JPH035377A - Method for calcining piezoelectric ceramic formed body - Google Patents

Abstract

PURPOSE:To omit a degreasing stage and to improve production efficiency by using a porous MgO vessel when a mixture of raw powder, a binder and pure water is granulated to form and the formed bodies are placed on one another in the vessel with ZrO2 powder in between and calcined. CONSTITUTION:Raw powders are weighed and mixed, a binder and pure water are added to the mixture, the obtained material is granulated and then press- formed to obtain a piezoelectric ceramic formed body 4, and the plural bodies 4 are placed on one another on an alumina bottom board 2 with ZrO2 powder 3 in between. The assembly is placed in the vessel 6 consisting of a bottom board 1 and a lid 5, and the vessel 6 is introduced into an electric furnace and heated to obtain a piezoelectric ceramic body. A porous MgO vessel is used as the vessel 6 in this method. As a result, the decomposed gas from the binder generated when the formed body 4 is heated is discharged to the outside through the pores of the vessel 6 and removed. Accordingly, the formed body is linearly heated from room temp. to the calcination temp. and calcined.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for firing a piezoelectric ceramic body used in a laminated piezoelectric actuator element.

(Prior art) A laminated piezoelectric actuator has a large number of piezoelectric ceramic bodies and internal electrodes alternately laminated, these internal electrodes are connected in parallel, and voltages of different polarities are applied to every other layer. Since it is capable of expanding and contracting at low voltage and at high speed, it is expected to be used in a wide range of fields such as mechatronics and electronics, such as minute positioning for robot operation.

The piezoelectric ceramic body used in such a laminated piezoelectric actuator element is usually manufactured like a cloth.

First, lead oxide (PbO), titanium dioxide (TiO),
Zirconium oxide (ZrO), niobium pentoxide (Nb, 0
．． ), raw material powder of oxide such as nickel oxide (NIP) is weighed and blended to a predetermined composition, and an organic binder such as PVA and pure water are added using a ball mill.
The mixture is mixed using the hour-hour method and then ground.

Next, this is dried, calcined at 800°C for 2 hours, and purified using a ball mill with the addition of pure water.Next, binder (PVA) is added again, slurry is adjusted, and granulated. , and press to produce a molded piezoelectric ceramic body. The thus obtained molded body was heated to 1100~
It is fired at 1150°C to form a sintered body with a thickness of 500 to 700 nm.

This firing process is usually carried out as follows:
FIG. 5 is a schematic cross-sectional view showing a container used during firing and a molded piezoelectric ceramic body set therein. As shown in Fig. 5, an alumina bottom plate 2 is placed on an alumina bottom plate 1, zirconia powder 3 is spread as a release agent on this bottom plate 2, and the molded bodies 4 and zirconia powder 3 are stacked alternately. , about 5 to 10 molded bodies 4 are stacked, and an M5 made of alumina is placed over the bottom plate 1, and the bottom plate 1 and the lid 5 form an alumina container, in which the stacked molded bodies 4 are accommodated. After this, the entire container is placed in an electric furnace and heated to obtain a piezoelectric ceramic body. At this time, the container 6 prevents the Pb component of the composition from evaporating and escaping.

[Problem to be solved by the invention]

However, the above-described firing process of the piezoelectric ceramic molded body has the following problems. The alumina container shown in Figure 5 is a heating container with high strength and fire resistance, but because it is a dense material, decomposition gas generated during heating of the binder contained in the compact escapes to the outside. This remains in the sintered body and forms pores, which causes deterioration of the properties of the piezoelectric ceramic body. Therefore, in the firing process of the compact, as shown in the temperature program form in Figure 6,
The temperature was maintained at 550°C for 5 hours at a heating rate of 50°C/hr to diffuse the binder decomposition gas to the outside.
The lid 5 of the alumina container 6 shown in the figure must be removed and the container 6 placed in an oven condition, and - once returned to room temperature, it is heated to 1150° C. at a heating rate of 100'tl:/hr.
The molded body 4 is fired by holding the temperature for 2 hours, but using such a temperature program requires heating and cooling twice before the firing process is completed, which requires a lot of work. The firing process, including the above, takes a long time, significantly reducing manufacturing efficiency.

The present invention has been made in view of the above-mentioned points, and its purpose is to provide a piezoelectric ceramic that can obtain good characteristics even if the heating process for removing the binder is omitted when firing a piezoelectric ceramic molded body. An object of the present invention is to provide a method for firing a ceramic body.

[Means to solve the problem]

In order to solve the above problems, the method for firing a piezoelectric ceramic molded body of the present invention involves stacking a plurality of molded bodies with zirconia powder sandwiched between them, storing them in a magnesia container, and heating the piezoelectric ceramic molded body together with the container in the atmosphere at a temperature ranging from room temperature to The temperature is linearly raised to 100%, held for a predetermined period of time, and then allowed to cool.

[Effect]

As mentioned above, since the method of the present invention uses a porous magnesia container as the container for housing the molded body during firing, there is no need to set the temperature to 550°C to remove the decomposed gas of the binder, and the temperature can be reduced to room temperature. During the process of linearly increasing the temperature from the temperature to the firing temperature, the binder decomposed gas is degassed from the pores of the porous magnesia container, and the binder decomposed gas has no effect on the resulting sintered body. In addition, this container prevents the Pb component in the compact composition from deviating, making it possible to obtain a sintered compact with a stable composition similar to when using an alumina container, and the piezoelectric ceramic body exhibits good properties. show.

〔Example〕

The present invention will be explained below based on examples.

The firing method of the present invention is the same as the conventional method, except that the molded body is placed in a container and fired in order to prevent the Pb acid component contained in the molded piezoelectric ceramic body from being lost by evaporation. The difference from the conventional method is that the container used in the process is made of porous magnesia instead of alumina, and the temperature program for firing is different from conventional ones. Therefore, since the method for producing the molded bodies and the state in which they are stacked and housed in a container are the same as the schematic cross-sectional view shown in FIG. 5, the explanation thereof will be omitted, but will be described again with reference to FIG. 5.

The container material used in the present invention has a purity of 97% and an apparent porosity of 2.
It is made of approximately 0% porous magnesia. When the container i made of porous magnesia is used, the decomposed gas of the binder generated during heating from the molded body 4 placed therein can escape to the outside through the pores in the grain boundaries of the container. Therefore, the temperature program diagram for firing can be made as shown in FIG.

That is, the temperature during the firing process of the compact 4 is increased from room temperature to 115°C at a rate of 50°C/hr, as shown in Figure 1.
The temperature was raised linearly to 0°C, maintained at this temperature for 2 hours, and then allowed to cool. At this time, the decomposition gas of the binder generated from the molded body 4 is dissipated to the outside through the pores of the container by the time the molded body 4 reaches its firing temperature of 1150°C. There is no need to set a temperature program for time processing. This can be seen from the comparison between Figures 1 and 6.
This makes it possible to significantly shorten the firing time.

In the case of the present invention, zirconia powder 3 is spread between the molded bodies 4 on the alumina bottom plate 2, and the molded bodies 4 are stacked, but if the number of molded bodies 4 to be stacked at one time is 5 or less, it is difficult to hold them down. There is a risk that the molded body 4 may warp.
If it is more than 0, the weight will increase and it will be difficult to shrink uniformly, so it is better to use about 5 to 10 blocks.Also, increase the number of blocks stacked with molded bodies 4, and use a container with a large internal volume. It goes without saying that if used, mass production effects can be expected.

Next, the density of the piezoelectric ceramic sintered body produced as described above is shown in the diagram of FIG. 2 in relation to the firing temperature. The density of the sintered body is 8.2, which is the same as before. Figures 3 and 4 show piezoelectric properties obtained by assembling a laminated piezoelectric actuator element using the sintered body obtained by the method of the present invention, and the characteristic values are expressed in relation to the firing temperature of the sintered body. FIG. FIG. 3 shows the relative dielectric constant (ε/ε.), which rises significantly at 1100°C and reaches a peak value of 5700 around 1150°C. FIG. 4 shows the electromechanical coupling coefficient (K7), which similarly becomes 0.5 or more at around 1150°C. ε/ε. Both the values of and 1 are equivalent to those obtained when piezoelectric ceramics are fired using a conventional alumina container, and as in the present invention, a magnesia container is used and the temperature program in the binder removal process is omitted. This shows that even when fired, a sintered body with good piezoelectric properties can be obtained.

〔Effect of the invention〕

When firing a piezoelectric ceramic molded body, if the molded body is placed in a dense alumina container, the binder contained in the molded body is removed during heating.
-While it is necessary to first remove the lid of the container and hold it at an intermediate temperature, as in the present invention, it is possible to use a container made of porous magnesia, store the molded object in it, and then fire it. As a result, the decomposition gas of the binder dissipates to the outside through the pores of the porous magnesia container during heating, so the firing temperature program can be raised linearly from room temperature to the firing temperature, and as a result, the molding The time required for firing the piezoelectric ceramic body is significantly shortened, the production efficiency of the piezoelectric ceramic sintered body is increased, and the piezoelectric properties of the obtained sintered body are as good as those of the conventional piezoelectric ceramic body.

[Brief explanation of the drawing]

Figure 1 is a diagram of the firing temperature program for piezoelectric ceramic molded bodies obtained by the method of the present invention, Figure 2 is a diagram of the relationship between firing temperature and density of the piezoelectric ceramic sintered body obtained by the method of the present invention, and Figure 3 is Similarly, Figure 4 is a diagram showing the relationship between firing temperature and dielectric constant, Figure 4 is a diagram showing the relationship between firing temperature and electromechanical coupling coefficient, and Figure 5 is a schematic cross-sectional view showing the state of the molded body housed in the container during firing. , FIG. 6 is a diagram of a conventional firing temperature program. 1; Bottom plate, 2: Bottom plate, 3: Zirconia powder, 4; Molded object,
5; lid, i: container.

Claims (1)

[Claims] 1) After weighing and mixing the raw material powders, adding a binder and pure water and granulating them, in order to fire the press-molded piezoelectric ceramic compact, a plurality of the compacts are stacked with zirconia powder sandwiched between them to form a porous structure. 1. A method for firing a piezoelectric ceramic molded body, which comprises placing the molded body in a magnesia container, raising the temperature linearly together with the container from room temperature to a predetermined firing temperature in the atmosphere, holding it for a predetermined time, and then allowing it to cool.