JPS58109844A - Gas sensor and its preparation - Google Patents

Abstract

PURPOSE:To improve the mechanical strength and a characteristic of a sensor, by forming a temperature sensor part by winding a platinum wire coated with glass around a rod-shaped glass body. CONSTITUTION:A platinum wire 11 having <=50 microns wire diameter is immersed in molten glass and glass coating is carried out. The wire 11 is wound round on a rod-shaped glass body 12 having 0.25mm. diameter in coil shape and electrode parts 13 are formed by removing both ends of a glass coated part by hydrogen fluoride. Next, a catalyst pipe having 0.4mm. inner diameter and 1mm. outer diameter, is formed by sintering catalyst materials and a temperature sensor part 10 is inserted into said pipe and then, powdered glass is filled in a gap. A gas sensor is formed by heating up to melting temperature of the powdered glass and fixing it. Hereby, the mechanical strength and a characteristic of the sensor are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas sensor using a platinum wire and a method for manufacturing the same.

The structure of a conventional gas sensor of this type is shown in FIG. 1 and explained. This gas sensor uses a platinum coil 1 formed by coiling a platinum wire with a wire diameter of about 50 ocrons as a temperature sensor part. This platinum coil 1 is coated with a catalytic material made of rhodium (Ilh), palladium (pa), etc. and baked to form a catalytic layer 2, and a lead 4 is fixed to the electrode part 3. be.

Such a gas sensor detects a reaction generated by the catalytic action of the test gas when it comes into contact with the catalyst layer 2 while the platinum coil 1 is preheated to a constant temperature by passing a constant current through the platinum coil 1. The calorific value of the gas to be detected and the presence or absence of the gas can be detected by utilizing the change in the resistance value of the platinum filter 1 depending on the temperature of the heat. However, in the conventional gas sensor described above, the platinum coil is used as a preheater section and a temperature sensor section using a platinum wire with a wire diameter of about 50 microns in order to have a resistance of about 101 to 103 times that of the electrodes and other conductive wire sections. 9th, its mechanical strength, especially its high-temperature strength, becomes extremely weak. In addition, since the catalyst material in the catalyst layer and the platinum wire are in direct contact, platinum, which is a relatively stable metal, does not form an alloy with the catalyst material, resulting in deterioration of the sensor characteristics. There was a drawback to doing so.

The present invention has been made in view of these points, and its purpose is to wind a platinum wire coated with glass around a rod-shaped glass body, and to combine the platinum wire as a catalyst layer and a temperature sensor part. An object of the present invention is to provide a gas sensor that can improve mechanical strength and characteristics as a sensor by separating the gases and gases with glass, and a method for manufacturing the same.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is an explanatory diagram for explaining one embodiment of the method for manufacturing a gas sensor according to the present invention. In Figure 2, 10
1 is a temperature sensor part, and this temperature sensor part 10 is made by immersing a platinum wire 11 with a diameter of 50 microns or less in a molten glass tank and coating the surface of the platinum wire 11 with glass (not shown). Coating and glass coating. next,
0.25 in diameter? A platinum wire 11 coated with glass is tightly wound into a coil around a rod-shaped glass body 12 having a thin film. It is assumed that the coil length t of the platinum wire 11 at this time is 2ξ.

Next, the glass covering portion to be connected to the conducting wire of the platinum wire 11 is dissolved and removed with hydrogen fluoride to form the electrode portion 13. However, by cutting and separating the electrode portions 13 individually, a temperature sensor portion 10a constituting the gas sensor main body having the structure shown in FIG. 3 is formed. In addition, when forming the temperature sensor part, R1. ./R.=i, one with high purity of about 389 is preferable.

Next, a cylindrical catalyst layer pipe having an inner diameter of 0.4 mm and an outer diameter of 1 mm is prepared by sintering the catalyst material, and a temperature sensor section shown in Fig. 3 is installed inside this pipe. and fill the gap with powdered glass. Thereafter, a gas sensor can be produced by heating the powdered glass to the melting temperature and solidifying it.

In addition, when forming the above-mentioned catalyst layer pipe, since the catalytic action occurs on the surface of the catalyst material, it is necessary to increase the surface area of the catalyst material. To this end, it is desirable that the catalyst material be sintered into a porous structure in which microcrystalline grains are interconnected.

Additionally, when an oxidation reaction occurs on the catalyst surface, the oxidation heat generated causes the catalyst to reach a very high temperature. As a result, the catalyst becomes semi-molten, sintering of adjacent catalyst crystal grains progresses, the crystal grains grow, and at the same time, the surface area decreases and the catalytic ability is improved. In order to avoid this, the fine powder of metal oxidizer as a catalyst material is mixed with the fine powder of alkaline metal as a catalyst carrier in a volume ratio of 1:9 and sintered into a porous structure. A catalyst bed pipe was obtained.

According to the gas sensor manufactured in this way, the catalyst layer pipe and the platinum wire as the temperature sensor section are separated by glass coated with glass, and the catalyst layer and temperature sensor section are separated from each other. Factors that cause performance deterioration can be removed. In other words, when a platinum wire comes into direct contact with a catalyst material, the platinum also forms an alloy with the catalyst material, degrading the characteristics of the temperature sensor. The coating provides a protective effect on the glass to prevent alloying with the catalytic material.

In addition, both glass and platinum wire have a thermal expansion coefficient of 1.02X.
10=, stress is not generated in the platinum wire over a wide range of temperatures (the temperature coefficient becomes smaller when stress is applied to the platinum wire), and the characteristics of the temperature sensor section are improved. However, since the platinum wire is wound around the rod-shaped glass body, it has the advantage of improving its mechanical strength.

In addition, when using the gas sensor according to the present invention, preheating to increase the activity of the catalyst is performed by heating the temperature sensor part at 1.
It may be used in a constant temperature atmosphere of about 20°C. Further, the present invention is not limited to the embodiments described above, and it goes without saying that the numerical values of the embodiments described above can be changed.

As explained above, according to the present invention, in addition to forming a temperature sensor section by winding a glass-coated platinum wire around a rod-shaped glass body, its mechanical strength and characteristics as a sensor can be improved. There is an effect that can be done.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a conventional gas sensor, and FIGS. 2 and 3 are explanatory diagrams showing an example of the method for manufacturing a gas cell/cell according to the present invention. IQ, IQa...temperature sensor section, 11...platinum wire, 12...glass body, 13...electrode section. Patent Applicant: Yamatake No. 1 Newel Co., Ltd. Representative: Masaki Yamakawa (and 1 other person) 7- Figure 1 Figure 3

Claims (1)

[Scope of Claims] (11) A gas sensor in which a gas to be detected is brought into contact with a catalyst layer and the temperature of reaction heat due to the catalytic action is sensed by a temperature sensor section, wherein the temperature sensor section includes a rod-shaped glass body;
It is composed of a platinum wire that is wound into a coil around the glass body and is coated with glass, and an electrode portion that is formed by removing the glass that is coated on both ends of the platinum wire. A gas sensor characterized by: (2) In a gas sensor in which the temperature of the reaction heat caused by the catalytic action of the gas to be detected is detected by the temperature sensor section by bringing the gas to be detected into contact with the catalyst layer Km, the temperature sensor section includes a platinum wire whose surface is coated with glass. A method for producing a gas sensor, comprising: winding a glass-coated platinum wire around a rod-shaped glass body, and then removing the glass-coated portion of the platinum wire, which is to be used as an electrode of a temperature sensor section, to form an electrode section. .