EP2113127A1

EP2113127A1 - Selective absorber for converting sunlight into heat, and method and device for the production thereof

Info

Publication number: EP2113127A1
Application number: EP05733673A
Authority: EP
Inventors: Peter Lazarov
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-04-20
Filing date: 2005-04-20
Publication date: 2009-11-04
Also published as: DE102004019061B4; WO2005104173A1; DE102004019061A1

Abstract

The invention relates to a selective absorber for converting sunlight into heat, said absorber being composed of thin layers on a substrate, preferably aluminum, copper, or steel. The thin layers are made of two layer systems. The first layer system, which borders the substrate, comprises at least one layer that is made of tight, i.e. void-free material composed of titanium, aluminum, nitrogen, carbon, and oxygen. Said material has the chemical formula TiaAlßNxCyOz. The superimposed second system comprises at least one layer that is made of a mixture of TiOz and Al2O3.

Description

Selective absorber for converting sunlight into heat, a method and a device for the production thereof

The invention relates to a selective absorber for converting sunlight into heat, a method for its production, and a device for its production.

So far, substrates made of a metallic material that have been provided with a selectively absorbing layer have mostly been used for selective absorbers. Such selectively absorbing layers have been known since H. Tabor 1955 ("Selective Radiation I. Wavelength Discrimination" in Bull. Res. Counc. Israel 5A (1956) p.119). These layers have the property of absorbing sunlight as completely as possible due to the solar absorption level CISO _L and at the same time to emit as little energy as possible in the thermal radiation range, described by the thermal emissivity ε-m- Furthermore, these layers must be suitable for use in solar collectors, which means a temperature stability up to 250 ° C and moisture stability A number of selective absorbers are known, for example DE 28 04447 C3, DE 36 15 181 A1, DE 4425 140 C1 or DE 196 20 645 C2, and they are also explicitly referred to DE 43 44 258 C1 This discloses a material made of TiN _x Oy with empty spaces, which forms a selective absorber as a thin layer on preferably copper The outstanding optical properties of these absorbers (αsoL> 0.94 and £ _TH <0.05) have the disadvantage that the required temperature stability is not met.

Thin layers of compounds of Group IVa metals with nitrogen, oxygen or carbon are also known. DE 36 37 810 C2 discloses a decorative layer with titanium, oxygen, nitrogen and carbon. This layer is described as gray to black. It can be seen from this that the ε _{TH will be} unacceptably high. DE 31 17 299 C2 discloses TiNO and TiCO layers produced by means of electron steel evaporation. It is known that layers produced in this way are porous, ie they contain empty spaces as disclosed in DE 32 10 420 A1 and in DE 43 44 258 C1. These layers also have stability problems.

DE 41 15 616 C2 discloses a TiAIN _x layer as a hard material system for tools. Experience has shown that metal nitrides lead to low α _S oι and are only of limited use as selective absorbers.

The object of the present invention is to provide a selective absorber which has the good optical properties mentioned above without their disadvantages. Furthermore, the object of the present invention is to provide a method and a device with which the selective absorber can be produced.

According to the invention the object is solved by the subject matter of claims 1, 8 and 13. Advantageous refinements are the subject of the dependent claims.

The selective absorber for converting sunlight into heat according to claim 1 consists of thin layers on a substrate, preferably aluminum, copper or steel. The thin layers in turn consist of two layer systems. The first, the system adjacent to the substrate, contains at least one layer of dense, ie void-free material made of titanium, aluminum, nitrogen, carbon and oxygen. This material has the chemical formula Ti _α AlßN _x CyO _z . The sum of α and β is 1 and α to β is 1 to (0.05 to 1), preferably 1 to (0.05 to 0.6) and particularly preferably (0.05 to 0.09) ). Furthermore, for this material it applies that x + y + z is in the range from 0.8 to 2, preferably in the range from 1.2 to 2 and particularly preferably in the range from 1.5 to 5. For the individual constituents, 0 <x ≤ 1, 2, preferably 0.0 <x ≤ 0.1; 0.2 <y ≤ 2, preferably 1 <y <2 and 0.05 <z <2. The second system above contains at least one layer made of a mixture TiO _z and Al ₂ 0 exists. The following applies to this layer 1 <z <2. The possibility of designing system one with at least one further layer of dense, ie space-free material made of titanium, nitrogen, carbon and oxygen with the chemical formula TiN _x C _y O _z allows one Faster production of the selective absorber with the same properties. This layer is described in that x + y + z is in the range from 0.9 to 2, preferably in the range from 1.3 to 2. Furthermore, 0.0 x x <1, 2, preferably 0.0 <x <0.1; 0.2 <y <2, preferably 1 <y <2 and 0.05 <z <2. All of the above ratios relate to the number of particles or to the molar ratios.

The second layer system can further contain at least one of one of the following materials Si0 ₂ , Zr0 ₂ , Ti02, Ba ₂ θ3, Al ₂ 0 ₃ , Pb0 ₂ , or Zn0 ₂ or combinations thereof. The selective absorber can be passivated by such an oxide layer, thereby increasing its service life.

The thickness of the first system is in the range from 50 to 150 nm, preferably in the range from 70 to 120 nm. The thickness of the second system is in the range from 80 to 300 nm, preferably in the range from 90 to 180 nm. This embodiment of the invention Allows selective absorbers with excellent properties to be produced with a low use of material and thus at low cost.

Reference is made in full to the parallel German patent applications DE 10 2004 019 060.7 and DE 10 2004 019 062.3 and the corresponding international applications which were filed at the same time as the present application and incorporated into the present application.

The present invention is further achieved by a method for reactive arc evaporation (ARC) according to claim 8. According to the invention, titanium and aluminum are formed on a substrate during the deposition of the metals by maintaining a gas atmosphere which min. contains at least one of the gases argon, nitrogen, carbon dioxide and oxygen, an oxide, nitride or carbide compound. In order to obtain dense, void-free layers, no thermal evaporation processes are used, but arc evaporation. In this process, a plasma is used to deposit the target material and leads to a high ionization rate of the material to be evaporated. The result is dense layers. In a vacuum chamber, the substrate to be coated is guided over two groups of rows of arc evaporators. The rows of evaporators are arranged transversely to the direction of movement of the substrate. The evaporators in the first group in the direction of movement are equipped with titanium targets and those in the second with targets consisting of a mixture of titanium and aluminum. The volume fraction of aluminum in this target is 5 to 45%, preferably 15 to 33%. The reaction gases nitrogen and carbon dioxide are supplied near the first group of evaporators. The distance between the evaporator and the gas supply is smaller than the distance between the two groups. Oxygen is supplied near the second group, closer than half the distance between the two groups. Argon is also supplied between the two groups. The total pressure is set to a value in the range 10 ^"3 to 10 ^{" 2} via the inflow of argon or optionally oxygen. According to the invention, the ratio of the inflows of the gases 0 ₂ to C0 ₂ to N _{2 is} 1 to (0.05 to 5) to (0 to 0.25). The inflow of N ₂ gas is adjusted depending on the evaporator rate of the first group according to the formula: inflow [in sccm / s] = rate [in, 6. g / sec] * f, being the factor. is in the range from 0 to 2, preferably in the range from 0.05 to 1.3. The proportion of argon in the gas mixture is in the range 0 to 50%.

A preferred embodiment of the invention is that after the second group of evaporators, further thermal evaporators are used in order to reactively deposit dielectric layers made of SiO ₂ , ZrO ₂ , TiO ₂ , Ba ₂ O ₃ , Al ₂ O ₃ , PbO ₂ or ZnO ₂ . Furthermore, a bias voltage of preferably 50 to 1000 V, particularly preferably 150 to 750 V, can be used between the arc evaporator and the substrate, so that contaminated substrates can also be coated with the process in an adherent manner.

Furthermore, it is advantageous to choose the substrate temperature in the range from 150 ° C to 500 ° C. This can improve the adhesive strength. The possibility of replacing or supplementing C0 ₂ with methane and / or CO permits more flexible production of the absorber according to the invention.

In the device according to the invention for producing the selective absorber according to the above method, a layer system is deposited in a cylindrical vacuum chamber by means of reactive arc evaporation. The cylindrical, evacuable vacuum chamber (3) has a door (2) on at least one side of the cylinder. A support tube (1) on which a winding device (17) is fastened passes through this door (2). Between two end plates (4,5) there is an unwinding roller (8), a winding roller (9) at least two deflection rollers (6,7) and at least one dancer roller (12,13) and at least one pressure roller (11), the axes of all Rollers are parallel to the axis of the support tube (1) and the support tube (1) and door (2) are independently attached to a carriage. This trolley runs on rollers or rails parallel to the cylinder axis of the chamber (3), so that the winding device (17) can be completely moved into the chamber (3) and the door (2) closes the chamber (3) in a vacuum-tight manner. Furthermore, the winding device (17) has dancer rollers (12, 13), each of which is pulled in the direction of the support tube (1) by two spring assemblies (14). The substrate tape to be coated forms a free path between the wrapping rollers (6, 7). Below this are groups of arc evaporators. These evaporators are fastened in ventilated vessels (21) which are positioned in the chamber (3).

The invention is further described with reference to the figures, which show:

1 shows the reflection as a function of the wavelength of Example 1. Fig. 2 shows schematically the structure of the device according to Example 4.

3 shows the reflection as a function of the wavelength of Example 2.

4 shows the reflection as a function of the wavelength of Example 3.

The invention is further described on the basis of the examples.

Example 1:

Evacuated in an vacuum chamber by an oil diffusion pump followed by a roots pump and a two-stage rotary vane pump are two commercially available 0 69 mm arc vaporizers. 0.2 mm thick copper substrate strips are guided over the evaporators by means of a manipulator. Both evaporators are equipped with 20% Al-Ti mixed targets. 5 mm before the first evaporator 100 sccm N ₂ and 350 sccm C0 _{2 are} introduced. 5 mm behind the second evaporator 1000 sccm 0 _{2 are} fed. Before and during the coating process, the arc evaporators burn at 60A each. The substrates are passed over the evaporators in such a way that the desired layer thickness is produced. This is measured with quartz crystals, which are also moved with the substrates. 250 ° C. was chosen as the substrate temperature. After coating, the solar emissivity and the thermal emissivity were determined with spectrometers. The layer composition was determined by means of eye spectroscopy. The following results were measured:

ÖSOL = 0.94; ε ™ = 0.04 of Ti _α AlßN _x CyO _z with (α = 0.8; β = 0.2; x = 0.1; y = 1, 1; z = 0.6) with a thickness of 90 nm and Ti0 ₂ / Al ₂ 0 ₃ - 105 nm thick layer on copper.

Example 2:

The parameter set in Example 2 differs from Example 1 as follows: The titanium to aluminum mixture was 90% titanium and 10% Aluminum. The N ₂ gas flow was 50 sccm and that of 0 ₂ 2000 sccm. The following results were measured: αsoι_ = 0.95; ε-m = 0.04 of Ti _α Al _ß N _x C _y O _z with (α = 0.9; ß = 0.1; x = 0.02; y = 0.9; z = 1, 08) the thickness 85 nm and Ti0 ₂ / Al ₂ 0 ₃ - layer of thickness 100 nm on copper.

Example 3:

In this example, the first evaporator was only equipped with titanium, the

Second with an aluminum content of 45%. The N ₂ gas flow was 400 sccm; C0 ₂ 500 sccm; Methane 500 sccm and 0 ₂ 1000 sccm. The following results were obtained in this example:

O _SOL = 0.95; ε _TH = 0.05 from System I: 40 nm TiN _x C _y O _z with (x = 0.3; y = 1.0; z = 0.7); 55 nm Ti _α Al _ß N _x C _y O _z with (o = 0.7; ß = 0.3; x = 0.1; y = 1, 0; z = 0.9) and System II: Ti0 ₂ / Al ₂ 0 ₃ layer 105 nm thick on copper tape.

Example 4:

The coating device consists of a cylindrical vacuum chamber (3), a winding device (17) which is attached to a support tube (1). The support tube (1) and door (2) of the vacuum chamber (3) are attached to a trolley. The carriage runs on a rail system in such a way that the door (2) and support tube (1) with the winding device (17) can move into the vacuum chamber (17). The door (2) and the chamber (3) are both provided with a sealing flange (18) so that the door (2) seals the chamber (3) in a vacuum-tight manner.

The winding device consists of two end plates (4,5) on which the rollers, unwinding and winding rollers (8,9), deflection rollers (6,7), pressure rollers (10,11), dancer rollers (12,13) and the spring assemblies ( 14) are attached. The strip to be coated is passed from the unwinding roller (8) over the deflection roller (6). It is guided and stretched by the dancer roller (13) so that a defined wrap angle is created on the deflection roller (6). The deflection roller (6) is designed as a heating roller in this example. For this purpose, electrical lines are laid through the pipe (1) and reach the vacuum side via electrical feedthroughs (19). From there, the lines to the heating roller (6) are laid on the vacuum side. The heating roller (6) itself is designed such that it consists of a hollow tube which is rotatably mounted. A cylindrical electric radiant heater is fixed in this hollow tube. The belt forms a free path from the heating roller (6) to the deflection roller (7). Below this free path there are two rows of arc evaporators, each row consisting of three evaporators, attached to the chamber (3) with which the running strip is coated. Each individual evaporator is placed in a ventilated vessel (21) in such a way that it can be freely positioned in the chamber (3).

Behind the deflection roller (7), the tape is guided around a second dancer roller (12) to the take-up roller (9). Furthermore, the winding device (17) is provided with two pressure rollers (11). These allow a degree of cutting to be pressed on metal strips and lead to better winding quality. The winding (9) and unwinding rollers (8) are connected to motors (16) via drive shafts (20) via a rotary vacuum feedthrough. The motors are attached to the door (2) on the air side.

There are two gas inlet nozzles next to each evaporator. There is a nozzle for argon in the middle between the rows of evaporators.

Bezuqszeichenliste: (I) support tube (2) door (3) vacuum chamber (4) bearing plate (5) bearing plate (6) deflection roller; Heating roller (7) Deflection roller (8) Unwinding roller (9) Winding roller (10) Pressure roller (II) Pressure roller (12) dancer roller

(13) dancer roller

(14) Spring pack

(15) Seal ring (16) Motor

(17) winding device

(18) Sealing flange

(19) Electrical feedthroughs

(20) Drive shaft (21) Vessel for attaching the arc evaporator

Claims

claims

1. Selective absorber for converting sunlight into heat, characterized in that two layer systems are applied to a substrate, the system closest to the substrate being at least one layer of dense, ie void-free material made of titanium, aluminum, nitrogen, carbon and contains oxygen with the chemical formula Ti _α Al _β N _x C _y O _z , where α + β = 1 and α to β behaves like 1 to (0.05 to 1) and x + y + z = 0, 8 to 2 and 0.0 <x <1.2 and 0.2 <y <2 and 0.05 <z <2, further that the overlying second system contains at least one layer consisting of a mixture consists of TiO _z and AI2O3, with 1 ≤ z <2.

2. Selective absorber according to claim 1, characterized in that the material in the first system made of titanium, aluminum, nitrogen, carbon and oxygen contains more carbon than oxygen.

3. Selective absorber according to claim 1 or 2, characterized in that one of the layers of the system closest to the substrate consists of dense, ie void-free material made of titanium, nitrogen, carbon and oxygen with the chemical formula TiN _x CyO _z where x + y + z = 0.9 to 2 and 0.0 ≤ x ≤ 1, 2 and 0.2 <y <2 and 0.05 <z <2.

4. Selective absorber according to one of claims 1 to 3, characterized in that at least one of the layers in the second system consists of at least one of the following materials: Si0 ₂ , Zr 0, Ti0 ₂ , Ba ₂ 0 ₃ , Al ₂ 0 ₃ , Pb0 ₂ , or Zn0 ₂ or combinations of these.

5. Selective absorber according to one of claims 1 to 4, characterized in that the thickness of the first system is in the range of 50 to 150 nm.

6. Selective absorber according to one of claims 1 to 5, characterized in that the thickness of the second system is in the range 80 to 300 nm.

7. Selective absorber according to one of claims 1 to 6, characterized in that the substrate is a strip of copper, aluminum or steel.

8. A method for producing the selective absorber according to one of claims 1 to 7 by means of reactive arc discharge, characterized in that the substrate to be coated is guided over two groups of rows of arc evaporators in a vacuum chamber, the rows of the evaporators transverse to the direction of movement of the substrate are arranged, the evaporators of the first group in the direction of movement are equipped with titanium or a mixture of titanium and aluminum as the evaporator material, the second are equipped with a mixture of titanium and aluminum with 5 to 45% by volume of aluminum, and the gases Nitrogen and carbon dioxide are supplied near the evaporator of the first group, at a distance that is a maximum of half the distance between the two groups and oxygen near the second group, also at a distance that is less than half the distance between the two groups is, and likewise Argon is fed between the two groups, the total pressure being regulated via the inflow of argon or optionally from oxygen to 10 ^"3 to 10 ^{" 2} , the ratio of the inflows of the gases 0 ₂ to C0 ₂ to N ₂ increasing as 1 (0.05 to 5) is related to (0 to 0.25) and the inflow of N ₂ gas is regulated via the evaporator rate of the first group according to the formula: inflow [in sccm / s] = rate [in μg / sec] ^* f, where f is in the range of 0 to 2 and the proportion of argon in the gas mixture is in the range 0 to 50%.

9. The method according to claim 8, characterized in that after the second group in the direction of movement follows a further group of thermal evaporators which are equipped with materials Si, Zr, Ti, Ba, Al, Pb, or Zn and deposit appropriate dielectrics by reactive evaporation ,

10. The method according to claim 8 or 9, characterized in that in addition or instead of the gas C0 ₂ , methane and / or CO can also be supplied.

11. The method according to any one of claims 8 to 10, characterized in that the substance is kept at a temperature in the range from 150 ° C to 500 ° C during the coating.

12. The method according to any one of claims 8 to 11, characterized in that a voltage of 50 to 1000 V is applied between the arc source and Substart.

13. Device for producing the selective absorber on tape-shaped substrates by means of the method according to one of claims 8 to 12, consisting of a cylindrical evacuable vacuum chamber (3), with a door (2) arranged at least on one side of the cylinder and a winding device ( 17), characterized in that through the door (2) leads a support tube (1) on which the winding device (17) is fastened, which consists of two end plates (4,5), between which there is an unwinding roller (8), one Winding roller (9) has at least two deflecting rollers (6, 7) and at least one dancer roller (12, 13) and at least one pressure roller (11), the axes of all rollers being parallel to the axis of the support tube (1) and support tube (1 ) and door (2) are attached separately or independently of one another on a trolley, wherein this carriage can be moved on rollers or rails parallel to the cylinder axis of the chamber (3) and each dancer roller (12, 13) is pulled in the direction of the support tube (1) by two spring assemblies (14) and under the free path between the wrapping rollers (6, 7) groups of ventilated vessels (21) with arc evaporators are attached to the vacuum chamber (3).

14. The apparatus according to claim 13, characterized in that in addition to each evaporator of group one a gas nozzle for the supply of C0 ₂ and one for the supply of N _{2 is} attached, in the middle between group one and two at least one nozzle for argon and next to each evaporator in group two there is a nozzle for the supply of oxygen.

15. The apparatus according to claim 13 to 14, characterized in that at least one deflecting roller is designed as a heating roller.