JPH08169713A - Cerium based sinterable multiple oxide, cerium based multiple oxide sintered compact and its production - Google Patents

Abstract

PURPOSE: To suppress gas diffusion and to improve the degree of sintering at low temp., workability, moldability and sintered density by burning and sintering precipitate of a multiple salt containing Ce ion and specified metallic ion. CONSTITUTION: The soln. containing 50-99.9mol.% Ce ion and 1-50mol.% rare earth element ion other than Ce, and Mg, Ca, Sr, Ba, Zr, Hf, Nb, Ta ions or these mixture and having 30-500g/l concn. expressed in terms of metallic oxide, aq. NH3 soln., aq. (NH4 )2 CO3 soln., aq. NH4 HCO3 soln., aq. oxalic acid soln. or these mixture are mixed in the wt. ratio of 1:(1-10) to obtain a multiple precipitate. The precipitate is dried and burned at 700-1200 deg.C, then sintered at 1250-1600 deg.C to obtain a sinterable multiple oxide containing 50-99.9mol.% Ce2 O3 and 1-50mol.% rate earth metal oxide except the Ce, MgO, SrO, BaO, ZrO2 , HfO2 , Nb2 O5 , Ta2 O5 or these mixture and having >=95% relative density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a cerium-based sinterable composite oxide which has excellent sinterability at low temperature and can be used as a raw material for electrolyte members such as solid oxide fuel cells (SOFC) and high temperature steam electrolyzers. , A sintered body obtained by sintering the oxide, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, cerium-based composite oxides are mainly composed of powdered cerium oxide, and powdered other components such as oxides, carbonates and hydroxides are crushed, mixed and then baked. It is produced by a method such as. Such complex oxides are used as raw materials for electrolyte members such as SOFCs and high-temperature steam electrolyzers, and have physical properties such as high density after sintering and gas diffusion during processing as much as possible. Is desired.

However, the cerium-based composite oxide produced by the conventional production method has poor sinterability at low temperatures,
The fact is that a relative density of 95% or more cannot be obtained unless sintering is performed at 1650 ° C. or higher. When sintering is performed at such a high temperature, the obtained sintered body has poor workability, it is difficult to suppress gas diffusion during processing, and further, there is a problem that the cost becomes high. is there.

Further, when a conventional cerium-based composite oxide is sintered to produce a molded body, it is necessary to add water or the like as a molding aid, which complicates the manufacturing process and causes Addition of additives may cause deterioration of the physical properties of the obtained sintered body.

[0005]

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a cerium-based sinterable composite oxide having excellent sinterability at low temperature and excellent workability and formability. Another object of the present invention is to provide a cerium-based composite oxide sintered body which is easy to process, can suppress gas diffusion during processing, and is inexpensive. Another object of the present invention is to produce a cerium-based composite oxide sintered body which is capable of preparing the above-mentioned sintered body with good reproducibility, easily, and at low cost, and which is also effective as an industrial method. To provide the law.

[0006]

According to the present invention, cerium oxide is contained in an amount of 50 to 99.9 mol%, and further, one or more rare earth metal oxides other than cerium, magnesium oxide, calcium oxide, strontium oxide, and oxide. In a cerium-based composite oxide containing 0.1 to 50 mol% of barium, zirconium oxide, hafnium oxide, niobium oxide, tantalum oxide, or a mixture thereof, the relative density of the sintered body when sintered at 1250 to 1600 ° C. Provided is a cerium-based sinterable composite oxide (hereinafter referred to as composite oxide A) characterized by exhibiting 95% or more. Further, according to the present invention, there is provided a cerium-based composite oxide sintered body obtained by sintering the composite oxide A at 1250 to 1600 ° C and having a relative density of 95% or more. Furthermore, according to the present invention, the cerium ion has a molar ratio of 50 to 99.9 mol%, and one or more rare earth metal ions other than cerium, magnesium ion, calcium ion, strontium ion, barium ion, zirconium ion, and hafnium ion. , Niobium ions, tantalum ions or mixtures thereof 0.1-50
After adjusting the concentration of the solution to 30 to 500 g / liter in terms of the content of the metal oxide, the ammonia solution, ammonium carbonate solution, ammonium hydrogen carbonate solution, oxalic acid solution or these solutions are prepared. The complex salt precipitate is obtained by mixing with the mixture of 1), and the obtained complex salt precipitate is calcined at 700 to 1200 ° C.
There is provided a method for producing the cerium-based composite oxide sintered body, which comprises sintering at 1600 ° C.

The present invention will be described in more detail below. The composite oxide A of the present invention contains cerium oxide as a main component, contains a specific metal oxide described later, and has a relative density of 95% or more when sintered at 1250 to 1600 ° C. At this time, the relative density of the sintered body is a value calculated by relative density (%) = (apparent density / theoretical density) × 100. Here, the theoretical density refers to the lattice constant of the complex oxide before sintering to be measured, and the lattice constant of the sample (composite oxide sintered body) is determined based on the diffraction of the (200) plane with sodium chloride as an internal standard. It is a value calculated from the value obtained by correcting the diffraction angle. The apparent density is a value calculated from the mass and volume of the sample.

The complex oxide A of the present invention comprises cerium oxide 5
0-99.9 mol% is included. Cerium oxide content is 5
When it is less than 0 mol%, the sinterability is poor and when sintered at 1250 ° C. or higher, the relative density of the sintered body does not reach 95% or higher.

The complex oxide A of the present invention comprises, in addition to the cerium oxide, one or more rare earth metal oxides other than cerium, magnesium oxide, calcium oxide, strontium oxide, barium oxide, zirconium oxide, hafnium oxide, and oxides. It contains 0.1 to 50 mol% of niobium, tantalum oxide or a mixture thereof. Examples of the rare earth metal oxides include yttrium oxide, lanthanum oxide, praseodymium oxide, neodymium oxide, samarium oxide, and gadolinium oxide. These components are components known as effective components of known cerium-based composite oxides. In addition to these metal oxides, if the above-mentioned relative density after sintering is 95% or more, for example, components and the like inevitably mixed due to raw materials at the time of production are included. May be.

The shape of the complex oxide A of the present invention is preferably granular or powdery, the average particle size is 0.1 to 3 μm, and the specific surface area is 5.
It is desirable that the range is ˜20 m ² / g and the tap density is 1.0 to 1.6 g / cm ³ .

In the method for producing the complex oxide A, first, cerium ions are contained in a molar ratio of 50 to 99.9 mol%, and one or more rare earth metal ions other than cerium, magnesium ions, calcium ions, strontium ions, and barium. Ions, zirconium ions, hafnium ions, niobium ions, tantalum ions or mixtures thereof 0.1
A solution containing ˜50 mol% is prepared. Rare earth metal ions other than cerium include yttrium ions,
Examples thereof include lanthanum ion, praseodymium ion, neodymium ion, samarium ion, and gadolinium ion. To prepare a solution containing these ions, a method of mixing each ion as an aqueous nitric acid solution or the like can be used.

Next, the concentration of the obtained solution is adjusted to 30 to 500 g / liter, preferably 300 to 500 g / liter, in terms of metal oxide contained. When the concentration of this solution exceeds 500 g / liter in terms of metal oxide, crystallization occurs and a uniform solution is not obtained. When it is less than 30 g / liter, crystals of precipitate grow and It adversely affects the reaction.

Then, the solution whose concentration has been adjusted is mixed with an aqueous ammonia solution, an aqueous ammonium carbonate solution, an aqueous ammonium hydrogen carbonate solution, an aqueous oxalic acid solution or a mixture thereof to obtain a complex salt precipitate. At this time, the concentration of these solutions mixed with the adjusted solution is preferably 1 to 2 N, particularly preferably 1 to 1.5 N in the case of aqueous ammonia solution, and preferably 50 in the case of aqueous ammonium carbonate solution or aqueous ammonium hydrogen carbonate solution. To 200 g / liter, particularly preferably 100 to 150 g / liter, and in the case of an oxalic acid aqueous solution, 50 to 100 g / liter, particularly preferably 50.
It is in the range of up to 60 g / liter. Further, the mixing ratio of the solution whose concentration is adjusted to the aqueous ammonia solution, the aqueous ammonium carbonate solution, the aqueous ammonium hydrogen carbonate solution, the aqueous oxalic acid solution or a mixture thereof is 1: 1 to 1: 1 by weight.
10 is preferable. Examples of the complex salt precipitate obtained at this time include complex hydroxides and complex carbonates.

The complex salt precipitate obtained next is preferably dried and then 700 to 1200 ° C., preferably 750 to 10 ° C.
By firing at 00 ° C. for 1 to 10 hours, the desired composite oxide A having excellent low-temperature sinterability can be obtained. At this time, if the sintering temperature is out of the range of 700 to 1200 ° C., the complex oxide A having the desired relative density cannot be obtained.

The cerium-based composite oxide sintered body of the present invention is
It is a sintered body obtained by sintering the composite oxide A at a sintering temperature of 1,250 to 1,600 ° C. and a relative density of 95% or more.

In the method for producing a sintered body according to the present invention, after the composite oxide A is prepared, the sintering temperature is 1250 to 160.
Sinter at 0 ° C., preferably 1-20 hours. Preferably, the obtained composite oxide A is crushed by an automatic mortar or the like to have an average particle size of preferably 0.1 to 3 μm and molded into a desired shape using a known molding machine or the like, and then an electric furnace It can be carried out by a method of sintering using the above. At this time, in the molding step, unlike the conventional cerium-based composite oxide, the molding can be easily carried out without using a molding aid such as water. Further, the crushing process before molding can be performed more easily than the conventional one.

[0017]

The composite oxide A of the present invention is 1250 to 1
When it is sintered at 600 ° C., it has a relative density of 95% or more, and thus it is excellent in low-temperature sinterability and workability, and is useful as an electrolyte member raw material for a solid electrolyte. Further, the sintered body of the present invention,
Since the composite oxide A is used as a raw material, it is easier to process as compared with the conventional cerium-based composite oxide sintered body, and since the sintered density is high, when used as an electrolyte, gas diffusion is suppressed. It has excellent electrical characteristics and is inexpensive. Further, according to the production method of the present invention, such a sintered body can be obtained easily with good reproducibility, at low cost, and is an industrially effective method.

[0018]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[0019]

Example 1 Cerium nitrate aqueous solution (manufactured by Santoku Metal Industry Co., Ltd .: 500 g / liter as cerium oxide)
And samarium nitrate aqueous solution (manufactured by Santoku Metal Industry Co., Ltd .:
250 g / liter as samarium oxide),
In terms of _{oxide, CeO 2: SmO 1 5 =} 80:. 20 were mixed in a molar ratio, and the solution total weight 500g was prepared. Here SmO _{1. 5} is agree with the following formula of 1.

[0020]

Embedded image

Then, 16 was prepared separately in the obtained solution.
3 liters of 0 g / liter ammonium carbonate aqueous solution was mixed and reacted to obtain a complex salt precipitate. The obtained precipitate was not matured, immediately filtered, dried at 150 ° C. for 20 hours, and then calcined at 900 ° C. for 3 hours. The obtained fired product was crushed in an automatic mortar to obtain a composite oxide having an average particle size of 1.37 μm. This crushing required 15 minutes.

2.5 g of the obtained composite oxide was added to a rectangular parallelepiped tablet press (manufactured by Toyo Hydraulic Machinery Co., Ltd .: 2.5 cm × 0.5 c).
m) and a press (made by Shimadzu Corporation).
Alumina board (Nippon Kagaku Sangyo Co., Ltd., trade name "S
SA-A alumina "purity 99.5%) is laid with a composite oxide having the same composition as bed sand, the molded composite oxide is placed on the sand, and the temperature rising rate is 10 ° C / min using an electric furnace. Under the above conditions, the temperature was raised to the sintering temperature shown in Table 1 and 1
Sintered for 0 hours at that temperature. After that, the cooling rate is 10 ℃ /
It was cooled to room temperature under the condition of minutes to obtain a sintered body. The resulting sintered body was made of water resistant abrasive paper (No. 80,
180, 320, 600, 1000, 1500
No.) was used for sequential polishing. Next, the outer diameter of the sintered body after polishing was measured using a caliper, and the weight was weighed with an electronic balance (accuracy: 0.1 mg) to measure the apparent density. Table 1 shows the apparent density and the relative density of the sintered body at each temperature. The theoretical density was determined by crushing the obtained sintered body
The line diffraction pattern was obtained and calculated from the lattice constant.

[0023]

[Example 2] Cerium nitrate aqueous solution (manufactured by Santoku Metal Industry Co., Ltd .: containing 500 g / liter as cerium oxide)
And samarium nitrate aqueous solution (manufactured by Santoku Metal Industry Co., Ltd .:
250 g / liter of samarium oxide was added, and a calcium nitrate solution (calcium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in nitric acid to give a concentration of calcium oxide of 4
(Adjusted to 00 g / liter) in terms of oxide
_{2: SmO 1 5:. CaO} = 85: 10: 5 were mixed in a molar ratio, and the solution total weight 500g was prepared. Thereafter, a composite oxide was obtained in the same manner as in Example 1, and the sintering temperature was 150.
A sintered body was prepared in the same manner as in Example 1 except that the temperature was 0 ° C., and the apparent density, theoretical density, and relative density were measured. The results are shown in Table 1.
Shown in

[0024]

Example 3 Cerium nitrate aqueous solution (manufactured by Santoku Metal Industry Co., Ltd .: 500 g / liter as cerium oxide contained)
And samarium nitrate aqueous solution (manufactured by Santoku Metal Industry Co., Ltd .:
250 g / liter of samarium oxide) and a strontium nitrate solution (strontium nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in water to adjust the concentration to 400 g / liter of strontium oxide) in terms of oxide. _{CeO 2: SmO 1 5:.} SrO = 85: 10: 5 were mixed in a molar ratio, and the solution total weight 500g was prepared. Hereinafter, a composite oxide was obtained in the same manner as in Example 1, and a sintered body was prepared in the same manner as in Example 1 except that the sintering temperature was 1500 ° C., and the apparent density, theoretical density, and relative density were measured.
The results are shown in Table 1.

[0025]

[Example 4] Cerium nitrate aqueous solution (manufactured by Santoku Metal Industry Co., Ltd., containing 500 g / liter of cerium oxide)
And samarium nitrate aqueous solution (manufactured by Santoku Metal Industry Co., Ltd .:
250 g / liter of samarium oxide was added, and a barium nitrate solution (barium nitrate (manufactured by Wako Pure Chemical Industries)) was dissolved in water to give a concentration of 50 g / barium oxide.
(Adjusted to liters) and, in terms of oxide, CeO ₂ : Sm
_{O 1 5:. BaO = 85} : 10: 5 were mixed in a molar ratio, and the solution total weight 500g was prepared. Hereinafter, a composite oxide was obtained in the same manner as in Example 1, and a sintered body was prepared in the same manner as in Example 1 except that the sintering temperature was 1500 ° C., and the apparent density, theoretical density, and relative density were measured. The results are shown in Table 1.

[0026]

The Comparative Example 1] Cerium oxide particulate and samarium _{oxide, CeO 2: SmO 1 5 =} 80:. The proportions of 20 (molar ratio), such that the total weight is 50 g, respectively weighed by electronic balance, The mixture was crushed and mixed for 30 minutes in an automatic mortar (Nitto Kagaku Co., Ltd.). Then, it was transferred to an alumina crucible, heated to 1350 ° C. at a temperature rising rate of 10 ° C./min using an electric furnace, calcined in the atmosphere for 10 hours, and then cooled to room temperature at a temperature lowering rate of 10 ° C./min. Then, it was crushed in an automatic mortar in the same manner as in Example 1 to obtain a composite oxide having an average particle size of 1.79 μm. This pulverization required twice the time (30 minutes) as in Example 1. About 20 μl of water as a molding aid was added to 1.9 g of the obtained composite oxide, and the mixture was mixed in an agate mortar for 15 minutes.

This was molded using a rectangular parallelepiped tablet molding machine (manufactured by Toyo Hydraulic Machinery Co., Ltd .: 2.5 cm × 0.5 cm) and a pressure machine (manufactured by Shimadzu Corporation). Alumina board (Nippon Kagaku Sangyo Co., Ltd., trade name "SSA-A Alumina" purity 9
9.5%) with a composite oxide of the same composition as the sand, the molded composite oxide was placed on the sand, and a temperature rising rate of 10 ° C./min was used in an electric furnace under the conditions shown in Table 1. The temperature was raised to the sintering temperature shown in, and sintering was performed at that temperature for 10 hours in the atmosphere. Then, it was cooled to room temperature at a temperature decreasing rate of 10 ° C./min to obtain a sintered body. In addition, the sinterability did not improve when the molding aid was not added. After treating the obtained sintered body in the same manner as in Example 1, the apparent density, theoretical density, and relative density were measured. The results are shown in Table 1.

[0028]

[Comparative Example 2] Cerium oxide particulate, samarium oxide and calcium carbonate _{CeO 2: SmO 1 5:.} CaO = 85:
A composite oxide was prepared in the same manner as in Comparative Example 1 after weighing with an electronic balance so that the total weight was 50 g at a compounding ratio of 10: 5 (molar ratio). The obtained composite oxide is 1
Treated in the same manner as Comparative Example 1 except that sintering was performed at 650 ° C.,
The apparent density, theoretical density and relative density were measured. The results are shown in Table 1.

[0029]

[Comparative Example 3 The particulate cerium oxide, samarium oxide and strontium _{carbonate, CeO 2: SmO 1 5:} . SrO =
85: 10: 5 (molar ratio) and a total weight of 50
Each was weighed with an electronic balance so that the weight became g, and then a composite oxide was prepared in the same manner as in Comparative Example 1. The apparent density, theoretical density, and relative density were measured by treating in the same manner as in Comparative Example 1 except that the obtained composite oxide was sintered at 1600 ° C. The results are shown in Table 1.

[0030]

[Comparative Example 4] The cerium oxide particulate, samarium oxide and barium carbonate _{CeO 2: SmO 1 5:.} BaO = 85: 1
A composite oxide was prepared in the same manner as in Comparative Example 1 after weighing with an electronic balance so that the total weight was 50 g at a compounding ratio of 0: 5 (molar ratio). The resulting composite oxide was 16
The same treatment as in Comparative Example 1 was carried out except that the sintering was carried out at 00 ° C., and the apparent density, theoretical density and relative density were measured. The results are shown in Table 1.
Shown in

[0031]

[Table 1]

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[Procedure amendment]

[Submission date] December 21, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0002

[Correction method] Change

[Correction content]

[0002]

2. Description of the Related Art Conventionally, cerium-based composite oxides are mainly composed of powdered cerium oxide, and powdered other components such as oxides, carbonates and hydroxides are crushed, mixed and then baked. It is produced by a method such as. Such composite oxide, SOFC, are used in raw material for the electrolyte member such as high-temperature steam electrolysis apparatus, density after sintering, and moth
It is desired to have physical properties and the like that can suppress diffusion of sulfur as much as possible.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

However, the cerium-based composite oxide produced by the conventional production method has poor sinterability at low temperatures,
The fact is that a relative density of 95% or more cannot be obtained unless sintering is performed at 1650 ° C. or higher. When sintered at such a high temperature, the obtained sintered body has poor workability.
In addition, it is difficult to suppress the gas diffusion , and there is a problem that the cost becomes high.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0005

[Correction method] Change

[Correction content]

[0005]

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a cerium-based sinterable composite oxide having excellent sinterability at low temperature and excellent workability and formability. Another object of the present invention is easy processing and gas expansion.
Disclosed is to provide a cerium-based composite oxide sintered body that can suppress dusting and is inexpensive. Another object of the present invention is to produce a cerium-based composite oxide sintered body which is capable of preparing the above-mentioned sintered body with good reproducibility, easily, and at low cost, and which is also effective as an industrial method. To provide the law.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

[0026]

[Comparative Example 1] The powdery cerium oxide and samarium _{oxide, CeO 2: SmO 1 5 =} 80:. The proportions of 20 (molar ratio), so that the total weight is 50 g, respectively were weighed with an electronic balance , And crushed and mixed for 30 minutes in an automatic mortar (Nitto Kagaku Co., Ltd.). Then, it was transferred to an alumina crucible, heated to 1350 ° C. at a temperature rising rate of 10 ° C./min using an electric furnace, calcined in the atmosphere for 10 hours, and then cooled to room temperature at a temperature lowering rate of 10 ° C./min. Then, it was crushed in an automatic mortar in the same manner as in Example 1 to obtain a composite oxide having an average particle size of 1.79 μm. This pulverization required twice the time (30 minutes) as in Example 1. About 20 ml of water as a molding aid was added to 1.9 g of the obtained composite oxide, and mixed for 15 minutes in an agate mortar.

Claims (3)

[Claims] 1. At least one rare earth metal oxide other than cerium, containing 50 to 99.9 mol% of cerium oxide,
Magnesium oxide, calcium oxide, strontium oxide, barium oxide, zirconium oxide, hafnium oxide, niobium oxide, tantalum oxide or mixtures thereof.
In a cerium-based composite oxide containing 1 to 50 mol%,
A cerium-based sinterable composite oxide, wherein the relative density of the sintered body when sintered at 1250 to 1600 ° C. is 95% or more. 2. At least one rare earth metal oxide other than cerium, containing 50 to 99.9 mol% of cerium oxide,
Magnesium oxide, calcium oxide, strontium oxide, barium oxide, zirconium oxide, hafnium oxide, niobium oxide, tantalum oxide or mixtures thereof.
1250 a cerium-based composite oxide containing 1 to 50 mol%
A cerium-based composite oxide sintered body having a relative density of 95% or more, which is sintered at 1600C. 3. A cerium ion in a molar ratio of 50 to 99.
9 mol% and one or more kinds of rare earth metal ions other than cerium, magnesium ion, calcium ion, strontium ion, barium ion, zirconium ion,
A solution containing 0.1 to 50 mol% of hafnium ion, niobium ion, tantalum ion, or a mixture thereof is prepared, and the concentration of the solution is 30 to 30 in terms of metal oxide contained.
After adjusting to 500 g / liter, aqueous ammonia solution,
An aqueous solution of ammonium carbonate, an aqueous solution of ammonium hydrogen carbonate, an aqueous solution of oxalic acid or a mixture thereof is mixed to obtain a complex salt precipitate, and the obtained complex salt precipitate is 700-120.
The method for producing a cerium-based composite oxide sintered body according to claim 2, wherein the firing is performed at 0 ° C and then the sintering is performed at 1250 to 1600 ° C.