JP2962010B2 - Ozone sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small and lightweight ozone sensor for controlling ozone concentration in an ozone generator or an ozone utilization device, or for detecting ozone.

[0002]

2. Description of the Related Art Since ozone has a strong oxidizing effect,
Conventionally, it has been used in many fields such as water and sewage water treatment, medical treatment, and the food industry for the purpose of deodorization and sterilization. However, even a very small amount of ozone is harmful to the human body, so it is necessary to reliably control the amount of generated ozone and detect leaked ozone.

Hitherto, the measurement and detection of ozone concentration have been exclusively performed by redox titration, absorption spectroscopy, ultraviolet absorption spectroscopy and the like.

On the other hand, a sensor element using In ₂ O ₃ has been proposed as a simpler method for measuring ozone concentration.

[0005]

However, such a conventional method for detecting ozone generally has a disadvantage that it requires a large-scale apparatus and complicated operations, and is expensive and cannot be easily used. . On the other hand, In ₂ O _{3, which} has been proposed as a material for a simple sensor element, can obtain relatively high sensitivity at a low temperature, but is slightly unstable thermally and has a problem in long-term stability.

An object of the present invention is to solve such a problem and to provide an inexpensive and simple ozone sensor having high reliability.

[0007]

In order to solve the above-mentioned problems, the present invention provides a method in which the Sn content is 3 times the total amount of In and Sn.
By adopting a sensor element having a film-shaped gas sensitizer composed of a material mainly composed of In ₂ O ₃ and SnO _{2 of 10} to 10 mol%, it exhibits excellent characteristics such as element resistance, sensitivity, and operating temperature. It is intended to realize a small, lightweight and inexpensive sensor element with high reliability.

[0008]

According to the ozone sensor of this configuration, the Sn content is In.
In ₂ O ₃ and Sn which are ₃ to 10 mol% of the total amount of Sn and Sn
Since a film-shaped gas sensitive body made of a material mainly composed of O ₂ is used, it has excellent sensitivity and responsiveness to ozone, is thermally stable, and has high reliability. Further, since the size and weight of the sensor element can be easily reduced, a sensor element which is easy to handle and inexpensive can be provided.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An ozone sensor according to an embodiment of the present invention will be described below with reference to the drawings. 1 (a), (b),
(C) shows the configuration of the ozone sensor of this embodiment. FIG.
FIG. 2B is a cross-sectional view taken along line AA ′ of FIG. On an alumina substrate (3 × 5 × 0.5 mm) 1, a coating solution prepared mainly with an organometallic compound of In and Sn is applied to the alumina substrate and baked at 600 ° C. to form In ₂ O ₃ and SnO.
Gas sensitive body consisting of ₂ (2 x 5 mm, thickness about 700 mm) 2
Is provided. In order to see the relationship between the composition of the sensitive body 2 and various characteristics of the ozone sensor, the Sn content was 0, 1, 2, 3, 5, 7, 10, 15, 20 (mo) of the total amount of In and Sn.
1%), to prepare a sensitizer 2. A platinum electrode 3 is previously formed on the alumina substrate by sputtering so that the width of the sensitive body bonding portion is 1 mm, and a platinum heater 4 for heating the element is formed on the opposite side of the alumina substrate 1 by sputtering. .

FIG. 2 shows the relationship between the element resistance at 350 ° C. in air and the Sn content of each sensor element manufactured as described above. FIG. 2 shows that when the Sn content is less than 3 mol%, the element resistance becomes extremely large. Also,
Even if it exceeds 10 mol%, a tendency that the element resistance increases is recognized. Even if the element resistance becomes too large, there is a point that it is practically difficult to use, and it is desirable to suppress the element resistance to several kΩ or less. As described above, the Sn content is 3 mol% or more and 20 mol%.
Is considered to be desirable.

Next, the response characteristics of the fabricated sensor element to ozone were measured. The sensor element is fixed in a quartz glass measuring tube, the element temperature is controlled to a predetermined value by a heater, and the resistance of the sensor element when air and air containing 1 ppm ozone alternately flow through the sensor element. The change was measured. The sensor element resistance in air was changed to R _A and air containing ozone was changed to R _G1 , and the sensor element resistance after one minute was determined as R _G1 to obtain R _G1 / R _A, which was defined as the sensor sensitivity.
FIG. 3 shows the relationship between the temperature and the sensitivity of the ozone sensor of each composition obtained in this manner. Sn content is 1mol%
Although the characteristics of the element of 3 mol% and 3 mol% are not shown,
The characteristics of the device having the n content of 1 mol% were almost equal to the characteristics of the device having 0 mol%, and the characteristics of the device having 3 mol% were almost equal to the characteristics of the device having 5 mol%. From this result,
It has been clarified that when the Sn content is small, the sensitivity at low temperatures becomes relatively high. It is a practically advantageous point that the sensor has a high gas sensitivity at a low temperature, and in view of this, it can be said that it is desirable that the Sn content does not exceed 10 mol%.

Further, the recovery speed of the element resistance was evaluated using the above-mentioned sensor. The return speed is the speed at which the element resistance changes when returning from air containing ozone to air.
It was evaluated by the formula _{(R G3 -R A ') /} (R G3 -R A) resistivity recovery ratio defined in × 100 (%). Where R _A is the element resistance in air, R _G3 is the element resistance three minutes after changing from air to ozone-containing air, and R _A 'is the element resistance one minute after returning from ozone-containing air to air again. is there. Ozone concentration is 1
ppm, and the sensor element temperature was 350 ° C. FIG. 4 shows the measurement results. As shown in the figure, the Sn content is 10 mol.
% Or less, the resistance return ratio is relatively large, and there is little difference depending on the composition. It is also practically advantageous that the resistance return speed is high.
It is considered that the content should be 0 mol% or less.

Next, a change in sensitivity with time was measured to evaluate the thermal stability of the device. The heater is continuously energized to heat and hold the sensor element at 400 ° C., and the electrical resistance change at 350 ° C. is measured every 200 hours in the same manner as described above, and the sensor sensitivity (R _G1 / R _A ) is measured over a total of 1000 hours.
Was measured over time. FIG. 5 shows the measurement results. Although the characteristics of the devices having the Sn contents of 7 mol% and 15 mol% are not shown, they showed stable characteristics with almost no change over time as in the case of the devices having 5 to 20 mol%. As a result,
In the range where the Sn content is 2 mol% or less, it has been found that the smaller the Sn content, the greater the change with time in the sensor sensitivity. On the other hand, when the Sn content is 3 m
When the content was more than ol%, almost no change with time was recognized, and it became clear that these sensors had very stable characteristics thermally. Also, there is no deterioration of the heater,
It has also been found that it guarantees stable operation for a long time.

As in the above embodiment, when the Sn content is In
In ₂ O ₃ and Sn which are ₃ to 10 mol% of the total amount of Sn and Sn
An ozone sensor having a film-shaped gas sensitive body formed of a material mainly composed of O ₂ has excellent sensitivity characteristics and can be expected to operate stably for a long period of time.

In this embodiment, the case where the coating method is used as the gas sensitive body manufacturing method has been described. However, a wet film forming method such as offset printing or other printing method or spin coating method,
Alternatively, a dry film forming method such as sputtering or vacuum deposition can be used, and in any case, a highly active gas sensitive material can be produced.

In addition, the gas-sensitive material starting material is not limited to this embodiment, and any material suitable for film formation can be appropriately selected and used. The structure and configuration of each part of the sensor element, the substrate material, the electrode material, and the heater material can be freely designed or used as long as they do not depart from the gist of the invention.

[0017]

As is clear from the above description of the embodiment, the Sn content is 3 to 10 mol% of the total amount of In and Sn.
By adopting a sensor element having a film-shaped gas sensitive body made of a material mainly composed of In ₂ O ₃ and SnO ₂ , it is excellent in gas detection characteristics and thermal stability, and is small, lightweight and inexpensive. Therefore, it is suitable for applications such as ozone concentration control in an ozone generator or an ozone utilization device, or ozone detection.

[Brief description of the drawings]

FIG. 1A is a plan view showing a configuration of an ozone sensor according to an embodiment of the present invention. FIG. 1B is a cross-sectional view taken along line AA ′ of FIG. 1C.

FIG. 2 is a diagram showing the relationship between the Sn content and the element resistance of the same ozone sensor.

FIG. 3 is a diagram showing the relationship between the temperature of the ozone sensor and the sensor sensitivity.

FIG. 4 is a diagram showing the relationship between the Sn content and the resistance return rate of the ozone sensor.

FIG. 5 is a diagram showing a change over time in sensor sensitivity of the ozone sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Gas sensitive body 3 Electrode 4 Heater

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Akihiko Yoshida 1006 Kadoma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Nobuyuki Yoshiike 1006 Odaka Kadoma Kadoma, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-4-152258 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 27/12

Claims (1)

(57) [Claims] 1. A pair of electrodes formed on one surface of an insulating substrate, and a film-shaped gas sensitive body made of a material mainly composed of In ₂ O ₃ and SnO _{2 in contact} with the pair of electrodes. A sensor element having a heater formed on the other surface of the insulating substrate, wherein the Sn content is 3 to 10 m which is the total amount of In and Sn.
ozone sensor which is ol%.