JPS63222014A - Production of oxide fine powder of perovskite type - Google Patents

Abstract

PURPOSE:To readily obtain oxide fine powder of perovskite type without requiring grinding process, by blending a nitric acid solution containing metallic ions of Pb, Zr and Ti with a urea aqueous solution, heating, drying formed coprecipitated substance and calcining. CONSTITUTION:A nitric acid solution containing metallic ions of Pb, Zr and Ti is blended with an aqueous solution of urea and heated to form coprecipitated substance. Then the coprecipitated substance is dried and calcined to give oxide fine powder of perovskite type. Consequently, in forming coprecipitated metallic hydroxides, since urea is adopted instead of ammonia which has been conventionally used, the calcined coprecipitated substance will not become lump as it occurs in a conventional method, fine powder of submicron can be produced without being passed through grinding process and oxide fine powder of perovskite type with a small amount of admixture of impurities because of elimination of the process can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing perovskite-type oxide fine powder by a neutralization coprecipitation method using urea.

[Conventional technology]

Perovskite oxides are generally PbZrxTi1XO
! It is a solid solution represented as 1. The powder is in practical use as a raw material for electrical components such as ferroelectrics and piezoelectrics.

Since higher electrical properties (for example, electromechanical coupling coefficient) are required for the purpose of use, the oxide is required to have high purity and an average particle size of submicrons.

Various methods for producing perovskite-type oxide powder have been developed, but the ammonia-neutralized coprecipitation method (wet method), which has a low production cost and a simple process, has been industrially adopted.

This production method was developed based on the fact that metal hydroxides of Pb + Z r + T are poorly soluble in water. That is, ammonia water is dropped into a mixed solution in which each metal ion of Pb, Zr, and Ti is dissolved, or conversely, the mixed solution is dropped into ammonia water to make the mixed solution pH 6 to 8.
In this method, each ion of Pb, Zr, and Ti is coprecipitated as hydroxide, and the resulting coprecipitate is filtered, dried, and calcined to produce a robskite-type oxide powder.

[Problem that the invention seeks to solve]

The primary particles of the oxide powder produced by the ammonia neutralization coprecipitation method are fine and uniform in composition. However, in this method, each precipitate produced in the precipitate formation stage coagulates and coprecipitates, and the dried material becomes a very hard lump that retains its shape in the trench after calcination.

Therefore, in the neutralization coprecipitation method, the oxide powder is generally produced by pulverizing the dried material after drying or the calcined product after calcination using a pulverizer equipped with wear-resistant lining and media.

However, since the above-mentioned pulverization method is based on mechanical means,
The average particle size is only a few μm at most;
A major drawback of the conventional neutralization coprecipitation method was that the grinding process also took a long time, so contamination with impurities due to wear of the lining etc. was unavoidable.

[Failure to solve the problem]

Therefore, the present inventors improved the ammonia neutralization coprecipitation method and researched a method for producing perovskite-type oxide fine powder that does not require a pulverization process. The present invention was completed by discovering that the drawbacks of the method can be overcome.

That is, the present invention uses a nitric acid solution (hereinafter simply referred to as "nitric acid solution") containing metal ions of Pb, Zr, and Tj, and an aqueous solution (hereinafter simply referred to as "nitric acid solution") in which urea is dissolved in an amount greater than the amount required to react with the metal ions and cause co-precipitation. After mixing with urea solution J), the urea is decomposed by heating, reacted with each metal ion to form a hydroxide, and co-precipitated.The resulting coprecipitate is filtered, dried, and calcined. The gist of this paper is a method for producing perovskite-type oxides.

The present invention will be explained in detail below.

As the urea used in the present invention, a commercially available product with high purity is used.

The amount of urea added when preparing the urea solution is at least 6 mol or more, preferably 6 to 60 mol, per 1 mol of the lobskite type oxide to be produced. If the amount is less than 6 mol, the entire amount of each metal ion may not be coprecipitated.
If the amount exceeds 30 moles, urea may remain in the calcined product, which may require a very long calcining time, which is undesirable.

To dissolve urea in water, a urea solution is prepared according to a conventional method.

Next, we will explain how to make a nitric acid solution.

A nitric acid solution is prepared by dissolving a compound containing metal atoms of Pb and Zr+Ti in concentrated nitric acid. The dissolution method is a conventional method.

Examples of compounds include inorganic compounds such as nitrates and oxynitrates, as well as organic compounds such as metal alkoxides and acetates. It is acceptable for one compound to contain two or more of the above metal atoms.

The compounding ratio of the compound may be such that the atomic ratio of each metal of Pb, Zr, and Ti becomes a desired perovskite type oxide upon calcining, and the ratio is not particularly limited in the present invention.

Next, we will explain how to make a coprecipitate.

Add the urea solution to the nitric acid solution prepared as described above, or vice versa, and mix.

At this time, it is important to maintain the pH of the mixed solution at 2 or less in order to prevent precipitation of Pb, Zr, and Ti. The mixture is then heated while stirring. Urea is decomposed by heating and reacts with each metal ion of Pl:) + Zr and T1 to generate respective metal hydroxides and co-precipitate.

The heating temperature of the mixed liquid may be a temperature at which urea is efficiently decomposed, and is preferably 50 to 105°C. Below 50℃, the decomposition reaction is slow and precipitation formation is slow;
Exceeding this is not preferable because the urea decomposition products become gas and volatilize during heating.

The coprecipitate formed in the mixed solution is filtered and dried. The obtained dried product is mostly in the form of a fluffy powder of primary particles.

The obtained dried product is calcined in air at 500 to 100°C to obtain a perovskite type oxide fine powder with an average particle size of submicron.

[Effect]

The reason why the dried product or calcined product produced by the present invention does not form into lumps as in the conventional method but instead becomes a fluffy powder is not known, but it can be assumed as follows.

That is, by heating the mixed solution, urea partially decomposes and exists as urea and ammonium ions, making the mixed solution alkaline, while Pb, Zr, and Ti in the ionic state
Each metal reacts with an alkali to form a gel (hydroxide).

It is thought that urea and/or ammonium ions are adsorbed on the gel surface, repelled from each other, and co-precipitated without agglomeration, resulting in the dried product becoming fine and fluffy.

〔Example〕

Perovskite-type oxide fine powder was manufactured using a commercially available aqueous zirconium oxynitrate solution, titanium isopropoxide, and anhydrous lead nitrate.

Zirconium oxynitrate aqueous solution 52.5m/(ZrO0
6mol/7) with concentrated nitric acid filter Om7! After adding 44.4 m/! of titanium isopropoxide! (Tiro 32mo
1. //-) was added dropwise and stirred to give a clear solution. 101.0ii' of anhydrous lead nitrate was added to this solution and dissolved to form Pb and Zr.

A nitric acid solution with an atomic ratio of 1:0.52:0.4.8 was prepared.

On the other hand, a urea solution was prepared by dissolving the amount of urea shown in Table 1 in 1000 ml of pure water.

When a nitric acid solution was added to these urea solutions to prepare respective mixtures, the pH of each mixture was approximately 1.6. Next, each mixed liquid was heated under the conditions shown in Table 1 to cause coprecipitation, and at this time, the pH of each mixed liquid was approximately 8.

Each mixed solution was suction filtered (P paper 5C) to separate the coprecipitate, and
It was dried at ℃ for 24 hours. Each dried product obtained was a fluffy fine powder.

Each dried product was calcined in an electric furnace at 600° C. for 1 hour (2 hours only for Example 8) to produce a perovskite-type oxide. Each of the manufactured samples had a particle size of 5417 and was in a fine powder state.

The average particle diameter of each oxide fine powder was determined using a natural sedimentation particle size analyzer, and the results are also listed in Table 1. In addition, when the mineral composition was examined using an X-ray diffractometer, all samples contained PbZr1), 5
2T was a single mineral of 4.803.

Table 1 [Effects of the Invention] Since the present invention employs urea to create a coprecipitate of metal hydroxide, the calcined product does not form lumps unlike the conventional method, and the fine powder of Zabumicron is not subjected to the pulverizing process. The perovskite-type oxide fine powder can be produced without any process, and the perovskite-type oxide fine powder with less impurities can be obtained.

Claims (1)

[Claims] A nitric acid solution containing metal ions of Pb, Zr, and Ti and an aqueous solution in which urea is dissolved are mixed, heated to form a coprecipitate, and then the coprecipitate is dried and calcined. A method for producing perovskite-type oxide fine powder characterized by producing