JPS6255243B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a powder consisting of barium titanate crystal particles elongated in the crystal axis direction and a method for producing the same.

In the field of magnetic materials, powder consisting of acicular or columnar magnetic crystal particles that are mainly composed of iron oxide and elongated in a specific crystal direction has been produced for a long time, and these powders are mixed with organic matter. In this way, a film or sheet-like composite material in which acicular or columnar magnetic crystal grains are arranged in one direction is produced. These materials are widely used in magnetic tape and other purposes. In addition, in the field of magnetic ceramic materials, at least one of the raw materials is a powdered raw material consisting of particles with special shapes such as needles or plates, and the mixture is sintered by the so-called hot press method. , ceramics in which crystal grains of magnetic substances are oriented in specific directions have been manufactured. This material is widely used as a magnetic head material for video tape recorders and the like as a ceramic magnetic material whose magnetic properties differ significantly depending on the direction.

In this way, in the field of magnetic materials, materials that utilize the remarkable anisotropy of the magnetic properties of magnetic crystal grains are widely used in practical use. In the field of dielectric and piezoelectric materials, which form the twin worlds, very few materials have been created that take advantage of the anisotropy of dielectric and piezoelectric properties of crystal grains. slightly,
It has been reported that particle-oriented ceramics can be fabricated using Bi layered compounds, but the dielectric and piezoelectric properties of Bi layered compounds are not as good as those of perovskite compounds, which play a leading role in the fields of dielectric and piezoelectric materials. It looks inferior. It would be desirable if ceramics with oriented grains made of perovskite compounds could be produced, but there have been no reports of this being produced to date.

This is because Bi layered compounds have a layered crystal structure, and when hot-press sintering is performed, crystal grains whose layered structure is perpendicular to the pressing direction are likely to be formed, resulting in poor orientation. This is what ceramics are formed from. However, in perovskite compounds, the crystal structure itself does not have a characteristic structural part such as a layered structure that tends to cause grain orientation, so when ordinary raw materials are used, ceramics with uniform crystal grain orientation cannot be produced. Cannot be produced. In perovskite compounds, if we can create a powder consisting of crystal grains with a characteristic particle shape and crystal orientation, we can create a composite of these particles and an organic compound to create a composite with oriented crystal grains, such as magnetic tape. Ceramic dielectrics and piezoelectric materials with oriented grains can be created by creating body materials or by creating pressure-molded bodies with these particles oriented in advance and sintering them. This opens up new fields of application as piezoelectric and dielectric materials. Also, _BaTiO3
In grain boundary layer type ceramic capacitor materials that utilize the interaction between particles and grain boundaries, and ceramic semiconductor materials with PTC characteristics, by providing a particle orientation structure, anisotropy can be achieved in their electrical properties. There is also a great potential for new applications to be found as a material with a long life.

The present invention is directed to so-called potassium titanate fibers.
K ₂ O・nTiO ₂ and barium oxide or a barium compound that thermally decomposes to barium oxide when heated to high temperature are mixed, fired and reacted to replace the potassium component in the potassium titanate fiber with the barium component. This causes the formation of barium titanate (BaTiO ₃ ) crystal particles extending in the crystal axis direction,
The method is characterized in that the BaTiO ₃ crystal particles thus formed are taken out by removing components mainly composed of potassium that are liberated at this time with water or acid.

Examples will be explained below.

<Example 1> Potassium titanate fibers having a composition of K ₂ O.nTiO ₂ (n=6) were produced by a reported flux method using K ₂ MoO ₄ as a flux. That is, K ₂ CO ₃ , TiO ₂ and K ₂ MoO ₄ are mixed, placed in a platinum crucible, fired at 1200℃, and heated to 4℃~
It was cooled to room temperature at a cooling rate of 10° C./hour, and then the flux was washed and removed with cold water and then dried. The obtained fibers were fibers that were elongated in the direction of the crystal axis, as reported.

Next, the obtained potassium titanate fiber was
BaO, Ba(OH) ₂ , Ba(NO ₃ ) ₂ , BaCO ₃ , Ba
(COO) ₂ , etc., at a ratio of 6 mol of BaO per 1 mol of K ₂ O・nTiO ₂ (n=6), and heated at 800°C.
Calcined at 900°C and 1000°C, respectively. As a result of X-ray analysis of the fired product, BaTiO ₃ was formed no matter which barium compound was used, and an unknown substance thought to be a potassium component was formed. This unknown substance can be easily dissolved and removed with water (including hot water) or acid, and the powder sample after drying is
It consisted of a single phase of _BaTiO3 . obtained
As a result of observation using an optical microscope or an electron microscope, the BaTiO ₃ particles were found to have a needle plate shape or a columnar shape, and the elongation direction was found to be the direction of the crystal axis of BaTiO ₃ as a result of electron beam diffraction.

<Example 2> Potassium titanate fibers having a composition of K ₂ O.nTiO ₂ (n=4) were produced by a reported flux method using K ₂ MoO ₄ as a flux. That is, K ₂ CO ₃ , TiO ₂ and K ₂ MoO ₄ are mixed, placed in a platinum crucible, fired at 1100°C, and heated to 4°~
It was cooled to room temperature at a cooling rate of 10° C./hour, and then the flux was washed and removed with cold water and then dried. The obtained fibers were fibers elongated in the direction of the crystal axis, as reported.

Next, the obtained Chitakari fiber was treated with BaO, Ba
(OH) ₂ , Ba(NO ₃ ) ₂ , BaCO ₃ and Ba(COO) _{2 ,} etc., are mixed at a ratio of 4 mol of BaO to 1 mol of K ₂ O・nTiO ₂ (n=4), and 800 ℃, 900℃ and
Each was fired at 1000℃. As a result of X-ray analysis of the fired product, BaTiO ₃ was formed no matter which barium compound was used, and an unknown substance thought to be a potassium component was formed. This unknown substance is easily dissolved and dissolved in water (including hot water) or acids.
After removal and drying, the powder sample consisted of a single phase of BaTiO ₃ . The obtained BaTiO ₃ particles were found to have a needle-like or columnar shape as a result of observation using an optical microscope or an electron microscope, and the direction of elongation was found to be the direction of the crystal axis of BaTiO ₃ as a result of electron beam diffraction.

In the examples, potassium titanate fibers represented by K ₂ O.nTiO ₂ with n of 4 and 6 are used, but fibers with n of 1, 2, etc. are also known. In potassium titanate fibers, the crystal structure includes a structural part in which TiO ₆ octahedrons are connected in parallel with shared vertices, and the connection direction of the shared vertices matches the elongation direction of the fiber, and
Since the structure is similar to the perovskite structure in which TiO ₆ octahedrons share vertices and are connected in parallel in the crystal axis direction, it is assumed that crystal grains extending in the crystal axis direction of the BaTiO ₃ perovskite compound are formed. Conceivable. Therefore, potassium titanate fibers in which n is 1 or 2 also have the same effect as in the example.

All of the barium compounds other than BaO used in the examples decompose at high temperatures and release carbon dioxide, water, nitrogen oxide, etc., and become BaO.
Of course, barium compounds other than those mentioned above may be used as long as they similarly decompose to BaO when heated.

In addition, in the examples, firing was performed at 800°C and 900°C.
℃ and 1000℃, but other temperatures may be used. In short, it is important that potassium titanate and a barium compound that decomposes at high temperature to become BaO react at high temperature to generate BaTiO ₃ and liberate the potassium component.

Since the BaTiO ₃ powder produced in the above example consists of particles extending in the axial direction of the crystal,
It is useful as a raw material for piezoelectric and dielectric materials that have oriented particles with organic substances mentioned above, as well as BaTiO ₃ ceramic piezoelectric materials that have oriented particles. In addition, acicular or columnar particles of solid solutions with other perovskite compounds are prepared, and these are used as raw materials for composite materials of solid solution perovskite compounds with organic substances, particle-oriented ceramic piezoelectric materials, and dielectric materials. It can be expected to have a wide range of uses. Furthermore, since BaTiO ₃ is widely used as a ceramic capacitor material and a ceramic semiconductor material exhibiting so-called PTC characteristics, these materials with particle orientation can be easily produced using the BaTiO ₃ powder produced according to the present invention. This means that we can fully expect new materials with anisotropy in electrical properties.

Claims (1)

[Claims] 1. A barium titanate powder characterized by comprising barium titanate particles elongated in the crystal axis direction. 2 Barium titanate is produced by mixing potassium titanate fibers represented by K ₂ O・nTiO ₂ and barium oxide or a barium compound that decomposes at high temperature to become barium oxide and firing. A method for producing barium titanate powder, characterized in that the produced barium titanate crystal particles are taken out by dissolving and removing components mainly composed of potassium that are liberated at this time with water or acid. .