Optical detection of tracer gases in a gas discharge cell having unexposed electrodes

Abstract

Tracer gas sensing device comprising a gas discharge cell having cell walls defining a discharge volume and a tracer gas inlet into the discharge volume, an optical spectrometer arrangement having a radiation source on a first side of the discharge cell for emitting radiation into the discharge cell and a radiation detector on a second side of the discharge cell opposite to the first side for detecting radiation which was emitted by the radiation source through the discharge volume, and electrodes on opposing sides of the discharge cell for generating a plasma within the discharge cell, said electrodes being unexposed plasma electrodes. The discharge cell may be a dielectric barrier discharge cell and the electrodes may be powered by an AC power source.

Claims

1. A tracer gas sensing device comprising: a gas discharge cell having cell walls defining a discharge volume and a tracer gas inlet into the discharge volume, wherein the tracer gas inlet comprises a gas selective membrane comprising a layer of thermally densified spin-on glass dielectric; an optical spectrometer arrangement having a radiation source on a first side of the gas discharge cell for emitting light into the gas discharge cell and a radiation detector on a second side of the gas discharge cell opposite to the first side for detecting radiation that is emitted by the radiation source through the discharge volume; and electrodes on opposing sides of the gas discharge cell for generating a plasma within the gas discharge cell, said electrodes being unexposed plasma electrodes.

2. The tracer gas sensing device according to claim 1, wherein an electrically insulating material is provided between each electrode and the discharge volume.

3. The tracer gas sensing device according to claim 2, wherein each electrode is covered by said electrically insulating material.

4. The tracer gas sensing device according to claim 2, wherein the electrically insulating material is a portion of a cell wall of the gas discharge cell.

5. The tracer gas sensing device according to claim 1, wherein the gas discharge cell is a dielectric barrier discharge cell.

6. The tracer gas sensing device according to claim 1, wherein the electrodes are powered by an AC power source.

7. The tracer gas sensing device according to claim 1, wherein the discharge volume comprises a buffer gas.

8. The tracer gas sensing device according to claim 7, wherein the buffer gas comprises argon.

9. The tracer gas sensing device according to claim 1, wherein the gas discharge cell comprises a buffer gas inlet and a buffer gas outlet.

10. The tracer gas sensing device according to claim 1, wherein the discharge volume has a cross-sectional width of less than 10 mm in a plane lateral with regard to a direction of radiation traveling from the radiation source to the radiation detector.

11. The tracer gas sensing device according to claim 1, wherein the layer of thermally densified spin-on glass dielectric is leveled and/or capped with a thermally re-flown layer of chemical vapor deposition borophosphosilicate glass.

12. The tracer gas sensing device according to claim 1, wherein an inner surface of at least a portion of the cell walls of the gas discharge cell comprises a dielectric material.

13. The tracer gas sensing device according to claim 1, wherein electrons of the gas discharge cell are excited by a high frequency source.

14. The tracer gas sensing device according to claim 1, further comprising at least a further radiation source.

15. A method for separating a gas component from a gas, by employing a spin-on glass wafer as a gas selective membrane for separating the gas component.

16. The method according to claim 15, wherein the spin-on glass wafer is a silica oxide semiconductor.

17. The method according to claim 15, wherein the spin-on glass wafer comprises a layer of thermally densified spin-on glass dielectric.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, embodiments of the invention are described with reference to the Figures.

(2) FIG. 1 shows a schematic view of a first embodiment,

(3) FIG. 2 shows a schematic view of a second embodiment,

(4) FIG. 3 shows a schematic view of a third embodiment,

(5) FIG. 4 shows a schematic view of a fourth embodiment,

(6) FIG. 5 shows a schematic view of a fifth embodiment,

(7) FIG. 6 shows a schematic view of a sixth embodiment,

(8) FIG. 7A shows a schematic view of an embodiment of the membrane arrangement,

(9) FIG. 7B shows a schematic view of an further embodiment of the membrane arrangement and

(10) FIG. 7C shows a schematic view of an even further embodiment of the membrane arrangement,

(11) FIG. 8 shows a perspective view of an embodiment,

(12) FIG. 9 shows a perspective view of another embodiment and

(13) FIG. 10 shows a perspective view of an even further embodiment.

DESCRIPTION OF THE INVENTION

(14) In FIG. 1, the gas discharge cell 12 has cell walls 14 made of glass, forming a glass cell. The tracer gas inlet 16 carries an inlet housing 18 in which a tracer gas selective membrane 19 is housed. The tracer gas inlet 16 is further connected to a line 20 carrying a valve 22 connected to the tracer probe. The line 20 is connected to a further valve 24 connected to a calibrated leak for calibration purposes.

(15) An optical spectrometer arrangement comprises a radiation source 26 in the form of a laser diode. The radiation source 26 is located at a first end of the discharge cell 12. On a second end opposite to the first end, a radiation detector (photo cell) 28 is located. Radiation emitted by the radiation source 26 enters the discharge cell, travels all the way through the discharge volume 30 surrounded by the cell walls 14, leaves the discharge cell at the opposite end and hits the radiation detector 28 where it is detected.

(16) Two electrodes 32 are located on further opposing sides of the discharge cell 12. The electrodes are unexposed to the gas within the discharge cell 12 because the glass cell walls 14 are arranged between the electrode 32 and the discharge volume 30.

(17) The electrodes 32 are provided with AC high voltage at a frequency in the kilohertz or MHz range provided by the voltage generator 34.

(18) A buffer gas source 36 is connected to a buffer gas inlet 38 of the discharge cell 12 via a buffer inlet line 40 and a buffer inlet valve 43. The buffer gas entering the discharge volume 30 through the buffer gas inlet 38 flows through the discharge cell 12 and leaves the cell through the buffer gas outlet 42 at an end of the cell 12 close to the photo detector 28. From the buffer gas outlet 42, the buffer gas is lead through a buffer gas outlet line 44 and a buffer gas outlet valve 46 to a rotary vane pump 48 pumping the gas from the source 36 through the cell 12.

(19) The embodiment of FIG. 2 differs from the embodiment of FIG. 1 in that the discharge cell is a static cell without a buffer gas inlet and a buffer gas outlet.

(20) Rather, the buffer gas is maintained within the discharge volume 30. The housing 18 of the tracer gas inlet 16 is connected via a vacuum line 50 and a valve 52 to a pump arrangement comprised of a turbo pump 44 and a diaphragm pump 46.

(21) The embodiment according to FIG. 3 differs from the embodiment according to FIG. 2 in that the vacuum line 50 and vacuum valve 52 are connected to a diaphragm pump only rather than to the pump system of FIG. 2. Further, the housing 18 of the gas inlet 16 is connected via a second vacuum line 58 and a second vacuum valve 60 to a source 62 of pumping gas which is pumped via a filter 64 through the second vacuum line 58, the second vacuum valve 60 and the housing 18 of the gas inlet and from their via the first vacuum line 50 and the first vacuum valve 52 to the diaphragm pump 56. The pumping gas is guided past the membrane 19 within the gas inlet housing 18.

(22) The embodiment of FIG. 4 also has a static gas discharge cell 12 without a buffer gas inlet and buffer gas outlet. The electrodes 32 are electrically connected to a radio frequency power generator 62, supplying an AC voltage having a frequency in the megahertz range to the electrodes 32.

(23) The gas discharge cell 12 contains a buffer gas mixture comprising ambient helium and neon, argon, nitrogen or oxygen. An excited state buffer gas mixture results from the radio frequency power supplied via the electrode 32.

(24) The gas inlet 16 of the gas discharge cell 12 carries a housing 18, an outer wall of which is formed by a membrane 19 having a heat activated thin section, examples of which are shown in further detail in FIGS. 7A, 7B and 7C. Like membranes are also employed in the embodiments of FIGS. 5 and 6. The housing 18 further comprises a hydrogen getter 64.

(25) The embodiment of FIG. 5 differs from the embodiment in FIG. 4 in that the gas discharge cell 12 comprises a buffer gas inlet 38 connected to a buffer gas refill container 66 via a refill valve 67. A buffer gas outlet is not provided. The buffer gas may be helium, hydrogen, neon, argon, nitrogen or oxygen.

(26) A further difference over the embodiment of FIG. 4 is that the portion of the gas inlet housing 18 carrying the membrane 19 is connected to an evacuated test object 68 in the form of a vacuum chamber which is under leak test. The outside of the test object 68 may be sprayed with the tracer gas which enters into the test object 68 through a leak 70. Alternatively, ambient gases entering through the leak 70 may be employed as tracer gas. The tracer gas which has entered into the test object 68 enters the gas discharge cell 12 through the membrane 19 and the tracer gas inlet 16. The membrane 19 carries a heat activated thin section as described above with regard to FIG. 4 and as shown in further detail in FIGS. 7A-7C.

(27) The embodiment of FIG. 6 differs from the embodiment of FIG. 5 in that the gas discharge cell 12 has no buffer gas inlet 38 connected to a buffer gas container. Rather, the discharge cell 12 is prefilled with the buffer gas which may be argon, nitrogen or oxygen, being excited within the discharge cell 12. The electrodes 32 are also powered by radio frequency AC voltage in the megahertz range supplied by the RF power generator 62.

(28) FIGS. 7A, 7B and 7C each show embodiments of the membranes 19 employed in FIGS. 4, 5 and 6, each having a heat activated thin section. In FIG. 7A, a thermally densified spin-on-glass film 72 having a thickness in the range of 30-200 nm is coated onto a porous support 74. In FIG. 7B, an additional borophosphosilicate glass layer 76 is coated onto the spin-on-glass film 72 via chemical vapor deposition.

(29) In the embodiment in FIG. 7C, the porous support layer 74 carrying a spin-on-glass layer 72 and a borophosphosilicate glass layer 76 on top of the layer 72 is coated onto a support structure 78. The porous support layer 74 may be a spin-on-glass layer doped with tin and platinum (for example) having a pore size in the range of 3-70 nm.

(30) FIG. 8 shows a perspective view of the discharge cell 12 in FIG. 1. The discharge cell 12 is arranged as a one path cell, i.e. a single laser beam 80 is guided through the cell from the radiation source 26 to the photo detector 28. The length of the electrode is 50 mm and the cross section of the cells outer dimensions in a plain lateral to the direction of the laser beam 80 has a width of 3 mm and a height of 2 mm.

(31) FIG. 9 shows an embodiment in which the discharge cell 12 is arranged to be a 10 path cell, i.e. 10 laser beams 80 are guided through the cell 12 in parallel. A mirror 82 may reflect the radiation beams 80. The mirror 82 may be considered a radiation source at an end of the cell opposite to the photo detector which is not shown in FIG. 9. The width of the cell in FIG. 9 is 15 mm rather than 3 mm in FIG. 8.

(32) FIG. 10 shows a 100 path cell in which the gas discharge cell 12 is formed as a cube surrounded by a tubular electrode 32 entirely surrounding the cell 12. The cross section of the gas discharge volume 30 is ring-shaped.