JPS60144659A - Production of combustion detecting element - Google Patents

Abstract

PURPOSE:To suppress the impedance of a combustion detecting element and to decrease the amt. of the costly electrode material to be used by sticking a rhodium film to a platinum electrode formed on the surface of a sintered ceramics constituting the combustion detecting element. CONSTITUTION:A sintered zirconia body 1 is dipped in a soln. contg. platinum prepd. by dissolving platinum chloride in ethanol except a part of the open port on one side thereof and thereafter said body is heat-treated. The sintered body is immersed in a chemical plating liquid of platinum and is then washed and dried to form a platinum film on the inside and outside surface of the body 1; A rhodium soln. prepd. by dissolving 0.5pt.wt. rhodium chloride into 100pts.wt. ethanol is coated on the platinum film and the body is heat-treated at 1,000 deg.C to form platinum electrodes 6, 7 stuck with the rhodium film. MgAl2O4 powder is plasma-sprayed on the surface of the electrode 7, by which a porous ceramic film 8 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a combustion detection element for detecting oxygen concentration in a combustion atmosphere of combustion equipment.

(Structure of conventional example and its problems) Conventionally, as a typical example of this type of combustion detection element, zirconia porcelain made of Z ro 2 and Y2O5 or Z r O 2 and CaO, which are oxygen ion conductive porcelains, was used. Things can be given.

FIG. 1 shows a combustion detection element using such a zirconia sintered ceramic. Platinum electrodes 2 and 3 are placed on the inner and outer surfaces of a cylindrical zirconia sintered ceramic 1 with one end sealed. are formed, and their platinum electrodes 2.3 are connected to conductive metal terminals 4, 5 for electrical continuity.

In the combustion detection element having such a structure, the sintered ceramic 1
When the above-mentioned porcelain partition wall with platinum electrodes 2 and 3 is kept at a temperature of about 400°C or higher and both sides of the partition wall are brought into contact with oxygen gas having different partial pressures, an electromotive force is generated between the partition walls, and this Can detect oxygen weakness. Here, the electromotive force E generated between the conductive metal terminals 4.5 is expressed as follows.

The platinum electrode of the combustion detection element having this structure is related to the oxygen concentration in the sintered porcelain, the oxygen partial pressure in the gas atmosphere, and the oxygen ion concentration equilibrium in the sintered porcelain.

Conventionally, in a combustion detection element having such a structure, reaction combustion occurs on the surface of the platinum electrode due to the catalytic action of the platinum electrode in a flammable gas atmosphere, resulting in extremely high temperatures. As a result, agglomeration of the platinum electrodes occurs due to heat, and the area of the platinum electrodes on the surface of the sintered porcelain decreases, leading to an increase in internal impedance that shortens the life of the combustion detection element. However, in practical use in combustion equipment, it had the disadvantage of poor long-term reliability.

As a countermeasure to this problem, it is possible to suppress the agglomeration of the platinum electrode by increasing the thickness of the platinum electrode, but this requires the use of a large amount of extremely expensive platinum, and as a result, the combustion detection element It could not be said to be effective as it would result in a significant cost increase of 7'.

(Object of the Invention) The present invention aims to eliminate such conventional drawbacks, and to suppress the internal impedance of a combustion detection element in a combustion atmosphere and improve long-term reliability. It is.

(Structure of the Invention) In order to achieve this object, the method for manufacturing a combustion detection element according to the present invention is to apply platinum chemical plating to the surface of the sintered porcelain constituting the combustion detection element, and then apply rhodium salts 05 to 0. ．．
Apply a solution prepared by dissolving 5 parts by weight in water or 10.0 parts by weight of an organic solvent.
Heat treatment at a temperature of tl:.

Furthermore, a porous ceramic material is coated thereon.

(Description of Examples) Examples of the present invention will be described below with reference to the drawings.

FIG. 2 shows a combustion detection element in an embodiment of the present invention. In FIG. 2, numeral 1 is a cylindrical zirconia sintered ceramic with one end sealed, numeral 6.7 is a platinum electrode to which a rhodium film is attached, and numeral 8 is a porous ceramic film.

[Example 1] First, leaving a part of the open opening on one side of the zirconia sintered porcelain 10, 1.0 parts by weight of chloroplatinic acid was added to 100 parts by weight of ethanol.
After being immersed in a solution of platinum dissolved in parts by weight, it was heat-treated at 500° C. for 30 minutes. Next, this was immersed in a commercially available platinum chemical plating solution at 40° C. for 24 hours, thoroughly washed with water, and dried to coat the inner and outer surfaces of the sintered porcelain 1 with a film thickness of 1. , O1
A 1 m platinum film was formed in each case. Next, sintered porcelain 1
On the platinum film formed on the outer surface, rhodium chloride 0.5
After applying a rhodium solution (1.0% by weight of rhodium chloride) dissolved in 100 parts by weight of ethanol, this was heat-treated at 1000° C. for 2 hours to form platinum electrodes 6 and 7 with rhodium films attached. . The film thickness at this time is approximately 1.2μ
It was m.

Furthermore, M
A porous ceramic film 8 was formed by plasma spraying gAt2o4 powder.

Finally, in order to obtain electrical continuity of the platinum electrode 6.7 to which the rhodium film was attached, a conductive metal terminal 4.5 was connected to form a combustion detection element.

[Example 2] First, 1.0 parts by weight of chloroplatinic acid was added to 100 parts of ethanol, leaving a part of the open opening on one side of the zirconia sintered porcelain 1.
After being immersed in a platinum solution dissolved in parts by weight, it was heat-treated at 500° C. for 30 minutes.

Next, this was immersed in a commercially available platinum chemical plating solution at 40°C for 24 hours, thoroughly washed with water, and dried to obtain sintered porcelain 1.
A platinum film with a thickness of 1.011 m was formed on the inner and outer surfaces of.

Next, on the platinum film formed on the inner and outer surfaces of the sintered porcelain l,
After applying a rhodium solution (4.5% by weight of rhodium nitrate) in which 4.5 parts by weight of rhodium nitrate was dissolved in 100 parts by weight of water, this was heat-treated at 1400°C for 2 hours to form a platinum electrode 6 with a rhodium film attached. .7 was formed. The film thickness at this time was about 2.5 μm.

Furthermore, a platinum film f! with a rhodium film attached! MgAt204 powder was plasma sprayed on the surface of i17 to form porous ceramic i18.

Finally, the platinum electrodes 6 and 7 to which the rhodium film was attached
In order to obtain electrical continuity, a conductive metal terminal 4.5 was connected to form a combustion detection element.

Note that FIG. 3(a) shows the surface of the platinum electrode 2 of the combustion detection element manufactured by the conventional manufacturing method, and FIG.
) shows the surface of the platinum electrode 60 on which the rhodium film of the combustion detection element according to the above-mentioned [Example 1] of the present invention is stuck. As is clear from FIGS. 3(a) and 3(b), the platinum electrode 6 to which the rhodium film according to the present invention is attached
11-1: It can be seen that there is almost no agglomeration of the electrode compared to platinum electrode 2 manufactured by the conventional method, and the electrode has a uniform film shape.

Incidentally, the combustion detection elements according to [Example 1] and [Example 2] of the present invention and the combustion detection elements manufactured by the conventional manufacturing method were mounted in an oil stove, and a continuous combustion durability test using commercially available white kerosene was conducted. When the internal impedance between the conductive metal terminals 4 and 5 was measured, the results were as shown in FIG. In the figure, A is the conventional example, B is [Example 1],
C is the characteristic of each element according to [Example 2]. This clearly shows that the combustion detection element according to the present invention suppresses internal impedance shutoff and improves long-term reliability.

In addition, in [Example 1] and [Example 2] of the present invention, after chemical plating with platinum was applied, a solution of rhodium chloride or rhodium nitrate dissolved in ethanol or water was applied, and then the temperature was 1000°C to 1400°C. This is because the strongest electrode film can be formed in this treatment temperature range.

That is, if the temperature is below 1000°C, a strong electrode film cannot be formed, and if the temperature is above 1400°C, the electrode film will deteriorate due to heat, which is undesirable.

In addition, in [Example 1] and [Example 2] of the present invention, a solution containing 0.5 parts by weight to 45 parts by weight of rhodium chloride or rhodium nitrate was applied. This is because platinum aggregation can be suppressed in the content/ml range of 1.5 to 45 parts by weight, and the cost of a platinum electrode to which a rhodium film is attached is less than the cost of a platinum electrode produced by a conventional manufacturing method.

That is, if it is less than 0.5 parts by weight, there is no effect of suppressing agglomeration of platinum, and if it is more than 4.5 parts by weight, rhodium costs increase, which is not preferable.

Rhodium salts that can be used in the present invention include rhodium chloride, rhodium nitrate, and rhodium sulfate.

Further, alcohol-based solvents such as 2-n-butanol and ethylene glycol, and ether-based solvents such as n-butylcarpitol can be used.

However, the coating of the porous ceramic material is MgA
In addition to t204, At206. It can also be formed by plasma spraying a powder such as ZrO2 or by mixing and applying an inorganic binder and baking.

(Effects of the Invention) As is clear from the above description, the manufacturing method of the present invention has a remarkable effect of suppressing internal impedance during long-term installation in combustion equipment, compared to methods using conventional platinum electrodes. This improves long-term reliability as a combustion detection element.

In addition, the film thickness of the platinum electrode to which the rhodium film of the present invention is attached is about 12 to 2.5 μm, whereas the film thickness of the conventional platinum electrode is about 2.8 μm, and expensive electrode materials are used. The amount can be reduced, thus contributing to cost reduction.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional combustion detection element. Figure 1@2 is a cross-sectional view of a combustion detection element obtained by an example of the present invention, Figure 3 (a) is a diagram showing the surface of a platinum electrode produced by a conventional manufacturing method, and Figure 3 (b) -j: A diagram showing the surface of a platinum electrode to which a rhodium film is attached according to an embodiment of the present invention,
Figure 4 is a diagram showing the internal impedance characteristics of the combustion detection element through a continuous combustion durability test, where A is the conventional ν11, B
is the characteristic of each element of [Example 1] of the present invention, and C is the characteristic of each element of [Example 2]. 1... Sintered porcelain, 4, 5... Conductive metal glue,
6.7...Platinum electrode with rhodium membrane attached, 8. Porous ceramic membrane. First cause Figure 2 (a) (b) Figure 4

Claims (1)

[Claims] The process of chemically plating platinum on the surface of the sintered porcelain that constitutes the combustion detection element, and the process of applying rhodium salt-free on the plating film.
After coating a solution prepared by dissolving 5 to 45 parts by weight of water or organic solvent in 100 parts by weight of organic solvent,
A method for manufacturing a combustion sensing element, comprising the steps of heat treatment at a temperature of 0° C. and further coating with a porous ceramic material.