JPS63190755A - Zirconia-base solid electrolyte - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zirconia solid electrolyte suitable for gas sensors, fuel cells, oxygen pumps, etc., which has excellent thermal shock resistance, low electrical resistance, and is capable of low-temperature operation.

It is used in gas sensors, fuel cells, oxygen pumps, etc., and is currently used as an oxygen sensor for automobile air-fuel ratio control, sensors for detecting oxygen concentration in molten steel, sensors for industrial furnace exhaust gas, etc. If impermeable, Wp resistance: impact resistance, low temperature operation.

Although it has extremely excellent performance such as response speed, as shown below, it is difficult to industrially produce it with good lateral variation using conventional ceramic molding methods.

In other words, while the pressure molding method allows for large-scale production and high-speed molding, it is difficult to fill the raw material uniformly, and the lateral variation does not occur easily.
It is difficult to form a film, and for that purpose, post-processing is required.

(K) Also, a slurry molding method is a method for easily obtaining a complex molded body without distortion with simple operations.

However, this casting method has a slow working speed and poor quality. Furthermore, there is a problem that it is difficult to produce a sintered body with high strength and high W degree.

On the other hand, the hot press method and hot isostatic press method, which perform molding and firing at the same time, can promote P4 warts and densification of the microstructure of the sintered body, and compared to other methods,
This is an extremely effective method as trenches can be completed in a relatively short time and at a lower temperature.

However, it is difficult to produce products with complex shapes and thinness, and there is a tendency that mass production is not possible and product costs are high.

Although the sheet forming method is extremely effective for producing thin sintered bodies, it produces simple plate shapes and cannot produce products with complex shapes.

As mentioned above, when trying to manufacture a high-strength, dense, sintered body using zirconia as a raw material using the existing method, it was difficult to manufacture a complex shape or a thin body. On the other hand, when the purpose is to produce multiple, separated shapes or thin products, it has not been possible to produce high-strength, dense sintered bodies. In this way, there has been an antinomic relationship between mechanical strength and microdensity and the production of complex shapes and thin objects.

(Problems to be solved by the invention) In view of the above-mentioned problems of existing methods, the present inventors have
As a result of intensive research, we have completed the present invention,
The objective is to provide a zirconia solid electrolyte that is highly strong, extremely thin, dense, and gas impermeable. Further objects and advantages will become apparent from the description below.

(Means for Solving the Problems) The above object is to provide at least one stabilizer selected from the group consisting of yttrium oxide, calcium oxide, and magnesium oxide, which is blended with zirconium oxide (4) in an amount of at most 16 mol%. (6) A pre-fired molded product or a powder or a powder molded product made of a ceramic raw material with an average particle diameter of 1 μm or less, which has a main component of
This is achieved by using a zirconia solid electrolyte whose conductivity at 0'C is 1O-4 (Ω·cm)-1 or more.

P≧8X10-87X (1600-t)14+0. I
P≦5 t≦1600 The ceramic raw material according to the present invention is zirconium oxide (Z
r02) (: Yttrium oxide (Y208) + Calcium oxide (C!aO) and Magnesium oxide (MgO
The main ingredient is aluminum oxide, which is usually added to ceramic raw materials.

Additives such as sintering aids represented by silicon oxide and bismuth oxide, or Sc, La, Pr, Nd, Pm, and Sm.

Eu, Gd, Tb, Dy, EIo,
This does not mean that oxides of rare earth elements such as Er, Tm, Yb, Lu, and ce may be added and blended in small amounts as appropriate. The responsibility of the stabilizer (B) added to the zirconium oxide (4) varies depending on the properties required of the target zirconia solid electrolyte, the 4 types of stabilizer (6) to be mixed, etc., but at most 16 It is necessary to keep it within the range of mol%. The stabilizer () imparts oxygen ion conductivity to zirconium oxide, but if it exceeds 16 mol%, the conductivity becomes low.9 Furthermore, particles of the raw material grow during plastic processing, resulting in a decrease in plastic resistance. This increases, making plastic working difficult.

The preferred range of the stabilizer (B) to be added to zirconia oxide is 2 to 12 mol% for yttrium oxide;
For calcium oxide and magnesium oxide, it is about 4 to 16 mol%. If the particle size of the ceramic raw material is large, a rapid particle growth phenomenon occurs during plastic working, and as mentioned above, plastic working becomes virtually impossible. In the present invention, it is preferable that the average ν core particle size of the ceramic raw material is 1 μm, and that the particle size distribution is uniform.

G4 production of these ceramic raw materials may be carried out by appropriately selecting from known methods, and the methods are broadly classified into dry methods and wet methods. In the dry method, for example, a predetermined amount of stabilizer powders such as zirconium oxide and yttrium oxide are mixed using a ball mill or the like.

There are methods such as heat treatment after pulverization and subsequent mechanical pulverization. Furthermore, examples of the wet method include the following methods.

(1) A precipitant such as ammonia is added to a mixed aqueous solution of a water-soluble zirconium salt such as zirconium oxychloride and a water-soluble salt of gold 1, which serves as a stabilizer such as yttrium chloride, to stabilize the zirconium and yttrium. A method of forming a sol of hydroxide with a curing agent, followed by filtration, washing, drying, and subsequent heat treatment.

(Coprecipitation method) (2) A mixed aqueous solution similar to the above coprecipitation method is heated to generate a sol such as hydroxide, and then filtered and washed.

A method of drying and subsequent heat treatment. (Hydrolysis method) (3) A zirconium alkoxide such as zirconium isopropoxide and a metal element alkoxide constituting a stabilizer such as yttrium isopropoxide are mixed and dissolved in an organic solvent, and water is added to the solution. After adding and hydrolyzing the alkoxide to produce a sol, filtration, washing,
A method of drying and subsequent heat treatment. (Alkoxide method) As a method for preparing these ceramic raw materials, a wet method is preferable since particles are fine, the particle size distribution is narrow, and a uniform composition can be obtained.

Next, the ceramic raw material prepared in this manner is used to produce a precursor for plastic working.

When a powder is used as a precursor, the ceramic raw material may be used as it is, but it is preferably used in the form of granules with a diameter of 100 to 200 μm, which have excellent fluidity.

A slurry of a ceramic raw material containing a water-soluble resin such as granular polyvinyl alcohol and hydroxyethyl cellulose can be prepared using a spray dryer or the like.

When using a powder compact as a precursor, there are two methods: a pressure molding method in which the granules are pressed, and a casting method in which a slurry of ceramic raw material is poured into a mold made of plaster or the like.

An extrusion molding method in which a pharyngeable mixture consisting of an organic binder, a ceramic raw material, and water is extruded through a die, and an isostatic press molding method in which the ceramic raw material is filled as it is or granules are filled into a rubber mold and pressure is applied isotropically.

Select an appropriate method from among known methods, such as injection molding, in which a mixture of thermoplastic resin and ceramic raw materials is extruded into a mold under heating, and sheet molding, in which a mixture of resin binder and ceramic raw materials is made into a thin film using a doctor blade, etc. death,
Prepare a powder compact.

When the calcined product is used as a precursor, the powder compact is heat-treated at a temperature of 600 to 1200° C. under normal pressure to obtain UI4a.

The heating section Jl is usually carried out in an oxidizing atmosphere such as an air atmosphere, an inert atmosphere such as a nitrogen atmosphere, or a vacuum atmosphere, but an oxidizing atmosphere in which the organic substances contained therein are removed by incineration is advantageous. Heat treatment is done in electric furnace or gas furnace.

The test is carried out by appropriately selecting and using commonly used high-temperature furnaces such as heavy oil furnaces. Normal sintered bodies are extremely difficult to cut due to the presence of paraffin, etc. However, in the case of the above-mentioned temporary phosphorus product, cutting processing using a lathe or the like can be easily performed, so the temporary phosphorous product is cut and shaped into an approximate shape, and the portion t- The advantage of extending the traces is that products with complex shapes can be manufactured efficiently with simple operations.

In the present invention, plastic working is carried out at a temperature t expressed by the following formula.
('C) and pressure p (xgf/mm2) o.

P≧8X10-87X (1600-t)14+0. I
P≦5. t≦1600 The range represented by the above formula is illustrated in FIG. 1.

If it greatly deviates from the above range, the plastic working resistance will be extremely high, making it difficult to industrially obtain a dense sintered body, or requiring complicated operations and expensive and complicated equipment. Alumina is used for plastic processing.

Rolling using a jig made of silicon carbide, carbon, etc.

Processing that utilizes plastic deformation such as extrusion, drawing, and 7-piece construction is performed. For example, in a high-temperature furnace using electrical heating, gas combustion heating, dielectric heating, etc., an oxidizing atmosphere such as atmospheric atmosphere, or an inert atmosphere such as nitrogen atmosphere.

This is carried out by applying tensile or compressive force using a hydraulic mechanism or the like in a flffi atmosphere such as a vacuum pig enclosure.

The heating method, atmosphere, etc. may be appropriately selected from known methods.

The zirconia solid electrolyte according to the present invention needs to be a dense Fi body, and its porosity is 8% or less, preferably 1% or less. When the porosity exceeds 8%, gas permeation through the pores becomes noticeable when the hood is made thinner, and airtightness is lost. For example, when used as a gas sensor, the test gas and the standard gas will be mixed through the sensor, which is undesirable as the measured value will be inaccurate.

The bending strength of the zirconia solid electrolyte according to the present invention is 10
Kg/2 or more dishes, preferably 20 Kg/2 or more dishes. Zirconia solid electrolytes are usually used at high temperatures, so they must have so-called thermal shock resistance, which means they will not break even after rapid heating and cooling. Therefore, the bending strength of the zirconia solid electrolyte is 10 kg.
If it is less than /mm2, it is unsatisfactory.

Generally, it is desirable that the zirconia solid electrolyte has high electrical conductivity. That is, in the gas sensor, high sensitivity, low temperature operability, and quick response can be obtained. In fuel cells, it is possible to improve the extraction power efficiency by lowering the internal resistance, and in the same way, in oxygen pumps, it is possible to improve the oxygen extraction efficiency by decreasing the internal resistance. The electrical conductivity of the zirconia solid electrolyte according to the present invention is 1 at 800'C.
0-4 (Ω·Cm)-1 or more f6, preferably 1O-8 (0° cm)-1 or more.

The zirconia solid electrolyte according to the present invention has a thickness of Q
, preferably 8 mm or less. If the thickness of the solid electrolyte is large, the internal resistance of the system will increase, and the efficiency will decrease for the same reason as described in the effect of conductivity above. Further, an increase in thickness is undesirable because it causes a decrease in thermal shock resistance.

The zirconia solid electrolyte according to the present invention can be produced into various shapes such as simple shapes such as plate shapes, complex shapes where part of the material is thin, etc. by appropriately selecting the shape of the jig used for plastic working. It can be manufactured in any shape.

(Effects of the invention) The zirconia solid electrolyte of the present invention has a small porosity and
It is dense and has high strength, and even after post-processing, it has excellent dimensional accuracy and is extremely thin. Therefore, the zirconia solid electrolyte of the present invention has excellent thermal shock resistance, low-temperature operability, response speed, etc., and is suitable for use in gas sensors, fuel cells, oxygen pumps, and the like.

The present invention will be specifically explained below in Examples.

In addition, in the examples, bending strength and conductivity wt ratio at 800°C.

The porosity and average particle size were measured by the following method.

(1) Bending strength: Determined using the 4-point bending test method in accordance with JI8 R1601. However, the sample is a sintered body of a predetermined thickness with a width of 4 plates and a diameter of 40 mm.
A plate cut to the length was used.

(2) Electrical conductivity at 800°C Electrodes were provided on both sides of the sintered body of a predetermined size by platinum sputtering. Complex in-beam dance analysis was performed using alternating current at a frequency of 10 to 107H2, and the volume conductivity was taken as the conductivity of the sample. In addition, the sample was placed in an air atmosphere at 8
After holding in an electric furnace set at 00°C for 80 minutes, measurements were conducted.@(3) Porosity In accordance with JI8 R2205, the apparent pores were measured by immersing 5 samples in water at 20°C. rate? This is the value calculated from the average value.

(4) Break the average particle size sample and observe the broken surface with an electron microscope.
This is a value calculated from the average value of the measured particle diameters.

(5) Average particle size of ceramic raw material Observe the ceramic raw material using a transmission electron microscope.
This is a value calculated from the average value of the measured particle diameters of particles with a 0-inclusion value.

Example 1 A ceramic raw material with a particle size of 0.05 μm containing various amounts of yttrium oxide as shown in Table 81 below, manufactured by coprecipitation method, was placed in a mold and pressure-molded at 20°C with a pressure of 10 kg f/mm2. , calcined and molded in an electric furnace. Temperature was increased to 150°C at a rate of 15°C/min, held at 1150°C for 60 minutes, and then heated to 150°C.
Cooling was performed at a cooling rate of °C/rn 1 n.

Next, the calcined molded product was placed in a silicon carbide mold and heated for 12 hours in an electric furnace.
After raising the temperature at a rate of 25°C/min to 00°C and 10°C/min from 1200°C to 1500°C, a stress of i Kg f/mm2 was applied and pressure was applied from both sides for 80 minutes. . At the beginning of the pressurization, rapid contraction occurred, and after densification progressed, plastic deformation gradually occurred.

After depressurizing, it was cooled at a cooling rate of 15°C/min to produce a zirconia solid electrolyte with a thickness of Q, 1 mm,
Its physical properties were measured. The results are shown in Table 1.

(Hereinafter referred to as 'margins') As is clear from Table 1 above, as the amount of yttrium oxide compounded increases, the degree of grain growth in the plastic working process increases, and the plastic deformation resistance gradually increases.

Therefore, an increase in porosity and a decrease in bending strength were observed,
The effect is particularly noticeable in Run 7.

Example 2 A zirconia solid electrolyte was prepared in the same manner as in Example 1, except that ceramic raw materials containing calcium oxide and magnesium oxide listed in Table 2 below were used in place of ib-11um oxide. was created. The results * are shown in Table 2. - (Hereinafter blank) From the above table, even if calcium oxide and magnesium oxide are used as stabilizers instead of yttrium oxide,
It can be seen that it shows the same tendency as yttrium oxide.

Example 8 Ceramic raw materials of various particle sizes produced by the alkoxide method and containing 6 mol% of yttrium nonaoxide were placed in a mold.
After pressure molding at 0°C and a pressure of 10 Kg f/mm2, calcination molding was performed in an electric furnace. Calcination molding is 1100
The temperature was raised at a heating rate of 10°C/min to 110°C.
After being held at 0'C for 80 minutes, it was cooled at a cooling rate of 15-C/min.

Next, in Example 1, plastic working was carried out in the same manner as in Example 1 except that the plastic working temperature was 1400° C. to produce a zirconia solid electrolyte. The results are shown in Table 8.

As is clear from the above table, as the particle size of the ceramic raw material used increases, the degree of particle growth in the plastic working process increases, and the plastic deformation resistance gradually increases. Therefore, the porosity of the plastically worked molded body gradually increases.

Comparative Example 1 In Example I Run No. 3, after the ceramic raw material was processed and formed, it was not under the pre-firing condition but under 150
Plastic working was attempted using a precursor that was baked at 0°C under normal pressure for 4 hours and made into a so-called fired product, and other conditions were the same as in Example 1, but the plastic deformation resistance was extremely large and plastic working was not possible. was impossible.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the range of preferable conditions during plastic working according to the present invention, where the horizontal axis represents the temperature L("c>" and the vertical axis represents the applied stress P(g-f/s). ) Represents the outsourcer Yamana-Ododo Kanebo Co., Ltd.

Claims (5)

[Claims] (1) Average particles whose main components are zirconium oxide (A) and at least one stabilizer (B) selected from the group of yttrium oxide, calcium oxide, and magnesium oxide in a proportion of at most 16 mol%. A calcined molded product, powder, or powder molded product made of a ceramic raw material with a diameter of 1 μm or less is made plastic under the conditions of temperature t (°C) and applied stress P (Kgf/mm^2) shown by the following formula. Processed porosity is 8% or less, bending strength is 10Kg/mm
^2 or more, conductivity at 800℃ is 10^-^4 (Ω・c
m) A zirconia solid electrolyte having a pH of ^-^1 or more. P≧8×10^-^8^7×(1600-t)^1^4
+0.1P≦5, t≦1600 (2) The zirconia solid electrolyte according to claim (1), wherein the zirconia solid electrolyte has a thickness of 0.3 mm or less. (3) The zirconia solid electrolyte according to claim (1) or (2), wherein the zirconia solid electrolyte has a porosity of 1% or less. (4) Zirconia solid electrolyte has a bending strength of 20 kg/m
The zirconia solid electrolyte according to any one of claims (1) to (3), which has a zirconia solid electrolyte of m^2 or more. (5) Claims (1) to (4) in which the zirconia solid electrolyte has an electrical conductivity of 10^-^8 (Ωcm)^-^1 or more at 800°C. The zirconia solid electrolyte according to any one of the above.