JP3041411B2 - Method for producing raw material powder for piezoelectric ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a raw material powder of a piezoelectric ceramic which is important as an actuator material. It is intended to increase the mechanical strength and enlarge the amount of piezoelectric displacement. By applying this technology, it is possible to use piezoelectric ceramics under more severe conditions, and it is expected that new fields of application will be expanded.

[0002]

2. Description of the Related Art Piezoelectric ceramics are ceramics which have the property that, when an external force is applied, polarization occurs to induce electric charge, and when a voltage is applied, strain proportional to the voltage is induced. Most applications of piezoelectric ceramics use their vibration characteristics, such as ultrasonic oscillators, filter resonators, electro-acoustic transducers, microphones, and acoustic sensors. It has been put to practical use as a positioner, a piezoelectric damper, a small ultrasonic motor, and the like. These actuators were originally designed to displace a lightweight object, and almost achieved the purpose with ceramics obtained by an ordinary solid-phase reaction method. Meanwhile, recently,
In the fields of automobiles, railways, ships, aviation / space, civil engineering / construction, etc., there is a growing trend to use ceramic actuators for health care such as vibration suppression and posture correction of huge machines and systems. When ceramics is used as an actuator for such a huge machine or system, the mechanical strength and the amount of displacement are absolutely insufficient.

The most widely used piezoelectric ceramics at present are lead zirconate (Pb) which is a perovskite type compound.
ZrO ₃ , PZ) and lead titanate (PbTiO ₃ , PT)
Is a so-called PZT-based ceramic having a solid solution of about 53:47. Usually, a mixture of lead oxide (PbO), zirconium oxide (ZrO ₂ ) and titanium oxide (TiO ₂ ) is reacted at a high temperature and sintered. It is manufactured by the solid-phase reaction method described below. Barium titanate (BaTiO ₃ , B
T), strontium titanate (SrTiO ₃ , S
T), lead magnesium niobate (PbMg _1/3 Nb _2/3
O ₃ , PMN), lead nickel niobate (PbNi _1/3 N)
b _2/3 O ₃ , PNN) and other perovskite compounds
It is used as a solid solution component for improving the properties of ZT ceramics.

In the case of the solid-state reaction method, a perovskite phase is formed by heating a raw material mixture at a temperature of at least 950 ° C.
A two-stage heating process of sintering at a temperature around 50 ° C. is required. In particular, in the step of forming a perovskite phase, it is necessary to repeat a procedure of heating, re-grinding, mixing, and heating to obtain a single phase. The solid phase reaction method is often not suitable for obtaining a dense sintered body, because abnormal sintering temperature is high and abnormal grain growth often occurs, and pores are left in the sintered body. In order to obtain ceramic actuators with even greater mechanical strength and displacement, dense sintering that does not include pores that has been strictly controlled in composition, such as particle composition, particle size, particle shape, and grain boundary phase, than ever before Preparing a body is a prerequisite, and it is essential to establish a method for synthesizing the raw material powder in consideration of this point.

On the other hand, general piezoelectric ceramics are perovskite-type compounds containing lead oxide as a main component or solid solutions thereof. Therefore, there is a problem in that the composition shifts due to evaporation of lead oxide in the process of manufacturing a sintered body, and the firing is difficult. Certain measures are required, such as devising the structure of the sheath and adding lead oxide in excess of the stoichiometric amount. In order to reduce such annoyance, it is increasingly important to establish a method for producing a raw material powder for piezoelectric ceramics that is fine, has excellent dispersibility, generates a perovskite phase at a lower temperature, and can be sintered. Has become.

As a general method for obtaining high-purity fine ceramic raw material powder, a coprecipitation method in which an inorganic salt of a metal is dissolved in water, and an alkali such as ammonia is added to hydrolyze is known. I have. However, in the case of the aqueous solution method, the presence of water is rather an obstacle in obtaining powder having good dispersibility in many cases. That is, this is because, in the aqueous solution method, the precipitate is often a hydroxide or a hydrated hydroxide, and a hydrogen bond occurs via a hydroxyl group (OH group), so that the precipitated particles are easily aggregated. . In order to enhance dispersibility, some measures such as addition of a surfactant have been devised, but this is not always a perfect method. In addition, in the aqueous solution method, there is always a problem of deviation from the stoichiometric composition because the pH adjustment for complete precipitation is troublesome, and the precipitate is required to be washed and filtered.

On the other hand, as another method for producing a precipitate from a solution, there is an alkoxide hydrolysis method. this is,
The metal alkoxide is dissolved in an organic solvent and hydrolyzed by reacting with water in some form. The particle size and dispersibility can be controlled by appropriately selecting the type of alkoxide and the concentration of the alkoxide solution. It is characterized by the ability to obtain finer and more dispersible precipitated particles than the aqueous solution method, because the hydrolysis reaction is slow and hydroxide is formed due to the presence of only a small amount of water. It is considered difficult. At present, the alkoxide hydrolysis method is attracting attention as the best raw material powder production method for obtaining functionally controlled functional ceramics, but because the alkoxide is expensive and generally unstable. The drawback is that care must be taken when handling in air.

[0008]

Considering the current situation where the application fields of piezoelectric ceramics are expanding more and more, in a simple manufacturing method using raw materials as inexpensive as possible, they are fine, have good dispersibility, and are sintered at low temperatures. It is desired to develop a method for producing a possible raw material powder. When considering such a manufacturing method, it is appropriate to grasp the problems of the conventional method and find a method for improving it. There is nothing better than the solution precipitation method in that the particle diameter and dispersibility can be easily controlled. Inorganic salts of metals are relatively inexpensive and widely marketed, and are worth considering as starting materials. Therefore, as a method for producing a raw material powder for piezoelectric ceramics, a technique has been established which is a solution precipitation method and can produce a finer and more dispersible powder than before, in which the starting material is an inorganic metal salt. A big ripple effect can be expected for the industrial world.

The inventors of the present invention have conducted intensive studies on how to obtain a fine and highly dispersible raw material powder for piezoelectric ceramics based on the above prerequisites. To find a way to decompose and co-precipitate
The present invention has been completed. Here, an organic solvent containing an amine is used as the non-aqueous solvent. Since the amine is alkaline, it reacts with the metal inorganic salt and plays a role of generating oxide precipitate. In addition, since the alkalinity of the amine is lower than that of ammonia, the reaction with the inorganic salt is slow, and a fine precipitate is easily obtained. The amine alone may be used as the organic solvent. However, in order to form a more uniform and fine precipitate, it is preferable to dilute the organic solvent with another organic solvent such as an alcohol. In particular, alcohol is considered to be optimal as a diluting liquid because it has the effect of dehydrating the water of crystallization contained in the inorganic salt, preventing the formation of hydroxide and increasing the dispersibility of the precipitate. Here, the diameter of the precipitated particles depends on the concentration of the amine,
It can be controlled by changing the amount of inorganic salt charged, the heating temperature, and the like.

That is, based on the above findings, the present invention decomposes a mixture of an inorganic salt of a metal while heating the mixture in an organic solvent containing an amine to form a precipitate.
A coprecipitated powder having a composition of a piezoelectric perovskite compound or a solid solution thereof by heating and firing at a temperature of 00 ° C. or more, which is fine and excellent in dispersibility, and a perovskite phase is generated at a lower temperature, It is another object of the present invention to provide a method for producing a raw material powder for piezoelectric ceramics that can be sintered.

[0011]

The present invention for solving the above-mentioned problems is a method for producing a coprecipitated powder having a composition of a piezoelectric perovskite compound or a solid solution thereof in a non-aqueous solution system, which contains a perovskite component. The mixture of the inorganic salt of the metal is decomposed by heating in an organic solvent containing an amine to form a precipitate.
A powder composed of a single phase of a piezoelectric perovskite compound or a solid solution thereof, which is further characterized by evaporating or decomposing substances other than oxides remaining by heating and firing at a temperature of at least ℃. Manufacturing method. The present invention also relates to a non-aqueous solvent for amines and alcohols.
, A method for producing the powder, and perovskite conversion
Powder consisting of a single phase of the compound or its solid solution
Lead titanate (PZT), lead zirconate (PZ), titanium
Lead titanate (PT), barium titanate (BT), titanium
Strontium acid (ST), lead magnesium niobate
(PMN), lead nickel niobate (PNN)
And a method for producing the powder.

[0012]

Next, the present invention will be described in more detail. The present invention aims to solve the problems of the prior art by a precipitation reaction in which water is replaced with alcohol and ammonia is replaced with amine in a conventional aqueous solution precipitation method. As a starting material, an inorganic salt containing lead, zirconium, titanium, barium, strontium, magnesium, niobium, nickel, or the like is used. After decomposing these inorganic salts, a mixture weighed in such a ratio as to give a perovskite compound or a solid solution composition thereof is heated under reflux with an appropriate amount of an amine and an alcohol, and furthermore a small amount of an organic surfactant. When the precipitation reaction is completed, the condenser is switched from reflux to evaporative collection to remove the organic solvent from the precipitate. Here, other methods such as vacuum can be used to evaporate the organic solvent. Next, the precipitate is calcined at a temperature of 500 ° C. or higher, preferably around 550 ° C., to completely evaporate the remaining substances other than oxides. Since it is necessary to remove residues other than oxides by calcination, nitrates, oxalates, acetates, carbonates and the like are suitable as inorganic salts.

The amine is generally commercially available such as propylamine, butylamine, ethanolamine and the like. If the compound is an organic compound having an amino group, the difference between primary amine, secondary amine and alcoholamine is essential. Not that. However, from the viewpoint that the precipitation reaction needs to proceed sufficiently and the ease of handling thereafter, 100 to 100
Those having a boiling point around 150 ° C. are desirable. Considering that alcohols are collected and recycled after completion of the precipitation reaction, it is desirable to use the same group of alcohols such as propanol when using propylamine as an amine and butanol when using butylamine. This is not essential. Thus, the method of the present invention uses no water other than the water of crystallization contained in the metal inorganic salt, removes the organic solvent and other residues by evaporation and heating at a higher temperature, and removes the pure precipitate. The advantage is that the charged composition is accurately inherited to the final product.

[0014]

According to the powder production method according to the above procedure, lead zirconate titanate (PZT) which is important as piezoelectric ceramics
In addition, lead zirconate (PZ) and lead titanate (PT) as its end components, barium titanate (BT) and strontium titanate (ST), which are important as solid solution components for improving the properties of PZT, A powder of a perovskite compound such as magnesium lead niobate (PMN) or nickel lead niobate (PNN) and exhibiting excellent sintering characteristics can be easily produced. The resulting precipitate is
(1) extremely fine, (2) good dispersibility, (3) good mixing, (4) high reactivity, etc. Therefore, the precipitate is calcined at about 550 ° C. At this stage, a single perovskite phase is obtained.

[0015] The formation temperature of this perovskite phase is surprisingly low compared to the prior art. The reason for this is considered to be that the precipitated particles are in the form of fine colloids and have extremely high reactivity, which is a feature of the method of the present invention. In the aqueous solution precipitation method, agglomeration of the powder further proceeds in the process of calcining the precipitate, which causes pores to be taken into the sintered body.
Even if it is calcined, the essential characteristics of the powder for producing a dense sintered body, such as (1) extremely fine, (2) good dispersibility, and (3) good sinterability, are maintained. It has been done. As described above, in order to obtain a perovskite phase sintered body by the solid-state reaction method, it is necessary to form a perovskite phase by heating at about 950 ° C.
A two-stage heating process for sintering at a temperature around 50 ° C. is required. In the case of the lead-containing perovskite phase, there is a problem that attention must be paid to the evaporation of lead oxide during the sintering process. However, if the powder according to the method of the present invention is used, such problems of the prior art can be greatly improved.

That is, the powder according to the method of the present invention is already composed of a perovskite phase and exhibits excellent sinterability, so that the sintering temperature of the prior art can be greatly reduced, and the problem of lead oxide evaporation is reduced. Even so, it can be solved with simpler measures. Further, when the powder according to the method of the present invention is used, a sintered body exhibiting practically appropriate piezoelectric characteristics (electromechanical coupling coefficient) can be obtained even by a simple molding method and sintering at a low temperature such as 1100 ° C. As described above, the present invention is an inexpensive and simple method for obtaining a raw material powder that is fine, has excellent dispersibility, and is excellent in sinterability, which is important for obtaining dense, high mechanical strength and large displacement piezoelectric ceramics. Thus, the present invention is expected to further expand the application fields of piezoelectric ceramics.

[0017]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. EXAMPLES As an inorganic metal salt as a starting material, lead nitrate Pb (N
O ₃ ) ₂ , basic lead acetate Pb (CH ₃ COO) · Pb
(OH) _2, zirconyl nitrate ZrO (NO _{3) 2} · 2H
₂ O, zirconyl acetate ZrO (CH ₃ COO) ₂ , titanyl ammonium oxalate (NH ₄ ) ₂ TiO (C ₂ O
_{4) 2} · 2H ₂ O, barium nitrate Ba (NO _{3) 2,}
Barium oxalate BaC ₂ H ₄ .2H ₂ O, strontium nitrate Sr (NO ₃ ) ₂ , magnesium oxalate Mg
C ₂ O ₄ .2H ₂ O, nickel oxalate NiC ₂ O _4.
2H ₂ O, niobium hydrogen oxalate Nb (HC ₂ O ₄ ) _5.
2H ₂ O or the like was used. Approximately 20 to 30 g of these inorganic metal salts are weighed in such a ratio as to have a perovskite composition after decomposition, and the mixture is placed in a separable flask of 500 ml together with 100 ml of amine and 100 ml of alcohol and 35 pours of Brigzy surfactant, and Heating was continued for 3 hours while stirring and refluxing to form a precipitate. After the precipitation reaction, the condenser was switched to evaporate and collect the organic solvent.At the stage when the evaporation was almost completed, the cover of the flask was removed, the flask was transferred to a heating mantle, and the temperature was slightly higher than the boiling point of the solution. Heated to completely evaporate the organic solvent. Next, the precipitate is placed in a platinum crucible and heated to about 550 ° C.
The remaining substances other than oxides were removed by evaporation or decomposition by calcination at a temperature of. With respect to the powder thus obtained, the generated phase was examined by X-ray diffraction. In addition, the powder having the piezoelectric composition was formed into tablets using a molding machine, sintered at 1100 ° C., and the relative density and the piezoelectric characteristics were measured. Table 1 shows the starting composition, precipitation conditions, and the results of calcining at 550 ° C.

[0018]

[Table 1]

Of these examples, 1 to 8 are shown as reference examples, 1 to 4 are perovskite-type compounds which are end components of the perovskite phase PZT which actually shows piezoelectricity, and 5 to 8 are characteristics of PZT. The present invention relates to a perovskite compound which is important as a solid solution component for improvement.
All of these formed a single perovskite phase by calcination at 550 ° C. regardless of the type of inorganic salt, amine and alcohol. What is particularly noteworthy is that a single-phase synthesis of the complex perovskite compounds PMN and PNN, which is originally considered to be very difficult, was possible. PZT
In addition, it can be easily imagined that a solid solution in which PZT is combined with the above perovskite compound can be synthesized. As shown in Examples 9 to 12, as expected, a single phase of PZT was obtained under various conditions.

The PZT powders obtained in Examples 9 to 12
Particles having a particle size of 0.1 μm or less are press-formed into a disk having a diameter of 12 mm at a pressure of about 200 MPa, and a sintered body is produced by heat treatment at 1100 ° C. for 2 hours. When the density was measured, all were 9
The value was close to 6%. In general, examples of ceramics whose sintering density is close to the theoretical value by using cold isostatic pressing in addition to press molding are well known, but considering the molding method and sintering conditions of this embodiment, The sintering density of this embodiment is not necessarily low, and there is room for further densification. Further, after performing the polarization treatment on the thus obtained sintered body, the electromechanical coupling coefficient was measured. Examples 9, 10 and 12 were around 0.5, and Example 11 was 0.6.
5 is shown. The reason why Example 11 showed a high value is presumably because it was closer to the piezoelectric composition. These values are
Commercially available P with improved properties by adding various solid solution components
This is a value comparable to that of ZT ceramics.

[0021]

As described above, the present invention improves the problem of the cohesiveness and compositional deviation of the particles, which are the drawbacks of the aqueous solution precipitation method, and avoids the incorporation of pores in the production of a sintered body. It was made for the purpose of obtaining. According to the method of the present invention, not only raw material powder for piezoelectric ceramics having excellent fineness and good sinterability excellent in uniformity of particle composition, particle diameter and particle shape can be manufactured in an inexpensive and simple manufacturing process, Production of oxide-based functional materials is also possible. Further, since the powder according to the method of the present invention is already composed of a perovskite phase and exhibits excellent sinterability, the use of the powder according to the method of the present invention enables a simple molding method and a low temperature of 1100 ° C. A sintered body exhibiting practically appropriate piezoelectric characteristics can be obtained by sintering. In addition, the method of the present invention has features of facilitating cost reduction and mass production, so that its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a precipitated powder having a PZT composition obtained by a method of Example 9 after calcination [calcination temperature:
(A) 450 ° C, (b) 550 ° C, (c) 650 ° C].

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/00 C01G 25/00 C01G 23/00 C01G 33/00 C01G 53/00

Claims (3)

(57) [Claims] 1. A method for producing a coprecipitated powder having a composition of a piezoelectric perovskite compound or a solid solution thereof in a non-aqueous solution, wherein a mixture of a metal inorganic salt containing a perovskite component is converted to an amine. A precipitate is formed by decomposition while heating in an organic solvent containing, and then, the precipitate is heated and calcined at a temperature of 500 ° C. or more to further evaporate or decompose remaining substances other than oxides. And producing a powder comprising a single phase of a piezoelectric perovskite compound or a solid solution thereof. 2. Use of a non-aqueous solvent of an amine and an alcohol.
The method for producing a powder according to claim 1. 3. A perovskite compound or a solid solution thereof.
Powder consisting of a single phase of lead zirconate titanate (PZ)
T), lead zirconate (PZ), lead titanate (PT), titanium
Barium titanate (BT), strontium titanate (S
T), magnesium lead niobate (PMN), niobate niobate
Claims 1. It is selected from nickel lead (PNN).
2. The method for producing a powder according to 1.