JPS63109360A - Gas sensor - Google Patents

Abstract

PURPOSE:To prevent the disconnection of an electrode lead, by connecting an atmosphere-sensitive substance layer and a stem by at least one electrode lead and providing looseness sufficient to absorb the thermal deformation of a metal heat generator to the electrode lead. CONSTITUTION:The atmosphere-sensitive substance layer 14 of a gas sensor 2 is composed of a metal oxide semiconductor such as SnO2 and an electrode lead 16 is connected to the responsive substance layer 14 by a fritless gold paste 18 and fixed to a stem 8 by welding. Herein, looseness 22 sufficient to absorb the thermal deformation of a heat generator 10 is formed to the lead 16. When the sensor 2 is heated, the heat generator 10 thermally expands and stress acts on the lead 16. Since the looseness 22 is formed to the lead 16, the thermal deformation of the lead 16 is absorbed by the looseness 22 and the disconnection of the lead 16 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a gas sensor for detecting gases such as flammable gases, toxic gases, oxygen, and water vapor.

[Prior Art] The inventor proposed a gas sensor in which an atmosphere-sensitive material layer is supported on the surface of a metal heating element via a heat-resistant insulating coating (patent application (1) dated today). A feature of this sensor is that it does not require an insulating substrate supporting an atmosphere-sensitive substance or a sintered body of an atmosphere-sensitive substance. As a result, the heat capacity and heat radiation area of the sensor are reduced, and the power consumption and thermal time constant of the sensor are also reduced. In addition, heavy rings such as the base body and sintered body are eliminated,
The lead wire that supports it will also be better if it is thinner. Furthermore, the main part of the sensor is formed on a metal heating element, making it suitable for automation, which also increases the productivity of the sensor.

Here, the inventor faced the problem of disconnection of the electrode lead. The cause of the disconnection was thermal deformation of the metal heating element. If a coil-shaped electrode or heater is embedded in a normal sintered body of an atmosphere-sensitive material, disconnection of the electrode or heater will not occur. This is because deformation of the electrodes and heaters is absorbed by the sintered body and deformation is suppressed. Additionally, coils inherently have tolerance for deformation. Even in sensors in which an atmosphere-sensitive material layer is printed on a heat-resistant insulating substrate such as alumina, lead wire breakage rarely occurs. This is because the substrate containing the heat generating part is made of ceramic and does not deform.

[Problem of the Invention] An object of the present invention is to prevent disconnection of electrode leads in a sensor in which an atmosphere sensitive material layer is supported on a metal heating element via a heat-resistant insulating film.

[Structure of the Invention] The present invention provides a gas sensor in which an atmosphere sensitive material layer is supported on the surface of a metal heating element via a heat-resistant insulating coating, in which the atmosphere sensitive material layer and a stem are connected by at least one electrode lead, and , the electrode lead is characterized by having sufficient play to absorb thermal deformation of the metal heating element. This play is provided, for example, by reversing the connection direction of the electrode lead to the atmosphere sensitive material layer and the connection direction to the stem.

The play in the electrode leads absorbs thermal deformation of the metal heating element and prevents disconnection.

[Example] In Figures 1 and 2, (2) is a gas sensor, (4)
is a housing, which is covered with a cover (not shown) from above to provide explosion protection and protection for the sensor.

(6) is a heater stem fixed to the housing, and (8) is an electrode stem also fixed to the housing.

(10) is a metal heating element welded to the stem (6), Pd
-Ir alloy, noble metals such as Pt and Ir, or Fe-C
Base metal wire diameter 10μ such as r-Al alloy or Ni-Cr alloy
A wire rod of about 80 μm is used. The metal heating element (10) is
For example, it may be plate-shaped.

(12) is a heat-resistant insulating coating that covers the surface of the metal heating element (10) except for the welded part to the stem (6), and is made of alumina, silica, mullite, etc. It is a coating due to rating etc. The thickness of the coating (12) is, for example, 5OA-10μ, more preferably 100A-5μ. According to experiments, 10
0A alumina coating is coated with PT or Pd by plasma CVD.
- When provided on Ir alloy, Fe-Cr-A1 alloy, IM
An insulation resistance of Ω or more was obtained.

The coating 1 (12) may be provided by applying and baking alumina sol or silica sol, or by thermally decomposing an organic compound of aluminum or silicon such as aluminum isopropoxide. However, in this case, the adhesive strength and insulation strength of the coating (12) are low, and coating and baking or thermal decomposition are repeated.
Try to get a strong film. The appropriate number of treatments is 3 to 5 times or more for sol application and baking, and 8 to 10 times or more for thermal decomposition of aluminum isopropoxide. Note that the term "insulation" here means that the insulation resistance is sufficiently large compared to the internal resistance of the atmosphere-sensitive material layer. For example, when using low-resistance 5nOt as the atmosphere-sensitive material layer, high-resistance Ti ( It is also possible to use L as an insulating coating (12).The coating (12) can also be used as a heating element (1
0) from the atmosphere and protect it from the atmosphere, as well as the heating element (10
) and the atmosphere sensitive material layer (14).

(14) is an atmosphere sensitive material layer, such as SnO2 or Fe.
tO3, In2O5, B aS no 3, I, a
Metal oxide semiconductors such as N i O3, or M g
Ceramics such as Cr 204 whose electrical conductivity changes by adsorption of water vapor, and antimonic acid (HtS bz
Oe) and antimony phosphate (I4S bP v Os
) and other proton conductors are used.

In the case of ceramics such as MgCr, O, etc., water vapor can be detected from surface conduction due to water adsorption. In the case of a proton conductor, an electromotive force is generated depending on the ratio of H2a degrees, and H7 can be detected from this. In this case, for example, one of the electrodes (described later) is isolated from the atmosphere with a ceramic coating or the like to create a difference in hydrogen concentration between the electrodes, and detection is performed.

These materials are formed into a film on the coating (12) by sputtering, vacuum deposition, powder dipping, CVD, or the like.

(16) is a pair of electrode leads, which are made of noble metal wires such as Au, Pt, Ir, Ir-Pd, etc., with a wire diameter of about 10 to 60 μm. The electrode leads (16) are connected to the sensitive material layer (14), for example by fritless gold paste (18), and fixed to the stem (8) by welding or silver brazing. Note that the insulation coating (12) is partially removed and the heating element (10)
may also be used as an electrode; in this case, the electrode lead (16
) is better with just one.

Here, the electrode lead (16) is provided with play (22) sufficient to absorb thermal deformation of the heating element (lO).

The play (22) is formed, for example, by providing a folded portion between the weld (20) to the stem (8) and the connection to the atmosphere sensitive material layer (14) as shown in FIG.

In this case, the connection direction to the atmosphere sensitive material layer (14);
The welding direction to the stem (8) is reversed, and a folded portion is provided. The two connection directions are not limited to being 180° opposite, but may be different as long as they can absorb thermal deformation of the heating element (10). Although not particularly limited, a preferable range of difference in connection direction is 90° or more.

Also, instead of the folded part, welded part (20
) and the connection to the atmosphere sensitive material layer (14),
A loop may be formed in the electrode lead (16). However, the work of providing loops on the electrode leads (16) is somewhat complicated, and the workability is lower than that of making the connection directions different. Also, instead of the folded part, simply the electrode lead (16
) may have a play of around 15 to 30%.

However, in this case, stress acts on the connection portion with the atmosphere sensitive material layer (14) due to the bending of the electrode lead (16). Furthermore, connecting the electrode leads (16) with a margin in length reduces work efficiency. Therefore, the most preferable one is the atmosphere sensitive material layer (14) of the electrode lead (16).
and the stem (8) in different directions.

The operation of the gas sensor (2) will be explained. Heating element (IO)
energizes and heats the sensor. This heating is performed by, for example, Sn
For sensors of combustible gases such as O, LntO3, etc., this is done to maintain the sensor at an operating temperature, and for sensors such as humidity sensors and proton conductor hydrogen sensors, this is done for heat cleaning. When the sensor is heated, the heating element (10) thermally expands and stress is applied to the electrode lead (I6). Electrode lead (
If I6) is provided with play (22), thermal deformation will be absorbed by the play and no wire breakage will occur. On the other hand, if there is no play, the electrode lead may peel off from the atmosphere sensitive material layer (14) at the gold paste portion (18) or the like due to stress.

For example, the heating element (10) is subjected to 3 thermal cycles between room temperature and 500°C, with a cycle of 4 minutes per cycle, energizing for 2 minutes and stopping for 2 minutes.
Added 00 times. In the case where the leads (16) were stretched linearly between the stem (8) and the atmosphere sensitive material layer (14) without any play, three out of 10 leads were broken. On the other hand, in the example shown in FIG. 1, no wire breakage occurred.

Further, even when a loop was provided in the electrode lead (I6) or a margin of about 20% was provided in the length of the electrode lead (16), no disconnection occurred.

Sensor characteristics will be explained using a gas sensor using SnO2 as an example. Pe-Cr-Al alloy (1
0) was coated with an alumina coating (12) having a thickness of approximately 1 μm by plasma CVD. This is coated with a Sn0w film (SnOt
97vt%, catalyst Pd03wt%) was sputtered to form an atmosphere sensitive material layer (14) with a thickness of about 5000A.
And so. Using gold paste (18), electrode leads (16) with a wire diameter of 20 μm were attached as shown in FIG. 1 to complete the sensor. The resistance value of the heating element (10) at room temperature is 3.3Ω,
Heating power to 300℃ is 100mW, thermal time constant is I O
It was about Om5ec. Also, instead of Pe alloy, wire diameter 2
When using a 0μ Pd-Ir alloy (Pd80.Ir20), the resistance value at room temperature is 3Ω, and the heating power to 300℃ is 8
It was 0mW.

10% each in air using an atmosphere of 20°C and 65% relative humidity.
00 ppm H in ethanol, CO.

The resistance value was measured in isobutane. Isobutane is a representative flammable gas. The response characteristics to ethanol, co, etc. at 300°C are shown in Figure 3. Also Table 1
Table 2 shows the resistance values in each atmosphere at 300°C.
The resistance value is shown in °C.

Table l Sensor characteristics 300℃ in air 2.4M ethanol 40K Co 200K Hz 350℃ in air 1.2M ethanol 50℃ in isobutane 400K H, 300K [Effects of the invention] This invention provides a small gas sensor with low power consumption. At the same time, disconnection of the electrode lead can be prevented.

[Brief explanation of the drawing]

Figure 1 is a front view of the gas sensor of the example, and Figure 2 is its
It is a sectional view in the −■ direction. Moreover, FIG. 3 is a characteristic diagram of the example gas sensor. (8) Stem, (10) Metal heating element (I2
) heat-resistant insulating coating, (14) atmosphere sensitive material layer, (16) electrode lead, (22) play area.

Claims (2)

[Claims] (1) In a gas sensor in which an atmosphere sensitive material layer is supported on the surface of a metal heating element via a heat-resistant insulating coating, the atmosphere sensitive material layer and the stem are connected by at least one electrode lead, and the electrode lead includes: A gas sensor characterized by having sufficient play to absorb thermal deformation of a metal heating element. (2) In the gas sensor according to claim 1, the play is formed by making the connection direction of the electrode lead to the atmosphere sensitive material layer and the connection direction of the electrode lead to the stem different. Features: Gas sensor.