JPH0469566B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a transparent film made of alumina particles having an extremely fine particle size and a method for producing the same.

[Technical background of the invention and its problems]

The particle size of metals or metal compounds, etc.
Ultrafine particles of 100 nm or less have an extremely large specific surface area, so they are expected to have properties different from those of bulk particles.

Conventionally, fine particles having a particle size of, for example, about 20 to 500 nm have been known, and gas evaporation methods, solvent freezing methods, plasma methods, etc. have been used as methods for producing them. However, the fine particles produced by these methods were not fully satisfactory in terms of uniform particle size, stability, ease of handling, and the like. For example, when fine particles are produced using conventional methods, even if fine particles are obtained as primary particles, since they themselves have high activity, aggregation occurs between each particle, resulting in only large particles. Moreover, it was difficult to redisperse this aggregated particle mass into smaller particles.

As a countermeasure to this problem, there are two methods: generating fine particles in a microemulsion and coating the particle surface with an appropriate surfactant, or freezing and condensing the particles obtained by evaporation with an appropriate solvent. etc. are being carried out. However, with these methods, it is difficult to produce a uniform microemulsion and to set the conditions for producing fine particles in the former, and in the latter, secondary aggregation tends to occur when the solvent is removed; It is also difficult to remove surfactants and solvents.

As mentioned above, ultrafine particles, especially those with a particle size of
It is difficult to produce ultrafine particles with a diameter of less than 100 nm, and for this reason, it has been almost impossible to produce films using them. Conventionally known films include:
For example, a silica or alumina film produced by a sol-gel method using alkoxide hydrolysis, a colloidal material of a layered compound, or a mixture of the colloidal material and a monomer having a functional group such as an imino group or a vinyl group. An inorganic film consisting of
(see publication). However, these films
Due to the large particles contained, there were problems with transparency.

[Purpose of the invention]

It is an object of the present invention to solve the above-mentioned problems and provide a film that is made of extremely fine alumina particles and has high transparency.

[Summary of the invention]

As a result of intensive research to achieve the above object, the present inventors have found that extremely fine alumina particles can be obtained by appropriately adjusting the aging and decomposition conditions when producing alumina from aluminum salt. Furthermore, we discovered that this film made of ultrafine alumina particles has high transparency.
The present invention has now been completed.

That is, the present invention relates to a transparent film made of fine alumina particles having an amorphous structure, characterized in that the fine alumina particles have a particle size of 3 to 30 nm, and a method for manufacturing the same.

The amorphous fine alumina particles constituting the transparent film of the present invention are produced by producing aluminum hydroxide from an aluminum salt aqueous solution, and then by appropriately selecting the aging and decomposition conditions. , and alumina fine particles with uniform particle size can be obtained.

Examples of the aluminum salt used here include aluminum sulfate, aluminum chloride, and aluminum nitrate.

A known method can be used to generate aluminum hydroxide from these aluminum salts. That is, by dissolving the above-mentioned aluminum salt in water and then adding excess aqueous ammonia to this solution, aluminum hydroxide can be precipitated. Next, the produced precipitate is aged as it is under constant pH conditions for a certain period of time. The pH in this case is preferably 5 to 7, preferably 5.8 to 6.3.
The pH is adjusted by adjusting the amount of ammonia water added so that it falls within the above pH range. Also, the aging time is 12-24 hours, preferably 15
~20 hours is good.

After aging the aluminum hydroxide precipitate thus produced, the precipitate is separated by centrifugation or filtration, and thoroughly washed with water. Next, acetic acid and water were added to the precipitate, and the mixture was heated and refluxed at 65 to 85°C to reduce the particle size to 3 to 30 nm.
A dope liquid consisting of alumina fine particles having an amorphous structure can be obtained. In this case, the amount of acetic acid and water added is 6 to 20% each based on the weight of the precipitate.
%, and 100-300%, preferably 10-16%, and 150-250%. In addition, heating and reflux are
3.5 to 6 hours is preferred.

Next, the alumina dope solution obtained in this way is cast or sprayed onto a suitable smooth surface, for example, onto a releasable substrate such as a metal plate or glass plate coated with silicone resin or a polyethylene plate. etc. to make it uniform. Although the amount of casting in this case is not particularly limited, it is preferable that the thickness of the formed film is 10 to 50 microns.

Then the film formed on the substrate, 20-30
By slowly evaporating water at ℃ for 20 to 60 hours, a colorless and transparent film consisting of alumina fine particles with an amorphous structure can be obtained.

The film of the present invention thus obtained is
Because it maintains its amorphous structure and is transparent even at temperatures close to 1000°C, it is suitable for rare earth salts that thermally decompose and become colored at high temperatures, such as Pr.
(NO ₃ ) ₃ (green), Nd (NO ₃ ) ₃ (purple), Sm (NO ₃ ) ₃
(yellow), Eu(NO ₃ ) ₃ , etc. are added to the alumina dope solution, formed into a film, and then sintered.
A transparent and colored film can be obtained.

Furthermore, a highly flexible film can be obtained by adding a polymer or monomer having a functional group to the alumina dope and forming it into a film. The blending amount of this polymer or monomer is 30% based on the weight of alumina in the dope solution.
~80%. Polymers or monomers used here include polyvinyl alcohol,
Examples include polymers such as polyacrylic acid, polymethacrylic acid, polyacrylamide, polyethyleneimine, and carboxymethyl cellulose, and monomers constituting them.

Furthermore, a sol or liquid substance of inorganic oxide fine particles or an aqueous solution of a water-soluble metal compound can be added to the alumina dope liquid, and then a transparent composite film can be obtained in the same manner as described above.

Inorganic oxides that can be used as other components of the composite film include SiO ₂ , CuO, MgO, CaO, BaO,
SrO, SnO ₂ , MnO ₂ , NiO, CoO, TiO ₂ ,
Examples include ThO ₂ , ZnO, PbO, ZrO ₂ , Fe ₂ O ₃ and V ₂ O ₅ .

Examples of methods for preparing these inorganic oxides into fine particle sol or liquid substances are as follows.

(1) SiO ₂ ; By adding Si(OC ₂ H ₅ ) liquid to the alumina dope, it is hydrolyzed by the water in the dope and becomes a sol-like substance.

(2) TiO ₂ ; Proceed as in (1) using ₄ TiC liquids.

(3) SnO ₂ ; Proceed as in (1) using a concentrated solution of SnC ₄ .

(4) V ₂ O ₅ ; Add 0.5N hydrochloric acid to a 10% NH ₄ VO ₃ aqueous solution, filter the red precipitate, and then wash with water. The initial filtrate after washing with water is discarded, and the filtrate, which is peptized and turns into a red liquid, is dispersed and used as a sol solution.

(5) Fe ₂ O ₃ ; 12 ml of 30% FeC ₃ solution in 700 ml of boiling water
to make an aqueous solution.

(6) ZrO ₂ ; 0.2 mol ZrOC ₂ 8H ₂ O aqueous solution at 90%
After heating at ℃ for 5 to 6 hours, it is cooled to form an aqueous solution.

(7) ThO ₂ ; An aqueous solution in which 25 g of ThC ₄ .2H ₂ O is dissolved in 300 ml of water is heated to 90° C. for 5 to 6 hours, and then cooled to form an aqueous solution.

These inorganic oxide sol or liquid substances are based on the alumina weight of the alumina dope liquid.
Mix and use at a concentration of 0.1 to 5%.

Further, when an aqueous solution of a water-soluble metal compound is used as another component of the composite film, it is preferable to use the water-soluble metal compound as an aqueous solution of 5 to 10% by weight. In this case, water-soluble metal compounds include Ni(NO ₃ ) ₂ , Co(NO ₃ ) ₂ , ZnC ₂ , MnC
₂ , RhC ₃ , RuC ₃ , IrC ₃ , Cu(NO ₃ ) ₂ ,
ZrOC ₂ , NaNO ₃ , KNO ₃ , Fe(NO ₃ ) ₂ , Pb
Examples include (NO ₃ ) ₂ , Fe(NO ₃ ) ₃ and LiNO ₃ .

This water-soluble metal is mixed in an amount of 0.1 to 5% based on the weight of alumina in the alumina dope.

The film of the present invention can be used for 400 min after forming the film.
By heating and sintering at a temperature of ~900℃ for 10~24 hours, the diameter of the film becomes 50~90℃.
It can be made into a porous film having micropores of 20 nm. This porous film can be used as a gas separation membrane, a conductive membrane, and a separation membrane with catalytic action.

When the film of the present invention is a composite film made of alumina and an inorganic oxide or a water-soluble metal compound, it is also possible to make an alumina-supported catalyst by thermally decomposing the composite film in air or in a reducing atmosphere. .

[Embodiments of the invention]

Hereinafter, the present invention will be explained in further detail with reference to Examples.

Example 50 g of aluminum chloride was dissolved in 200 ml of water, and 100 ml of 6N ammonia water was added to this solution over 3 hours while stirring to form a precipitate of aluminum hydroxide. The pH after addition was adjusted to 6. Then, after aging at room temperature for 24 hours, centrifugation
The precipitate was separated and washed with 1 portion of water. This precipitate
Add 20 ml of water and 2 ml of acetic acid to 10 g, stir thoroughly, and heat under reflux at 80°C for 5 hours until the particle size is 5 to 5.
A dope solution consisting of 10 nm alumina fine particles was obtained.
This dope solution was cast onto a glass plate to a thickness of 30 μm, and then dried at 20° C. for 60 hours to obtain a transparent film.

This film was further sintered at 500 to 900°C to obtain a colorless transparent film having micropores with a diameter of 40 to 100 Å. The gas permeability coefficient P (×10 ⁹ ) of this film at 20°C is H ₂ ; 1.5,
He; 0.8, CH ₄ ; 1.3, N ₂ ; 0.4, O ₂ ; 0.8, CO ₂ ;
It was 3.6.

Reference example Alumina dope solution prepared in the example and 0.1M
Ni(NO ₃ ) ₂ aqueous solution was mixed at a volume ratio of 2:1 and then cast onto a glass plate to form a green transparent film. This film has a moisture content of
Slowly dry until it becomes 20-30%, then heat it all at once to 400℃, and then in a hydrogen stream.
By reducing at 450℃ for 2 hours, a diameter of 45Å was obtained.
An amorphous alumina-supported nickel catalyst containing Ni fine particles was obtained. When cyclooctadiene and 4-tert-butyl-methylenecyclohexene were reduced using this catalyst, the reactivity and selectivity to monoene and cyclohexane were superior to that of Raney Ni.

〔Effect of the invention〕

As described above, according to the production method of the present invention, particle sizes of 3 to 3
Alumina ultrafine particles with a 30 nm amorphous structure can be easily produced, and a highly transparent film can be obtained using these alumina ultrafine particles. Furthermore, the transparent film of the present invention is
By heating and sintering it under certain conditions, it can be made into a porous film with gas separation ability, etc., and its industrial value is extremely large.

Claims (1)

[Scope of Claims] 1. A transparent film made of alumina fine particles having an amorphous structure, wherein the alumina fine particles have a particle size of 3.
A transparent film characterized by ~30nm. 2 Obtained by adding ammonium water to an aqueous aluminum salt solution, leaving it to ripen, separating the resulting precipitate, washing it, adding acetic acid and water to the precipitate, stirring and heating at 65 to 85°C. A method for producing a transparent film, which comprises directly casting an alumina dope containing alumina fine particles with an amorphous structure onto a substrate and drying it.