JPH03285876A - Roasting method for piezoelectric ceramics - Google Patents

Abstract

PURPOSE:To roast a piezoelectric ceramics molded body without causing deterioration and mutual melt-sticking of the molded body by adding ZnO2 powder to powder having the same component as the piezoelectric ceramics molded body to form a green sheet and interposing either ZnO2 particles having large diameter due to calcination or the formed green sheets between the respective piezoelectric ceramics molded bodies in the case of laminating these molded bodies at a plurality of stages and roasting them. CONSTITUTION:Piezoelectric ceramics molded bodies 1 are laminated on an aluminum plate 3 spread on the bottom of a roasting vessel 2 and sealed by a cover 5 and introduced into a heating furnace and roasted at a high temp. of 1150-1200 deg.C. ZnO2 particles whose particle diameter is made large by calcining treatment or a green sheet 6 described hereunder are placed between the alumina plate 3 and the piezoelectic ceramics molded body 1 placed thereon. The green sheet 6 is formed by mixing ZnO2 powder with powder having the same component as the piezoelectric ceramics molded body. Further the coarse ZnO2 or the green sheets 6 are interposed between the laminated respective molded bodies 1. Thereby the piezoelectric ceramics molded bodies 1 are roasted with good yield without changing the composition thereof and melt-sticking the molded bodies with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for firing piezoelectric ceramics used in laminated piezoelectric elements and the like.

[Conventional technology]

Piezoelectric ceramics (hereinafter abbreviated as PZT) are sometimes used alone, but in order to obtain large displacements and generated forces, PZT and internal electrodes are alternately laminated as a multilayer piezoelectric element, and these internal electrodes are connected in parallel. By applying voltages of different polarities to every other layer and expanding and contracting the PZT sandwiched between internal electrodes, high-speed expansion and contraction is possible with low voltage. It is expected that it will be widely used in fields such as electronics and electronics.

PZT used in such laminated piezoelectric elements is
It is usually made like a garment. First, lead oxide (PbO
), titanium dioxide HiL), zirconylum oxide (Zr
Ox), niobium pentoxide (NbzOs), dioxide, Kel (
Weigh and blend raw material powder of oxides such as NiO) to a predetermined composition, add an organic binder such as polyvinyl alcohol (PVA) and pure water using a ball mill,
After mixing in a 24-hour method, it is ground.

Next, this is dried and calcined at 800° C. for 2 hours, and pure water is added again and pulverized for 96 hours using a ball mill.

Next, PVA is added again to prepare a slurry and granulate it, followed by pressing to produce a piezoelectric ceramic molded body. The molded body thus obtained was placed in the atmosphere at a temperature of 1150
By firing at ~1200℃, the thickness is 500~70℃.
PZT can be obtained as a sintered body of 0JIIl.

Of the above PZT manufacturing methods, the firing process of the molded body will be described in more detail. This firing process is carried out in a conventional manner. FIG. 8 is a schematic cross-sectional view showing a state in which the piezoelectric ceramic molded bodies 1 are stacked in several stages in the firing container 2 and arranged in several rows. In Figure 8,
On the alumina plate 3 that serves as the bottom plate of the firing container 2,
5 to 10 molded bodies 1 are stacked one after another, and at this time, they are passed through an 80-mesh sieve on the alumina plate 3 so that the specific surface area is 2. (Sprinkle ZrO□ powder 4 having a particle size of about 1+”/g uniformly, place the compact 1 on top of it, and then
After sprinkling r0t powder 4, placing the molded body 1 (this process is repeated, and the ZrO powder 4 and molded body 1 are piled up alternately so that the upper layer is again ZrO and powder 4. In this way, the molded body The reason for interposing the Zr01 powder 4 between the molded bodies 1 and 1 is to make it easier to peel off the molded body 1 after firing.
The purpose of stacking the molded bodies 1 is to increase the yield of the sintered body obtained by multiple firings. Then, the firing container 2 is covered with a lid 5, and heated as described above using an electric furnace or the like (not shown).
By heating to 1150 to 1200°C, a large number of PZT sintered bodies can be obtained at the same time.

[Problem to be solved by the invention]

However, the above-described firing process of the piezoelectric ceramic molded body has the following problems. That is, as mentioned above, since the firing temperature is as high as 1,150 to 1,200°C, the Zr0t powder seizes or welds to the molded body, causing damage to the sintered body.
IM becomes difficult in some cases, and some of the constituent components of the piezoelectric ceramic molded body, especially Pb, easily evaporate and react with the ZrO powder interposed between the molded bodies.
The problem is that the composition of PZT after firing differs from the original composition. As a result, as a matter of course, defective @ separation lowers the manufacturing yield, and changes in the composition of the sintered PZT impair its properties.

The present invention has been made in view of the above-mentioned points, and its purpose is to prevent welding between PZT after firing and to prevent compositional deviation of PZT when firing a piezoelectric ceramic molded body. The purpose of the present invention is to provide a firing method.

[Means to solve the problem]

In order to solve the above problems, a first method of the present invention involves pre-calcining ZrO2 powder to increase the particle size before firing a piezoelectric ceramic molded body.
Using this calcined powder, it is sandwiched between stacked piezoelectric ceramic molded bodies and fired, and the second method is to use powder having the same components as this piezoelectric ceramic molded body and Z
A green sheet produced using a mixed powder with r01 powder is sandwiched between piezoelectric ceramic molded bodies and fired.

[Effect]

In the first method, ZrO□ powder is added in advance to 1250 to 1
Calcination treatment at 350℃, specific surface area force 0.5-1.0
A calcined powder of ZrO with a large particle size in the range of m"7g is sandwiched between each piezoelectric ceramic molded body, and fired in a state where many gaps are formed in contact with the piezoelectric ceramic molded body. Therefore, when the particle size of the Zr01 powder is small during the firing process of the piezoelectric ceramic molded body, there are many point contact areas between the powder and the piezoelectric ceramic molded body (this causes a reaction with the piezoelectric ceramic molded body, causing welding and warping. It is possible to eliminate the drawback that peeling occurs easily and to obtain a healthy PZT sintered body at a high yield.

The green sheet used in the second method was made by mixing Zr0t powder with a powder having the same components as the piezoelectric ceramic molded body to create a powder coarser than the raw material used to make the piezoelectric ceramic molded body, and processing this into a green sheet shape. During the firing process, the piezoelectric ceramic molded body and the green sheet are sintered at the same time, but at this time, the green sheet, which has a larger grain size than the piezoelectric ceramic molded body, contains Zrot particles that have a higher sintering temperature. Therefore, sintering takes longer than piezoelectric ceramic molded bodies, and the atmosphere inside the firing container is controlled to be rich in PB, which works to suppress the evaporation of the PB acid component during firing of the piezoelectric ceramic molded body. At the same time, since the components evaporated from the piezoelectric ceramic molded body and the green sheet do not actively react with each other, they do not seize or weld to each other until the piezoelectric ceramic molded body is completely fired.

〔Example〕

The present invention will be explained below based on examples.

In the first method of the present invention, the method of firing the piezoelectric ceramic molded body itself is basically the same as that shown in FIG. I will refer to it and describe it. In FIG.
The difference between this method and the conventional one is that the specific surface area is 2.0 m”/g.
Rather than using the conventional ZrOx powder 4 as it is, it is calcined at a high temperature in advance to further reduce the specific surface area, that is, Zr01 with a larger particle size.
This is because the calcined powder 4a was used.

The calcination treatment of the Zr01 powder 4 is carried out by storing it in an alumina container or the like and heating and maintaining it at a high temperature of 1250-1350 t in an electric furnace. Figure 1 shows the 1250°C calcination treatment of the obtained ZrOx calcined powder 4a. FIG. 3 is a diagram showing the relationship between keep time and specific surface area in FIG. According to Figure 1, ZrOx
The specific surface area of the calcined powder 4a shows a tendency for the particle size to increase until the keeping time is about 8 hours, but after that, the specific surface area value is almost within the range of 0.5 to 1.0 g + 7 g. No change was observed, which means that the treatment temperature was 1300℃, 13
It was found that the same tendency was observed even at 50℃, so
The Zr0t calcined powder 4a used in the first method of the present invention is 12
Use one kept at 50°C for 8 hours. This ZrO
□Peeling occurs when the calcined powder 4a and the piezoelectric ceramic molded body 1 are alternately stacked and fired.

Welding 9 In order to determine the optimum calcination time that does not cause warping, the state of the sintered body after firing was examined by varying the holding time, and the results are shown in Table 1.

Table 1 In Table 1, ○ indicates that the PZT after firing was all good, Δ indicates that some were good depending on the stacking position of the piezoelectric ceramic molded bodies 1, and × indicates that the PZT was defective.

As can be seen from Table 1, the Zr0t powder 4a with a calcination keeping time of 8 hours or more satisfies both peeling and welding warpage.

Next, the bulk density of the PZT sintered body obtained by firing the piezoelectric ceramic molded body l using this ZrOx calcined powder 4a,
zrO! The relationship with the powder calcination keeping time was determined and the results are shown in the diagram in Figure 2. As shown in Figure 2, the bulk density of the sintered body increases with the ZrOx powder calcination keeping time, but when the keeping time is 6. Until the time, the particle size of the ZrO2 powder is small and the bulk density is low, and after 8 hours, the particle size becomes large and the bulk density of the sintered body becomes high. This shows good correspondence with the relationship with the specific surface area in FIG. Figure 3 shows the piezoelectric properties of PZT and Zr0t calcined powder 4a using this sintered body.
This is a diagram showing the relationship between calcination keeping time and the vertical axis is the electromechanical coupling coefficient (K,). From the results in Figure 3,
It can be seen that the longer the calcination keeping time, the better the piezoelectric properties can be obtained.

As described above, in the process of firing the piezoelectric ceramic molded body, the ZrO and calcined powder 4a interposed between the molded bodies are pre-calcined to increase the particle size, that is, to reduce the specific surface area to 0.
．． 5-1. By using this ZrO and calcined powder 4a, it is possible to easily peel off after firing without causing welding or warping, and to maintain stable piezoelectric properties of the PZT sintered body. Obtainable.

As described above, in the first method of the present invention, the Z
r (h If the particle size of the powder 4 is small as in the conventional case, there will be many point contact areas between each molded body 1 and the ZrO2 powder 4, which will easily cause a reaction with the molded body 1, resulting in welding and warping. It becomes difficult to peel off, whereas Zr(h powder 4 is 1250~1
By using the ZrO□ calcined powder 4a, which has been calcined at 350°C for about 8 hours to increase its particle size, there are many gaps between the powder and the molded body 1, making it difficult to react and causing drawbacks such as welding. A healthy PZT sintered body can be obtained without causing any damage.

Next, the second method of the present invention will be described. Figure 4 is the second
8 is a schematic cross-sectional view showing a state in which piezoelectric ceramic molded bodies 1 are stacked and arranged in a firing container 2 by the method of FIG. The difference between FIG. 4 and FIG. 8 lies in the material used to separate the molded bodies 1 between them. In the second method, this material is a powder having the same composition as each molded body 1. The green sheet 6 is separately prepared from a mixed powder of ZrO□ powder and ZrO□ powder.

The method for manufacturing green sheet 6 is to add Zr to PZT raw material powder.
The process of mixing O2 powder and re-pulverizing using a ball mill was the same as in the case of the piezoelectric ceramic molded body 1 described above, but whereas the crushing time was 96 hours for the piezoelectric ceramic molded body 1, When producing the green sheet 6, the crushing time is 24 hours. This is to make the green sheet 6 have coarser particles than the molded body 1, so that it is less likely to react than the molded body 1 at the same firing temperature. After that, this mixed powder is dried, a predetermined amount of a solvent such as toluene is added, and PVA is further added.
Mix for 4 hours. A green sheet with a thickness of 300 to 500 us can be produced from the obtained slurry by a doctor blade method. This is punched out to have the same diameter as the molded body 1 and used.

When firing the piezoelectric ceramic molded body 1 using the green sheet 6 obtained in this way, in order to find the optimal amount of ZrO□ powder to be added as the raw material powder of the green sheet 6, the amount added is varied and The welding state of the molded body I was examined. The results are shown in Table 2.

Table 2 In Table 2, ○ indicates that all of the PZT after firing has peeled off, Δ indicates that some of the PZT has peeled off, and × indicates that seizure or welding has occurred.

As can be seen from Table 2, the firing temperature was 1100℃, 11
The one that satisfies both the conditions of 50'C and 1200°C is one in which the amount of ZrO□ powder added is 30% by weight.

Therefore, when the piezoelectric ceramic molded body 1 was fired using the green sheet 6 made by adding 30 weight 2 of ZrOx powder to the raw material powder having the same composition as the piezoelectric ceramic molded body 1, the difference between the obtained PZT and the green sheet 6 How the shrinkage rate after sintering changes depending on the firing temperature is determined, and the results are shown in the diagram in FIG. ) represents the change in shrinkage rate of PZT.

If the difference in shrinkage rate after sintering between PZT and green sheet 6 is too large, shape changes may occur during the firing process, resulting in a healthy P
There is a concern that it will be difficult to obtain ZT, but as shown in Figure 5, there is a certain difference in the shrinkage rate between the two at lower firing temperatures, but as the firing temperature increases, the difference becomes smaller, and it is actually difficult to form piezoelectric ceramics. 120 to fire body 1
It was found that there was no problem at around 0°C.

Next, FIG. 6 shows the piezoelectric properties of PZT obtained using the same green sheet 6 as in FIG. It is a relationship diagram in which the axis is the electromechanical coupling coefficient (K,). Curve (A) in FIG. 6 is the second method 1 curve (
B) represents the piezoelectric properties obtained by the conventional method. As shown in Figure 6, the improvement in properties is greater at lower firing temperatures, but overall the second method of the present invention has better properties. It has been obtained.

Similarly, FIG. 7 is a diagram showing the relationship between firing temperature and bulk density by comparing the second method of the present invention and the conventional method, and the curve (a) in FIG. Method 2.

The curve (b) represents the change in bulk density of the conventional method. The bulk densities tend to be similar to each other with respect to the firing temperature, but the present invention maintains a higher value.

The fact that the results shown in FIGS. 6 and 7 are obtained above indicates that the evaporation of the Pb acid component is suppressed during the firing process of the piezoelectric ceramic molded body 1, and no deviation occurs in the composition of PZT. This is because, in the second method of the present invention, since the green sheet 6 is interposed between the molded bodies 1, the atmosphere in the firing container is conveniently adjusted to be Pb1J in the firing process. Particularly in the case of the second method of the present invention, sintering of both the piezoelectric ceramic molded body l and the green sheet 6 progresses simultaneously during the firing process, but the particles contained in the green sheet 6 having ZrO2 having a high sintering temperature are molded. The fact that the green sheet 6 is coarser than the particles contained in the green sheet 1 means that it takes longer for sintering to proceed at the same sintering temperature, and in this respect, it is easier to peel off after sintering the green sheet 6. This contributes to both the atmosphere adjustment and the prevention of PZT composition deviation. As a result, stable P with improved characteristics
ZT can be obtained.

〔Effect of the invention〕

When piezoelectric ceramic molded bodies are stacked and fired, a Z is placed between each molded body to prevent the molded bodies from welding together.
The conventional method of placing r01 powder was insufficient not only because of the problem of welding but also because it caused compositional deviation after firing.However, as described in the examples of the present invention, the first method Rather than using the Zr01 powder with a small particle size as it is, it is calcined at high temperature to make the particle size larger with a specific surface area of about 0.5 to 1.0 m''/g. By interposing the piezoelectric ceramics between each compact and increasing the gap between them and making it difficult to react with the compact, welding can be prevented and the sintered compact can be easily peeled off, ensuring healthy PZT. Obtainable.

In addition, in the second method, a green sheet is used instead of ZrJ powder, and this green sheet is used to create a piezoelectric ceramic molded body by mixing powder with the same components as the piezoelectric ceramic molded body and Zr(h powder). Because it is processed into a green sheet as a powder coarser than the raw material, the sintering speed is slower than that of a piezoelectric ceramic molded body during the firing process. Since there is no reaction between the piezoelectric ceramic molded body and the green sheet, they will not seize or weld to each other until the piezoelectric ceramic molded body is finished firing.
In this way, in the second method, since PZT is used in the form of a green sheet, it is difficult to peel off the PZT.
This simultaneously solves the problem of composition deviation.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the calcination keeping time and specific surface area of ZrOx powder in the first method of the present invention, and Figure 2 is a diagram showing the relationship between the calcination keeping time and bulk density of ZrO□ powder. Figure 3 shows the relationship between the calcination keeping time of Zr0t powder and the piezoelectric properties of PZT, and Figure 4 shows the relationship between the piezoelectric properties of PZT and the calcination keeping time of Zr0t powder. Schematic sectional view showing the arranged state, No. 5
The figure is a diagram showing the change in shrinkage rate after sintering in the second method of the present invention by comparing the green sheet and the molded body. Figure 6 shows the piezoelectric properties of PZT in the second method of the present invention and the conventional method. Figure 7 is a diagram showing the relationship between firing temperature and bulk density in comparison between the second method of the present invention and the conventional method. FIG. 2 is a schematic cross-sectional view showing a state in which piezoelectric ceramic molded bodies are stacked and arranged inside the housing.

Claims (1)

[Scope of Claims] 1) A plurality of piezoelectric ceramic molded bodies are stacked and housed in a firing container, and the piezoelectric ceramic molded bodies are heated together with the firing container to a predetermined temperature, so that the piezoelectric ceramic molded bodies are calcined in advance. A method for firing piezoelectric ceramics, characterized in that ZrO_2 powder is sandwiched between the piezoelectric ceramic molded bodies and the firing is performed. 2) A method for firing piezoelectric ceramics according to claim 1, characterized in that the calcination treatment is carried out for 8 hours or more. 3) Powder having the same composition as the piezoelectric ceramic molded body is used when firing the piezoelectric ceramic molded body by stacking a plurality of piezoelectric ceramic molded bodies and storing them in a firing container and heating them together with the firing vessel to a predetermined temperature. A method for firing piezoelectric ceramics, characterized in that the firing is performed by sandwiching a green sheet formed using a mixed powder of ZrO_2 powder and ZrO_2 powder between the piezoelectric ceramic molded bodies.