JPH0320660A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To efficiently perform glass coating work by providing a baked body prepared by baking a mixture of a ceramic powder and a metal powder on the electrode positioned on a solid electrolyte on one side thereof. CONSTITUTION:A baked body 13 formed by baking a mixture obtained by mixing a metal powder of platinum or gold with a ceramic powder of alumina or zirconia is provided on the electrode 11 positioned on a solid electrolyte 1 on one side thereof. By this method, the flowing of the ceramic powder is prevented when a glass sealing material 14 is applied to the upper surface of the baked body 13. Therefore, glass coating work can be efficiently performed.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a limiting current type oxygen sensor 1 used for preventing oxygen deficiency accidents in basements, controlling combustion in boilers, etc.

"Prior Art" In recent years, limiting current type oxygen sensors using solid electrolytes made of stabilized zirconia are being put into practical use.

As shown in Fig. 3, this oxygen sensor has a gas diffusion hole IA that penetrates vertically in the center, and has stabilized zirconia (
For example, Z rot-8 Y t 0 . 3) A thin solid electrolyte 1 made of an ionic conductive material such as 3), and a porous platinum electrode 2A provided on both sides of the solid electrolyte 1 to which a constant sensor monitoring voltage is applied.
2B, a ceramic powder 3 is provided on the electrode 2Δ located on one side of the solid electrolyte 1, and the entire ceramic powder 3 is provided on the outside of the ceramic powder 3. A glass sealing material 4 is provided to cover the.

In the oxygen sensor configured in this way, oxygen taken in from the gas diffusion hole IA flows as ions in the solid electrolyte 1 due to the oxygen pumping action.
The ambient oxygen concentration is measured from the current value of this ion current.

"Problems to be Solved by the Invention" By the way, in the oxygen sensor described above, the gaps formed between the particles of the Ceraminoku powder 3 are used as flow paths for oxygen introduced from the gas diffusion holes IA, so it is difficult to manufacture the oxygen sensor. Similarly, the platinum electrodes 2A and 2B cannot be sintered until the ceramic powder 3 is placed at a high temperature and reaches a high strength state. Similarly, the platinum electrodes 2A and 2B are
It is obtained by firing a platinum paste containing an organic binder applied to
00 to 1000°C, and therefore, the ceramic powder 3 cannot be sintered at a high temperature exceeding this temperature range.

In other words, due to the two reasons mentioned above, ceramic powder 3
cannot be sintered to a high strength state by placing it under high temperature, and as a result, on this ceramic powder 3,
When attempting to apply a glass paste for forming the glass sealing material 4, the ceramic powder 3 moved easily and the application could not be performed smoothly.

In addition, in order to solve the above-mentioned problems, glass powder is sometimes added to the ceramic powder 3 and fired.
In this case, the binding strength of the ceramic powder 3 can be increased, but on the other hand, there is a problem that the two electrodes may be coated with glass, and the effective area of the electrode 2A is reduced.

This invention was made in view of the above circumstances, and the ceramic powder 3 is strengthened by bonding the particles of the ceramic powder 3 within the range of the firing temperature of the platinum paste forming the electrode. It is an object of the present invention to provide an oxygen sensor that can increase the temperature of the ceramic powder, combine the particles of the ceramic powder 3 without using glass, and prevent a decrease in the effective area of the electrode.

"Means for Solving the Problem" In order to achieve the above object, electrodes to which a predetermined voltage is applied to each surface of a solid electrolyte having ionic conductivity are provided,
In a limiting current type oxygen sensor that measures the ambient oxygen concentration from the current value of the ionic current flowing between these electrodes, metal powder is added to the ceramic powder on the electrode located on one side of the solid electrolyte. A fired body is provided by mixing and firing, and a glass sealing material that covers the entire fired body is provided on the outside of the fired body.

"Function" According to the present invention, on the one side 71 of the solid electrolyte, a combined body as a fired body made by mixing metal powder with ceramic powder and firing it is provided, so that on the upper surface of the fired body, This prevents the ceramic powder from flowing when applying the glass sealant.

Furthermore, by creating the fired body by mixing a small amount of metal powder with ceramic powder, the minute gaps formed between the ceramic powders are secured as passages for gas diffusion, and the Particles of Ceramisophyllum powder are partially combined.

In addition, by mixing the same metal powder as the main part of the electrode into the ceramic powder, the combined body, which is a sintered body, can be formed at a temperature equivalent to the firing temperature of the electrode (or at a recrystallization temperature lower than that). Obtainable.

``Example'' First, an example of the present invention will be described with reference to FIG. 1 and FIG. 2.

FIG. 1 is an overall schematic diagram of the oxygen sensor, and what is indicated by the reference numeral 10 in this figure is a material (such as stabilized zirconia).
For example, Zro t- 8 Yso 3) It is shaped like Nyoriura Atsushi, and there is a gas diffusion hole that penetrates vertically in the center! OA is a shaped ionic conductor.

Moreover, those indicated by the symbol It-12 are each to which a predetermined voltage is applied and the ionic conductor 1. These are porous cathode and anode electrodes that cause diffusion rate limiting to zero. Note that these porous cathode electrodes 11 and anode electrodes l2 are made by printing platinum paste containing an organic binder on the surface of the ionic conductor 10,
Obtained by annealing in the temperature range of 1000'C.

Moreover, what is indicated by the symbol l3 is a cathode iu+. located on one side of the solid electrolyte l. The fired body provided on i, indicated by the reference numeral 14, is a glass sealing material provided on the surface of the fired body l3 to cover the entire fired body 13.

The fired body 13 is made by adding metal powder to ceramic powder and firing it, and the ceramic powder used is alumina, zirconia, magnesia, calcia, steatite, forsterite, etc. As the metal powder, platinum, gold, copper, palladium, silver, or a mixture of these elements is used.

As for the metal powder, it is best to use platinum, which is the same as the metal component of the electrodes 11 and 12. ! tK1
+. It is preferable to use the platinum paste for forming -12 by de-kneading the ceramic powder.

In addition, the proportion of the metal powder mixed with the ceramic powder is set at a low ffi(
(about 0.1 wt%), but depending on the experiment, O l~
It is possible to mix metal powder in a wide range of 50 wt%. Further, the manufacturing temperature when manufacturing the fired body 13 may be 500°C or higher, which is the recrystallization temperature of the metal powder, and the -L limit is the temperature when firing the platinum paste. It is preferable to set the temperature to 700 to 1000'C or less. Further, the particle size of the metal powder is 0.1 to 50 μm, whereas the particle size of Ceraminokukari is 0.1 to 50 μm.
It is preferable to use a material with a diameter of about 1 μm.

As explained above, according to the oxygen sensor shown in this embodiment, a fired body 13 formed by adding metal powder to ceramic powder and firing it is placed on the electrode 11 located on one side of the solid electrolyte 1.
Since the glass sealing material 1 is provided on the upper surface of the fired body 13,
When attempting to apply No. 4, the ceramic powder is prevented from flowing as in the conventional case, and the application work can be performed efficiently.

In addition, by preparing the fired body 13 by adding a small amount of metal powder to ceramic powder, as shown in FIG. ), the fine gaps formed between the particles of the ceramic powder are secured as paths for gas diffusion, thereby making it possible to obtain a stable limiting current value.

In addition, when manufacturing the fired body l3, if some metal powder similar to that of the electrodes l1 and 12 is mixed into the ceramic powder,
For example, if platinum is selected and mixed into the metal,
Ceraminoku particles can be bonded by the metal powder at a low recrystallization temperature below LOOO'C, and it is possible to prevent the electrodes 11 and 12 from changing shape and deteriorating their performance at the firing temperature.

"Effects of the Invention" As explained in detail above, according to the present invention, the fired body of Ceraminoku and metal powder provided on one side electrode of the solid electrolyte makes it possible to efficiently apply glass to the upper surface of the solid electrolyte. can do well.

In addition, by creating the fired body by mixing a small amount of metal powder into ceramic powder, the particles of the ceramic powder are partially bonded, and the minute gaps formed between the ceramic powder are used for gas diffusion. As a result, a stable limit current value can be measured.

In addition, by mixing the same metal powder as the main component of the electrode into the ceramic powder, it is possible to perform the firing at a temperature equivalent to the firing temperature of the electrode (or at a temperature lower than that (recrystallization temperature of the metal powder)). A sintered body can be obtained as a bonded body, and it is possible to prevent the electrode from changing its shape and deteriorating its performance due to the firing temperature.

[Brief explanation of drawings]

FIGS. 1 and 2 are diagrams showing a practical example of the present invention,
FIG. 1 is a front cross-sectional view showing the entire oxygen sensor, FIG. 2 is a view showing the state of bonding between ceramic particles and metal particles, and FIG. 3 is a front cross-sectional view showing a conventional oxygen sensor. 10... Ionic conductor (oxygen ion conductor),
10A... Gas diffusion hole, 11, 12... Electrode,
13...Sintered body, l4...Glass sealing material. Dewajin Fujikura Electric Cable Co., Ltd.Figure 1Figure 2Figure 3

Claims (1)

[Claims] Electrodes to which a predetermined voltage is applied are provided on each surface of a solid electrolyte having ionic conductivity, and the ambient oxygen concentration is measured from the current value of an ionic current flowing between these electrodes. In the limiting current type oxygen sensor, a fired body made by mixing metal powder with ceramic powder and firing is provided on the electrode located on one side of the solid electrolyte, and the fired body is placed on the outside of the fired body. An oxygen sensor characterized by having a glass sealing material covering the entire surface.