JPH0389162A - Detecting material of inflammable gas and method for defecting inflammable gas - Google Patents

Abstract

PURPOSE:To detect an inflammable gas by the use of photo-signals by utilizing the change in the light absorptivity corresponding to the concentration of the gas of a specific metal oxide. CONSTITUTION:The light absorptivity of an oxide of Cr, Mn, Fe, Ao, Ni or Ru is changed through contact with an inflammable gas in the presence of oxygen. The reason is that, in the case of cobalt oxide, for example, oxygen removes electrons from the cobalt oxide when the surface of the cobalt oxide is in contact with the air, and the removed electrons are absorbed to the surface of the cobalt oxide as oxygen cathode ions. If an inflammable gas is mixed in the air at this time, the absorbed oxygen cathode ions react wit the inflammable gas, thereby oxidizing the inflammable gas and returning the electrons from the oxygen cathode ions to the oxide cobalt. Therefore, when the concentration of the inflammable gas is high, the density of electrons in the cobalt oxide becomes high, whereas, if the concentration of the inflammable gas is low, the density of electrons is decreased. Since the light absorptivity of the cobalt oxide is changed by the density of electrons, it can be resumed that the cobalt oxide shows the change of light absorptivity corresponding to the change of the concentration of the inflammable gas.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to combustible gas detection materials and combustible gas detection methods.

Conventional technology and its problems Detection of so-called flammable gases such as carbon monoxide, hydrogen, and hydrocarbon gases is important for environmental and safety issues such as prevention of poisoning, explosion prevention, and fire prevention, as well as for the chemical industry. This is important in connection with automatic process control, etc. In recent years, with the progress of home automation and factory automation, the detection, measurement, and control of flammable gases using sensors has become increasingly important.

Conventionally, methods for detecting flammable gas include, for example, (
(b) A method of catalytically burning a combustible gas using a catalyst and measuring the reaction heat (so-called catalytic combustion gas sensor method); (b) A semiconductor formed when a flammable gas is adsorbed on the surface of a semiconductor such as Sn02. A method of measuring changes in electrical resistance (so-called semiconductor gas sensor method) is used.

In these conventional methods, it is necessary to supply driving power and perform electrical heating using a heater to drive the gas sensor. Therefore, there is a risk of igniting the flammable gas due to heating of the heater, generation of sparks due to a short circuit in the power line, or poor contact. Additionally, since the gas detection signal is extracted as an electrical signal, when gas detection is performed over a wide area by remote control, such as in chemical plants or coal mines, strong electromagnetic waves and noise emitted from various sources may be used. The disadvantage is that the gas detection signal is easily interfered with. Furthermore, with these gas detection methods based on electrical signals, it is difficult to directly combine them with information systems and control systems configured based on optical signals, which have been put into practical use in recent years. equipment is required to do so.

Therefore, there is a need for the development of a gas detection device that has excellent explosion-proof properties, is less susceptible to electromagnetic interference, and can be easily combined directly with optical information systems and optical control systems.

As a method for detecting combustible gases using optical signals, (a) a detection method using a detection material made of tungsten dioxide and palladium (light wave technique) contact, voj2.24.N
(Ll, PP, 9-17 (1986)) and (b) Detection method using ultrafine particles of gold, silver or copper (catalyst,
voj;j, 30. Na4. PP, 295~
300 (1988)) is known. However, the former has the disadvantage that it can only detect hydrogen gas, and the latter cannot detect flammable gas in an atmosphere where oxygen coexists, such as air.

Means for Solving the Problems In view of the problems of the prior art as described above, the inventor of the present invention
We have been conducting extensive research to find a method that can detect various flammable gases using optical signals in an oxygen-containing atmosphere. As a result, when at least one metal oxide of chromium, manganese, iron, cobalt, nickel, and ruthenium comes into contact with a flammable gas in the presence of oxygen, the light absorption rate corresponds to the concentration of the flammable gas. It was discovered that by utilizing this characteristic, it is possible to detect combustible gases using optical signals.

That is, the present invention provides a combustible gas detection material and a combustible gas detection method shown below.

■ A detection material for detecting combustible gases using optical signals, characterized by containing an oxide of at least one metal selected from chromium, manganese, iron, cobalt, nickel, and ruthenium.

■ At least one metal oxide selected from chromium, manganese, iron, cobalt, nickel and ruthenium;
and a sensing material for detecting a combustible gas using an optical signal, comprising at least one noble metal selected from platinum, gold, silver, palladium, iridium, and rhodium.

(2) A combustible gas detection method comprising measuring the light absorption rate of the detection material described in (1) or (2) above when it comes into contact with a combustible gas in the presence of oxygen.

In the present invention, a metal oxide of at least one of chromium, manganese, iron, cobalt, nickel, and ruthenium is used as a material for detecting combustible gas. These oxides have a property that their light absorption rate changes when they come into contact with combustible gas in the presence of oxygen. Although the reason for this phenomenon is not clear,
For example, taking cobalt oxide (CO304) as an example, it is presumed that the following principle is used. That is,
When the surface of cobalt oxide is in contact with a gas containing oxygen, such as air, oxygen takes electrons from the cobalt oxide and is adsorbed on the surface of the cobalt oxide as oxygen anions. When flammable gas mixes into the air that is in contact with cobalt oxide, the adsorbed oxygen anions and the flammable gas undergo a chemical reaction and the flammable gas is oxidized (catalytic oxidation). Electrons are pushed back into the cobalt. Therefore, when the concentration of combustible gas is high, the electron density in cobalt oxide becomes high, and when it is low, the electron density becomes low.

The light absorption rate of cobalt oxide changes depending on the electron density; when the electron density is high, the light absorption rate is low, and when the electron density is low, the light absorption rate is high. As described above, the light absorption rate of cobalt oxide changes in response to changes in the combustible gas concentration.

This phenomenon does not occur with all metal oxides; (a) oxygen anions on the surface are reversibly adsorbed and desorbed in equilibrium with oxygen in the gas phase; and (b) with flammable gases. It has catalytic activity that facilitates chemical reactions with adsorbed oxygen anions,
(c) The light absorption rate changes with changes in electron density.
It is thought that this can be achieved only with metal oxides that satisfy the conditions.

The above-mentioned oxides of chromium, manganese, iron, cobalt, nickel, and ruthenium all exhibit changes in lead plate yield corresponding to changes in combustible gas concentration.

In the present invention, these metal oxides can be used alone or in combination. Moreover, it may be used not only as a monoxide of a single component metal element but also as a composite oxide. Among composite oxides, AB20a (A is Mg, Fe, Cos Ni, Cu%M
n, Zn, etc., B is Al1, Fe, 00% Ti
, Cr, etc.), ABO3 having a perovskite crystal structure (A and B are respectively A g s Na
SK s Ca s S r 1BaSPbSLa,B
i, Y, Ce, Th5LL.

Cu, Mg5Ti%v, Rh5Pt, NbSMo.

(Indicates W%Cr, Mn, Fes Co5Ni%Ru, etc.)
Because they have stable crystal structures, they are suitable for operation in high temperature ranges. Furthermore, metal oxides of chromium, manganese, iron, cobalt, nickel, or ruthenium can be used in combination with various substances such as other metal oxides, glass, ceramics, and polymeric materials. When mixed with a substance, the rate of change in light absorption rate decreases, so it is necessary to adjust the mixing ratio appropriately depending on the flammable gas concentration, detection means, etc.

In the present invention, the shape of the metal oxide described above is not particularly limited, and can be in various shapes such as a thin film shape or a powder shape depending on the detection means. For example, in the method of measuring light absorption rate using the transmission method described below, it is common to use a thin film, and when measuring by the diffuse reflection method,
It is generally in the form of a powder or a bottom-shaped pellet.

Thin films are typically formed on transparent substrates such as glass, quartz, or sapphire. The method of forming the thin film is not particularly limited, and may include so-called gas phase methods such as sputter deposition, vacuum deposition, and CVD, and a method of applying a solution of metal alkoxide, metal nitrate, etc. onto a substrate and thermally decomposing it. Various known methods can be applied.

The thickness of the thin film is not particularly limited, but changes in light absorption mainly occur only at the surface of the thin film, so if the thin film becomes too thick, the rate of change in light absorption decreases and detection sensitivity decreases. . Normally, in the case of a homogeneous thin film such as a thin film formed by sputter deposition, the surface area is relatively small, so a thickness of about 5 to 20 nm is appropriate. Since the surface area of the thin film is relatively large, changes in light absorption can be detected even with thicker films.

Further, when the metal oxide is used in powder form, it is preferably in the form of fine powder, and suitably has a particle size of about 1 μm or less.

Furthermore, in the combustible gas sensing material of the present invention, platinum, gold, silver, palladium,
When at least one noble metal of iridium and rhodium is used in combination, the response speed can be improved. This is considered to be because the presence of these noble metals improves the rate of adsorption and desorption of oxygen anions and the rate of chemical reaction between the combustible gas and adsorbed oxygen anions.

At least one of the above-mentioned noble metals of platinum, gold, silver, palladium, iridium, and rhodium is preferably supported on a metal oxide in the form of fine particles, and the particle size is preferably about 1 nm to 1100 rt. The amount supported is
0.01 to 10 relative to the total amount of metal oxide and noble metal
A range of about % by weight is appropriate.

The noble metal may be supported by a known method, such as forming a metal oxide film, applying an aqueous solution containing the above-mentioned noble metal and firing, or applying an aqueous solution containing the above-mentioned noble metal to a metal oxide powder. A method in which a noble metal is deposited on a metal oxide film by sputter deposition, a method in which a metal oxide and the above noble metal are simultaneously deposited by a sputter deposition method, and a solution containing a metal oxide and the above noble metal. Examples include a method of coating the substrate on a substrate and thermally decomposing it.

When the sensing material of the present invention comes into contact with a combustible gas in the presence of oxygen, a change in light absorption occurs. The amount of oxygen present is not particularly limited, and if oxygen of about 0, Qlvo, 17% or more is present, it is possible to detect a change in light absorption rate, but usually oxygen of about 1 to 100voJ2% Preferably, it is a concentration. When the oxygen concentration increases, the amount of oxygen adsorbed on the surface of the metal oxide increases, and many electrons are taken away from the metal oxide, resulting in a decrease in the electron density of the metal oxide. Therefore, the oxygen concentration affects the change in the yield of the front plate of the sensing material, and as the oxygen concentration increases, the light absorption rate tends to increase. Therefore, to find the flammable gas concentration,
It is necessary to determine the relationship between the combustible gas concentration and the light absorption rate in the oxygen concentration of the measurement atmosphere.

The objects to be detected in the present invention are flammable gases, such as hydrocarbon gases such as methane, ethane, ethylene, and propane, hydrogen, carbon oxide, and alcohol vapor.

In the flammable gas detection method of the present invention, it is sufficient to measure the light absorption rate of the detection material when it comes into contact with a combustible gas in the presence of oxygen. Any method can be applied. For example, there is a method of measuring the light absorption rate of transmitted light using a sensing material in which a thin metal oxide layer is formed on a transparent substrate;
Various known methods are available, including a method of measuring using a diffuse reflection method using a metal oxide such as a pellet, a method of measuring by attaching a metal oxide to the surface of a guiding waveguide, and a method of measuring using a photoacoustic effect. method is possible.

Light absorption rate can be evaluated using various commonly used standards such as absorbance, absorbance, and transmittance.

The wavelength of the measurement light is not particularly limited, but is 300ro+
It is preferable to set it to approximately +11100n.

Measurement of light absorption rate is carried out at 100-5 to increase response speed.
It is preferable to conduct the heating at a temperature of about 00°C, but the heating is not limited thereto.

Effects of the Invention According to the present invention, it is possible to detect combustible gas using an optical signal. Therefore, it is possible to manufacture a gas detection device that has excellent explosion-proof properties and is less susceptible to electromagnetic interference, and it also becomes possible to combine it with an optical information system or an optical control system.

Example EXAMPLES The present invention will be explained in more detail below with reference to Examples.

Example 1 Cobalt oxide (Co3) with a thickness of 10 nm was deposited on a glass substrate.
04) A thin film was formed by sputter deposition.

A cobalt oxide thin film was maintained at 300°C, and (a) standard air (21% oxygen + 79% nitrogen), (b) air containing 1% ethylene, (C) air containing 1% hydrogen, (d) 1 air containing % carbon monoxide, or (e) 15% oxygen + 85%
Visible light absorption spectra of transmitted light were measured in either of the gas mixtures of % nitrogen. The results are shown in Figure 1.

Comparison of (a) and (b) to (C) reveals that the presence of flammable gas in the air reduces the absorbance of cobalt oxide.

By comparing (a) and (e), it can be seen that the absorbance of cobalt oxide decreases as the oxygen concentration decreases.

In addition, the cobalt oxide thin film was maintained at 250°C, and the atmosphere was changed from standard air to air containing 1% carbon monoxide.
Wavelength 700 when returned to standard air after 0 minutes
The change in absorbance of the oxidized conort thin film with respect to nm light was investigated. The results are shown in Figure 2. It can be seen that the absorbance of cobalt oxide changes reversibly depending on the presence or absence of carbon monoxide in the air.

The cobalt oxide thin film was maintained at 250° C., and the atmosphere was changed to standard air and air containing 0.5% to 10% carbon monoxide, and changes in absorbance of the cobalt oxide thin film to light with a wavelength of 700 nm were investigated. The results are shown in Figure 3. It can be seen that the absorbance changes depending on the carbon monoxide concentration in the air.

Example 2 A 10 nm thick cobalt oxide (CO304) thin film was formed on a glass substrate by sputter deposition, and palladium in an amount equivalent to 0.5 nm thick was deposited on the surface by sputter deposition. It is estimated that palladium is attached to the surface of the cobalt oxide thin film as ultrafine particles of about 1 nm in size.

This thin film was kept at 150°C, and (a) standard air and (b)
) The light absorption spectrum of transmitted light was measured in air containing 1% hydrogen. The results are shown in Figure 4.

It can be seen that the absorbance decreases due to the presence of hydrogen, and that hydrogen can be detected even at 150° C. with cobalt oxide to which palladium is attached.

Example 3 Cobalt nitrate, manganese nitrate, iron nitrate, nickel nitrate,
Aqueous solutions of silver nitrate, lanthanum nitrate, strontium nitrate, chromium nitrate, ruthenium chloride, or chloroauric acid each having a metal ion concentration of 0.2 m o j2/42 were prepared separately. These were mixed to have the atomic ratio shown in the oxide composition column of Table 1, coated on a quartz substrate, and dried in air at room temperature for 2 hours to form a metal salt film on the surface. A quartz plate was obtained. This quartz plate was placed in a glass container filled with ammonia vapor and left for one hour. The product was again left in the air at room temperature for 1 hour, and then fired in the air at 400° C. to 700° C. for 3 hours in an electric furnace to obtain the desired oxide thin film.

The absorbance of these thin films was examined in air and in air containing 1% carbon monoxide. The results are shown in Table 1.

It is clear that the presence of carbon monoxide reduces the absorbance.

i 1 Table oxide Composition Measurement temperature Measurement light wavelength Absorption [(abs)Ag:Co=
l:l 250 500 0.290
710.2879Fe:Co=l:2 25
0 500 0.798310.7923Ni:C
o=1:2 250 500 0.95
2210.9499Au:Co=l:19 2
00 800 0J92810J909Ag:Mn
=l+1 250 600 1.524
/1.496La:Sr:Co-0,8:0.2:1
350 600 1.18B /1.179La
:Sr:Mn=0.8:0.2:L 350 50
0 1.053 /1.047Mn=1
250 500 0J50510.3481
Co:Mn=l:2 250 500
1.225/1.196Cr:Co=l:2
350 700 1.133 /1.119

[Brief explanation of drawings]

Figure 1 shows visible light absorption spectra in various atmospheres, Figure 2 shows changes in absorbance due to contact with -carbon oxide, and Figure 3 shows the relationship between carbon monoxide concentration and absorbance. FIG. 4 is a diagram showing light absorption spectra in air and in air containing 1% hydrogen. (that's all)

Claims (5)

[Claims] (1) A sensing material for detecting combustible gases using optical signals, which is characterized by containing an oxide of at least one metal selected from chromium, manganese, iron, cobalt, nickel, and ruthenium. (2) Contains an oxide of at least one metal selected from chromium, manganese, iron, cobalt, nickel, and ruthenium, and at least one noble metal selected from platinum, gold, silver, palladium, iridium, and rhodium. A sensing material for detecting combustible gases using optical signals, which is characterized by: (3) A fine particle noble metal is supported on an oxide of at least one metal selected from chromium, manganese, iron, cobalt, nickel, and ruthenium. Sensing material. (4) The sensing material according to any one of claims 1 to 3, wherein the metal oxide is formed in the form of a thin film on a transparent substrate. (5) A combustible gas detection method, comprising measuring the light absorption rate of the detection material when the detection material according to any one of claims 1 to 4 comes into contact with a combustible gas in the presence of oxygen. .