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WO1995030889A1 - Methode et dispositif pour la detection opto-electronique de composes chimiques - Google Patents

Methode et dispositif pour la detection opto-electronique de composes chimiques Download PDF

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Publication number
WO1995030889A1
WO1995030889A1 PCT/AU1995/000266 AU9500266W WO9530889A1 WO 1995030889 A1 WO1995030889 A1 WO 1995030889A1 AU 9500266 W AU9500266 W AU 9500266W WO 9530889 A1 WO9530889 A1 WO 9530889A1
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WO
WIPO (PCT)
Prior art keywords
gas
sensor
layer
sensitive material
optical properties
Prior art date
Application number
PCT/AU1995/000266
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English (en)
Inventor
Michael Gal
Anatoli Alexander Chtanov
Michael Brungs
Original Assignee
Unisearch Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Unisearch Limited filed Critical Unisearch Limited
Priority to AU23416/95A priority Critical patent/AU2341695A/en
Publication of WO1995030889A1 publication Critical patent/WO1995030889A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated

Definitions

  • the present invention relates to methods for the optical detection of gases, apparatus for the optical detection of gases and sensors for the optical detection of gases .
  • the invention relates to the optical detection of hydrogen gas .
  • Optical detection is the favoured method in most remote sensing applications, as well as in dealing with toxic and hazardous pollutants . Not all chemical species however are equally easy to detect. Hydrogen for example, is one of the most difficult gases to monitor because the molecular structure of H2 prohibits the application of conventional analytical techniques such as optical (infrared) absorption. Non-optical methods, such as monitoring of the electrical conductivity, are considered unsafe in explosive environments. A recent study (1) has shown that no commercial sensors exist which are capable of monitoring hydrogen at percentage levels (i.e. near the explosive limit) .
  • the present invention consists in a method for the detection or assay of a gas comprising the following steps:
  • the senor comprises a plurality of layers including a support layer and a semi-transparent layer of the gas-sensitive material.
  • the gas- sensitive material is covered by a layer of material protective for the gas-sensitive material.
  • the protective layer helps protect the gas-sensitive material from deterioration but which allows permeation of the gas to the gas-sensitive material.
  • the protective material is gold.
  • a portion of the layer of gas-sensitive material is covered by a layer of transparent gas-impermeable material so that only the uncovered portion of the gas-sensitive material is changeable in its optical properties when the sensor is exposed to the gas.
  • the differential change in the optical properties of the uncovered and covered portions of the gas-sensitive material is measured.
  • the transparent gas-impermeable material can be Si ⁇ 2 , Al 2 ⁇ 3 or similar compounds. Other materials, however, can be used for this layer including epoxy resins .
  • the gas is hydrogen and the gas-sensitive material is palladium.
  • the layer of palladium of the sensor is preferably less than lOOnm thick. More preferably the palladium layer has a thickness of between 10 and 50nm. In a yet still further preferred embodiment of the first aspect of the present invention the sensor is maintained at a temperature of at least 60°C.
  • the measurement of the change in the optical properties of the material sensitive to the gas can be by measuring transmission of light through the sensor or by measuring reflectance of the sensor.
  • the present invention consists in an apparatus for the optical detection or assay of a gas comprising: (a) a sensor having a layer of gas-sensitive material that changes its optical properties when contacted with the gas in a manner proportional to the concentration of the gas;
  • the senor comprises a plurality of layers including a support layer and a semi-transparent layer of the gas-sensitive material.
  • the gas- sensitive material is covered by a layer of material protective for the gas-sensitive material.
  • the protective layer helps protect the gas-sensitive material from deterioration but allows permeation of the gas to the gas- sensitive material.
  • the protective material is gold.
  • a portion of the layer of gas-sensitive material is covered by a layer of transparent gas-impermeable material so that only the uncovered portion of the gas-sensitive material is changeable in its optical properties when the sensor is exposed to the gas.
  • the differential change in the optical properties of the uncovered and covered portions of the gas-sensitive material is measured.
  • the transparent gas-impermeable material can be Si ⁇ 2 , Al 2 ⁇ 3 or similar compounds. Other materials, however, can be used for this layer including epoxy reins.
  • the gas is hydrogen and the gas-sensitive material is palladium.
  • the layer of palladium of the sensor is preferably less than lOOnm thick. More preferably the palladium layer has a thickness of between 10 and 50nm.
  • the heating means maintains the sensor at a temperature of at least 60°C.
  • the measurement of the change in the optical properties of the material in the sensor can be by measuring transmission of light through the sensor or by measuring reflectance of the sensor.
  • the apparatus optionally comprises a thermal noise reducing means.
  • This thermal noise reducing means can comprise a transparent shield arrangement between the heating means and the optical measuring means.
  • Other arrangements of this kind known to the art can also be used.
  • the present invention consists in a sensor for the optical detection or assay of a gas comprising a plurality of layers including a support layer and a semi-transparent layer of gas-sensitive material, wherein the gas-sensitive material changes its optical properties when contacted with the gas in a manner proportional to the concentration of the gas.
  • the gas-sensitive material is covered by a layer of material protective for the gas-sensitive material.
  • the protective layer protects the gas-sensitive material from deterioration but allows permeation of the gas to the gas-sensitive material.
  • the protective material is gold.
  • a portion of the gas-sensitive material is covered by a layer of transparent gas-impermeable material so that only the uncovered portion of the gas- sensitive material is changeable in its optical properties when the sensor is exposed to the gas .
  • the transparent gas-impermeable material can be Si ⁇ 2 , Al 2 ⁇ 3 or similar compounds. Other materials, however, can be used for this layer including epoxy resins.
  • the gas is hydrogen and the gas- sensitive material is palladium.
  • the layer of palladium of the sensor is preferably less than 60nm thick. More preferably, the palladium layer has a thickness of between 10 and 50nm.
  • Figure 1 is a schematic representation of a sensor according to the present invention.
  • Figure 2 is a schematic representation of an apparatus according to the present invention wherein the optical measuring means comprises two light sources and one photodetector;
  • Figure 3 is a schematic representation of an apparatus according to the present invention wherein the optical measuring means comprises one light source and two photodetectors;
  • Figure 4 is a schematic representation of an apparatus according to the present invention wherein the optical measuring means measures reflectivity of the sensor;
  • Figure 5 is a schematic diagram of an electronic circuitry for an apparatus according to the present invention.
  • Figure 6 is a graph showing the response of an apparatus according to the present invention to a burst of
  • Figure 7 is a graph showing a response of an apparatus according to the present invention to increasing concentrations of hydrogen gas.
  • Figure 8 is a graph showing a response of an apparatus according to the present invention to hydrogen gas with and without the presence of carbon monoxide gas .
  • the present invention consists in a detector 10 for measuring hydrogen by optical means. Since the molecular structure of H2 prohibits optical (infrared) absorption, the present method relies on the permeation of hydrogen from the area surrounding the detector 10 into a specially designed sensor 20 having a thin film 22 of a material sensitive to hydrogen and optically" detecting the hydrogen in this material by the change in the optical properties of the material.
  • the sensor 20 consists of a multi-element layer structure where its optical properties change as a function of the concentration hydrogen.
  • the key component in this structure is a thin film layer of palladium (Pd) 22 which is well known to preferentially absorb hydrogen (2).
  • FIG.l The schematics of the structure of the multi-layer sensor 20 are shown in Fig.l.
  • the gold layer 23 is used to minimise the oxidation and deterioration of the Pd layer 22 so as to ensure that the Pd layer 22 is able to absorb hydrogen.
  • the thickness of the Pd layer 22 is determined by the required sensitivity of the sensor 20 while the gold layer 23 thickness is determined by its optical transparency.
  • a portion 27 of this structure can be covered by layer 25 of another transparent gas-impermeable material, such as Si ⁇ 2 , or Al 2 ⁇ 3 , while the other portion 28 of the sensor 20 is uncovered.
  • the thin gold film 23 is permeable to hydrogen but the Si ⁇ 2 (or Al 2 ⁇ 3 ) film 25 is not. Thus upon exposure to hydrogen, only the palladium not covered by Si ⁇ 2 will be able to absorb hydrogen, the other portion 27 will be unaffected by it.
  • the sensor is heated to a temperature of 50°C or higher. Preferably, a temperature of at least 60°C is used.
  • the measurement of hydrogen is based on the difference in the transparency of the two portions 27, 28 of the sensor.
  • SUBSTT ⁇ UTE SHEET(Rule26) The present inventors found that using glass quartz or sapphire as the support 21 material alone resulted in poor sensor 20 stability and problems of long term drift (due to impurity diffusion from the substrate into the Pd film 22). To overcome this problem, a "buffer" layer 24 was applied between the support 21 and the Pd film 22.
  • Several metal layers, such as chromium or aluminium, and also with dielectric materials, such as Al 2 ⁇ 3 (by oxidising Al) , Si ⁇ 2 , SiO x and MgF 2 were tried. Metal films were soon abandoned due to the opaqueness of the thicker films. Of the dielectric materials tried, MgF 2 was found to be the best. It forms the necessary "screen” to suppress the impurity diffusion from the support 21 into the metal, has the correct optical transparency and also proved to have the required mechanical properties .
  • the sensor 20 was insensitive to the thickness of the MgF 2 film. An approximately 0.5 ⁇ m thick layer 24 between the glass support 21 and the Pd film 22 was used.
  • the protective layer 23 which covers the Pd film 22.
  • This layer had to protect the active layer (Pd) 22 from deteriorating with time due to oxygen, moisture etc, but at the same time had to be optically transparent, stable and, most importantly, had to be permeable to hydrogen.
  • a number of films such as Ag, In, Bi, Si ⁇ 2 , polyamide, etc were tested and several of them satisfied one or other of the requirements but only an approximately 35nm thick gold film fulfilled all the requirements adequately. Therefore, in the sensors, the "active" Pd film 22 is covered by an approximately 35nm thick gold film 23.
  • the question of the Pd film 22 thickness is important as it significantly affects the key device parameters: mechanical stability, time constant and sensitivity.
  • thermally evaporated thick films d > lOOnm
  • Thin films d ⁇ 50nm
  • the optimum layer thicknesses were found to be in the lOn ⁇ d ⁇ 50nm thickness range.
  • the mechanical stability of thicker layers could be improved by depositing the films onto other supports such as chromium on glass, or by using other deposition methods, such as sputtering.
  • the film 22 thickness was also found to affect the sensor 10 time constant. As expected from diffusion considerations, the time constant increases monotonically with the Pd film 22 thickness. In the range lOnm ⁇ d ⁇ 50nm the time constant is less than 20/s as can be seen in Fig. 6.
  • the sensitivity of the sensor 20 is also a function of the Pd film 22 thickness. Thinner films were more sensitive to lower concentrations of hydrogen, while thicker films were more sensitive to higher concentrations of hydrogen. The thickness range lOnm ⁇ d ⁇ 50nm was found to be optimal for the 1%-10% hydrogen range.
  • a portion 27 of the layer structure is covered with a hydrogen impenetrable layer 25 and left the portion 28 half "bare". To achieve this, half of the glass MgF 2 d/Au layer structure 27 was covered with either Si ⁇ 2 , Al 2 ⁇ 3 or a thin epoxy layer, while leaving the other half 28 uncovered.
  • the measurement of hydrogen is based on the difference in the transparency (reflectivity) of the two portions 27 and 28 of the palladium film 22.
  • the in situ monitoring of the layer thickness is important. This is conventionally done with a built-in thickness monitor which is calibrated for the different materials and systems .
  • the inventors developed and used an inexpensive optical method of monitoring the layer thickness during growth using the transmission of the film itself as a measure of the film thickness. This involved a light emitting diode and a photodiode built into the evaporation equipment. After accurate calibration, this method proved to be suitable for the requirements .
  • the optical measurement is based on a technique called differential transmission, shown in Fig. 2.
  • This technique is capable of measuring very small differences in optical constants.
  • the sensor 20 is illuminated alternatively by a light source 41 in the form of two light emitting diodes (LED's) and the light transmitted through the sensor 20 is detected by a photodetector 42. If there is no hydrogen in the area surrounding the sensor 20, the two portions 27, 28 of the palladium film 22 will have identical transparencies and the photodetector 42 will only generate a DC (constant) signal.
  • the transparencies of the two portions 27, 28 of the palladium film 22 will differ (because only one portion 28 of the Pd films "sees” the hydrogen) and therefore the photodetector 42 will generate two different signal levels depending which LED is on.
  • the resulting AC signal is proportional to the amount of hydrogen in the Pd film 22, and thus proportional to the amount of hydrogen in the area surrounding the sensor 20. This AC signal is carefully measured by an ensuing electronic circuitry as set out in Fig. 5.
  • the electronic circuitry of the apparatus was designed to have the following general properties: (*) high sensitivity and low noise
  • the primary modules of an apparatus having two photodetectors is shown in Fig. 5 are a low noise pre ⁇ amplifier, a follow-on amplifier, a phase-locked detector, an oscillator and a voltmeter.
  • a separate unit was used to control and monitor the temperature of the sensor.
  • the role of the low noise pre-amplifier is to amplify the difference signal generated by the two photodetectors. It is this signal which is proportional to the hydrogen concentration. This was achieved by using two low-noise instrumental amplifiers (XR 5533) and 100% negative feedback loops for AC and DC components of the signal.
  • the photodetectors are included in the negative feedback loops so that the whole input stage is stabilised by the high quality amplifiers.
  • the AC component of the signal is first amplified by an adjustable gain amplifier (XR 5533) then rectified by the phase-locked detector.
  • the ensuing DC signal is amplified by the buffer amplifier, measured by a voltmeter and is displayed on a liquid crystal display.
  • the signal may be converted to hydrogen percentage by examining the calibration curve of the given sensor.
  • An op-amp generates the sine current for the LED's.
  • the phase-locked detector, oscillator and output buffer-filter are all components of the same integrated circuit (SE 5521).
  • the reference signal for the phase- sensitive detector and the LED power supply are generated by the oscillator which operates at audio frequencies (few hundred HZ)
  • the method is independent of the angle of incidence, the polarisation and the wavelength of light and provides great flexibility in the optical alignment of the system.
  • a different version of the optical arrangement is shown in Fig. 3, where only one LED is used as the light source 41 which illuminates both portions 27 and 28 of the palladium film 22, and the differential nature of the technique is achieved by using two photodetectors 42 which are alternately turned on and off.
  • Figs . 3 and 4 also shows the placement of the heating means 30 for the sensor 20. The differences in optical transmission of the two portions of the sensor are measured and amount of hydrogen present is determined.
  • the hydrogen concentration is determined from the measured optical (electrical) signal by examining the calibration curve of the given sensor 20.
  • the calibration of each sensor 20 was achieved by the use of known concentrates of hydrogen/air mixtures .
  • a typical calibration for a 20nm thick Pd film 22 is shown in Fig.7.
  • the chosen concentration range of hydrogen includes the explosive limit (4%).
  • the sensitivity of the detector 10 to other gases was also tested. There was no detectable response from the detector to the following species: N2, He, Ar, CO2 , H2O, CH4.
  • the chemical selectivity of this detector 10 for hydrogen is obtained by the use of palladium as the active material owing to its capacity to selectively absorb hydrogen. The simplicity of the design ensures either a portable unit or a fibre optic system capable of monitoring hydrogen in hazardous environments .
  • differential reflectance may be desirable.
  • the change in reflectivity of the two portions 27 and 28 of the Pd film 22 is measured.
  • this measurement is also a function of the optical constants it is therefore just as sensitive to hydrogen as the differential absorption method described above.
  • the sensor 20 may be used in the reflectivity mode, as shown in Fig. 4.
  • the support layer 21 has a layer 26 having a reflective characteristic (for example a mirror) .
  • This reflective layer 26 reflects light coming from the light source 41.
  • This method has additional advantages as compared to the transmission method as light propagates through the gas-sensitive material film 22 twice thereby increasing the sensitivity of the detector 10. It also makes the heating of the sensor simple as all the optical measuring means 40 is on one side of the sensor 20.
  • Carbon monoxide (CO) is a gas which in coal mines often coexists with hydrogen. To selectively detect hydrogen the sensor should not be affected in any way by CO or any other gas .
  • the inventors have found that by using a heating means 30 and heating the sensor 20 containing the palladium film 22 to at least 50°C the deleterious effect of CO can be eliminated. A temperature of 60°C or greater was also found to overcome the effect of CO. Furthermore, only the sensor 20 containing the Pd film 22 needs to be heated and the measuring means 40 may be at room temperature. The results of the device operating at 60°C detecting 1% hydrogen in air with the presence of 5% of CO in given in Fig. 8. This would be an extreme case occurring in a coal mine and demonstrates that the detector and sensor works under these extreme conditions . In order to minimise any thermal noise from heating means 30 to the optical measuring means 40, the present inventors found that this can be achieved by placing between the heating means 30 and the optical measuring means 40. One form of the means to reduce thermal noise found suitable was a transparent shield arrangement in the form of glass plate or plates between the heating means and the optical measuring means 40. Other insulating means known to the art would also be suitable for the present invention.

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Plasma & Fusion (AREA)
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Abstract

La présente invention concerne des méthodes de détection ou de dosage d'un gaz, consistant à mettre un appareil (10) comprenant un détecteur (20) en présence de ce gaz pendant une durée déterminée. Le détecteur (20) porte une couche (22) d'une substance qui est sensible au gaz et dont les propriétés optiques changent lorsqu'elle est en contact avec le gaz, d'une manière proportionnelle à la concentration du gaz. Ensuite, on chauffe le détecteur à une température d'au moins 50 °C en utilisant un dispositif de chauffage (30), puis on mesure le changement des propriétés optiques de la substance (22) sensible aux gaz du détecteur (20). La présente invention concerne également l'appareil pour détecter ou doser un gaz et des détecteurs comprenant une pluralité de couches dont une couche de support (21) et une couche semi-transparente (22) d'une substance sensible au gaz.
PCT/AU1995/000266 1994-05-09 1995-05-09 Methode et dispositif pour la detection opto-electronique de composes chimiques WO1995030889A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU23416/95A AU2341695A (en) 1994-05-09 1995-05-09 Method and device for optoelectronic chemical sensing

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPM5519 1994-05-09
AUPM5519A AUPM551994A0 (en) 1994-05-09 1994-05-09 Method and device for optoelectronic chemical sensing

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WO1995030889A1 true WO1995030889A1 (fr) 1995-11-16

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000005570A1 (fr) * 1997-03-24 2000-02-03 Westinghouse Savannah River Company Systeme capteur a fibres optiques de temperature et de concentration d'hydrogene gazeux
WO2007121935A1 (fr) * 2006-04-20 2007-11-01 Hochschule Wismar Capteur d'hydrogène
EP1998169A1 (fr) * 2006-03-20 2008-12-03 Kabushiki Kaisha Atsumitec Capteur a hydrogène
CN112649161A (zh) * 2020-11-27 2021-04-13 宝武清洁能源有限公司 气敏色变传感器及基于气敏色变传感的加氢站安全盾系统

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108240967B (zh) * 2018-01-11 2023-05-12 重庆理工大学 一种带外罩的气敏特性响应曲线测试装置

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU3135184A (en) * 1983-08-12 1985-02-14 Hochiki K.K. Gas sensor
JPS61201141A (ja) * 1985-03-04 1986-09-05 Agency Of Ind Science & Technol 水素検知光センサ−
JPS62170840A (ja) * 1986-01-23 1987-07-27 Agency Of Ind Science & Technol 水素検知光センサ
JPS62251638A (ja) * 1986-04-24 1987-11-02 Hochiki Corp 水素センサ
JPS62251637A (ja) * 1986-04-24 1987-11-02 Hochiki Corp 水素センサ
GB2198844A (en) * 1986-07-17 1988-06-22 Atomic Energy Authority Uk Gas sensor
JPH04109157A (ja) * 1990-08-29 1992-04-10 Riken Corp ガス検知素子
JPH05196569A (ja) * 1992-01-22 1993-08-06 Nippon Sheet Glass Co Ltd 水素センサ

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU3135184A (en) * 1983-08-12 1985-02-14 Hochiki K.K. Gas sensor
JPS61201141A (ja) * 1985-03-04 1986-09-05 Agency Of Ind Science & Technol 水素検知光センサ−
JPS62170840A (ja) * 1986-01-23 1987-07-27 Agency Of Ind Science & Technol 水素検知光センサ
JPS62251638A (ja) * 1986-04-24 1987-11-02 Hochiki Corp 水素センサ
JPS62251637A (ja) * 1986-04-24 1987-11-02 Hochiki Corp 水素センサ
GB2198844A (en) * 1986-07-17 1988-06-22 Atomic Energy Authority Uk Gas sensor
JPH04109157A (ja) * 1990-08-29 1992-04-10 Riken Corp ガス検知素子
JPH05196569A (ja) * 1992-01-22 1993-08-06 Nippon Sheet Glass Co Ltd 水素センサ

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000005570A1 (fr) * 1997-03-24 2000-02-03 Westinghouse Savannah River Company Systeme capteur a fibres optiques de temperature et de concentration d'hydrogene gazeux
EP1998169A1 (fr) * 2006-03-20 2008-12-03 Kabushiki Kaisha Atsumitec Capteur a hydrogène
EP1998169A4 (fr) * 2006-03-20 2011-10-12 Atsumitec Kk Capteur a hydrogène
WO2007121935A1 (fr) * 2006-04-20 2007-11-01 Hochschule Wismar Capteur d'hydrogène
CN112649161A (zh) * 2020-11-27 2021-04-13 宝武清洁能源有限公司 气敏色变传感器及基于气敏色变传感的加氢站安全盾系统

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