JPH05271992A - Formation of aluminum oxide film and electrolyte used therefor - Google Patents

Abstract

PURPOSE:To form a large-area porous oxide film by anodizing Al in a nonaqueous electrolyte obtained by dissolving the quaternary ammonium salt of phthalic acid in a specified org. solvent. CONSTITUTION:The quaternary ammonium salt such as tetramethylammonium salt of phthalic acid is dissolved in an org. solvent such as gamma-butylolactone to obtain a nonaqueous electrolyte contg. <=0.1wt.% water. Al is dipped in the electrolyte kept at 0-120 deg.C and used as an anode, and a current is applied at 0.5-50mA/cm<2> density to anodize the Al surface. A fibrous or porous oxide film having a large surface area is formed on the Al surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an aluminum oxide film, that is, a method for producing aluminum having an anodic oxide film, and an electrolytic solution used therefor. The oxide film obtained by the method of the present invention is a fibrous porous film, and aluminum having the oxide film is expected to be applied to various functional applications.

[0002]

2. Description of the Related Art Anodization of aluminum has been a well-known technology for a long time, and industrially, it is required to have corrosion resistance and weather resistance for construction, vehicles, ships, aircraft materials, and electrically insulating materials. Required anodized wire, printed wiring board, semiconductor circuit, electrolytic capacitor, switching element,
Electrophotographic drum, magnetic recording disk, humidity sensor,
Solar heat absorption plate, reflection plate, multicolored alumite, photosensitive alumite, light emitting (fluorescent) element, I, where light and heat characteristics are important
In addition to C heat dissipation plate, lubricating alumite, PS printing plate, catalyst,
It has been applied to adsorbents, permeable membranes, filtration membranes, etc.

It is known that anodic oxidation is usually carried out in an aqueous electrolytic solution, and roughly two types of oxide films are formed depending on the type of electrolytic solution. One of them is a porous film with a large surface area called a porous type that is formed in an acidic solution such as sulfuric acid or oxalic acid. The pores are functionalized by filling a third substance or by sealing. The other is a so-called dense and highly insulating film called a barrier type formed in a neutral solution such as ammonium borate or ammonium adipate, which is used for aluminum electrolytic capacitors.

On the other hand, although a method using a non-aqueous electrolytic solution has also been studied, the present situation is that none of them has been industrially implemented, and it is insoluble in water as a functional substance and soluble in an organic solvent. There is a problem that it is difficult to use the substance.

[0005]

The present invention is capable of forming a porous anodic oxide film having a large surface area by using a non-aqueous electrolytic solution instead of the conventional aqueous electrolytic solution, and is insoluble in water and compatible with organic solvents. It is intended to provide a novel method for forming an aluminum oxide film, which enables the use of various soluble functional substances, and an electrolytic solution used therein.

[0006]

That is, the present invention is characterized in that aluminum is anodized in an organic solvent solution of a quaternary ammonium salt of phthalic acid having a water content of 0.1% by weight or less. The present invention provides a method for forming an oxide film and an electrolytic solution used for the method.

The quaternary ammonium salt of phthalic acid used in the electrolytic solution of the present invention is a symmetrical alkyl type such as tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium;
Trimethylethylammonium, dimethyldiethylammonium, triethylmethylammonium, trimethylpropylammonium, dimethyldipropylammonium, tripropylmethylammonium, trimethylbutylammonium, dimethyldibutylammonium, tributylmethylammonium, triethylpropylammonium, diethyldipropylammonium, tripropylethyl Asymmetrical alkyl type such as ammonium, triethylbutylammonium, diethyldibutylammonium, tributylethylammonium, tripropylbutylammonium, dipropyldibutylammonium, tributylpropylammonium, methylethylpropylbutylammonium; N, N-dimethylpyrrolidinium, N, N-Dimethy Piperidinium, N, N-dimethylmorpholinium, N-methyl-N-ethylpyrrolidinium, N-methyl-N-ethylpiperidinium, N-methyl-N-ethylmorpholinium, N, N-diethylpyrrolinium Dinium, N, N-diethylpiperidinium, N,
N-diethylmorpholinium, N, N-tetramethylenepyrrolidinium, N, N-tetramethylenepiperidinium, N, N-tetramethylenemorpholinium, N, N-
Alicyclic types such as pentamethylene piperidinium and N, N-pentamethylene morpholinium; and aromatic compounds such as N-ethylpyridinium, N, N-dimethylimidazolium and N-methyl-N-ethylimidazolium Examples thereof include quaternary ammonium salts of the type. Among these, those having an alkyl group of a methyl or ethyl group are preferable because they show high electric conductivity, and tetramethylammonium, tetraethylammonium, trimethylethylammonium, dimethyldiethylammonium, triethylmethylammonium, N, N-dimethylpyrrolidinium are preferable. , N-methyl-N-ethylpyrrolidinium and the like are preferable. In particular, tetramethylammonium, tetraethylammonium, and triethylmethylammonium salts are more easily available and more preferable.

As the solvent for dissolving the quaternary ammonium salt of phthalic acid used in the electrolytic solution of the present invention, N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N, N-diethylformamide, N-
Methylacetamide, N, N-dimethylacetamide,
An amide solvent such as N-methylpyrrolidinone; a lactone solvent such as γ-butyrolactone, γ-valerolactone and δ-valerolactone; a carbonate solvent such as ethylene carbonate, propylene carbonate and butylene carbonate; an alcohol solvent such as ethylene glycol and methyl cellosolve; Examples thereof include nitrile solvents such as 3-methoxypropionitrile and glutaronitrile; and phosphate ester solvents such as trimethyl phosphate and triethyl phosphate. These solvents can also be used as a mixed solvent of two or more solvents. Of these, γ-butyrolactone is the most practically preferred.

The amount of the quaternary ammonium salt of solute phthalic acid dissolved in the above-mentioned solvent varies depending on the specific resistance of the electrolytic solution to be obtained and the formation voltage, but it is generally below the saturation concentration, preferably 1 to 40% by weight. is there. In order to achieve the object of the present invention, the water content of the electrolytic solution is 0.1% by weight.
Hereafter, it is necessary to regulate the content to preferably 0.05% by weight or less. If the water content is too high, a porous film having a large surface area cannot be formed.

As a method of anodizing treatment, a method which has been generally put into practical use can be adopted. The anodizing treatment is performed in an electrolytic bath in a temperature range of 0 to 125 ° C.
It is performed at a current density of 5 to 50 mA / cm ² . The spark voltage of the electrolytic solution can be raised to about 500 V by decreasing the concentration of the electrolytic solution, but the resistance of the electrolytic solution increases, heat generation during formation becomes intense, and power loss also increases. The formation voltage is preferably 200 V or less.

[0011]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below. (Example 1) Tetramethylammonium hydrogen phthalate salt was dissolved in γ-butyrolactone solvent in an amount of 21% by weight to prepare an electrolytic solution, and the water content in the electrolytic solution was adjusted to 0.01% by weight. The specific resistance of this electrolytic solution at 25 ° C. and the spark voltage when the aluminum foil was anodized at 5 mA / cm ² in this electrolytic solution were 101 Ωcm and 90 V, respectively.

(Example 2) Using the electrolytic solution of Example 1, an aluminum foil was formed at room temperature at 5 mA / cm ^{2 up} to 90V.
The result of observing the obtained oxide film with a scanning electron microscope is shown in FIG. The film formed was porous with a large surface area in the form of fibers.

Example 3 Tetramethylammonium hydrogen phthalate was dissolved in a γ-butyrolactone solvent in an amount of 10% by weight to prepare an electrolytic solution, and the water content in the electrolytic solution was adjusted to 0.04% by weight. The specific resistance of this electrolytic solution at 25 ° C. and the spark voltage when the aluminum foil was anodized at 5 mA / cm ² in this electrolytic solution were 134 Ωcm and 100 V, respectively. Aluminum foil is 10mA at room temperature using this electrolyte.
FIG. 2 shows the results of observing the resulting oxide film with a transmission electron microscope after forming the film at 100 V / cm ^{2 up} to 100 V. The film formed was fibrous.

(Comparative Example 1) The same electrolytic solution as in Example 1 was used except that the water content of the electrolytic solution in Example 1 was changed to 1% by weight.
In this electrolytic solution, an aluminum foil of 90 V was prepared in the same manner as in Example 2.
When the film obtained by chemical conversion was observed with a scanning electron microscope, the film surface was relatively smooth as shown in FIG. 3, and a film having a fibrous form was not obtained.

[0015]

According to the present invention, a fibrous porous film having a large surface area can be formed with a non-aqueous electrolyte. Aluminum having an oxide film obtained by the method of the present invention is expected to be applied to various fields such as building materials, magnetic recording disks, humidity sensors, solar heat radiation plates, absorption plates, multicolor alumites, light emitting devices, lubricating alumites, and catalysts. To be done.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph of a cross section of an anodized film obtained in Example 2.

FIG. 2 is a transmission electron micrograph of the cross section of the anodized film obtained in Example 3.

FIG. 3 is a scanning electron micrograph of a cross section of the anodized film obtained in Comparative Example 1.

Claims (4)

[Claims] 1. A method for forming an aluminum oxide film, which comprises anodizing aluminum in an organic solvent solution of a quaternary ammonium salt of phthalic acid having a water content of 0.1% by weight or less. 2. The method according to claim 1, wherein the anodizing treatment is performed in an electrolytic bath at a temperature of 0 to 125 ° C. and a current density of 0.5 to 50 mA / cm ^2. 3. The water content of the quaternary ammonium salt of phthalic acid used in the method according to claim 1 dissolved in an organic solvent.
1 wt% or less electrolyte 4. The electrolytic solution according to claim 3, wherein the organic solvent is γ-butyrolactone.