KR100236185B1 - Particulate lead titanate ceramic and method thereof - Google Patents

Abstract

The invention tea calculation lead (PbTiO ₃₎ relates to the production method, and an object thereof is to provide a hard, non-cracking phase lead titanate (PbTiO ₃₎ ceramic manufacturing method to provide.

In order to achieve the above object, the present invention provides a method for producing lead titanate (PbTiO ₃ ), after weighing PbO powder and TiO ₂ powder in the same molar ratio, pulverizing and mixing them, and then calcining the mixture; Repeating the grinding and calcining process several times; And a step of sintering the calcined powder at a temperature of 1200 ° C. or higher after molding. The technical subject matter relates to a method for manufacturing single-phase lead titanate ceramics, including:

Description

Manufacturing method of single phase lead titanate (PbTiO3) ceramics

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing lead titanate (hereinafter referred to as 'PbTiO ₃ '), and more particularly, to a method for producing hard, crack-free single-phase PbTiO ₃ ceramics.

PbTiO ₃ is a typical perovskite ferroelectric and has a tetragonal crystal structure at room temperature and a cubic crystal structure at 490 ° C. or higher. In addition, the crystal lattice constant ratio (c / a) is 1.063 or less at 490 ° C. or less and has a very high structural anisotropy.

It is known that PbTiO ₃ having such crystal structure characteristics is difficult to manufacture into a rigid sintered body. This is because a large volume change occurs due to the high anisotropy of the crystal structure during the phase transition from the cubic to the tetragonal crystal, so that stresses are generated in the sintered body, and thus microcracks occur throughout the sintered body. (J.Am.Ceram.Soc., Vo149, No.4, pp.229, 1966)

However, PbTiO ₃ has superior ferroelectricity, piezoelectricity, and pyroelectricity compared to other ferroelectrics, and has a high Curie temperature (phase transition temperature) and a small change in physical properties over time. Therefore, various methods have been proposed for commercialization. . Conventionally, products commercially used and used, for example, transition metals, alkalis, and rare earth ions are added to PbTiO ₃ as a sintering aid to make a rigid sintered body having relatively low structural anisotropy, and to high frequency such as piezoelectric vibrator or surface acoustic wave device. It has been developed as an element to be used. In addition, it is mixed with organic polymers such as rubber, plastic, epoxy, etc. to produce a composite, and has been mainly used as a sonar detection device (piezoelectric material manufacturing and application, CMC Series, 1984).

On the other hand, recently, a thin film PbTiO ₃ has been developed and received as a material such as nonvolatile memory device, infrared sensor, etc., and the thin film is mainly manufactured by sputtering. However, since the production of pure PbTiO ₃ targets is difficult, a mixture of PbO and TiO ₂ powders or a molded body of PbTiO ₃ powders is used as the target, or multiple Pb and Ti metal targets are used in an oxygen atmosphere. This short, difficult to handle, it is very difficult to produce a uniform chemical composition and reproducible thin film.

Accordingly, the present inventors have proposed the present invention by paying attention to its own characteristics of PbTiO ₃ in which micro cracks and fractures occur due to high structural anisotropy when PbTiO ₃ passes through the phase transition point in order to solve the conventional problem. _It is an object of the present invention to synthesize a PbTiO ₃ powder having a particle size distribution that is easy to sinter by repeating the calcination and pulverization process of ₃ powder, and to prepare a hard, crack-free single-phase PbTiO ₃ sintered body by using this powder.

1 is a graph showing the change behavior of the sintered density according to the number of repeated calcination-crushing process of the raw material powder.

FIG. 2 is a graph showing the change behavior of the fine Vickers hardness of the sintered compact according to the number of repeated calcination processes of the raw material powder.

In order to achieve the above object, the present invention provides a method for producing lead titanate (PbTiO ₃ ), after weighing PbO powder and TiO ₂ powder in the same molar ratio, pulverizing and mixing them, and then calcining the mixture; Repeating the grinding and calcining process several times; And a step of sintering the calcined powder at a temperature of 1200 ° C. or higher after the molding.

Hereinafter, the present invention will be described in detail.

The present invention sinters after molding using fine PbTiO ₃ powder of appropriate particle size distribution obtained by repeating the pulverization and calcining process of the powder several times, thereby suppressing or minimizing the stress generated in the sintered body when passing the phase transition point in the sintering process. There is a characteristic.

To this end, first, commercially available high purity PbO and TiO ₂ powders are weighed in the same molar ratio, pulverized and mixed, and then the mixture is calcined in the PbTiO ₃ synthesis temperature range. Thereafter, it is preferable to repeat the pulverization and calcination process several times, because the powder is calcined to synthesize PbTiO ₃ , and then cooled, the synthesized PbTiO ₃ has high structural anisotropy when passing through the phase transition point in the cooling process. There are a myriad of fine cracks and breakages in the sintering process. Regrinding can yield fine PbTiO ₃ powders with an appropriate particle size distribution. In addition, the composition distribution becomes uniform due to the diffusion of Pb in the repeated calcination process, and the physical stress is uniform in the repeated grinding process, so that the local stress due to excessive growth of particles generated due to segregation of Pb during the sintering process It can be prevented and a hard sintered compact can be manufactured. At this time, the repetition frequency of the grinding and calcining process is more preferably 2 to 5 times.

The repeated calcination conditions may be performed in the PbTiO ₃ synthesis temperature range, but more preferably in an inert atmosphere for 1 to 4 hours at a temperature range of 1000 to 1200 ° C. After cooling the powder calcined as described above, pulverized and molded, the molded body was placed in an alumina crucible and sealed using PbTiO ₃ powder prepared in the calcination process beforehand, and then, to a temperature of 5 to 1200 ° C. in a conventional manner. The temperature is raised to 20 ° C./min and sintered in an air atmosphere at that temperature for 0.5 to 2 hours.

In such a process, a relatively hard and crack-free single phase perovskite PbTiO ₃ ceramics can be obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples.

EXAMPLE

After PbO and TiO ₃ powders were weighed in the same molar ratio, these powders were mixed and pulverized by a ball-mirror method for 24 hours using zirconia balls and ethanol as a dispersion medium. After the ball-milling mixed powder was dried, it was placed in an alumina crucible, heated to 5 ° C / min, and calcined in a nitrogen atmosphere for 2 hours under the calcination temperature conditions shown in Table 1 below.

TABLE 1

The calcined powder was quenched to room temperature in air and then regrind by ball-milling for 24 hours.

The powder was again calcined under the same conditions as the above-described step, followed by quenching and regrinding. This process was repeated 1 to 5 times to prepare a final PbTiO ₃ powder. After using the powder to prepare a molded body by cold hydrostatic molding at a pressure of 2ton / cm ² , the molded body was placed in an alumina crucible and sealed using PbTiO ₃ powder as an atmosphere powder, and then to 5 ℃ / min to 1200 ℃ After heating up and sintering in an air atmosphere at that temperature for 1 hour, the sintered density and microhardness were measured, and the results are shown in FIGS. 1 and 2, respectively.

As a result of the PbTiO ₃ ceramics X-ray diffraction analysis of Inventive Example (1,2) prepared by the above-described process, except for a part, only the perovskite single phase existed and the second phase (PbTi ₃ O ₇ , PbO, TiO _2, etc.) did not exist. Some of them had a calcination temperature of 1200 ° C. and a calcination-milling repetition frequency of 5 or more, in which case a small amount of TiO ₂ was observed in addition to PbTiO ₃ . When the calcination-grinding process was repeated one or six times, cracks occurred in the final sintered body regardless of the calcination temperature. Some cracks were observed in the reproducibility test when repeated two or five times. On the other hand, in the case of repeating 3 to 4 times, micro cracks could not be observed by the optical microscope as well as the naked eye.

On the other hand, as shown in Figure 1, the sintered density of PbTiO ₃ ceramics showed a relative density of about 94 _~ 96% with respect to the theoretical density (8.01 / cm ³ ) of PbTiO ₃ according to the number of calcination-milling iterations. The highest sintered density was 96.5% of the theoretical density in the case of Inventive Example (1) when the calcination temperature was 1000 ° C. and the calcination-milling repetition frequency was four times. In addition, as shown in FIG. 2, the fine Vickers hardness of PbTiO ₃ ceramics was about 330-600 kg / mm ² depending on the number of calcination-milling repetitions. The maximum hardness value was the same as the condition showing the highest sintered density in the case of Inventive Example (1) when the calcination temperature was 1000 ° C. and the calcination-milling repetition frequency was four times. Among the general Pb-based ceramics, the fine Vickers hardness value of Pb (Zr _0.65 Ti _0.35 ) O ₃ ceramics, which is known as a very sintering material, is about 430-520kg / mm ² , and the fracture resistance (K _IC ) value is 1.0-1.5 MN / m ^3/2 (Piezoelectric / electric distortion actuator, Japan Industrial Technology Center, pp.68, 1986). This and the calcination temperature 1000 ℃ in the present invention is a calcined-crushed if the number of iterations is compared to the hardness value of PbTiO ₃ ceramic prepared in 3-4 hoein conditions, PbTiO ₃ ceramic of the present invention on a plain Pb as a solid, relatively dense ceramic It can be judged to have a characteristic almost comparable to the ceramics.

On the other hand, in the case of Comparative Example PbTiO ₃ powder synthesis, PbTiO ₃ ceramics were prepared under the same conditions as the invention example at the calcination temperature conditions of 800 ~ 900 ℃ known as a general calcination temperature. As shown in FIG. 1 and 2, the sintered density was lower than that of Inventive Example (1, 2) by 90 to 93% of the theoretical density, and the fine Vickers hardness of the sintered body representing the mechanical strength was 180 to 250 kg / The values much lower than those of Inventive Example (1, 2) were shown in mm ² . In addition, cracks were observed in most sintered bodies regardless of the number of calcination-grinding repetitions.

As described above, the present invention can provide single-phase PbTiO ₃ ceramics which are pure perovskite single phase and no cracking, and also have a mechanical strength almost similar to that of conventional general Pb-based ceramics as compared with the conventional materials, Ceramics can be used not only for the production of high-frequency piezoelectric elements, but also for the production of PbTiO ₃ ceramics for sputtering targets, which has recently increased rapidly in Pb-based thin film manufacturing.

Claims (3)

In the manufacturing method of lead titanate (PbTiO ₃ ), after weighing the PbO powder and TiO ₂ powder in the same molar ratio, pulverizing and mixing it, and then calcining the mixture; Repeating the grinding and calcining process several times; And sintering the calcined powder at a temperature of 1200 ° C. or higher after molding. The method according to claim 1, wherein the pulverizing and calcining step is repeated 2 to 5 times. The method according to claim 1 or 2, wherein the calcination is performed in an inert atmosphere for 1 to 4 hours in a temperature range of 1000 to 1200 ° C.