JPS61251516A - Production of perovskite type oxide - Google Patents

Abstract

PURPOSE:To obtain the titled oxide at a low cost, by specifying the ionic concentration of a specific element and amount of ethanol in a process for producing the titled oxide by reacting the respective component elements in an aqueous solution with oxalic acid in the presence of the ethanol, and thermally decomposing the resultant precipitates. CONSTITUTION:A solution of oxalic acid in ethanol is dropped into an aqueous solution containing ions of elements to constitute a perovskite type oxide expressed by the formula ABO3 (A is one or more of Ba, Sr, Ca and Pb; B is one or more of Ti and Zr) while stirring the aqueous solution. The ionic concentration of the element (A) in the above-mentioned aqueous solution is adjusted to 0.2-1mol/l, and the amount of the ethanol to be used is 0.5-4vol. based on one vol. above-mentioned aqueous solution. Thus, precipitates of a precursor of the above-mentioned oxide are formed and thermally decomposed to give the above-mentioned oxide. According to this process, the sufficient amount of the ethanol to be used is small, and the productivity of reactors, distillation cost of the ethanol and distillation loss, etc., are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an ABOa perovskite oxide. More specifically, the present invention provides that a specific A
The present invention relates to a method for producing an oxide powder with excellent powder properties at a low manufacturing cost by using an aqueous solution with an ionic concentration and a specific volume ratio of the aqueous solution and ethanol.

Peropskite-type oxides, either by themselves or in the form of a solid solution of two or more of these oxides, are widely used as ferroelectric and piezoelectric materials in capacitors and the like. Most of these materials are commercialized as sintered bodies obtained by baking and solidifying their powders. The quality in this case is significantly influenced by the degree of sintering, and therefore, a powder with excellent powder properties is desired as a raw material for producing a good sintered body.

Prior Art The following method is known as a method for producing perovskite-type oxides.

(1) A method in which oxide powders of each component element are mixed and the mixture is heated to a high temperature to cause a solid phase reaction.

(2) A method in which oxalic acid is dropped into an aqueous solution containing ions of each component element to coprecipitate each component element as an oxalate salt, and the coprecipitated oxalate salt is thermally decomposed.

(3) A method in which a mixture of alkoxides of each component element is hydrolyzed and coprecipitated, and the coprecipitated hydrolyzate is thermally decomposed.

However, these methods have some problems and are not necessarily satisfactory. for example,
The solid-phase reaction (1) not only has problems with the manufacturing process in that it requires high temperatures and long periods of time, but also has problems with the product powder. That is, the powder obtained by this method cannot be sintered and therefore it is necessary to use a high temperature or use a sintering accelerator in the final stages of sintering. In the coprecipitation method (2), it is difficult to coprecipitate each component in the desired ratio because the solubility of each component in water, which is the coprecipitation medium for oxidation, is different, and it is difficult to coprecipitate each component in a single phase. The disadvantage is that it is difficult to obtain a composition with the same composition. Further, although the coprecipitation method (3) has the advantage of producing a product with high purity and high uniformity, it has the disadvantage that it is not easy to manufacture since each component is used as an alkoxide.

Yamamura et al. have proposed an improvement to the oxalate method described in (2) above as a method to eliminate the drawbacks of these conventional methods. That is, oxalic acid is soluble in ethanol, and Zr ions, T
i ion oxalate and PbXBa.

Utilizing the property that oxalates of ions selected from the Sr or Ca group (hereinafter collectively referred to as A ions) are completely insoluble in ethanol, A ions and Ti ions can be combined in ethanol. and react with oxalic acid to co-precipitate these ions as oxalate salts (Japanese Patent Application Laid-open No. 1983-1995).
No. 9-39722 Publication Ti) ions are co-precipitated as oxalate salts (Japanese Patent Application Laid-open No. 59-131505) to obtain a precipitate of high purity and uniform particle size with a desired composition (
Active ATiOs, which is a precursor of perovskite-type oxides, is obtained which is extremely easy to sinter when thermally decomposed.

A Zr Oa or A (Zr-Ti) Oa
A fine powder is obtained. In the technology disclosed therein,
The A ion is used as an aqueous solution or an ethanol-containing aqueous solution of the nitrate. On the other hand, it is said that titanium ions and zirconium ions are preferably used in the form of an Lt ethanol solution rather than an aqueous solution of titanium oxynitrate or zirconium oxynitrate. This is because when chloride is used as a source of these ions, chloride ions tend to remain in the coprecipitate, and even if the coprecipitate is fired at a high temperature, chloride ions remain and the fired product (i.e., the target oxide) ) may have an adverse effect when sintering.
Further, when Pb is used as the A ion, insoluble lead chloride is generated in the mixed aqueous solution. The method for producing titanium oxynitrate is to hydrolyze titanium tetrahedron with aqueous ammonia to precipitate it as a hydroxide, and then filter the resulting titanium hydroxide into nitric acid and dissolve it to form oxynitric acid. A method for obtaining a titanium solution is disclosed, and it is also disclosed that a zirconium oxynitrate solution can be obtained in exactly the same manner using zirconium oxychloride as a raw material.

Titanium ions or zirconium ions from these compounds and A ions are reacted with oxalic acid in the presence of ethanol to obtain an oxalate coprecipitate, which is filtered, dried, and pulverized to prevent thermal decomposition. If the baking is completed at a temperature (700-1000℃) at which weight change is no longer observed,
The desired perovskite type oxide is obtained, but
According to the disclosure, the produced pottery is ground and mixed again, and this powder is molded and heated to 1000-140
Sintering is performed at 0°C.

That is, in this prior improved technology, the coprecipitate ■
The finely powdered perovskite oxide obtained by sintering cannot be used directly for molding because the particles are fused together, so a re-pulverization and mixing step was necessary.

This re-grinding and mixing step, which is necessary in the prior improved invention, not only increases the process cost and reduces the reliability of the final product due to the contamination of impurities, but it is also problematic considering the characteristics of the perovskite-type oxide powder. be. In other words, the development of technology for manufacturing highly flexible piezoelectric films by compounding these perovskite-type oxide powders with polyvinyl fluoride IJ resin, polyoxymethylene resin, nitrile butadiene rubber, etc. is progressing. In this case, an easily dispersible fine powder with a uniform particle size distribution and no crystal distortion is required, but the fine powder obtained by re-grinding and mixing causes crystal distortion and does not meet expectations. This is because it is known that the performance that can be obtained cannot be obtained.

Yamamura and the present inventors have conducted intensive studies on the phenomenon of mutual fusion of fine particles of baked goods, and in this advanced improved technology, a small amount of chlorine ions remaining in the mixed aqueous solution of starting material ions are
It was discovered that the mutual fusion phenomenon of fine particles was induced during the firing stage, and furthermore, it was discovered that fusion could be suppressed by lowering the chlorine ion concentration to a predetermined value or less.
Application No. 13910/1983) was reached.

Problem with the prior art B: An easily dispersible type can be obtained by the method of Yamamura and the present inventors, in which sulfuric acid salts are precipitated in the presence of ethanol from an aqueous solution containing no more than an O or OS atom of chlorine ions per atom of element B or an aqueous solution containing ethanol. It became possible to obtain fine powder of perovskite-type oxide. However, when carrying out this method, it is said that it is preferable to use a large amount of ethanol, about 200 moles per mole of oxalic acid used as a precipitant. Reaction conditions are used that significantly increase the price of the final product, such as poor performance, high ethanol distillation costs, and distillation losses. Therefore, coupled with the preference for using expensive titanium alkoxides as starting materials for titanium, Yamamura and our method
This method has the disadvantage of being an expensive powder manufacturing method compared to the conventional oxide calcining method.

The present inventors conducted extensive studies on the reaction conditions of Yamamura and the present inventors' prior application (% Application No. 13910/1981), and obtained the following new knowledge, leading to the present invention.

When titanium oxynitrate is synthesized by the method disclosed in Japanese Patent Application No. 13910/1982, a highly concentrated aqueous solution of 2 to 3 mol Ti/L can be synthesized and is stable in the temperature range of 0 to 10°C. on the other hand,
The concentration of titanium oxynitrate synthesized by the method of Yamamura et al. (Japanese Unexamined Patent Publication No. 59-39722) was 0.01 in Example 1.
912? /Cr is disclosed. This is 0.39
Compatible with 9 mol Ti/l. Yamamura et al. prepared a mixed solution with lead nitrate and obtained an aqueous solution with a lead nitrate concentration of 0.133 mol/l. Approximately 4 ml of ethanol per 1 volume of this solution
．． The oxalate precipitation reaction is carried out using 9 volumes. This solution is mixed with ethanol of about 120 - to the PbTiOa 1y obtained by the precipitation reaction.

The previous application by Yamamura and the present inventors also discloses conditions in which exactly the same amount of ethanol is used.

The present inventors focused on the fact that high concentrations of titanium oxynitrate can exist stably in aqueous liquids with low chlorine content, and investigated to what concentration lead nitrate can be dissolved. In a precipitated filtration aqueous solution system of lead nitrate and/or titanium oxynitrate even at a concentration of about 0.6 mol Pb/l at a liquid temperature of around 0°C, the method disclosed in the prior application of Yamamura et al., Yamamura and the present inventors It was found that the aqueous solution was stable even without the low metal ion concentrations used.

Since the amount of water used in the Pb-Ti system can be reduced to about the same level as in the conventional application, it has been found that it is possible to reduce the amount of ethanol used to 6 even if the amount of ethanol added per volume of solution remains the same as before.

On the other hand, when oxalate is synthesized from a high-concentration metal ion solution, the concentration of by-product nitrate ions also increases proportionally. The effect of nitrate ions on the solubility of the precipitate is considered to be a salt effect. In particular, in nitric acid solutions, effects other than hydrogen ion concentration often appear and increase solubility (Kimome Seibu, ``
``Gravimetric Analysis'' Chapter 5, Kyoritsu Shuppan, 1965), there was a concern that the metal precipitate would be redissolved.

On the other hand, there is a possibility that the by-produced nitric acid reacts with titanyl lead peroxide, resulting in a large amount of T1 remaining in the mother liquor according to the following formula.
No. 8 (1965), etc.).

Pb Ti O (0204) t + 2 HNO3→
PbCzO4+ Ti 0(NO3)2 + HzCz
O<It is known that even in the prior invention, the dissolution of Ti cannot be completely suppressed even by the presence of ethanol, so if the concentration becomes high, an even larger amount of Ti will be re-eluted, and in the prior invention, the dissolution of Ti cannot be completely suppressed even by the presence of ethanol. It was thought that Pb, whose elution was virtually ignored, might re-elute. From these facts, it was predicted that the possibility of reducing the amount of ethanol in a highly concentrated solution system was low.

However, in the high-concentration metal ion aqueous solution system defined in the present invention, not only does the conventional amount of ethanol per volume of aqueous solution (i.e., 200 moles or more of ethanol per mole of oxalic acid) not require 0. By adding .5 to 4 volumes, preferably 1 to 3 volumes of ethanol, not only can the amount of Pb eluted be kept to a virtually negligible amount, but also the amount of Ti
Experiments have confirmed that the absolute amount of elution can be suppressed to the conventional amount.

In other words, the development of a method for synthesizing a high-concentration TiO(NOx)2 aqueous solution made it possible to increase the concentration of a Pb-Ti aqueous solution that could not be made conventionally, and as a result, something that could not have been predicted. However, it was discovered that even if the amount of ethanol used was reduced to about 1/1 of the conventional method, the produced precipitate was not affected at all, leading to the present invention.

In other words, under the reaction conditions disclosed in Example 1 of the present application, PbT
Only about 1 lid of ethanol is used per iO21, reducing the amount of ethanol used to 9% of the amount of ethanol used in the previous application (about 120 d).
We have succeeded in synthesizing Os powder.

A significant reduction in the amount of aqueous solution and ethanol can lead to a reduction in equipment-related costs mainly due to improved reactor production efficiency, leading to a reduction in production costs.

Furthermore, it is possible to reduce the size of the distillation column and reduce energy costs when reusing the ethanol used in the reaction through distillation purification. Furthermore, although several distillation losses occur for each distillation operation, a significant reduction in the amount used per unit of production means a significant reduction in the amount of expensive replenishment ethanol, resulting in a significant reduction in variable costs.

Furthermore, in the present invention, improvements have been made to the process of washing and removing the reaction mother liquor containing nitrate radicals, unreacted oxalic acid, etc. remaining in the produced precipitate with ethanol, and in Japanese Patent Application No. 13910/1983, PbTi0a 1 was heated at 120 d/min. By changing the precipitation and disintegration method, the amount of ethanol that used to be used was reduced to about 10
It has been found that even if the amount is reduced to -, the physical properties such as mutual fusion and particle size of the resulting oxides are not affected. A significant reduction in the amount of ethanol used in the washing process will lead to a significant reduction in distillation and purification costs, as in reaction applications, and will greatly contribute to lower production costs.

The peropskite oxide targeted by the present invention is ABOa
type, in which the A element is at least one element selected from the group consisting of Ba, Sr, (:a and Pb, and the B element is at least one element selected from the group consisting of Ti and Zr. That which is an element of.

Both Ti and Zr used in the present invention are subjected to the reaction as titanium oxynitrate and zirconium oxynitrate.

Peropskite oxides that can be synthesized by the method of the present invention include PbTiOa, PbZrOs, and Pb(Ti-
Zr) Ox, BaTiO3, Sr TiO3, CaT
iO3, BaZrO3, SrZrO3 and (:a Z
rO3 etc. can be mentioned.

Water-soluble compounds of element A necessary for synthesizing these compounds can be suitably combined and subjected to the sulfate precipitate formation reaction, but salts other than chlorides, especially nitrates, are most suitable. In either case, in an aqueous solution containing various ions or an ethanol-containing aqueous solution, Ct/T
t % Ct/ Zr 1 or C1/ (Tt +
Zr) It is the same as the first invention that it is necessary to select the purity of the raw material so that Ka is 0.05 or less, preferably Ha 0.02 or less.

The coprecipitated perovskite-type oxide precursor is obtained as a coprecipitate by reacting an aqueous solution of a compound of each element that provides element A ions and element B ions with oxalic acid in the presence of ethanol.

Specifically, an ethanol solution of citric acid is added dropwise to the aqueous solution, preferably with vigorous stirring.

Conversely, a method may be used in which the aqueous solution or the ethanol-containing aqueous solution is dropped into an ethanol solution of oxalic acid.

In carrying out the present invention, the ion concentration of element A in the aqueous solution is adjusted to 0.2-1 mol/1%, preferably 0.3-1 mol/1%.
tz is more preferably 0.5-1 mol/lK, and the amount of ethanol added together with oxalic acid is 0.5-4 L, preferably 1-3 volumes per volume of the aqueous solution. becomes.

According to the method of the present invention, there is no need for an ethanol-containing aqueous solution as claimed in the prior invention.

Embodiments of the present invention The concentration of the elemental ions to be used should be selected in the range of 0.2-1 mol/l depending on the amount of the elemental compound used dissolved in the aqueous solution in which titanium nitrate coexists. It is a quantity that fluctuates and is closely related to both.

Therefore, when using a relatively sparingly soluble salt such as barium nitrate, an ion concentration of about 0.3 mol/ml should be selected at a reaction temperature near room temperature. On the other hand, when using easily soluble salts such as calcium nitrate and lead nitrate, an ion concentration of about 0.6 mol/ml at 0°C can be easily selected.

There was no correlation between the amount of ethanol used per volume of the aqueous solution and the A ion concentration;
．． It can be determined in the range of 5-4 volumes. For example, PbTiO3
For the precursor, 2 volumes is enough to achieve the desired goal.

The amount of oxalic acid needs to be at least an amount that completely converts each elemental metal ion into an oxalate salt, but it is preferable to add about 25% more than the theoretical amount. The temperature of the oxalate salt formation reaction can be from 0°C to around room temperature.

A white precipitate forms upon addition of oxalic acid. Filter this to obtain a white cake. In order to remove nitrate ions, unreacted oxalic acid, chloride ions, etc. contained in the cake, it is preferable to redisperse the cake in ethanol and remove the remaining mother liquor by replacing it with ethanol.

The obtained white cake is dried and then crushed to obtain a perovskite-type oxide precursor powder. It is important to ensure the flow of an appropriate amount of oxygen during the crushing at this stage and the subsequent sintering. Note that the dry cake can be easily pulverized by a weak grinding force, and there is no need to completely disperse the particles at this stage, so there is no risk of contamination with impurities from the pulverizing means.

Preparation of perovskite type oxide fine powder
Bake at ℃. It is desirable that the firing temperature is low, but since the temperature at which thermal decomposition is completely completed varies depending on the compound, it is necessary to carry out the firing at a temperature at which no weight change is observed.

Commercially available tetraisopropyl titanium 500 - distilled water 70
00m to obtain hydroxide, which was filtered and washed three times with 10,100O pure water to obtain titanium hydroxide. Add this to 200 d of ice-cooled commercial special grade concentrated nitric acid,
After standing for day and night, it was filtered to obtain a titanium oxynitrate solution. T
i, determined gravimetrically as 11 degrees t-Ti 02, giving a result of 0.002 fromo Ti/v.

Titanium oxynitrate solution 427d to special grade lead nitrate 332.8
In addition to a mixed solution of 6f and 1277d of pure water, a Pb concentration of 0
．． 588 mol/L-aqueous solution Ti/Pb (atomic ratio)
A solution of = 1.17 was obtained and placed in a 101 (DSUS-27) reactor, which was cooled to -1°C. Ethanol 3
．． Oxalic acid-ethanol solution was prepared by dissolving 547.2 f of oxalic acid dihydrate in 4 t and cooled to -2°C. About 100 d/d of the cooled solution was stirred vigorously.
Oxalic acid ethanol was supplied using a rotary pump at a rate of 10 min to obtain a white precipitate. The reaction solution containing this white precipitate was transferred to a pressure filter (using AAF paper) with a filtration area of 530 d, and filtered with a back pressure of 1 g/dG.
was recovered. The obtained white cake was transferred to the above-mentioned Ioz reactor, 1.5 t of pure ethanol was added thereto, and the mixture was vigorously stirred for 15 minutes to break up the cake, which was then filtered using the above-mentioned pressure filter. This washing operation was repeated one more time, and the resulting white cake was dried in a vacuum dryer at 150°C for 2 hours. A portion of the dried cake was crushed in an agate mortar and then heated in a Matsufuru furnace at 800°C for 1 hour. After firing, the BET surface area is 3.8 W? /f, Ti
/Pb ratio (atomic ratio) = 1.02, and the crystal form determined by X-rays was mainly tetragonal PbTiO3, with a small amount of Pb'l'130y coexisting. A lead titanate powder was obtained having a crystal grain size of 450× determined from the 202 plane diffraction peak and a particle size of 0.20 μm determined from the BET surface area.

This lead titanate is suspended in water for about 30 seconds by applying vibrations using an ultrasonic cleaner, and a portion of the suspension is dropped onto a scanning electron microscope sample stage using a dropper, then dried and processed normally. After performing this, the state of the particles was observed. It was observed that particles having a diameter of 0.1 to 0.4 μm were well dispersed.

Claims (1)

[Claims] 1. ABO_3 type perovskite oxide (however, ABO_3 type perovskite oxide
represents at least one element selected from the group consisting of Ba, Sr, Ca and Pb, and B represents at least one element selected from the group consisting of Ti and Zr). A in the aqueous solution is brought into contact with oxalic acid in the presence of ethanol to produce a precipitate of a precursor of the oxide, and the precursor precipitate is thermally decomposed to produce the oxide. The ion concentration of the element is 0
．． 2-1 mol/l, and the amount of ethanol used is 0.5-4 volumes per 1 volume of the aqueous solution.
A method for producing perovskite-type oxides. 2. The method according to claim 1, wherein the ion concentration of element A is 0.3-1 mol/l. 3. The amount of ethanol used per 1 volume of the aqueous solution is 1-3
A method according to claim 1, characterized in that: