JPH04144970A - Burned structure of piezoelectric ceramics - Google Patents

Abstract

PURPOSE:To suppress deformation of piezoelectric ceramic sintered compacts by arranging piezoelectric ceramic compacts in a gap between a pair of holding plates oppositely through specific spacers and burning the aforementioned compacts. CONSTITUTION:A pair of holding plates 3 are arranged oppositely through a pair of spacers 2, having a larger thickness than that of piezoelectric ceramic compacts 1 before burning and providing a smaller thickness than that of the compacts 1 with a higher shrinkage factor than that of the compacts 1 after the burning and the compacts 1 are placed in the gap between the holding plates 3. The resultant sandwich is then arranged in a sheath and heated to reduce the thickness of the spacers 2 from that of the compacts 1 and a load of the holding plates 3 is applied to carry out the burning.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a piezoelectric ceramic firing structure for firing a piezoelectric ceramic molded body used for a piezoelectric laminate or the like.

[Prior Art] Piezoelectric ceramics are formed by forming a predetermined ceramic powder into a thin plate shape and then firing it.

During firing, this ceramic molded body is likely to warp or deform. In order to prevent this warping and deformation, methods are used such as slowing down the rate of temperature rise in the initial stage of firing, and baking with a bedding powder that acts as a so-called lubricant around the molded body.

For example, Japanese Patent Application Laid-Open No. 18474 discloses that, when firing using bed powder, a weight of 0.5 to 2 times the weight of the molded body is applied to the ceramic molded body through the bed powder. A method of firing and preventing warping and deformation is disclosed.

[Problems to be Solved by the Invention] Although the above method can suppress deformation of the piezoelectric ceramic in the thickness direction, deformation is more likely to occur in the length direction. This is because, in the early stages of firing, the bedding powder sinks into the surface of the ceramic molded body, creating unevenness, which locally prevents shrinkage in the length direction, causing deformation and, in some cases, cracking of the fired body.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fired piezoelectric ceramic body that suppresses warping and deformation.

[Means for Solving the Problems] The piezoelectric ceramic firing structure of the present invention includes: a piezoelectric ceramic molded body to be fired; a pair of opposing plates holding the piezoelectric ceramic molded body within a space therebetween; A piezoelectric ceramic firing structure comprising at least a pair of spacers arranged within a gap between the retaining plates and adjusting the size of the interval between the retaining plates during firing of the piezoelectric ceramic molded body, the spacer comprising: The thickness of the piezoelectric ceramic molded body is greater than the thickness of the piezoelectric ceramic molded body before firing, and is less than the thickness of the piezoelectric ceramic molded body after firing, and has a shrinkage rate that is greater than the contraction rate of the piezoelectric ceramic molded body.

This piezoelectric ceramic firing structure suppresses deformation of the piezoelectric ceramic fired body by adjusting the load applied to the piezoelectric ceramic during firing by changing the thickness of the spacer.

This spacer is made of a ceramic molded body that has a shrinkage rate different from that of the piezoelectric ceramic molded body, and is thicker than the piezoelectric ceramic molded body at the start of firing, and smaller than the piezoelectric ceramic molded body at the end of firing. use something

That is, at the initial stage of firing when dimensional changes are large, the holding plate is supported by a spacer that is larger than the thickness of the piezoelectric ceramic molded body, and no direct load is applied to the piezoelectric ceramic molded body, so that it can freely contract. As firing progresses, the shrinkage rate of the ceramic molded body making up the spacer is greater than that of the piezoelectric ceramic molded body, so the thickness of the spacer becomes smaller than that of the piezoelectric ceramic molded body midway through, and the load is directly applied to the piezoelectric ceramic molded body. Firing proceeds in this state. In the area where the overall contraction has decreased, the load is applied, so
The obtained fired body will not be deformed.

For this reason, the spacer needs to have a higher shrinkage rate than the piezoelectric ceramic molded body. To achieve this, for example, if ceramic powder is used and molded at a low pressure during molding, the shrinkage rate can be made larger than when molded at a high molding pressure. That is, when molding is performed at a low molding pressure, the distance between particles within the molded object is widened, and during firing, the distance between the particles is narrowed and the molded object shrinks significantly compared to the dimensions of the molded object. The shrinkage rate of the ceramic molded body can also be increased by increasing the amount of binder added to the ceramic molded body.

The spacer is preferably formed using the same ceramic powder as the piezoelectric ceramic, and the molding pressure is lower than that of the piezoelectric ceramic molded body, or the amount of binder used is larger than that of the piezoelectric ceramic molded body. It can be formed by

Piezoelectric ceramics are not particularly limited as long as they have a piezoelectric effect; for example, perovskite crystal a
3aT i 03 and PbT i 03 or CaT
Solid solution with + 03, PbZrO3 and PbT i 0
A solid solution of No. 3 (PZT) can be used.

The holding plate supported by the spacer may be heat resistant, for example, plate-shaped, not deformed at the firing temperature, capable of applying a load to the piezoelectric ceramic molded body, and not reacting with the piezoelectric ceramic molded body.

[Function] In this firing structure, the spacer that supports the load applied to the piezoelectric ceramic molded body during firing is formed from the same type of ceramic powder as the ceramic molded body, and its thickness is larger than that of the piezoelectric ceramic molded body, and the shrinkage rate due to firing is large. things are used. When the contraction is large in the early stage of firing, the piezoelectric ceramic molded body is not subjected to any load and freely contracts.

Therefore, since shrinkage in the length direction is not hindered, cracks and the like can be prevented. Then, in the latter stage of firing, the thickness of the spacer becomes equal to or smaller than that of the piezoelectric ceramic molded body, so the spacer is fired under a load. As a result, warpage and deformation of the obtained fired body can be suppressed.

[Example] Hereinafter, this will be explained in detail using examples.

FIG. 1 shows a side sectional view of this firing structure before firing, FIG. 2 shows a side sectional view at an early stage of firing, and FIG. 3 shows a side sectional view at a later stage of firing.

A piezoelectric ceramic molded body 1 to be fired, a holding plate 3 that holds the piezoelectric ceramic molded body 1 within the interval between a pair of opposing plates, and a holding plate 3 arranged within the interval between the holding plates 3 to hold the piezoelectric ceramic molded body 1 during firing. It is comprised of at least a pair of spacers 2 for adjusting the size of the interval between the plates 3. The thickness of the spacer 2 is greater than the thickness of the piezoelectric ceramic molded body 1.

The holding plate 3, the piezoelectric ceramic molded body 1, and the spacer 2 were manufactured as follows.

The holding plate 3 is made by mixing ZrO2 with an average particle size of 1.00 μm and PZT powder with an average particle size of 30 μm at a weight ratio of 8=2, and adding 0.2% by weight of polyvinyl alcohol (PVA) to this. 150X150X5 by mold press
It was formed by molding it into a size of 100 mm and baking it at 1250° C. for 5 hours.

The piezoelectric ceramic molded body 1 is made of Pb (Zro).

s 2Tioo, 4B Pb so that the composition is >03
Each powder of ZrO2, ZrO2, and TiO2 was weighed and mixed with water 24 hours a day in a ball mill. After drying, this was calcined at 800° C. for 6 hours to form PZT. Then, it was ground in a ball mill until the average particle size was 1 μm. Add 0.5% by weight of PVA as a binder to this, granulate it, and press it with a mold press at a pressure of 1°5 tons/7t of Cl to reduce the diameter to 1.
8All! , and a thickness of 11IIn.

The spacer 2 undergoes the same process as the piezoelectric ceramic described above up to calcination. Next, the average particle size was 1.0 μm using a ball mill.
PVA was added in an amount of 0.5% by weight, and after granulation, the diameter was 18all+1. It was molded to a thickness of 1.2 Bm.

The holding plate 3, spacer 2, and piezoelectric ceramic molded body 1 formed as described above are held as shown in FIG.
This was fired in an alumina pod at 1250'C for 2 hours to obtain a piezoelectric ceramic fired body.

Before firing, the spacer 2 supports the holding plate 3. At the initial stage of firing, the spacer 2 is still thicker, and the piezoelectric ceramic molded body 1 can freely contract. In the later stage of firing, the thickness of the spacer 2 becomes smaller than that of the piezoelectric ceramic compact 1, and the spacer 2 is fired under the load of the holding plate 3.

The obtained piezoelectric ceramic fired body had a diameter of 15 mm and an ellipticity (difference between the maximum and minimum outer diameters of the fired body) of 20 μm.
It was below. Moreover, the fired body placed on the fixed plate had no warpage that would cause the thickness gauge to be inserted between them, and had excellent parallelism.

(Comparative Example) This is a case where the holding plate 3 was placed directly on the piezoelectric ceramic molded body 1 without using the spacer 3, and fired under the same firing conditions as in the example. The obtained fired piezoelectric ceramic bodies had a large ellipticity of 30 to 200 μm, and were highly deformed in the radial direction, and cracks were observed in the radial direction in 2 to 3 out of 100 fired bodies. It was done.

Therefore, according to the structure of the present invention, a fired piezoelectric ceramic body without warping or deformation was obtained.

[Effect] According to the firing structure of the present invention, the contraction rate of the spacer during firing is greater than the contraction rate of the piezoelectric ceramic molded body, so that the piezoelectric ceramic molded body can freely contract without being subjected to any load at the initial stage of firing. In the later stages of firing, the thicknesses of the spacer and the piezoelectric ceramic molded body are reversed, and a load is applied to the piezoelectric ceramic molded body. Therefore, even if warping or deformation occurs due to the heating rate being increased in the initial stage when the molded body shrinks greatly, the warping or deformation can be suppressed in the final product because the load is applied in the later stages of firing. Therefore, there is no need to perform the initial heating slowly over a long period of time as in the conventional method, and the heating during firing can be easily controlled.

The obtained fired body has less warpage and deformation, and it is possible to reduce processing costs when commercializing the product. It also becomes possible to omit processing steps.

In addition, spacers can easily have a higher shrinkage rate than piezoelectric ceramics by lowering the pressure during molding.
No special process required.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of the fired structure before firing, FIG. 2 is a side sectional view of the fired structure at the initial stage of firing, and FIG. 3 is a side sectional view of the fired structure at the end of firing. 1... Piezoelectric ceramic molded body 2... Spacer 3... Holding plate Patent applicant Toyota Motor Corporation

Claims (1)

[Claims] A piezoelectric ceramic molded body to be fired, a pair of opposing plates that hold the piezoelectric ceramic molded body within the interval, and a piezoelectric ceramic molded body disposed within the interval between the retaining plates. A piezoelectric ceramic firing structure comprising at least a pair of spacers for adjusting the distance between the holding plates during firing of the body, the spacer being larger than the thickness of the piezoelectric ceramic molded body before firing, A fired piezoelectric ceramic structure characterized in that after firing, the thickness is less than or equal to the thickness of the piezoelectric ceramic molded body, and the shrinkage rate is greater than the shrinkage rate of the piezoelectric ceramic molded body.