JPS5832519B2 - Manufacturing method of piezoelectric material containing lead - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In recent years, as the development of high-performance filters has become more active, high-quality and high-performance piezoelectric bodies have been required.

Especially television receivers and FM radio receivers. Piezoelectric filters for so-called mass-produced products such as CB transceivers are characterized by no adjustment, so the variation accuracy required for the center frequency of the filter is ±0.5% or less. Therefore, the variation in material properties of the piezoelectric body is also required to be ±0.5% or less.

The present invention relates to a manufacturing method that can reduce variations in the material properties of piezoelectric bodies and facilitate manufacturing, and particularly relates to a method of manufacturing piezoelectric bodies containing lead.

Conventionally, the production variation of ceramics has generally been around 5%, and in particular when manufacturing the lead-containing piezoelectric body related to the present invention, the lead component (
PbO (hereinafter referred to as PbO) is rapidly evaporated.
It has become necessary to control the evaporation of molten metal, and for this purpose various improvements have been made to the original method of molding.

On the other hand, since it is important for the piezoelectric material used as a filter material to have a high density, the evaporation of PbO is approximately 1000
1200-1350℃ even though it is from around ℃
Currently, firing is performed at high temperatures for times ranging from several minutes to several hundred minutes.

The above-mentioned evaporation temperature of PbO is easily influenced by the molding pressure and molding means, and the higher the molding pressure is, the higher the temperature is, and the higher the temperature becomes possible.

It is also known that the evaporation temperature of PbO changes depending on the blending ratio of raw materials.

Therefore, it is natural that the firing conditions (temperature, time, etc.) vary depending on the composition, molding pressure, and molding method.

However, since the evaporation of PbO cannot be suppressed,
In order to control the evaporation of PbO, it is non-porous and Pb
It is common practice to place the molded body in a container made of a material that is less reactive with bO, such as high-purity alumina or high-purity magnesia, and seal it tightly to prevent PbO from evaporating outside the container. It is.

Moreover, the evaporation of PbO rises rapidly with respect to temperature, and the vapor pressure of PbO in a closed container changes sensitively to temperature, so it is necessary to control the variation in firing temperature to about ±3°C. It is also necessary to sufficiently control the cooling conditions after firing.

However, temperature control within a range of ±3°C is industrially extremely difficult, and taking into account variations in furnaces and temperature control equipment, the limit is around ±10°C.

In addition, the evaporation of pbo is extremely sensitive to other firing atmospheres, especially carbon dioxide caused by binder combustion during firing.
O gas components etc. easily reduce the above PbO, so when a binder is used during powder molding, the binder is burned at a temperature of 200 to 700°C before firing to remove harmful CO gas components etc. from PbO. It is common practice to release the material from within the molded body, and then fire the molded body in a sealed manner.

For this purpose, a calcination step is required. Furthermore, even if calcining is performed, it is difficult to sufficiently remove the CO generation valve, and CO is inevitably generated from the molded body during firing.

Therefore, it is difficult to sufficiently suppress variations in material properties of the final piezoelectric body.

On the other hand, non-sealing methods are sometimes adopted industrially, but in this case, the material properties vary widely, and it is difficult to obtain the material variation required for piezoelectric filter materials. Not suitable as a manufacturing method.

In this way, in consideration of the current state of manufacturing methods for piezoelectric materials containing lead, the manufacturing method of the present invention is provided in order to reduce manufacturing variations required for piezoelectric materials used as high-performance filter materials in recent years. be.

Before explaining the present invention, a conventional manufacturing method of a lead zirconate titanate piezoelectric material will be explained.

The manufacturing method is a wet method, and roughly speaking, the steps are: blending the required composition → mixing in a ball mill → drying → calcination → pulverization in a ball mill → drying → granulation → molding → baking with binder → main baking.

The original method for firing is high-purity alumina with an inner diameter of 1
A piezoelectric material containing lead and a thin layer of ZrO2 powder 2 as a powder that does not easily react with the crucible are placed in a crucible 1 having a flat bottom shape of 0 CWL square, and on top of this a piezoelectric material containing lead and a ZrO2 powder 2, which is a powder that does not easily react with the crucible, are spread, and on top of that a piezoelectric material having a length of 34 mm, a width of 24 mm, and a thickness of 24 mm is molded at 700 kg/crtl. Molded body 4 with a length of 7.3 mm
After baking the binder at about 700° C. for 2 hours, the 20 molded bodies were arranged and the crucible 1 was covered with a lid 3 made of high-purity alumina.

This state is shown in FIG. Nao, the composition of the molded body 4 is Pb(Zn3.(Nb2A)o, □2sTio, 48Z
ro, 38.03+IW1% Mr102+0.5wt%
This is Al2O3, which is first calcined at 850°C for 2 hours, then pulverized in a ball mill at 192,000 rotations for a molding process. Table 1 shows the results of main firing for 2 hours each.

Here, the dynamic range is the difference in voltage output level at the first resonance and anti-resonance frequencies in the length direction of the sintered body (molded body), and the frequency constant is the difference between the resonance frequency and the length dimension of the sintered body. It is the product.

Among these characteristics, the particularly important one is the dielectric constant (ε3
3T/ε0) and a frequency constant, and both require manufacturing variations of ±0.5% or less.

As can be seen from this result, as the firing temperature increases, the above-mentioned material characteristic values reach a maximum around 1240° C., and the higher the main firing temperature, the smaller the variation in these values tends to be.

However, it is not possible to satisfy the variation required for piezoelectric materials for filters.

In this way, the characteristic values themselves show considerable dependence on the firing temperature, but as mentioned above, the decrease in the apparent density and other characteristic values after reaching 1240°C has a very strong relationship with the evaporation of PbO. Even in a closed system, evaporation of PbO is unavoidable, and the fact that the characteristic values are not stable indicates that it is extremely difficult to control the evaporation of PbO*.

Table 2 shows the results of varying the firing time at the optimum temperature of 1240°C, and it can be seen that the characteristic values and dispersion vary greatly depending on the firing time.

As described above, the conventional manufacturing conditions have a major drawback in that they are subject to extremely severe manufacturing constraints regarding the evaporation of PbO.

Next, a method for manufacturing a piezoelectric body containing lead according to the present invention will be explained.

The gist of the present invention is to use an open crucible to enable constant exchange of air inside and outside the crucible (particularly for removing CO gas).

The basic idea is to surround the molded bodies placed side by side with a piezoelectric material.
It also proposes specific conditions.

When firing a piezoelectric body containing lead, intense evaporation of PbO from the molded body occurs at around 1200°C, as is well known.

According to the manufacturing method of the present invention, extremely stable firing can be performed in the temperature range of 1100° C. to 1240° C. and for a firing time of 1 to 10 hours.

The specific features of the production method of the present invention include the original method and firing conditions (temperature: 1 hour).

The original method is as shown in Figures 2 to 4, a piezoelectric material containing lead and a crucible 1 are placed at the bottom of a flat-bottomed low-quality aluminum crucible 1'.
A powder (for example, Zr 02 powder) 2 that does not easily react with the crucible 1' is spread around the crucible 1', and a fired piezoelectric body 5 containing lead is placed as a dummy along the inner peripheral surface of the crucible 1'. A molded body 4 is placed on the bottom surface of the crucible 1' surrounded by 5.
The above-mentioned Zr 02 powder was spread thinly on top of the molded body 4, and a piezoelectric body 6 having the same composition as the first dummy piezoelectric body 5 was placed as a dummy, and the molded body 4 was visible when viewed from above. I'll post it so it doesn't exist.

Here, the height of the first dummy piezoelectric body 5 is higher than that of the molded body 4, and the height of the crucible 1' is higher than the height of the second dummy piezoelectric body 6 placed on the molded body 4. In addition, the area occupation ratio of the second dummy piezoelectric body 6 to the area surrounded by the first dummy piezoelectric body 5 is made to be 25% or more.

Next, as an embodiment of the present invention, a molded body 4 having the same composition as that described in FIG.
Arrange the molded bodies 4 in two rows of 10 molded bodies 4 in a flat-bottomed low-quality aluminum crucible 1' with an rL angle so that there is no gap between each molded body 4, and place powder 2 and a dummy piezoelectric on top of the molded bodies 4. Table 3 shows the results of firing at a firing temperature of 1140° C. for 2 hours using the original method in which Body 6 was used.

As is clear from Table 3, according to the method of the present invention, the first
It can be seen that, compared to the conventional example shown in the table, both the relative permittivity dynamic range and the characteristic values are higher, and the variation in each characteristic value is also extremely small.

In the above embodiment, the dummy piezoelectric body 5 In the above embodiment, the floor area occupied by the molded body 4 with respect to the bottom surface surrounded by the dummy piezoelectric body 5 is 82%, and the dummy piezoelectric body 6 The area occupancy rate is 92%.

As can be seen from the above embodiments, while the conventional example described above is a closed type, the present invention is an open type without a lid.

Therefore, in the conventional closed system, since the crucible is sealed, it is thought that the crucible is naturally filled with PbO, but in the present invention, the crucible 1' is also filled with PbO.

That is, since PbO gas is heavier than air, PbO generated from the molded body 4 tends to accumulate in the crucible 1', while on the open side, PbO gas evaporates and scatters from the dummy piezoelectric body 6 placed on the molded body 4. Since the molded body 4 is wrapped from above, combined with the low firing temperature, less PbO evaporates and scatters than the molded body 4.

As a result, the surface of the molded body 4 has a uniform black color, similar to the conventional sealing method.

Incidentally, even if the composite mold bodies 4 are initially arranged so that there are no gaps between them, each mold body shrinks during the firing process, and gaps are created between each mold body as shown in FIGS. 3 and 4. Vapor deposition of PbO and C
O can now be generated freely from the main surface of each molded body.

If firing is performed with the dummy piezoelectric body 6 removed,
Even if the molded body 4 is fired at a low temperature of 1100°C for 1 hour, the surface color of the molded body 4 remains white at the top and slightly blackish at the bottom, but if the firing temperature is further increased to 1240°C, The surface color became more whitish, indicating that the evaporation and scattering of PbO was inevitable.

For example, with the dummy piezoelectric body 6 removed, the firing temperature is 1.
When fired at 140℃ for 2 hours, each characteristic value is ε33T
Ao = 673 ± 7 wards variation 11.1%), frequency constant -1752 ± 28 (1.54%), dynamic range -30 ± 8 (26.7%), apparent density = 7
．． 35? /cr/l, and showed very poor results compared to the present invention.

In this way, in the original method of the present invention, it is thought that a large amount of PbO evaporation and scattering from the molded body 4 is avoided and a PbO atmosphere similar to that of the closed method is created, but it is essentially different from the closed method. The point is that since it is an open type, the air outside the crucible 1' can always be replaced with the air inside the crucible 1'.

Therefore, even if the unburned part of the binder in the molded body remains in the crucible 1' during binder firing, it can be scattered outside the crucible 1', and the CO gas components due to the binder combustion can be vaporized. There is no need to do this.

Therefore, there is no need for a binder firing step.

In the above original method, the height of the crucible 1' is made higher than the height of the dummy piezoelectric body 6 because it takes advantage of the fact that PbO gas is heavier than air. This is to reduce the scattering of PbO gas.

The usage limit of the dummy piezoelectric body 6 is 5 on average.
It can be used for 0 firings, and after 50 firings, the top surface of the dummy piezoelectric body 6 becomes almost whitish, and at the same time,
Cracks develop on the top surface, making it unusable.

On the other hand, the dummy piezoelectric body 5 placed along the inner peripheral surface of the crucible 1' could be used about 100 times.

Further, the material of the crucible 1' is not limited to only high-purity alumina, but low-quality alumina, such as that used in the above embodiments, and having an apparent density of about 85% is sufficient.

In this case, when using a crucible made of high-purity aluminum, there is no problem of the crucible becoming more likely to break as the number of times it is used increases.
It is extremely practical and economical.

All 20 of the molded bodies fired in this manner exhibit desired characteristics and have the advantage that they can be used effectively.

This is an example shown in Table 3, in which one dummy piezoelectric body 6
Even when firing was performed 50 times, the variation in each characteristic value was within ±0.45%, confirming that it was still effective.

However, if, for example, a cracked dummy piezoelectric body 6 is used and the molded body 4 is seen from between the cracks in the dummy piezoelectric body 6 when viewed from above, the part of the molded body 4 corresponding to the cracks will be It becomes whitish and the characteristic variation is 0.
．． This is not desirable because it exceeds 5%.

In the embodiment shown in FIGS. 2 to 4, one dummy piezoelectric body 6 is used for each row, but a plurality of dummy piezoelectric bodies are used to form a wide area corresponding to the dummy piezoelectric body 6. It was confirmed that the same effect as in the above embodiment can be obtained by making the molded bodies 4 invisible when viewed from the top when the molded bodies 4 are obtained and arranged side by side.

Furthermore, the area occupation rate of the dummy piezoelectric bodies 6 relative to the area surrounded by the piezoelectric bodies 5 arranged in parallel along the inner peripheral surface of the crucible 1' also influences the variation in the characteristic values.

In the original method of the present invention described above, the area occupation rate can be changed by changing the size of the dummy piezoelectric body 6 (of course, it goes without saying that it can be made so large that the molded body 4 is not visible when viewed from the top.

), and the results of firing at 1200° C. for 1 hour are shown in Table 4.

From this, it can be seen that when the area occupation rate of the piezoelectric body 6 becomes smaller than 25%, the variation in the characteristic values increases.

Therefore, in the present invention, the area occupation rate of the dummy piezoelectric body 6 with respect to the area surrounded by the dummy piezoelectric body 5 is set to 25% or more.

The area occupation rate of the dummy piezoelectric body 6 of the present invention was determined from this.

Next, in the composition in the example described above, 19200
5700 kg/c after 0 rotation ball milling for 1 hour
Table 5 shows the results of firing the molded bodies molded using rrt at various firing temperatures and firing times.

At a very low firing temperature of 1100°C, firing time 2
It shows a low variation in properties over time, and even after firing for 10 hours, the variation hardly changes.

At 1140°C, even lower variation in properties is shown at any firing time.

It is also shown that this tendency remains almost unchanged even at 1200°C.

At 1240° C., the variation in characteristics tends to increase slightly, but even this is less than ±0.5%.

As described above, according to the present invention, it is possible to obtain a high-quality, high-performance piezoelectric material with extremely low variation in characteristic values at a firing temperature that is unprecedentedly low.

Next, in the present invention, 20 molded bodies were fired in the same manner as in the embodiment using the above method with different lead contained in the piezoelectric body, and Table 6 shows the results.

From this result, all of the lead-containing piezoelectric bodies shown in the above examples show a low characteristic value variation of ±0.5% or less when fired at a temperature of 1200°C or less for 2 to 4 hours. I understand.

Furthermore, it can be seen that even if a piezoelectric body containing lead, which is different from that of the molded body 4, is used as the DA-piezoelectric body 6, no inconvenience occurs.

The same holds true for the other dummy piezoelectric body 5.

In order to further develop the idea of the present invention, crushed powder of a sintered product having the same composition that has already been sintered is placed in a crucible 1' shown in FIG. As a result of embedding the powder so that it could not be seen and firing it for 3 hours at a firing temperature of 1140° C., it was found that the pulverized powder and the molded product were likely to react, making it extremely unsuitable for industrial use.

Furthermore, regarding the above composition, a high-purity aluminum crucible is used instead of the low-quality aluminum crucible 1'.
Cover this crucible with a high-purity aluminum alloy,
As a result of firing at 1160℃ for 3 hours, the apparent density was 7.
．． 51? /crtl, which shows a tendency that sintering does not proceed easily, and has a relative dielectric constant εaa ¥l:.

=705±9 (1,28%), frequency constant 1758±1
1 (0.63%) were both small and their dispersion was large.

In addition, in order to examine the mass productivity of the present invention, 60 molded bodies were placed in a flat-bottomed crucible made of low-quality aluminum with an inner diameter of 20 crIl square, and the area occupation rate of the piezoelectric body 6 was set at 95%. As a result of firing at 1140℃ for 3 hours, the dielectric constant is ε33T/ε.

-7475±3 (0.4%), frequency constant -1790±
6 (0.34%), apparent density -7.69? /cr! I was able to fire it without any problems.

As explained above, according to the manufacturing method of the present invention, by constantly exchanging the air inside and outside the crucible, surrounding the arranged compacts to be fired with a piezoelectric body, and limiting the conditions as described above, A lead-containing piezoelectric body with extremely low variation in characteristic values can be obtained even after firing at a low firing temperature for a long time, and the crucible used in this process can be used repeatedly.

[Brief Description of the Drawings] Figure 1 is a diagram for explaining a conventional method for manufacturing a piezoelectric body containing lead, and Figures 2 to 4 are diagrams for manufacturing a piezoelectric body containing lead in an embodiment of the present invention. FIG. 2 is a perspective view, a sectional view, and a plan view for explaining the method. 1'... Crucible, 2... NrO2 powder, 4... Molded body, 5, 6... Dummy piezoelectric body.

Claims (1)

[Claims] 1. A mixed powder of a piezoelectric material containing lead and a material that does not easily react with the crucible is placed on the bottom of a flat-bottomed crucible, and a first piezoelectric sintered body plate containing lead is placed in the crucible. A plurality of dummy plates are arranged along the inner peripheral surface, and a plurality of molded plates to be sintered to become a piezoelectric body are arranged on top of the mixed powder in a portion surrounded by the first piezoelectric sintered plate. Powder of a material that does not easily react with the crucible is spread on the plurality of molded body plates, and a second piezoelectric sintered body plate containing lead is placed on top of this as a dummy, and the plurality of molded bodies are placed on top of this as seen from above. The plurality of molded bodies are fired by placing the crucible in such a way that the plates are not visible and at least a portion of the opening of the crucible is open, and the crucible is surrounded by the first piezoelectric sintered body plate. The area occupation rate of the second piezoelectric sintered body plate with respect to the area of the crucible is set to 25% or more, and the height of the side wall of the crucible is higher than the height of the mounting position of the second piezoelectric sintered body plate,
A method for manufacturing a piezoelectric body containing lead, characterized in that the height of the first piezoelectric sintered body plate is the same as or higher than the height of the plurality of molded body plates. 2. The method of manufacturing a piezoelectric body containing lead according to claim 1, wherein the first and second piezoelectric sintered bodies have the same composition as the molded body plate.