Methods and Apparatus for Delivering Feedstocks for Plasma Treatment

Abstract

The present application relates to methods and apparatus for delivering liquid or solid feedstocks into a plasma treatment vessel. More specifically, the invention provides a method for treating a sample using glow discharge plasma in an apparatus comprising a treatment vessel, the method comprising (i) delivering a gaseous plasma forming feedstock into the treatment vessel through a gas supply line under the control of a gas flow controller, and causing formation of a glow discharge plasma in the treatment vessel from the gaseous plasma forming feedstock; and simultaneously (ii) delivering a reagent into the treatment vessel under the control of a reagent dosing controller, wherein the reagent is a liquid or a solid; and (iii) contacting the sample with the glow discharge plasma and the reagent; wherein the gas flow controller and the reagent dosing controller allow independent control of the rate of delivery of the gaseous plasma forming feedstock and the reagent.

Claims

1. A method for treating a sample using glow discharge plasma in an apparatus comprising a treatment vessel, the method comprising: delivering a gaseous plasma forming feedstock into the treatment vessel through a gas supply line under the control of a gas flow controller, and causing formation of a glow discharge plasma in the treatment vessel from the gaseous plasma forming feedstock; and simultaneously delivering a reagent into the treatment vessel under the control of a reagent dosing controller, wherein the reagent is a liquid or a solid; and contacting the sample with the glow discharge plasma and the reagent; wherein the gas flow controller and the reagent dosing controller allow independent control of the rate of delivery of the gaseous plasma forming feedstock and the reagent.

2. A method according to claim 1, wherein the reagent is a liquid.

3. A method according to claim 2, wherein the reagent dosing controller is a pump.

4. A method according to claim 3, wherein the pump is a positive displacement pump.

5. A method according to claim 4, wherein the pump is a piston pump or a plunger pump.

6. A method according to claim 5, wherein the pump is a syringe pump.

7. A method according to claim 2, wherein the liquid is a non-volatile liquid.

8. A method according to claim 2, wherein the liquid is a silane.

9. A method according to claim 1, wherein the reagent is a solid.

10. A method according to claim 9, wherein the reagent dosing controller is a conveyor system or a pellet gate system.

11. A method according to claim 10, wherein the reagent dosing controller is a conveyor system.

12. A method according to claim 9, wherein the solid is a metal.

13. A method according to claim 12, wherein the metal is a precious metal.

14. A method according to claim 1, wherein the reagent dosing controller is adjustable to allow the rate of delivery of the reagent to be varied during the method for treating the sample.

15. A method according to claim 1, wherein the reagent dosing controller is continuously adjustable.

16. A method according to claim 1, wherein the reagent is combined with a gas before delivery into the treatment vessel, preferably wherein the reagent is delivered into the treatment vessel as an aerosol.

17. A method according to claim 1, wherein the gas flow controller is a gas regulator, a mass stream controller or a mass flow controller.

18. A method according to claim 1, wherein the apparatus comprises a vacuum pump in fluid communication with the treatment vessel and a vacuum pump valve configured to control the level of vacuum applied by the vacuum pump to the treatment vessel.

19. A method according to claim 18, wherein the apparatus further comprises a pressure feedback system which obtains pressure data from the treatment vessel and actuates the vacuum pump valve based on the pressure data.

20. A method according to claim 1, wherein the sample is a particulate sample.

21. A method according to claim 1, wherein the sample is agitated by rotating the treatment vessel about an axis during treatment.

22. Apparatus suitable for treating a sample in a method as defined in claim 1, the apparatus comprising: a treatment vessel, a gas supply line fluidly connected to the treatment vessel for delivering a gaseous plasma forming feedstock to the treatment vessel, a gas flow controller connected to the gas supply line and a reagent supply system comprising a reagent dosing controller, for delivery of a liquid or solid reagent to the treatment vessel wherein, the gas flow controller and the reagent dosing controller allow independent control of the rate of delivery of a gaseous plasma forming feedstock and reagent to the treatment vessel.

23. Apparatus according to claim 22, wherein the reagent dosing controller is a pump.

24. Apparatus according to claim 23, wherein the pump is a syringe pump or a peristaltic pump.

25. Apparatus according to claim 22, wherein the reagent dosing controller is a conveyor system.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0240] The present proposals are now explained further with reference to the accompanying figures in which:

[0241] FIG. 1 is a diagram showing a plasma treatment apparatus according to the present invention;

[0242] FIG. 2 is a diagram of the injector system;

[0243] FIG. 3 is a diagram of the fluid delivery system for the plasma treatment apparatus;

[0244] FIG. 4 shows the mechanism of attachments of APTES to an oxygenated graphene;

[0245] FIG. 5 is an XPS scan of untreated graphene materials;

[0246] FIG. 6 is an XPS scan of silanated graphitic materials using the process according to the present invention;

[0247] FIG. 7 is an XPS scan of raw boron nitride;

[0248] FIG. 8 is an XPS scan of silanated boron nitride using the process according to the present invention with HMDSO as the reagent;

[0249] FIG. 9 is an XPS scan of silanated boron nitride using the process according to the present invention with GLYMO as the reagent.

DETAILED DESCRIPTION

[0250] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although, any methods and materials similar or equivalent to those described herein can be used in practice for testing of the present invention, the preferred materials and methods are described herein. In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below. Unless clearly indicated otherwise, use of the terms a, an, and the like refers to one or more.

[0251] FIG. 1 is diagram of a plasma treatment apparatus according to the present invention, for delivering a liquid reagent. The apparatus consists of a treatment vessel 39 mounted on a electrode 37 via mounting plate 36, with electrode 37 and mounting plate 36 serving as an axle around which the treatment vessel rotates during operation. The treatment vessel 39 serves as a counter-electrode, such that a glow discharge plasma can be created within the treatment vessel through applying a voltage between electrode 37 and treatment vessel 39.

[0252] Electrode 37 includes a hollow channel 38 for the delivery of plasma-forming feedstock into the treatment vessel. Channel 38 is integrally formed with a feed channel 35, onto which the plasma-forming feedstock supplies are attached. Two different supply routes are provided. Firstly, a liquid-filled syringe 31 is secured to channel 35 by a grommet 32. Secondly, channel includes an inlet for a gaseous feedstock 33, close to the exit of the liquid-filled syringe, such that liquid delivered from the syringe is entrained by the gaseous feedstock 33 during operation. Delivery of the gaseous feedstock 33 is controlled by a mass flow controller (not shown).

[0253] To use the equipment, a sample is loaded into the treatment vessel 39, via a removable lid. The pressure in the treatment vessel is reduced by applying a vacuum to an evacuation port on the vessel housing. Next a gaseous feedstock is supplied to the treatment vessel interior with a liquid reagent entrained in the gas via the channel 38 in the electrode, and a voltage applied between electrode 37 and treatment vessel 39 to cause formation of a glow discharge plasma. During processing, the treatment vessel 39 is rotated relative to the housing, such that the sample held in the treatment vessel is tumbled through the plasma. The sample may be rotated by continuously rotating the treatment vessel or alternatively the treatment vessel may be rocked back and forth.

[0254] FIG. 2 is a diagram of an injection unit for delivering liquids into the treatment vessel. The injection unit comprises an injector syringe, a channel leading into the treatment chamber, a grommet through which the needle of the syringe can be pushed in order to carry out the injection step and a gas inlet to the channel into the treatment vessel.

[0255] FIG. 3 is a diagram of the how gas, liquids or vapours may be delivered to a treatment vessel. Gases, liquids or vapours may be delivered through vents along the length of a central electrode A, through a vent at the end of a central electrode B, through vents in the front wall of the treatment vessel C, through vents in the side walls of the treatment vessel D or through vents in the rear wall of the treatment vessel. An injection unit allows liquid or vapour to be delivered into the treatment vessel. A mix box comprising a mass flow controller allows two or more different gases to be fed into the treatment vessel. The gas lines may also contain bubblers allowing volatile liquids to be delivered into the treatment vessel as vapours. The gas lines may also comprise trace heaters, which allow the gas lines to be held at a particular temperature.

[0256] FIG. 4 is a diagram showing the mechanism of attachment of APTES to oxygenated graphene. The APTES reacts with (condenses with) functional groups containing oxygen on the surface of the graphene. This condensation reaction results in the cross-linking of the oxygen containing functional groups on the surface of the graphene.

EXAMPLES

Example 1

[0257] The plasma treatment apparatus incorporating a system for delivering a liquid into the treatment vessel according to FIG. 1 was used to demonstrate that the plasma treatment apparatus could be used for silane functionalisation.

[0258] Tests were conducted with graphitic materials. A sample of graphitic material was loaded into the treatment vessel and subjected to treatment with plasma, formed using argon gas at 0.7 mbar with 50 W of power supplied via a 1.5 kV transformer for 60 minutes. GLYMO liquid was delivered using the injector system at a rate of 10 mL/hour. The weight percentage of carbon, oxygen, nitrogen, silicon and sulfur was determined using X-Ray Photoelectron Spectroscopy (XPS).

[0259] The spectrum for before the treatment is shown in FIG. 5, the spectrum for after the treatment are shown in FIG. 6.

Example 2

[0260] The plasma treatment apparatus incorporating a system for delivering a liquid into the treatment vessel according to FIG. 1 was used to demonstrate that the plasma treatment apparatus could be used for silane functionalisation.

[0261] Tests were conducted with boron nitride.

Example 2a

[0262] A sample of boron nitride was loaded into the treatment vessel and subjected to treatment with plasma, formed using oxygen gas at 0.7 mbar with 50 W of power supplied via a 1.5 kV transformer for 60 minutes. HDMSO liquid was delivered using the injection system at a rate of 10 mL/hour. The weight percentage of carbon, oxygen, nitrogen, silicon, boron and sulfur was determined using X-Ray Photoelectron Spectroscopy (XPS).

[0263] The spectrum for before the treatment is shown in FIG. 7, the spectrum for after the treatment is shown in FIG. 8.

Example 2b

[0264] A sample of boron nitride was loaded into the treatment vessel and subjected to treatment with plasma, formed using argon gas at 0.7 mbar with 50 W of power supplied via a 1.5 kV transformer for 60 minutes. GLYMO liquid was delivered using the injection system at a rate of 10 mL/hour. The weight percentage of carbon, oxygen, nitrogen, silicon, boron and sulfur was determined using X-Ray Photoelectron Spectroscopy (XPS).

[0265] The spectrum for before the treatment is shown in FIG. 7, the spectrum for after the treatment is shown in FIG. 9.

[0266] The results of these experiments (examples 2a and 2b) show that both carbon and boron nitride show a marked increase in silicon from the XPS scans. The high vacuum used in XPS is known to remove volatiles, so it can be concluded that the silanes are chemically bonded to the respective substrates. These examples also demonstrate silane treatment with a number of different reagents.

Example 3

[0267] The plasma treatment apparatus according to FIG. 1 was used to demonstrate that the plasma treatment apparatus could be used for silane functionalisation.

[0268] Two different graphitic materials were treated under similar conditions to those used in example 2. The results of these tests are given in table 1 below.

TABLE-US-00001 TABLE 1 O1s C1s N1s F1s Si2p Material: Edge Oxidised Graphene Oxide.sup.1 Raw (Ave) 4.86 94.53 0.61 0 0 Treated 8.87 90.24 0.59 0 0.29 Material: Graphene Nanoplatelets.sup.2 Raw (Ave) 4.28 95.35 0 0 0.3 Treated 6.95 90.29 0.96 0.05 1.75 .sup.1The power was modulated during the treatment of the edge oxidised graphene oxide; .sup.2The power was held at a constant level during the treatment of the graphene nanoplatelets.

[0269] Experiments demonstrated that silicon can be incorporated onto the surface of the carbon materials after treatment.

[0270] The above experiments demonstrate that the liquid injection system can be used to provide plasma feedstocks to effectively functionalise the carbon and boron nitride materials.