JPS6359065B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solar heat absorber used in solar water heaters and the like. As a solar energy absorber, it has a high absorption rate for electromagnetic waves in the visible and near-infrared regions.
Moreover, it is required to have low emissivity in the infrared region. Conventionally, various solar heat absorbers have been devised that have coatings on their surfaces that absorb solar energy well and emit little heat in the infrared region (generally called selective absorption coatings). As a selective absorption film, a cuprous oxide (Cu ₂ O) film or a cuprous oxide (Cu 2 O) film is used.
Copper oxide coatings such as copper (CuO) coatings or coatings containing a trace amount of cuprous oxide in cupric oxide are widely known. However, conventional solar heat absorbers in which a selective absorption film made of copper oxide is formed on the surface of a base material generally have poor heat resistance, so that they may be exposed to sunlight during use without conducting heat medium. In some cases, temperatures can reach temperatures as high as 200°C, causing deterioration. Therefore, near-infrared region (wavelength
0.7 to 2.5 microns), the absorption rate decreases, and
Since the underlying copper component is oxidized and the thickness of the selective absorption film gradually increases, problems with heat resistance such as increased heat radiation in the infrared region often occur. This invention was made in view of the above circumstances, and provides a solar heat absorber that has a high solar heat absorption rate and excellent heat resistance. This will be explained below. In solar heat absorbers, not only the performance of the selective absorption film but also the performance of the underlying base material is important.
From this point of view, the inventors previously proposed selecting nickel as the base metal. That is, it was proposed to use a base material whose surface at least is made of nickel. Afterwards, further research revealed that in such base materials, the surface properties of the nickel base have a large effect on the absorption characteristics of the solar heat absorber. It has been found that if the base material is selected satisfactorily, an excellent solar heat absorber can be obtained. This invention was completed in this way, and is a solar heat absorber that is provided with a base material whose surface is made of nickel at least, and on which a selective absorption film of copper oxide is formed using the surface of this base material as a base material. The gist thereof is a solar heat absorber characterized in that the base material is a base material whose surface properties satisfy either of the following conditions (a) and (b). (a) The absorption rate of the nickel base shall be 0.4 or more in the visible region, 0.2 or more in the near-infrared region, and 0.2 or less in the infrared region. (b) The surface roughness of the nickel base shall be 0.1 to 3 microns in terms of center line average roughness. This will be discussed in detail below. The base material is made entirely of nickel,
Alternatively, a material in which a nickel layer is formed on the surface of a core material (base metal) such as metal is used. The purpose of using nickel as the base of the selective absorption film is to improve the corrosion resistance and heat resistance of the solar heat absorber. That is, even with black chromium or black nickel selective absorption membranes, the membrane is extremely porous, so it is difficult to prevent corrosion of the base material. Furthermore, the base material may be oxidized if it is heated in the atmosphere. For example, when a solar heat absorber is used and is exposed to sunlight without conducting heat medium, the temperature can sometimes reach as high as 200°C, which causes oxidation of the base material. When the material is oxidized, the absorption characteristics α and radiation characteristics ε of the selective absorption film deteriorate. In this respect, nickel, which is chemically and thermally stable, is preferably used as the base metal of the selective absorption film because the base material will not be corroded or oxidized. The nickel base used as the base of the selective absorption film in the solar heat absorber according to the present invention is characterized in that its surface is not flat but rough. That is, if the surface of the nickel base is flat, the nickel base itself has almost no selective absorption characteristics. On the other hand, if the surface of the nickel base is microscopically rough and uneven,
The nickel base itself also has selective absorption properties. In this case, the roughness of the nickel base surface needs to be 0.1 to 3 microns (μ) in terms of center line average roughness. Typical examples of the form in which the nickel base surface has an uneven and rough surface include those in which the base nickel layer is made of leaf-like, fibrous, granular, or polyhedral crystals, but the present invention is not particularly limited to these. isn't it. The nickel substrate with a rough surface as described above causes multiple reflections on the surface of visible and near-infrared light, so it absorbs visible light and near-infrared light well, but it absorbs visible light and near-infrared light well, but it absorbs visible light and near-infrared light well. It is thought that it acts as a flat surface for infrared light, and reflects infrared light well.
Therefore, the emissivity is small. When a selective absorption film of copper oxide is formed on a nickel substrate having such a rough surface, a mutual effect appears between these films, and the absorption characteristics of the solar heat absorber are further improved. As seen above, the nickel base with its rough surface has absorption capacity itself, and this cooperates with the copper oxide selective absorption film formed on it to improve the performance of the solar heat absorber. The surface properties of the nickel base can also be defined by its absorption rate. When viewed from this perspective,
The absorption rate of the nickel base is in the visible region (0.3
~0.7 micron) and more than 0.4 in the near-infrared region (0.7 ~
2.5 microns) and 0.2 or more in the infrared region (2.5 to 20 microns). The nickel base may contain small amounts of impurities such as trace amounts of oxides due to surface oxidation. There are no clearly defined standards as a general concept regarding the absorption rate and emissivity that a solar heat absorber should have in practice. However, one of the criteria for a commercially available solar heat absorber would be an absorption rate of 0.91 or more and an emissivity of 0.3 or less. Then, the two conditions mentioned above (conditions based on center line average roughness and conditions based on absorption rate)
By using a base material that satisfies either of the following, it is possible to reliably obtain a solar heat absorber that satisfies the above criteria. A nickel substrate with such a rough surface can also be obtained by roughening the surface of a base material with a smooth nickel surface using an appropriate method such as a chemical method or a mechanical method. is obtained by forming a nickel layer on a core material.
The nickel layer (usually a kind of film-like material) that serves as the base can be formed by various methods, such as electrolytic plating, electroless plating, vacuum evaporation, and sputtering. is not limited. Various metal materials such as iron plate, steel plate, copper plate, etc. can be used as the core material. It may be made of other than metal. When performing such a nickel plating treatment on the surface of a core material made of an iron plate or a copper plate, it is generally necessary to perform pretreatment such as degreasing (electrolytic degreasing if necessary) and pickling. When using a stainless steel plate as the core material and applying the above-mentioned nickel plating to it, the following careful pretreatment is usually required, for example. That is, after degreasing with conventional chemicals and electrolytic degreasing, an activation treatment is carried out by cathodic electrolysis using 5 to 30% sulfuric acid, and then nickel strike plating is carried out under the following conditions. (Processing liquid composition) Nickel chloride 50-300g/Hydrochloric acid 50-200g/ (Processing conditions) Solution temperature: Room temperature Current density: 5-10A/dm ² Processing time: 0.5-5 minutes In this way, perform the necessary pretreatment. When the core material is nickel-plated by the plating method described above, a black-gray or grayish nickel plating layer is formed on the surface of the core material. At that time, it is preferable to select plating conditions within the above range so that the thickness of the nickel plating layer is 0.1 to 3 μm. The nickel plating film obtained in this manner is composed of clusters of leaf-shaped, fibrous, or granular crystals, so it actually has complex irregularities and a fine structure. Therefore, since it is usually measured by plating thickness measurement method, etc., the film thickness mentioned above is expressed as a value converted to a state in which these unevenness is smoothed out and there are no voids. . Next, by forming a selective absorption film of copper oxide on the nickel base thus formed as described later, a highly practical solar heat absorber with excellent selective absorption properties can be obtained. I can do it. That is, although solar heat absorbers equipped with copper oxide-based selective absorption films generally have excellent selective absorption properties, they have the disadvantage of poor heat resistance and corrosion resistance, and gradually deteriorate after long-term use. If the selective absorption film made of copper oxide is formed on the base metal layer made of nickel, the durability is further improved because the base metal layer is thermally and chemically stable. In addition, since the nickel base itself has absorption capacity, the overall absorption properties are improved. Such a selective absorption film made of copper oxide can be produced by, for example, forming a copper thin film layer on a nickel base using a plating method, sputtering method, vacuum evaporation method, etc., and then subjecting it to oxidation treatment using chemical conversion treatment. It is formed as a result. In this case, the above-mentioned nickel base having an uneven surface has extremely good adhesion to the copper oxide selective absorption film formed thereon, and also has the function of firmly holding the copper oxide layer. This is because the above-mentioned nickel base has extremely fine uneven surfaces when viewed microscopically.
It is thought that the uneven portions and the copper oxide crystals are intricately intertwined and their mutual bond becomes strong. When the copper oxide layer consists of a small amount of cuprous oxide (Cu ₂ O) and cupric oxide (CuO), which has a leaf-like or fibrous crystal form, the two components may be mixed with each other. However, it is usually divided into two layers: a cuprous oxide layer and a cupric oxide layer. The total thickness of the copper oxide layer that becomes the selective absorption film is
It is preferably 0.05 to 0.50μ. Film thickness is 0.50μ
This is because if it exceeds 0.05 μm, thermal radiation increases, and if it is less than 0.05 μm, sufficient blackness cannot be obtained and the absorption rate tends to decrease. The solar heat absorber thus obtained has excellent selective absorption properties (sunlight absorption properties, heat radiation properties) because the nickel base has a rough surface. In addition, the selective absorption film has strong adhesion to the substrate, and has excellent durability and heat resistance. Next, examples of the present invention will be described together with comparative examples. Example 1 A copper plate with a thickness of 0.5 mm was used as a core material, and after degreasing with alkaline and pickling with 3% HCl, a plating solution consisting of 200 g of nickel chloride and 40 g of boric acid was used, and the liquid temperature was 60°C. °C, current density
Nickel plating was carried out under the conditions of 2 A/dm ² and a plating time of 3 minutes. The thickness of the obtained nickel film is
It was 1μ. At this time, the surface quality of the nickel plated layer had a center line average roughness (Ra) of 0.96μ,
The optical properties are that the absorption rate in the visible region is 0.90, the absorption rate in the near-infrared region is 0.63, and the absorption rate in the infrared region is 0.90.
It was 0.125. Copper was plated on the obtained nickel film to a thickness of 0.15μ using a copper sulfate plating solution. Add 80 g of sodium chlorite and 60 g of caustic soda to this copper plating layer.
Oxidation treatment was carried out for 5 minutes with a treatment solution consisting of
A selective absorption film of copper and cupric oxide was formed. The respective film thicknesses are Cu ₂ O 0.01μ and CuO 0.13μ,
The absorption rate was α0.96 and the emissivity was ε0.125. Example 2 A stainless steel plate with a thickness of 0.3 mm was used as the core material,
After performing alkaline degreasing and electrolytic degreasing, 5% sulfuric acid was used to remove the current density at room temperature.
Pretreatment was carried out by cathodic electrolysis at 10 A/dm ² for 30 seconds. Next, nickel chloride 200g/, hydrochloric acid
Using a plating solution consisting of 50 ml, the current density
Primary nickel plating was performed under the conditions of 10 A/dm ² , liquid temperature of 20 to 25°C, and plating time of 0.5 minutes to form a primary nickel film on the surface of the core material. Continuing on top of this plating layer, nickel chloride 300g/, boric acid
Using a plating liquid consisting of 50 g/m, the current density
Secondary nickel plating was performed under the conditions of 2 A/dm ² , liquid temperature of 60° C., and plating time of 2 minutes. The primary nickel plating is for improving adhesion to stainless steel, and the secondary nickel plating is for forming a nickel film with a rough surface. The thickness of the obtained nickel film was 1.1μ. The surface properties of the nickel metal layer at this time are as follows:
The centerline average roughness (Ra) was 1.13μ, and the optical properties were 0.91 in the visible region, 0.65 in the near-infrared region, and 0.11 in the infrared region. On the obtained Ni film, the thickness was
0.10μ copper plating was performed. This sample was mixed with 100g of sodium chlorite and 100g of caustic soda.
A black selective absorption membrane was obtained by treatment with a chemical conversion treatment solution (solution temperature: 50°C) for 8 minutes. The composition and thickness of this film are Cu ₂ O 0.007μ,
CuO was 0.08μ, absorption rate α0.96, and emissivity ε0.11. Example 3 A stainless steel plate (SUS430) with a thickness of 0.4 mm was used as the core material, and this was subjected to alkaline degreasing, electrolytic degreasing, and
After sequentially performing cathodic electrolysis using % sulfuric acid, nickel strike plating for stainless steel was performed under the following conditions. (Strike plating liquid composition) Nickel chloride 200g/Hydrochloric acid 100g/ (Processing conditions) Temperature: 25℃ Current density: 5A/dm ² hours: 3 minutes On this surface, add nickel chloride 250g/, boric acid
Using a plating liquid showing 30g/, the current density is 3A/
Nickel was applied under the conditions of dm ² , plating liquid temperature of 40° C., and plating time of 2.5 minutes to form a nickel plating layer with a thickness of 0.7 μm. The surface properties of the nickel plating layer at this time include a center line average roughness (Ra) of 0.75μ, an optical property of absorption rate in the visible region of 0.83,
The absorption rate in the near-infrared region is 0.60, and the absorption rate in the infrared region is 0.60.
It was 0.125. Next, copper plating was performed on the surface of this nickel plating layer with a copper sulfate plating solution at a current density of 1A/dm ² and a plating time of 1.5 minutes to form a copper plating layer with a thickness of 0.20 μm. Oxidation treatment was performed using a chemical conversion treatment solution containing 90 g of soda at a chemical conversion temperature of 70° C. for a treatment time of 3 minutes, thereby converting the copper plating layer into a copper oxide layer. Its composition and film thickness were Cu ₂ O 0.01 μ and CuO 0.16 μ, and its absorption rate was α 0.96 and emissivity ε 0.125. Example 4 A copper plate with a thickness of 0.5 mm was used as a core material, and after degreasing with alkaline and pickling with 2%-HCl, 400 g of nickel chloride and 45 g of boric acid were used.
Nickel plating was carried out using a plating solution consisting of 50.0 g/g/g/g/g/g under the conditions of a solution temperature of 55 DEG C., a current density of 2 A/ ^dm.sup.2 , and a plating time of 3 minutes. Note that during the plating process, the plating solution was sufficiently stirred. The thickness of the obtained Ni film was approximately 1 μm. At this time, the surface properties of the Nickel Mekki tank had a center line average roughness (Ra) of 0.53, an optical property of 0.70 in the visible region, and 0.70 in the near-infrared region.
0.60, and the absorption rate in the infrared region was 0.11. After completing this Ni plating, copper was further plated to a thickness of 0.1μ using a copper sulfate based plating solution. Next, in order to oxidize this copper plating layer, an oxidation treatment was performed for 5 minutes at a liquid temperature of 60°C using a chemical conversion treatment solution consisting of 45 g of sodium chlorite and 70 g of caustic soda. A selective absorption film of cupric oxide consisting of black crystals was used. The composition and film thickness of the copper oxide obtained were Cu ₂ O 0.008μ,
CuO was 0.08μ. The characteristics of the solar heat absorber thus obtained were an absorption rate α of 0.97 and an emissivity of ε 0.11. Example 5 A stainless steel (SUS304) plate with a thickness of 3 mm was used as the core material, and after being subjected to alkaline degreasing and electrolytic degreasing, cathodic electrolysis was performed at room temperature for 30 seconds at a current density of 10 A/dm ² using 5% sulfuric acid. Pretreatment was performed using Next, nickel chloride 200g/,
Using a plating solution consisting of 50 ml of hydrochloric acid, the current density
First-order nickel plating was carried out under the conditions of 10 A/dm ² , liquid temperature of 20 to 25° C., and plating time of 0.5 minutes. On top of this plating layer, nickel chloride 360g/, boric acid 40g
Secondary plating was carried out using a plating solution consisting of 2.5 g/g/g/g/g/g of plating solution at a solution temperature of 55° C., a current density of 2 A/dm ² , and a plating time of 2 minutes. The thickness of the obtained nickel film was 1.1μ. The surface properties of the nickel plating layer at this time have a center line average roughness (Ra) of 0.55μ, an optical property of absorption in the visible region of 0.72, and absorption in the near-infrared region.
0.63, and the absorption rate in the infrared region was 0.12. On the obtained Ni film, the thickness was
Copper plating with a thickness of 0.15 μm was applied, and the sample was treated with a chemical conversion solution (liquid temperature: 60° C.) containing 40 g of sodium chlorite and 60 g of caustic soda for 6 minutes to obtain a black selective absorption membrane. The composition and film thickness were Cu ₂ O 0.01 μ and CuO 0.14 μ, and the absorption rate was α 0.97 and the emissivity ε 0.12. Example 6 Ni plating was applied to the core material in accordance with Example 1, and copper was then plated to a thickness of 0.19 μm using a copper sulfate plating solution. Add sodium chlorite to this copper plating layer.
65g/, caustic soda 95g/, liquid temperature 95℃
An oxidation treatment was carried out for 10 minutes using a treatment solution of 100% to form a cupric oxide selective absorption film consisting of fibrous black crystals. The film thickness was 0.14μ, absorption rate α0.94, and emissivity ε0.12. The surface quality of the nickel plating layer at this time was such that the center line average roughness (Ra) was 0.42μ, and the optical properties of the absorption rate in the visible region were 0.88,
The absorption rate in the near-infrared region is 0.62, and the absorption rate in the infrared region is 0.62.
It was 0.12. Example 7 Using a Ni-plated base material according to Example 5,
Copper plating with a thickness of 0.18μ is applied to this, and this copper plating layer is coated with 70g of sodium chlorite and 90g of caustic soda.
The oxidation treatment was carried out for 8 minutes with a treatment solution consisting of
A copper selective absorption film was formed. The thickness of this cupric oxide layer was 0.14 μm, and the absorption coefficient α was 0.95 and the emissivity was ε 0.11. The surface properties of the nickel plating layer at this time include a center line average roughness (Ra) of 0.50μ, an optical property of 0.70 in the visible region, 0.62 in the near-infrared region, and 0.62 in the infrared region. The absorption rate was 0.11. Comparative Example 1 A copper plate with a thickness of 0.5 mm was used as a core material, and after degreasing with alkaline and pickling with 3% HCl, 260 g of nickel sulfate and 35 g of nickel chloride were added.
g/, boric acid 35g/, cobalt sulfate 15g/
Nickel plating was carried out using a plating solution consisting of 25 g/25 g of formic acid, and 2 g/g formalin under the conditions of pH 4.0, liquid temperature 60° C., current density 3 A/dm ² , and plating time 3 minutes. At this time, the surface quality of the nickel plated layer has a center line average roughness (Ra) of 0.05μ.
, and the absorption rate in the visible region, which is an optical property, is
0.3, the absorption rate in the near-infrared region was 0.2, and the absorption rate in the infrared region was 0.11. The thus obtained nickel substrate was plated with copper using a copper sulfate plating solution. Add this copper plating to 80g of sodium chlorite and 60g of caustic soda.
An oxidation treatment was performed for 10 minutes using a treatment solution of 70° C. containing 1.5 g/ml of copper oxide to form a selective absorption film of cupric oxide. The film thickness was Cu ₂ O0, CuO 0.14 μ, absorption rate α 0.88, and emissivity ε 0.11. Comparative Example 2 In Comparative Example 1, the oxidation treatment in the oxidation treatment bath was
A nickel base was prepared under the same conditions as in Comparative Example 1, except that the temperature was 70° C. for 5 minutes, and a selective absorption membrane was also prepared. The film thickness of the selective absorption film is Cu ₂ O 0.01μ, CuO 0.13μ
The absorption rate was α0.90 and the emissivity was ε0.12. The above Examples and Comparative Examples are listed in Table 1, and the Examples all show better results than the Comparative Examples.

【table】

〔Test method〕

Film thickness: Based on the constant current reduction method, the film thickness was calculated from the amount of electricity required for reduction. Therefore, this film thickness is expressed as the thickness of a dense film with no voids or a flat film with no irregularities. When determining the thickness of the first copper layer and the second copper layer,
X-ray diffraction method was also used. Surface roughness: The surface roughness of the nickel base is JIS
Measured using a Kosaka surface roughness meter based on BO601. Absorption rate: Visible region and near-infrared region are for vapor-deposited aluminum mirrors. Visible area (α) = ∫ ^0.7 / _0.3 α〓・I〓dλ／∫ ^0.7 / _0
.3 I〓dλ Near-infrared region (α) = ∫ ^2.5 / _0.7 α〓・I〓dλ／∫ ^2.5
/ _0.7 I〓dλ Where, α; Absorption rate α〓; Absorption rate at wavelength λ I〓; Radiation intensity of sunlight at wavelength λ Since α in the infrared region corresponds to emissivity (ε),
This is expressed as follows. Infrared region (ε)=∫ ²⁰ / _2.5 S〓 _T=150・ε〓dλ／∫ ²⁰ /
_2.5 S〓 _T=150 dλ Where, ε: Emissivity (relative to the total energy radiated by the black body) S〓 _T=150 ; Radiation intensity at wavelength λ from a black body at 150°C ε〓; Emissivity at wavelength λ (black In addition, the reflectance P〓 in the infrared region was measured using an infrared spectrophotometer, and it was set as ε〓=1−P〓.

Claims (1)

[Scope of Claims] 1. A solar heat absorber comprising a base material at least the surface of which is made of nickel, on which a selective absorption film of copper oxide is formed using the surface of the base material as a base material, wherein the base material is , whose surface properties meet the following conditions:
A solar heat absorber characterized by using a base material that satisfies either (a) or (b). (a) The absorption rate of the nickel base shall be 0.4 or more in the visible region, 0.2 or more in the near-infrared region, and 0.2 or less in the infrared region. (b) The surface roughness of the nickel base shall be 0.1 to 3 microns in terms of center line average roughness.