JPH0811692B2 - Method for producing polycrystalline body formed of fibrous alkali metal titanate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polycrystal composed of a fibrous alkali metal titanate, and relates to an improved invention of Japanese Patent Application No. 61-68221, more specifically a titanium source. The present invention relates to a method for producing a sintered body composed of fibrous crystals by synthesizing an amorphous titanium alkali metal oxide from a compound, an oxygen-containing alkali metal compound and a trace amount of aluminum oxide, and then molding and firing the same. .

Fibrous alkali metal titanate is excellent in mechanical properties such as high bending strength, and also has high electrical insulation, thermal,
Or, it is a material having characteristics such as chemical stability and negative thermal conductivity-temperature coefficient characteristics. Therefore, it is widely used for plastic reinforcing materials, antifriction materials, battery diaphragms, heat insulating structural materials, excess materials, adsorbent materials, catalysts and their supports, pigments and the like.

(Prior Art) Regarding the production method of amorphous titanium oxide fiber, Kruczyns
A report by ki et al. (Nature 291: 399 (1981)) has been made. The method relates to the production of a titanium oxide amorphous body consisting of long fiber bundles by making a hydrogel of titanium oxide by neutralizing an aqueous solution of titanium tetrachloride with potassium hydroxide, and by freeze-drying and aging at about 120 ° C. is there.

Various methods have already been proposed for the production of crystalline alkali metal titanate fibers. That is, a firing method, a melting method, a hydrothermal property, a flux method and a partition method are known. Generally, in any of the methods, there are many examples in which titanium oxide and a basic oxygen-containing alkali metal compound are adopted as the raw materials.

For example, in Japanese Examined Patent Publication No. 27264/1987, TiO ₂ products in a commercially available sulfate method for producing hydrous titania as a titanium source, anatase TiO ₂ , pigments, electronic material powders or catalysts,
Well refined anatase pigments, ground rutile ores and commercial ilmenite are disclosed. Also disclosed are alkali metal hydroxides and alkali metal carbonates as basic oxygen-containing alkali metal compounds. Above Japanese Patent Publication Sho 42-
No. 27264 is one that synthesizes a fibrous alkali metal titanate by firing a non-liquid mixture of the titanium source and a basic oxygen-containing alkali metal compound at 200 to 1150 ° C., and has a diameter of 0.005 to 0.1 micron. 20 to produce a rich colloidal form with a particle size of at least 10 times the diameter
Baking at 0 ~ 850 ℃, if you want to produce a rich pigment type with a particle size of 0.1 ~ 0.6 micron and a length of 10 ~ 100 times the diameter, 850 ~ 975 ℃ When producing a rich insulating type having a particle size of 0.6 to 3 microns and a length of 100 to 1000 times the diameter, it is possible to obtain the desired fibrous alkali metal titanate by firing at 975 to 1150 ° C. Has been described. Also disclosed is a manufacturing method in which an alkali metal halide is added to a non-liquid mixture of raw materials and then the mixture is fired.

By the way, it is considered very difficult to form a titanate of amorphous or crystalline fiber obtained by the above method into a predetermined shape and fire it to form a sintered body. That is, many of the fibrous titanate is excellent in mechanical strength, for example, the fibers are broken in the molding step, or the fibers are entangled with each other even if they are not broken, and do not sinter unless pressurized. It is considered that there are many problems in the substantial manufacturing method, including the point that an appropriate sintering aid is required. In addition, a sintered body having a porous structure has not been established with a reproducible manufacturing method, although it has a wide range of applications as described above.

(Problems to be Solved by the Invention) An object of the present invention is to provide a fibrous titanic acid having a large aspect ratio, a large mechanical strength such as bending strength and tensile strength, and high porosity with high reproducibility. It is to provide a method for producing a polycrystalline compact of an alkali metal salt.

Further, the object of the present invention is to control the shape and size of the fibrous alkali metal titanate salt from the crystallization and sintering conditions of the amorphous material, and to produce the fibrous alkali metal salt having a predetermined fiber structure and porous structure. To do.

(Means for Solving Problems) In producing a polycrystalline fibrous alkali metal titanate of the present invention, a titanium source compound, an oxygen-containing alkali metal compound and aluminum oxide are mixed at a temperature of 600 to 1100 ° C. The present invention relates to a method for producing a fibrous polycrystalline body, which is characterized in that it is pressure-molded and re-fired at 900 to 1350 ° C.

The titanium source compound of the present invention is a compound substantially containing TiO ₂ , and specific examples thereof include titanium oxide, rutile ore, titanium hydroxide wet cake, and hydrous titania. The particle shape is preferably fine particles as much as possible. For example, a so-called "jet crushed product", in which anatase type fine particles are crushed by colliding particles at high speed in rutile ore in titanium oxide, is preferable. Particle size is 200
A range of ~ 425 mesh is suitable.

The oxygen-containing alkali metal compound used in the present invention is preferably an alkali metal nitrate which produces M ₂ O (M is an alkali metal) upon firing, and examples thereof include nitrates of potassium, sodium, cesium and rubidium. Examples of such compounds include KNO ₃ , NaNO ₃ , CsNO ₃ and RbNO ₃ .

In addition to aluminum oxide, aluminum hydroxide that becomes aluminum oxide during firing, an organic aluminum compound, or the like can be used as the aluminum oxide.

It is not clear for what reason the addition of aluminum oxide in the present invention has stable reproducibility and is effective in producing a high-porosity polycrystal, but in the atmosphere during polycrystal synthesis, that is, Dissociation of Al ³⁺ ions occurs in a highly alkaline atmosphere, which is a K ₂ O-H ₂ O system, and these Al ³⁺ ions have the effect of stably controlling the fiber growth of potassium titanate that constitutes a polycrystalline body. It is estimated that

Further, as is clear from FIG. 1 as a demonstration that the interposition of Al ³⁺ ions has an effect on the fiber growth in the polycrystal, as compared with the synthetic product in the platinum crucible, it is possible to improve the growth under the same conditions. Differences are apparent in the relative densities of the crystalline composites. Furthermore, from the observation of the appearance of the reaction product, the polycrystal synthesized in the platinum crucible showed that the volume of the molded product before and after the reaction was contracted, whereas the reaction product under the condition of Al ³⁺ ion intervention It was confirmed that it was expanding.

The mixing ratio of the titanium source compound and the oxygen-containing alkali metal compound is TiO ₂ / M ₂ O (M is an alkali metal) converted molar ratio.
The range of 4 to 1.5 is preferred. The amount of aluminum oxide added is 1.25 x 10 with respect to 1 mol of the titanium source compound (as TiO ₂ ).
A range of ^{−2 to} 2.5 × 10 ⁻³ mol is preferable. On the contrary, addition of more than that inhibits fiber growth, and addition of less does not show a significant difference from the case without addition. The same effect can be obtained by carrying out the reaction in an alumina crucible instead of adding aluminum oxide.

In the present invention, the titanium source oxide, the oxygen-containing alkali metal compound and aluminum oxide may be mixed as they are, or water-added slurry may be used and then spray-dried. The method for adjusting the mixture of the raw materials is not limited to the above, but the raw material mixture obtained by spray-drying the slurry-like raw material has the oxygen-containing alkali metal uniformly and finely adhered to the particle surface of the titanium source compound. It becomes a fluid for granulation, and this granule is extremely preferable because it has extremely high reactivity.

In the present invention, these mixed raw materials are treated at about 600 to 1100 ° C.
At about 850-1000 ° C, usually about 2
Bake for ~ 20 hours to obtain an amorphous alkali metal titanate salt.

Since the obtained amorphous alkali titanate is a nodule, it is put into cold water, and individual particles are dispersed by, for example, performing ultrasonic treatment for about 30 minutes. By this operation, elution of an excessive amount of alkali can be confirmed. However, just because it takes less time to disperse
This operation should not be performed with acid. That is, it is clear that even if the acidity is weakly acidic, the structure and composition of the amorphous alkali metal titanate are changed.

Furthermore, it is preferable to wash and dry with distilled water.
In order to mold the amorphous product obtained in this step, press molding is usually performed under a pressure condition of about 10 to 200 MPa. At the stage of this operation, it is possible to freely change the bulk density after molding by adding a small amount of an organic sizing agent, a surfactant or the like to the above product. The same effect can be obtained by adding a boron compound. The polycrystalline molded body of the present invention thus obtained by press molding is useful when a fiber reinforced plastic (FRP), a fiber reinforced metal (FRM) or the like is prepared by a preforming method. That is, by injecting a molten resin or molten metal into a polycrystalline molded body of the present invention which has been molded into a predetermined shape in advance, the content ratio of the fibers in the composite can be increased or the contact time between the metal and the fibers in a high temperature state can be shortened. Since the time can be set, problems such as fiber quality and deterioration due to the reaction can be suppressed.

Next, by firing the above-mentioned molded body in a wide temperature range of about 900 to 1350 ° C., M ₂ O · nTiO ₂ (M is an alkali metal, n is an integer of 4,6,8 or a mixture thereof) It can be obtained by gradually crystallizing the fibrous polycrystalline material represented by

In an amorphous compact, crystallization from the surface is likely to occur due to the temperature gradient formed on the surface. Therefore, in order to deposit fine crystals in the entire amorphous material, it is preferable to maintain the temperature at a predetermined temperature for 10 minutes / minute to 20 ° C / minute and for 45 minutes to 10 hours. Further, it is preferable to gradually cool to about 600 ° C. at a temperature decreasing rate of 2 to 10 ° C./min. In particular, in the case of unidirectional crystallization by the temperature gradient method, a cooling rate within an appropriate time is required while relaxing thermal stress strain. A difference in the aspect ratio, which is the ratio of average fiber length / diameter, is recognized in the fibrous crystals obtained by rapid cooling, as compared with the slow cooling method.

In the present invention, the amorphous alkali metal titanate salt obtained in the first constitutional reaction is re-baked to produce a fibrous polycrystalline compact formed of a crystalline alkali metal titanate salt. I am trying. Further, depending on the firing temperature, the composition of the obtained alkali metal titanate is represented by the general formula
A sintered body represented by M ₂ O · nTiO ₂ (M is an alkali metal, n is a real number of 4,6,8 or a mixture thereof) and has a porous structure with a porosity of up to about 45%. It is also possible to produce a body.

(Examples) Hereinafter, detailed description will be given with reference to Examples.

Example 1 A commercially available reagent titanium oxide (anatase type) and potassium nitrate were weighed so that the molar ratio of TiO ₂ / K ₂ O was 2/3, and further aluminum oxide was 2.0 × 10 ⁻ per 1 mol of TiO _2. Add ³ mol and mechanically mix for a sufficient time. Next, this raw material powder was filled in a platinum crucible and placed in a heating furnace. The temperature rising rate was 10 ° C./min, and the temperature was maintained at 1000 ° C. for 6 hours. The obtained nodule was roughly crushed, immersed in water overnight, and then overdried to obtain amorphous potassium titanate. The thus obtained product was molded under a pressure of 200 MPa with a mold having a diameter of 60 mm. Next, it was put again in the platinum crucible and the temperature rising rate was set to 10 ° C./min in the pine cone and the temperature was maintained at 1050 ° C. for 10 hours to obtain a fibrous potassium hexatitanate crystal.

 The relative density of this polycrystal was 75%.

Example 2 Amorphous potassium titanate and a polycrystalline substance were synthesized in an alumina crucible without adding aluminum oxide, and the same reaction as in Example 1 was performed, resulting in a relative density of 67%.
A fibrous potassium hexatitanate polycrystal was obtained. In FIG. 1, the relative density of the polycrystals at each molding pressure was plotted.

Example 3 The same reaction as in Example 1 was carried out except that an alumina crucible was used for the reaction. The relative density of the polycrystal at a molding pressure of 200 MPa was 55%.

Moreover, it was 41% at a molding pressure of 100 MPa, and a polycrystal having a high porosity could be synthesized.

Comparative Example 1 A polycrystalline body was synthesized in the same manner as in Example 1 except that aluminum oxide was not added. The relative density of the obtained polycrystal was 81%. The relative densities of the polycrystalline bodies molded under the respective molding pressures are plotted in FIG.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the molding pressure and the relative density of polycrystalline bodies in Examples and Comparative Examples. A to C show Examples 1 to 3, and D shows Comparative Example 1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayoshi Suzue Inventor Masayoshi Suzue 463 Kagasuno, Kawauchi-cho, Tokushima City, Tokushima Prefecture, Tokushima Laboratory, Otsuka Chemical Co., Ltd. (56) Reference JP-A-61-63529 (JP, A)

Claims (5)

[Claims] 1. When producing a polycrystal of fibrous alkali metal titanate, a titanium source compound, an oxygen-containing alkali metal compound and aluminum oxide are mixed and the mixture is heated to 600 to 1100 ° C.
A method for producing a fibrous polycrystalline compact, which is characterized in that after firing at a temperature of 1 to form an amorphous substance, this is further pressure-molded and re-fired at 900 to 1350 ° C. 2. The method according to claim 1, wherein the mixing ratio of the titanium source compound and the oxygen-containing alkali metal compound is 0.4 to 1.5 in terms of the molar ratio of TiO ₂ / M ₂ O (M represents an alkali metal). Manufacturing method. 3. The amount of aluminum oxide added is 1.25 × 10 ^{−2 to} 2.5 × 10 5 with respect to 1 mol of the titanium source compound (as TiO ₂ ).
^The method according to claim 1, which is ^-3 mol. 4. The method according to claim 1, wherein the oxygen-containing alkali metal compound is a nitrate of an alkali metal. 5. A fibrous alkali metal titanate is represented by the general formula M ₂
The method according to claim 1, which is a compound represented by O · nTiO ₂ (M is an alkali metal, n is an integer of 4,6,8 or a mixture thereof).