JPS5822845A - Solar heat adsorbing body - Google Patents

Abstract

PURPOSE:To obtain at low cost the titled solar heat adsorbing body which has a high degree of durability and an excellent heat adsorbing property by a method wherein an underlying metallic layer consisting of a granular crystalline nickel film is formed on a substrate and a selective adsorbing film of copper oxide is formed on the underlying metallic layer. CONSTITUTION:Various kinds of metallic materials such as an iron plate, a steel plate, a copper plate, etc., are used as the substrate 1 and the underlying metallic layer 2 consisting of the granular crystalline nickel film is formed over the substrate 1 by plating after the substrate is subjected to pretreatment such as fat removing and pickling processes. In this case, the average diameter of the crystalline particles 2' forming the underlying metallic layer 2 is in the range of 0.1 to 1 micron, the average interval l among them is in the order of 0.1 to 0.4 microns, and the thickness of the nickel film is in the order 0.1 to 3 microns. Further, the selective adsorbing film 3 of copper oxide is formed over the underlying metallic layer 2, thereby obtained the solar heat adsorbing body.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solar heat absorber used in solar water heaters and the like.

Solar heat absorbers are known to have a selective absorption film formed on the surface of a base material made of metal, which has a high absorption rate in the visible range of sunlight and a low emissivity in the infrared range. It is being As such one-selective absorption films, there are black chromium-based selective absorption films, copper oxide-based selective absorption films, and selective absorption films obtained by subjecting the surface of stainless steel to oxidation treatment.
Among these conventional selective absorption membranes, black chromium-based selective absorption membranes have limited economic efficiency, copper oxide-based selective absorption membranes have poor heat resistance and corrosion resistance, and stainless steel-based selective absorption membranes have disadvantages. has problems in terms of thermal conductivity and workability, etc.
Both had major practical drawbacks.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a solar heat absorber equipped with a selective absorption film that has excellent durability and is cheaper to manufacture than a black chromium-based film. This will be explained below.

This solar heat absorber according to the present invention has a base metal layer made of a nickel film with a granular crystal shape formed on a base material, and a selective absorption film of copper oxide is formed on the base metal layer. It is a feature. A nickel film composed of such granular crystal particles has selective absorption characteristics for sunlight, but this is because sunlight in the visible and near-infrared regions undergoes multiple reflections on the surface of this nickel film. This is thought to be because it becomes easier to absorb. The shape of the granular crystal grains is as shown in FIGS. 1 to 3, and each crystal grain has a relatively rounded shape. In addition to these granular crystals, nickel crystal particles include elongated fibrous crystals and leaf-like crystals with sharp edges. When a film is used as a base metal layer, the thermal emissivity (-
) becomes high by about 0.02 to Q.03, which is not preferable. Microscopically, the nickel film that functions as a selective absorption film is not a single continuous film, but a film-like cluster of the above-mentioned crystal particles. If we were to diagrammatically show what would happen if it were to take on a very simple form, it would be divided as shown in Figure 4. Crystal particle 2'
The average grain size of is preferably in the range of 11 to 1 micron (jm), and the average spacing of crystal grains (the average distance separating adjacent crystal grains from each other, as shown by I in Figure 4) is preferable. ) is preferably in the range of 0.1 to 0.4 microns.

Such a nickel film causes multiple reflections on the film surface for visible light and near-infrared light, but is thought to act as a flat surface for infrared light with a wavelength of 15 microns or more.
The third type, which reflects infrared light well and therefore has a low emissivity.
The figure shows an example in which the average spacing of crystal grains is larger than 14 microns, but if a nickel film with such crystals is used as the underlying metal layer, the absorption rate in the near-infrared region will decrease slightly. Selective absorption characteristics tend to be a little worse. Note that the nickel film may contain a small amount of impurity such as a small amount of oxide due to surface oxidation.

Next, such a nickel film can be formed by various methods such as electrolytic plating, electroless plating, vacuum evaporation, and sputtering. In this case, the formation of the nickel film is extremely easy, and the formed nickel film has excellent durability.

Various metal materials such as iron plates, steel plates, and copper plates can be used as the base material. When performing nickel plating on the surface of a base material made of iron plate or 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 a base material and subjecting it to the above-mentioned nickel plating, the following pretreatment is usually required, for example. That is,
After degreasing with ordinary chemicals and electrolytic degreasing,
Activation treatment is performed by depolarizing electrolysis using 5 to 30% sulfuric acid, and then nickel strike plating is performed under the following conditions.

(Treatment liquid composition) Nickel chloride 50~300f/V Hydrochloric acid 50~200f/1 (Treatment conditions)
Liquid temperature: Room temperature Current density: 5-16 A/dmj Processing time: 0.5-5 minutes In this way, before the necessary time! When nickel plating is applied to the base material 1 coated with Lll, a gray or pale yellow-gray nickel plating layer is formed on the surface of the base material. At that time, the plating conditions should be selected within the above range so that the thickness of the nickel plating layer is 0.1 to 3 microns (-).
Since the nickel plating film is composed of clusters of crystals as described above, it actually has complex irregularities and a fine structure. Therefore, the above-mentioned film thickness is calculated based on a state in which these irregularities are smoothed out and there are no voids. Generally, it is measured according to the method for measuring plating thickness.

By forming a selective absorption film of oxidized steel on the nickel film thus formed, it is possible to obtain a highly practical solar heat absorber with excellent selective absorption characteristics. That is, although solar heat absorbers equipped with copper oxide-based selective absorption films generally have excellent selective absorption properties, they have the drawback of poor heat resistance and corrosion resistance, and that they gradually deteriorate when used during the mourning period. If a selective absorption film made of copper oxide is formed on the base metal layer made of the nickel film,
Durability is further improved because the underlying metal layer is thermally and chemically stable. Such a selective absorption film made of oxidized steel is formed by, for example, forming a copper thin film layer on a nickel film by plating or the like, and then applying an oxidation layer to this by chemical conversion treatment. In this case, the nickel film 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 thought to be because the nickel film has an extremely fine uneven surface when viewed microscopically, and the uneven portions and the copper oxide crystals become intricately intertwined, thereby strengthening their bond with each other. The thickness of such a nickel film as a base metal layer is preferably a, 1 to S microns; if it is thinner than 0.1 tm, the adhesion of the copper oxide layer formed thereon tends to decrease. This is because, if the thickness is thicker than 3t chrome, the thermal emissivity will increase and the selective absorption characteristics will tend to decrease.

Further, it is desirable that the composition of the copper oxide used as the selective absorption film is almost entirely cupric oxide (C110). Further, the thickness of the selective absorption film made of copper oxide, which preferably has a leaf-shaped or fibrous crystal shape, is a, 0.
It is preferable to set it as 5-Q, S micron, and 0.06-0
．． This film thickness -b, which is more preferably 2 microns
If it is thinner than ia or os microns, the absorption rate in the visible range will be low, and if it is thicker than 0 or s microns, the heat radiation will increase, so either case is not very preferable. In addition, when the crystal shape is leaf-like or fibrous-like, the average length in the long direction, that is, the average length in the long axis direction is 0.6 to 2. ．． Preferably, the thickness is 0 micron. This is because when the length is less than 6 microns, the selective absorption characteristics tend to deteriorate.

FIG. 5 is a schematic diagram of the structure of a solar heat absorber obtained by heating as shown in C, and includes an iron plate and a stainless steel plate.

A base metal layer 2 made of a nickel film is formed on the surface of a base material l made of a copper plate or the like, and a selective absorption film 3 made of copper oxide is formed thereon. As mentioned above, the nickel film that becomes the base metal layer 2 has fine irregularities on its surface and acts as a kind of selective absorption film, so it was layered with a copper oxide selective absorption film. In this case, extremely good selective absorption characteristics can be obtained. Figure 6 is a graph showing this situation, and A shows the characteristics of a nickel film with granular crystals used as the base metal layer and a selective absorption film made of cupric oxide (Cwt) formed thereon. , and L shows the characteristics of a smooth nickel film as the base metal layer and a similar selective absorption film made of Gθ formed on top of it. What was used as the metal layer was
In particular, the absorption rate in the near-infrared region (wavelength (L7 to 2.5)) is high.
This is thought to be because the base layer absorbs light that is not absorbed by the copper layer alone due to multiple reflections. Conventionally, copper oxide-based selective absorption films have been superior in price to black chromium-based selective absorption films, but have been inferior in selective absorption properties. However, as described above, by forming a copper oxide-based selective absorption film on a granular nickel film, a selective absorption film with performance equivalent to or better than a black chromium-based selective absorption film can be obtained at a relatively low cost. This makes it possible. In this case, since the underlying layer also functions as a selective absorption film, if necessary, the thickness of the Cwt film can be made thinner than the thickness of the Cwt film when the selective absorption film is composed of only a copper oxide layer.

Next, implementation failures of the present invention and comparative examples will be explained.

[Example 1] A copper plate with a thickness of 0.5 IIua was used as a base material, and after being subjected to alkaline degreasing and pickling with 2% HCl, it was treated with nickel chloride 4001/I and boric acid 45 f/1.
Using a plating solution consisting of, the solution temperature was 55℃ and the current density was 2A/
Nickel plating was performed under the conditions of dml and plating time of 3 minutes. The plating solution was sufficiently stirred during the plating process. The thickness of the obtained nickel film was approximately 1 μm. When the melt was observed using an electron microscope (7,600 times magnification), it was confirmed that granular crystals as shown in FIG. 1 were formed.

After completing this nickel plating, copper was further plated to a thickness of O,l#lI using a copper sulfate based plating solution. Next, in order to oxidize this copper plating layer, sodium chlorite 45
Using a chemical conversion treatment solution consisting of 1/l and caustic soda 101/I, oxidation treatment was performed at a liquid temperature of 90° C. for 5 minutes to form a selective absorption film of cupric oxide consisting of fibrous black crystals. The thickness of the cupric oxide obtained was approximately 0.08 mm, and the average length of the crystals in the major axis direction was L5. #l! It was a.

The properties of the solar heat absorber thus obtained were that the absorption rate () was O, SS, and the emissivity <s> was 11.

[Example 2] A stainless steel plate (SUS318) with a thickness of 111 mm was used as a base material, and after being subjected to alkaline degreasing and electrolytic degreasing, the current density IQ was reduced using 2% sulfuric acid at room temperature.
A,/ba! An activation layer was formed by cathodic electrolysis for 1 minute. Next, using a plating solution of 250 f/l of nickel chloride and 50 f/l of hydrochloric acid, electrolytic IEWI change I
Q A/d1m! , liquid 1i20~25℃, /”/
Primary nickel plating was performed for 4 hours and 2 minutes to form a primary nickel film on the surface of the base material. On top of this plating layer, 350 f/l of nickel chloride is applied.

Secondary nickel plating was performed using a plating solution containing 601/l of boric acid under the conditions of current density I A/dxxht , solution temperature of 85° C., and plating time of 8 minutes. The primary nickel plating is for improving adhesion to stainless steel, and the secondary nickel plating is for forming a nickel film made of the granular crystals. The thickness of the obtained granular nickel film was 1.5 mm, and the fine structure of the surface was as shown in FIG.

Next, copper plating (copper layer thickness: 408 m) was performed on this nickel film using a copper sulfate plating solution.

This was subjected to an oxidation treatment using the chemical conversion treatment solution used in Example 1 to form a cupric oxide coating having a thickness (LO71B? average length in the major axis direction of the crystals of 1.4-).

The absorption rate (c4 is Q, 96. Emissivity (-) of the solar heat absorber thus obtained was 0.12.

[Example 3] Stainless steel plate (SUS 304) with a thickness of 0.3 mm
is used as a base material, and this is subjected to alkaline degreasing, electrolytic degreasing, $
and activation by cathodic electrolysis using 5% sulfuric acid, and then nickel strike plating for stainless steel was applied under the following conditions.

(Strike plating wave composition) Nickel chloride 2 G 0 f/1 Hydrochloric acid 1
G 0 f/1 (Processing conditions) Temperature: ZS"C Current density: 5A/dm! Time: 3 minutes on this surface nickel chloride 350f#, boric acid 40
Using a nickel plating solution consisting of f/l, the solution temperature was 55°C,
Current density I A/dia! Nickel plating was performed for a treatment time of 1.5 minutes to form a nickel plating layer with a thickness of about 0.3-.

On top of this nickel plating layer, using a blue copper plating solution,
Current density: 2A/dm, plating time: 1 minute.

Copper plating was applied at a plating temperature of 25℃, and the thickness (L4
All copper plating layers were formed.

Caustic soda 901/1. Using a chemical conversion treatment solution containing 9017 g of sodium chlorite, 1.
Oxidized J6il at a temperature of 90°C and a treatment time of 15 minutes.
The copper plating layer was changed to a copper oxide layer.

The average length in the major axis direction of the &3-1 crystal was 0.8μ, and the absorption rate (→ was 0.95) of the obtained solar heat absorber.The emissivity (ε) was tentatively 1G.

The method for testing the optical characteristic values of the above Example Ktd is as follows.

where a; absorption rate (relative to total solar energy) αλ;
Absorption rate Iλ at wavelength λ; radiation intensity of sunlight at wavelength λ, where C; emissivity (relative to the total energy of blackbody radiation) Sλ7=8. . ; Radiation intensity ελ of wavelength λ from a black body at 150°C; Emissivity (relative to black body) of wavelength λ Measure the reflectance rλ in the infrared region with an infrared spectrometer needle, Cλ=1−Pλ
And so.

[Brief explanation of the drawing]

Figure 11, Figure 2, and Figure 3 are electron micrographs (X7, 60G) showing the crystalline form of the nickel film, Figure 4 is a schematic cross-sectional view of the crystal of the nickel film, and Figure 5 is the solar heat absorption. FIG. 6 is a schematic diagram showing the structure of one example of the body, and a graph showing the optical properties. 1... Base material 2... Base metal layer 2'... Nickel crystal 3... Selective absorption film Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 0) A solar heat treatment system in which a base metal layer consisting of a nickel film with a granular crystalline form is formed on a base material, and a selective absorption film of copper oxide is formed on the C base metal layer. Absorber. (2) The average grain size of nickel crystals in the base metal layer is 0.1 to
1 micron, and the average spacing is 0.1 to 0.4 micron. The solar heat absorber according to claim 1. 0) The solar heat absorber according to claim 1 or 2, wherein the nickel film has a thickness of 0.1 to 3 microns. (4) The solar heat absorber according to any one of claims 1 to 3, wherein the selective absorption film is made of cupric oxide having a leaf-like or fibrous crystal form. Excellent) The solar heat absorber according to claim 4, wherein the thickness of the selective absorption film is O,OS ~ 0.5 microns, and the average length in the long axis direction of the crystals is 0.6 to 2.0 microns. .