JPH0210375B2 - - Google Patents

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]

Conventionally, as a sensor for detecting hydrogen, as _shown in FIG.
A pair of electrodes 10 facing each other with an interval on 01
A semiconductor sensor 105 is known in which sensors 2A and 102B are provided, and a heating heater 103 and a heating electrode 104 are arranged on the back side.

In the semiconductor sensor 105 described above, when hydrogen gas is chemically adsorbed on the semiconductor layer 101, electrons are generally exchanged between the hydrogen gas and the semiconductor.
As a result, the carrier concentration increases over a certain thickness range from the surface of the semiconductor layer 101.
The electrical resistance of electrodes 102A and 102B decreases.
The current flowing through 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 structures that utilize the rectifying effect of a metal gate and semiconductor junction or the gate effect of a MOSFET for hydrogen gas detection.

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

[Problem that the invention seeks to solve]

The conventional hydrogen gas detection sensor using an oxide semiconductor described above has a slow reaction rate at room temperature, so it must be heated to about 350°C before use, and a heating heater must be installed.

There is also 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. Additionally, for flammable and explosive gases such as hydrogen gas, special construction must be done to make the wiring from the sensor part 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 for solving problems]

An optical waveguide is provided in the substrate, and a substance that reacts with dissociated hydrogen to change the optical absorption coefficient is applied to the end face of the optical waveguide exposed to the side edge of the substrate or the divided end face formed by making a transverse cut in the middle part of the waveguide. A sensor is constructed by providing a light absorption layer made of, for example, tungsten oxide (WO ₃ ), and a hydrogen absorption layer made of a substance that adsorbs and dissociates hydrogen, such as palladium (Pd), which is laminated on this layer.

[Effect]

In a sensor with the above structure, when hydrogen gas is adsorbed on the adsorption layer on the surface, it dissociates and generates electrons and protons, which enter the light absorption layer below the above layer, resulting in a change in the light absorption coefficient of the light absorption layer. Therefore, the amount of light that is transmitted through the waveguide, passes through these layers, and is emitted changes. Therefore, by inputting light from one end of the waveguide and measuring the amount of light emitted from the other end of the waveguide, the concentration of hydrogen gas present near the sensor can be detected from the amount of change in the amount of received light. Can be done.

〔Example〕

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

In FIGS. 1 and 2, reference numeral 1 denotes a substrate made of glass, plastic, etc. that is transparent to the wavelength used, and an optical waveguide 2 is embedded in this substrate 1.

The optical waveguide 2 has a circular cross section with approximately the same diameter as the core diameter of the fiber connected thereto, and has a refractive index distribution in which the refractive index is maximum on the central axis and gradually decreases parabolically toward the periphery. Such a refractive index gradient type optical waveguide with a circular cross section is produced by, for example, masking a glass substrate 1 by leaving an opening in the waveguide pattern on one side, and passing a glass material such as thallium (Tl) or lithium (Li) through the masking opening. By diffusing ions that make a large contribution to increasing the refractive index into the substrate, and after removing the masking, ions that make a large contribution to reducing the refractive index of glass, such as potassium (K) and sodium (Na), diffuse into the substrate. It can be formed by

A substrate 1 in which the optical waveguide 2 as described above is embedded is provided with a cut groove 3 having a minute width and extending in a direction perpendicular to the optical axis of the waveguide so as to divide the waveguide 2 at an intermediate point. This groove 3 is cut from the substrate surface to below the lower end of the waveguide 2. A light absorption layer 4 made of a thin film of a substance whose light absorption coefficient changes by reacting with dissociated hydrogen is provided on one side wall 3A of the groove 3 where the divided end surface 2C of the optical waveguide 2 is exposed. Furthermore, this light absorption layer 4
A hydrogen adsorption layer 5 made of a thin film of a substance that adsorbs and dissociates hydrogen is laminated thereon. That is, one divided end surface 2C of the optical waveguide 2 is covered with both the layers 4 and 5.

The material for the hydrogen adsorption layer 5 is preferably palladium or platinum. In addition, WO ₃ is suitable for the light absorption layer 4, and other inorganic materials that generally exhibit electrochromic properties, such as MoO ₃ ,
V ₂ O ₅ , TiO ₂ , Ir(OH)n, Rh ₂ O ₃ xH ₂ O, etc. can be used.

Further, the light absorption layer 4 may be composed of an organic material,
For example, hepuel viologen, cyanophenyl viologen, cobalt pyridyl complex, polymerized tetrathiofulvalene (TTF), lutetium diphthalocyanine, etc. can be used.

An optical fiber 6A is connected to one end of the waveguide 2 of the sensor, and the other end of the fiber 6A is connected to a light source 7. An optical fiber 6B is also connected to the other end of the waveguide 2, and the other end is connected to a photodiode. The amount of received light is measured by connecting it to a photodetector 8 such as the following. For example, in the sensor 10 having the above structure, Pd
When hydrogen gas comes into contact with the adsorption layer 5 consisting of a membrane, Pd
Electrons and protons are generated by the hydrogen reduction action of the film 5, and these are absorbed into the light absorption layer 4 made of, for example, _WO3 .
The following reaction occurs.

WO ₃ +xH ⁺ +xe ⁻ →HxWO ₃ (1) As the above reaction progresses, the light absorption layer 4 of WO ₃ is colored and the light absorption coefficient increases. It is the reduction action of hydrogen gas by the Pd film 5 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.

As a result, when the light that has passed through one of the divided optical paths 21 of the optical waveguide 2 enters the other divided optical path 22 at the groove 3, it is absorbed and attenuated by the absorption layer 4, and the light exits the waveguide 2. Since the amount of light emitted by the
By measuring the amount of change in the amount of received light, the hydrogen gas concentration can be determined from a calibration curve created by measuring the relationship between the known hydrogen gas concentration and the amount of received light.

In the illustrated example above, the light absorption layer 4 and the adsorption layer 5
is provided only on one side wall 3A of the groove 3, but may be provided on opposing both side walls 3A and 3B. Also,
The groove 3 in which the light absorption layer 4 and the adsorption layer 5 are provided is not limited to one location, but may be provided at multiple locations at intervals in the optical axis direction of the waveguide 2. When forming the light absorption layer 4 and adsorption layer 5 on the side wall 3A of the groove 3, as shown in FIG.
It is preferable to perform vapor deposition with the opening sides of the substrates facing each other and the substrate 1 held at an angle.

Next, a specific numerical example is shown.

First, an optical waveguide with a circular cross section and a refractive index gradient of about 50 μm in diameter is formed just below the surface of the glass substrate by the ion exchange method described above, and then a waveguide with a width of 20 μm is formed across this optical waveguide. A groove with a depth deeper than the lower end of the waveguide was cut using a dicing saw. Then, a light absorption layer 4 is formed on one side wall surface of the groove where the divided end surface of the waveguide is exposed.
A WO ₃ film was vacuum deposited to a thickness of 1 μm.

WO ₃ is produced by resistance heating vapor deposition of pellets with a purity of 99.99% using a W-wire crucible coated with alumina. The deposition conditions were: oxygen pressure 1×10 ^-4 Torr, high frequency power for ionization 200W, and ion acceleration voltage −500V.
And so. The substrate temperature during vapor deposition was 300°C, and the obtained WO ₃ thin film was polycrystalline and colorless and transparent. Furthermore, Pd was deposited as a hydrogen adsorption layer 5 on this WO ₃ film to a thickness of 100 Å by electron beam heating evaporation. An input optical fiber and an output optical fiber are connected to the sensor prepared as described above, and the sensor is installed in the atmosphere to be detected.
LED light (wavelength 1.3 μm) is input from the input fiber, and a photodetector is installed on the output side to measure the output light amount. As a result, the hydrogen gas concentration range of 10 to 2000 ppm can be measured with an accuracy of ±5%. I was able to do that.

In the above example, the optical waveguide is formed by the ion exchange method, but other materials include quartz glass formed by the CVD method, lithium niobate or lithium tantalate in which titanium is thermally diffused, and even plastic materials. It may be hot. Moreover, the optical waveguide 2 is
As shown in FIG. 4, the optical fiber 6 may be embedded and adhesively fixed in a fiber fixing groove 12 provided in the substrate 1. Furthermore, in addition to providing the light absorption layer 4 and the adsorption layer 5 in the groove that divides the optical waveguide 2 in the middle as in the above-described embodiment, the light absorption layer 4 and the adsorption layer 5 are provided in one or both of the waveguide end faces 2A and 2B exposed at the side edge of the substrate. It is also possible to omit the above-mentioned dividing groove by providing it so as to cover it.

〔effect〕

According to the present invention, not only can all hydrogen gas be detected using only optical signals, but it is also smaller, more reliable, and more reliable.
You can take advantage of all the advantages of light, such as heat resistance, electromagnetic induction resistance, fire resistance, and explosion resistance. Oil refining plants and other plants use hydrogen gas extensively to reform petroleum products, and there is a high demand for safe and highly reliable remote sensing. Furthermore, local loops using optical fibers have been introduced into measurement systems, and in the sense of signal transmission, there is a tendency for information and measurement data to be treated equally. Therefore, a technology that allows sensing using only light without converting optical signals into electrical signals is extremely compatible with the above-mentioned optical fiber loop.

Furthermore, according to the present invention, by fabricating a large number of embedded waveguides on one large substrate, a large number of hydrogen detection optical sensor chips can be efficiently manufactured in the same manufacturing process as integrated circuits, resulting in mass production and economy. Excellent.

[Brief explanation of drawings]

FIG. 1 is a side sectional view showing an embodiment of the present invention, and FIG.
3 is a plan view of the same, FIG. 3 is a sectional view showing an example of the method of depositing a light absorption layer and a hydrogen adsorption layer in a groove in an embodiment of the present invention. FIG. FIG. 5 is a plan view showing an embodiment, and a perspective view showing a conventional hydrogen detection sensor. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Optical waveguide, 3... Waveguide dividing groove, 4... Light absorption layer, 5... Hydrogen adsorption layer, 6,
6A, 6B...Optical fiber, 7...Light source, 8...
...Photodetector, 9...Vapor deposition source, 10...Sensor.

Claims (1)

[Claims] 1. The light input/output end face exposed at the side edge of the substrate of the optical waveguide provided in the substrate or the divided end face formed by making a transverse cut in the middle part of the waveguide is made of a substance whose light absorption coefficient changes by reacting with dissociated hydrogen. What is claimed is: 1. A hydrogen-detecting optical sensor comprising: a light-absorbing layer made of a light-absorbing layer; and a hydrogen-adsorbing layer made of a substance that adsorbs and dissociates hydrogen, laminated on this layer.