JPH05254932A - Zirconia electrolyte and its production - Google Patents

Abstract

PURPOSE:To obtain a solid electrolyte of stabilized zirconia excellent in thermal shock resistance and stability even in a molten metal. CONSTITUTION:Stabilized zirconia contg. 6-13mol% calcia as a stabilizing agent is mixed with stabilized zirconia contg. 6-12mol% oxide of a rare earth element as a stabilizing agent in (90:10)-(50:50) weight ratio to obtain a solid electrolyte of stabilized zirconia. This electrolyte has high thermal shock resistance, chemical stability and stable electromotive force.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zirconia electrolyte having a high ionic conductivity and having extremely little deterioration over time, and a method for producing the same.

[0002]

_2. Description of the Related Art Zirconia (ZrO ₂ ) has long been known as a solid electrolyte. Since it is an oxygen ion conductor, it is used as an oxygen concentration sensor for combustion control or as a dissolved oxygen concentration sensor in slag, and recently as a solid electrolyte fuel. It is used in various fields such as used as batteries. In addition, it is used in many passenger cars as a sensor for detecting the oxygen concentration in the exhaust gas for the purpose of controlling the air-fuel ratio of the automobile, and has greatly contributed to exhaust gas purification and fuel efficiency reduction.

Zirconia which is generally used as a ceramic is yttria (Y
₂ O ₃ ), calcia (CaO), magnesia (MgO)
Stabilized by the addition of several to ten and several mol% is used. 1 for exhaust gas sensors and fuel cells
Yttria-stabilized zirconia electrolyte that exhibits high ionic conductivity in the temperature range of 000 ° C or less is used. For the dissolved oxygen sensor in slag, magnesia-stabilized zirconia or calcia-stabilized zirconia electrolyte with excellent thermal shock resistance is used. It is used.

[0004]

However, a calcia-stabilized zirconia electrolyte, which has low reactivity with molten metal and is stable and has excellent thermal shock resistance, is generally used as a dissolved oxygen sensor in molten metal, particularly molten non-ferrous metal. However, when used as a sensor, there is a problem in that the electromotive force to be measured will vary greatly due to its low ionic conductivity.

[0005]

The present invention is to solve the above-mentioned problems, and the solid electrolyte comprising zirconia of the present invention contains, as a stabilizer, a stabilized zirconia containing both calcia and a rare earth oxide. A zirconia electrolyte consisting of a mixture of both calcia-stabilized zirconia and rare earth oxide zirconia, or calcia,
It is possible to use any of a mixture of a rare earth oxide and zirconia, which is then baked.

The rare earth oxides which can be used as the stabilizer of the present invention include ytterbia (Yb ₂ O ₃ ), yttria (Y ₂ O ₃ ), Samaria (Sm ₂ O ₃ ), and gadolinia (Gd ₂ O ₃ ). , Dysprosia (Dy ₂ O ₃ ), holmia (Ho ₂ O ₃ ), erbia (Er ₂ O ₃ ), and the like.

When using calcia-stabilized zirconia and rare earth oxide-stabilized zirconia, the molar ratio of calcia and zirconia is preferably 10/90 to 13/87, and rare earth oxide-stabilized zirconia is used. The mixing ratio of rare earth oxide and zirconia is 7/93 to 10
It is preferably / 90. The mixing weight ratio of calcia-stabilized zirconia and rare earth oxide-stabilized zirconia is preferably 9/1 to 5/5. In the case of those containing zirconia, calcia and ytterbia, the ratio of zirconia / calcia / ytterbia is 0.80 to 0.95 / 0.02 to 0.10 / 0.
It can be expressed as 01 to 0.05.

[0008]

The zirconia containing the calcia and the rare earth oxide of the present invention as a stabilizer is capable of enhancing the ionic conductivity without impairing the thermal shock resistance of the calcia-stabilized zirconia electrolyte, and can be used as a sensor. When used, it becomes possible to stably measure dissolved oxygen and the like.

[0009]

EXAMPLES The present invention will be described in more detail below by showing Examples of the present invention. Example 1 Calcia using ytterbium as a rare earth oxide and zirconia containing a rare earth oxide as a stabilizer were produced by mixing calcia-stabilized zirconia and ytterbium-stabilized zirconia and firing the mixture.

Both of the calcia-stabilized zirconia and the ytterbium-stabilized zirconia used had the composition showing the lowest electric resistance. That is, as calcia-stabilized zirconia, one containing 11 mol% of calcia was used, and as ytterbium-stabilized zirconia, 8 mo was used.
One containing 1% of ytterbium was used, and both of them had a molar ratio of CaO / ZrO ₂ = 11/89, Yb ₂ O ₃ / ZrO ₂
= 8/92, wet kneaded with a ball mill, dried, and calcined at 1200 ° C. As calcia, chemically stable calcium carbonate was used.

A calcined powder of the obtained calcia-stabilized zirconia and ytterbium-stabilized zirconia was added in a weight ratio of 10
0: 0, 90:10, 75:25, 50:50, 25:
A mixture of 75, 10:90 and 0: 100 was wet crushed in a ball mill, kneaded, dried, and then 100
It was molded into pellets having a diameter of 10 mm and a thickness of 5 mm at a pressure of 0 kg / cm ² , and was fired at 1650 ° C. The firing temperature is as follows when the oxide mixing method is used to adjust the raw materials.
For calcia-stabilized zirconia, 1650-18
00 ° C, 16 for ytterbium-stabilized zirconia
The temperature was set to be 0 to 1650 ° C., and the temperature at which good characteristics were obtained was selected. Platinum paste was applied to both sides of the sample pellet, baked at 1000 ° C., then heated to each measurement temperature using an infrared heating furnace, and the electrical resistance at a frequency of 1 kHz was measured using an impedance meter. The thermal shock resistance was determined by holding a sample pellet at a temperature for 30 minutes, immediately putting it in water and leaving it for 5 minutes, and checking for cracks using a color check solution.
The thermal shock resistance was defined as the temperature difference when cracks occurred.

In FIG. 1, the weight ratio of calcia-stabilized zirconia to ytterbium-stabilized zirconia used in Example 1 and 5
Regarding the relationship with the electric resistance at 00 ° C., the horizontal axis represents the mixing ratio, and the vertical axis represents the electric resistance logarithmically. In FIG. 2, the horizontal axis shows the mixing ratio of calcia-stabilized zirconia and ytterbium-stabilized zirconia, and the vertical axis shows the temperature difference at which cracks occur as the thermal shock resistance.

From these results, the electric resistance changes almost linearly according to the weight ratio, and the thermal shock resistance is different from the case of the electric resistance, and the ratio of calcia-stabilized zirconia: ytterbia-stabilized zirconia is 100: 0. At ~ 50: 50, the high thermal shock resistance of calcia-stabilized zirconia is maintained, but at 50: 50-0: 100, a sharp decrease is observed. To achieve a state where the electrical resistance is lowered to some extent while maintaining a higher thermal shock resistance than these results,
It is preferable that the weight ratio of calcia-stabilized zirconia: ytterbia-stabilized zirconia is 100: 0 to 50:50.

Further, in the above method, the calcined powders are mixed, but Z is adjusted so that the same composition as above is obtained when the raw materials are kneaded.
Approximately the same result was obtained when rO ₂ , CaCO ₃ , and Yb ₂ O ₃ were mixed and started. Further, the Ln ₂ O ₃ -ZrO ₂ of Ln ₂ O ₃ plays an action of lowering the electrical resistance, Y
In addition to b ₂ O ₃ , Y ₂ O ₃ and Sm which belong to the group that also has a relatively low electric resistance among the stabilized ZrO _2
2 O ₃ , Gd ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂
Similar results were obtained with O ₃ and the like.

FIG. 7 shows the relationship between the mixing weight ratio and the electric resistance when gadria-stabilized zirconia and holmia-stabilized zirconia were used instead of ytterbium-stabilized zirconia. Although the electric resistance is not as low as that of the ytterbium-stabilized zirconia, the electric resistance is reduced to about half when 50 wt% is mixed. Regarding the thermal shock force, the same result as in the case of ytterbium-stabilized zirconia shown in FIG. 2 was obtained.

Example 2 Next, 6mo having high thermal shock resistance and relatively low electric resistance.
Stabilized zirconia containing 1% of calcia and 6 mol% of ytterbia were used, and 6mo
Stabilized zirconia containing 1% of calcia and stabilized zirconia containing 8 mol% of ytterb, and 11 mol%
Sample pellets of the stabilized zirconia containing calcia and the stabilized zirconia containing 6 mol% of ytterbia were prepared in the same manner as in Example 1, and the electrical resistance and thermal shock resistance were measured.

In FIG. 3, the weight ratio of the stabilized zirconia containing 6 mol% of calcia to the stabilized zirconia containing 8 mol% of ytterbia was plotted along the horizontal axis, and the electric resistance at 500 ° C. was expressed in logarithm.

In FIG. 4, the weight ratio of the two is shown on the horizontal axis, and the vertical axis shows the temperature difference at which cracks occur in terms of thermal shock resistance. Figure 5
In Fig. 6, the weight ratio of the stabilized zirconia containing 11 mol% of calcia to the stabilized zirconia containing 6 mol% of ytterbia is represented on the horizontal axis, and the vertical axis represents the electric resistance at 500 ° C in logarithm. Shows the weight ratio of the two and the temperature difference at which cracks occur as the thermal shock resistance on the vertical axis. In the same manner as in Example 1, the electrical resistance changes almost linearly with the weight ratio, and the thermal shock resistance is calcia-stabilized zirconia:
The ytterbium-stabilized zirconia weight ratio is 100: 0.
At ~ 50: 50, the high thermal shock resistance of calcia-stabilized zirconia is maintained, and at 50:50 to 0: 100, a sharp decrease is observed.

[0019]

INDUSTRIAL APPLICABILITY The stabilized zirconia containing calcia and rare earth oxide of the present invention has high stability to molten metal, high thermal shock resistance, and high ionic conductivity, and is used in molten metal. A sensor having excellent characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a relationship between a mixing ratio of 11 mol% calcia-stabilized zirconia and 8 mol% ytterbium-stabilized zirconia and electric resistance at 500 ° C.

FIG. 2 is a diagram for explaining the relationship between the thermal shock resistance and the mixing ratio of zirconia stabilized with 11 mol% calcia and zirconia stabilized with 8 mol% ytterbia.

FIG. 3 is a diagram illustrating a relationship between a mixing ratio of zirconia stabilized with 6 mol% calcia and zirconia stabilized with 8 mol% ytterbia and electric resistance at 500 ° C.

FIG. 4 is a diagram illustrating the relationship between the thermal shock resistance and the mixing ratio of zirconia stabilized with 6 mol% calcia and zirconia stabilized with 8 mol% ytterbia.

FIG. 5 is a diagram illustrating a relationship between a mixing ratio of zirconia stabilized with 11 mol% calcia and zirconia stabilized with 8 mol% ytterbia and electric resistance at 500 ° C.

FIG. 6 is a diagram illustrating the relationship between the thermal shock resistance and the mixing ratio of zirconia stabilized with 11 mol% calcia and zirconia stabilized with 8 mol% ytterbia.

FIG. 7 is a diagram illustrating the relationship between the mixing ratio of 11 mol% calcia-stabilized zirconia to 8 mol% holmia-stabilized zirconia or 8 mol% gadria-stabilized zirconia and the electrical resistance at 500 ° C.

Claims (3)

[Claims] 1. A zirconia electrolyte, wherein the zirconia electrolyte contains both calcia and a rare earth oxide as a stabilizer. 2. Calcia and rare earth oxide are 6 to 13 m
stabilized zirconia containing ol% of calcia, 6-
The zirconia electrolyte according to claim 1, wherein both 12 mol% of the rare earth oxide-stabilized zirconia are mixed in a weight ratio of 90:10 to 50:50. 3. A method for producing a zirconia electrolyte, comprising:
Stabilized zirconia containing 6 to 13 mol% of calcia and 6 to 12 mol% of rare earth oxide-stabilized zirconia were mixed at a weight ratio of 90:10 to 50:50 and then calcined at 1600 to 1800 ° C. A method for producing a zirconia electrolyte, which is characterized by the following.