JPH01265151A - Forming method for limited current type sensor element - Google Patents

Abstract

PURPOSE:To easily form a diffusion hole and to curtail the manhour by decomposing sodium nitrite by heat so that a mixing material foams, and forming a gas diffusion hole, at the time of sintering a glass material layer. CONSTITUTION:A porous electrode anode 2 and a cathode 3 consisting of platinum, etc. are formed on both faces of an ion conductive plate 1 consisting of a solid electrolyte. Subsequently, on the cathode 3, inorganic powder is stuck as a paste-like slurry by a solvent, a part corresponding to a cavity is formed, half calcined at about 1,000 deg.C, and an inorganic porous body 11 is formed. Also, by applying a paste-like glass material to its surface, a glass material layer 12 is formed, and to its center part, a mixing material 13 which has mixed 1-50 weight % sodium nitrite into a glass material is instilled by a suitable quantity, and thereafter, the glass material layer 12 is calcined at about 900 deg.C. By this sintering, the mixing material 13 foams, and a cap 12' in which a gas diffusion hole 14 is formed is formed. In such a way, a desired sensor element is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of forming a limiting current type sensor element.

(Prior Art) Limiting current type sensors that measure oxygen concentration, hydrogen concentration, humidity, etc. in gases are known, but since these have a nearly hierarchical structure, it is difficult to understand the oxygen sensor element in the oxygen sensor. An example is shown in FIG. In the figure, a porous electrode anode 2 and a cathode 3 made of platinum or the like are provided on both sides of an oxygen ion conductive plate 1 made of a solid electrolyte such as stabilized zirconia, and made of ceramic or the like with minute gas diffusion holes 4. The camp 5 is capped and integrally sealed to the ion conductive plate l to form the cavity 6.
is formed, and a heater 7 is provided on the upper surface of the cap 5.

In the above oxygen sensor element, when a voltage is applied between both electrodes while being heated to a high temperature by the heater 6, the oxygen in the gas to be measured becomes oxygen ions at the cathode 3, and these oxygen ions pass through the ion conductive plate 1. The oxygen ions are transferred to the anode 2, and a current using oxygen ions as carriers flows due to a so-called bombing effect. This current occurs due to the diffusion rate of oxygen inflow due to the gas diffusion holes 4 in a certain region of the applied voltage, and exhibits current characteristics with a flat part called the limiting current value. Oxygen concentration can be determined by measuring the current value.

Various methods are known for forming the oxygen sensor element as described above, but after forming porous electrodes 2 and 3 on both sides of an ion conductive plate 1 made of a solid electrolyte as shown in FIG. 2 by a conventional method, A ceramic plate prepared in advance by compacting and firing ceramic powder is subjected to so-called counterbore processing using a machine tool to form a cap 5 having a cavity 6 shown in FIG. 2, and gas diffusion 7L is performed using a laser beam or the like. There is a way to form 4.

Furthermore, a method using green sheets is known as an efficient method. To give an example, on one side of the ion conductive plate 1 provided with porous electrodes 2 and 3 in the same manner as above,
The part corresponding to the molded cavity of the cap 5 is molded with resin so as to cover the cathode 3, and at the same time, pin-shaped protrusions with minute diameters for forming the gas diffusion holes 4 are formed. There is a method in which a green sheet is closely attached to the upper part and then fired, and the resin is burned off during the sintering to form the cap 5 having the gas diffusion holes 4. The pin-like protrusion may be formed of the above-mentioned resin, or its tip may be embedded in the resin using a low-melting point hard plastic or a low-melting point aluminum wire formed separately with a micro-diameter.

In addition to the above, as a prior art (Utility Application No. 62-197415) filed by the same applicant as the present invention, the portion corresponding to the cavity in FIG. 2 is formed of an inorganic porous material, the cap 5 is made of a glass material, There is one in which a capillary tube is planted in the part to provide gas diffusion holes 4.

(Problem B to be Solved by the Invention) In the conventional method for forming a sensor element as described above, the formation of gas diffusion holes requires considerable effort and is inefficient.

(Means for Solving the Problems) The present invention has been made in view of the above-mentioned circumstances, and porous electrodes are provided on both sides of an ion-conducting plate made of a solid electrolyte by a conventional method. After the cap is formed, an inorganic powder slurry layer such as alumina is provided in the part corresponding to the cavity, and this is semi-sintered at a temperature lower than the complete sintering temperature to form an inorganic porous body. A paste-like glass material is applied to completely cover the glass material to form a glass material layer, and 1 to 50% by weight of sodium nitrite (NaN) is added to the glass material in the center of the surface.
Provided is a method for forming a sensor element, in which a mixed material containing O□) is dripped, the glass material layer is fired, and a cap is formed with gas diffusion holes formed by foaming of the mixed material that occurs at the same time. It is something to do.

(Function) When the glass material layer is sintered as described above, the sodium nitrite is decomposed by the heat, the mixed material foams, and gas diffusion holes are formed. Gas diffusion holes of a desired size can be obtained by controlling the mixing ratio and dripping amount of sodium nitrite in the mixed material. In addition, the inner inorganic porous body is in a semi-sintered state and becomes a sufficiently sparse porous body, but this state is caused by the glass material layer being lower than the semi-sintering temperature of the porous body. It does not change due to sintering of the layers. Further, the glass material layer has a dense structure due to complete sintering.

By controlling the porosity of the above-mentioned inorganic porous material, the air permeability can also be controlled.

(Example) Figure 1 (→ is a cross-sectional view of a sensor element for explaining the method of forming a sensor element according to the present invention, in which both sides of an ion-conducting plate l made of a solid electrolyte are made of platinum etc. by a conventional method. Forming the porous electrode anode 2 and cathode 3 Next, on the cathode 3, inorganic powder such as alumina is made into a paste-like slurry using a solvent, and a portion corresponding to the cavity is formed by a method such as screen printing.
The inorganic porous body 11 is semi-baked at 000° C. to form a sparse inorganic porous body 11. Furthermore, a glass material layer 12 is formed by applying a paste-like glass material by a method such as screen printing so as to completely cover the surface of the inorganic porous body 11, and sodium nitrite is added to the glass material in the center of the glass material layer 12. 1-5
After dripping an appropriate amount of the mixed material 13 containing 0% by weight, the glass material layer 12 is sintered at about 900°C. By this sintering, the mixed material 13 is foamed to form a cap 12'' in which gas diffusion holes 14 are formed as shown in FIG.

(Effects of the Invention) According to the method for forming a sensor element of the present invention, it is extremely easy to form gas diffusion holes in the cap, and the process is performed simultaneously with the firing of the cap, which reduces the number of man-hours and is extremely efficient.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view for explaining the method of forming a limiting current type sensor element according to the present invention, FIG. 1(b) is a cross-sectional view of an oxygen sensor element formed by the method of the present invention, and FIG. The figure is a cross-sectional view of a conventional oxygen sensor element. 1: Ion conductive plate, 2, 3: Porous electrode, 11: Inorganic porous body, 12”: Cap, 13: Mixed material, 14: Gas diffusion hole. Patent attorney Mamoru Takeuchi

Claims (1)

[Claims] (1) In a method for forming a limiting current type sensor element in which porous electrodes are provided on both sides of an ion conductive plate made of a solid electrolyte, and a cap having gas diffusion holes is attached to one side, the An inorganic powder slurry layer is provided in the part corresponding to the cavity, this is semi-sintered to form an inorganic porous body, and a paste glass material is applied so as to completely cover the outside of the inorganic porous body to form glass. After forming a material layer and dripping a mixture of glass material and 1 to 50% by weight of sodium nitrite onto its surface,
A method for forming a limiting current type sensor element, comprising firing the glass material layer and simultaneously foaming the mixed material to form gas diffusion holes.