JPH04276545A - Ozone sensor - Google Patents

Abstract

PURPOSE:To increase the bonding strength between a response body film and an insulating substrate, to improve thermal shock resistance and to improve stability for a long period in ozone sensor used in ozone generators and ozone utilizing apparatuses. CONSTITUTION:An intermediate layer 3 comprising the same material as a response body 4 is formed between a response body film 4 which is formed by a wet-type film forming method and an insulating substrate 1. The bonding strength between the intermediate layer formed by a dry-type film forming method and the insulating substrate is high. The sensor is resistant against thermal shock. Since both the intermediate layer and the response body are made of the same material, the bonding state is stable, and the characteristics of the sensor are not impaired.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ozone sensor used for ozone concentration control or ozone detection in ozone generators and ozone utilization equipment.

0002

BACKGROUND OF THE INVENTION Ozone exhibits a strong oxidizing effect and is therefore used in many fields such as water and sewage water treatment, medical care, and the food industry for purposes such as deodorization and sterilization. However, while it has such useful utility, even a very small amount of ozone is extremely harmful to the human body, so it is necessary to reliably control the amount generated and detect leaked ozone.

Under these circumstances, methods such as redox titration, spectrophotometry, and ultraviolet absorption spectroscopy have conventionally been used to measure and detect ozone concentration. In response to this, recently there has been a demand for a simpler method for measuring ozone concentration, and as one method, a small ozone sensor using a metal oxide such as In2O3 has been proposed.

0004

[Problems to be Solved by the Invention] However, in the case of the spectrophotometric method, which has been used exclusively in the past, it generally requires large-scale equipment and complicated operations, and is expensive, so it cannot be used easily. have. On the other hand, among the ozone sensors that use metal oxides as sensitive bodies, which have been proposed as a simple method for measuring ozone concentration, thin-film ozone sensors made by wet film forming methods such as printing methods have a high sensitivity and response. However, since the bonding strength between the sensitive film and the substrate is somewhat insufficient, there are problems in terms of reliability, such as the sensitive film sometimes peeling off due to thermal shock or the like. Therefore, a highly reliable, small, lightweight, and inexpensive ozone sensor is strongly desired.

[0005] The present invention solves the above problems,
It is an object of the present invention to provide an ozone sensor that has excellent strength against thermal shock and also has excellent gas detection characteristics.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a pair of electrodes formed on an insulating substrate;
It has an intermediate layer formed by a dry film forming method between the electrodes, and a sensitive body made of the same material as the intermediate layer is formed on the intermediate layer by a wet film forming method.

[0007]

[Function] Therefore, according to the present invention, the film-like intermediate layer formed by the dry film forming method can increase the bonding strength with the substrate and improve the stability against thermal shock. Furthermore, although the sensitive material is formed by a wet film forming method, since the intermediate layer is made of the same material as the sensitive material, the bonding state between the sensitive material and the intermediate layer is extremely excellent. Therefore, it is possible to provide a highly reliable ozone sensor with excellent mechanical strength without impairing sensor characteristics.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of an ozone sensor according to an embodiment of the present invention. In the figure, 1 is an alumina substrate, 2 is a platinum electrode formed on the alumina substrate 1, and 3 is an I
An intermediate layer formed by vacuum evaporating n and Sn (
4 was formed by screen printing using an ink prepared mainly from an organometallic compound of In and Sn, and baked at 500°C.
%) and SnO2 (5 wt%) (thickness: approximately 800 Å).

As a comparative example, an ozone sensor (sensor thickness: approximately 900 Å) was fabricated without forming the intermediate layer 3. Except for the thickness of the sensitive body 4 produced by the wet film forming method, the shape, dimensions, production conditions, etc. of the element components were the same as in the example. Note that the intermediate layer 3 has the same composition as the sensitive body 4.

Using these ozone sensors, response characteristics to ozone were measured by the method described below. First, the ozone sensor was fixed to a heater for heating the element, set in a measurement box filled with clean air, and the heater was energized to set the sensor temperature at 350°C. Next, 1 ppm of ozone was injected into the measurement box, uniformly diffused, and brought into contact with the ozone sensor, and the electrical resistance of the ozone sensor was measured. Measurements were made for five elements in each of the examples and comparative examples, and the average values are shown in FIG. Note that the electrical resistance was expressed on an arbitrary scale. There is a difference in that the electrical resistance of the ozone sensor of the example is slightly smaller than that of the ozone sensor of the comparative example both in air and in ozone-mixed air. (divided by electrical resistance) were found to be equivalent. Since the film formed by the dry film forming method (intermediate layer 3) is denser than the film formed by the wet film forming method (sensor 4), the film of the example (intermediate layer 3 + sensitive member 4) is It is thought that the electrical resistance has become smaller. On the other hand, since the sensitivity is substantially controlled by the film (sensor 4) printed on the surface, it is considered that both the Examples and Comparative Examples exhibit equivalent sensitivity characteristics.

Next, in order to confirm the thermal shock resistance of the ozone sensor, a test was conducted using the following method. The ozone sensor was placed in an electric furnace, the temperature was raised and lowered from room temperature to 500°C in about 1 minute, and the electrical resistance of the ozone sensor at room temperature was measured every 50 times.This was repeated 300 times in total to determine the change in electrical resistance. I checked to see if it was there. The results are shown in FIG. As a result, it was revealed that the electrical resistance of the ozone sensor of the example hardly changed from the initial stage. On the other hand, it became clear that the electrical resistance of the ozone sensor of the comparative example significantly increased by the 100th test, and continued to gradually increase thereafter. As a result of observing the interface between the sensitive body 4 and the alumina substrate 1 of the ozone sensor after the test using a scanning electron microscope, it was found that in the ozone sensor of the example, the interface between the intermediate layer 3 and the alumina substrate 1, and the interface between the intermediate layer 3 and the sensitive body 4 No abnormality was observed in the bonding state of any of the interfaces of the films. On the other hand, in the ozone sensor of the comparative example, many partial peelings were observed at the interface between the film of the sensitive body 4 and the alumina substrate 1. It is thought that this resulted in an increase in the electrical resistance of the ozone sensor. Film produced by vacuum evaporation (intermediate layer 3)
In this example, it was confirmed that the bonding state of the bonding material to the alumina substrate 1 was extremely good. Note that good bonding can be obtained not only by vacuum evaporation but also by sputtering or the like. Since the intermediate layer 3 and the sensitive body 4 are composed of the same material compositionally, there is no problem in joining them even though the film forming conditions are different, and they are substantially integrated during the film forming process including firing. Conceivable.

Next, the change in sensor sensitivity over time was measured. Leave the ozone sensor in an air atmosphere at 450°C.
The sample was taken out every 200 hours, and the change in electrical resistance at 350°C was measured in the same manner as above in the measurement box, to determine the change in sensor sensitivity over time. Sensor sensitivity is the value obtained by dividing the electrical resistance (RG) of the ozone sensor in ozone-mixed air by the electrical resistance (RA) of the ozone sensor in air (RG/R
It is expressed as A). This was carried out for a total of 2000 hours, and the results are shown in FIG. In the case of the ozone sensor of the example in which the intermediate layer 3 was formed, almost no change in sensitivity over time was observed, but in the ozone sensor of the comparative example in which the intermediate layer 3 was not formed, it was clear that the sensitivity gradually decreased. became.

As described above, according to the above embodiment, the sensitive body 4
Since it is provided on the alumina substrate 1 via the intermediate layer 3 having the same composition as the sensitive body 4, an ozone sensor with extremely excellent thermal shock resistance can be obtained.

In the embodiment, the ozone gas sensitive body 4
We have described the case where a printing method was used as a manufacturing method.
Various wet film forming methods such as a coating method and a spin coating method can be used, and in any case, it is possible to produce a highly active sensitive body 4 with a high surface area similar to that of the example. In this embodiment, a vacuum evaporation method is used as a method for forming the intermediate layer 3, but the method is not limited to this, and it is possible to use a sputtering method or other film forming method suitable for the material or shape. be. Further, in the example, the ratio of In2O3 and SnO2 for the sensitive body 4 and the intermediate layer 3 is 95:
Although the case where a material having a ratio of 5 is used has been described, similar results can be obtained when using other ratios or using other materials. Further, the starting materials are not limited to those in the examples, and materials suitable for the film forming method can be appropriately selected and used. The structure and configuration of each part of the ozone sensor, as well as the substrate material and electrode material, can be freely designed or used as long as they do not go against the spirit of the invention.

[0016]

Effects of the Invention As is clear from the above embodiments, the ozone sensor of the present invention comprises forming an intermediate layer having the same composition as the ozone gas sensitive material on an insulating substrate on which electrodes are formed by a dry film forming method. By having a structure in which a sensitive body is provided on the top by a wet film forming method, it has an effect that it has excellent gas detection characteristics and also excellent thermal stability. Furthermore, since it is small, lightweight, and inexpensive, it is extremely useful for controlling ozone concentration and detecting ozone in ozone generators and ozone utilization equipment.

[Brief explanation of the drawing]

FIG. 1 A schematic cross-sectional view of an ozone sensor in an embodiment of the present invention.

[Figure 2] Characteristic diagram comparing the response characteristics of ozone sensors of Example and Comparative Example

[Fig. 3] Characteristic diagram showing the influence of thermal shock on the electrical resistance of the ozone sensors of Examples and Comparative Examples in air

[Figure 4] Characteristic diagram showing changes in sensitivity over time of ozone sensors of Examples and Comparative Examples

[Explanation of symbols]

1 Alumina substrate (insulating substrate) 2 Electrode 3 Middle class 4. Sensing body

Claims (1)

[Claims] Claim 1: A pair of electrodes formed on an insulating substrate;
A film-like intermediate layer made of a material mainly composed of metal oxide formed between the pair of electrodes by a dry film forming method, and the intermediate layer formed on the intermediate layer by a wet film forming method. An ozone sensor characterized by having a film-like sensitive body made of the same material.