JPH03122021A - Oxide powder for piezoelectric porcelain and production of piezoelectric porcelain - Google Patents

Abstract

PURPOSE:To provided oxide powder for piezoelectric porcelain supplying a dense sintered material free from cracks by making specific surface area of perovskite type lead-containing compound oxide powder produced by hydrothermal reaction <=a specific value. CONSTITUTION:A perovskite type lead-containing compound oxide powder produced by hydrothermal reaction is heat-trated at 500-1,000 deg.C to give <=20m<2>/g specific surface area thereof. The powder is blended with a binder, compression molded, and the binder is removed to give a molded article having >=50% theo retical density, which is calcined. Shrinkage percentage of molded article during calcining is reduced with decrease in specific surface area of powder. When specific surface ara is <=20m<2>/g, shrinkage percentage is <=20%, a piezoelectric porcelain having a few cracks is obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an oxide powder that is a raw material for piezoelectric ceramics made of a perovskite-type lead-containing composite oxide, and a method for manufacturing piezoelectric ceramics using the powder. In particular, the present invention relates to a method for producing high-density piezoelectric ceramics using fine powder raw materials produced using hydrothermal reactions while suppressing deformation and cracking during firing.

(Conventional technology) Lead zirconate titanate [Pb(Zr, Ti)Oz)
Lit device compositions made by firing perovskite-type lead-containing composite oxides, typified by , are being widely put into practical use as piezoelectric Agie I.

There are various methods for producing powder of such perovskite-type lead-containing composite oxide, which is the raw material for porcelain.
For example, a manufacturing method using a hydrothermal reaction as disclosed in JP-A No. 63-85014 is most preferred in that a uniform and fine powder can be obtained. The present inventors also utilized this hydrothermal reaction to develop a method for producing $5) powder of a perovskite-type lead-containing composite oxide with a uniform composition and excellent powder properties. A patent application was filed as No.-30844. The raw material powder for the pressure WJi device (hereinafter referred to as "hydrothermal synthesis 'j5) powder" synthesized by such hydrothermal reaction is:
Not only is the composition uniform, but the particles are fine, so
Compared to raw material powder etc. synthesized by dowa reaction,
One advantage is that the firing temperature can be lowered.

However, when hydrothermal synthetic powder is mixed with a binder, molded using a mold press, and fired, the density of the molded product before firing is low, and therefore the shrinkage rate during firing becomes large, resulting in deformation and cracking. There are many things.

(Problems to be Solved by the Invention) An object of the present invention is to solve the following problems in the production of piezoelectric ceramics using a hydrothermally synthesized powder of perovskite-type lead-containing complex oxide.
The object of the present invention is to produce a dense fired body without cracks, and to improve the powder itself and to provide a method for producing a piezoelectric device using the powder.

(Means for solving the problem) The main reason why deformation and cracks occur when a molded body of hydrothermally synthesized powder is fired is that the density of the molded body is low and shrinkage during firing is large. . It is presumed that the reason why the density of the compact is low is that the hydrothermally synthesized powder is fine and its specific surface area is extremely large. Therefore, the present inventors investigated the relationship between the specific surface area of the powder before firing and the shrinkage rate of the molded body during firing. Figure 1 is a graph summarizing the survey results. As shown in the figure, as the specific surface area of I5) becomes smaller, the shrinkage rate also becomes smaller. Specific surface area is 20
If it is m2/g or less, the shrinkage rate will be 20% or less, and a dense fired body with few cracks will be obtained.

The present invention is based on the above findings, and its gist lies in the following (1) oxide powder and (2) piezoelectric ceramic manufacturing method.

(1) A perovskite-type lead-containing composite oxide powder produced using a hydrothermal reaction and having a specific surface area of 208/Ifi" or less.

(2) A method for manufacturing piezoelectric ceramics comprising the following steps 1 to 2.

■Process of producing perovskite-type lead-containing composite oxide powder using hydrothermal reaction; ■Process of heat-treating the powder at 500 to 1000°C to cause grain growth and reduce its specific surface area to 20 m"/g or less , ■
The process of mixing the binder and molding, ■Remove the binder from the molded product and reduce the theoretical density to 50%.
% or more, ■ a step of firing the above molded body.

The above perovskite-type lead-containing composite oxide has the general formula A B 0 ! It is expressed as However, A is
pb or pb and Sr, Ca, Ba, La,...
At least one component such as Li, B is Zr
, Ti, Nh, Mg, Ni, Fe, W, Mn
At least one component such as 0 is oxygen.

As a method for producing perovskite-type lead-containing composite oxide powder using a hydrothermal reaction, the above-mentioned Japanese Patent Application Laid-Open No. 63-8
Although the method described in Japanese Patent Application No. 5014 can also be used, it is preferable to use the method of the present inventors' earlier invention (Japanese Patent Application No. 1-30844).

The method generally consists of the following steps.

(a) A step in which water-soluble lead oxide is reacted with a low concentration alkali metal aqueous solution in a reaction vessel to generate a lead-based hydroxide precipitate; (b) Hydroxide other than lead-based hydroxide in the reaction vessel. (C) A step of raising the temperature and pressure inside the reaction vessel to cause a hydrothermal reaction, (d) Filtration, washing and drying. Process.

Note that the hydrothermal reaction (C) above is preferably carried out at P) 112 or higher and a temperature of 150 to 200°C.

The obtained powder was heated to 500-100% prior to compression molding.
The grains were heat-treated at 0°C and grown until the specific surface area became 20 m"/g or less (step ■). The heat treatment atmosphere was air,
The processing time may be about 1 to 5 hours.

The heat-treated powder is mixed with a binder and compression molded using a mold press or the like (step (■)).

The molding pressure is approximately 1 to 3 tons/Cm''.

The above molded body is heated at 400 to 600°C for about 1 to 2 hours to remove the binder and reduce the density to 50% of the theoretical density.
The above molded body is obtained (step (■)).

As will be explained in detail later, if you add the heat treatment described in ■,
After removing the binder, a density of 50% or more and up to about 70% of the theoretical density can be easily obtained.

The molded body thus obtained is fired to form a porcelain composition.
(Step (■)) This firing may be performed at a temperature of about 800 to 1300°C for about 1 to 5 hours. The firing atmosphere is a lead atmosphere or air.

(Function) Hydrothermal synthetic powder usually has a specific surface area of 20 to 70rr? /
g, which is a very large value, and the converted particle size, assuming that they are spherical particles, is 0.05μ or less. Therefore, as a binder, for example, an aqueous solution of 8% by weight of polyvinyl alcohol is added and mixed in an amount of 5 to 10% by weight, and then the powder is press-molded at a pressure of 1 to 2 tons/c4 and heated at 600°.
The density of the molded product after removing the binder for 2 hours at C does not reach 50% of the theoretical density. Therefore, if you want to obtain a fired product close to the theoretical density by firing it, a shrinkage rate of 20% or more is required. As a result, deformation (warp) and cranking occur in the molded product. This is because the particle size of the powder (W) is too small and the porosity of the molded body becomes large. If the specific surface area of the powder is set to 20rd/g or less in advance and the molded body is treated to remove the binder as described above, a molded body having a density of 50% or more of the theoretical density can be obtained, and when this is fired, the shrinkage will be reduced. The rate is
As shown in FIG. 1, it is less than 20%, and the occurrence of deformation and cracking is extremely small.

Prior to molding, the hydrothermally synthesized powder is heated to 500-1000'C.
When heat treated with
．． The thickness can be set to 0.05 μm or more. Thereafter, the density of the compact formed by the same method as above was 50 to 7 of the theoretical density.
It reaches 0%. If this molded body is fired, a dense fired body with a small shrinkage rate and less deformation and cranking can be obtained.

(Example) A hydrothermally synthesized powder was produced using the following steps.

1. Potassium hydroxide (KOj+): Dissolve 1375 g in water to make a total amount of 3500 d, and add lead nitrate (I
A solution prepared by dissolving 650.0 g of 'b(NO,) in 1500 ml of water was added, and the mixture was allowed to react at room temperature for 30 minutes.
A lead-based precipitate is formed.

11. Next, zirconium oxychloride (ZrOCl).

81hO): 393.4 g dissolved in 500 mN water and a T1Cf-aqueous solution (Ti content: 16.7L%): 179. g and lanthanum nitrate (1, a(N
Oi)s ・61bO) :69. Og to 150ml of water
A mixed solution with an aqueous solution dissolved in was added and reacted at room temperature for 30 minutes to produce a zirconium-based precipitate, a titanium-based precipitate, and a lanthanum-based precipitate.

iii. Contains the above precipitate! The Q suspension was transferred to an autoclave and reacted at 180'C for 5 hours. After thoroughly washing the resulting precipitate with water, it was dried at 120°C for 7'15 hours.

The properties and sinterability of the powder obtained in the above steps were investigated.

Figure 2 shows the specific surface area measured by the BET method of the powder obtained in the above process (without heat treatment) and the powder heat-treated at 500 to 900°C for 1 hour, and its conversion as spherical particles. The powder without heat treatment shows a large specific surface area value of 40 nf/g, and its particle size is extremely fine as 0.02 μm.On the other hand,
The t)) powder heat-treated at 900°C for 1 hour has particles with a diameter of about 1 μm.

Next, sinterability was tested using powders heat-treated at 700°C for 1 hour and powders that were not heat-treated.

% polyvinyl alcohol was added as a binder to each powder and mixed well in a mortar. Next, use a mold press to create a diameter of 1
It was press-molded into a molded body of 6 mm and 5 InI11 thickness. The pressure at this time was 1 ton/c4. This molded body was heated at 600° C. for 2 hours to remove the binder, and then the density of the molded body was measured. The results are shown in Table 1.

Table 1: The theoretical density is 7.8 g/cm. As shown in Table 1, the density of the heat-treated powder is:
4.7g/c4, and the density of the powder that has not been heat treated is 3.0g/c4, which is the theoretical density (7.8g/c4).
od) were about 60% and about 38%, respectively.

This is because powder that has not been heat treated is ultrafine particles, as seen from the specific surface area, and the adhesive force that acts between the particles
It is thought that the effect of cohesive force is large, the porosity increases, and the molding density does not increase. On the other hand, heat-treated powder does not have the above problem because the grains are grown to a certain degree of dog size, and the compact density value increases.

Next, using these molded bodies, 1000 to 1250'
Firing was performed for 2 hours at c, and the firing density and radial shrinkage rate were examined. The results are shown in FIGS. 3 and 4, respectively. FIG. 3 shows the relationship between firing temperature and firing density, and FIG. 4 shows the relationship between firing temperature and radial shrinkage rate. In these figures, "Example" is the one obtained by firing the molded article (2) in Table 1, and "Comparative Example" is the one obtained by firing the molded article (2).

In the example, the theoretical density was almost reached at a firing temperature of 1100°C or higher, and the shrinkage rate was about 15%, resulting in a dense fired body without cracks. On the other hand, in the comparative example, 1250°
The theoretical density was not reached even at the firing temperature of C, and the shrinkage rate was 1100.
At a firing temperature of °C or higher, it was as high as 20% or more, and most of these fired bodies had cranks.

Furthermore, the fired bodies of Examples were extremely good not only in density but also in other physical properties (flexural strength, dielectric constant, dielectric tU loss, translucency, etc.).

(Effects of the Invention) According to the present invention, a hydrothermally synthesized powder with fine particles and a highly uniform composition is used as a raw material, and a dense pressure N Eft that suppresses deformation and cranking during firing is used. equipment can be provided. The method of the present invention can be applied to piezoelectric 6i of perovskite-type lead-containing composite oxides whose applications have been expanding in recent years.
This is an extremely excellent method for making pottery.

[Brief explanation of drawings]

Figure 1 shows the relationship between the specific surface area of the hydrothermally synthesized t5 powder and the shrinkage rate when the same powder is molded and fired, and Figure 2 shows the
Figure 3 shows the specific surface area of the hydrothermally synthesized powder before heat treatment and the powder heat treated at 500 to 900°C for 1 hour, and the particle size converted to spherical particles. FIG. 4 is a diagram showing the relationship between the sintering temperature and the sintered density of the sintered body, and FIG. 4 is a diagram also showing the relationship between the sintering temperature and the radial shrinkage rate.

Claims (2)

[Claims] (1) Perovskite-type lead-containing composite oxide powder produced using a hydrothermal reaction and having a specific surface area of 20 m^2/g or less. (2) Powder of a perovskite-type lead-containing composite oxide produced using a hydrothermal reaction is heat-treated at 500 to 1000°C to have a specific surface area of 20 m^2/g or less, and then mixed with a binder and compression molded. A method for manufacturing piezoelectric ceramics, which comprises: removing the binder to form a molded body having a theoretical density of 50% or more; and firing the molded body.