JPH0688789B2 - Method for producing lead zirconate fine particles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing fine particles of lead zirconate, which is an antiferroelectric material used for electronic parts such as capacitors and electrostrictive materials. In particular, the present invention relates to a method for producing cubic phase lead zirconate fine particles having a cubic crystal system.

[Outline of Invention]

The present invention, when synthesizing fine particles of lead zirconate which is an antiferroelectric material, a hydrolysis product of a zirconium compound or a water-soluble zirconium salt and a water-soluble lead compound are heated and reacted in a strong alkaline aqueous solution,
The present invention is intended to enable wet synthesis of cubic phase lead zirconate fine particles having a fine and uniform particle size and a cubic crystal system.

[Conventional technology]

In recent years, ceramic materials have made remarkable progress as functional materials such as electronic materials, and it is said that the starting material significantly affects the subsequent molding, sinterability and properties of the final product. The method of synthesis and its properties have become important. In particular, a ferroelectric material having a small particle size and a uniform size is desired.

For example, in a multilayer ceramic capacitor, it is necessary to reduce the thickness of the ceramic layer in order to increase the capacity and reduce the size and weight, and it is an important issue to make the ferroelectric material, which is the raw material, into fine particles. There is. Further, it is strongly expected that the atomization as a raw material for electrostrictive materials, piezoelectric materials, transparent ceramic materials and the like will improve sinterability and temperature characteristics. Further, from the viewpoint of the withstand voltage of the capacitor, abnormal grain growth and generation of non-uniform particles in the sintering stage are not preferable, and development of a method for synthesizing uniform fine particles is urgently required.

On the other hand, as an antiferroelectric material of this kind, lead zirconate (PbZrO ₃ ) having various excellent properties has been attracting attention.

Conventionally, the lead zirconate (PbZrO ₃ ) fine particles are, for example, lead carbonate (PbCO ₃ ) or lead oxide (PbO) and zirconium oxide (ZrO ₂ ) are mixed and pulverized and mixed in a ball mill,
A so-called solid-phase reaction method is known in which calcination is performed at a high temperature of 1200 ° C., pulverization is performed again with a ball mill or the like until uniform, sieving is performed, and main calcination is performed. The crystal system of the lead zirconate fine particles is an orthorhombic system (orthorombic phase).

By the way, when synthesizing lead zirconate fine particles by such a method, evaporation of PbO becomes a big problem.
That is, the higher the temperature during the calcination, the more the amount of PbO vaporized exponentially increases, and the composition of the lead zirconate fine particles to be obtained changes, and the composition unevenness is microscopically within one particle. May occur. Therefore,
In order to avoid this, firing in a PbO atmosphere, etc.
It is necessary to perform fairly strict control during heat treatment. Alternatively, in order to suppress the evaporation of PbO, lower the temperature of calcination,
Although it is possible to carry out the main calcination after that, in this case, a considerable amount of unreacted PbO remains at the end of the calcination, and the unreacted PbO is vaporized in the stage of the main calcination. There is fear, and it is necessary to control the atmosphere here as well.

[Problems to be solved by the invention]

As described above, the lead zirconate fine particles obtained by the conventional solid-phase reaction method have a poor particle size distribution because they are pulverized by a ball mill, and in addition coarse particles cannot be avoided, and further, it takes a long time to pulverize. For this reason, it is difficult to obtain fine lead zirconate fine particles because impurities such as metal oxides are mixed.

Therefore, the present invention has been proposed in view of the above circumstances, and provides a method for producing lead zirconate fine particles having a fine particle size, a uniform particle size distribution, and no impurities mixed therein. The purpose is to In particular, lead zirconate is generally widely recognized as an orthorhombic phase, but an object of the present invention is to provide a synthetic method for producing lead zirconate in a cubic phase by selecting synthetic conditions.

[Means for solving problems]

The present inventors have developed a synthetic method capable of wet-synthesizing lead zirconate fine particles having a uniform fine particle size distribution and high purity, as a result of extensive research over a long period of time, pH value,
It was found that the cubic phase of lead zirconate was obtained as a single phase and the particle size distribution was uniform and fine by performing the wet synthesis with the Pb / Zr molar ratio and the reaction temperature set to predetermined values.

The present invention has been completed based on such findings, and a hydrolysis product of a zirconium compound or a water-soluble zirconium salt and a water-soluble lead compound are heated and reacted in a strong alkaline aqueous solution to form a cubic phase zirconium acid. It is characterized by producing lead fine particles.

That is, in the present invention, in order to produce the cubic phase lead zirconate fine particles, the hydrolysis product of the zirconium compound or the water-soluble zirconium salt and the hydrolysis product of the water-soluble lead compound or the water-soluble salt thereof are mixed. , Wet-react in a strong alkaline aqueous solution at a specified temperature range, wash the formed precipitate with water or warm water, and wash with K ⁺ , N
Alkali cations such as a ⁺ and Li ⁺ and anions such as Cl ⁻ may be completely removed, and filtration and drying may be performed.

Examples of the hydrolysis product of the zirconium compound or the water-soluble zirconium salt include zirconium chloride ZrCl ₄ ,
Zirconium oxyacid ZrOCl ₂ · 8H ₂ O, zirconium hydroxide Zr (OH) _4, zirconium oxynitrate (zirconyl _{nitrate) ZrO (NO 3) 2 ·} 2H 2 O, zirconium oxyacetate ZrO (CH ₃ C
OO) ₂ etc.

Further, as the water-soluble lead compound, lead acetate Pb (CH ₃ COO)
₂ · 3H ₂ O, lead nitrate Pb (NO _{3) 2,} etc. lead chloride PbCl ₄ can be used. However, when lead chloride is used, it is preferable to treat it with alkaline hot water in advance.

Further, as described above, as a device used when reacting at a high temperature of 100 ° C. or higher, a device called a so-called autoclave is used, and its inner container has a high alkali, a material capable of withstanding high temperature, For example, it is preferable to use polytetrafluoroethylene (so-called Teflon) or platinum.

Here, the pH of the aqueous solution during the reaction, the Pb / Zr molar ratio and the reaction temperature are important, and the crystal system of the obtained lead zirconate fine particles depends on the temperature and the Pb / Zr molar ratio. Is.

According to the experiments of the present inventors, in the above wet reaction, the pH of the aqueous solution is 13.5 or more and 14.5 or less, preferably pH 13.7 to 14.0.
And the molar ratio of Pb and Zr (hereinafter abbreviated as Pb / Zr)
Is 0.8 or more, preferably Pb / Zr = 1.0 to 1.7, reaction temperature 170
It was found that cubic phase lead zirconate (PbZrO ₃ ) fine particles can be synthesized in the range of ℃ to 250 ℃, preferably 200 to 220 ℃.

For example, while changing the pH of the aqueous solution, the Pb / Zr molar ratio of the starting material is set to 1.3, and a wet reaction is performed in the autoclave at a reaction temperature of 220 ° C. for 8 hours (not including the raising / lowering time. The same applies hereinafter), and When the relative amount of the cubic phase lead zirconate fine particles obtained after washing with water, filtration and drying was measured, the results shown in FIG. 1 were obtained. The relative amount of fine particles of lead zirconate produced here is the copper target.
It is a value obtained from the (110) peak area of the obtained diffracted X-ray peak by performing X-ray diffraction using a nickel filter (hereinafter the same). From FIG. 1, it was confirmed that the cubic phase lead zirconate fine particles were synthesized in a high yield as a single phase when the pH of the aqueous solution was 13.5 or more and 14.5 or less, preferably pH 13.7 to 14.0. . If the pH value is outside the range, lead zirconate fine particles are not synthesized at all.

On the other hand, the molar ratio Pb / Zr of Pb and Zr contained in the starting material is Pb / Zr.
Zr = 0.8 or more, preferably Pb / Zr = 1.0 to 1.7. For example, changing the mixing molar ratio of the starting materials to adjust the pH
14.0, the wet reaction was carried out in an autoclave at a reaction temperature of 215 ° C for 7 hours, and the relative amount of cubic phase lead zirconate fine particles after washing, filtration and drying was measured, and the results shown in Fig. 2 were obtained. It was From this Figure 2,
It was confirmed that when Pb / Zr = 0.8 or more, lead zirconate fine particles were produced in a single phase and in high yield, and the production amount was maximized particularly in the range of Pb / Zr = 1.0 to 1.7. Also, Pb
When /Zr=0.8 or less, the synthesized lead zirconate is in an orthorhombic phase, and when Pb / Zr = 1.7 or more, PbO is mixed and cubic phase lead zirconate cannot be obtained in a single phase.

In the above wet reaction, the reaction temperature is 170 ° C or higher and 250
The temperature may be lower than or equal to ℃, preferably 200 to 220 ℃. For example,
The reaction temperature was changed to pH 14.0, Pb / Zr = 1.0, wet reaction was carried out for 8 hours in an autoclave, and further washing with water, filtration,
When the relative amount of cubic phase lead zirconate fine particles after drying was measured, the results shown in FIG. 3 were obtained. From FIG. 3, it was confirmed that the relative amount of fine particles of lead zirconate produced increased as the reaction temperature increased, and the reaction temperature should be in the range of 170 ° C. or higher and 250 ° C. or lower. It was confirmed that when Pb / Zr = 1.0 and the temperature exceeded 220 ° C., the obtained lead zirconate fine particles were in an orthorhombic phase, and below 175 ° C., lead zirconate fine particles were not formed. . Also, Pb / Z
It was also found that when the r molar ratio was set to 1.7, the production temperature range of the cubic phase lead zirconate fine particles was expanded to 250 ° C.

Furthermore, in the above wet reaction, the reaction time was changed to
When /Zr=1.0 and pH14.0, the reaction temperature was set to 220 ° C in an autoclave, the wet reaction was performed, and the relative production amount of cubic phase lead zirconate fine particles after water washing, filtration, and drying was measured. The results shown in are obtained.
From FIG. 4, it was found that the production amount depends on the reaction time, and that the yield of the cubic phase lead zirconate fine particles tends to increase as the reaction time increases.
It was also confirmed that when Pb / Zr = 1.0, lead zirconate fine particles in the ortholonebic phase were produced when the reaction time exceeded 8 hours.

The water-soluble lead compound, which is a raw material component in the solution, has the property of precipitating as Pb, PbO, or PbO ₂ or evaporating when the temperature and time during the reaction become excessive. This deposited and evaporated substance is essential for the original synthesis of lead zirconate (PbZrO ₃ ). Therefore, the Pb / Zr molar ratio is substantially reduced, and when the Pb / Zr molar ratio is small, the crystal system becomes an ortholonebic phase. On the other hand, by adding an excessive amount of a water-soluble lead compound in advance to increase the apparent Pb / Zr molar ratio, the temperature and time range during the reaction for obtaining the cubic phase lead zirconate can be expanded. Is possible.

[Action]

A cubic phase lead zirconate having a fine and uniform particle size and no impurities mixed by heating and reacting a hydrolysis product of a zirconium compound or a water-soluble zirconium salt with a water-soluble lead compound in a strong alkaline aqueous solution. The fine particles are wet-synthesized. Further, the composition ratio of the obtained cubic phase lead zirconate fine particles can be accurately maintained by determining the reaction conditions.

〔Example〕

Hereinafter, the present invention will be described with reference to specific examples. Needless to say, the present invention is not limited to these examples.

Example 1 50 g of zirconium chloride ZrCl ₄ was dissolved in 100 ml of ice water over 2 to 3 minutes to prepare an aqueous zirconium chloride solution. Approximately 200 ml of 200 g / l potassium hydroxide KOH solution was added to this aqueous solution to prepare a suspension, and potassium hydroxide KOH was added to this suspension.
Was added to bring the pH to 7.0, and water was added to make 500 ml.

Then, this suspension was 50ml harvested, lead acetate _{Pb (CH 3 COO) 2 ·} 3H
8.14 g of ₂ O was added, potassium KOH was added subsequently, and water was further added to make 100 ml. The pH of this aqueous solution was 14.0.

Then, the above aqueous solution was reacted at 220 ° C. for 8 hours while stirring in a closed container using an autoclave. After the reaction, impurities such as alkali ions were removed by repeating decantation on the produced white precipitate, further filtered and washed with water, and then dried at 100 ° C. overnight.

FIG. 5 shows the result of the X-ray diffraction analysis of the fine particles obtained by the above operation. The diffraction pattern shown in Fig. 5 is AS
It was similar to the 20-608 orthorhombic (orthorhombic phase) lead zirconate (PbZrO ₃ ) of TM (The American Society for testing Materials) card. However, each diffraction peak was not a separated peak that is characteristic of the orthorhombic phase, but a peak without separation observed in the cubic system (cubic phase). Since this diffraction pattern can be indexed in the cubic phase, it was found to be cubic phase lead zirconate fine particles. A scanning electron microscope (SEM) photograph of the cubic phase lead zirconate fine particles (PbZrO ₃ ) fine particles is shown in FIG.

In addition, the calculation of the lattice constant was carried out by measuring X of the sample subjected to the above reaction.
It was determined from the line diffraction data. As a result, it was confirmed that the obtained lead zirconate fine particles were cubic crystals with a _o = 4.164Å.

Example 2 Pure water was dropped into 50 g of zirconium chloride ZrCl ₄ placed in a beaker over 2 to 3 minutes to prepare an aqueous zirconium chloride solution. To this aqueous solution, 40 g of potassium hydroxide KOH was added to form a white suspension, and potassium hydroxide KOH was added to this suspension.
After the solution was added to adjust the pH to 7.0, water was added to make 500 ml.

Then, the solution was 50ml harvested, lead acetate _{Pb (CH 3 COO) 2 ·} 3H 2 O
Was added to adjust the Pb / Zr molar ratio to 1.7. continue,
A potassium hydroxide KOH solution was added to this solution, and water was further added to make 100 ml. The pH of this aqueous solution was 14.0.

Next, this aqueous solution was reacted at 250 ° C. for 3 hours while stirring in a closed container using an autoclave. After the reaction, impurities such as alkali ions were removed by repeating decantation on the produced white precipitate, further filtered and washed with water, and then dried at 90 ° C. for 24 hours.

When the fine particles obtained by the above-mentioned operation were analyzed by the X-ray diffraction method, they were exactly the same as the diffraction pattern shown in FIG. 5 and could be indexed as a cubic phase. Further, the SEM photograph of the fine particles was a crystal having a shape and size similar to the crystal shown in FIG. Therefore, the particles are cubic lead zirconate particles (PbZrO ₃ ).
It turned out that

Example 3 50 g of zirconium chloride ZrCl ₄ was dissolved in 100 ml of ice water over 2 to 3 minutes to prepare a zirconium chloride aqueous solution. To this aqueous solution, concentrated ammonia water NH ₄ OH was added to form a white suspension, and ammonia water NH ₄ OH was added to this suspension to adjust the pH to 8.0.
Then, water was further added to make 500 ml.

Next, take 50 ml of this solution, add 7.11 g of lead nitrate PbNO ₃ ) _2, and add sodium hydroxide NaOH solution and water to obtain 100 ml.
And The pH of this aqueous solution was 13.7.

Next, this aqueous solution was reacted at 220 ° C. for 8 hours while stirring in a closed container using an autoclave. After the reaction, impurities such as alkali ions were removed by repeating decantation on the produced white precipitate, further filtered and washed with water, and then dried at 90 ° C. for 24 hours.

When the fine particles obtained by the above operation were analyzed by an X-ray diffraction method, they were exactly the same as the diffraction pattern shown in FIG. 5, and could be indexed as a cubic phase. The SEM photograph of the fine particles was a crystal having a shape and size similar to those of the crystal shown in FIG. Therefore,
These particles are cubic lead zirconate particles (PbZr
O ₃ ).

Example 4 200 g water in 100 g zirconium chloride ZrCl ₄ in a beaker
ml was added dropwise over 2 to 3 minutes to prepare a zirconium chloride aqueous solution. A 60 g sodium hydroxide NaOH solution was added to this aqueous solution to form a white suspension, and this suspension was mixed with lead nitrate Pb (N
142.13 g of O ₃ ) ₂ was added, and a predetermined amount of sodium hydroxide NaOH was further added to adjust the pH to 7.0, and water was further added to make 800 ml.

Next, 80 ml of this solution was sampled, and sodium hydroxide NaOH and water were added to make 100 ml. The pH of this solution was 14.0. In addition, the concentration of this solution is about twice as high as that of Examples 1 to 3.

Next, this solution was reacted at 220 ° C. for 8 hours while stirring in a closed container using an autoclave. After the reaction
The white precipitate thus formed was repeatedly decanted to remove impurities such as alkali ions, further filtered and washed with water, and then dried at 100 ° C. for a whole day and night.

By the above-mentioned operation, the amount of fine particles obtained was about twice as much as that of Examples 1 to 3. When the fine particles were analyzed by an X-ray diffraction method, they were exactly the same as the diffraction pattern shown in FIG. 5 and could be indexed as a cubic phase. Further, the SEM photograph of the fine particles was a crystal having a shape and size similar to the crystal shown in FIG. Therefore, these particles were found to be cubic cubic phase lead zirconate particles (PbZrO ₃ ).

〔The invention's effect〕

As is clear from the above description, according to the present invention, a hydrolyzate of a zirconium compound or a water-soluble zirconium salt and a water-soluble lead compound are subjected to a wet reaction in a strong alkaline aqueous solution under predetermined conditions. Since the cubic phase lead zirconate fine particles are synthesized in this manner, cubic cubic lead zirconate fine particles having a fine particle size and a uniform particle size distribution can be synthesized. Therefore, since the obtained lead zirconate fine particles are minute and uniform, they are suitable for various electronic materials such as electrostrictive materials, piezoelectric materials and transparent ceramic materials.
Further, the obtained lead zirconate fine particles have a cubic phase, have no directionality, and are excellent in dispersibility, so that various electronic materials can be easily molded.

Further, since the obtained fine particles are fine crystal particles, it becomes possible to sinter at a heat treatment temperature lower than that of the conventional one. Further, no special heat treatment step is required as compared with the solid-phase reaction method, and impurities such as metal oxides are not mixed. further,
A heating device is not required, and manufacturing time can be shortened or productivity can be improved.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the pH dependency of the relative production amount of lead zirconate fine particles, and FIG. 2 is a characteristic diagram showing the Pb / Zr (molar ratio) dependency of the relative production amount of lead zirconate fine particles.
FIG. 4 is a characteristic diagram showing the temperature dependence of the relative production amount of lead zirconate fine particles, FIG. 4 is a characteristic diagram showing the wet reaction time dependence of the relative production amount of lead zirconate fine particles, and FIG. 5 is the production of the present invention. The diffracted X-ray spectrum of the cubic phase lead zirconate fine particles produced by the method, and FIG. 6 are scanning electron micrographs of the obtained cubic phase lead zirconate fine particles.

Claims (1)

[Claims] 1. Zirconium characterized in that a hydrolysis product of a zirconium compound or a water-soluble zirconium salt and a water-soluble lead compound are heated and reacted in a strong alkaline aqueous solution to produce cubic lead zirconate fine particles. Method for producing lead oxide fine particles.