JP2707603B2 - Method for producing composite oxide fine powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a composite oxide fine powder which is a raw material of ceramics for electronic materials or structural materials.

(Prior Art and Problems Thereof) As a method for synthesizing a fine powder of a composite oxide, a solid phase reaction method in which raw material powders containing the constituent components of each oxide are mixed and synthesized at a high temperature is often used.

In the case of such a solid-phase reaction method, a large amount of heat energy is consumed for the reaction, and a reaction product is obtained in a state of a sintered body. Therefore, a pulverization step is required thereafter.

Therefore, in order to synthesize a composite oxide, a method that can be processed at a low temperature is desired. However, the types of composite oxides that can be synthesized by a solution reaction method at around room temperature are limited, and other than that, only a precursor or a coprecipitated hydroxide can be obtained. Although the obtained powder is excellent in uniformity and fineness, it is inferior in crystallinity, and a firing step is indispensable for forming a composite oxide. For this reason, it has the same problems as the solid phase reaction.

Further, as a method of synthesizing a crystalline composite oxide,
There is a method using a hot solution. According to this method, since the treatment is performed at a high temperature equal to or higher than the boiling point of the solution, a container which is maintained at a high pressure to prevent evaporation of the solution, that is, an autoclave is used. According to this method, the higher the temperature, the higher the pressure, so that the conditions such as the material and capacity of the autoclave become strict. For example, when oxidizing a metal under conditions of high temperature and high pressure, Ti or Nb is 400 to 500 ° C.
Atmospheric pressure or higher is required, but only a small material with a small capacity can be used for such an autoclave.

On the other hand, there is a method in which a metal is electrochemically oxidized by an electric current in an aqueous solution to form an oxide, which is known as an anodization method. However, what is produced by this anodic oxidation method is a single oxide, and it is difficult to produce a composite oxide.

(Object of the Invention) The present invention provides a new method by which anodic oxidation under hydrothermal conditions enables a composite oxide fine powder to be synthesized at lower temperature and lower pressure than conventional hydrothermal synthesis under high temperature and high pressure conditions. Is to provide.

(Means for Solving the Problem) In other words, the present invention immerses a metal arranged in an autoclave in a solution, and electrochemically oxidizes the metal by flowing a current through the metal in the solution in a high-temperature and high-pressure state. And simultaneously reacting with a dissolved component contained in the high-temperature and high-pressure solution to obtain a composite oxide fine powder.

Here, as the metal to be placed in the autoclave,
Al, Ti, Nb, Zr, Hf, W, Mo, V, Sn, Pb, etc.
These metals are the working electrode side in the autoclave where the anode of the DC power supply is electrically connected. As the solution to be put into the autoclave, one containing a component that reacts with an oxide generated by anodic oxidation of the metal under high-temperature and high-pressure conditions is used, for example, barium nitrate, lithium nitrate, or the like is used. . In the autoclave containing such a solution, a counter electrode electrically connected to the cathode side of the DC power source is disposed so as to face the working electrode.

In such a configuration, when the autoclave is heated by the heater, the solution in the autoclave is in a high-temperature and high-pressure state. On the other hand, when a direct current is applied between the working electrode and the counter electrode, the metal on the working electrode side is in an anodized state. As a result, the complex oxide is dissolved in the solution and reacts with a dissolved component contained in the solution to form a composite oxide.

In the production of the composite oxide, the temperature, pressure, applied voltage, and applied current are mutually related in accordance with the type of the metal or the solution. However, conditions may be determined by appropriately selecting the metal and the solution to be used. I just need.

(Effect) According to the production method of the present invention, compared with the conventional high-temperature and high-pressure solution reaction in an autoclave, an accelerated reaction effect by applying an electric current is added, so that the composite oxide can be directly formed at a relatively low temperature and low pressure. It can be synthesized.

FIG. 1 is a schematic view of an apparatus used in carrying out the method of the present invention.

In this figure, 1 indicates the body of the autoclave,
Reference numeral 2 denotes an outer container, around which a heater 3 is arranged. An inner container 4 is disposed inside the outer container 2, and a working electrode 5 and the working electrode 5 are provided inside the inner container 4.
The counter electrode 6 is arranged to face the counter electrode. The inner container 4 contains, for example, a barium nitrate solution. The working electrode 5 and the counter electrode 6 are electrically connected to a DC power supply 7, the working electrode 5 is electrically connected to the anode side, and the counter electrode 6 is connected to the cathode side. Reference numeral 8 denotes a lid for sealing the main body 1 of the autoclave.

(Examples) Hereinafter, a method for producing a composite oxide fine powder of the present invention will be described in detail.

Example 1. Ba (NO ₃ ) ₂ with 0.5 regulation in the inner container of an autoclave
Was put. Next, 99.9% pure metal Ti was used as the working electrode.
Using a plate, a Pt plate was used as a counter electrode, and each of these metal plates was placed in an inner container. Temperature 250 ° C, saturated vapor pressure 3.8
Under MPa, a direct current of 100 mA / cm ² was passed. About after energizing
After 10 minutes, BaTiO ₃ started to form.

When the relationship between the bath voltage applied between the metal Ti plate as the working electrode and the Pt plate as the counter electrode and the processing time was measured, the results as shown in FIG. 2 were obtained.

As can be seen from FIG. 2, the voltage of the bath monotonously increases at the initial stage during the treatment, and then repeatedly increases and decreases rapidly. This is presumably because the oxide film was formed on the surface of the metal Ti plate in the initial stage of the treatment, and thereafter the macroscopic dissolution and growth of the oxide film were repeatedly occurring. Also, the bath voltage will be ± 50V at the stage when 10 minutes have passed after energization.
It vibrates rapidly between. Such a change is considered to be based on the dielectric breakdown of the oxide film generated by the local discharge.

Further, when the obtained powder was analyzed by X-ray diffraction, the resulting BaTiO ₃ powder was a single phase, which was secondary particles of several microns in which submicron particles were aggregated.
Dispersibility was relatively good.

FIG. 3 is a diagram showing an X-ray diffraction analysis of the BaTiO ₃ powder obtained in this example.

Example 2 In this example, the concentration of Ba (NO ₃ ) ₂ used in Example 1 was set to 0.1 N, and the other conditions were the same as in Example 1.

Although the obtained BaTiO ₃ powder contains a few unknown phases,
Most were BaTiO ₃ products.

FIG. 4 is a diagram showing an X-ray diffraction analysis of the BaTiO ₃ powder obtained in this example.

Example 3 0.1N LiNbO ₃ was placed in the inner container of an autoclave. Next, an Nb plate was used as a working electrode and a Pt plate was used as a counter electrode, and each of these metal plates was placed in an inner container. 100mA / cm ² under temperature 250 ℃, saturated vapor pressure 3.8MPa
Was passed. After energization, LiNbO ₃ powder began to be generated, and the obtained powder contained almost no impurities.

It has been confirmed that a composite oxide fine powder can also be obtained by using a metal oxide instead of a metal and electrochemically reacting it with a dissolved component in a high-temperature and high-pressure solution in an autoclave.

[Brief description of the drawings]

FIG. 1 is a schematic view of an autoclave device used for carrying out the method of the present invention. FIG. 2 is a diagram showing a relationship between a treatment time and a voltage of a bath applied between a metal Ti plate as a working electrode and a Pt plate as a counter electrode in Example 1. FIG. 3 is a diagram showing an X-ray diffraction analysis of the BaTiO ₃ powder obtained in Example 1. FIG. 4 is a diagram showing an X-ray diffraction analysis of the BaTiO ₃ powder obtained in Example 2. 1 is an autoclave main body, 2 is an outer container, 3 is a heater,
4 is an inner container, 5 is a working electrode, 6 is a counter electrode, 7 is a DC power supply, and 8 is a lid.

Claims (1)

(57) [Claims] 1. A method in which a metal placed in an autoclave is immersed in a solution and electrochemically oxidized in the solution in a high-temperature and high-pressure state to form an oxide, and simultaneously reacted with a dissolved component in the high-temperature and high-pressure solution. A method for producing a composite oxide fine powder, characterized by obtaining a composite oxide fine powder by the method.