JPS62214184A - Production of solar heat absorbing body - Google Patents

Abstract

PURPOSE:To inexpensively and easily produce a solar heat absorbing body having an excellent heat collecting characteristic by plating iron to the surface of a metallic base material essentially consisting of copper, then subjecting the surface to a chemical conversion treatment by an alkaline soln. to form a selective absorptive film on the surface. CONSTITUTION:The surface of the base material consisting of the metal essentially consisting of copper having excellent corrosion resistance or stainless steel is subjected to mirror finishing or finishing by cold rolling. The iron plating film of about 0.1-1mu film thickness is uniformly formed on the surface of such base material by using the iron plating liquid essentially consisting of, for example, ferrous sulfate. This base material is immersed the alkaline soln. to form the selective absorptive film consisting of the iron oxide essentially consisting of triiron tetraoxide or the composite of the iron oxide and the metallic element or oxide to constitute the alkaline soln. on the surface. A soln. mixture which is prepd. by using sodium hydroxide as an essential component and is added with an oxidizing agent such as sodium nitrite is preferable as the alkaline soln. The solar heat absorbing body having the selective absorptive film which is controlled in film thickness, has low emissivity, excellent heat resistance and heat collecting characteristic is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method of manufacturing a solar heat absorber that is inexpensive, easy to process, and has high heat collection efficiency.

BACKGROUND OF THE INVENTION The field of solar thermal utilization has long attracted great expectations as a new form of energy, and has been gradually developing despite being affected by fluctuations in crude oil prices. Among them, the solar radiation conditions are bad,
In addition, high-performance vacuum tube solar collectors that meet the demand during winter when outside temperatures are low are expected to become increasingly popular in the future. In general, vacuum tube solar collectors are selected to have low reflectance (high absorption rate) in the visible light region and high reflectance (low emissivity) in the infrared light region in order to efficiently collect solar heat in addition to vacuum insulation. It has a solar heat absorber with an absorption film on its surface. - Hitherto, methods such as electrolytic coloring of aluminum substrates, black chrome plating of copper substrates, and chemical conversion treatment of stainless steel substrates have been used for solar heat absorbers having such selective absorption films on their surfaces. However, the problems with (2) are that the substrate is expensive, (2) the plating process is expensive, and (2) it is difficult to control the film thickness and the film tends to be thick, resulting in poor heat collection properties compared to (2).

In the case of copper substrates, in addition to expensive black chrome plating, it is also possible to form copper oxide on the substrate surface by chemical conversion treatment, but the heat resistance is 250 degrees Celsius or less, and it is difficult to process during the manufacturing process like vacuum tube solar collectors. It cannot be used if baking at around 400°C is required. In addition, for stainless steel, there is an electrolytic oxidation method that allows film thickness control and has relatively excellent heat collecting properties compared to chemical conversion treatment methods that are difficult to control film thickness and tend to result in thick films. Because the processing time is long, it is expensive like the black chrome plating method.

Furthermore, with regard to iron substrates, there is a method of immersing them in a high-temperature alkaline solution and using a chemical conversion treatment method to form a selective absorption film mainly composed of triiron tetroxide, which is inexpensive and easy to process. This method also had difficulty controlling the film thickness, tending to result in a thick film, and generally had a high emissivity and poor heat collection characteristics.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for easily manufacturing a solar heat absorber having excellent heat collecting properties at low cost.

Structure of the Invention The method for manufacturing a solar heat absorber of the present invention is to apply iron plating to the surface of a base material made of a metal containing copper as a main component or stainless steel, and then apply a chemical conversion treatment with an alkaline solution to coat the surface with a selective absorption film. By controlling the thickness of the iron plating, it is possible to control the thickness of the selective absorption film using an alkaline solution chemical conversion treatment method.

Next, the present invention will be specifically explained. As the base material of the solar heat absorber, a copper-based metal or stainless steel, which has excellent corrosion resistance and is suitable as a heat collecting tube, is used. As for the surface finish, a mirror finish is desirable, but a cold rolled finish may also be used. Next, iron plating is applied to the surface of this base material, but the plating solution used here needs to be able to form an iron plating layer uniformly on the surface of the base material and control the film thickness to 0.1 to 1 micron. For example, A liquid whose main component is ferrous sulfate is desirable.

After that, the iron-plated base material is immersed in an alkaline solution, and a selective absorption film is formed on the surface, that is, an iron oxide whose main component is triiron tetroxide, or a mixture of iron oxide and metal elements and oxides that make up the alkaline solution. Form a complex. The alkaline solution used here is preferably a mixed solution containing sodium hydroxide as a main component and an oxidizing agent such as sodium nitrite, that is, a so-called black dyeing solution.

In addition, unless an oxidizing agent such as potassium persulfate, which is used for blackening copper, is used in the alkaline solution, copper will not be colored (oxidized) and only the iron plating layer will be oxidized, so the solution temperature is not necessarily high (e.g. 130°C or higher). It does not have to be at medium temperature (for example, 7
The process can be carried out satisfactorily even at a temperature of around 0°C, making work management easier and extending the melting life.

Example Examples of the present invention are shown below.

Phosphorus deoxidizing steel pipe (Cl220T, φ90xtO, 4x 5
00) was degreased with trichlene and pickled, then ferrous sulfate 240
A stainless steel plate was placed in this solution, and the solution temperature was 60°C and the current density was 10A/1, using the phosphorus deoxidizing steel tube as the cathode and the stainless steel plate as the anode.
dw? Iron plating was performed by electrolytic treatment for 5 minutes under the following conditions.

After washing the iron-plated steel pipe with water, add 400g of sodium hydroxide.
/l, sodium nitrite 60g/J, phosphorous acid 100
After being immersed in a mixed solution of GH at 70° C. for 3 minutes, it was thoroughly washed with water and dried.

The spectral reflection spectrum of the film formed on the light-receiving surface of the absorber thus manufactured was measured, and the results are shown in the drawings. For the selective absorption film of the obtained absorber, the solar energy absorption rate α was calculated based on the spectral reflection spectrum curve shown in the drawing, and the emissivity ε was calculated based on the blackbody radiance determined by Planck's formula. was calculated.

As a result, the α and ε values showed good values of 0.90 and 0.18, respectively.

Effects of the Invention As described above, the method for manufacturing a solar heat absorber of the present invention is capable of producing an alkaline heat absorber by applying iron plating to the surface of a base material made of copper-based metal or stainless steel, which is suitable as a material for a heat collecting tube. The film thickness can be controlled using a solution chemical conversion treatment method, which allows a thin chemical conversion film to be formed and the emissivity to be lowered, making it possible to create a selective absorption film with excellent heat resistance and heat collection properties at low cost and easily. can be obtained.

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[Brief explanation of drawings]

The drawing is a spectral reflection spectrum curve diagram of a solar heat absorber obtained according to an example of the present invention. Patent applicant Nippon Electric Glass Co., Ltd. Representative Kishi 1) Saku Kiyoshi

Claims (1)

[Claims] A method for producing a solar heat absorber, which comprises iron plating the surface of a base material made of copper-based metal or stainless steel, and then chemically treating the surface with an alkaline solution to form a selective absorption film on the surface. .