JPH0346432B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF INDUSTRIAL APPLICATION The present invention relates to a method for producing fibrous barium titanate having a hollandite structure. For more details,
This invention relates to a method for producing fibrous barium titanate having a hollandite-type structure and having a one-dimensional extremely large tunnel structure that has high-temperature insulation properties and is excellent as a high-temperature insulation material, a water-resistant material, etc. Prior Art Asbestos is a high-temperature insulation material that has been widely used in the past. However, asbestos has the disadvantage of causing pollution, and there is a demand for the development of alternative materials. One of the inventors of the present invention previously developed a new potassium titanate fiber as an alternative material to asbestos (see Japanese Patent Publication No. 55-25157). However, although this potassium titanate fiber has outstanding insulation properties among ceramics, it has a low melting point.
Since it is 1370℃, the actual usable temperature is 1200℃.
There were some problems to a certain extent. OBJECTS OF THE INVENTION An object of the present invention is to provide a method for producing a high-temperature heat insulating material that can be used at higher temperatures than the potassium titanate fibers. Structure of the Invention As a result of many years of research into potassium titanate, the present inventors have revealed that the cause of its heat insulating properties is related to its one-dimensional tunnel structure. As a result, they conducted intensive research to obtain a substance with a larger tunnel structure than potassium titanate and a higher melting point, and when they synthesized a single crystal of barium titanate with a hollandite structure, they found that the thermal conductivity was It was discovered that the material has an extremely small amount of heat and exhibits heat insulating properties that can withstand high temperatures. In addition, a single crystal of barium titanate with a hollandite structure has the general formula B _x (B _y Ti _z ) ₈ O ₁₆ (where B is Mg, a divalent transition metal, Al, Fe, Cr
and Ga, x is 0.5 to 3, y is
It has been found that it can be obtained by crystal growth using a specific flux from a barium titanate having a hollandite structure (0.5 to 3, z representing 5 to 8) or a raw material for its production. The present invention was completed based on these findings. The gist of the present invention is that the above-mentioned barium titanate having a hollandite structure or a raw material for its production has a general formula A ₂ MoO ₄ .nMoO ₃ (where A represents K, Rb or Cs, n = 0 to 3). ) or its production raw materials are mixed, the mixture is melted, and crystals are grown from the melt. Mg, Cu, Zn, which is the B component represented by the general formula having a hollandite structure in the present invention,
Ni, Co, divalent transition metals, Al, Fe, Cr, and Ga are all present in the TiO ₆ octahedron that forms the tunnel framework.
It is a metal that can replace and occupy the seat of Ti. In particular, Mg and Al are preferable because they can easily replace Ti, facilitate sample preparation, and have a high melting point. Moreover, the B component may be a solid solution component of two or more of the above-mentioned elements. In addition, both x and y shown in the general formula must be in the range of 0.5 to 3,
Preferably it is in the range of 1.0 to 2.4. Outside this range, a phase other than the barium titanate having the desired hollandite structure is formed, resulting in a mixed phase, which increases thermal conductivity and reduces mechanical strength. Moreover, z needs to be 5-8. Outside this range, it is difficult to obtain a TiO ₆ octahedron with a tunnel structure. The barium titanate having a hollandite structure used in the present invention is produced by the following method. Barium oxide (BaO), general formula B〓O
(However, B〓 represents Mg or divalent transition metal)
Metal oxides represented by or represented by the general formula B〓 ₂ O ₃ (where B〓 represents Al, Fe, Cr or Ga), and titanium oxide (TiO ₂ )
In terms of molar ratio, BaO:B〓O: _TiO2 = 2:1:3 to 5:2:3 or BaO:B〓O: _TiO2 = 2:1:3 to 4:3:3. The raw material for production is a mixture or solid solution of In place of the raw material BaO, a barium compound that generates BaO upon heating, such as Ba(OH) ₂ ,
_BaCO3 , Ba( _NO3 ) ₂ , _BaF2 , _BaCl2 , _{BaB4O7 ,}
BaSO ₄ etc. can also be used. In addition, instead of the metal oxide of component B, a compound that generates the metal oxide upon heating, such as MgCO ₃ ,
Carbonates of divalent transition metals, Mg(OH) ₂ , hydroxides of divalent transition metals, MgH ₂ (CO ₃ ) ₂ , deuterium carbonates of divalent transition metals, Al(OH) ₃ , Fe(OH) ) ₃ , Cr
(OH) ₃ , Ga(OH) ₃ , Al ₂ (CO ₃ ) ₃ , Fe ₂ (CO ₃ ) ₃ ,
Cr ₂ (CO ₃ ) ₃ , Ga ₂ (CO ₃ ) ₃ and the like can also be used. Similarly, a compound that generates TiO ₂ upon heating can be used as the TiO ₂ mentioned above. When a metal compound other than these metal oxides is used, the molar ratio is determined in terms of the metal oxide. The general formula
A molybdate metal salt represented by A ₂ MoO ₄ .nMoO ₃ (A and n represent the same metals and numbers as above) is mixed. These molybdate metal salts act as a flux, and MoO ₃ acts to increase solubility. And it has low volatility,
There is no concern about pollution due to volatilization, and since it is easily soluble in water, the produced fibers can be easily separated and recovered. The mixing ratio of both is preferably 10:90 to 50:50 in mol%. The appearance of production differs somewhat depending on the mixing ratio.
Due to the difference in basicity of the melt, if the basicity is low, the melt may become a mixture with the rutile phase, or if the basicity is too high, it may be difficult to crystallize. In such cases, as a regulator
The quantity ratio may be controlled using the K ₂ O component and the MoO ₃ component. When these mixtures are melted at, for example, 800° C. to 1500° C. to form a melt, and crystals are grown from the melt, a fibrous single crystal of barium titanate having a hollandite structure is obtained. Methods for growing crystals from a melt include (1) a slow cooling method in which the temperature of the melt is slowly cooled to approximately 700°C; (2)
An evaporation method that evaporates flux components while maintaining a constant temperature. (3) Temperature difference method that creates a temperature difference between the top and bottom of the crucible. (4) A local cooling method in which air is blown onto the bottom of the crucible or a cooling substance is brought into contact with the crucible to locally cool it, and (5) a combination of the above methods can be used. The barium titanate obtained by the method of the present invention has a tunnel structure made of TiO ₆ octahedrons and has a structure in which Ba occupies the tunnel.
It has a one-dimensional structure extending in the axial direction. In addition, fibrous crystals of barium titanate having a hollandite structure in which barium and alkali metals, particularly potassium, and Cu ions, which are divalent transition metals, are solidly dissolved can also be obtained. Example 1 Barium carbonate, aluminum oxide, and titanium oxide powders were prepared in a molar ratio of BaCO ₃ :Al ₂ O ₃ :
TiO ₂ was mixed at a ratio of 4:4:6. In addition, each powder of potassium molybdate and molybdenum oxide was mixed in a molar ratio of K ₂ MoO ₄ :MoO ₃ =1:0.5.
mixed in the ratio of Both mixtures are expressed in mol% as (BaCO ₃ ) ₄ .
(Al ₂ O ₃ ) ₂・(TiO ₂ ) ₆ : (K ₂ MoO ₄ )・(MoO ₃ ) _0.5 =
The mixture was mixed at a ratio of 20:8 and used as a starting material. Approximately 30g of this starting material was filled into a 30ml platinum crucible,
It was heated at 1300°C for about 10 hours in a 5kW silicon carbide electric furnace. The obtained melt is heated at 8℃/h until it reaches around 950℃.
It was cooled at a rate of . After cooling, the crucible was taken out of the electric furnace and allowed to cool to room temperature. The crystals were separated by dissolving the flux in hot water. The obtained crystals were fibrous and gray in color, extending in the C-axis direction. As a result of X-ray powder diffraction, it is barium titanate with a hollandite structure, and its chemical composition is (Ba, K) _0.8
(Al _1.6 Ti _6.4 ) ₈ O ₁₆ , with a trace amount of potassium,
It was in solid solution with barium. The maximum crystal size is 0.2 x 5 mm, and the average size is 0.01 x 1 mm.
The melting point was approximately 1500°C. Examples 2 to 7 Crystals were grown in the same manner as in Example 1 except that the composition of barium titanate having a hollandite structure was changed and the slow cooling rate was 8° C./h. The results were as follows.

[Table] Note that instead of Al ₂ O ₃ in Example 1, Fe, Cr,
Almost the same results were obtained when Ga oxide was used. Also, instead of K for flux,
Almost similar results were obtained when Rb and Cs were used. Example 8 A Ba _1.4 Al _2.8 Ti _5.2 O ₁₆ crystal was produced in the same manner as in Example 1. For comparison, a sintered body of K _2.0 Al _2.0 Ti ₆ O ₁₆ was prepared, and the specific heat capacity Cp, thermal diffusivity α, and thermal conductivity K of each sample at room temperature and 1000K were determined.
The results of the measurements were as follows. K=ρ・
Cp・α (ρ represents density)

[Table] From the above table, the barium titanate of the present invention shows a value that is 20% or more lower than that of the potassium hexatitanate sintered body. Furthermore, it exhibits lower thermal conductivity at 1000K than at room temperature, indicating that it has excellent heat insulation properties at high temperatures. Effects of the Invention According to the method of the present invention, a fibrous barium titanate having a hollandite structure, which has a melting point of 1500°C or higher, can withstand high temperatures, and has excellent properties of high heat insulation, is obtained, and this is used as a material for making pine wood. It can be effectively used as sheet materials, electric wire and steel frame covering materials, various heat insulating materials, and fireproofing materials. Powdered materials can also be used as materials for heat-resistant heat-insulating paints.

Claims (1)

[Claims] 1 General formula Ba _x (B _y Ti _z ) ₈ O ₁₆ (B is Mg, divalent transition metal, Al, Fe, Cr
and Ga, x is 0.5 to 3, y is
0.5-3, z represents 5-8. ), or a mixture _of barium titanate having a _hollandite -type _structure or a compound as a raw material for its production, is added to a mixture of barium titanate having a hollandite-type structure or a raw material compound for its production. 1. A method for producing a fibrous barium titanate having a hollandite structure, which comprises mixing molybdate metal salts represented by () or raw materials for producing the same, melting the mixture, and growing crystals from the melt. 2 A mixture of raw material compounds for producing barium titanate having a hollandite structure represented by the general formula B _x (B _y Ti _z ) ₈ O ₁₆ is BaO, the general formula B〓O (where B〓 is Mg or represents a divalent transition metal) or has the general formula B〓 ₂ O ₃ (however,
B〓 represents Al, Fe, Cr or Ga) and TiO ₂ in molar ratio, BaO:B〓O:TiO ₂ = 2:1:3 to 5:2:3 or BaO The fibrous barium titanate having a hollandite structure according to claim 1, which is a mixture or a solid solution thereof in a ratio of :B〓 ₂ O ₃ :TiO ₂ = 2:1:3 to 4:3:3. manufacturing method. 3. The manufacturing method according to claim 1, wherein the method for growing crystals from a melt is a slow cooling method, an evaporation method, a temperature difference method, a local cooling method, or a combination thereof.