and a second operative state, in which said Radio-Frequency generator (209, 303) generates said RF plasma with said high-frequency generator (208, 301) in said first operative state.

10. Atmospheric plasma minitorch device according to claim 9, characterized in that said control means comprise at least one electronic control unit connected to said high-frequency generator (208, 301) and to said Radio-Frequency generator (209, 303), and programmed for controlling the activation of said Radio-Frequency generator (209, 303), controlled in said second operative state, during pulse trains generated by the high-frequency generator (208, 301) controlled in said first operative state.

11. Atmospheric plasma minitorch device according to claim 8, characterized in that it comprises at least one supply source connected to the inlet section of said tubular duct (201, 401, 501) and arranged for introducing said process gas into said tubular duct (201, 401, 501), which can be modulated both with regard to the entering flow and the composition, in mixture form containing at least one noble gas and at least one reactive gas.

12. Atmospheric plasma minitorch device according to claim 8, wherein the tubular duct (201) has circular section and is made of dielectric material such as glass, ceramic, polymer, composite or other dielectric material and wherein the external diameter of the tubular duct is comprised between 1 mm and 15 mm.

13. Atmospheric plasma minitorch device according to claim 8, wherein the body of the device is a tubular duct with rectangular section (501) and wherein the shorter side is comprised between 1 mm and 15 mm (509).

14. Atmospheric plasma minitorch device according to claim 8, wherein the high-frequency generator (208) operates in the range comprised between 1 and 100 kHz and wherein the duration of the pulse is comprised in the range between 1.25 and 20 ms with a duty cycle in the range comprised between 10 and 98%; wherein the Radio Frequency generator (209) operates in the range comprised between 1 and 30 MHz; and wherein the activation of said radio-frequency generator (209) is susceptible of being controlled by said pulse trains generated by the high-frequency generator.

15. Atmospheric plasma minitorch device according to claim 8, which also comprises: a transport duct (409), through which a liquid precursor or a precursor in the form of a particle suspension in a liquid can be flowed, such duct (409) positioned inside and coaxial with respect to the tubular duct (401), with the free emission end placed inside said tubular duct at a distal position from the outlet section of said tubular duct (401).

16. Atmospheric plasma mini torch device according to claim 15, which also comprises: a separation duct (408) made of dielectric material with larger internal diameter with respect to the transport duct (409) and with smaller external diameter with respect to the tubular duct (401), coaxially interposed between said transport duct (409) and said tubular duct (401), and it too equipped with an outlet section; an annular cavity being defined by the external surface of the transport duct (409) and by the internal surface of said separation duct (408), into which a nebulizer gas flows which, by intercepting the fluid exiting from the transport duct (409), generates an aerosol at the free emission end of said transport duct (409).

17. Atmospheric plasma minitorch device according to claim 15, which also comprises: a separation duct (408) made of dielectric material with larger internal diameter with respect to the transport duct (409) and with smaller external diameter with respect to the tubular duct (401), coaxially interposed between said tubular duct (401) and said transport duct (409); an annular cavity being defined by the external surface of the transport duct (409) and by the internal surface of said separation duct (408), into which a process has flows in the form of vapors or aerosols of chemical precursors, such process gas interacting with the RF plasma at the outlet section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a block diagram that illustrates the mechanisms for generating the atmospheric plasma and the operation principle of the device in accordance with the present invention;

(2) FIG. 2 is a schematic representation of the device for generating the atmospheric plasma jet with low temperature and low power in accordance with the present invention;

(3) FIG. 3 is a circuit diagram that illustrates the mode of generating the atmospheric plasma in accordance with the present invention comprising the connections and the general electrical layout of the device;

(4) FIG. 4 is a schematic representation of the device for generating said atmospheric plasma jet with low power and low temperature in which said tubular transport and separation ducts for allowing the deposition are also reported;

(5) FIG. 5 is a schematic representation of the device for generating said atmospheric plasma jet in accordance with the present invention which implements the use of said tubular duct with parallelepiped form.

DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS

(6) FIG. 1 illustrates a block diagram in which the different steps necessary for striking and sustaining the atmospheric plasma jet in accordance with the present invention are reported. The first step regards flowing the gas through said tubular duct made of dielectric material.

(7) The aforesaid gas can be a monatomic noble gas (He, Ar, Ne, Kr) or a mixture thereof or a molecular gas (nitrogen, oxygen, carbon dioxide, hydrocarbons, water vapor, etc.) or mixtures of these, or a mixture of one or more monatomic gases with one or more molecular gases. Advantageously, the process gas, introduced into the tubular duct (201, 401, 501) through the inlet section thereof, comprises a mixture containing:

(8) at least one noble gas, in particular selected from among He, Ar, Ne, Kr, and at least one reactive gas, selected in particular from among nitrogen, oxygen, carbon dioxide, hydrocarbons, sulfur hexafluoride, fluorocarbons, ammonia, etc.

(9) The second regards positioning the first pair of coaxial electrodes connected to said high-frequency generator outside the tubular duct. The third step regards positioning said second pair of electrodes connected to the radio-frequency generator with said impedance adaptation circuit placed outside the tubular duct and in position downstream of the first pair of electrodes with respect to the flow of the gas in the tubular duct. Said impedance adaptation circuit of the Radio Frequency can be external or integrated inside the generator itself or integrated inside the body of the device. The fourth step regards setting the value of voltage applied by the high-frequency generator such to strike the filamentary plasma; for the correct operation of the device, it is not necessary to increase the voltage beyond the strike voltage. The high-frequency generator can also work with pulse trains, and in such case also the parameters of the pulse train must be set. The fifth step regards setting the value of power applied by the radio-frequency generator; such set value must be selected on the basis of the plasma density desired at the outlet of the outlet section of the tubular duct.

(10) The sixth step regards turning on the generators and forming the filamentary plasma and the RF plasma and the formation of the reactive species.

(11) The filamentary plasma and the RF plasma, which exit from the outlet section of the tubular duct (201, 401, 501), comprise at least one neutral gas at the outlet having temperature not higher than about 100 C.

(12) Advantageously, during the generation of the second RF plasma, by the Radio-Frequency generator (209, 303), the high-frequency generator (208, 301) is substantially always operative for generating the aforesaid first filamentary plasma.

(13) More in detail, preferably, the high-frequency generator (208, 301) is always maintained operative during the operation of the Radio-Frequency generator (209, 303), providing charged species that ensure the sustenance and extraction of the RF plasma even in the presence of process gases comprising mixtures of one or more noble gases with one or more reactive or transport gases.

(14) The radio-frequency generator, in the case of use of pulse trains with the high-frequency generator, will only be active in said pulse trains.

(15) Finally, the seventh step regards the exit of the gas from the duct and the flowing out of a jet or plume of plasma that can be used for surface activation purposes or for the deposition of surface coatings depending on the type of device employed.

(16) FIG. 2 illustrates a preferred device in accordance with the present invention; as in the preceding description, a tubular duct 201 is made of dielectric material and represents the body of the atmospheric plasma minitorch device; said dielectric material can be a ceramic material, glass and special glass, quartz or a polymer or composite material with high dielectric rigidity; a transport gas flows through the tube, 202.

(17) Advantageously, as stated above, the device comprises a supply source connected to the inlet section of said tubular duct (201, 401, 501) and arranged for introducing, into the tubular duct (201, 401, 501), the process gas in the form of the aforesaid gas mixture. More in detail, preferably, the supply source comprises a gas cylinder or multiple gas cylinders (containing pure gases or gas mixtures) whose opening is regulated by valves. The cylinders are connected with the inlet section of the tubular duct (201, 401, 501) by means of a connector tube intercepted by a flow meter or another device that controls the inflow of the process gas, in the form of the gas mixture, into the tubular duct (201, 401, 501), for the regulation of the entering flow.

(18) Advantageously, as stated above, the atmospheric plasma device comprises control means connected to the high-frequency generator (208, 301) and to the Radio-Frequency generator (209, 303) and arranged for controlling the high-frequency generator (208, 301) between a first non-operative state and a first operative state, and for controlling the radio-Frequency generator (209, 303) between a second non-operative state and a second operative state, in a manner such that, when the Radio-Frequency generator (209, 303) is controlled in its second operative state, the high-frequency generator (208, 301) is controlled in its first operative state, providing the charged species for the sustenance and extraction of the RF plasma.

(19) For example, the aforesaid control means comprise a first switch interposed between the high-frequency generator (208, 301) and an electrical power source, and a second switch interposed between the radio-Frequency generator (209, 303) and the aforesaid electrical power source, such switches actuatable for connecting the corresponding generator to the electrical power source in order to enable the turning on thereof (and therefore determining the generation of the corresponding plasma).

(20) In accordance with a particular embodiment, the aforesaid switches can be manually actuated, by means of corresponding buttons of the device.

(21) Otherwise, the aforesaid switches are controlled in an automated manner by the aforesaid electronic control unit of the control means, which preferably comprises an electronic circuit board equipped with programmable CPU.

(22) The two said pairs of coaxial electrodes, respectively 203 and 204, 205 and 206, are externally positioned with respect to said tubular duct; the electrodes are made of electrically conductive material and are typically metal; in the preferred device of the present invention, the electrode 203 is polarized by means of a high-frequency pulse generator (1-100 KHz), 208; the pulses can be in square or triangular wave form, or other wave forms; the electrode 205 is polarized by means of a Radio-Frequency generator, 209, which operates in the frequency range 1-30 MHz; the Radio-Frequency generator is equipped with said suitable circuit for the impedance adaption, 210, which can be integrated inside the generator itself or positioned on the body of the device; the electrodes 204 and 206 are grounded; the body of the device is also grounded; the gas which flows inside the body of the torch, passing through the region of space comprised between the electrodes, is ionized and consequently a plasma in DBD (Dielectric barrier Discharge) mode is struck, hence without providing for the presence of any electrode within the volume of said tubular duct and in particular the volume comprised between the electrodes; said ionized gas flows along the tubular duct, 212, and finally flows out of the duct as a jet or plume of plasma, 207; the positions of the electrodes can be varied along the main axis of the tubular duct according to the mode illustrated in 213, for the purpose of fine-controlling the mechanisms and the plasma generation mode and thus regulating the size and temperature of the plasma plume, 207; the two pairs of electrodes worked in a combined manner during the entire process and allow obtaining a plasma with low temperature, preserving high efficiency in the ionization; the use of the double frequency is beneficial to the extent in which it is able to combine the positive characteristics both of the high-frequency (HF) discharges and the Radio-Frequency discharges (RF); the RF torches tend in this sense to ensure greater plasma densities but with plasma jet of smaller size than that obtainable in HF, hence less effective and versatile from the application standpoint; on the other hand, the high voltages necessary for striking are much easier to obtain in HF than in RF; the combination of the two generators thus allows having stable ignitions, plasma jets of size comparable to those obtainable in HF but characterized by greater plasma densities and lower temperatures, as typically observed in the RF plasmas; the use of the high-frequency generator also allows increasing the extension of the plasma plume 207 beyond the tubular duct.

(23) FIG. 3 reports a circuit diagram of said system constituted by 2 pairs of coaxial electrodes. In the preferred device in accordance with the present invention, said first pair of electrodes, 307 and 308, is connected to said high-frequency generator employed in pulsed mode, 301. The generator in the preferred device operates at a frequency of 28 KHz and a peak voltage of 15 Kvolts; nevertheless, in future devices, the frequencies employed can be comprised in the range 1-100 KHz with peak voltages up to 40 KVolts. The preferred pulsation in the device is obtained with a frequency of 500 Hz and a useful work cycle of 80%; nevertheless, in future devices the frequency can be varied from 50 to 800 Hz and the useful work cycle in the range between 10 and 98%. Said second pair of electrodes, 309 and 310, is connected to said generator RF, 302, and the impedance of the circuit is adapted due to said adaptation circuit, 303. The frequency in the preferred device is 13.56 MHz, though in future devices it can be comprised in a range between 1 and 30 MHz. The two generators are coupled due to the coupling of the pulse of the high-frequency generator with the signal at Radio Frequency or vice versa in order to ensure a positive phase coupling between the two signals. In addition, once the plasma has been struck, 306, the separation distance between the two pairs of electrodes is suitably set in order to ensure the coexistence of the two discharges within the same plasma region, leading to the obtainment of a plasma combined in double-frequency. Both generators are grounded, 304 and 305, just as the counter-electrodes of each pair, 307 and 309, are grounded in a distinct and separate manner, respectively for the HF and RF generators.

(24) FIG. 4 shows an example of the device in accordance with the present invention equipped with a configuration specifically ideated for the deposition of coatings and hereinbelow termed coaxial nebulizer. The distribution and consequent flow of the precursor, as described in the present invention, is coaxial with respect to the flow of process gas. Within the tubular duct, made of dielectric material, 401, a transport duct, 409, is inserted with a separation duct made of electrically insulating material, 408, interposed between the tubular duct and the transport duct. The process gas is flowed as in the previously-described device starting from the bottom, 402, before then passing through the annular duct comprised between the separation duct, 408, and the tubular duct and made of dielectric material, 401. The role of the separation duct is also that of preventing the transport duct, 409, from being exposed to the plasma. In addition, a liquid precursor or precursor in suspension form can be flowed into the transport duct, 409, while a second gas or precursor in vapor or aerosol form can be flowed into the annular cavity comprised between the internal surface of the separation duct, 408, and the external surface of the transport duct, 409; in case of flowing a fluid precursor or suspension into the transport duct, and a gas into the annular cavity between the transport duct and the separation duct, at the outlet of the ducts the two flows reach in contact with the formation of a dispersion or aerosol. Further devices can implement more than 1 transport duct within the separation duct in order to allow the individual and separate inflow of multiple precursors in different zones of the plasma, thus fine-controlling the process chemistry. The four electrodes belonging to the two said pairs of coaxial electrodes, 404, 405, 406 and 407 are positioned as in the case of the preferred device. The precursor flowing mode occurs starting from the bottom, 403, through the transport duct up to the terminal part of the device. The final position of the transport duct, 411, can be moved along the main axis of the device in order to regulate the length and thus the contact time between the precursor and the plasma. This particular device allows finely regulating the entrance position of the precursor in the plasma zone and hence controlling the chemical reactivity of the precursor, the density and type of the radical and chemically active species produced and which constitute the plasma plume projected on the surface to be treated, 410. The chemical precursors that can be used in this device include organic precursors, metalorganic precursors and suspensions containing nanoparticles of any nature and species. The transport duct can have internal diameters comprised between 0.1 mm and 1.0 mm while the separation duct can have internal diameters comprised between 0.3 and 2.0 mm and in any case necessarily larger than the external diameter of the transport duct. The thickness of the transport duct can also vary and is typically comprised between 0.1 mm and 0.3 mm while the thickness of the separation duct is typically comprised between 0.4 and 1.0 mm.

(25) FIG. 5 shows an example of the device in accordance with the present invention provided with a tubular duct with parallelepiped form and made of dielectric material, 501, which represents the body of the atmospheric plasma device; the dielectric material can be ceramic, glass, quartz or a polymer or composite material with dielectric characteristics; the transport gas flows through said tubular duct, 502, and can be a monatomic noble gas such as He, Ar, Ne or a molecular gas such as nitrogen, oxygen, hydrogen, carbon dioxide, methane or other hydrocarbons, water vapor or any mixture of monatomic, diatomic gases, or mixed monatomic and molecular gases; two said pairs of electrodes, with rod-like form, respectively 503 and 504, 505 and 506 are positioned outside the body of the device; the electrodes are made of conductive material and are typically metallic, 503 is polarized by a high-frequency generator (1-100 kHz) and used in pulsed mode; the pulses can have square or triangular wave form or other wave forms; 505 is polarized at radio frequency by means of a generator that operates in the range 1-30 MHz; the electrodes 504 and 506 are grounded; the body of the device is also grounded; the plasma is generated within the tubular duct and a plasma blade flows out from the end of the body of the device, 507; the size of the body of the device with parallelepiped form 508, 509 and 510, i.e. respectively the length, width and height, can be comprised between 10 and 1000 mm and the aspect ratio of the device defined as the ratio between the height and width of the device can vary between 1 (device with square section) and 100 (device with sheet-like plasma).

Example 1

Removal and Erosion of Polymer Coatings and Organic/Inorganic Hybrids

(26) A first example of practical use of the present invention, in accordance with the device represented in FIG. 2, is its use in the removal of some polymer products like acrylic products and epoxy resins. Acrylic products such as Paraloid B72 and the like (Paraloid B67, Primal, Acryil 33, etc.), typically used as transparent protections for handmade items of cultural heritage interest, must be removed and replaced after a certain period of exposure to weathering agents. For such use, a mixture of Argon containing 0.3% Oxygen is used as ionizing gas; it is flowed at a velocity of 10 L/min and introduced by means of the tubular duct, 401. The two pairs of electrodes, that at high frequency and that at radio frequency, are made to work at a power of 15 W and 90 W, respectively, in direct or pulsed mode, at a frequency of 30 kHz and 27 MHz. By placing the material to be treated with the polymer coating to be removed at a distance of 2 mm, a removal velocity of 20 m/min was obtained for Paralod B72. The maximum temperature of the device does not exceed 40 C., even for continuous treatments of 600 s, and makes possible the manual use of the device by an operator. Also the temperature on the surface of the treated materials is maintained below 50 C., thus allowing the use of the device for treating, sensitive materials. The plasma conditions are very stable and no electric arc generation phenomenon was observed during such experiments. The present invention is thus advantageous in the safe and controllable removal of protective polymer coatings applied to handmade items of historical-cultural interest, allowing the restorer to operate manually, directly controlling the advancement of the desired cleaning process.

(27) In addition to the polymer coatings employed as protections, the present invention allows assisting the cleaning and removal of graffiti and spray paints typically used by the writers to sully urban decoration pieces and objects of historical-cultural interest. For this type of application, the power applied to the pair of RF electrodes is 160 W in pulsed conditions. After a treatment of 120 s, the polymer binder of the paint (acrylic, alkyd, nitrocellulose, etc.) is visibly removed, and the organic pigments lose cohesion, becoming easily removable by means of operation with moist cloth. By repeating such procedure multiple times, the graffiti is completely removed. Alternatively, the device, object of the present invention, has been successfully used following a cleaning operation conducted with solvent; the residues of the polymer paints, which after having been dissolved by the solvent tend to penetrate into the pores of the substrate, were successfully removed by the cold plasma produced by an exemplar of the present invention, by applying the above-described parameters.

(28) It is observed that the use of the proposed method and device is not limited to the removal of only acrylic polymers, but generally it can be extended to the removal and erosion of all polymer materials and all organic/inorganic hybrid materials containing a polymer fraction. In addition, by using the torch exemplar in the above-described conditions, the complete cleaning and removal of the soot from stone surfaces is obtained; a few minutes of precise treatment are sufficient for completely removing the soot from a surface area of about 1 cm.sup.2.

Example 2

Deposition of Thin Organic, Inorganic and Hybrid Films

(29) The exemplar of the present invention, equipped with the coaxial nebulizer in accordance with the device, object of the present invention, and represented in FIG. 4, was employed in the deposition of thin silica films. The liquid precursor, hexamethyldisiloxane (other precursors with organo-silicate base can alternatively be employed), is introduced into the transport duct, 409, at a velocity of 0.1 mL/min, and nebulized due to a flow of air or Argon or Argon/Oxygen, blown inside the separation duct, 408, at 5 L/min. Through the main tubular duct, the ionizing gas (Argon, or Argon containing 0.3% Oxygen, at 10 L/min) is instead made to flow, which in addition to generating the plasma allows the chemical precursor to polymerize and produce the thin film. By applying a power of 20 W to the low-frequency generator, and a power of 50 W to the radio-frequency generator, a silica film with 1 m thickness is obtained, for a sample placed at 2 mm distance from the outlet, and for a precise treatment of 10 s duration. The exemplar of the present invention is therefore able to deposit in APLD (atmospheric plasma liquid deposition) mode.

(30) The exemplar of the present invention (as represented in FIG. 4), can deposit thin silica films, introducing in the plasma the vapors of the selected chemical precursor (hexamethyldisiloxane, tetraethoxysilane, or other silica-based precursors), working in APVD (atmospheric plasma vapor deposition) mode. The gas carrier (Argon or Argon/Oxygen) is made to flow, at 0.25 L/min, inside the recipient containing the liquid chemical precursor in a manner such to capture the volatile fraction of the chemical precursor itself and carry it into the plasma by using the separation duct, 408. By applying the conditions described in the preceding paragraph, a silica film with 400 nm thickness is obtained, which indicates a deposition efficiency of 40 nm/s.

(31) The above-described two deposition modes (APLD, APVD) were also employed for the deposition of polymer films such as, but not limited to, polymethylmethacrylate (PMMA). By operating in the above-described APVD conditions, a deposition efficiency of the PMMA is obtained that is equal to 60 nm/s. In general, the higher the vapor tension of the starting monomer, the greater the efficiency will be in the deposition of the corresponding polymer.

(32) Due to the multi-coaxiality of the exemplar of the present invention (as represented in FIG. 4), the deposition system allows the creation of coatings with organic/inorganic hybrid character. A dispersion containing nanoparticles (ceramic, polymer, metallic, hybrid), but not limited to nanoparticles, is introduced through the transport duct, 409, and nebulized due to a flow of Argon or Argon/Oxygen that has previously passed through the vapors of a chemical precursor, such as hexamethyldisiloxane (but not limited to the latter), and that is introduced through the separation duct, 408. In this manner, at the outlet of the nozzle, the precursor polymerization reaction takes place, which leads to the deposition of a thin film which will incorporate the nanoparticles exiting from the transport duct.

(33) It is observed that the use of the method and exemplar of the present invention is not limited to the deposition of silica films, but in general can be extended to the deposition of: zirconium oxide, titanium oxide, aluminum oxide, cerium oxide. Analogously the deposition of polymer films is not limited to PMMA, but generally can be extended to all polymers whose starting monomers are available in solution.

Example 3

Application of a New Cultural Heritage Protocol

(34) By means of the use of an exemplar of the present invention (as represented in FIG. 4), it was possible to create a new protocol for the deposition of protective polymer films and for their possible controlled removal, to be used in the scope of cultural heritage conservation. By exploiting the multi-coaxiality of an exemplar of the present invention, a first gas carrier constituted by Argon or Argon/Oxygen is made to flow into a recipient containing methyl-methacrylate monomer (MMA) in a manner so as to capture the vapors, and introduced into the separation duct, 408. A second gas carrier, still constituted by Argon or Argon/Oxygen, is instead flowed into a second recipient containing ethyl-acrylate monomer (EtA), in order to then be introduced into the transport duct, 409. In this manner, as suggested by Totolin et al. (described in Totolin et al. Journal of Cultural Heritage 12 (2011) 392 and enclosed herein for reference), a copolymerization in plasma is obtained that leads to the formation of the analogous commercial product Primal AC33 (Rohm and Haas), widely used in the field. The polymer film is deposited on a silicon substrate, and after having aged the polymer due to the action of a UV lamp (aging time=500 h), it was removed by means of plasma, obtaining a removal velocity comparable to that obtained in the removal of the Paraloid B72.

Example 4

Reducing Treatments: Cleaning of Metal Oxides and Sulfides

(35) The device of the present invention (as represented in FIG. 2) can also be employed in the reducing cleaning of metal oxides and sulfides. For this application, the best results are obtained by using a mixture of Argon with 2% Hydrogen as ionizing gas; the power applied to the two pairs of electrodes was 15 W and 80 W, respectively for the two high-frequency and radio-frequency generators, while the nozzle-sample distance, for this treatment type, was brought to 5 mm in a manner so as to be able to work with the device in After glow conditions, i.e. the conditions in which the material to be treated is placed outside the beam produced by the plasma, and not in direct contact therewith. In these conditions, with a precise treatment of 2 minutes, the total removal of the silver sulfide from a sample of Ag999 and Ag925 aged naturally is obtained. It is observed that also for this treatment type, the temperature measured at the substrate never exceeded 25 C.; the use of the present invention has therefore proven to be extremely effective even for the specific treatment of thermosensitive materials.

(36) Due to the use of an exemplar of the present invention, (as represented in FIG. 4), it is possible to assist the cleaning of metals, by nebulizing solutions with reducing behavior in the plasma. A diluted HCl solution (0.1M) is introduced into the transport duct, 409, while a flow of Argon is introduced into the separation duct, 408, in order to nebulize the solution at the outlet of the plasma. In these conditions, with a precise treatment of 2 minutes, the total removal of the copper sulfide from sample of naturally-aged Cu999 was obtained.

Example 5

Surface Cleaning, Sterilization and Activation

(37) A further example of use of the present invention (as represented in FIG. 2) is the more common surface activation and cleaning. The plasma produced by the different exemplars proposed is able to increase the wettability of the treated surfaces, facilitating the processes of overprinting and adhesion. A polymer material such as polystyrene or polypropylene can increase its surface energy from 34-36 mN/m to 70-72 mN/m. Correspondingly, the contact angle values of the water pass from 80-100 for non-treated materials to 10-15 for the materials treated in the following conditions used in example 1. The effectiveness of the cleaning action is also given by the capacity of the produced plasma to degrade possible organic substances, oils and fats possibly present on the surface of interest, and in the case of polymer materials is also given by the effect of the controlled mild erosion of the polymer itself, which is renewed on the surface.

(38) The surface cleaning action produced by the plasma generated by the present invention can also be exploited in surface sterilization processes, and in processes for removing bacteria and other dangerous biological organisms. The effect of the sterilization action can also be increased by means of the use of the exemplar in accordance with the present invention (as represented in FIG. 4) and in particular by introducing into the plasma, by means of the transport duct, 409, reagents such as water vapor, which lead to the formation of peroxide ions useful for such purpose.

Example 6

Attachment of Surface Chemical Functionalities

(39) If the simple surface activation and cleaning does not suffice for solving some problems tied to the adhesion between different materials, an exemplar of the present invention can be used for attaching, on the surfaces of interest, several chemical functionalities suitably selected and useful for the adhesion between dissimilar materials. By using an exemplar in accordance with the present invention (as represented in FIG. 4), in the operative conditions described in example 2, and introducing by means of the separation duct 408 organic monomer vapors containing chemical functionalities such as: acrylic groups, epoxy groups, amines (but not limited to these), the adhesions between materials that use epoxy joints, urethane joints and acrylic joints have significantly improved. This type of surface functionalization has also allowed designing processes capable of substituting the application of the solvent-based primers, with the surface deposition of the abovementioned chemical functionalities.

(40) Analogous to that described in the preceding point, by using chemical precursors such as allylamine, acrylic acid or the like, it is possible to fix, on the surface of the treated materials, functionalities of amine and/or carboxylic type that are useful for biomedical materials or for materials in which it is desired to boost and accelerate cellular growth.