JPS5819948B2 - 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 a method of forming.

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 which the first
The process involves using an aqueous solution of sulfuric acid, oxalic acid, phosphoric acid, etc. as an electrolyte, using aluminum, carbon, stainless steel, etc. as a counter electrode, and applying direct current (current density 0601 to 0.5 A/d7).
7L2) or alternating current (current density 0.1-0.8A/a
m2) is applied to perform electrolysis to generate a porous anodic oxide film on the surface of the aluminum material, and then in a second step, the aluminum material with this oxide film is treated with nickel salt, cobalt salt, copper salt, tin. Electrolyzing is performed by applying alternating current (current density 0.1 to 0.8 A/dm2) in an aqueous solution containing a metal salt such as a salt, and the fine pores of the oxide film are precipitated and filled with metal to blacken it, The desired selective absorption membrane is obtained.

However, such conventional electrolytic coloring methods have the disadvantage that the electrolysis time is quite long.

That is, the first step usually takes 10 to 15 minutes, and the second step usually takes 10 to 15 minutes.
For blackening process, it takes 5 minutes at the earliest, usually 10 to 15 minutes.
It has the drawback that it requires more than 10 minutes, resulting in poor productivity.

SUMMARY OF THE INVENTION The present invention aims to solve these problems, particularly in the second electrolytic treatment step for blackening, and to significantly shorten the treatment time.

Therefore, the present invention involves anodizing an aluminum material (including aluminum and aluminum alloys) to form a porous oxide film, and then electrolytically treating it in an aqueous solution containing a metal salt to form the porous oxide film. In a method for forming a selective solar energy absorption film in which metal is precipitated and filled into the fine pores of the film, electrolytic treatment in an aqueous solution containing the metal salt is carried out so that the concentration of the metal salt is 80 to 200% in the case of nickel salt.
9/e, 80-2009/e in cobalt salts.

30-100g/e for copper salt, 15-100g/e for tin salt
509/e, iron salt in the range of 60 to 2009/e, in a metal salt aqueous solution with a relatively higher concentration than that used in the conventional electrolytic treatment, and at a liquid temperature of 45 to 85 ° C. It is characterized by being held and carried out.

In the above, the "liquid concentration used in the conventional electrolytic treatment" as used in this specification means: Nickel < 20-509/e Cobalt salt 20-509/e Copper salt 159/e Tin salt 5 g/e The above-mentioned concentration used in the present invention is set to a relatively high value compared to this conventional concentration.

The reason for limiting the concentration range of the metal salt aqueous solution in this invention is that if it is less than the lower limit, it will take a long time to form a good selective absorption membrane, and if the concentration exceeds the upper limit, it will be costly. This is because as the amount of water increases, the colorability deteriorates, making it difficult to form a good selective absorption film.

A particularly preferable concentration range is 9 for the nickel salt.
0-1309/l, 90-13 in ml Hardt's salt
09/e, 40-5o9/e for copper salts, 20-309/e for tin salts, 70-100'j for iron salts
/e range.

On the other hand, the temperature of the metal salt aqueous solution is set to a considerably higher value of 35 to 85°C, compared to the conventional general processing conditions of 20 to 30°C.

If this temperature is lower than 45°C, as in the case where the concentration is too low, the blackening of the film will progress slowly and it will take a long time to form a good selective absorption film, thus achieving the intended purpose of the present invention. Can not do it.

On the other hand, at high temperatures exceeding 85° C., the dissolution effect of the film is too strong, making it difficult to form a good selective absorption film.

Particularly preferred temperatures are in the range 40-60''C.

The other electrolytic conditions may be approximately the same as conventional ones, for example, stainless steel, carbon, etc. may be used for the counter electrode, and the power source may be alternating current, direct current, or a waveform similar to these, and the voltage lO ~30V, current density 0.5~2
．． Good treatment can be achieved with as little as 5 A/d 12.

According to this invention, the metal salt treatment for blackening the anodic oxide film is carried out for 0.5 to 2.0 minutes by electrolytic treatment in a high-concentration, high-temperature metal-containing salt aqueous solution as described above. The processing time can be completed in an extremely short time, compared to the conventional processing that normally takes 10 to 15 minutes under the general processing conditions mentioned above. It is possible to shorten the time, enable continuous high-speed processing using the coil, and significantly improve productivity.

; Furthermore, this invention is based on the second electrolytic coloring method as described above.
The target is metal salt treatment, which is a step, and therefore, the first step, anodizing treatment, is not particularly limited (it is acceptable under conventional general treatment conditions).

However, as mentioned above, this anodizing treatment also
When using the conventional method, the treatment required a long time of 10 to 15 minutes, but the treatment was carried out at a concentration of 50 g.
/e or more in a highly concentrated phosphoric acid aqueous solution, and at a temperature of 3.
It is carried out at a high temperature of 5 to 80°C; by doing so, it can be processed in an extremely short time of 0.5 to 30 minutes, and a stable oxide film with a thickness of 1 μm or less with good selective absorption property is formed. It becomes possible to generate .

Therefore, by performing the metal salt treatment of the present invention in combination with such anodic oxidation treatment, the overall treatment time for forming a selective absorption film can be significantly shortened, and the absorption rate α is 0.90 or more, and emissivity ε is 0.
This makes it possible to form a good selective absorption membrane having excellent performance in the relative evaluation of 10 or less.

Specific examples of this invention are shown below.

In Examples 1 to 5, the anodizing treatment in the first step was performed under the above-mentioned improved treatment conditions, that is, in a high concentration, high temperature phosphoric acid aqueous solution, and in Examples 6 to 8, The anodic oxidation treatment was performed under conventional and general treatment conditions.

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

As shown in Table 1, good blackening of the oxide film can be achieved by finishing the second step in 2 minutes, and the resulting selective absorption film has a thickness of 0.4μ and an absorption rate α= It had extremely good selective absorption of solar thermal energy with an emissivity of 0.94 and an emissivity of ε2 of 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.

As shown in the table above, the electrolytic treatment time in the second step was 2 minutes, and the total treatment time with the first step was 3 minutes, and the selective absorption film obtained had a film thickness of 0.2μ and α=0.94. ,.

It had good selective absorption of ε20.06.

Example 3 1 Processing was carried out in the same manner as in Example 1 using the electrolytic solution composition and electrolytic conditions shown in Table 3.

As shown in the table above, the processing time of the second step was also completed in 2 minutes, and the obtained selective absorption film had a film thickness of 0.3μ, α,
= 0.95 and ε = 0.07.

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

The processing time of the second step was 1.5 minutes to achieve sufficient blackening of the film, and the obtained selective absorption film had a film thickness of 0.5μ, α=
It had good selective absorption of 0.95 and ε=0.06.

Example 5 In the same manner as in Example 1, treatment was carried out using the electrolytic composition and electrolytic conditions shown in Table 5.

As shown in the table above, the second step was completed in 1.5 minutes, and the oxide film was successfully blackened.

The selective absorption membrane obtained had values of α=0.92 and ε=0.08.

Example 6 In the same manner as in Example 1, treatment was carried out using the electrolyte composition and electrolysis conditions shown in Table 6.

As mentioned above, the second step was completed in 2 minutes, and good blackening of the oxide film was achieved.

The selective absorption membrane obtained in this way has α=0.92, ε=
It had good selective absorption of 0.8.

Example 7 In the same manner as in Example 1, treatment was carried out using the electrolytic solution composition and electrolytic conditions shown in Table 7.

The second step was completed in 2 minutes, and good blackening of the oxide film was achieved.

The selective absorption membrane obtained in this way has α=0.93, ε=
It had a good selective absorption of 0.09.

Claims (1)

[Scope of Claims] 1. In a method for forming a selective solar energy absorption film by anodizing an aluminum material and then electrolytically treating it in an aqueous solution containing a metal salt, the electrolytic treatment in an aqueous solution containing the metal salt is performed. 80 to 2009/e in the metal salt concentration of nickel salt. 80-2o09/e for cobalt salts, 30-1009/e for copper salts, 15-509/f for tin salts!
, in an aqueous metal salt solution with an iron salt concentration in the range of 60 to 200' J/e, which has a relatively higher concentration than that used in the conventional electrolytic treatment, and the liquid temperature is maintained at 45 to 85 ° C. A method for forming a selective absorption film for solar thermal energy on the surface of an aluminum material.