JPS6323460B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field This invention is applicable to the production of solar heat collector plates etc. using aluminum or aluminum alloy as a base.
The present invention relates to a method for forming a selective solar energy absorption film on the surface of an aluminum material. Conventional technology Conventionally, as a general method for forming a film that selectively absorbs solar thermal energy on the surface of an aluminum material, the aluminum material is first anodized to form a porous anodic oxide film on its surface. There is a known method in which the oxide film is then electrolytically treated in an aqueous solution containing a metal salt to precipitate and fill the fine pores of the oxide film, thereby obtaining the desired blackened selective absorption film. be. By the way, in general, solar heat selective absorption films are evaluated by comparing the absorption rate α of sunlight in relation to the emissivity ε. Particularly preferable selective absorption films are those with an absorption rate α of 0.90 or more and a radiation The rate ε
It is necessary that the thickness be 0.10 or less, but in order to satisfy this, it is first necessary to form a film with a thickness of 1 μm or less. If this exceeds 1μ, even if solar thermal energy is absorbed, much of it will be emitted as radiant energy, resulting in poor emissivity ε. Therefore, the anodic oxidation treatment reduces the thickness of the film.
Although it is preferable to control the thickness to 1μ or less, the secondary electrolytic treatment performed on such a thin anodic oxide film in the next step can be carried out without causing film destruction.
Moreover, consideration must be given to obtaining a sufficiently good coloring effect. Conventionally, this two-state electrolytic treatment has generally been carried out by electrolyzing with alternating current in order to obtain a mild metal deposition effect. Problems to be Solved by the Invention However, when using the conventional secondary electrolytic treatment using alternating current, the treatment time is long, and it generally takes 5 to 10 minutes or more to achieve good blackening. Since this method requires a long processing time, there is a problem in that the efficiency of forming the selective absorption membrane is poor. Means for Solving the Problems In view of the above problems, the present invention aims to shorten the treatment time, particularly in the second step of metal salt treatment. They discovered that the electrolysis time could be significantly shortened by using a specific waveform current, and this was completed. That is, the present invention provides a method in which an aluminum material is anodized to form an anodic oxide film with a thickness of 1 μm or less, and then electrolytically treated in an aqueous solution containing a metal salt to form a selective solar energy absorption film. Electrolytic treatment in an aqueous solution containing the metal salt,
The positive and negative currents are changed alternately and the negative voltage is 5~
This method is characterized by using a PR waveform current of 25V, which is 1.1 to 1.5 times higher than the positive voltage, to form a selective absorption film for solar thermal energy on the surface of an aluminum material. The PR waveform (Periodic
The current (reverse) is one in which the positive and negative currents are asymmetrically and alternately converted, and the positive and negative peak values, that is, the voltage conditions, greatly affect the metal salt treatment effect. Negative voltage particularly affects the metal deposition (coloring) rate and film performance, and this can be
It is necessary to adjust to the 25V range. This is
If the voltage is less than 5 V, the effect of accelerating the coloring speed is poor, and the desired effect of shortening the electrolytic coloring process cannot be sufficiently achieved. On the other hand, if the voltage exceeds 25V, hydrogen gas is generated due to electrolysis, resulting in defects such as destruction of the film. The positive voltage depends on the negative voltage value, but is preferably set in the range of 5 to 15V. Regarding the relative relationship between both positive and negative voltage values, if the positive voltage value is 1, then the negative voltage value should be set in the range of 1.1 to 1.5 times, and if it deviates from this range, the voltage range will change to the specified value. The same disadvantages arise when deviating from The positive and negative current application times vary depending on the treatment bath, but
It is more effective to shorten the coloring time by making the negative energization time longer than the positive energization time. However, if it is too long, hydrogen gas will be generated and a spalling phenomenon will occur. As described above, the present invention is characterized by the electrolysis waveform used for the purpose of shortening the time required for the metal salt treatment as the second step. Therefore, the conditions for the anodizing treatment in the first step are not limited at all, and the treatment can be carried out by any conventional method. However, when this anodic oxidation treatment is performed using the conventional method,
Whereas it used to take a long time of 15 minutes,
By performing this treatment in a highly concentrated phosphoric acid aqueous solution with a concentration of 50 g/l or more and setting the liquid temperature at a high temperature of 35 to 80°C, the treatment can be carried out in an extremely short time of 0.5 to 3.0 minutes. It becomes possible to produce a stable oxide film with a thickness of 1 μm or less that has good selective absorption properties. Therefore, by carrying out the metal salt treatment of the present invention in combination with such anodic oxidation treatment, the overall processing time for forming a selective absorption film can be significantly shortened, and moreover, the absorption It becomes possible to form a good selective absorption film having excellent performance in relative evaluation of radiation rate (α) and emissivity (ε). Effects of the Invention According to the method of the present invention, which uses a current with a special waveform as described above for secondary electrolysis, the ultrathin anodic oxide film produced in the first step, that is, the thickness of 1 μm or less, becomes black. The secondary electrolytic treatment for oxidation, that is, the metal salt treatment, requires only 1 to 2 minutes, and a good selective absorption membrane can be obtained, compared to 5 to 10 minutes when conventional alternating current is used. This makes it possible to significantly shorten processing time and significantly improve productivity. Examples Next, examples of the present invention will be shown in comparison with comparative examples. Using a 1 mm thick aluminum plate with JIS/A1050P purity, it was degreased using the usual pretreatment method, and then heated at 8 V DC using carbon as a counter electrode in a 40 g/phosphoric acid aqueous solution at a temperature of 30°C. Anodized for 15 minutes. Next, as a second step, the aluminum plate obtained in the first step was electrolyzed in an electrolytic solution at 25°C having the following liquid compositions A and B using alternating current and direct current with various PR waveforms, and for an electrolytic treatment time. Electrolytic treatment was performed by changing the Electrolyte composition A: Nickel acetate 45g/boric acid 45g/PH 6.4

【table】

[Table] As is clear from the above table, according to this invention,
The metal salt treatment in the second step can be carried out in an extremely short time of 1 to 2 minutes, and a selective absorption membrane having excellent selective absorption performance can be obtained.

Claims (1)

[Claims] 1 Aluminum material is anodized and has a thickness of 1μ
In the method of forming the following anodic oxide film and then electrolytically treating it in an aqueous solution containing a metal salt to form a film that selectively absorbs solar thermal energy, the electrolytic treatment in an aqueous solution containing the metal salt is performed depending on the polarity of the current. Forming a selective absorption film for solar thermal energy on the surface of an aluminum material, which is characterized by alternating conversion and using a current with a PR waveform in which the negative voltage is 5 to 25 V and is 1.1 to 1.5 times higher than the positive voltage. Method.