JPS6011227A - Manufacture of fibrous barium titanate having hollandite type structure - Google Patents

Abstract

PURPOSE:To obtain the titled fibrous salt proof against high temp., having a significant heat insulating effect, and suitable for use as a heat insulating material at high temp. by mixing barium titanate having a hollandite type structure with a metallic molybdate, melting the mixture, and growing crystals from the melt. CONSTITUTION:Barium titanate having a hollandite type structure represented by formula I (where B is Mg, a bivalent transition metal, Al, Fe, Cr or Ga, each of (x) and (y) is 0.5-3, and (z) is 5-8) or a mixture of compounds as starting materials for manufacturing the barium titanate is mixed with a metallic molybdate represented by formula II (where A is K, Rb or Cs, and (n) is 0-3) or starting materials for manufacturing the metallic molybdate. The resulting mixture is melted, and crystals are grown from the melt by a slow cooling method, an evaporation method, a temp. difference method, a local cooling method or a combination thereof to obtain desired fibrous barium titanate having a hollandite type structure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing fibrous barium titanate having a hollandite structure. More specifically, the present 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 fire-resistant material, etc.

PRIOR TECHNOLOGY We have developed this as a high-temperature heat insulating material that has been widely used in the past (see Japanese Patent Publication No. 55-25157). However, although this potassium titanate fiber has outstanding heat insulation properties among ceramics, its melting point is 1370°C, so
There was a problem in that the temperature at which it could actually be used was up to about 1200°C.

OBJECTS OF THE INVENTION An object of the present invention is to provide 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 and higher melting point than potassium titanate, and synthesized a single crystal of barium titanate with a hollandite structure. It was discovered that the thermal insulation properties are extremely low and can withstand high temperatures.

1,:j,'Also, a single crystal of barium titanate with a hollandite structure has the general formula Bax(ByTi2)8016(
However, B is Mg, divalent transition metal + ” + Fe
, a metal selected from Cr and Ga, X is 0.5 to 3,
It can be obtained by growing crystals using barium titanate having a hollandite structure represented by 0.5 to 3.2 (y represents 5 to 8) or a specific 7 lux from its manufacturing raw material. I found out that it can be done. The present invention was completed based on these findings.

The gist of the present invention is that the barium titanate having the hollandite structure or the raw material for its production has the general formula A
2MoO4・nMOO, (A is K.

The method involves mixing a molybdate metal salt represented by Rb (as, n=o to 3) or a raw material for its production, melting the mixture, and growing crystals from the melt.

It has a hollandite type structure in the present invention. In particular, Mg and Ai are preferable because they can easily replace Ti, make samples easier, and have a high melting point. However, component B may be a solid solution component of two or more of the above-mentioned elements. Further, xly represented by the general formula must all be in the range of 0.5 to 3, preferably 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 the conductivity and lowers the mechanical strength.

Moreover, 2 needs to be 5-8. Outside this range, it is difficult to obtain a TiO2 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 BII.

(However, Blr and Mg represent divalent transition metals.)
← metal oxide or general formula B203 (however,
■ ■ represents Aj, , Fe, Or, or Ga) and is used for uncoated metal oxides, and titanium oxide (TiO2).
) in molar ratio, BaO:BI[0:Ti02==2:1:3~5:2:
3 or a mixture or solid solution in the ratio of BaO:BO:Ti02==2:1:3 to 4:3:3 is used as the production raw material.

Instead of the raw material BaO, a barium compound that generates BaO when heated, such as Ba(OH)2. BaGO
,s,,B5(NO5)2 + BaF21 BeLO
12, BaB407 + BaSO4, 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 Mg0O.

Carbonates of divalent transition metals, Mg(OH), , hydroxides of divalent transition metals, MgH2(00g) 2 deuterium carbonates of divalent transition metals, Al(on), , Fe
(OH)316r(OH), .

Ga(01()3.A12(co3), , Fe2
(00,)S, 0r2(005)S.

The metal ratio is determined by converting it into metal oxide.

The above-mentioned barium titanate having a hollandite structure or its manufacturing raw material has the general formula A2M004.1M.
A molybdate metal salt represented by 003 (where A and n represent the same metals and numbers as above) is mixed.

These molybdate metal salts act as a flux, and Moo has the property that there is no concern about pollution due to its solubility, 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 terms of mol%.

The appearance of production differs somewhat depending on the mixing ratio.

Due to the difference in the basicity of the melt, it may form a mixture with the rutile phase in the case of low basicity, or it may crystallize and form a mixture with the rutile phase in the case of high basicity. .

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 a temperature of approximately 700°C; (2) An evaporation method that evaporates the 7-lux component while maintaining it at a constant temperature. (
5) Temperature difference method that creates a temperature difference between the top and bottom of the crucible. (4)
This can be carried out by a local cooling method in which air is blown onto the bottom of the crucible or by bringing a coolant into contact with the crucible to locally cool the bottom, and (5) a method using a combination of the above methods.

Crystals can also be obtained.

Example 1 Barium carbonate, aluminum oxide, and titanium oxide powders were prepared in molar ratios of Ba, OO3: Al2O3:Ti0
They were mixed at a ratio of 2=4:4:6.

In addition, each powder of potassium molybdate and molybdenum oxide was mixed in a molar ratio of 2MoO4: Mob5=1:0.
．． They were mixed at a ratio of 5:5.

(BaO05) 4 ・(A
'205)2 ・(TiO2)62(K2MOO4),
・(MoO2). , 5==2o:s and used as a starting material. Approximately 30 kg of this starting material was charged into a 30-cm platinum crucible; 5. kW carbonization 1. It was separated. The obtained crystal is elongated in the C-axis direction! 2↑It was fibrous and gray in color, and had a hollandite-type structure in X-ray powder diffraction. Its chemical composition was (Ba + K) o, a(”+, 6Ti6.4) a0
In No. 16, a small amount of potassium was found in solid solution with barium.

The maximum size of the crystal is 0.2 x 5 mm, and the average size is 0.2 x 5 mm. OIXlmm, and the melting point was about 1500°C.

Examples 2 to 7 Crystals were grown in the same manner as in Example 1 except that the composition of the barium titanate having a hollandite structure was changed and the slow cooling rate was 8°C/h.The results were as follows. .

('Note 1) The X phase is a powdered barium molybdate phase.

Note that AJ20. in Example 1. Instead, Fe, Or.

Almost the same results were obtained when oxides of Ga and Ga were used. Also, instead of K in the flux, Rh.

Almost similar results were obtained when Os was used.

Example 8゜Ba1,4A'2,8Ti5,2 in the same manner as Example 1
The K2A12Ti6016 sample is a disk-shaped sintered body with a thickness of 1.921 mm, an outer diameter of 7.80 mm, and a density of 3.429 crn-3. did.

(2) Chromel-cons on one side of the disk-shaped sample From the above table, the barium titanate of the present invention shows a value 20% or more lower than that of the potassium hexatitanate sintered body. In addition, the thermal conductivity is lower at 1000 K than at room temperature,
This shows that it has excellent heat insulation properties at high temperatures.

Effects of the Invention According to the method of the present invention, it can withstand high temperatures with a melting point of 1500°C or higher, and has excellent properties of high heat insulation, and can be effectively used as steel frame covering materials, various heat insulating materials, and fireproofing materials. . In addition, the powdered material can be used as an additive material for heat-resistant heat-insulating coatings.

Claims (1)

[Claims] 1. General formula Bax(ByTi2)80,6 (however,
B is Mg, a divalent transition metal, ju, and Fe. Metal selected from Or and Ga, X is 0.5 to 3, y
represents 0.5 to 3, and 5 to 8. ) The mixture of norium titanate having the hollandite type structure shown in Table 1 or the raw material compound for its production has the general formula % (Tata, A is K, Rb or Os%, n is θ~
A fibrous lithium titanate having a hollandite-type structure is produced by mixing molybdate metal salt represented by 3) or its manufacturing raw material, melting the mixture, and growing crystals from the melt. A method for producing barium titanate having a lherhollandite structure represented by the general formula Bax(ByTiz)8o16. A metal oxide represented by the general formula B2O5 (representing a transition metal) or a metal oxide represented by the general formula B2O5 (where Bn [represents kl, Fe, Or or Ga) and TiO2 in a molar ratio, BaO:BMO:Ti02 =2:1:3~5:2:3 or BaO:B'HO,:Ti02=2:1:3~4:3:
3. The method for producing a fibrous barium titanate having a hollandite structure according to claim 1, wherein the fibrous barium titanate has a hollandite structure. 3. The manufacturing method according to claim 1, wherein the crystal growth method from the melt is a slow cooling method, an evaporation method, a temperature difference method, a local cooling method, or a combination thereof.