JPS5999342A - Gas detecting element - Google Patents

Abstract

PURPOSE:To improve humidity resistance with high sensitivity being maintained, by providing a catalyst layer, which comprises one or more insulating materials that are selected among Al2O3, SiO2, and ZrO2 including one or more noble metals selected from Pt, Pd, Rh, Ir, and Ru in addition to Ag, on the surface of a gas response body comprising a metal oxide semiconductor. CONSTITUTION:A catalyst material, wherein a specified amount of Al2O3 powder is added in the aqueous solution of palladium chloride and sufficiently mixed, and a catalyst material, wherein a specified amount of Al2O3 powder is added into the aqueous solution of silver nitrate and sufficiently mixed, are mixed. Said mixture is dried and then made to be powder. The powder is burned and a catalyst including Pd and Ag is prepared. Said catalyst is applied to the outer surface of a gas response body 3 and burned, a tubular catalyst layer 4 is formed, and an element body 5 is manufactured. Then the element body 5 is mounted on an insulating plate 7, through which 6 terminals 6... are pierced and supported. A heater coil 8 is inserted in an insulating pipe 2 of the body 5. Both ends of the coil are connected to two pieces of the terminals 6. Two lead wires 9... are connected to a pair of facing electrodes 11 (12) of the element body 5. The other ends of the lead wires are connected to the remaining terminals 6.... Thus a gas detecting element is assembled.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to improvement of gas detection elements [Technical background of the invention and problems thereof] Conventionally, 8nO □、
Gas detection elements whose main constituents are metal silicides belonging to n-type semiconductors such as ZnO and k″e20. Then, since positive ions are adsorbed, its electrical conductivity increases and its resistance value decreases.
When it comes into contact with a oxidizing gas, negative ions are absorbed, so that the electrical conductivity of the semi-exclusive metal chloride decreases and the resistance value increases. However, in general, metal-based conductors alone have low sensitivity (and are not necessarily fully satisfactory as gas detection elements).For this reason, recently, gold oxide semiconductors have been used with Pt,
Attempts have been made to improve the sensitivity by adding a noble metal catalyst such as Pd or by coating the semiconductor with a catalyst layer supported by a noble metal carrier such as M2O3. However, these gas sensing elements have a problem in terms of moisture resistance. In particular, when exposed to high humidity of 90 degrees or higher, a phenomenon of low resistance may occur, or when exposed to high humidity for a long period of time, gas sensitivity characteristics may deteriorate significantly. There was a problem with.

[Purpose of the invention]

An object of the present invention is to provide a scum detection element that has improved moisture resistance while maintaining high sensitivity.

[Summary of the invention]

In the present invention, a gas sensitive body made of a metal oxide is provided on an insulating substrate or an insulated tube provided with a pair of opposing electrodes and a heater, and the surface thereof is coated with Pt, Pd, and Rh.

k120. containing Ag and a precious metal of at least 10% selected from lr, ru. , 8 i02. By providing a catalyst layer made of at least one insulating material selected from ZrO□, the effect of moisture on the entire catalyst layer is suppressed by a subsequent reaction with moisture caused by Ag in the catalyst layer, Furthermore, the main objective is to obtain a gas detection element that improves moisture resistance and effectively exhibits the high sensitivity of precious metals.

The content of noble metal in the catalyst layer is 0.05 to 20 wt%
It is desirable to keep it within the range of . The reason for this is that if the precious metal content is less than 0.05wt%, sufficient sensitivity improvement cannot be achieved;
If it exceeds %, the effect will be rather impaired and the initial change over time will become large.

The content of Ag in the catalyst layer is preferably in the range of 0.05 to 20 wt%. The reason for this is that when the Ag content is less than 0.05 wt%, a highly effective pot with moisture content is sufficiently achieved1, but when the content exceeds 20 wt%, the repellency to silkworms is rather impaired.

The thickness of the gas sensitive member is preferably 0.2 .mu.m to 1 .mu.m, and the thickness of the catalyst layer is preferably in the range of 10 to 50 .mu.m.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings.

First, octyl tin was quantitatively weighed and dissolved in n-butanol to prepare a lQwt% tin octylate bath solution. I□m (22) was applied to the outer peripheral surface of the formed insulation 'b°2, dried in air for about 30 minutes, and dried at about 120°C for 30 minutes to remove n-butanol. Evaporate at 400-700°C for 30 minutes [
BJ-fired 5n02 thin film with a thickness of 0.5μm
A cylindrical gas sensitive body 3 was prepared. In this case, rapid thermal quenching is preferred. Also, J exchange) 9 to f! In order to do this, it is desirable to repeat the coating and firing process 1 to 4 times.

Next, D1 Al2O3 powder was added to the palladium chloride aqueous solution.
A catalyst material that was added in a fixed amount and thoroughly mixed was mixed with a catalyst material that was prepared by adding a predetermined amount of Al2O3 powder to a silver nitrate water bath and thoroughly mixing it. Subsequently, this mixture was dried under reduced pressure for 1 to 2 hours, and then sufficiently dried at about 100°C.The dried product was then powdered and heated to 400 to 800°C using a quartz crucible.
Calcinate at 0°C to produce Pd l wt, Ag l wt
% catalyst was prepared. The catalyst is coated on the outer circumferential surface of the gas sensitive body 3 and heated to about 300 to 400'O
A cylindrical contact layer 4 having a thickness of 30 .mu.m was prepared by firing with a temperature of 30 .mu.m to form an element body 5 (as shown in FIG. 1).

Next, an insulating plate 7 through which six terminals 6 are supported
Place the element main body shown in FIG. Connected. Subsequently, a pair of opposing electrodes z, I (72
), and the other terminals 9:M were connected to the terminals 6... to assemble the scum detection element (as shown in Figure 2).

On the other hand, as a comparative example, 1. A gas sensing element having the same structure as in the example was assembled except that a catalyst layer containing Pd of Qwtφ was provided on the circumferential surface of the gas sensitive body 94.

Therefore, the resistance value (Ra) of the gas detection elements of this example and comparative example at 30°C and 90% III
and 30°C, 90% l ([1 CO gas x 200 ppm
The change over time in the resistance value (Rg) was investigated. The results are shown in Figure 3. In addition, A1 in FIG. 3 is the resistance value change % gonad % A of the gas detection element of this example in high humidity air.
2 is the resistance change characteristic line of the same element in commercial temperature CO scum, B
, is the same characteristic line% of the gas detection element of the comparative example in high humidity air.
B is the characteristic line of the same element in high-humidity CO gas. As is clear from FIG. 3, in the gas sensing element of the comparative example equipped with a catalyst layer containing only (,1'd), both Ra and g gradually became high in resistance during high-humidity energization, and the sensitivity (Ra/) t
g) decreases. On the other hand, it can be seen that the gas sensing element of this example, which is equipped with a catalyst layer containing Pd and Ag, is extremely stable, does not suffer from humidity effects, and has moisture resistance.

In the above example, a gas sensitive material made of 5n02 was used, but other materials such as sZnO, Fe, 0. A similar effect was obtained when it was formed from other metallobaride half-bases such as.

Further, in the above embodiment, a catalyst layer containing Pd and Ag was used, but Pt, phosphorus, Ir, Ru, or Pd was used instead of Pd.
Similar effects were obtained when a mixture of , Pt, Rh, Ir, and U was used.

Furthermore, in the Saturday and Sunday examples, M2O3 was used as an insulating material for the catalyst.
was used, but instead of Ae2o3, S io2. ZrO
2 or At20. , S i 02 and z'02, similar effects were obtained.

〔Effect of the invention〕

As described in detail above, the present invention can provide a gas detection element that is highly sensitive and moisture resistant and has reliable gas detection performance for a long period of time.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the element body used in the gas detection element of the present invention, FIG. 2 is a perspective view of the gas detection element showing an example of the invention, and FIG. 3 is a gas detection element of the example and comparative example. Sensing element at 30°C, 90% version in air and 30°O+90
%1. It is a characteristic diagram showing the change in resistance value over time in the COO20 current test of LH. ksclt)...Counter electrode, 2...Insulating tube, 3...
・Gas sensitive body, 4...Catalyst layer, 5...Element body, 7
...Insulating plate, 8...Heater coil. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Time (hr)

Claims (1)

[Scope of Claims] (i) A gas sensitive body consisting of a metal banditized semi-core whose resistance value increases when it comes into contact with scraps on an insulating substrate, a pair of gas sensitive bodies for detecting the resistance of the gas sensitive body; In a 416-frame gas sensing element, which is provided with a single pole and a heater that heats a gas sensitive body, and a catalyst layer is provided on the gas sensitive body, Pt, Pd,
, 1, Ir, Ru, AI containing at least 1 Yu or more of money disease and Ag! 20. ．． 8i0□,Z"
A scum detection element characterized by providing a contact S layer made of an insulating material of at least 1447 or more selected from 0□ on the gas sensitive body. (2) The gas sensing element according to claim 1, wherein the catalyst layer is formed by a thick film method.