JP3171734B2 - Carbon monoxide gas sensing element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon monoxide gas sensing element provided with a semiconductor portion mainly composed of a metal oxide semiconductor whose valence is controlled.

[0002]

2. Description of the Related Art Conventionally, as such a carbon monoxide sensing element, there is an element using tin oxide (SnO ₂ ) as a metal oxide semiconductor and carrying palladium (Pd) or the like. Generated carbon monoxide gas (C
O) was detected and an alarm was issued to prevent carbon monoxide poisoning of the user of the appliance.

[0003]

In the above-described carbon monoxide gas detecting element, at a high temperature of, for example, 300 ° C. or more, a gas to be detected (hereinafter, referred to as a sample gas) is detected. Because of the low selectivity of carbon monoxide, detection of a sample gas at a low temperature of, for example, 200 ° C. or less has been performed. In general, when oil and fat components, dust, and the like (hereinafter abbreviated as dust and the like) contained in the atmosphere of the site adhere to the semiconductor portion, the gas detection may not be performed normally. In the gas detection element, even if the dust adheres to the semiconductor portion, it cannot be easily removed as it is. Therefore, it is necessary to periodically raise the temperature of the element and perform a so-called “purge” for decomposing and removing the dust. Was.

[0004] In addition, the detection operation cannot be performed during the purge, but the sensor output is not stabilized immediately after the purge is performed.
There was a drawback that it was not possible to detect carbon monoxide gas constantly. Further, when a means for automatically performing such a purge is provided periodically, it is difficult to manufacture a detecting device including a carbon monoxide gas detecting element at low cost, for example, because a detecting circuit becomes complicated.

An object of the present invention is to provide an inexpensive carbon monoxide gas detecting element capable of performing carbon monoxide gas detection constantly and with high performance without purging in view of the above circumstances. is there.

[0006]

According to a first aspect of the present invention, there is provided a semiconductor device having a valence-controlled metal oxide semiconductor as a main component and a lanthanoid metal or yttrium (Y). At least one kind of metal oxide and gold (Au) are supported, and the feature of the second invention is that a lanthanoid metal or yttrium is added to a semiconductor portion mainly composed of a metal oxide semiconductor whose valence is controlled. (Y) in which at least one metal oxide and gold (Au) and an alkaline earth metal oxide are supported.
a ₂ O ₃ ), and the lanthanum oxide (La ₂ O ₃ ) is 1 mol% or more and 20 mol% with respect to the metal oxide semiconductor.
It is preferable that gold (Au) be contained in the metal oxide semiconductor in an amount of 4 × 10 ⁻⁴ atm% or more and 0.5 atm% or less, and further, the lanthanum oxide (L)
a ₂ O ₃ ) in an amount of 2 mol% based on the metal oxide semiconductor.
Not less than 10 mol%, and the gold (Au) is contained in the metal oxide semiconductor in an amount of 1 × 10 ⁻³ atm% to 0.1%.
It is more preferable that the metal oxide is contained at 1 atm% or less, and the metal oxide is yttrium oxide (Y ₂ O ₃ ), and the yttrium oxide (Y ₂ O ₃ ) is 3 m with respect to the metal oxide semiconductor.
ol% or more and 11 mol% or less, and the gold (Au)
Is 1 × 10 ⁻³ atm% with respect to the metal oxide semiconductor.
Above 8 × 10 ^-2 atm% may be contained, and the operation and effect are as follows.

[0007]

In other words, by supporting lanthanum oxide (La ₂ O ₃ ) or yttrium oxide (Y ₂ O ₃ ), the negatively-charged adsorbed oxygen (O ²⁻ ) on the surface of the metal oxide semiconductor is stabilized, or , Basic reforming, etc., to reduce the high oxidation activity of the metal oxide semiconductor, to lower the sensitivity to fuel gas such as methane, propane, isobutane, hydrogen (H ₂ ), etc. By carrying Au), carbon monoxide gas adsorbability on the surface of the metal oxide semiconductor,
Oxidation activity is enhanced, the sensitivity of detecting carbon monoxide gas (CO) is improved, and carbon monoxide gas (CO) can be detected with high selectivity from other fuel gases, hydrogen (H ₂ ), etc. It is thought that it became.

In addition, gold (Au) is formed on the surface of the metal oxide semiconductor.
In a carbon monoxide gas sensing element carrying only carbon monoxide gas, for example, carbon monoxide gas selectivity cannot be obtained unless the operating temperature is set to a low operating temperature of 100 ° C. or less, whereas the carbon monoxide gas selectivity is obtained as described above. It was also found that the carbon monoxide gas sensing element can maintain high carbon monoxide gas selectivity even when the sensing operation is performed at a high temperature. This effect is considered to be due to a combined effect of lanthanum oxide (La ₂ O ₃ ) or yttrium oxide (Y ₂ O ₃ ) and gold (Au). It has been found that high carbon monoxide gas selectivity can be obtained even at a high temperature of ° C. As a result, the present invention has been made based on a new finding that carbon monoxide gas (CO) can be selectively detected even at a high temperature operation by the combined action, and the detection operation at a high temperature can be performed even without performing purging. Since dust and the like adhering to the semiconductor portion are easily decomposed, the carbon monoxide gas detecting operation can be constantly performed.

Further, lanthanum oxide (La ₂ O ₃ ) is supported on the metal oxide semiconductor in an amount of 1 mol% to 20 mol%, and gold (Au) is supported in an amount of 4 × 10 ⁻⁴ atm% to 0.5 atm%. If yttrium oxide (Y ₂ O ₃ ) is supported at 3 mol% or more and 1 mol% or less on the metal oxide semiconductor, a carbon monoxide gas detecting element which can be used as a household carbon monoxide gas alarm can be obtained. I can do it.

Further, if lanthanum oxide (La ₂ O ₃ ) is supported on the metal oxide semiconductor by 2 mol% or more and 10 mol% or less, still higher sensitivity can be obtained.

According to the regulation of carbon monoxide gas sensitivity based on the city gas alarm inspection standards set by the Japan Gas Alarm Inspection Association (hereinafter simply referred to as sensitivity regulation), 100 ppm of carbon monoxide gas (CO) is contained. Detect the sample gas,
Along with measuring the sensitivity output, a sample gas containing a gas other than carbon monoxide is detected by a carbon monoxide gas detecting element, and the concentration of another gas showing a sensitivity output equal to or higher than the sensitivity output (hereinafter, referred to as When the concentration of carbon monoxide is measured, the carbon monoxide is 100 pp.
800 ppm when the concentration corresponding to m is hydrogen gas (H ₂ )
As described above, it is specified that isobutane is 500 ppm or more, and methane is 1000 ppm or more.

When tin oxide (SnO ₂ ) or indium oxide (In ₂ O ₃ ) is used as the metal oxide semiconductor, stability, durability, reliability, and the like can be obtained, which is practically suitable.

[0013]

As described above, the carbon monoxide gas can be constantly detected at a high performance without purging, and the carbon monoxide gas can be detected without providing a circuit for periodically purging. Now that we can manufacture the equipment,
An inexpensive carbon monoxide gas detecting device can be manufactured using the carbon monoxide gas detecting element of the present invention.

Further, by performing the detection operation at a high temperature, the influence of humidity can be reduced, and the sensitivity can be stabilized.
Dust and the like adhering to the semiconductor portion are easily decomposed, so that the sensitivity is stabilized.

Further, the high-speed operation makes the response speed to the detection of carbon monoxide gas fast, and the sensitivity is stabilized in a short time.

As a result, a high-performance carbon monoxide gas sensing element that could not be obtained conventionally can be obtained.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a carbon monoxide gas sensor using a carbon monoxide gas detecting element of the present invention will be described below with reference to the drawings. Hereinafter, the structure of the carbon monoxide gas detecting element 3, the method of preparing the semiconductor portion, the method of supporting the carrier, the sensor circuit, and the characteristics of the sensor will be described in this order.

<Structure of Carbon Monoxide Gas Detecting Element> FIG. 1 shows the structure of a hot-wire type carbon monoxide gas detecting element 3 as an embodiment of the present invention. In the figure, in order to show the internal configuration of the carbon monoxide gas detecting element 3, a part is shown in a cross section. As shown in the figure, the carbon monoxide gas detecting element 3 includes a semiconductor unit 2 on a platinum coil 1,
The semiconductor part 2 is a sintered body obtained by sintering tin oxide (SnO ₂ ), and lanthanum oxide (La ₂
O ₃ ) and gold (Au).

<Method for Preparing Semiconductor Part> A commercially available aqueous solution of tin tetrachloride (SnCl ₄ ) was prepared at a constant concentration, and antimony pentachloride (Sb
Cl ₅ ) to 0.6 a with respect to tin tetrachloride (SnCl ₄ ).
tm%. When aqueous ammonia is dropped into this solution, tin hydroxide (Sn (OH) ₄ ) is precipitated by hydrolysis. This is washed with distilled water and dried to obtain a gelled tin hydroxide (Sn (OH) ₄ ). This tin hydroxide (Sn (OH) ₄ ) is converted to 60 in an electric furnace.
When pyrolyzed under the firing conditions of 0 ° C. for 4 hours, a lump of tin oxide (SnO ₂ ) is obtained. The tin oxide (SnO ₂ ) thus obtained is pulverized by a pulverizer. Distilled water is added to this to form a paste, and as shown in FIG. 1, a spherical shape having a diameter of 0.45 mmφ is attached so as to cover the periphery of the platinum coil 1 (20 μmφ). An electric current is applied, and firing is performed at 600 ° C. for 1 hour due to the heat generated. Thus, the semiconductor portion 2 can be formed.

<Method of Carrying Carrying Material> First, a commercially available lanthanum nitrate (La (NO ₃ ) ₃ ) is converted into an aqueous solution to prepare aqueous solutions of various predetermined concentrations. This aqueous solution is impregnated into the semiconductor part 2, the semiconductor part 2 is dried, and again
The coil is heated by flowing an electric current, pyrolyzed at 600 ° C. for 1 hour, and fired to obtain tin oxide (S
lanthanum oxide (La ₂ O ₃ ) can be supported on the surface of nO ₂ ). Next, chloroauric acid (HAuC)
l ₄ ) is converted into an aqueous solution to prepare aqueous solutions of various predetermined concentrations. When impregnation and firing are performed in the same manner as above, tin oxide (S
Gold (Au) can be supported as a metal on the surface of nO ₂ ). The semiconductor portion 2 supporting the lanthanum oxide (La ₂ O ₃ ) and gold (Au) becomes the carbon monoxide gas detecting element 3.

<Sensor Circuit> The carbon monoxide gas detecting element 3 is incorporated in a Wheatstone bridge circuit shown in FIG. 2 and used as a sensor. In the figure, reference numeral 4a denotes a resistor connected in series as a load resistor for this sensor, and resistors 4b and 4c are reference resistors connected in series with each other to determine a reference potential of the circuit. The sensor and the series resistor 4a are connected to other reference resistors 4b and 4c.
Are connected in parallel with respect to the power supply 4d, and the potential difference (mV) between the intermediate points A and B of the resistors can be obtained as the output of this sensor. When measured by the circuit, the sensor output (V) corresponds to the potential difference between the two points A and B and is given by the following equation.

[0022]

(Equation 1)

Here, E is the voltage of the carbon monoxide gas sensor, R _S is the resistance value of the carbon monoxide gas detecting element 3,
R ₀ , R ₁ and R ₂ are resistance values of 4a, 4b and 4c, respectively. Resistor R _S is reduced in the carbon monoxide gas (CO) acts carbon monoxide gas sensing element 3, R _S + ΔR _S
(ΔR _S ≦ 0). At this time, the sensor sensitivity is defined by a change (ΔV) in the sensor output and is given by the following equation.

[0024]

(Equation 2)

<Sensor Characteristics> The performance characteristics of the carbon monoxide gas sensor will be described below. Here, the carbon monoxide gas sensor was operated at about 350 ° C. to examine the sensor sensitivity.

(1) Dependence of Sensor Sensitivity on Lanthanum Oxide Loading The lanthanum oxide (La ₂ O ₃ ) loading on the semiconductor portion 2 is 0.4 to 25 mol%, and the gold (Au) loading is 0 Various carbon monoxide gas sensing elements 3 having a concentration of 0.02 atm% were prepared, each of them was incorporated into a sensor circuit, and the sensor output for a sample gas containing 100 ppm of carbon monoxide gas (CO) in the air was measured, and hydrogen was measured. A concentration equivalent to 100 ppm of carbon monoxide gas (refers to the concentration of hydrogen gas in the sample gas when the sample gas containing hydrogen gas in the air exhibits an output equal to the sensor output. As well). Further, the concentration of isobutane gas corresponding to 100 ppm of carbon monoxide and the concentration of methane gas corresponding to 100 ppm of carbon monoxide were examined.

The results are as shown in Table 1. It should be noted that methane gas showed only a very low sensor sensitivity and could not measure a concentration equivalent to 100 ppm of carbon monoxide of methane gas.

[0028]

[Table 1]

According to Table 1, to satisfy the above-mentioned sensitivity regulation,
Lanthanum oxide (La) against tin oxide (SnO ₂ )
It was found that the amount of added ₂ O ₃ ) should be 1 mol% or more.

Further, the response of the carbon monoxide gas sensor at this time was examined. FIG. 3 shows the responsiveness of a carbon monoxide gas sensor in which 4 mol% of lanthanum oxide (La ₂ O ₃ ) and 0.02 atm% of gold (Au) are supported on the semiconductor portion 2 made of tin oxide (SnO ₂ ). FIG. 4 shows tin oxide (SnO).
The semiconductor unit 2 consisting of _2), lanthanum oxide (La ₂ O ₃₎
The responsiveness of a carbon monoxide gas sensor carrying 25 mol% and 0.02 atm% of gold (Au) is shown. Note that FIG.
In FIG. 4, the horizontal axis is on a common scale. Here, for various gases, the gas concentration is changed when the detection sensitivity output becomes constant, and gas detection is continuously performed.

That is, the shorter the detection time at each concentration of various gases, the better the responsiveness. For example, in FIG. 3, the sensitivity becomes constant in a short time (it takes about 10 seconds for the sensitivity of 100 ppm to become constant with carbon monoxide gas), whereas in FIG. 4, it takes a long time. If the sensitivity does not become constant (it takes about 2 minutes and 30 seconds for the sensitivity of 100 ppm to become constant with carbon monoxide gas), the response of the carbon monoxide gas sensor used in FIG. It can be determined that the responsiveness of the carbon monoxide gas sensor is excellent.

[0032] As a result, if the carried amount of lanthanum oxide (La ₂ O ₃₎ in the following 20 mol%, found that a good response can be obtained, 20 mol amount of supported lanthanum oxide (La ₂ O ₃₎ %, The response was reduced and the detection sensitivity was lowered.

As a result, if the amount of lanthanum oxide (La ₂ O ₃ ) is 1 mol% or more and 20 mol% or less, high sensitivity as a household carbon monoxide gas alarm can be obtained.
In addition, if it is 2 mol% or more and 10 mol% or less,
It can be seen that a carbon monoxide gas detecting element 3 with higher performance can be obtained.

(2) Dependence of Sensor Sensitivity on Gold Carrying Amount The amount of lanthanum oxide (La ₂ O ₃ ) carried on the semiconductor portion 2 is 4 mol%, and the amount of gold (Au) carried on the semiconductor portion 2 is 3 × 10 ⁻⁴ or less.
Various carbon monoxide gas detecting elements 3 of 1 atm%
Prepared, incorporated in the sensor circuit for each, measured the sensor output for a sample gas containing 100 ppm of carbon monoxide in the air, 100 ppm of carbon monoxide of hydrogen gas
The equivalent concentration, the concentration of 100 ppm of carbon monoxide in isobutane gas, and the concentration of 100 ppm of carbon monoxide in methane gas were examined.

The results are as shown in Table 2. For methane gas, only very low sensor sensitivity is shown.
It was not possible to measure a concentration equivalent to 100 ppm of carbon monoxide of methane gas.

[0036]

[Table 2]

From Table 2, it can be seen that to satisfy the sensitivity regulation,
The amount of gold (Au) added to tin oxide (SnO ₂ ) was 4
It has been found that it is sufficient if the content is set to × 10 ^{−4 to} 0.5 atm%. Further, it can be seen that a carbon monoxide gas detecting element 3 with even higher performance can be obtained if the concentration is 1 × 10 ⁻³ atm% or more and 0.1 atm% or less.

Alternative Embodiment 1 The lanthanum oxide (La ₂ O ₃ ) in the previous embodiment was changed to yttrium oxide (Y ₂ O ₃ ), and a carbon monoxide gas sensing element 3 was similarly prepared.
The sensor characteristics were investigated. That is, yttrium oxide (Y ₂ O ₃ ) was carried on the semiconductor portion 2 as follows.

<Method of Carrying Carrying Material> First, a commercially available yttrium nitrate (Y (NO ₃ ) ₃ ) is converted into an aqueous solution to prepare aqueous solutions of various predetermined concentrations. The aqueous solution is impregnated with the semiconductor part 2, the semiconductor part 2 is dried, and the coil is heated again by applying a current to the coil, thermally decomposed at 600 ° C. for one hour, and baked, thereby oxidizing. It can be supported on the surface of tin (SnO ₂ ) as yttrium oxide (Y ₂ O ₃ ). Next, chloroauric acid (HAu
Cl ₄ ) is converted to an aqueous solution to prepare aqueous solutions of various predetermined concentrations. When impregnation and firing are performed in the same manner as described above, gold (Au) can be supported as a metal on the surface of tin oxide (SnO ₂ ). The semiconductor section 2 supporting yttrium oxide (Y ₂ O ₃ ) and gold (Au) serves as a carbon monoxide gas detecting element 3.

As a result, the following sensor characteristics were obtained. Here, the sensor sensitivity was examined by operating at about 325 ° C.

<Sensor Characteristics> (1) Dependence of Sensor Sensitivity on Yttrium Oxide Loading Amount of yttrium oxide (Y ₂ O ₃ ) loading on the semiconductor portion 2 is 0.4 to 25 mol%, and the sensitivity of gold (Au) is Various carbon monoxide gas sensing elements 3 having a carrying amount of 0.02 atm% were prepared, and each of them was incorporated into a sensor circuit, and the sensor output for a sample gas containing 100 ppm of carbon monoxide in air was measured, and hydrogen gas was measured. Carbon monoxide 100
ppm equivalent concentration, isobutane gas carbon monoxide 100p
A concentration corresponding to pm and a concentration corresponding to 100 ppm of carbon monoxide of methane gas were examined.

As a result, the results are as shown in Table 3.

[0043]

[Table 3]

As shown in Table 3, in order to satisfy the above sensitivity regulation,
Yttrium oxide (Y ₂ O) against tin oxide (SnO ₂ )
It has been found that it is sufficient if the amount of addition ₃ ) is 3 mol% or more and 11 mol% or less. At this time, it was found that good responsiveness was obtained.

(2) Dependence of sensor sensitivity on amount of gold carried The amount of yttrium oxide (Y ₂ O ₃ ) carried on the semiconductor portion 2 is 0.02 mol%, and the amount of carried gold (Au) is 3 ×
Various carbon monoxide gas detecting elements 3 having a concentration of 10 ^{-4 to 1} atm% are prepared, and each of them is incorporated in a sensor circuit, and the sensor output for a sample gas containing 100 ppm of carbon monoxide in air is measured. Carbon oxide 100
ppm equivalent concentration, isobutane gas carbon monoxide 100p
A concentration corresponding to pm and a concentration corresponding to 100 ppm of carbon monoxide of methane gas were examined.

As a result, the results are as shown in Table 4.

[0047]

[Table 4]

From Table 4, it can be seen that to satisfy the sensitivity regulation,
The amount of gold (Au) added to tin oxide (SnO ₂ ) is 1
It has been found that it is sufficient to set the value between × 10 ^{−3 and} 8 × 10 ⁻² .

[Alternative Embodiment 2] The tin oxide (SnO ₂ ) in the previous embodiment was changed to indium oxide (In ₂ O ₃ ).
Similarly, a carbon monoxide gas sensing element 3 was prepared, and its sensor characteristics were examined. That is, the semiconductor unit 2 was prepared as follows.

<Method for Preparing Semiconductor Part> Commercially available indium oxide (In ₂ O ₃ ) (purity 99.99%) is pulverized in an agate mortar to obtain fine powder. Distilled water was added to this to form a paste, and as shown in FIG. 1, a platinum coil 1 (20 μm
After being dried, a current is applied to the platinum coil 1 and the resultant is baked at 600 ° C. for 2 hours.

In this semiconductor portion 2, lanthanum oxide (La)_Two
O_Three) At 4 mol% and gold (Au) at 0.02 atm.
% Sensor characteristics of carbon monoxide gas sensing element 3 loaded
Was examined at about 350 ° C.
The concentration corresponding to 100 ppm was 900 ppm.
Sobutane carbon monoxide 100ppm equivalent concentration is 2000
ppm, and the same applies to methane gas.
It shows very low sensitivity, and the sensor output
Concentration of methane gas in sample gas at the same output
Could not be measured. In other words, metal oxide semiconductor
The body is made of indium oxide (In)_TwoO_ThreeSen)
It can be seen that the metal oxide semiconductor
Is tin oxide (SnO) _Two)
It turns out that various things are used.

Another Example 3 Lanthanum oxide (La ₂ O ₃ )
And yttrium oxide (Y ₂ O ₃ ) and gold (Au)
Are prepared, and each of them is incorporated in a sensor circuit, and the sensor output for a sample gas containing 100 ppm of carbon monoxide in the air is measured. The concentration corresponding to 100 ppm, the concentration corresponding to 100 ppm of carbon monoxide in isobutane gas, and the concentration corresponding to 100 ppm of carbon monoxide in methane gas were examined.

That is, the amount of gold (Au) carried is set to 0.02 at.
With the total amount of lanthanum oxide (La ₂ O ₃ ) and yttrium oxide (Y ₂ O ₃ ) being 5 mol%, the composition dependence was examined at an operating temperature of about 325 ° C. As a result, the results are as shown in Table 5. The sensor output for a sample gas containing 100 ppm of carbon monoxide in the air is shown as a relative sensitivity ratio, with the output when the amount of lanthanum oxide (La ₂ O ₃ ) carried is 5 mol% as 1.

[0054]

[Table 5]

From Table 5, it can be seen that when lanthanum oxide (La ₂ O ₃ ) is supported, it has the effect of improving the selectivity of carbon monoxide to other gases, and when yttrium oxide (Y ₂ O ₃ ) is supported, It turns out that it has the effect of improving the sensor output for carbon oxide. In other words, in order to improve the selectivity of carbon monoxide, lanthanum oxide (La ₂ O ₃ ) is supported, and when it is desired to detect carbon monoxide with high sensitivity under the condition of little influence of other gases, yttrium oxide is used. (Y ₂ O ₃ )
It can be seen that the composition can be selected according to the purpose. Another Embodiment 4 The lanthanum oxide (La) in the previous embodiment
₂ O ₃ ) was replaced with cerium oxide (CeO ₂ ) and praseodymium oxide, and a carbon monoxide gas sensing element 3 was similarly prepared.
The sensor characteristics were examined.

<Method of Carrying Carrying Material> First, commercially available cerium nitrate (Ce (NO ₃ ) ₃ ) is converted into an aqueous solution to prepare aqueous solutions of various predetermined concentrations. This aqueous solution is impregnated into the semiconductor part 2, the semiconductor part 2 is dried, and again
The coil is heated by flowing an electric current, thermally decomposed at 600 ° C. for 1 hour, and then fired, whereby cerium oxide (CeO ₂ ) can be supported on the surface of tin oxide (SnO ₂ ). Next, chloroauric acid (HAuCl
₄ ) is converted to an aqueous solution to prepare aqueous solutions of various predetermined concentrations.
When impregnated and fired in the same manner as above, tin oxide (Sn
Gold (Au) can be supported as a metal on the surface of O ₂ ). This cerium oxide (CeO ₂ ), gold (Au)
Is the carbon monoxide gas detecting element 3. In addition, praseodymium oxide (PrO ₂ ) is supported on the surface of tin oxide in the same manner to form a carbon monoxide gas sensing element 3.

Cerium oxide (CeO) is applied to the semiconductor portion 2.
₂ ) Various carbon monoxide gas sensing elements 3 having a supported amount of 6 mol% and a supported amount of gold (Au) of 0.02 atm%, and praseodymium oxide (Pr)
O ₂ ) carrying amount is 6 mol% and gold (Au) carrying amount is 0.02 atm%. The sensor output for a sample gas containing 100 ppm of carbon monoxide was measured, and a concentration of 100 ppm of hydrogen monoxide, a concentration of 100 ppm of carbon monoxide of isobutane gas, and a concentration of 100 ppm of methane gas were measured.
The concentration corresponding to 00 ppm was examined.

As a result, the results are as shown in Table 6. For methane gas, only very low sensor sensitivity is shown.
It was not possible to measure a concentration equivalent to 100 ppm of carbon monoxide of methane gas. Here, the sensor sensitivity was examined by operating at about 350 ° C.

[0059]

[Table 6]

From Table 6, it was found that a carbon monoxide gas (CO) sensitivity satisfying the above sensitivity definition was obtained. That is, in addition to lanthanum oxide (La ₂ O ₃ ), a metal oxide of a lanthanoid metal may be used, and it was found that various metal oxides were used. [Fifth Embodiment] A carbon monoxide gas sensing element 3 in which an alkaline earth metal oxide is further supported on the semiconductor section 2 in the previous embodiment was prepared, and its sensor characteristics were examined. That is, the carbon monoxide gas sensing element 3 was prepared as follows.

<Method of Loading Carrying Material> First, a commercially available aqueous solution of lanthanum nitrate (La (NO ₃ ) ₃ ) is prepared at various concentrations. The aqueous solution is impregnated into the semiconductor part 2, the semiconductor part 2 is dried, and the coil is heated again by applying a current to the coil, thermally decomposed at 600 ° C. for one hour, and baked, thereby oxidizing. Tin (S
lanthanum oxide (La ₂ O ₃ ) can be supported on the surface of nO ₂ ). Next, calcium nitrate (Ca
(NO ₃ ) ₂ ) An aqueous solution of various predetermined concentrations of strontium nitrate (Sr (NO ₃ ) ₂ ) or barium nitrate (Ba (NO ₃ ) ₂ ) is prepared. When impregnation and baking are performed in the same manner as described above, tin oxide (SnO ₂ ) can be carried on the surface of calcium oxide (CaO), strontium oxide (SrO), or barium oxide (BaO).
Further, chloroauric acid (HAuCl ₄ ) is converted into an aqueous solution to prepare aqueous solutions of various predetermined concentrations. Impregnated as above,
When firing is performed, gold (A) is applied to the surface of tin oxide (SnO ₂ ).
u) can be carried as a metal.

As a result, the following sensor characteristics were obtained. Here, the sensor was operated at about 350 ° C. to check the sensor sensitivity.

<Sensor Characteristics> The amount of lanthanum oxide (La ₂ O ₃ ) carried on the semiconductor portion 2 was 12 mol%, the amount of calcium oxide (CaO) carried was 3 mol%, and the amount of gold (Au) carried Is 0.02 atm%, and the carbon monoxide gas detecting element 3 and the lanthanum oxide (L
a ₂ O ₃ ) A carbon monoxide gas detection element 3 having a supported amount of 7.5 mol%, a supported amount of barium oxide (BaO) of 3 mol%, and a supported amount of gold (Au) of 0.02 atm%. , And lanthanum oxide (La)
₂ O ₃ ) was carried at 7.2 mol%, strontium oxide (SrO) was carried at 14 mol%, and gold (A
Each of the carbon monoxide gas detection elements 3 having a carrying amount of u) of 0.02 atm% is prepared and incorporated into a sensor circuit, and the sensor output for a sample gas containing 100 ppm of carbon monoxide gas (CO) in the air is measured. Then, a concentration corresponding to 100 ppm of carbon monoxide in hydrogen gas, a concentration corresponding to 100 ppm of carbon monoxide in isobutane gas, and a concentration corresponding to 100 ppm of carbon monoxide in methane gas were respectively examined.

As a result, the results are as shown in Table 7. It should be noted that methane gas showed only a very low sensor sensitivity and could not measure a concentration equivalent to 100 ppm of carbon monoxide of methane gas. Here, the sensor sensitivity was examined by operating at about 350 ° C.

[0065]

[Table 7]

From Table 7, it was found that a carbon monoxide gas (CO) sensitivity satisfying the above sensitivity specification was obtained. In other words, even if the basic metal oxide is further supported on the semiconductor portion 2 of the previous embodiment, a good carbon monoxide gas (CO)
It can be seen that detection can be performed.

[Sixth Embodiment] In the previous embodiment, lanthanum oxide (La ₂ O ₃ ) and gold (Au) are simultaneously supported to prepare a carbon monoxide gas sensing element 3, and the sensor characteristics thereof are measured. Examined. That is, the carbon monoxide gas sensing element 3 was prepared as follows.

<Method of Loading Carrying Material> First, commercially available lanthanum nitrate (La (NO ₃ ) ₃ ) and chloroauric acid (HA)
uCl ₄ ) is converted into an aqueous solution to prepare a mixed aqueous solution having various predetermined concentrations. By impregnating the semiconductor portion 2 with the mixed aqueous solution, further drying the semiconductor portion 2, heating the coil again by applying a current to the coil, and thermally decomposing at 600 ° C. for 1 hour, followed by firing. Lanthanum oxide (La ₂ O ₃ ) and gold (Au) can be supported on the surface of tin oxide (SnO ₂ ).

<Sensor Characteristics> The amount of lanthanum oxide (La ₂ O ₃ ) carried on the semiconductor portion 2 was 4 mol%, and gold (A)
u) is 0.01 atm%, and the carbon monoxide gas detecting element 3 and the lanthanum oxide (La ₂
O ₃ ) a carbon monoxide gas sensing element 3 having a supported amount of 4 mol% and a supported amount of gold (Au) of 0.02 atm%,
And lanthanum oxide (La ₂ O ₃ ) for the semiconductor portion 2
The supported amount was 4 mol%, and the supported amount of gold (Au) was 0.1%.
Each of the carbon monoxide gas detecting elements 3 having a concentration of 04 atm% was prepared and incorporated in a sensor circuit, and the sensor output for a sample gas containing 100 ppm of carbon monoxide gas (CO) in air was measured. 100 ppm
The equivalent concentration, the concentration of 100 ppm of carbon monoxide in isobutane gas, and the concentration of 100 ppm of carbon monoxide in methane gas were examined.

As a result, the results are as shown in Table 8. Here, the sensor sensitivity was examined by operating at about 350 ° C.

[0071]

[Table 8]

From Table 8, it was found that although the sensitivity was slightly lower than in the case of the previous embodiment, sufficient carbon monoxide gas sensitivity could be obtained to satisfy the above sensitivity specification. In other words, even if the carbon monoxide gas detecting element 3 is prepared by simultaneously supporting lanthanum oxide (La ₂ O ₃ ) and gold (Au) on the semiconductor portion 2 of the previous embodiment, a high monoxide is similarly obtained. Carbon gas sensitivity was obtained, and it was found that the order of loading the supported material was not limited to lanthanum oxide (La ₂ O ₃ ) and gold (Au) in that order. Further, gold (Au) and lanthanum oxide (L
It can be expected that the same result can be obtained even if they are carried in the order of a ₂ O ₃ ). Further, the lower sensitivity than in the case of the previous embodiment means that lanthanum oxide (La ₂ O ₃ ) is supported so as to secure a sufficient contact area with tin oxide, and gold (A)
u) indicates that it is desirable to support the carbon monoxide gas so as to secure a sufficient contact area with the carbon monoxide gas. However, lanthanum oxide (La ₂ O ₃ ), gold (Au)
Considering the chemical role of carbon monoxide gas (CO), it is considered that a high carbon monoxide gas sensitivity is obtained by the combined action of these supports, as in the previous embodiment.

Further, lanthanum oxide (La)
_{If 2} O ₃ ) and gold (Au) are simultaneously carried, the number of steps for carrying the carrier on the semiconductor portion 2 can be reduced, and there is an advantage that the productivity of the carbon monoxide gas detecting element is improved.

[Alternative Embodiment 7] The preceding embodiment shows an example in which the present invention is applied to a carbon monoxide gas sensor for home use.
It can also be used for detecting carbon monoxide gas in exhaust gas.

Further, in the above embodiment, the hot wire type sensor as shown in FIG. 1 is used. However, the present invention is not limited to this, and a detection electrode and a heater may be separately provided. The substrate type sensor shown in FIG. That is,
FIG. 5a shows a precious metal coil 1 in the previous embodiment,
Instead of using a rectangular wave-shaped electrode 1b deposited on a substrate 5 of alumina or the like and sintering the semiconductor portion 2 in a spherical shape, the semiconductor portion 2 is formed on the substrate 5 in the same manner as in the present embodiment. However, the electrode 1b is sintered so as to cover the electrode 1b, and has a structure in which the electrode 1b is used as a heater for heating the carbon monoxide gas detecting element 3 as in the previous embodiment. FIG. 5B shows the configuration of FIG.
Is replaced by a comb-shaped electrode 1c, and a heating heater 6 is further provided so that the carbon monoxide gas detecting element 3 can be heated.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view of a carbon monoxide gas sensing element of the present invention.

FIG. 2 is a circuit diagram of a carbon monoxide gas sensor.

FIG. 3 is a diagram showing a response waveform of the gas sensor of the present invention.

FIG. 4 is a diagram showing a response waveform of a conventional gas sensor.

FIG. 5 shows another embodiment of the present invention.

[Explanation of symbols]

 2 Semiconductor section

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-134552 (JP, A) JP-A 64-83142 (JP, A) JP-A-53-141091 (JP, A) JP-A 54-83 32397 (JP, A) JP-A-62-75244 (JP, A) JP-A-57-137846 (JP, A) JP-A-51-14398 (JP, A) JP-A-53-135699 (JP, A) JP-A-2-126146 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/12

Claims (6)

(57) [Claims] 1. A carbon monoxide gas sensing element comprising a semiconductor portion mainly composed of a metal oxide semiconductor whose valence is controlled, wherein said semiconductor portion includes at least one of a lanthanoid metal and yttrium (Y). A carbon monoxide gas sensing element carrying a metal oxide and gold (Au). 2. A carbon monoxide gas sensing element comprising a semiconductor portion mainly composed of a metal oxide semiconductor whose valence is controlled, wherein said semiconductor portion includes at least one of a lanthanoid metal and yttrium (Y). A carbon monoxide gas sensing element carrying a metal oxide, gold (Au) and an alkaline earth metal oxide. 3. The method according to claim 1, wherein the metal oxide is lanthanum oxide (La ₂
O ₃ ), wherein the lanthanum oxide (La ₂ O ₃ ) is contained in an amount of 1 mol% or more and 20 mol% or less with respect to the metal oxide semiconductor, and the gold (Au) is mixed with the metal oxide semiconductor. The carbon monoxide gas sensing element according to claim 1, wherein the element is contained in an amount of 4 × 10 ⁻⁴ atm% or more and 0.5 atm% or less. 4. The method according to claim 1, wherein the metal oxide is lanthanum oxide (La ₂
O ₃ ), wherein the lanthanum oxide (La ₂ O ₃ ) is contained at 2 mol% or more and 10 mol% or less with respect to the metal oxide semiconductor, and the gold (Au) is mixed with the metal oxide semiconductor. The carbon monoxide gas sensing element according to any one of claims 1 to 3, wherein the element is contained in an amount of 1 x ^10-3 atm% or more and 0.1 atm% or less. 5. The method according to claim 1, wherein the metal oxide is formed of yttrium oxide (Y
₂ O ₃ ), and the yttrium oxide (Y ₂ O ₃ ) is 3 mol% or more and 11 mol% with respect to the metal oxide semiconductor.
The gold (Au) is contained in an amount of 1 × 10 ⁻³ atm% or more to 8 × 10 ⁻² atm with respect to the metal oxide semiconductor.
The carbon monoxide gas sensing element according to claim 1, wherein the element is contained in an amount of up to m%. 6. The method according to claim 1, wherein the metal oxide semiconductor is tin oxide (S
The carbon monoxide gas sensing element according to claim 1, wherein the element is at least one of nO ₂ ) and indium oxide (In ₂ O ₃ ).