JP4481746B2 - Method for producing lead-free piezoelectric material - Google Patents

Description

The present invention, vibrators, actuators, sensors, can be suitably used in the manufacture of such filters relates to a method of manufacturing a lead-free piezoelectric substances containing as a component an alkali metal element or an alkaline earth metal element.

  Conventionally, lead-based materials such as PZT (solid solution of lead zirconate and lead titanate) and PLZT (with lanthanum added to PZT) have been used as piezoelectric materials. In order to use it, there is an urgent need for an environment-friendly alternative to lead-free materials because of lead scattering during production and environmental considerations.

  The main lead-free piezoelectric materials include barium titanate (BT), bismuth sodium titanate (BNT), bismuth potassium titanate (BKT) and mixed crystals thereof, sodium niobate, niobium There are potassium acid, lithium niobate and mixed crystal systems thereof. These are all compounds belonging to the perovskite crystal system.

  The lead-free piezoelectric material as described above is obtained by pulverizing and mixing a raw material containing an alkali metal element and an alkaline earth metal element (hereinafter referred to as an alkali metal or the like) with a pulverizer such as a ball mill. In many cases, raw material components such as alkali metals remain as unreacted substances (meaning that they are not constituents of crystals) in the manufactured product. The unreacted component applied to the alkali metal or the like is easily ionized, and has been a cause of impairing the electrical characteristics and the temporal stability of the piezoelectric body using the piezoelectric material in which these unreacted components remain. In order to solve such a problem, these unreacted components related to the alkali metal and the like must be sufficiently removed at the manufacturing stage so as not to remain in the manufactured piezoelectric material.

  On the other hand, since unreacted components related to alkali metals and the like are easily ionized, it is difficult to remove these components from the lead-free piezoelectric materials. In the lead-free piezoelectric materials currently manufactured, In addition, it could not be said that the unreacted components on the alkali metal and the like were sufficiently removed. On the other hand, the present inventors are configured so that they can be washed with water in the final manufacturing process, so that there is little residual ion content such as unreacted components on alkali metals, etc., and conventional lead-based piezoelectricity We have found that it is easy to manufacture lead-free piezoelectric materials that can withstand actual use and achieve the same properties as materials, and methods for manufacturing lead-free piezoelectric materials containing alkali metals as constituents, and lead-free materials A piezoelectric substance has been proposed (Japanese Patent Application No. 2004-196084).

  However, in order to replace a conventional lead-based piezoelectric material such as PZT with a lead-free piezoelectric material containing a component such as an expensive alkali metal, non-lead containing an alkali metal or the like as a constituent element There is a need for further improvement in characteristics of the piezoelectric material (hereinafter referred to as a lead-free alkali-containing piezoelectric material). In the manufacturing method described above, the remaining ions such as unreacted components on the alkali metal and the like are more sufficiently removed by washing with water in the final step of the manufacturing. As a result, the lead-free alkali-containing piezoelectric element having excellent characteristics is obtained. I have a sex substance.

  The present invention has been made in view of the above points, and further improves the lead-free alkali-containing piezoelectric material in which the residual ions such as unreacted components on the alkali metal described above are reduced, Lead-free alkali-containing piezoelectric material that can realize more stable piezoelectric characteristics when used as a piezoelectric material, suppressing ion elution of unreacted components on water-soluble alkali metals, etc. that remain slightly in the substance. Is to provide sex substances.

The above object is achieved by the present invention described below. That is, the present invention relates to a process for preparing a powdery lead-free piezoelectric material having a piezoelectric performance comprising as a component an alkali metal element or an alkaline earth metal element, were mixed thoroughly pulverized material, a step of calcining the mixture at 800 to 1100 ° C., the particle surface of the powder of the burned material and a step of performing water repellent treatment with a lipophilic substance having a carboxy group, are lipophilic substances having the carboxy group, Caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid or ricinolenic acid. In the water-repellent treatment step, water is added to the powdered fired product to peptize. Then, an aqueous solution which is an alkali salt of a lipophilic substance having a carboxy group is added to the obtained slurry to further peptize, and the electric conductivity of the filtrate is 300 μs / cm or less. A method for producing a lead-free piezoelectric material, characterized by washed with water until.

  According to the present invention, while being a lead-free alkali-containing piezoelectric material, the crystallinity is high, the residue of unreacted components on alkali metal etc. is suppressed to a very low level, and the material is stable in water. Contains lead-free alkali that can achieve a more stable piezoelectric body that can effectively prevent elution of ions even if a small amount of unreacted components on soluble alkali metals remain. A piezoelectric material is provided.

  That is, according to the present invention, when used as a piezoelectric body, the electrical characteristics and aging over and above that of the conventional lead-based piezoelectric substance lead zirconate titanate (PZT) are used. A lead-free alkali-containing piezoelectric material capable of achieving stability is provided.

  Next, the present invention will be described in more detail with reference to preferred embodiments. First, the background to the present invention will be described below. According to the study by the present inventors, for example, when a lead-free piezoelectric material such as a mixed crystal of barium titanate and bismuth titanate / potassium titanate containing an alkali metal or the like is produced by a conventional method. In the synthesis (firing), the alkali metal or the like which is a raw material component does not completely dissolve, but partially remains as an unreacted component. Further, in the solid phase reaction by firing, since alkali metal or the like acts as a kind of flux (flux) substance, the resulting particles become large, and in use, it is necessary to pulverize to a usable level with a ball mill or the like. . During this process, the crystal is broken by impact, and alkali metals and other remaining substances come out of the crystal system. When a piezoelectric body formed using such a lead-free piezoelectric substance is used in various applications, an unreacted residual substance such as an alkali metal acts as an ion. The stability over time can be significantly impaired.

  In order to solve the above-mentioned problems, it is necessary to thoroughly wash the lead-free alkali-containing piezoelectric material and remove residual components such as unreacted alkali metal and other ions. Since these remaining components are mostly ionic substances soluble in water, washing with water is considered to be the best. However, since the lead-free alkali-containing piezoelectric material is formed by dissolving an alkali metal or the like in a solid solution, it is soluble in water, and the remaining components cannot be sufficiently washed out. The inventor considers such points sufficiently, improves the uniformity of mixing and pulverization of the raw materials, and after firing this, the obtained fired product is further ground and then fired once. By doing the above, the crystallinity of the lead-free alkali-containing piezoelectric material is increased, the remaining of unreacted alkali metal, etc. is suppressed to a very low level, and it is possible to wash out with water in the final process. It has been found that an excellent lead-free alkali-containing piezoelectric material can be obtained.

  As a result of further development of the above-described technique and further studies to provide a lead-free alkali-containing piezoelectric material having better characteristics, the present inventors have obtained a piezoelectric material obtained as a powdered fired product. Furthermore, if it is treated with a lipophilic substance having a carboxy group, the water repellent effect is high, and the elution of ions such as unreacted components on the slightly remaining water-soluble alkali metal is effectively suppressed. As a result, the inventors have found that a lead-free alkali-containing piezoelectric material having excellent characteristics can be obtained. For example, according to the present invention, a piezoelectric material that achieves electrical characteristics and stability over time equivalent to or higher than that of the conventional lead-based piezoelectric material lead zirconate titanate (PZT). It becomes possible to obtain a body.

  Examples of the lead-free alkali-containing piezoelectric material used in the present invention include barium titanate (BT), bismuth / sodium titanate (BNT), bismuth / potassium titanate (BKT), and mixed crystals thereof, niobium Examples thereof include sodium oxide, potassium niobate, lithium niobate, and mixed crystal systems thereof, all of which contain an alkali metal or the like as a constituent element. Hereinafter, a method for producing a lead-free piezoelectric material and a lead-free piezoelectric material according to the present invention will be described using a bismuth titanate / sodium titanate material (hereinafter referred to as a BNT material) as an example. However, the lead-free alkali-containing piezoelectric material according to the present invention, its manufacturing method, and utility are of course not limited to this system.

  The lead-free alkali-containing piezoelectric material according to the present invention is made of a powdered fired product, and its particle surface is water-repellent treated with a lipophilic material having a carboxy group. As the lipophilic substance having at least a carboxy group used for water repellent treatment of a BNT substance, it is particularly preferable to use an aliphatic carboxylic acid substance. These may be used alone or in combination of two or more. Among the aliphatic carboxylic acid substances, those having a larger number of carbon atoms in the alkyl group than the carboxy group have a greater water repellent effect and are more effective. In particular, it is preferable to use a high molecular weight alkyl group having 7 or more carbon atoms in an alkyl group that is solid at room temperature because a large water repellency can be obtained. As the alkyl group in the aliphatic carboxylic acid-based substance, either a straight chain or a side chain can be used. However, alkyl groups having many unsaturated bonds have a large hydrophilic effect and should be avoided.

Specific examples of the aliphatic carboxylic acid material that can be suitably used in the present invention include, for example, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, ricinolenic acid and the like. Is mentioned . These may be used singly or in combination of two or more kinds.

  Hereinafter, a non-lead-based alkali-containing piezoelectric according to the present invention is obtained by using a lipophilic substance having at least a carboxy group as described above (also simply referred to as a lipophilic substance) to water-repellently treat the particle surface of the powdered fired product. A method for obtaining a sex substance will be described. The lead-free alkali-containing piezoelectric material according to the present invention is obtained by first sufficiently pulverizing and mixing raw materials containing each constituent element, and then firing the mixture at 800 to 1100 ° C. to obtain a powdered fired product. The water-repellent treatment is performed on the fired product. For example, when producing BNT, oxides, carbonates, hydroxides, basic hydroxides and the like corresponding to each element (bismuth, sodium, titanium) which are constituents are prepared as raw materials. Specifically, bismuth oxide, bismuth oxycarbonate, etc. can be used as the bismuth raw material, sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, etc. can be used as the sodium raw material, and titanium oxide is used as the titanium raw material. can do.

  Next, these raw materials are sufficiently pulverized and mixed. As the method, an alcohol such as ethanol or an organic solvent such as acetone may be used as a medium, and wet mixing and pulverization may be performed, or dry mixing and pulverization may be performed without using an organic solvent. In order to improve the reactivity between components because the particle sizes of the respective raw materials mentioned above are different, it is preferable to perform sufficient pulverization and mixing in the mixing and pulverization. Specifically, wet pulverization using a bead mill such as a ball mill, or dry pulverization using a pulverizer such as a ball mill such as a dry attritor, a Henschel mixer, a hammer mill, a ball mill, or a planetary mill.

  Next, the obtained mixture is fired at 800 ° C. to 1100 ° C. for about 1 hour to 5 hours. At this time, if the pulverization and mixing are performed in a wet manner, the mixture is dried and then fired. If the calcination temperature is 800 ° C. or higher, crystals grow sufficiently, and a baked product with low unreacted content is obtained with low water solubility. When the firing temperature exceeds 1100 ° C., the product is sintered, and pulverization performed during use becomes difficult.

  In the method for producing a lead-free alkali-containing piezoelectric material according to the present invention, after the fired product obtained as described above is pulverized, the pulverized product is further fired at 800 to 1100 ° C. in a preferable form. is there. Furthermore, it is also a preferable form to repeat the pulverization and firing of the fired product. In this way, a fired product with higher crystallinity can be obtained. The pulverization performed in the above case is not preferable if the pulverization is excessive, because the perovskite-type crystal structure generated by firing is destroyed and the generation of ionic components is promoted. In addition, if the pulverization at this time is insufficient, the generation of coarse particles is increased by the subsequent firing, and excessive pulverization is required during use, etc., and the generation of ionic components is increased as described above. It is not preferable.

  The fired product obtained as described above has a high crystallinity and a fine particle size, and there is almost no unreacted component remaining on the alkali metal or the like. In the present invention, for the purpose of further improving the properties, the powdered fired product is subjected to water repellent treatment on the particle surface using the lipophilic substance as described above, and the lead-free product according to the present invention. An alkali-containing piezoelectric material is obtained.

  Examples of the water-repellent treatment method include mixing the lipophilic substance as described above with the powdered fired product obtained as described above in a dry manner. However, in order to obtain a greater effect, it is preferable to perform a water repellent treatment by using a solvent and mixing in a wet manner as described below. For example, it is preferable to use a material obtained by dissolving an aliphatic carboxylic acid material in a solvent and treating the powdered fired product while peptizing. As the solvent used in this case, water, alcohol or the like can be used, but it is preferable to use water in consideration of workability and environmental applicability. When water is used, it is preferable to use a lipophilic substance that can be dissolved in water. For example, when an aliphatic carboxylic acid-based substance is used, it is preferable to use a carboxy group having high solubility in water as the alkali salt group. When a lipophilic substance is used as the alkali salt, the alkali salt component remains in the system, and thus it is preferably removed by washing in the final step.

  More specifically, the water-repellent treatment on the particle surface of the powdered fired product performed in the present invention will be described. As described above, the lipophilic substance as described above is dry-mixed and pulverized with a fired product that is a lead-free alkali-containing piezoelectric substance containing an alkali metal or the like, and has a water-repellent effect on the piezoelectric substance. Although it is possible to impart it, it is preferable to use a lipophilic substance dissolved in a solvent in order to exert a great water repellent effect with the piezoelectric substance. In the following, an example in which water is used as a medium and an aliphatic carboxylic acid-based substance is used as a lipophilic substance will be described as a particularly preferable embodiment.

  As described above, the aliphatic carboxylic acid-based substance is preferably used as a carboxylic acid alkali salt having a high solubility in water. That is, a powdery fired product obtained as described above is subjected to water repellent treatment as described below, using an aliphatic carboxylic acid-based material dissolved in water as an alkali salt as a lipophilic material. Water is added to the powdered fired product (average particle size is usually about 0.3 to 5 μm), and the powder is pulverized in advance with a peptizer such as a homomixer to obtain a slurry. Into this slurry, an aqueous solution containing the lipophilic substance prepared as described above is charged for treatment. At this time, in order to complete the process, peptization is further continued in the above state, and the process is completed in about 10 to 120 minutes. The amount of the aliphatic carboxylic acid material used at this time varies depending on the type, but is preferably 0.1 to 5.0% by weight, more preferably 0%, based on the piezoelectric material as a product. .1 to 3.0% by weight. If the amount used in this case is too small, there is a fear that a piezoelectric substance having a sufficient water repellency effect cannot be obtained. If it is too much, an excessive lipophilic substance remains, which is uneconomical. In particular, the use of a lipophilic substance as an alkali salt is not preferable because a large amount of alkali salt components remain in the system.

The peptization slurry obtained after the water-repellent treatment as described above, when an alkali salt of an aliphatic carboxylic acid substance is used as a lipophilic substance, the alkali salt component remains in the system, It is necessary to remove this by washing with water. For washing, using a method such as decantation, thoroughly washed with water until the electric conductivity of the filtrate becomes less than 300 [mu] s / cm. After washing with water, the paste obtained by filtration is dried at a temperature of about 110 ° C., whereby the lead-free alkali-containing piezoelectric material according to the present invention is obtained. The powdered lead-free alkali-containing piezoelectric material thus obtained has little residual ionic components such as unreacted alkali metal, and the particle surface has been subjected to a water-repellent treatment. When this is used as a piezoelectric body, more stable piezoelectric characteristics can be realized.

The relative difference of the ionic substance eluted from the powdered lead-free alkali-containing piezoelectric substance obtained as described above is based on the electrical resistivity measurement method according to the pigment test method JIS-K5101-18: 2004. It can be evaluated by the following method. That is, the water repellent effect can be confirmed thereby. The JIS method relates to pigment powder, but a piezoelectric substance powder is used as a specimen instead of pigment powder. Specifically, 20 g of piezoelectric substance powder and 180 ml of pure water are weighed in an Erlenmeyer flask, boiled at 100 ° C. for 5 minutes, filtered, and the electrical resistivity of the filtrate is measured at 20 ° C. In this method, since boiling is performed for 5 minutes, it is possible to sufficiently wash out soluble components in the powder, and the amount of ionic substance eluted from the piezoelectric substance is measured by the measured electric low efficiency of the filtrate. Indirect but relatively intelligible. As will be described later, when the powdered lead-free alkali-containing piezoelectric material obtained by the production method of the present invention was measured, an electric resistivity of 10 ⁶ Ω · m or more was shown. Such measured values are equal to or higher than those measured for conventional lead-based PZT powders, and almost no ionic components are eluted into water, and it can be confirmed that they can be used effectively as raw materials for piezoelectric materials. It was.

  The present invention will be specifically described below with reference to examples and comparative examples. First, the bismuth titanate / sodium titanate and sodium niobate used in each example were synthesized by the following method. These are obtained as a powdery fired product. The part is based on mass. The electrical resistivity was measured according to the pigment test method JIS-K5101-18: 2004 as described above.

(1) "Synthesis of bismuth titanate / sodium-barium titanate mixed crystal (hereinafter abbreviated as BNT (80) -BT (20) (numbers indicate molar ratio)")
A ball mill having a ceramic capacity of 3 liters was used as the wet pulverization mixer. Half of the glass beads having a diameter of 2 mm are previously placed in the ball mill as a dispersion medium. In this, 21.2 parts of sodium carbonate, 93.2 parts of bismuth oxide, 79.9 parts of titanium oxide, and 39.5 parts of barium carbonate was weighed, and further 600 parts of ethanol was added as a medium, followed by mixing and grinding for about 4 hours.

  Next, the obtained mixed pulverized product was dried, and the obtained dry powder was calcined at 830 ° C. for 3 hours. Next, the sintered product that had been sintered was placed in a 3 liter ball mill again, and wet grinding using ethanol as a medium was performed for 3 hours in the same manner as described above. After pulverization, the pulverized product was dried to obtain about 200 parts of dry powder. Next, the obtained dry powder was further baked at 1000 ° C. for 3 hours to obtain about 200 parts of a powdered baked product (average particle size 1.6 μm). The above synthesis was repeated three times in order to ensure the necessary amount for each example.

(2) "Synthesis of sodium niobate"
Synthesized by the same method as BNT (80) -BT (20) except that 162 parts of niobium pentoxide and 64.6 parts of sodium carbonate (soda ash) were used as the firing raw materials. About 200 parts of powdered calcined product of sodium niobate (average particle size 1.4 μm) was obtained. The above synthesis was repeated three times in order to ensure the necessary amount for each example.

<Example 1>
500 parts of piezoelectric material BNT (80) -BT (20), which is a powdered fired product obtained as described above, and 3,000 parts of water as peptized water are placed in a container, and about 30 by a homomixer. Break down. Separately from this, an aqueous solution of a lipophilic substance prepared by dissolving 7.5 parts of sodium oleate in 50 parts of water for use in water repellent treatment is prepared. And this aqueous solution is thrown into the slurry of the above-mentioned baked product, and further continues to decompose and paste 30 to complete the water repellent treatment.

  Next, the peptizer obtained by performing the water repellent treatment as described above was washed with water by decantation. Washing with water was repeated by repeating the decantation operation until the electric conductivity of the aqueous phase reached 300 μs / cm or less. After rinsing with water, the peptizer was filtered with a Nutsche funnel (Buchner funnel). Then, the filtered paste was sufficiently dried at 110 ° C. to obtain about 495 parts of the desired water-repellent powdered BNT (80) -BT (20) of this example.

In order to examine the water repellent effect of the obtained BNT (80) -BT (20), the electrical resistivity according to JIS-K5101-18: 2004 was measured. As a result, the water repellent treatment was 2.4 × 10 ⁶ Ω · cm. Moreover, when the measurement was performed on the product before the water repellent treatment, the electrical resistivity was 1.5 × 10 ⁶ Ω · cm.

<Example 2>
The water-repellent treatment was carried out in the same manner as in Example 1 except that 1.5 parts of sodium stearate was used as the water-repellent treatment substance. BNT (80) -BT (20) was obtained. It was 4.5 * 10 < ⁶ > ohm * cm when the electrical resistivity was measured about obtained BNT (80) -BT (20).

<Example 3>
A water repellent treatment was carried out in the same manner as in Example 1 except that 500 parts of sodium niobate was used as the piezoelectric material being a powdered fired product, and 5 parts of sodium oleate was used as the water repellent material. The intended water repellent treated powdered sodium niobate of this example was obtained. And when the electrical resistivity was measured about the obtained sodium niobate, it was 3.9 * 10 < ⁶ > ohm * cm. Further, the electrical resistivity of the material not subjected to water repellent treatment was 1.3 × 10 ⁶ Ω · cm.

<Example 4>
The water-repellent treatment was carried out in the same manner as in Example 3 except that 1.5 parts of sodium stearate was used as the water-repellent treatment substance. Sodium niobate was obtained. The electrical resistivity of the obtained sodium niobate was measured and found to be 5.2 × 10 ⁶ Ω · cm.

<Comparative Example 1>
In the same manner as in Examples 1 to 4 described above, the electrical resistivity of the commercially available lead-based piezoelectric lead zirconate titanate (PZT) and the pH value of the filtrate were measured. As a result, the electrical resistivity was 2.0 × 10 ⁶ Ω · m.

[Evaluation]
Table 1 shows the measurement results of electrical resistivity for each example. Further, the pH of the filtrate at the time of measurement is also shown. Furthermore, in each Example, the state in the pure water before and after the electrical resistivity measurement test was visually observed and shown together. In addition, the untreated product that has not been subjected to water repellent treatment and the PZT of the lead-based piezoelectric material of Comparative Example 1 are also shown in Table 1 for comparison. Obviously from Table 1, the water-repellent treated product has a higher electrical resistivity than the untreated product, and depending on what is 2-4 times that of the untreated product and PZT. Moreover, since the pH value of the water-repellent treated product is smaller than that of the untreated product, it can be seen that the elution of alkaline ionic substances is reduced. Furthermore, it can be seen that a good result is obtained by comparison with PZT, which is a conventional lead-based piezoelectric material.

  According to the present invention, a piezoelectric material having stable piezoelectric performance in which elution of ions such as unreacted components on alkali metal and the like is effectively suppressed by performing a water-repellent treatment with a lipophilic substance such as an aliphatic carboxylic acid. Provided is a powdered lead-free alkali-containing piezoelectric material capable of forming a body.

Claims (1)

  In a method for producing a powdered lead-free piezoelectric material having piezoelectric performance comprising an alkali metal element or an alkaline earth metal element as a constituent component, the raw material is sufficiently pulverized and mixed, and then the mixture is 800-1100. And a step of water-repellent treatment with a lipophilic substance having a carboxy group on the particle surface of the powdered fired product, wherein the lipophilic substance having the carboxy group is caprylic acid, capric acid, Lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid or ricinolenic acid, and in the water repellent treatment step, water is added to the powdered fired product to peptize, and the resulting slurry Then, an aqueous solution that is an alkali salt of a lipophilic substance having a carboxy group is added to further peptize, and the filtrate is washed with water until the conductivity of the filtrate is 300 μs / cm or less. Method of manufacturing a lead-free piezoelectric material, characterized in that.