JPH0772080A - Gas detector - Google Patents

Abstract

PURPOSE:To obtain a quick response from a gas sensor at the normal temperature by using a hydrouse tungsten oxide film instead of a solid body of a metal oxide. CONSTITUTION:After a hydrous tungsten oxide film 2 is formed on a substrate 1, a semi-transparent catalytic metallic film 3 is layered thereon, thereby to constitute a gas sensor. When the sensor is exposed to an environment containing hydrogen or a hydrogen-containing compound gas, a complex index of refraction of the tungsten film 2 is quickly changed. As a result, a reflectivity or transmittance of the sensor is quickly changed. A reflecting-type or transmitting-type gas detecting apparatus which converts the change of the reflectivity or transmittance into an electric amount and evaluates a concentration of a gas quickly is constituted by using the sensor.

Description

The present invention relates to an apparatus for detecting hydrogen or a hydrogen-containing compound gas, and can be used in the fields of gas leak detection, fire prediction, insulation oil deterioration prediction of transformers, and the like. Conventionally, in a gas sensor that utilizes the fact that the optical properties of a solid metal oxide are changed by a reducing gas such as hydrogen, the response of the sensor at room temperature is not quick, and the sensor needs to have a response time of about 1 minute. Had to heat up. The present invention aims to eliminate this drawback by using a hydrous tungsten oxide film instead of a solid metal oxide. An example of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the structure of the gas sensor. After forming the hydrous tungsten oxide film 2 on the substrate 1, a semitransparent catalytic metal film 3 is further deposited thereon. When this element is exposed to an atmosphere containing hydrogen or a hydrogen-containing compound gas, the complex refractive index of the hydrous tungsten oxide film changes rapidly, so that the light reflectance or light transmittance of the element changes rapidly. therefore,
A reflective or transmissive gas detection device for converting this change into an electric quantity to quickly evaluate the concentration of the gas can be constructed by using the present element. An example of this element in the reflection type gas detection device will be shown below. An anodic oxide film 2 having a film thickness of several thousand Å is formed on a flat tungsten substrate 1 in an acidic solution such as sulfuric acid, and then a palladium or platinum thin film 3 having a film thickness of several tens of Å is deposited by vacuum evaporation, sputtering or the like.
FIG. 2 shows a change in reflectance with respect to light having a wavelength of 1.4 μm in the device of the above-mentioned embodiment. When the atmosphere of the device is changed from normal air to air containing 1% hydrogen and then returned to air, the device responds to hydrogen in about 10 seconds at room temperature. This rapid response is based on the fast diffusion of hydrogen atoms or hydrogen ions in the hydrate of tungsten oxide formed during anodization. FIG. 3 shows an embodiment of a reflection type gas detection device. A gas sensor kept near room temperature is irradiated with an incident light beam 4 from a light source 6 such as an incandescent lamp, a light emitting diode, or a laser, and a reflected light beam 5 is incident on a light receiver 7 such as a photodiode, and the gas is output by the output of an electric signal. The concentration of is shown. The sensitivity to gas changes depending on the thickness of the anodic oxide film, the wavelength of light, and the like. In order to realize high sensitivity, optical elements such as filters, prisms and diffraction gratings can be installed in the optical path of the reflected light beam 5.
FIG. 4 shows another embodiment of the present invention, which is an apparatus using two optical fibers as waveguides for the light beams 4 and 5. Further, FIG. 5 is an example of an apparatus in which the emitting and receiving optical fibers of FIG. By using a low loss, flexible optical fiber, it is possible to transmit an optical signal to a remote place. The present invention also includes a transmission type gas detection device in which the substrate 1 is a transparent substrate such as a glass plate. However, in this case, the reflected light beam 5 and the light receiver 7 in FIG. 3 and the optical fiber 9 and the light receiver 7 in FIG. 4 are arranged below the substrate 1, and the light beam is transmitted from the film 3 to the substrate 1. In addition, in this transmission type gas detection device,
The same effect can be obtained even when the present element is turned upside down so that the substrate 1 is above the film 3.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of the structure of the gas sensor, FIG. 2 is a view showing changes in the reflectance of the film of the gas sensor when the atmosphere is first changed to air, then to hydrogen-containing air, and finally to air again.
FIG. 4 is a diagram showing an embodiment of a reflection type gas detection device, and FIG.
The figure which shows the reflection type gas detector which uses the optical fiber of the book,
FIG. 5 is a view showing a reflection type gas detection device using one optical fiber for emitting and receiving light. 1 ... Substrate 2, Tungsten oxide hydroxide film, 3 ... Catalyst metal thin film, 4 ... Incident light beam, 5 ... Reflected light beam, 6 ... Light source, 7 ... Light receiver, 8, 9 ... Optical fiber.

Claims (1)

[Claims] 1. A hydrogen or hydrogen-containing compound gas detector, comprising a gas sensor comprising a hydrous tungsten oxide film whose optical properties change rapidly under the influence of a gas to be detected, and an electric quantity of this change. And a device for evaluating the concentration of the gas by converting into gas