JPH0472770B2 - - Google Patents

Description

[Detailed description of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an ABO ₃ perovskite oxide. More specifically, the present invention relates to a method for producing an oxide powder having excellent powder properties by using isopropanol in a specific step in a known production method for this oxide. Perovskite 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. In this case, the quality is significantly influenced by the degree of sintering, and therefore, a powder with excellent powder characteristics is desired as a raw material for producing a good sintered body. Prior art As a method for producing perovskite-type oxides,
The following methods are known. (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, 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 is difficult to sinter, and therefore requires the use of high temperatures or the use of a sintering accelerator for sintering. In the coprecipitation method (2), it is difficult to coprecipitate each component in the desired ratio because the oxalates of each component have different solubility in water, which is the coprecipitation medium. 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 because 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 overcome the drawbacks of these conventional methods. That is, oxalic acid is soluble in ethanol, and Zr ion, oxalate of Ti ion, Pb,
Utilizing the property that oxalates of ions selected from the group of Ba, Sr, or Ca (hereinafter collectively referred to as A ions) are completely insoluble in ethanol, they can be combined with A ions in ethanol. Ti ions are reacted with oxalic acid to co-precipitate these ions as oxalate salts (Japanese Patent Application Laid-open No. 59-39722), and A ions and Zr ions or (Zr+
A precipitate (precursor of perovskite oxide) with a desired composition and high purity and uniform particle size can be obtained by co-precipitating Ti) ions as a sulfate salt (Japanese Patent Application Laid-Open No. 131505/1983). When this is thermally decomposed, active ATiO ₃ , AZrO ₃ or A(Zr·Ti)O ₃ fine powder, which is extremely easy to sinter, is obtained. In the technique disclosed therein, the A ion is used as an aqueous solution of the nitrate or an ethanol-containing aqueous solution. On the other hand, it is said that titanium ions and zirconium ions are preferably used as an aqueous solution or an ethanol-containing solution of titanium oxynitrate or zirconium oxynitrate. When chloride is used as a source of these ions, chlorine ions tend to remain in the coprecipitate, and even if the coprecipitate is fired at a high temperature, chlorine ions remain and the fired product (i.e., the target oxide) is sintered. This is because 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 tetrachloride with aqueous ammonia to precipitate it as a hydroxide, and then pour the titanium hydroxide obtained through this process into nitric acid and dissolve it to produce titanium oxynitrate. A method for obtaining the solution is disclosed, and it is disclosed that a zirconium oxynitrate solution can also be obtained in a similar manner as a raw material for zirconium oxychloride. 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. The desired perovskite-type oxide can be obtained by firing at a temperature (700-1000°C) at which it is completely finished and no weight change is observed; however, according to the disclosure, the fired product cannot be fired again. The powder is ground and mixed, and this powder is molded and sintered at 1000-1400°C. That is, in this prior improved technique, the finely powdered perovskite-type oxide obtained by sintering the coprecipitate cannot be directly used for molding because the particles are fused to each other. A re-grinding 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 also always poses a problem due to the characteristics of perovskite oxide powder. . In other words, the development of technology for manufacturing highly flexible piezoelectric films by combining these perovskite-type oxide powders with polyvinylidene fluoride resin, polyoxymethylene resin, nitrile butadiene rubber, etc. is progressing. In some cases, an easily dispersible fine powder with a uniform particle size distribution and no crystal distortion is required, but fine powder obtained by re-grinding and mixing causes crystal distortion, making it difficult to obtain the expected performance. This is because it is known that it will not be possible. Yamamura and the present inventors have conducted extensive studies on the mutual fusion phenomenon 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 cause the mutual fusion phenomenon of fine particles during the firing stage. They found that fusion was induced by lowering the chloride ion concentration to a predetermined value or less, and obtained an earlier invention (patent application filed in 1983).
No. 13910) was completed. The prior invention is an excellent method for obtaining easily dispersible ultrafine perovskite oxides, but it involves the problem that it is difficult to reduce production costs related to the distillation purification process due to the large amount of ethanol used. Was. In order to solve this problem, the present inventors discovered that by increasing the concentration of metal ions in an aqueous solution, it is possible to simultaneously reduce the amount of ethanol added to the aqueous solution, reducing the amount of ethanol used to 1/5 of the conventional amount.
- Confirmed that a fine powder with the desired properties could be obtained even if the reduction was reduced to 1/10 or less, and completed the invention entitled "Method for producing perovskite oxide" for which a patent application was filed on April 11, 1985. did. Problems with the prior art The invention of the prior application made it possible to significantly reduce the amount of ethanol used, but since ethanol is priced higher than methanol and isopropanol, the unit price of ethanol is low. The problem remained that it still occupies a large proportion of the synthesis process cost. SUMMARY OF THE INVENTION The present inventors have discovered that the present invention has similar properties to ethanol, namely: (1) It can dissolve oxalic acid. (2) Soluble in water in any proportion. (3) Dissolution of metal oxalates can be inhibited. In addition, we searched for an alcohol that satisfies the condition of being cheaper than ethanol, and obtained the following knowledge, leading to the present invention. Examples of alcohols that satisfy the above characteristics (1) and (2) include methanol, isopropanol, and normal propanol. According to Kagaku Kogyo Nippo's ``9285 Chemical Products,'' the above alcohol prices are approximately as follows (unit:
Kg).

[Table] Since normal propanol is not expected to be mass-produced like methanol and isopropanol, it does not meet the original purpose of the present invention. Since methanol is the most advantageous in terms of price, we attempted a PbTiO ₃ precursor precipitation synthesis reaction using methanol in place of ethanol in the amount used under conventional reaction conditions. The lead that only eluted was 0.7wt%.
It was also found that the particles were also eluted. In the inventors' previous invention, it was possible to control the Pb/Ti ratio in the precipitate by considering only the amount of titanium eluted. This is undesirable in that it makes effective control virtually impossible. Therefore, methanol is considered unsuitable as a substitute for ethanol. When a PbTiO ₃ precursor precipitation synthesis reaction was attempted using isopropanol and normal propanol in place of ethanol, the elution of lead into the solution was at the same level as when ethanol was used.
It has been found that the Ti/Pb ratio can also be easily controlled. Furthermore, it was found that the formed precipitate could be sufficiently separated using 4A paper. Namely, Yamamura et al.
The method of adding ethanol as a solubility control agent during oxalate precipitation synthesis, which has been proposed in the patent application filed on April 11, 2007, entitled "Production method of perovskite oxide", is based on the method of adding ethanol as a solubility control agent during oxalate precipitation synthesis. It has become clear that even if propanol is used instead, a precursor precipitate with the desired properties can be obtained. In addition, ethanol washing was conventionally carried out to remove unreacted oxalic acid contained in the precipitate and nitric acid produced by the reaction, but even if isopropanol and n-propanol are used in this washing process, lead still remains in the washing solution. It was confirmed that there were no adverse effects such as excessive dissolution. It was also confirmed that the amount of cleaning alcohol can be significantly reduced by selecting the crushing conditions, just as in the case of ethanol. Furthermore, it has been found that the method of synthesizing the precursor precipitation by adding 0.5 to 4 volumes of alcohol to 1 volume of the high ionic concentration aqueous solution and the aqueous solution disclosed in the prior invention can also be applied to isopropanol and n-promanol. Effects When forming an oxalate coprecipitate according to the present invention, it is possible to achieve a significant reduction in manufacturing costs, which could not be achieved with the prior invention. In other words, by converting the alcohol used from ethanol to isopropanol, the purchase price per kg decreases from 270 yen to 180-190 yen, which is 30-33% of the initial investment amount.
It becomes possible to reduce the cost of goods. Furthermore, it is obvious to those skilled in the art that this also means a reduction in the cost of replenishing losses caused by distillation operations and the like. When forming an oxalate co-precipitate according to the present invention, an alcohol solution containing oxalic acid is added dropwise to an aqueous solution of constituent element ions or an aqueous solution containing isopropanol, thereby forming a precursor that provides a perovskite-type oxide with excellent powder properties. A compound is obtained. That is, the oxide obtained by filtering, drying, crushing, and calcining the precursor compound precipitated as an oxalate does not have fine particles fused to each other, as in the prior art using ethanol. X-ray diffraction gives a perfect tetragonal perovskite oxide crystal structure. Detailed description of the invention Production of perovskite oxide precursor precipitate The perovskite oxide targeted by the present invention is
ABO type ₃ , in which the A element is Ba, Sr, Ca
and at least one selected from the group consisting of Pb
The element B is at least one element selected from the group consisting of Ti and Zr. Both Ti and Zr used in the present invention are subjected to the reaction as titanium oxide nitrate and zirconium oxide nitrate. Perovskite-type oxides that can be synthesized by the method of the present invention include PbTiO ₃ , PbZrO ₃ , Pb(Ti・Zr)
_O3 , _BaTiO3 , _SrTiO3 , _CaTiO3 , _BaZrO3 ,
Examples include SrZrO ₃ and CaZrO ₃ . The 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,
In particular, nitrates are most suitable. In either case, in the aqueous solution or ethanol-containing aqueous solution in which various ions are dissolved, C/Ti, C/Zr, or C/(Ti+Zr) is 0.05 or less, preferably
It is the same as the prior invention that it is necessary to select the purity of the raw material so that it is 0.02 or less. Co-precipitation The perovskite-type oxide precursor is obtained as a coprecipitate by reacting an aqueous solution or isopropanol-containing aqueous solution of a compound of each element that provides element A ions and B element ions with oxalic acid in the presence of isopropanol. Specifically, after adding isopropanol to the aqueous solution to an extent that no clouding occurs, an isopropanol solution of oxalic acid is added dropwise, preferably with vigorous stirring. Alternatively, a method may be used in which the aqueous solution or the isopropanol-containing aqueous solution is dropped into an isopropanol solution of oxalic acid. Depending on the type of metal ion, adding isopropanol to the aqueous solution may cause instability such as clouding.
An aqueous solution containing no isopropanol may be preferable as the solution of ions of each element. In particular, when the reaction is carried out in a system in which the A ion concentration in the aqueous solution is increased to 0.2-1 mol/ml, it is not necessary to prepare an isopropanol-containing aqueous solution. In addition, for such a high ion concentration aqueous solution, the amount of isopropanol added together with oxalic acid per volume of the aqueous solution is 0.5-
Even with a volume of 4, it is possible to obtain a perovskite-type oxide powder having sufficient desired properties. The amount of oxalic acid must 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 formation reaction can be from 0°C to around room temperature. A white precipitate forms upon addition of oxalic acid. After this process, a white cake is obtained. In order to remove nitrate ions, unreacted oxalic acid, chloride ions, etc. contained in the cake, it is preferable to redisperse the cake in isopropanol and remove the remaining mother liquor by replacing it with isopropanol. The obtained white cake is dried and then crushed to obtain a perovskite-type oxide precursor powder. Crushing at this stage is important in ensuring the flow of an appropriate amount of oxygen during 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. Production of perovskite type oxide fine powder The precursor powder is heated to an appropriate temperature, for example, 500-
Bake at 1000℃. It is desirable that the calcination temperature be low, but since the temperature at which thermal decomposition is completely completed varies depending on the compound, it is necessary to carry out the calcination at a temperature at which no weight change is observed. The content of the present invention will be explained in more detail below using experimental examples. Experimental Examples Example 1 200 ml of commercially available tetraisopropyl titanium was dropped into 2800 ml of distilled water to obtain hydroxide. After this was filtered, washing was repeated three times with 400 ml of pure water to obtain titanium hydroxide. This was added to 80 ml of ice-cooled commercially available special grade nitric acid, and the mixture was left to stand day and night and then filtered to obtain a titanium oxynitrate solution. The Ti concentration was determined gravimetrically as TiO ₂ and a result of 0.1256 g-Ti/ml was obtained. Add 17ml of titanium oxynitrate solution to special grade lead nitrate (purity 99.5wt)
%) 13.417g and 189.4ml of pure water,
Obtain a solution of Ti/Pb (atomic ratio) = 1.11 and store it at 1°C.
It was cooled to While stirring this mixed solution vigorously, 1505 ml of isopropanol cooled to 1°C containing 20.379 g of oxalic acid dihydrate was added at a rate of about 60 ml/min using a rotary pump, resulting in a white precipitate. I got it. This white precipitate was filtered under reduced pressure using a Buchner filter, the white cake obtained was stirred and dispersed in 490 ml of isopropanol, and the filtering operation was repeated three times. The white cake obtained was dried at 110°C.
It was ground in an agate mortar and fired in air at 700°C for 2 hours. BET surface area 9.0m ² /g, Ti/Pb (atomic ratio)
= 1.05, the crystal shape determined by X-rays is tetragonal
A PbTiO ₃ powder was obtained which was PbTiO ₃ and had a crystal grain size of 344 Å determined from its 202 plane diffraction peak and an average secondary particle size of 0.083 μm determined from its BET surface area. It was confirmed by X-ray diffraction that the amount corresponding to the excess Ti was present as PbTi ₃ O ₇ . When this lead titanate powder was observed using a scanning electron microscope, it was found to be an aggregate of fine particles of 0.1 μm or less. Furthermore, this lead titanate was suspended in water for about 30 seconds by applying vibrations using an ultrasonic cleaner, and a portion of the suspension was dropped onto an electron microscope sample stage using a dropper, then dried and subjected to normal processing. When the state of the particles was observed after performing this, it was observed that the fine particles were dispersed without mutual fusion. Example 2 15 ml of titanium oxynitrate (Ti = 0.1240 g/ml) obtained by the same method as Example 1 was mixed with commercially available special grade lead nitrate.
In addition to a mixed solution of 11.281g and 42.8ml of pure water, Ti/Pb
A solution with (atomic ratio)=1.14 was obtained and cooled to 0.5°C. 116 ml of isopropanol cooled to 0.5° C. containing 17.135 g of oxalic acid dihydrate was poured into the above mixed solution at a rate of about 5 ml/min while stirring vigorously to obtain a white precipitate. Filtration, washing, drying, crushing, and calcination (in air at 700°C for 2 hours) were carried out according to the procedure of Example 1, and the BET surface area was 2.6 m ² /g, and the presence of only tetragonal PbTiO ₃ with a crystal grain size of 500 Å was observed by X-rays. A powder was obtained in which it was confirmed that The average secondary particle diameter determined from the surface area was 0.29 μm, and observation using a scanning electron microscope did not show any fusion phenomenon between particles.

Claims (1)

[Claims] 1 ABO ₃ type perovskite oxide (however,
A represents at least one element selected from the group consisting of Ba, Sr, Ca and Pb, and B represents Ti and
At least one element selected from the group consisting of Zr) is brought into contact with oxalic acid in the presence of isopropanol to precipitate a precursor of the oxide. 1. A method for producing a perovskite-type oxide, the method comprising producing a perovskite-type oxide, and thermally decomposing the precursor precipitate.