JPS5819019B2 - Method for forming a selective absorption film for solar thermal energy on the surface of aluminum material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a selective absorption film of solar energy on the surface of an aluminum material such as a solar heat collector plate made of aluminum or an aluminum alloy as a base, particularly a selective absorption film using an electrolytic coloring method. The present invention relates to an improvement in the formation method.

The electrolytic coloring method, also called the Asada method, is known as a general method for forming a selective absorption film for solar thermal energy on the surface of an aluminum material, and has been widely adopted recently.

This method is generally based on a two-stage, two-bath method. In the first step, an aqueous solution of sulfuric acid, oxalic acid, phosphoric acid, etc. is used as the electrolyte, aluminum, carbon, stainless steel, etc. are used as the counter electrode, and direct current (current density) is used. 0.01~0.5A/dtr
? ) or alternating current (current density 0.1 to 0.8 A/dm"
) is applied to perform electrolysis to generate a porous anodic oxide film on the surface of the amyl minilum material, and then in the second step, the aluminum material with this oxide film is treated with nickel salt, cobalt salt, copper salt, and tin salt. Electrolysis is performed by applying alternating current (current density 0.1 to 0.8 A/dm") in an aqueous solution containing a metal salt such as, to precipitate and fill the fine pores of the oxide film to blacken the oxide film, The desired selective absorption membrane is obtained.

However, the conventional electrolytic coloring method has the disadvantage that the electrolysis time is quite long.

That is, the first step usually requires 10 to 15 minutes, and the second step blackening treatment also requires 5 minutes at the earliest, but usually 10 to 15 minutes or more, resulting in poor productivity.

In addition, the selective absorption membranes that can be produced do not necessarily have sufficient selective absorption properties;
Further improvement was desired.

The present inventors have conducted various studies to address these problems, and as a result have found the following.

Generally, the evaluation of a selective absorption film is based on the absorption rate α for sunlight.
Usually, the comparison is made in terms of the relationship between
is required to be 0.10 or less, but in order to satisfy this requirement, it is first necessary to form a film with a thickness of 1 μm or less.

If this exceeds 1 μ, even if solar thermal energy is absorbed, much of it will be emitted as radiant energy.
Emissivity ε becomes worse.

Therefore, the thinner the coating, the better the emissivity ε, but if it is too thin, good blackening cannot be obtained in the second step of blackening.

For this reason, the film thickness must be at least about 0.2 microns or more, and a range of 0.3 to 0.5 microns is particularly preferred.

On the other hand, even when an oxide film with a thickness of 1μ or less is formed, its surface condition has a great effect on selective absorption. It is preferable to use a film that maintains a balance between the production rate and the dissolution rate during the production process, and reaches an equilibrium state in which the production of the film does not increase.

The reason for this is not clear even to the inventors, but a stable and uniform oxide film can be obtained, and the coloring property of the film (
This is thought to be due to improved blackening (G,).

This invention is based on the above findings, and as a result of repeated experiments and research, the first step of anodizing treatment and the second step
By modifying the electrolytic operating conditions of the metal salt treatment process, we have discovered that a selective absorption membrane with extremely good selective absorption properties can be formed in an extremely short treatment time, and this has been completed.

Therefore, the first aspect of the present invention is to treat the treatment conditions of the first step of forming a porous anodic oxide film on the surface of the aluminum material, and the first step of the anodic oxidation treatment is to The method is characterized in that it is carried out in a phosphoric acid aqueous solution having a liquid concentration of 509/m above, and the liquid temperature is maintained at 35-780°C.

In addition, the second invention includes all of the configurations of the first invention, and further limits the processing conditions of the second step, and the electrolytic treatment of the second step is used for this. The concentration of metal salt in the electrolyte is 50 to 2 in nickel salt.
00? /l, 50-200 t/l in cobalt salt
l, 15-1001 in copper salt? /l, 5-50f in tin salt! /l.

In a metal salt aqueous solution with a higher concentration than the conventional method, such as 5 to 50 t/l for iron salts, and at a temperature of 35 t/l.
It is characterized by being carried out at a temperature of ~85°C.

Therefore, first, the processing conditions of the first step, which is the gist of the first invention, will be explained in more detail.

In carrying out the first step according to the present invention, an aluminum material made of aluminum or an aluminum alloy is pretreated in advance by a conventional method, and then the aluminum material is used as one electrode,
With stainless steel, carbon, lead, etc. as the other electrode, the concentration is 5.
01/ in a highly concentrated phosphoric acid aqueous solution, and the liquid temperature is maintained at 35 to 80°C, for example, a DC, AC, or similar waveform with a voltage of 10 to 30 V and a current density of 0.6 to 4 A/d-. is applied to electrolyze the aluminum material to form a porous anodic oxide film with a thickness of 1 μm or less on the surface of the aluminum material.

A treatment time of 0.5 to 5 minutes is sufficient.

In particular, the use of phosphoric acid aqueous solution as the electrolyte is
Compared to the case of using an aqueous solution such as sulfuric acid or oxalic acid, the thickness of the resulting film is thinner and the pore size of the pores is larger, resulting in a larger amount of metal precipitation, making it a better choice. It is based on the fact that an absorbent membrane can be obtained.

Conventional general treatment conditions for anodizing using a phosphoric acid aqueous solution are: solution concentration 20-30 t/11 solution temperature 20-30
°C, current density 0.2-0.4A/drr? Dc,
The processing time was approximately 15 minutes.

Compared to such conventional general processing conditions, the liquid concentration and liquid temperature of the present invention are set to considerably higher values.

Therefore, the liquid concentration of the present invention is 509 f/ or more, and the upper limit is not particularly limited, but considering economic efficiency and a good state of formation of the Otakashi film, it is 800 f/
is considered to be the upper limit.

On the other hand, if the concentration is less than 50 t/, it takes a long time to obtain the required film thickness, and a stable film cannot be obtained in a short time.

From this point of view, a particularly suitable concentration range is 80 to 300
f/l.

In addition, the liquid temperature is determined by the relative relationship with the liquid concentration, but if it is less than 35°C, it will take a long time to obtain the required oxide film thickness, and a stable film will not be obtained. to 8
If the temperature exceeds 0℃, the dissolution effect of the film becomes large, so
It becomes difficult to obtain the necessary film thickness, and the disadvantage is that the film becomes powdery and milky white.

In terms of the relationship between liquid concentration and temperature, the relative preferable range is 70 f/l to 150 r/Z for a liquid temperature of 45°C to 5.
A range of about 5°C is preferable.

According to the implementation of the first step according to the present invention as described above,
An extremely short treatment time of 0.5 to 3.0 minutes is sufficient to obtain the film thickness necessary for blackening the surface of an aluminum material, whereas conventional methods take about 10 to 15 minutes. It is possible to significantly shorten the processing time previously used, and to enable continuous high-speed processing using coils, resulting in a significant improvement in productivity.

In addition, the resulting film is formed into a thin film with a thickness of 1.0 μm or less, particularly preferably 0.3 to 0.5 μm.

Moreover, it is possible to obtain a stable product, and by using an aqueous phosphoric acid solution, a film with relatively large pores can be obtained. By doing this, the absorption rate α becomes 0.90
As described above, an extremely good selective absorption film having an emissivity ε of 0.10° or less can be obtained.

Next, processing conditions regarding the metal salt treatment in the second step will be explained.

In the second step, the aluminum material having the porous oxide film obtained in the first step is treated in a metal salt aqueous solution with a higher concentration than that used in conventional metal salt treatment.
Furthermore, electrolytic treatment is carried out while maintaining the liquid temperature at 35 to 85° C., whereby the pores of the oxide film are precipitated and filled with metal, thereby blackening the film.

In such metal salt treatment, stainless steel, carbon, etc. can be used for the counter electrode.

The power source may be AC, DC, or a similar waveform, with a voltage of 10V to 30V and a current density of 0.5 to 2.
5A/drr? Good blackening of the film can be achieved with an electrolysis time of 0.5 to 5 minutes.

By the way, as the metal salt used for this, one or more of nickel salts, cobalt salts, copper salts, tin salts, iron salts, etc. can be mentioned, as in the case of conventional methods.

In addition, regarding the concentration of these metal salts in the aqueous solution, the "concentration used in conventional metal salt treatment" as referred to in this specification.
refers to the following concentration.

Nickel salt 20-309/l Cobalt salt 20-30 t/l Copper salt 151/l Tin salt Less than 5 g/l Iron salt Less than 209/l Therefore, in the present invention, "higher concentration" than the above concentration means , especially the following ranges:

Nickel salt 50-200 f/l Cobalt salt 50-200 f/copper salt 15-100 f/tin salt 5-50 t/l Iron salt 20-200 t/l This concentration range and the above liquid temperature 35~ The limitation of the range of 85°C is that if the concentration is below the lower limit, it will take a long time to form a good selective absorption film, and if the concentration exceeds the upper limit, the cost will increase and the coloring property will increase. This is because the temperature becomes worse, making it difficult to produce a good selective absorption film, and if the temperature exceeds the upper limit, the dissolution effect of the film increases, making it impossible to obtain a good selective absorption film.

A particularly preferred concentration range for nickel salts is 80 to 1
30 t/l, 80-130 in cobalt salt? /
l, 30-501/1 in copper salt. 15 in tin salt
~30 t/60-100 in 11 iron salts? /l, and the temperature is particularly preferably in the range of 40 to 60°C.

According to the implementation of the second step according to the present invention, the metal salt treatment for blackening is carried out by electrolytic treatment in the above-mentioned high concentration, high temperature metal salt-containing aqueous solution.
．． Good blackening of the oxide film can be achieved in an extremely short treatment time of 0 minutes, compared to the usual 10 to 15 minutes required under conventional treatment conditions. In comparison, processing time can be significantly shortened and continuous high-speed processing can be performed using a coil, leading to a significant improvement in productivity.

Next, a specific example of this brewing will be shown.

In Examples 1 to 5, the improvement method according to the present invention was implemented in both the first step and the second step, and in Examples 6 to 7, the present invention was implemented only in the first step. , the second step uses a conventional metal salt treatment.

Example 1 An aluminum plate having a purity of JIS-A1030 was used, and it was degreased by a normal pretreatment method.The composition of the electrolytic solution and the electrolytic conditions shown in Table 1 were used in the first and second steps. Electrolytic treatments were performed sequentially.

The total electrolysis time of the first step and the second step is 3 minutes,
The obtained selective absorption film has a film thickness of 0.4μ and an absorption rate α=0.
．． 94, the firefly had an extremely good selective absorption of solar thermal energy with an emissivity ε=0.06.

Example 2 The same procedure as in Example 1 was carried out using the electrolyte composition and electrolytic conditions shown in Table 2.

. The electrolytic treatment time was 3 minutes in total, and the selective absorption film obtained had a film thickness of 0.2μ, α=0.94, and ε=OD6, and had good selective absorption properties.

2 In the same manner as in Example 1, treatment was performed using the electrolytic solution composition and electrolytic conditions shown in Table 3.

The total electrolytic treatment time was 3 minutes, and the obtained selectively absorbing film had a thickness of 0.3μ, and good selectively absorbing properties with α=0.95 and ε=0.07.

(Example 4) Treatment was carried out in the same manner as in Example 1 using the electrolytic solution composition and electrolytic conditions shown in Table 4.

The total electrolytic treatment time was 3 minutes, and the obtained selective absorption membrane had a thickness of 0.5μ, α=0.95, and ε=0.06°, and had good selective absorption properties.

Example 5 1 Processing was carried out in the same manner as in Example 1 using the electrolytic solution composition and electrolytic conditions shown in Table 5.

The total electrolytic treatment time was 3 minutes and the resulting selection.

The absorbing film had a thickness of 0.5 μm and good selective absorption properties with α=0.95 and ε=0.06.

>: Example 6 In the same manner as in Example 1, treatment was performed using the electrolytic solution composition and electrolytic conditions shown in Table 6.

Although the electrolysis time in the second step was 10 minutes compared to the 1 minute electrolysis time in the first step, the resulting selective absorption membrane had a thickness of 0.5 mm.
It had good selective absorption properties of 3μ, α=0.95, and ε=0.07.

*Example 7 Processing was carried out in the same manner as in Example 1 using the electrolyte composition and electrolysis conditions shown in Table 7.

The total electrolysis time was 9 minutes, and the selective absorption film obtained was
It had a film thickness of 0.4μ, α=0.94, and ε=0.06, and had good selective absorption properties.

Claims (1)

[Scope of Claims] 1. A method of anodizing an aluminum material and then electrolytically treating it in an aqueous solution containing a metal salt to form a selective absorption film for solar thermal energy, wherein the anodizing treatment is performed at a solution concentration of 50 t. A method for forming a selective absorption film of solar thermal energy on the surface of an aluminum material, characterized in that / is carried out in the above phosphoric acid aqueous solution and while maintaining a liquid pot at 35 to 80°C. 2. A method for forming a selective solar energy absorption film on the surface of an aluminum material according to claim 1, which produces a porous oxide film with a thickness of 1 μm or less. 3. In a method of anodizing an aluminum material and then electrolytically treating it in an aqueous solution containing a metal salt to form a selective solar energy absorption film, the anodizing treatment is performed at a solution concentration of 501? / or more. The electrolytic treatment is carried out in an aqueous phosphoric acid solution at a temperature of 35 to 80°C, and the electrolytic treatment is carried out at a concentration of metal salt in the electrolytic solution of 50 to 2009/l for nickel salt and 50 to 2009/l for cobalt salt.
~2001/l, copper salt 15~100v/11 tin salt 5~501j! /11 5-50 in iron salt
The method is characterized in that it is carried out in a metal salt aqueous solution with a relatively higher concentration than that used in the conventional electrolytic treatment, such as 9/l, and while maintaining the liquid temperature at 35 to 85 ° C. A method of forming a film that selectively absorbs solar thermal energy on the surface of an aluminum material. 4. A method for forming a selective absorption film for solar thermal energy on the surface of an aluminum material according to claim 3, wherein the porous oxide film in the first step is produced with a thickness of 1 μm or less.