JPH0225452B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an element for detecting malodorous gases such as methyl mercaptan (CH ₃ SH) and hydrogen sulfide (H ₂ S), alcohol gas, and humidity.

Measuring the concentration of CH ₃ SH, H ₂ S, etc., which are the main components of bad odors generated at human waste treatment plants, garbage treatment plants, etc.
Some of this is done using electrochemical methods, but it requires gas sampling and requires a complicated laboratory.
Furthermore, conventional semiconductor gas sensors have insufficient sensitivity and have not been used.

Conventionally, many alcohol gas detection methods have been used that utilize changes in electrical conductivity due to chemical adsorption of gases in metal oxide semiconductors such as SnO ₂ and ZnO. However, these same phenomena occur with other flammable gases such as methane, propane, carbon monoxide, and hydrogen. That is, there is no selectivity for gas species.

On the other hand, humidity sensing elements utilize the relative humidity dependence of the electrical conductivity of metal oxides, inorganic and organic electrolytes, and organic materials in which conductive substances are dispersed, due to their simplicity and compatibility with microprocessors. It has been often used due to its connectivity. Among these, metal oxides are preferred because they have good stability and heat resistance.

However, there is no one that can detect humidity and gas with a single integrated element, and also has stable moisture-sensing characteristics, high sensitivity to malodorous gases and alcohol gases, high selectivity, and gas-sensing characteristics with fast response speed. Ta.

This invention was made to solve the above-mentioned problem, and one integrated element can achieve 0 to 100%
The object of the present invention is to provide a gas- and humidity-sensitive element that selectively detects relative humidity, malodorous gas, and alcohol gas with high sensitivity.

This invention detects humidity using an apatite ceramic material, and detects malodorous gas and alcohol gas using a metal oxide between separated electrodes provided on an element substrate made of the apatite ceramic material.
Furthermore, the separation electrode is formed by baking ruthenium oxide, which helps increase the gas sensitivity.

The gas-sensitive and humidity-sensitive element of the present invention has an electrical resistance of 0 to 100% relative humidity and a malodorous gas concentration of 0 to 1000 ppm.
Alternatively, since the alcohol gas concentration varies greatly between 0 and 3000 ppm, relative humidity, malodorous gas, and alcohol gas can be easily detected by measuring the electrical resistance value.

The details of this invention will be explained below using examples.

Example 1 Hydroxyapatite powder in which 10% of Ca was replaced with Na was made into a 4 mm x 4 mm, 0.8 mm thick, 350 kg/
It is molded at a pressure of cm ² and baked in air at 1100° C. for 6 hours. This was polished to a thickness of 250 μm, and separated electrodes 2 and 3 (first and third electrodes) made of RuO ₂ paste were formed on the back side, as shown in the sintered body 1 in Fig. 1.
As shown in FIG. 2, an electrode 4 (second electrode) made of RuO ₂ paste is screen printed on the entire surface. Next, a titanium oxide TiO ₂ paste is screen printed between the separated electrodes 2 and 3 with an interval of 250 μm.
TiO ₂ paste is made by mixing special reagent grade powder at 1000℃.
It is made by baking it in the atmosphere for an hour, crushing it, passing it through a 400 mesh sieve, and adding butyl carbitol.
After printing TiO ₂ , attach lead wires 6, 7, and 8, and
Bake at ℃ for 10 minutes. The electrode formed in the above manner becomes a porous surface electrode, so that humidity easily reaches the sintered body through the electrode. Reference numeral 1 constitutes an element substrate made of a hydroxyapatite moisture-sensitive ceramic material. 5 is
_TiO2 is a gas-sensitive material. When detecting gas,
It is necessary to keep the element above 200℃. Therefore, it is necessary to install a Kanthal wire coil heater around the elements shown in Figures 1 and 2, or use a solid RuO ₂ heater as shown in Figure 2.
Two lead wires may be attached to the electrode to serve as both a heater and a moisture-sensitive electrode.

The measurements shown in FIGS. 3 to 5 are carried out using the gas- and humidity-sensitive element manufactured as described above.

Figure 3 shows the moisture sensitivity characteristics at 25°C. For measurement, electrodes 2 and 3 are short-circuited, and between this and electrode 4,
This was done by applying a 1V, 50Hz sine wave. electrode 2,
3 may be applied between one electrode and electrode 4 without shorting, but the measured resistance will increase.

As shown in the figure, the electrical resistance changes by more than four orders of magnitude when the relative humidity ranges from 0 to 100%, making it extremely sensitive. In addition, even when left in the laboratory for 6 months with or without 1V energized, the characteristics changed within the measurement error and remained very stable. This is a feature not found in other ceramic humidity sensors. The response time is also fast, taking 2 to 15 seconds.

FIG. 4 shows the gas sensitivity characteristics when the element temperature is changed. Measure the resistance between electrodes 2 and 3. 11 is 0ppm of CH ₃ SH in the atmosphere, 12 is 100ppm of CH ₃ SH
It is.

As shown in the figure, the resistance value changes by more than two orders of magnitude.

FIG. 5 shows the sensitivity S to 100 ppm each of CH ₃ SH, H ₂ S, ethanol (C ₂ H ₅ OH), hydrogen (H ₂ ), carbon monoxide (CO), and propane (C ₃ H ₈ ). Assuming that the resistance value in the atmosphere is Ra and the resistance value Rg in 100 ppm gas, the sensitivity S is Ra/Rg, which means the amount of change in the resistance value. In FIG. 5, the element temperature is 450°C. As can be seen from the figure, it shows almost no sensitivity to H ₂ , CO, and C ₃ H ₈ .

It showed almost the same sensitivity to methanol, isopropyl alcohol, etc. as ethanol.

Since apatite has a high gas adsorption capacity, it is highly likely that apatite also contributes to high sensitivity and high selectivity.

Example 2 The first half was manufactured under the same conditions as Example 1, but the process of forming the gas-sensitive material in the second half was different. In other words, the paste for forming the gas-sensitive material is reagent grade tin oxide SnO ₂
After passing the powder through a 400 mesh sieve and then adding butyl carbitol, the SnO ₂ paste was screen printed in the same position as in Example 1.
Attach lead wires 6, 7, and 8 and bake at 800℃ for 10 minutes. In this case, 1 is a hydroxyapatite moisture-sensitive ceramic, 2, 3, and 4 are electrodes made of RuO ₂ , and 5 is SnO ₂
It is a gas-sensitive material.

6th gas- and moisture-sensing element using SnO ₂ gas-sensitive material
The measurements shown in Fig. 7 were carried out. Figures 6 and 7
The figures correspond to FIGS. 4 and 5 of the first embodiment.
In this case, the sensitivity of CH ₃ SH is approximately 1000 times greater.

The element temperature in the measurement shown in FIG. 7 was 300°C.
Although ethanol is shown as a representative alcohol, almost the same sensitivity is shown for other alcohols such as methanol and isopropyl alcohol. Note that the measurement corresponding to FIG. 3 of Example 1 had the same measurement results in Example 2, so the description thereof will be omitted.

Example 3 The first half was manufactured under the same conditions as Example 1, but the second half was different in the formation process of the gas-sensitive material. The gas-sensitive paste is a tin oxide SnO ₂ paste containing 0 to 50 wt% of RuO ₂ and is screen printed at the same position as in Example 1. This paste is made by grinding reagent grade _SnO2 , 400
It is made by mixing RuO ₂ after passing through a mesh sieve and adding butyl carbitol. After printing, attach lead wires 6, 7, and 8 and bake at 800℃ for 10 minutes. In this case, 1 is hydroxyapatite moisture-sensitive ceramics,
2, 3, 4 are electrodes made of RuO ₂ , 5 is (SnO ₂ +
R ₂ O ₂ ) It is a gas-sensitive material.

Measurements shown in FIGS. 8 and 9 were carried out using a gas-sensitive moisture-sensitive element using a (SnO ₂ +RuO ₂ ) gas-sensitive material.

FIG. 8 shows the relationship between the gas sensitivity characteristics for CH ₃ SH and the RuO ₂ content when the device is kept at 300°C.
However, even if the RuO ₂ content is 0 wt%, the electrodes 2 and 3 whose main component is RuO ₂ are provided. The resistance between electrodes 2 and 3 in FIG. 1 is measured. 11 is in the atmosphere
0ppm and 12 of CH ₃ SH are in 100ppm of CH ₃ SH. The one containing 10wt% RuO ₂ shows approximately 2000 times the sensitivity. When RuO ₂ reaches 40 to 50 wt%, the resistance value in the atmosphere decreases and the sensitivity also decreases. The sensitivity mentioned here is the ratio Ra/Rg of the resistance value Ra in the atmosphere and the resistance value Rg at 100 ppm of ethanol.

Figure 9 shows CH ₃ SH, H ₂ S, C ₂ H ₅ OH, H ₂ , C ₃ H ₈
Sensitivity S at 100 ppm and CO at element temperature
300℃ _RuO2 content 10wt%. As can be seen from the figure, it shows almost no sensitivity to anything other than CH ₃ SH, H ₂ S, and C ₂ H ₅ OH. It exhibits almost the same sensitivity to alcohols such as methanol and isopropyl alcohol as to ethanol.

In FIG. 8, RuO ₂ :0wt% is the same as in Example 2.

Note that the measurement corresponding to FIG. 3 of Example 1 had the same measurement results in Example 3, so the description thereof will be omitted.

Example 4 The first half is manufactured under the same conditions as Example 1, but the second half, in which the process of forming the gas-sensitive material is different, is a zinc oxide ZnO paste containing 0 to 50 wt% of RuO ₂ . Screen print at the same location. This paste is made by pulverizing reagent grade ZnO.
It is made by mixing RuO ₂ and adding butyl carbitol after passing through a 400 mesh sieve. After printing, attach lead wires 6, 7, and 8 and bake at 800℃ for 10 minutes. In this case, 1 is hydroxyapatite moisture-sensitive ceramics,
2, 3, 4 are electrodes made of RuO ₂ , 5 is (ZnO+
RuO ₂ ) It is a gas-sensitive material.

Measurements shown in FIGS. 10 and 11 were carried out using a gas-sensitive moisture-sensitive element using a (ZnO+RuO ₂ ) gas-sensitive material. 10 and 11 correspond to FIGS. 8 and 9 of the third embodiment. In this case, the sensitivity to CH ₃ SH is about 2000 times higher since it contains 10 wt% of RuO ₂ as in Example 3, and the response speed from CH ₃ SH0 to 100 ppm is very fast at 1 second. The element temperature in the measurements shown in FIGS. 10 and 11 was 450°C. Although ethanol is shown as a representative alcohol, almost the same sensitivity is shown for other alcohols such as methanol and isopropyl alcohol.

Note that the measurement corresponding to FIG. 3 of Example 1 had the same measurement results in Example 4, so the description thereof will be omitted.

Example 5 Example 1 and the first sheet are manufactured under the same conditions, but the second half of the process for forming the gas-sensitive material is different.

The gas-sensitive paste is a magnesium ferrite paste containing 0 to 50 wt% of _RuO2 , and this is screen printed on the same position as in Example 1. This paste is made by calcining oxalate obtained by coprecipitation in the air at 1000°C for 1 hour, crushing it, passing it through a 400 mesh sieve, mixing it with RuO ₂ and adding butyl carbitol. The composition of ferrite _is MgFe _1.5 Al _{0.5 O 4}
It is. After printing, attach lead wires 6, 7, 8,
Bake at 800℃ for 10 minutes. In this case, 1 is hydroxyapatite moisture-sensitive ceramic, 2, 3, and 4 are electrodes made of RuO ₂ , and 5 is (magnesium ferrite +
RuO ₂ ) It is a gas-sensitive material.

The measurements shown in FIGS. ₁₂ and 13 were carried out using a gas-sensitive moisture sensing element using a (MgFe _1.5 Al _{0.5 O 4} +RuO ₂ ) gas-sensitive material. 12 and 13 correspond to FIGS. 4 and 5 of the third embodiment. In this case
The sensitivity to CH ₃ SH is the same as in Example ₃ .
Contains 10wt%, approximately 600 times, CH ₃ SH0 →
The response speed at 100ppm is extremely fast at 2 seconds. 1st
The element temperature in the measurement shown in Figure 3 was 250°C. Although ethanol is shown as a representative alcohol, almost the same sensitivity is shown for other alcohols such as methanol and isopropyl alcohol.

Note that the measurements corresponding to FIG. 3 of Example 1 had the same measurement results in Example 5, so their description will be omitted.

Although MgFe _1.5 Al _{0.5 O 4} was used above, MgFe ₂ O ₄ that does not contain Al has the same _sensitivity .

Magnesium ferrite differs from the materials of Examples 1 to 4 in that its resistance increases due to gas adsorption.
(Fig. 12) It is a P-type semiconductor. Therefore, only in this case is S=Rg/Ra.

Example 6 The first half was manufactured under the same conditions as Example 1, but the process of forming the gas-sensitive material in the second half was different. The gas-sensitive paste is a niobium oxide Nb ₂ O ₅ paste containing 0 to 50 wt% of RuO ₂ and is screen printed on the same position as in Example 1. This paste contains 1000 reagent grade Nb ₂ O ₅
℃, fired in the air for 1 hour, crushed, 400℃
It is made by mixing RuO ₂ after passing through a mesh sieve and adding butyl carbitol. After printing, attach lead wires 6, 7, and 8 and bake at 800℃ for 10 minutes. In this case, 1 is hydroxyapatite moisture-sensitive ceramics,
2, 3, 4 are electrodes made of RuO ₂ , 5 is (Nb ₂ O ₅
+RuO ₂ ) It is a gas-sensitive material.

(Nb ₂ O ₅ +RuO ₂ ) Measurements shown in FIGS. 14 and 15 were carried out using a gas-sensitive moisture-sensitive element using a gas-sensitive material. 14 and 15 correspond to FIGS. 4 and 5 of the third embodiment. In this case, the sensitivity to CH ₃ SH is about 600 times higher when RuO ₂ is contained at 10 wt% as in Example 3, and the response speed at CH ₃ SH0→100 ppm is very fast at 1 second. The element temperature in the measurements shown in FIGS. 14 and 15 was 300°C. Alcohol is shown as ethanol, but methanol,
It exhibits similar sensitivity to other alcohols such as isopropyl alcohol.

Note that the measurement corresponding to FIG. 3 of Example 1 had the same measurement results in Example 2, so the description thereof will be omitted.

In the above examples, hydroxyapatite was used as the apatite, but other apatites, such as those in which hydroxyl groups were replaced with halogens, or apatites in which calcium was replaced with strosium, barium, lead, etc., were used. It's okay. Also, the first
Although FIG. 2 shows a plate-shaped gas-sensitive and moisture-sensitive element, it may also be made into a cylinder, with electrodes coated entirely on the inner surface and separated electrodes on the outer surface, with a gas-sensitive paste applied between the separated electrodes.

first and second electrodes provided on the element substrate with a ceramic material interposed therebetween; a third electrode spaced apart from the first electrode and provided on the same surface as the first electrode of the element substrate;
Since it is a gas-sensitive and moisture-sensitive element that includes a metal oxide that is sensitive to gas and that is in contact with the electrode and the third electrode and is provided between the first and third electrodes, it can be used as one integrated element. ~100% relative humidity and malodorous gases,
Alcohol gas can be selectively detected with high sensitivity.

[Brief explanation of drawings]

FIGS. 1 and 2 are perspective views showing the structure of an embodiment of the present invention, with FIG. 1 showing its front surface and FIG. 2 showing its back surface. FIG. 3 is a characteristic curve diagram showing the moisture-sensitive characteristics of the present invention, FIGS. 4 and 6 are characteristic curve diagrams showing the temperature dependence of the gas-sensitive characteristics of each embodiment of the present invention, and FIGS. Figure 10, Figure 12 and Figure 14
The figures are characteristic curve diagrams showing the RuO ₂ content dependence of the gas-sensitive characteristics of each example of the present invention, and Figures 5, 7, 9, 11, 13, and 15 are , respectively, are characteristic graphs showing sensitivities to various gases in each example of the present invention. In the figure, 1 is an element substrate made of moisture-sensitive ceramics;
Reference numerals 2, 3, and 4 are electrodes corresponding to the first, third, and second electrodes, respectively. 5 is a gas-sensitive material, and 6, 7, and 8 are lead wires. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. An element substrate made of apatite ceramics,
First and second electrodes provided on the element substrate with the apatite ceramic interposed therebetween, and a third electrode spaced apart from the first electrode and provided on the same surface as the first electrode of the element substrate.
A gas-sensitive and moisture-sensitive element comprising: an electrode; and a metal oxide sensitive to gas, which is in contact with a first electrode and a third electrode and is provided between the first electrode and the third electrode. 2. The gas- and moisture-sensitive element according to claim 1, wherein the metal oxide is one of titanium oxide, niobium oxide, tin oxide, zinc oxide, and magnesium ferrite. 3. The gas- and moisture-sensitive element according to claim 1, wherein the metal oxide is a mixture of ruthenium oxide and one of titanium oxide, niobium oxide, tin oxide, zinc oxide, and magnesium ferrite. 4. The gas- and moisture-sensitive element according to any one of claims 1 to 3, wherein the electrode is a porous surface electrode. 5. The gas- and moisture-sensitive element according to any one of claims 1 to 4, wherein the first and third electrodes are formed by baking ruthenium oxide onto the element substrate.