JPS61204545A - Detecting photosensor for hydrogen - Google Patents

Abstract

PURPOSE:To measure the concentration of gaseous hydrogen by embedding a light guide in a substrate, forming a light absorbing layer which varies in coefficient of light absorption by reaction on dissociated hydrogen on the surface of the substrate, and providing a dissociative absorbing layer for gaseous hydrogen thereupon. CONSTITUTION:The light guide 2 which is larger in refractive index than the substrate is embedded in one body, and the light absorbing layer 3 made of a dielectric which varies in coefficient of light absorption by reaction on dissociated hydrogen and the adsorbing layer 4 made of a material which dissociate and adsorbs gaseous hydrogen are provided on the surface of the substrate to a sensor. Light from a light source 6 is made incident through one fiber 5A and the quantity of projection light from the other fiber 5B is measured by a photodetector 7. When hydrogen is adsorbed to the surface of the adsorbing layer of the sensor to cause dissociation, generated electrons and protons are received by the light absorbing layer under the adsorbing layer, so that the light absorbing layer increases in coefficient of light absorption. Consequently, the ratio of absorptive attenuation of an evanescent wave from the light guide to the light absorbing layer or light leaking from the light guide by the absorbing layer increases. The increase in coefficient of light absorption is proportional to the concentration of adsorbed gaseous hydrogen, so the concentration of the gaseous hydrogen is known.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sensor for optically detecting hydrogen useful in oil refining plants and the like.

[Description of prior art]

As shown in FIG. 6, conventional sensors for detecting hydrogen include an oxide semiconductor layer 10 such as 5N02 or ZnO on an insulating substrate 100, and a pair of electrodes placed on the semiconductor layer 10 and facing each other at a distance. 102Av102B is provided,
A semiconductor sensor ios is known in which a heating heater 103 and a heating electrode IO'l are arranged on the back side.

In the semiconductor sensor 103 described above, the semiconductor layer 10/
When hydrogen gas is chemically adsorbed on the semiconductor layer 10, electrons are generally exchanged between the hydrogen gas and the semiconductor, and as a result, the semiconductor layer 10
The carrier concentration increases over a certain thickness range from the surface of the semiconductor layer 10/, and the electrical resistance of the semiconductor layer 10/ decreases, so that the electrode 102
, the current flowing through 102B increases. Further, in order to increase the reaction speed, electricity is supplied to the heater 103 on the back surface of the substrate to maintain the substrate 100 at a high temperature.

In addition to the above structure, there are also known devices that utilize the rectifying action of a metal gate and a semiconductor junction, or the gate action of a MOSFET, for detecting hydrogen gas.

In this case, the hydrogen gas concentration is measured by changing the electron energy level difference between the metal and the semiconductor due to hydrogen gas adsorption.

[Problems to be Solved by the Invention] The conventional hydrogen gas detection sensor using an oxide semiconductor described above has a slow reaction rate at room temperature, and therefore usually J j
It must be heated to about O''C before use, and a heating heater must be installed.

Additionally, there is the problem that oxidation and deterioration, crystal grain growth, and precipitation occur on the sensor surface, and the detection performance deteriorates relatively quickly due to changes over time. Furthermore, for flammable and explosive gases such as hydrogen gas, special work must be done to make the wiring from part of the sensor explosion-proof. Furthermore, the selectivity for hydrogen gas is poor, and a highly reliable hydrogen gas detection sensor has not yet been put into practical use.

[Means to solve problems]

An optical waveguide with a refractive index higher than that of the substrate is integrally embedded near the surface of the substrate or partially exposed on the surface.
A light absorption layer made of a dielectric material whose light absorption coefficient changes upon reaction with dissociated hydrogen is provided on the substrate surface above this waveguide', and an adsorption layer made of a substance that dissociates and adsorbs hydrogen gas is provided on this light absorption layer. to configure the sensor.

Then, seven optical eyebars are connected to both ends of the optical waveguide, and light from a light source is made incident through one of the seven eyebars, and the amount of light emitted from the other fiber is measured.

[For production]

When hydrogen is adsorbed on the surface of the adsorption layer of the sensor having the above structure and dissociated, electrons and protons are generated, and upon receiving these electrons and protons, the light absorption coefficient of the light absorption layer under the adsorption layer increases.

As a result, the rate at which evanescent waves leaking from the optical waveguide into the light absorption layer or light leaking directly from the waveguide into the light absorption layer is absorbed and attenuated by the absorption layer increases. Since the increase in the optical absorption coefficient is proportional to the proton density, that is, the concentration of adsorbed hydrogen gas, the hydrogen gas concentration can be determined by measuring the decrease in the amount of light emitted from the optical waveguide.

〔Example〕

The present invention will be described in detail below based on embodiments shown in the drawings.

In Figures 1 and 2, / is a substrate made of glass, plastic, etc. that is transparent to the wavelength used;
An optical waveguide 2 is embedded therein and integrally with the substrate.

This optical waveguide 2 has a circular cross section approximately equal to the core diameter of the fiber to be connected, has a refractive index larger than that of the substrate, and has a distribution that is maximum on the central axis and gradually decreases toward the periphery. In order to create such a buried waveguide with a refractive index gradient, one side of the glass substrate is masked with an opening in the waveguide pattern, and through the opening, thallium ions, lithium ions, etc. contribute to the increase in the glass refractive index. Diffusion of ions into the substrate.

By the above-described first stage ion exchange treatment, a waveguide having a substantially semicircular cross section and a refractive index gradient is formed in the substrate directly under the masking opening.

When a second stage ion exchange process is performed in which ions are diffused while applying a DC voltage between both sides of the substrate, high refractive index ions move deep and low refractive index ions diffuse from above, forming a semicircular shape. The waveguide has a circular cross section.

A light absorption layer 3 is provided on the substrate surface /A directly above the optical waveguide 2 formed as described above, and a hydrogen adsorption layer q is further laminated on this light absorption layer 3. The hydrogen adsorption layer 1 is made of a substance that adsorbs and dissociates hydrogen gas to generate electrons and protons, and the light absorption layer 3 is made of a substance whose light absorption coefficient changes upon reception of the electrons and protons.

Palladium (Pa) or platinum (Pt) is suitable as the material for the adsorption layer t.

In addition, WO3 is suitable as a material for engraving the light absorption layer 3, and other inorganic materials that generally exhibit electrochromic properties, such as Gf M2O3 + V2O5 + TlO2yI
r(OH)n, Rh2O3.xH2O, etc. can be used.

Further, the light absorption layer 3 may be composed of an organic material, such as hebyl viologen, cyanophenyl pyrogen, cobalt pyridyl complex, polymerized tetra-opfulvalene (
TTF), lutetium diphthalocyanine, etc. can be used.

An optical fiber i is connected to one end of the waveguide 2 of the sensor described above, and the other end of the fiber 5A is connected to a light source B. An optical fiber 5B is also connected to the other end of the waveguide 2, and the other end is connected to a photodiode. The amount of light received is measured by connecting it to a photodetector 7 such as the following. When hydrogen gas comes into contact with the Pd film of the sensor 10 having the above structure, electrons and protons are generated by the hydrogen reduction action of the Pd film ψ.
The light is injected into the light absorption layer 3 made of O3, and the following reaction occurs.

WO3+xH10xe-→HxWO3 (1) As the above reaction progresses, the light absorption layer 3 of WO3 is colored and the light absorption coefficient increases. It is the reduction action of hydrogen gas by the Pd film l that provides the protons and electrons on the left side of equation (1), and the increase in the light absorption coefficient is proportional to the density of protons, in other words, the concentration of adsorbed hydrogen gas.

In this way, the light absorption layer 3 is colored according to the concentration of hydrogen gas present at the location where the sensor is installed, and light such as evanescent waves that leaks from the waveguide 2 and passes through the absorption layer 3 is absorbed. If you measure the amount of light received using a piece of paper that attenuates and reduces the amount of light emitted from the optical waveguide 2, the hydrogen You can know the gas concentration.

Next, a specific numerical example is shown.

A glass plate was used as the substrate, and a refractive index gradient waveguide having a substantially circular cross section was embedded in the substrate using the two-step ion exchange method described above.

Next, a thin film of tungsten oxide (WO3) was vacuum-deposited on the surface of the substrate 1 as a light absorption layer 3 to a thickness of 1 μm. W
O3 was deposited by resistance heating using a W-wire crucible coated with alumina from pellets with a purity of 99.99%. The deposition conditions were: oxygen pressure /
The three films were polycrystalline and colorless and transparent. Furthermore, palladium (
The Pa) film was deposited by electron beam thermal evaporation to a thickness of 100X.

The sensor fabricated as described above is installed in the atmosphere where the detector is to be detected, and the light is transmitted through an optical fiber connected to a waveguide.
When light from the ED (wavelength: 3 μm) was input, a PIN 7 photodiode was placed on the output side to detect the output light amount, and the hydrogen concentration was determined from a pre-prepared calibration curve, it was 110-2000pp. A detection accuracy of ±j% was obtained over a hydrogen gas concentration range of .

In the numerical example explained above, infrared light with a wavelength of 83 μm was used, but He-Ne laser (wavelength o, g 32 rμm) was used.
A similar effect can be obtained even if a semiconductor laser (wavelength: O6 spm) is used as a light source.

When using these wavelength regions, it is better to use amorphous as WO3. A method for producing amorphous WO3 is to lower the substrate temperature during vapor deposition to 2jO''C or less.

In the embodiment shown in FIGS. 1 and 1, the optical waveguide 2 with a circular cross section is completely embedded in the substrate l,
As shown in the figure, the top 2A of the waveguide is connected to the surface of the substrate.
A light absorption layer 3 may be provided in contact with this exposed portion. Furthermore, as shown in FIG. 4, a thin transparent film 1 may be added as a buffer 7 layer between the optical waveguide λ exposed on the substrate surface and the light absorption layer 3. Furthermore, in addition to forming the optical waveguide 2 by the ion exchange method, as shown in FIG. ,
The cladding layer 13 may be polished flush with the substrate 1 to the vicinity of the core portion 12 or to the core portion /2, and a predetermined light absorption layer 3 and a hydrogen adsorption layer may be provided thereon. Further, the cross section of the optical waveguide 2 is preferably circular in order to reduce the coupling loss with the fiber, but may be rectangular in some cases.

(Effects) According to the present invention, not only can hydrogen gas be detected using only optical signals, but also all the advantages of light such as miniaturization, high reliability, heat resistance, electromagnetic induction resistance, fire resistance, and explosion protection can be utilized. In oil refining plants and other plants, hydrogen gas is used extensively for reforming petroleum products, and there is a high demand for safe and highly reliable remote sensing.Moreover, the local loop using Hikari 7 AIPA can be used in the measurement system. In the sense of signal transmission, information and measurement data tend to be treated equally.Therefore, the technology that allows sensing using only light without converting optical signals into electrical signals is based on the optical fiber local technology described above. The compatibility with the loop is also very good.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a first embodiment of the present invention, Fig. 2 is a front view thereof, Fig. 3 is a front view showing a second embodiment of the invention, and Fig. ψ is a sectional view showing a third embodiment of the invention. FIG. 5 is a front view showing an example, FIG. 5 is a sectional view showing a second embodiment of the present invention, and FIG. 6 is a perspective view showing a conventional sensor.

Claims (6)

[Claims] (1) An optical waveguide with a higher refractive index than the substrate is integrally embedded in the substrate near the surface or partially exposed on the surface, and the substrate surface on the waveguide is formed by a reaction with dissociated hydrogen. 1. A hydrogen-detecting optical sensor, comprising: a light-absorbing layer made of a dielectric whose light absorption coefficient changes; and an adsorption layer made of a substance that dissociates and adsorbs hydrogen gas on the light-absorbing layer. (2) The hydrogen detection optical sensor according to claim 1, wherein the adsorption layer is palladium (Pd). (3) The hydrogen detection optical sensor according to claim 1, wherein the adsorption layer is platinum (Pt). (4) In claim 1, the light absorption layer is made of WO.
Hydrogen detection optical sensor formed with _3. (5) In claim 1, the light absorption layer is M
oO_3, V_2O_5, TiO_2, Ir(OH)_
A hydrogen detection optical sensor formed of at least one selected from n, Rh_2O_3 and xH_2O. (6) In claim 1, the light absorption layer includes hep-er viologen, cyanophenyl pyrogen, cobalt pyridyl complex, polymerized tetrathiofulvalene (
A hydrogen detection optical sensor formed of at least one organic material selected from TTF) and lutetium diphthalocyanine.