JP3185263B2 - Solid electrolyte material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte material, and more particularly to a solid electrolyte material having excellent oxygen ion conductivity.
Oxygen sensors, fuel cells, etc., utilizing the potential difference caused by the movement of oxygen ions when substances having different oxygen partial pressures are held in contact at both ends, or
The present invention relates to a solid electrolyte substance used for an oxygen pump or the like by utilizing the movement of oxygen ions by passing a current through the solid electrolyte substance.

[0002]

2. Description of the Related Art Conventionally, stabilized zirconia has been widely used as a solid electrolyte material. Pure zirconium oxide (ZrO ₂ ) has a monoclinic, tetragonal, and cubic structure from low to high temperatures.
In stabilized zirconia, when a low-valent metal oxide such as CaO, MgO, and Y ₂ O ₃ is used as a stabilizer and replaced by a predetermined amount to form a solid solution, a fluorite-type cubic crystal, which is the highest temperature phase, is formed in a low temperature range. Until it becomes a stable phase. Accordingly, a large number of defects (vacancies) are generated at the positions of the oxygen ions (O ²⁻ ), and the conductivity (oxygen ion conductivity) is improved. The oxygen ion conductivity is generally required to be 1.0 × 10 ⁻¹ (S · m ⁻¹ ) or more. There are other solid electrolyte materials having oxygen ion conductivity, but stabilized zirconia has been used for oxygen sensors, fuel cells, oxygen pumps, and the like in terms of stability, reliability, and high conductivity.

[0003]

SUMMARY OF THE INVENTION Stabilized zirconia has low strength against thermal shock. Therefore, when it is used for an oxygen sensor, a fuel cell, an oxygen pump, or the like, it is often used in combination with other materials. However, if the coefficient of thermal expansion differs between the joint surfaces with different materials,
Since stabilized zirconia operates at a high temperature (600 ° C. or higher), cracks are likely to occur at the joint surface. Therefore,
Various structures have been devised to structurally solve this. As an example, there is a direct insertion type oxygen sensor. That is, the conventional direct insertion type oxygen sensor 1 shown in FIG.
Then, since the tube 2 made of stabilized zirconia and having one end sealed is inserted into the measurement gas, the tube 2 needs to be formed long. However, since the stabilized zirconia is weak against thermal shock and has short heat cycle resistance, the breakage rate of the tube 2 is very high. Therefore, a direct insertion type oxygen sensor as shown in FIG. 3 has been devised. The oxygen sensor 3 is formed by joining a columnar element 5 made of stabilized zirconia to the tip of a tube 4 such as an alumina tube or a mullite tube which exhibits high strength at high temperatures. In the oxygen sensor 3, since the coefficient of thermal expansion of the alumina tube and the mullite tube is smaller than the coefficient of thermal expansion of the stabilized zirconia, cracks due to thermal shock are likely to occur at their joints. Accordingly, a technique for reducing the coefficient of thermal expansion of stabilized zirconia has been developed. It is Japanese Patent Publication 55-173
For example, there is a method in which alumina is contained in stabilized zirconia as disclosed in JP-A No. 40, and a method in which silica is incorporated in stabilized zirconia as disclosed in JP-A-1-108163. In either of these methods, the thermal expansion coefficient of the stabilized zirconia is reduced, but the oxygen ion conductivity is not significantly reduced.

[0004] However, the joining of stabilized zirconia with a material having a relatively high coefficient of thermal expansion, such as a metallic material, is still only attempted to solve the problem structurally. That is, at present, a technique for increasing the thermal expansion coefficient without significantly reducing the oxygen ion conductivity of stabilized zirconia has not yet been established.

[0005] It is, therefore, a primary object of the present invention to provide a solid electrolyte material that has a relatively low oxygen ion conductivity and a high coefficient of thermal expansion.

[0006]

The present invention comprises yttrium oxide (Y ₂ O ₃ ), calcium fluoride (CaF ₂ ) and zirconium oxide (ZrO ₂ ) and has a general formula a
A and b are in the range of 0.022 ≦ a ≦ 0.1500 and 0 <b ≦ 0.676, when represented by Y ₂ O ₃ .bCaF _2. (1-ab) ZrO ₂ , a solid electrolyte substance It is.

[0007]

The thermal expansion coefficient of the solid electrolyte material is about 10.1 × 10 ⁻⁶ cm / ° C. to 17.4 × 10 ⁻⁶ cm, which is equivalent to that of a metal material or the like.
/ ° C.

[0008]

According to the present invention, since the thermal expansion coefficient of the solid electrolyte material approaches the value of a material having a high thermal expansion coefficient such as a metal material, the solid electrolyte material according to the present invention is joined to a material having a high thermal expansion coefficient. In this case, there is an advantage that cracks are less likely to occur due to less thermal shock. Moreover, the solid electrolyte material according to the present invention has almost no change in oxygen ion conductivity as compared with the conventional stabilized zirconia. Therefore, when an oxygen sensor, a fuel cell, an oxygen pump, or the like is formed by using the solid electrolyte substance according to the present invention, the range of choice of composite materials is widened.

Furthermore, the solid electrolyte material according to the present invention has a thermal expansion coefficient of about 10.1 × 10 ⁻⁶ cm / ° C. to 17.4 × 10 ⁻⁶ cm / without significantly impairing the conductivity of oxygen ions.
Since it can be selected in the range of ° C., it is possible to correspond finely to the composite material. For this reason, materials that have not been possible so far can be selected as support materials, electrode materials, separator materials, and the like, and the effect of contributing to technological progress is great.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0011]

EXAMPLE First, ZrO ₂ and Y ₂ O _{3 were used} as raw materials.
Were weighed so as to have a molar ratio as shown in Table 1, and wet-mixed with a ball mill for 16 hours, and then evaporated to dryness to obtain a mixed powder.

[0012]

[Table 1]

Next, this mixed powder was calcined at 1150 ° C. for 2 hours to obtain a calcined product.

Then, CaF ₂ was mixed with the calcined product at a composition ratio as shown in Table 1 to obtain a raw material powder. This raw material powder has a composition as shown in Table 1 by mixing the calcined product and CaF ₂ at a volume ratio shown in Table 1.

Next, 5% by weight of vinyl acetate was added as a binder to the raw material powder, and the mixture was wet-mixed and pulverized again with a ball mill for 16 hours to obtain a pulverized product. Then, the pulverized material was evaporated to dryness, passed through a sieve, and sized to obtain a granular powder. The granulated powder obtained in this manner is dried by a dry press at 2 ton /
Pressing was performed at a pressure of cm ² to obtain a molded product.

Next, the obtained molded body is placed in air for 1 hour.
The resultant was held at 400 ° C. for 2 hours and fired to form a fired product. Then, these fired products were cut into chips having a size of 5 mm × 10 mm × 1 mm.

Then, as shown in FIG.
A porous platinum paste is applied to two ends in the longitudinal direction of 0 and two intermediate portions separated by 10 mm, and baked at 1000 ° C. to form porous platinum electrodes 12a, 12a.
b, 12c, and 12d were formed to obtain sample numbers 1 to 25.
Sample was obtained.

The conductivity σ of each sample was measured by the four-terminal method. Table 2 shows the results.

[0019]

[Table 2]

Further, the thermal expansion coefficient of each sample was measured. Table 2 shows the results.

As is clear from Table 2, the samples (solid electrolyte materials) within the scope of the present invention have a relatively small decrease in conductivity and a large coefficient of thermal expansion.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is an illustrative view showing one example of a conventional oxygen sensor as a background of the present invention;

FIG. 3 is an illustrative view showing another example of the conventional oxygen sensor as the background of the present invention.

[Explanation of symbols]

 10 chip 12a, 12b, 12c, 12d platinum electrode

────────────────────────────────────────────────── (5) References JP-A-1-173386 (JP, A) US Patent 4,514,277 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35 / 48 C01G 25/00 CA (STN) JICST file (JOIS) REGISTRY (STN)

Claims (1)

(57) [Claims] 1. Yttrium oxide (Y ₂ O ₃ ), calcium fluoride (CaF ₂ ) and zirconium oxide (Zr)
O ₂ ), and has the general formula aY ₂ O ₃ .bCaF _2. (1
-Ab) A solid electrolyte material in which a and b are in the range of 0.022 ≦ a ≦ 0.1500 and 0 <b ≦ 0.676 when represented by ZrO ₂ .