JP4375092B2 - Method for producing ceramic composition - Google Patents

Description

  The present invention relates to a method for producing a ceramic composition, and particularly to a method for producing a ceramic composition using a hydrothermal reaction.

  For example, in multilayer ceramic capacitors, in recent years, the dielectric ceramic layers provided therein have been increasingly made thinner and multilayered. Most recently, multilayer ceramic capacitors having a dielectric ceramic layer thickness of 1 μm and a number of laminated layers of several hundred layers have also been manufactured. When manufacturing such a multilayer ceramic capacitor, a barium titanate ceramic powder having a fine particle size of 0.1 μm or less and high crystallinity is used as a material constituting the dielectric ceramic layer.

  Similarly, in piezoelectric ceramic elements, in recent years, there has been an increasing demand for miniaturization and high performance. In order to meet such a demand, it is desired to realize, for example, a lead titanate (PT) -based powder having fine particles, high crystallinity, and extremely low impurities.

  In general, as a method for producing PT powder, a method (hydrothermal method) in which an aqueous solution of each component and an alkaline aqueous solution are mixed and subjected to a hydrothermal reaction is well known.

  Since this hydrothermal method does not require treatment at high temperature, the characteristics of the liquid phase reaction are utilized, the particles are fine and the composition is uniform, and it can be said to be the most preferable synthesis method.

  However, in the hydrothermal method, a hydrothermal reaction is performed using an alkaline aqueous solution as a mineralizer (reaction accelerator), so that a fatal amount of alkali metal element remains in the synthesized PT powder. There is a problem.

  For example, Non-Patent Document 1 describes a method of obtaining lead titanate (PT) powder of the order of several microns by hydrothermal method, but the residual amount of potassium as an alkali metal is reported to be 700 ppm by weight. Yes.

  On the other hand, in Patent Documents 1 and 2, hydrothermal synthesis of PT is carried out under conditions that do not contain an alkali.

  On the other hand, research and development of materials that can be used as substitutes for the above-described PT have been vigorously conducted. One candidate material that can replace PT is a bismuth layered compound. However, in a bismuth layered compound, the direction in which spontaneous polarization can be taken is two-dimensionally restricted. Therefore, when a normal ceramic is produced, even if a polarization treatment is performed, a large residual polarization cannot be obtained. There is a fatal drawback.

  Therefore, for example, as described in Non-Patent Document 2, an oriented ceramic is produced by using a particle blending technique such as hot forging to develop piezoelectric characteristics. In addition, as described in Non-Patent Document 3, attempts have been made to orient particles in a strong magnetic field.

  When producing an oriented ceramic using the particle orientation technique as described above, it is generally desired that the particles are monodispersed and single crystal-like particles. In particular, in the case of a bismuth layered compound, the single crystal has a unique shape such as a plate having a large aspect ratio.

One of the methods that can advantageously produce a bismuth layered compound having a unique shape as described above is the hydrothermal method described above. Non-Patent Document 4 reports that Bi ₄ Ti ₃ O ₁₂ single-phase particles were obtained by a hydrothermal reaction for 7 days at a temperature of 240 ° C., and Non-Patent Document 5 reported that a temperature of 240 ° C. for 3 days. There is a report that Bi ₄ Ti ₃ O ₁₂ single-phase particles were obtained by a hydrothermal reaction.

  However, these methods described in Non-Patent Documents 4 and 5 require a long-time hydrothermal reaction such as 7 days or 3 days and are not practically usable. In these methods, A large amount of potassium hydroxide is used, and these documents have no direct description, but there is a concern that a large amount of alkali metal element remains in the obtained powder.

  As mentioned above, some prior arts have to solve the problem of remaining large amounts of alkali metal elements. This is because, as is well known, alkali metal elements significantly reduce the sinterability of ceramics and the electrical characteristics of the obtained sintered body.

As a technique that is highly likely to solve the above-described problem, for example, there is a method described in Patent Document 3. In patent document 3, the synthesis | combination of barium titanate powder and strontium titanate powder is disclosed in the Examples, and the hydrothermal reaction powder is again subjected to hydrothermal reaction treatment on the hydrothermal synthesis powder obtained by hydrothermal reaction. It is described that the amount of residual alkali can be reduced.
JP 11-335122 A JP-A-9-286617 JP-A-7-69634 Proceedings of the 1993 Annual Meeting of the Ceramic Society of Japan, p.24-25 Tadashi Takenaka, Journal of the Ceramic Society of Japan, 110 [41] 2002, p.215-224 Proceedings of the 2002 Annual Meeting of the Ceramic Society of Japan, p.111 AV Prasda rao and S. Komarneni, ISAF '96, Proc. IEEE Int. Symp. Appl. Ferroelect., 10th, vol.2, Pub. Inst. Electro. Engineers, NY, 1996, p.923-925 Yanhui Shi, Changsheng Cao, Shouhua Feng, Materials Letters 46 (2000), p.270-273

  Patent Document 3 described above describes, as an example, the synthesis of a perovskite type compound containing an alkaline earth metal element such as barium titanate. However, even when the method disclosed in Patent Document 3 is applied as it is when synthesizing a perovskite type compound containing lead element such as PT or when synthesizing a bismuth layered compound, it is satisfactory. It is not always possible to obtain a correct result.

  In fact, Patent Document 3 discloses that a solvent having a pH of 7 to 10 is applied in the second hydrothermal reaction treatment step. As a result of the experiment, the present inventor found that a perovskite type compound containing lead element or bismuth was used. In the case of a layered compound, it has been found that the optimum pH of the aqueous solvent during the second hydrothermal reaction treatment for reducing the residual alkali amount is different from 7 to 10 disclosed in Patent Document 3.

  Therefore, the object of the present invention is to reduce the amount of residual alkali in the obtained ceramic composition while using a hydrothermal reaction, and to reduce the amount of alkali added to promote the hydrothermal reaction. An object of the present invention is to provide a method for producing such a ceramic composition, in which the synthesis can be performed and the obtained crystal grains can be reduced.

  Another specific object of the present invention is to provide a method capable of reducing the amount of residual alkali in a method for producing a ceramic composition having single-phase plate-like particles such as a bismuth layered compound.

The inventions, in a first aspect, is directed to a process for the preparation of a ceramic composition is lead titanate or bismuth titanate, in a second aspect, the bismuth layer containing bismuth and titanium and alkaline earth metal elements The present invention is directed to a method for producing a ceramic composition that is a compound, and is characterized by comprising the following steps in order to solve the technical problems described above.

  First, a first step of obtaining a hydroxide slurry by mixing a constituent element solution containing constituent elements of a ceramic composition to be obtained and an alkali hydroxide solution for taking out ions of the constituent elements as hydroxides It has. In the first step, the ions of the constituent elements are converted into hydroxides.

  Next, the hydroxide contained in the hydroxide slurry obtained in the first step is washed and adjusted so that the pH of the hydroxide slurry is 9 or less but not 6 or less. The second step is obtained, and then an alkali hydroxide solution as a mineralizer (reaction accelerator) is added to the washed product obtained in the second step, and a hydrothermal reaction is carried out to react. A third step is performed to obtain a product.

  The second step described above constitutes an important characteristic structure in the present invention. By carrying out the second step, impurities adhering to the hydroxide (mainly alkali hydroxide other than the constituent elements) are removed. In addition to being able to be removed, the constituent elements can be uniformly mixed at the molecular level, and therefore the reactivity of the cleaning material that causes the hydrothermal reaction in the third step can be increased. From the above, as a result, the amount of alkali hydroxide added in the third step can be reduced. And in a 3rd process, each structural element is synthesize | combined so that a composition may be produced | generated by hydrothermal reaction.

  Next, the 4th process which stir-washes with respect to the reaction material obtained at the 3rd process is implemented. In the fourth step, impurities attached to the reaction product in the third step are removed.

Next, after the fourth step, an aqueous solvent is added to the reaction product, the slurry is adjusted so that the pH is more than 5 and less than 7, and the hydrothermal reaction is performed again. The fifth step is performed. By carrying out this fifth step, impurities can be further removed.

Then, after the fifth step, a drying step is performed in which the reaction product is dried to obtain a dried product.

In the case of the aforementioned second aspect, in which the ceramic composition to be produced according to the present invention is a bismuth layered compound containing bismuth, titanium, and an alkaline earth metal element , in the first step, the constituent element solution is and a bismuth and titanium, in the third step, the washing product obtained in the second step, that further to the addition of the hydroxide solution or alkaline earth metals including alkaline earth metal element.

In the second aspect described above, in the first step, the constituent element solution may contain an alkaline earth metal element, but preferably does not contain it. This is because the alkaline earth metal element is eluted by the cleaning performed in the second step, and the alkaline earth metal element added in the first step does not substantially remain in the cleaning product obtained by the subsequent cleaning . It will be useless. Not only that, but the eluted bismuth titanate single phase or bismuth oxide phase is by-produced by, for example, Ca or Sr.

  In the third step, the amount of alkali hydroxide added as a mineralizer is reduced so that the normality of the alkali hydroxide solution is 0.01 N or less, and the hydrothermal reaction time is 1 hour. It is preferable to shorten the length as follows.

  Moreover, it is preferable to further include a heat treatment step in which the particles obtained from the dried product dried in the drying step are heat treated at a temperature of 400 ° C. or higher and 700 ° C. or lower.

  According to the present invention, in the second step before the third step in which the hydrothermal reaction is performed, the pH of the hydroxide slurry is adjusted to 9 or less but not to be 6 or less so as to obtain a washed product. Therefore, impurities adhering to the hydroxide can be removed and the constituent elements can be uniformly mixed at the molecular level. Therefore, it is possible to increase the reactivity of the washed product that causes the hydrothermal reaction in the third step, thereby reducing the amount of alkali hydroxide added as a mineralizer (reaction accelerator) added in the third step. it can. As a result, not only can the crystal grains of the obtained ceramic composition be reduced, but also the amount of residual alkali can be reduced, the sinterability of the ceramic due to alkali metal elements and the electrical properties of the sintered body can be reduced. Problems such as deterioration of characteristics can be advantageously avoided.

Further, according to the present invention, the reaction product obtained in the third step, the stirred wash, after the fourth step, the reaction product was added an aqueous solvent, and pH of greater than 5 The fifth step of adjusting the slurry so that it becomes less than 7 and allowing the hydrothermal reaction to be carried out again is carried out, so that impurities can be further removed, and the sintered body of the obtained ceramic composition The electrical characteristics can be further improved.

In particular, the ceramic composition to be produced according to the present invention is a bismuth such as, for example, bismuth calcium titanate (CBT: CaBi ₄ Ti ₄ O ₁₅ ) or bismuth strontium titanate (SBTi: SrBi ₃ Ti ₄ O ₁₅ ). In the case of the second aspect, which is a bismuth layered compound containing titanium, an alkaline earth metal element, the constituent element solution is bismuth and titanium in the first step while carrying out the first to fifth steps. wherein the door, in a third step, the washing product obtained in the second step, since as further addition of hydroxide solution or alkaline earth metals including alkaline earth metal element such as titanium Alkaline earth metals such as Ca and Sr that do not by-produce bismuth acid single phase or bismuth oxide phase and have higher electrical insulation To give a compound of the bismuth layer single phase containing hydrogen as a constituent element.

  Further, in the third step, particles obtained from the dried product dried in the drying step or the hydrothermal reaction time is set to one hour or less while the normality of the alkali hydroxide solution is set to 0.01 N or less. If the heat treatment is further performed at a temperature of 400 ° C. or higher and 700 ° C. or lower, the crystal grains of the obtained ceramic composition can be made extremely small, for example, 15 nm.

  On the other hand, when the normality of the alkali hydroxide solution exceeds 0.01 normal or the hydrothermal reaction time exceeds 1 hour, a product having a relatively large particle size such as 30 nm or more is directly generated. .

  If the normality of the alkali hydroxide solution is too low or the hydrothermal reaction time is too short, even if heat treatment is performed later, only an amorphous one may be obtained. Therefore, in order to obtain the above-described effect more reliably, the normality of the alkali hydroxide solution is 0.001 N or more and 0.01 N or less, and the hydrothermal reaction time is 5 minutes or more and 1 hour. The following is preferable.

  The temperature applied in the heat treatment step after the drying step is preferably 450 ° C. or higher and 600 ° C. or lower. Further, this heat treatment is preferably a rapid heat treatment, for example, the temperature is raised and lowered at a rate of 5 ° C./min or more, and the heat treatment keep time is preferably 10 minutes or less.

  On the other hand, when the heating / cooling rate is less than 5 ° C./minute, the heat treatment temperature exceeds 700 ° C., or the heat treatment keep time exceeds 10 minutes, grain growth occurs, for example, at 50 nm or more. Sometimes.

  The heat treatment atmosphere is not particularly limited, but a ceramic composition having a smaller particle size can be obtained in a neutral atmosphere such as nitrogen than in the air.

  Embodiments of the present invention will be described below based on examples.

  Titanium tetraisopropoxide: 28.34 g (containing 0.1 mol as titanium element) and isopropyl alcohol (IPA): 118.15 g were weighed to prepare an IPA solution of titanium tetraisopropoxide. On the other hand, 34.95 g of lead nitrate (containing 0.105 mol as a lead element) was dissolved in 170.37 g of pure water to prepare a lead nitrate aqueous solution.

  Next, while stirring the IPA solution of titanium tetraisopropoxide at high speed with a high speed stirrer, a lead nitrate aqueous solution was dropped using a micro tubing pump to prepare a mixed slurry of the lead nitrate aqueous solution and titanium hydroxide. Then, while stirring the mixed slurry at a high speed with a high speed stirrer, 8N potassium hydroxide solution: 34.86 g (containing 0.21 mol as potassium hydroxide) was dropped using a microtubing pump, and lead element and A hydroxide slurry in which titanium element was mixed was obtained (first step).

  Next, the hydroxide slurry obtained in the first step was dehydrated to obtain a dehydrated cake. Next, 300 g of pure water is added to the dehydrated cake to prepare a slurry, and the slurry is stirred at high speed for about 30 minutes using a high-speed stirrer and then dehydrated three times. As a result, lead element and titanium element were uniformly mixed at the molecular level, and impurities such as potassium hydroxide and potassium nitrate were removed. The pH of the filtrate obtained by the final dehydration in this step was 6.8 (the second step).

  Next, 8N potassium hydroxide solution: 0.498 g (containing 0.003 mol as potassium hydroxide) and pure water: 299.625 g with respect to the dehydrated cake as the washed product obtained in the second step Was added to make a slurry. In addition, the alkaline solvent normality at the time of the hydrothermal reaction of this slurry is 0.01 normal. Next, the slurry was stirred at a high speed for about 30 minutes using a high-speed stirrer, and then charged into a polytetrafluoroethylene beaker, and the beaker was attached to a stirring type autoclave having an internal volume of 0.5 liter. The hydrothermal reaction was carried out under conditions of 4 hours and 200 rpm (the third step).

  Next, after completion of the third step, the slurry was dehydrated to obtain a dehydrated cake as a reaction product. Next, 300 g of pure water was added to the dehydrated cake to prepare a slurry, and this slurry was stirred at high speed for about 30 minutes using a high-speed stirrer and then dehydrated three times ( The fourth step).

  Next, 300 g of pure water was added to the dehydrated cake obtained in the fourth step to prepare a slurry, and this slurry was stirred at a high speed for about 30 minutes using a high-speed stirrer. Thereafter, the slurry was put into a polytetrafluoroethylene beaker, and the beaker was attached to a stirring type autoclave having an internal volume of 0.5 liter, and subjected to a hydrothermal reaction again at 200 ° C. for 4 hours and 200 rpm. (The fifth step).

  Next, after completion of the fifth step, dehydration was performed, and the obtained dehydrated cake was placed in an oven set at a temperature of 100 ° C. and dried for 12 hours. Thereafter, the particle size was adjusted with a 40-mesh sieve to obtain the intended ceramic composition powder.

  The following evaluation results were obtained for the ceramic composition powder thus obtained.

  First, particles constituting the obtained ceramic composition powder were tetragonal lead titanate (PT) single phase particles as a result of XRD qualitative analysis. When precise XRD measurement was performed at the same time, the c / a axial ratio was 1.065, which was the same as in the bulk case. As a result of SEM and TEM observation, the particles constituting the ceramic composition had an anisotropic rectangular parallelepiped shape, and the particle size was 30 nm. Further, when an electron beam diffraction image was observed, a clear spot was observed, and it was revealed that the particles were single crystal-like lead titanate particles. Further, when the amount of residual potassium in the particles was analyzed, it was found that the amount of residual potassium was as extremely low as 40 ppm by weight.

  As described above, according to Example 1, it was possible to obtain single crystal-like lead titanate particles having an extremely small residual potassium content of 40 ppm by weight, uniform in composition, and having a particle diameter of 30 nm.

  For the purpose of removing impurities, it is common practice to wash the produced particles, which corresponds to the fourth step in Example 1 above. In Example 1 above, in addition to this washing operation, the fifth step is carried out, and here the washing operation under hydrothermal conditions is further carried out to reduce the residual potassium amount to 40 ppm by weight. Can do.

  In the washing operation under the hydrothermal condition described above, it is desirable to add an aqueous solvent so that the pH is more than 5 and less than 7. This is because when the pH is 7 or more, the effect of removing alkali metal elements such as potassium is reduced, and when the pH is 5 or less, the lead element is eluted. In relation to this, the above-mentioned Patent Document 3 discloses that the residual alkali amount can be reduced by re-hydrothermal treatment, but the solvent at that time may be neutral or alkaline (pH 7 to 10). It is preferred. This Patent Document 3 mainly discloses an example of synthesizing a perovskite type compound containing an alkaline earth metal element such as barium titanate. On the other hand, in Example 1 above, a perovskite type compound containing lead element is synthesized, and the optimum pH of the aqueous solvent in the fifth step of performing the hydrothermal treatment again is disclosed in Patent Document 3. It should be noted that the pH is different.

  Moreover, it is preferable that the reaction temperature under hydrothermal conditions is equal to or higher than the hydrothermal reaction temperature in the third step. In consideration of the heat resistance of the polytetrafluoroethylene beaker used, this temperature should be about 250 ° C. as an upper limit.

  Also, as is clear from Example 1 above, it should be noted that the alkali solvent normality during the hydrothermal reaction carried out in the third step can be made extremely small. More specifically, the alkali solvent normality during the hydrothermal reaction in Example 1 is as extremely small as 0.01 normal. In normal hydrothermal synthesis, the alkali solvent normality at the time of hydrothermal reaction is 1 N or more. For example, in the above-mentioned Patent Document 1, it is described as a requirement of the claims that the hydrothermal reaction is performed in an alkaline solvent of 1 N or more. On the other hand, in Example 1 described above, the second step is carried out, in which potassium hydroxide and potassium nitrate are removed and at the same time an operation of uniformly mixing lead element and titanium element at the molecular level is performed. Yes. As a result, the normality of the alkaline solvent during the hydrothermal reaction in the third step could be reduced.

  As described above, the normality of the alkaline solvent during the hydrothermal reaction in Example 1 is 0.01 N, which corresponds to about 12 in pH. Such a hydrothermal reaction in the third step is not limited to a pH of about 12, but is preferably carried out in an alkaline region of pH 8-14.

  The washing operation performed in the second step is performed so that the pH of the filtrate obtained by dehydration becomes 9 or less but not 6 or less. If the washing operation is performed more than necessary, and the pH of the filtrate is 6 or less, elution of the lead component occurs, causing a compositional deviation. On the other hand, if the washing operation is insufficient and the pH of the filtrate exceeds 9, This is because lead titanate single-phase particles may not be obtained, or the amount of residual potassium may exceed 100 ppm by weight in the final product powder. In addition, Preferably, washing | cleaning operation is implemented until pH of a filtrate will be 7-8.

  As in Example 1, titanium tetraisopropoxide: 28.34 g (containing 0.1 mol of titanium element) and IPA: 118.15 g were weighed to prepare an IPA solution of titanium tetraisopropoxide. On the other hand, 34.95 g of lead nitrate (containing 0.105 mol as a lead element) was dissolved in 170.37 g of pure water to prepare a lead nitrate aqueous solution.

  Next, while stirring the IPA solution of titanium tetraisopropoxide at high speed with a high speed stirrer, a lead nitrate aqueous solution was dropped using a micro tubing pump to prepare a mixed slurry of the lead nitrate aqueous solution and titanium hydroxide. Then, while stirring the mixed slurry at a high speed with a high speed stirrer, 8N potassium hydroxide solution: 34.86 g (containing 0.21 mol as potassium hydroxide) was dropped using a microtubing pump, and lead element and A hydroxide slurry in which titanium element was mixed was obtained (first step).

  Next, after removing about 200 ml of the supernatant of the hydroxide slurry obtained in the first step, 200 g of pure water was added to prepare a slurry, and this slurry was used for 30 minutes using a high-speed stirrer. Stir to high speed. This operation was repeated 6 times to obtain a slurry in which lead element and titanium element were uniformly mixed at the molecular level, and impurities such as potassium hydroxide and potassium nitrate were removed. The pH of the solvent in the finally obtained slurry was 7.1 (the second step).

  Next, after removing 0.498 g of supernatant liquid from the slurry as the washed product obtained in the second step, 8 N potassium hydroxide solution: 0.498 g (0.003 mol as potassium hydroxide) Content) was added to prepare a slurry. Next, the slurry was stirred at a high speed for about 30 minutes using a high-speed stirrer, and then charged into a polytetrafluoroethylene beaker, and the beaker was attached to a stirring type autoclave having an internal volume of 0.5 liter. The hydrothermal reaction was carried out for 4 hours and 200 rpm. In addition, the alkali solvent normality at the time of the hydrothermal reaction of this slurry was set to 0.01 normal (the above, 3rd process).

  Next, after removing about 200 ml of supernatant liquid from the slurry as a reactant obtained in the third step, 200 g of pure water was added to prepare a slurry, and this slurry was mixed with a high-speed stirrer. And stirred at high speed for about 30 minutes. This operation was repeated 6 times (the fourth step).

  Next, the slurry obtained in the fourth step is put into a polytetrafluoroethylene beaker, and this beaker is attached to a stirring type autoclave having an internal volume of 0.5 liter, under the conditions of 200 ° C., 4 hours and 200 rpm, The hydrothermal reaction was performed again (the fifth step).

  Next, after removing about 200 ml of supernatant liquid from the slurry obtained in the fifth step, 200 g of pure water was added to prepare a slurry, and this slurry was used for 30 minutes using a high-speed stirrer. Stir to high speed. This operation was repeated three times. Then, the finally obtained slurry was evaporated to dryness to obtain a dry powder, and then the dried powder was subjected to particle size adjustment with a 40 mesh sieve to obtain a target ceramic composition powder. .

  The ceramic composition powder thus obtained was evaluated in the same manner as in Example 1. First, as a result of XRD qualitative analysis, it was tetragonal lead titanate (PT) single-phase particles. . When the precise XRD measurement was performed simultaneously, the c / a axial ratio was 1.063. As a result of SEM and TEM observation, the particles constituting the ceramic composition had an anisotropic rectangular parallelepiped shape, and the particle size was 32 nm. Further, when an electron beam diffraction image was observed, a clear spot was observed, and it was revealed that the particles were single crystal-like lead titanate particles. Further, when the amount of residual potassium in the particles was analyzed, it was found that the amount of potassium was extremely small, 43 ppm by weight.

  In the third step of Example 1 above, 8N potassium hydroxide solution: 4.98 g (containing 0.03 mol as potassium hydroxide) and pure water: 296.25 g were added to the dehydrated cake to form a slurry. A ceramic composition powder was obtained in the same manner as in Example 1 except that was prepared. In addition, the alkali solvent normalization degree at the time of the hydrothermal reaction in the third step of Example 3 is 0.1 normal.

  The obtained ceramic composition powder was evaluated in the same manner as in Example 1. First, as a result of XRD qualitative analysis, it was tetragonal lead titanate (PT) single-phase particles. Further, when the precise XRD measurement was performed at the same time, the c / a axial ratio was 1.067, which was the same value as in the bulk case. As a result of SEM and TEM observation, the obtained particles had an anisotropic rectangular parallelepiped shape, and the particle size was 100 nm (0.1 μm). Further, when an electron beam diffraction image was observed, a clear spot was observed, and it was revealed that the particles were single crystal-like lead titanate particles. Further, when the amount of residual potassium in the particles was analyzed, it was found that the amount of residual potassium was as small as 60 ppm by weight.

  In the third step of Example 1, 8 N potassium hydroxide solution: 0.3984 g (containing 0.0024 mol as potassium hydroxide) and pure water: 299.602 g were added to the dehydrated cake to prepare a slurry. Except for the production, the fourth step was performed under the same conditions as in Example 1 above. In addition, the alkali solvent normalization degree at the time of the hydrothermal reaction in the third step of Example 4 is 0.008 normal.

Thereafter, without performing the step corresponding to the fifth step of Example 1, the dehydrated cake obtained in the fourth step was placed in an oven set at a temperature of 100 ° C. and dried for 12 hours. The fourth embodiment is outside the scope of the present invention in that the step corresponding to the fifth step of the first embodiment is not performed. Thereafter, the sizing was performed using a 40-mesh sieve. As a result of analyzing the particles obtained in this drying step by X-ray diffraction, it was found to be amorphous. Moreover, as a result of SEM observation, the particles were uniform in size and having a particle diameter of 10 nm.

  Next, the particles obtained in the drying step were heat-treated at a temperature of 500 ° C. for 1 minute in a nitrogen atmosphere to obtain a target ceramic composition powder.

  The obtained ceramic composition powder was evaluated in the same manner as in Example 1. First, as a result of XRD qualitative analysis, it was tetragonal lead titanate (PT) single-phase particles. Further, when the precise XRD measurement was performed at the same time, the c / a axial ratio was 1.065, which was the same value as in the bulk case. As a result of SEM and TEM observation, the obtained particles had an anisotropic rectangular parallelepiped shape, and the particle size was 15 nm. Further, when an electron beam diffraction image was observed, a clear spot was observed, and it was revealed that the particles were single crystal-like lead titanate particles. Further, when the amount of residual potassium in the particles was analyzed, it was found that it was very low at 38 ppm by weight.

  In the final heat treatment step in Example 4, a ceramic composition powder was obtained in the same manner as in Example 4 except that the heat treatment was performed in the air instead of the heat treatment in the nitrogen atmosphere.

  With respect to the obtained ceramic composition powder, the particle size of the lead titanate particles was determined to be 20 nm.

Bismuth oxychloride: 26.07 g (containing 0.1 mol as a bismuth element) was dissolved in 3N hydrochloric acid solution: 200 cm ³ to prepare a hydrochloric acid solution of bismuth oxychloride. On the other hand, titanium tetraisopropoxide: 21.108 g (containing 0.075 mol as titanium element) was mixed with IPA: 124.11 g to prepare an IPA solution of titanium tetraisopropoxide.

  Next, while stirring the IPA solution of titanium tetraisopropoxide with a high-speed stirrer, 8N potassium hydroxide solution: 498 g (containing 3 mol of potassium hydroxide) was dropped with a microtubing pump. Thereafter, a hydrochloric acid solution of bismuth oxychloride was similarly dropped with a microtubing pump to obtain a hydroxide slurry in which a bismuth element and a titanium element were mixed (the first step).

  Next, the hydroxide slurry obtained in the first step was dehydrated to obtain a dehydrated cake. Next, 800 g of pure water is added to the dehydrated cake to prepare a slurry, and the slurry is stirred at high speed for about 30 minutes using a high-speed stirrer and then dehydrated, and then the operation is repeated five times. Thus, the bismuth element and the titanium element were mixed uniformly at the molecular level, and impurities such as potassium hydroxide and potassium chloride were removed. The pH of the filtrate obtained by the final dehydration in this step was 8.5 (the second step).

  Next, 8N potassium hydroxide solution: 74.7 g (containing 0.45 mol as potassium hydroxide) and pure water: 543.75 g were added to the dehydrated cake obtained in the second step. A slurry was prepared. In addition, the alkali solvent normality at the time of hydrothermal reaction of this slurry is 0.75 normal. Next, the slurry was stirred at a high speed for about 30 minutes using a high-speed stirrer, and then charged into a polytetrafluoroethylene beaker. The beaker was attached to a 1.1 liter stirring autoclave and was heated at 220 ° C., 24 ° C. The hydrothermal reaction was performed under conditions of time and 500 rpm (the third step).

  Next, after completion of the third step, the slurry was dehydrated to obtain a dehydrated cake. Next, an operation of adding 800 g of pure water to the dehydrated cake to prepare a slurry, and stirring the slurry at a high speed for about 30 minutes using a high-speed stirrer and then dehydrating was repeated twice ( The fourth step).

  Next, 600 g of pure water was added to the dehydrated cake obtained in the fourth step to prepare a slurry, and this slurry was stirred at high speed for about 30 minutes using a high-speed stirrer. Thereafter, the slurry was put into a polytetrafluoroethylene beaker, and the beaker was attached to a stirring type autoclave having an internal volume of 1.1 liter, and subjected to a hydrothermal reaction again at 220 ° C. for 24 hours and 500 rpm. (The fifth step).

  Next, after completion of the fifth step, dehydration was performed, and the obtained dehydrated cake was placed in an oven set at a temperature of 100 ° C. and dried for 12 hours. Thereafter, the particle size was adjusted with a 40-mesh sieve to obtain the intended ceramic composition powder.

  The following evaluation results were obtained for the ceramic composition powder thus obtained.

  First, as a result of XRD qualitative analysis of the obtained ceramic composition powder, it was confirmed that it was orthorhombic bismuth titanate (BIT) single phase particles as shown in FIG. As a result of SEM observation, as shown in FIG. 1B, the particles had a plate shape and a particle size of about 5 μm. Further, when the amount of residual potassium in the particles was analyzed, it was found that the amount of potassium was extremely low, 90 ppm by weight.

  As described above, according to Example 6, it was possible to obtain bismuth titanate single-phase particles having a residual potassium amount as extremely low as 90 ppm by weight and having a plate shape with a particle size of about 5 μm.

  In the above-mentioned Non-Patent Documents 4 and 5, the hydrothermal reaction is carried out for a long time such as 7 days or 3 days at 240 ° C., whereas in Example 6 above, such as 24 hours at 220 ° C. Bismuth titanate single-phase particles could be obtained under sufficiently practical hydrothermal synthesis conditions. The reason for this is that, as described in Example 1, in the second step, potassium hydroxide and potassium chloride are removed, and at the same time, the operation of uniformly mixing the bismuth element and the titanium element at the molecular level is performed. It is. As a result, bismuth titanate single-phase particles could be obtained under hydrothermal reaction conditions at a lower temperature and in a shorter time than those reported in Non-Patent Documents 4 and 5.

  Moreover, in the said Example 6, the frequency | count of washing | cleaning in a 2nd process is 5 times. This is because in the first step, a hydrochloric acid solution of bismuth oxychloride is hydrolyzed using a relatively large amount of potassium hydroxide solution (containing 3 mol of potassium hydroxide). Regarding the washing operation in the second step, it is more important to determine the degree of pH of the filtrate than the number of washings. In the above-mentioned Examples 1, 3 and 4, PT was synthesized, and in the second step, the pH of the filtrate was 6.5 or 6.8. In Example 6, bismuth titanate was synthesized. In the second step, the filtrate was washed until the pH of the filtrate was 8.5. This means that the optimum pH value of the filtrate varies depending on the target compound.

Further, in Example 6, as in Examples 1 to 3, the normality of the potassium hydroxide solution in the third step exceeds 0.01 N, the hydrothermal reaction time exceeds 1 hour, and the drying step Although the subsequent heat treatment is not performed, in addition to the washing operation before the hydrothermal reaction treatment (second step), a washing operation under hydrothermal conditions (fifth step) is performed. Thereby, the amount of residual potassium was able to be reduced to 100 weight ppm or less. Incidentally , when it implemented only to the 4th process , the amount of residual potassium was 200-300 weight ppm.

  The second hydrothermal treatment described above is also disclosed in Patent Document 3. However, in Patent Document 3, this second hydrothermal treatment is performed in an aqueous solvent having a pH of 7 to 10. Incidentally, when the hydrothermal treatment was performed again using a barium hydroxide solution adjusted to pH 7, the amount of residual potassium was 180 ppm by weight, not 100 ppm by weight or less. Furthermore, when the hydrothermal treatment is performed again in an aqueous solvent having a pH of 5 or less, the bismuth element is significantly eluted. Therefore, it is necessary to set the pH of the aqueous solvent when performing the hydrothermal treatment again to be more than 5 and less than 7.

  The BIT single-phase particles obtained in Example 6 and the BIT single-phase particles obtained by solid phase reaction were mixed in an equal amount by weight ratio. Subsequently, after adding pure water and a binder with respect to this mixed powder, it knead | mixed using a ball mill, and the slurry was produced. Next, a ceramic green sheet was formed by applying a doctor blade method to the slurry.

  Next, a plurality of ceramic green sheets obtained as described above are laminated and pressed to produce a raw laminate, and then the raw laminate is cut into a predetermined size. A raw laminate chip was obtained.

  Next, the raw laminate chip was treated to remove the binder and then fired in the atmosphere at a temperature of 1000 ° C. for 2 hours to obtain a ceramic sintered body.

  The XRD analysis result of the obtained ceramic sintered body is shown in the upper part of FIG. 2 (“BIT oriented ceramics”). In the lower part of FIG. 2 (“BIT particle by hydrothermal method”), in order to facilitate comparison with the XRD analysis result of the ceramic sintered body shown in the upper part, the implementation shown in FIG. The XRD analysis result of the BIT single phase particle obtained in Example 6 is shown. Moreover, the SEM observation result of the surface of the ceramic sintered compact obtained in this Example 7 is shown by Fig.3 (a), and the SEM observation result of a cross section is similarly shown by FIG.3 (b).

  2 and 3 show that according to Example 7, a good BIT-oriented ceramic is obtained.

Bismuth oxychloride: 26.07 g (containing 0.1 mol as a bismuth element) was dissolved in 3N hydrochloric acid solution: 200 cm ³ to prepare a hydrochloric acid solution of bismuth oxychloride. On the other hand, titanium tetraisopropoxide: 28.31 g (containing 0.1 mol as titanium element) was mixed with IPA: 118.18 g to prepare an IPA solution of titanium tetraisopropoxide.

  Next, 100 g of pure water was dropped into the IPA solution of titanium tetraisopropoxide with a microtubing pump. Thereafter, while stirring this with a high-speed stirrer, 8N potassium hydroxide solution: 498 g (containing 3 mol of potassium hydroxide) was added dropwise with a microtubing pump. Subsequently, the hydrochloric acid solution of bismuth oxychloride prepared as described above was similarly dropped with a microtubing pump to obtain a hydroxide slurry in which a bismuth element and a titanium element were mixed (referred to above as the first). Process).

  Next, the hydroxide slurry obtained in the first step was dehydrated to obtain a dehydrated cake. Next, 800 g of pure water is added to the dehydrated cake to prepare a slurry, and the slurry is stirred at high speed for about 30 minutes using a high-speed stirrer and then dehydrated, and then the operation is repeated five times. Thus, the bismuth element and the titanium element were mixed uniformly at the molecular level, and impurities such as potassium hydroxide and potassium chloride were removed. Note that the pH of the filtrate obtained by the final dehydration in this step was 8.6 (the second step).

  Next, 8N potassium hydroxide solution: 133.215 g (containing 0.8025 mol as potassium hydroxide) and pure water: 399.69 g were added to the dehydrated cake obtained in the second step. A slurry was prepared and stirred at high speed for about 15 minutes. Thereafter, while stirring the slurry at a high speed, a calcium chloride solution (0.02625 mol of calcium chloride dissolved in 100 g of pure water) was added dropwise thereto using a microtubing pump. After dripping, the slurry stirred at high speed for about 15 minutes is put into a polytetrafluoroethylene beaker, and this beaker is attached to a stirring type autoclave having an internal volume of 1.1 liter, hydrothermally heated at 220 ° C. for 24 hours and 500 rpm. The reaction was carried out (the third step).

  Next, after completion of the third step, the slurry was dehydrated to obtain a dehydrated cake. Next, pure water: 600 g was added to the dehydrated cake to prepare a slurry, and the slurry was stirred at a high speed for about 30 minutes using a high-speed stirrer and then dehydrated three times. The fourth step).

  Next, 600 g of pure water was added to the dehydrated cake obtained in the fourth step to prepare a slurry, and this slurry was stirred at high speed for about 30 minutes using a high-speed stirrer. Thereafter, the slurry was put into a polytetrafluoroethylene beaker, and the beaker was attached to a stirring type autoclave having an internal volume of 1.1 liter, and subjected to a hydrothermal reaction again at 220 ° C. for 24 hours and 500 rpm. (The fifth step).

  Next, after completion of the fifth step, dehydration was performed, and the obtained dehydrated cake was placed in an oven set at a temperature of 100 ° C. and dried for 12 hours. Thereafter, the particle size was adjusted with a 40-mesh sieve to obtain the intended ceramic composition powder.

  The following evaluation results were obtained for the ceramic composition powder thus obtained.

First, as a result of XRD qualitative analysis of the obtained ceramic composition powder, as shown in the upper part of FIG. 4 (“product after hydrothermal treatment”), bismuth calcium titanate (CBT: CaBi ₄ Ti ₄ O ₁₅ ) single phase particles It was confirmed that. The lower part of FIG. 4 (“product after hydrothermal reaction”) shows the result of XRD qualitative analysis of the powder after the hydrothermal reaction in the third step.

  As a result of SEM observation, as shown in FIG. 5, the particles had a plate shape and a particle size of 0.2 to 0.3 μm. Further, when the amount of residual potassium in the particles was analyzed, it was found that the amount was extremely low at 95 ppm by weight.

  As described above, according to Example 8, it is possible to obtain bismuth calcium titanate single-phase particles having a residual amount of potassium as low as 95 ppm by weight and having a plate shape with a particle size of 0.2 to 0.3 μm. did it.

In Example 6 described above, it has been confirmed that the target bismuth titanate single phase particles have already been obtained after the third step. On the other hand, in the case of obtaining bismuth calcium titanate single phase particles as in Example 8, after the third step, as shown in the lower part of FIG. 4, bismuth titanate (Bi ₄ It was found that a Ti ₃ O ₁₂ ) phase and a bismuth oxide (Bi ₄ O ₇ ) phase were by-produced and were not a single phase of bismuth calcium titanate. In Example 8, bismuth calcium titanate single phase particles were obtained for the first time after completion of the fifth step in which the rehydrothermal reaction was performed.

  In Example 6, the fifth step showed a remarkable effect in reducing the amount of residual potassium. This effect is the same in the eighth embodiment. Incidentally, when it implemented only to the 4th process, the amount of residual potassium was about 400 weight ppm.

  In addition, in Example 8, since the bismuth calcium titanate single phase particles are to be obtained, the fifth step of performing the rehydrothermal reaction treatment is to remove the bismuth titanate phase and the bismuth oxide phase, It was found to be an indispensable process for obtaining bismuth calcium oxide single phase particles.

  In addition, the calcium-containing solution was added in the first step instead of the third step to try to synthesize bismuth calcium titanate. However, the calcium hydroxide elution occurred by washing, and the dehydration obtained by the subsequent dehydration. There was substantially no calcium remaining in the cake, and the produced particles had a bismuth titanate phase as the main phase. Moreover, in order to cope with this, when the amount of calcium hydroxide to be eluted was estimated and a calcium-containing solution was reacted excessively, a calcium titanate phase was by-produced and single-phase particles were not obtained.

  In Example 8, calcium was added in an excess of 5 mol% with respect to the stoichiometric value. This is because, when charged according to the stoichiometric value, the by-product of the bismuth titanate phase becomes prominent. On the other hand, if the amount is 10 mol% in excess of the stoichiometric value, the crystallinity of the produced particles is lowered. Therefore, it is preferable that the calcium amount is excessive by about 5 mol% with respect to the stoichiometric value. In addition, unlike the case of Example 8, when calcium is added not only in the third step but also in the first step, an appropriate amount of calcium may be determined in consideration of that amount.

  Further, the pH of the aqueous solvent used in the rehydrothermal treatment in the fifth step needs to be set to more than 5 and less than 7 as in the case of Example 6. This is because elution of the bismuth element becomes significant when the pH is 5 or less, and the residual potassium reduction effect is impaired when the pH is 7 or more.

  After adding pure water and a binder to the CBT single-phase particles obtained in Example 8 above, a slurry was prepared by kneading using a ball mill. Next, a ceramic green sheet was formed by applying a doctor blade method to the slurry.

  Next, a plurality of ceramic green sheets obtained as described above are laminated and pressed to produce a raw laminate, and then the raw laminate is cut into a predetermined size. A raw laminate chip was obtained.

  Next, the raw laminate chip was carefully debindered and then fired in the atmosphere at a temperature of 1200 ° C. for 2 hours to obtain a ceramic sintered body.

  The XRD analysis result of the obtained ceramic sintered body is shown in the upper part of FIG. 6 (“CBT oriented ceramics”). In the lower part of FIG. 6 (“CBT particle by hydrothermal method”), the XRD analysis of the CBT single-phase particles obtained in Example 8 is performed for comparison with the XRD analysis result of the ceramic sintered body shown in the upper part. Results are shown. Moreover, the SEM observation result of the surface of the ceramic sintered compact obtained in this Example 9 is shown by Fig.7 (a), and the SEM observation result of a cross section is similarly shown by FIG.7 (b).

  From these FIG. 6 and FIG. 7, it can be seen that according to Example 9, a good CBT oriented ceramic is obtained.

  In the same manner as in Example 8, a hydroxide slurry in which a bismuth element and a titanium element were mixed was obtained (the first step).

  Next, in the same manner as in Example 8, after the hydroxide slurry obtained in the first step was dehydrated to obtain a dehydrated cake, pure water was added to the dehydrated cake, stirred, and dehydrated. By repeating the operation of 5 times, the bismuth element and the titanium element were uniformly mixed at the molecular level, and impurities such as potassium hydroxide and potassium chloride were removed. The pH of the filtrate obtained by the final dehydration in this step was 8.4 (the second step).

  Next, to the dehydrated cake obtained in the second step, 8N potassium hydroxide solution: 124.5 g (containing 0.75 mol as potassium hydroxide) and pure water: 506.25 g were added. A slurry was prepared and stirred at high speed for about 15 minutes. Thereafter, strontium hydroxide octahydrate: 6.983 g (containing 0.02625 mol as strontium) was added to the slurry. After the addition, the slurry was put into a polytetrafluoroethylene beaker, this beaker was attached to a stirring type autoclave having an internal volume of 1.1 liter, and a hydrothermal reaction was performed at 220 ° C. for 24 hours and 500 rpm ( Thus, the third step).

  Next, in the same manner as in Example 8, the fourth step and the fifth step were performed, and after completion of the fifth step, dehydration was performed, and the obtained dehydrated cake was set to a temperature of 100 ° C. Placed in oven and dried for 12 hours. Thereafter, the particle size was adjusted with a 40-mesh sieve to obtain the intended ceramic composition powder.

  The following evaluation results were obtained for the ceramic composition powder thus obtained.

First, as a result of XRD qualitative analysis of the obtained ceramic composition powder, it was confirmed that it was bismuth strontium titanate (SBTi: SrBi ₄ Ti ₄ O ₁₅ ) single phase particles. As a result of SEM observation, the particles had a plate shape and a particle size of 0.2 to 0.3 μm. Further, when the amount of residual potassium in the particles was analyzed, it was found that the amount was very small as 87 ppm by weight.

  As described above, according to the tenth embodiment, the same effects as those of the eighth embodiment described above are obtained.

  In addition, although Example 8 thru | or 10 was implemented about the case where calcium and strontium were each contained as an alkaline-earth metal element, Example 8 thru | or 10 was carried out also when another alkaline-earth metal element was contained. It is possible to apply a method similar to the method implemented in the above and obtain the same effect.

The analysis result of the bismuth titanate single phase particle obtained in Example 6 is shown, (a) is a figure which shows an XRD chart, (b) is a figure which shows a SEM photograph. It is a figure which shows the XRD chart of the bismuth titanate oriented ceramic sintered compact obtained in Example 7 in the upper part, and the XRD chart of the bismuth titanate single phase particle obtained in Example 6 in the lower part. The SEM observation result of the bismuth titanate oriented ceramic sintered compact obtained in Example 7 is shown, (a) is a figure which shows the SEM photograph which imaged the surface of the ceramic sintered compact, (b) is a ceramic. It is a figure which shows the SEM photograph which imaged the cross section of the sintered compact. It is a figure which shows the XRD chart of the powder after the hydrothermal reaction in a 3rd process in Example 8 at the upper part in the XRD chart of the bismuth calcium titanate single phase particle | grains obtained in Example 8. FIG. It is a figure which shows the SEM photograph of the bismuth calcium titanate single phase particle obtained in Example 8. It is a figure which shows the XRD chart of the bismuth calcium titanate oriented ceramic sintered compact obtained in Example 9 in the upper part, and the XRD chart of the bismuth calcium titanate single phase particle obtained in Example 8 in the lower part. The SEM observation result of the bismuth calcium titanate oriented ceramic sintered compact obtained in Example 9 is shown, (a) is a figure which shows the SEM photograph which imaged the surface of the ceramic sintered compact, (b). It is a figure which shows the SEM photograph which imaged the cross section of the ceramic sintered compact.

Claims (4)

A method for producing a ceramic composition which is lead titanate or bismuth titanate,
A first step of obtaining a hydroxide slurry by mixing a constituent element solution containing constituent elements of a ceramic composition to be obtained and an alkali hydroxide solution for taking out ions of the constituent elements as hydroxides; ,
Washing the hydroxide contained in the hydroxide slurry obtained in the first step, adjusting the pH of the hydroxide slurry to 9 or less but not 6 or less, Obtaining a second step;
A third step of obtaining a reaction product by adding an alkali hydroxide solution as a mineralizer to the washed product obtained in the second step to cause a hydrothermal reaction;
A fourth step of stirring and washing the reaction product obtained in the third step;
After the fourth step, an aqueous solvent is added to the reaction product to adjust the slurry so that the pH is more than 5 and less than 7, and the hydrothermal reaction is performed again. Process,
The manufacturing method of a ceramic composition provided with the drying process of drying the said reaction material after the said 5th process and obtaining a dried material. A method for producing a ceramic composition, which is a bismuth layered compound containing bismuth, titanium, and an alkaline earth metal element,
A hydroxide slurry is prepared by mixing a constituent element solution containing bismuth and titanium as constituent elements of the ceramic composition to be obtained and an alkali hydroxide solution for extracting ions of the constituent elements as hydroxides. Obtaining a first step;
Washing the hydroxide contained in the hydroxide slurry obtained in the first step, adjusting the pH of the hydroxide slurry to 9 or less but not 6 or less, Obtaining a second step;
A hydrothermal reaction is performed by adding an alkali hydroxide solution as a mineralizer and a solution containing an alkaline earth metal element or an alkaline earth metal hydroxide to the washed product obtained in the second step. A third step of obtaining a reactant,
A fourth step of stirring and washing the reaction product obtained in the third step;
After the fourth step, an aqueous solvent is added to the reaction product to adjust the slurry so that the pH is more than 5 and less than 7, and the hydrothermal reaction is performed again. Process,
After the fifth step, the reaction product is dried to obtain a dried product,
A method for producing a ceramic composition comprising:   The ceramic composition according to claim 1 or 2, wherein in the third step, the normality of the alkali hydroxide solution is 0.01 N or less, and the time for performing the hydrothermal reaction is 1 hour or less. Production method.   The ceramic composition according to any one of claims 1 to 3, further comprising a heat treatment step of heat-treating particles obtained from the dried product dried in the drying step at a temperature of 400 ° C or higher and 700 ° C or lower. Manufacturing method.