JP2010138050A - Method of manufacturing compound oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process which is simplified and is decreased in the generation of inferior goods of a compound oxide. <P>SOLUTION: The process of manufacturing the compound oxide includes: a raw material preparing process in which a first compound of at least one of a compound which contains a first element and carries out hydration when coexisting with water and a compound after hydration containing the first element, and a second compound including a second element are mixed making water as a solvent to obtain a mixed raw material; a molding process which molds a mixed raw material to obtain a molded body; and a calcinating process which warms the molded body at a temperature raising rate below a range of a predetermined slowly raising rate to calcinate and to obtain a calcinated body. When the first element is magnesium and the second element is aluminum, 30°C/h or less (up to 600°C) and 100°C/h or less (600-1,500°C) are desirable. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a complex oxide. More specifically, the present invention provides a method for producing a complex oxide using as a raw material a compound that hydrates when coexisting with water.

Conventionally, as a composite oxide, magnesia particles having an average particle size of 50 μm or less and spinel particles having an average particle size of 50 μm or less are wet-mixed using alcohol as a solvent, and then molded and fired, and the relative density is 98% or more. Those having an impurity content of 1% or less have been proposed (see, for example, Patent Document 1). The composite oxide of Patent Document 1 can adjust the thermal expansion coefficient by changing the molar percentage of magnesia, and can be used, for example, as a sealing material for a fuel cell. In addition, magnesia particles with a purity of 97% or more and alumina particles with a purity of 97% or more are mixed and ground in an organic solvent to form submicron-sized particles. Magnesium aluminate spinel aggregates that have been made dense by production have been proposed (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 7-126061 JP 2000-290067 A

  However, in the method for producing a composite oxide described in Patent Documents 1 and 2, since raw materials are mixed using an organic solvent, the treatment of the organic solvent after mixing the raw materials is complicated.

  The present invention has been made in view of such problems, and it is a main object of the present invention to provide a method for producing a composite oxide that can further simplify the process and suppress the generation of defective composite oxides. Objective.

  As a result of diligent research to achieve the above-described object, the present inventors have mixed magnesium oxide and aluminum oxide with water as a solvent, heated at a more moderate heating rate, and fired. The present invention has been completed by finding out that it is possible to simplify the production of defective composite oxides and to suppress the generation of defective products.

That is, the method for producing the composite oxide of the present invention includes:
A method for producing a composite oxide containing a first element and a second element,
A first compound, which is at least one of a compound containing the first element and hydrated when coexisting with water and a compound after hydration containing the first element, and a second compound containing the second element are mixed using water as a solvent. Raw material preparation process to obtain mixed raw materials,
A molding step of molding the mixed raw material to obtain a molded body;
A firing step of obtaining a fired body by heating and firing the molded body at a temperature increase rate within a range of a predetermined slow temperature increase rate determined based on the molded body;
Is included.

In this method for producing a composite oxide, the process can be further simplified and the occurrence of defective composite oxides can be further suppressed. The reason why such an effect is obtained is estimated as follows, for example.
For example, in the case of using a raw material to be hydrated, if the raw material is mixed using an organic solvent, the raw material can be prevented from being hydrated, but a processing step of the organic solvent after mixing the raw material is required. On the other hand, when the raw materials are mixed using water as a solvent and fired, water vapor is generated during firing, and voids may be formed in the molded body. When firing is performed at a general temperature increase rate, shrinkage based on the voids occurs, and a large number of cracks are generated in the fired body. As a method for preventing this, a method of mixing the raw material with water and calcining the hydrated compound to form an oxide, and then forming and firing this can be considered, but a calcining step is necessary. Thus, the process becomes complicated. In the method for producing a composite oxide of the present invention, the solvent is easily treated using water as a solvent, and dehydration and void shrinkage are gradually performed by raising the temperature within a range of a predetermined slow temperature rise rate, followed by firing. It suppresses the occurrence of cracks in the body. Therefore, when mixing the raw material to be hydrated with water as a solvent, the calcination step is omitted to simplify the process, and the shrinkage due to dehydration and the like is further reduced, resulting in the generation of defective composite oxides. Can be suppressed.

  Next, the best mode for carrying out the present invention will be described. The method for producing a composite oxide of the present invention comprises (1) a first compound and a second compound which are at least one of a compound containing a first element and hydrating when coexisting with water and a compound after hydration containing the first element. A raw material preparation step of mixing a second compound containing an element with water as a solvent to obtain a mixed raw material; (2) a molding step of forming a mixed raw material to obtain a molded body; and (3) a molded body of the molded body. And a firing step in which a fired body is obtained by firing at a temperature rise rate in a range equal to or lower than a predetermined slow temperature rise rate determined based on the above. Here, for convenience of explanation, a case where the first element is magnesium and the second element is aluminum will be described.

(1) Raw material preparation step In the raw material preparation step of the present invention, a first compound that is at least one of a compound that contains magnesium and hydrates when coexisting with water and a hydrated compound that contains magnesium, and a second compound that contains aluminum Are mixed using water as a solvent to obtain a mixed raw material. Examples of the first compound include magnesium oxide and magnesium hydroxide. Examples of the second compound include aluminum oxide and aluminum hydroxide, and spinel that is a composite oxide of magnesium and aluminum. Among these, when magnesium oxide and spinel are used, the amount of magnesium oxide added can be easily determined. Further, when magnesium oxide and aluminum oxide are used, for example, the spinel synthesis step can be omitted, and thus the process can be further simplified. The mixing of the first compound and the second compound is performed using water as a solvent. In this way, for example, the subsequent solvent treatment becomes easier and safer than in the case of mixing using an organic solvent. For mixing the raw materials, for example, a pot mill, a planetary mill, an attritor or the like can be used. After mixing with water as a solvent, it is preferable to perform a granulation treatment of drying the water as the solvent after mixing and adjusting the particle size of the mixed raw material. In the granulation treatment, granulation may be performed within a predetermined particle size range using, for example, a spray dryer. In this case, since the mixed raw material is dried and granulated at the same time, the efficiency is good, and since the particle size can be made uniform, it is easy to perform the next process. Alternatively, after mixing with water as a solvent, the mixture may be dried, dry pulverized in a mortar or the like, and then classified into a predetermined particle size using a sieve to obtain a mixed raw material powder. The powder of the mixed raw material is preferably adjusted to a particle size suitable for the molding method in consideration of ease of molding. When magnesium oxide is used, the mixed powder is obtained in a state containing hydrated magnesium hydroxide.

(2) Molding step In the molding step of the present invention, the mixed mixed raw materials are molded to form a molded body, and the manufactured molded body is fired to obtain a fired body. The molding method in this step can be performed in any shape by, for example, die press molding, hot press molding, cold isotropic molding (CIP), hot isotropic molding (HIP), or the like.

(3) Firing step In the firing step of the present invention, the molded body is heated at a temperature rise rate in a range equal to or lower than a predetermined slow temperature increase rate determined based on the molded body to obtain a fired body. In this case, for example, the calcining step using the hydroxide contained in the mixed raw material as an oxide can be omitted before molding, and therefore the process can be further simplified. The predetermined slow heating rate determined on the basis of this molded body is obtained by experimentally determining the relationship between the temperature of the molded body, the composition of the molded body, the size of the molded body, and the like. The speed may be set as a predetermined slow temperature increase rate. In this firing step, the temperature may be increased at a constant slow temperature increase rate from the start to the end, and a predetermined slow temperature increase rate is determined for each of one or more temperature regions in which the components contained in the molded body react. The temperature may be raised. In the former, the molded body can be fired more reliably, and in the latter, the firing time can be shortened by increasing the rate of temperature rise in a temperature region that is not related to the reaction. Moreover, in this baking process, when setting a moderate temperature increase rate, it is good also as providing the period hold | maintained at a fixed temperature in the middle of temperature increase. If it carries out like this, rapid volume change can be suppressed by hold | maintaining at fixed temperature, and generation | occurrence | production of the defective product of complex oxide can be suppressed more. The temperature region held at this constant temperature is preferably a temperature region in which the volume change due to firing is large. Here, when a period for holding at a constant temperature is provided, the slow temperature increase rate means an average temperature increase rate including the period of the constant temperature. In the firing step of the present invention, for example, when aluminum oxide is used as the second compound containing aluminum in the raw material preparation step, the temperature rises within a predetermined first slow temperature increase rate in the magnesium hydroxide dehydration temperature region. The temperature may be increased at a temperature rate, and the temperature may be increased at a temperature increase rate in a range equal to or lower than a predetermined second slow temperature increase rate in a spinel generation temperature region generated by reaction between magnesium and aluminum. The magnesium hydroxide dehydration temperature region may be 300 ° C. or more and 400 ° C. or less, and the spinel formation temperature region may be 800 ° C. or more and 1100 ° C. or less. Further, the temperature is increased at a temperature increase rate in the range of 30 ° C./h or less as the predetermined first slow temperature increase rate, and the temperature is increased at the temperature increase rate in the range of 100 ° C./h or less as the predetermined second slow temperature increase rate. It is good also as what to do. By doing so, a fired body of the composite oxide can be obtained more efficiently. Thus, in the firing step, magnesium hydroxide is converted to magnesium oxide, and at least a part of magnesium oxide and aluminum react to produce spinel, which is a composite oxide containing magnesium and aluminum. -A spinel composite oxide can be produced.

  It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention.

  For example, in the above-described embodiment, the first element is magnesium and the second element is aluminum. However, at least one of a compound containing the first element and hydrating when coexisting with water and a compound after hydration containing the first element are included. If the first compound and the second compound containing the second element are used, the present invention can be applied without being particularly limited thereto. Further, in the firing step, in the dehydration temperature region of the hydrated compound containing the first element, the temperature is raised at a temperature rise rate in a range equal to or lower than a predetermined first slow temperature rise rate, and the compound of the first element and the second element is used. In a production temperature region of a certain third compound, the temperature may be increased at a temperature increase rate in a range equal to or lower than a predetermined second slow temperature increase rate. In addition, the range below a predetermined slow temperature increase rate shall be calculated | required empirically according to the kind of 1st element and 2nd element.

  Hereinafter, an example in which a magnesium oxide-spinel composite oxide is specifically prepared as the composite oxide will be described as an example.

[Example 1]
Magnesium oxide (manufactured by Kyowa Chemical Industry Co., Ltd.) and alumina (manufactured by Showa Denko KK) are weighed to a weight ratio of 5: 5, put in a pot mill and added with water as a solvent to make a 33 wt% slurry. And mixed and ground for 3 hours. The mixed and pulverized raw material was dried at 80 ° C. for 24 hours, then pulverized in a mortar, and classified to a particle size of 150 μm or less using a sieve to obtain a mixed raw material powder. The mixed raw material powder was subjected to die press molding so as to have a shape of 35 mm × 25 mm × 5 mm at 10 MPa, and then subjected to CIP treatment under a condition of 400 MPa using a solvent as water to obtain a molded body. The dry weight of this molded body at 25 ° C. was 20 g. In this molded body, a dehydration reaction of magnesium hydroxide occurs in the region near 350 ° C., and a spinel formation reaction occurs in the region of 800 ° C. to 1100 ° C. For this reason, this molded object was baked with the following baking schedules. First, the temperature was raised from room temperature to 600 ° C. at a rate of temperature increase of 20 ° C./h, and the temperature was raised from 600 ° C. to 1500 ° C. at a rate of temperature increase of 100 ° C./h, and kept at 1500 ° C. for 2 hours. Was fired, and the obtained fired body of magnesium oxide-spinel composite oxide was taken as Example 1. Table 1 shows the weight ratio of magnesium oxide and aluminum oxide, firing schedule, and evaluation of the appearance of the fired body in Example 1. Table 1 also shows Examples 2 to 10 and Comparative Examples 1 to 10 described later.

[Examples 2 to 5]
Except for weighing raw materials, magnesium oxide powder and aluminum oxide powder were weighed so that the weight ratio would be 6.5: 3.5, 8: 2, 8.5: 1.5, 9: 1. Were fired bodies of the magnesium oxide-spinel composite oxide obtained through the same steps as in Example 1, respectively, as Examples 2 to 5. In Examples 2 to 5, the dry weight of this molded body at 25 ° C. was 25 g.

[Examples 6 to 10]
The firing schedule was raised from room temperature to 350 ° C. at a heating rate of 20 ° C./h, held at 350 ° C. for 2 hours, and then heated from 350 ° C. to 1500 ° C. at a heating rate of 100 ° C./h, A fired body of magnesium oxide-spinel composite oxide obtained through the same steps as in Example 1 except that the molded body was fired for 2 hours at 1500 ° C. was designated as Example 6. In Example 6, since the temperature is maintained at 350 ° C. for 2 hours, the average rate of temperature increase from room temperature to over 350 ° C. can also be referred to as 17.8 ° C./h. The dry weight of this molded body at 25 ° C. was 20 g. Further, in the raw material blending, the magnesium oxide powder and the aluminum oxide powder are weighed so that the weight ratio is 6.5: 3.5, 8: 2, 8.5: 1.5, 9: 1, respectively. Except for the above, the fired bodies of magnesium oxide-spinel composite oxide obtained through the same steps as in Example 6 were designated as Examples 7 to 10, respectively. In Examples 6 to 10, the rate of temperature increase per unit dry weight was the same value as in Example 6.

[Comparative Examples 1-5]
The firing schedule was obtained through the same steps as in Example 1 except that the molded body was fired at a heating rate of 200 ° C./h from room temperature to 1500 ° C. and held at 1500 ° C. for 2 hours. A fired body of magnesium oxide-spinel composite oxide was used as Comparative Example 1. The dry weight of this molded body at 25 ° C. was 20 g. Further, in the raw material blending, the magnesium oxide powder and the aluminum oxide powder are weighed so that the weight ratio is 6.5: 3.5, 8: 2, 8.5: 1.5, 9: 1, respectively. Except for the above, the fired bodies of magnesium oxide-spinel composite oxide obtained through the same steps as in Comparative Example 1 were used as Comparative Examples 2 to 5, respectively. In Comparative Examples 1 to 5, the rate of temperature increase per unit dry weight was the same value as in Comparative Example 1.

[Comparative Examples 6 to 10]
The firing schedule is to raise the temperature from room temperature to 600 ° C. at a temperature increase rate of 40 ° C./h, and then increase the temperature from 600 ° C. to 1500 ° C. at a temperature increase rate of 100 ° C./h and hold at 1500 ° C. for 2 hours. As a comparative example 6, a fired body of magnesium oxide-spinel composite oxide obtained through the same steps as in Example 1 except that the molded body was fired. The dry weight of this molded body at 25 ° C. was 20 g. Further, in the raw material blending, the magnesium oxide powder and the aluminum oxide powder are weighed so that the weight ratio is 6.5: 3.5, 8: 2, 8.5: 1.5, 9: 1, respectively. Except for the above, fired bodies of magnesium oxide-spinel composite oxide obtained through the same steps as in Comparative Example 6 were referred to as Comparative Examples 7 to 10, respectively. In Comparative Examples 6 to 10, the rate of temperature increase per unit dry weight was the same value as in Comparative Example 6.

[Experimental result]
In the fired bodies of Comparative Examples 1 to 5 fired at a general temperature increase rate of 200 ° C./h, many fine cracks were observed on the surface. In addition, a comparison was made by firing at a slower rate of temperature rise and a rate of temperature rise of 40 ° C./h in the temperature range from room temperature to 600 ° C. and a rate of temperature rise of 100 ° C./h in the temperature range from 600 ° C. to 1500 ° C. Even in the fired bodies of Examples 6 to 10, many fine cracks were observed on the surface. On the other hand, in the fired bodies of Examples 1 to 10, no cracks were observed on the surface. From this result, after mixing the raw material of the magnesium oxide-spinel composite oxide with water as a solvent, firing in a range below a predetermined rate of temperature increase suppresses the generation of cracks due to dehydration and volume change accompanying the generation of spinel. It became clear that it was possible. In Examples 1 to 10, the total firing time may be long, but the calcination process and the pulverization process associated with calcination can be omitted. It was.

Claims (8)

A method for producing a composite oxide containing a first element and a second element,
A first compound, which is at least one of a compound containing the first element and hydrated when coexisting with water and a compound after hydration containing the first element, and a second compound containing the second element are mixed using water as a solvent. Raw material preparation process to obtain mixed raw materials,
A molding step of molding the mixed raw material to obtain a molded body;
A firing step of obtaining a fired body by heating and firing the molded body at a temperature increase rate within a range of a predetermined slow temperature increase rate determined based on the molded body;
The manufacturing method of the complex oxide containing this.   In the firing step, in the dehydration temperature region of the hydrated compound containing the first element, the temperature is increased at a temperature increase rate within a predetermined first slow temperature increase rate, and the first element and the second element are heated. 2. The method for producing a composite oxide according to claim 1, wherein the temperature is raised at a temperature rise rate in a range equal to or lower than a predetermined second slow temperature rise rate in a generation temperature region of the third compound as a compound. In the raw material preparation step, the first element is magnesium and the second element is aluminum to obtain a mixed raw material,
In the firing step, in the dehydration temperature region of magnesium hydroxide as the hydrated compound containing the first element, the temperature is raised at a temperature rise rate in a range equal to or lower than a predetermined first slow temperature rise rate, and spinel as the third compound The method for producing a composite oxide according to claim 2, wherein the temperature is raised at a temperature rise rate in a range equal to or lower than a predetermined second slow temperature rise rate in the generation temperature region.   In the firing step, the temperature is increased at a temperature increase rate in the range of 30 ° C./h or less as the predetermined first slow temperature increase rate, and the temperature is increased in the range of 100 ° C./h or less as the predetermined second slow temperature increase rate. The method for producing a composite oxide according to claim 3, wherein the temperature is increased at a temperature rate. In the raw material preparation step, after the mixing, the water as a solvent is dried and a granulation treatment for adjusting the particle size of the mixed raw material is performed to obtain the mixed raw material,
5. The method for producing a composite oxide according to claim 1, wherein in the forming step, the granulated mixed raw material is formed to obtain a formed body.   2. The method for producing a composite oxide according to claim 1, wherein in the raw material preparation step, a mixed raw material is obtained using magnesium as the first element and aluminum as the second element.   The method for producing a composite oxide according to claim 1, wherein in the raw material preparation step, magnesium oxide as the first compound and aluminum oxide as the second compound are mixed.   The method for producing a composite oxide according to claim 1, wherein in the raw material preparation step, magnesium oxide as the first compound and spinel as the second compound are mixed.