Solar selective coating having high thermal stability and a process for the preparation thereof

Patent metadata

Field	Value
Publication number	US-9803891-B2
Application number	US-201214365303-A
Country	US
Kind code	B2
Filing date	Jun 25, 2012
Priority date	Dec 15, 2011
Publication date	Oct 31, 2017
Grant date	Oct 31, 2017

Abstract

The present invention describes an improved multilayer solar selective coating useful for solar thermal power generation. Solar selective coating of present invention essentially consists of Ti/Chrome interlayer, two absorber layers (AlTiN and AlTiON) an anti-reflection layer (AlTiO). Coating deposition process uses Ti and Al as the source materials, which are abundantly available and easy to manufacture as sputtering targets for industrial applications. The present invention allows deposition of all the layers in a single sputtering chamber on flat and tubular substrates with high absorptance and low emittance, thus making the process simpler and cost effective. The process of the present invention can be up-scaled easily for deposition on longer tubes with good uniformity and reproducibility. The coating of the present invention also displays improved adhesion, UV stability, corrosion resistance and stability under extreme environments.

First claim

I claim:

1. An improved solar selective coating having high thermal, stability comprising
tandem stack of layers consisting of an interlayer of titanium (Ti)/Chrome followed by
a first absorber layer comprising aluminum-titanium nitride (AlTiN);
a second absorber layer comprising aluminum-titanium oxy-nitride (AlTiON); and
a third antireflection layer comprising aluminum-titanium oxide (AlTiO);

wherein said second absorber layer being deposited on the first absorber layer and said third antireflection layer being deposited on the second absorber layer at substrate temperature in the range 100-350° C. using a four-cathode reactive pulsed direct current unbalanced magnetron sputtering technique; and
wherein the first absorber layer contains Aluminium in the range of 25-55%, Titanium in the range of 10-25% and Nitrogen in the range of 30-50%, the second absorber layer contains Aluminium in the range of 15-30%, Titanium in the range of 10-15%, Nitrogen in the range of 10-20% and Oxygen in the range of 50-60%, and the third anti-reflection layer contains Aluminium in the range of 15-30%, Titanium in the range of 5-15% and O in the range of 40-80%.

2. An improved solar selective coating as claimed in claim 1 , wherein the thickness of the Titanium interlayer is in the range of 10-80 nm, thickness of the first absorber layer is in the range of 30-70 nm, thickness of the second absorber layer is in the range of 20-40 nm and thickness of the third antireflection layer is in the range of 30-55 nm.

3. An improved solar selective coating as claimed in claim 1 , wherein thickness of the chrome interlayer is in the range of 5-10 μm, deposited by conventional electroplating.

4. An improved solar selective coating as claimed in claim 1 , wherein the solar selective coating has absorptance greater than 0.92 and emittance less than 0.17 on stainless steel 304 substrate.

5. An improved solar selective coating as claimed in claim 1 , wherein the solar selective coating has absorptance greater than 0.92 and emittance less than 0.07 on copper substrates.

6. An improved solar selective coating as claimed in claim 1 , wherein the coating is thermally stable in air up to 350° C. for a duration of 1000 hrs on stainless steel substrates under cyclic heating conditions.

7. An improved solar selective coating as claimed in claim 1 , wherein the coating is thermally stable in vacuum (2.0-8.0×10 −4 Pa) up to 450° C. for a duration of 1000 hrs on stainless steel substrates under cyclic heating conditions.

8. An improved solar selective coating as claimed in claim 1 , wherein the coating is stable under exposure to ultraviolet (UV) irradiation.

9. An improved solar selective coating as claimed in claim 1 , wherein the coating is stable at temperature under −2° C. for more than 9600 hrs.

10. An improved solar selective coating as claimed in claim 1 , wherein the coating is stable when exposed to sun in ambient conditions including dust, rain and mist for more than 10000 hrs.

11. An improved solar selective coating as claimed in claim 1 , wherein the coating is stable when exposed to steam for up to 85 hrs.

12. An improved solar selective coating as claimed in claim 1 , wherein the coating deposited on stainless steel substrates qualifies salt spray test as per ASTM B117 standard and shows improvement in the corrosion resistance by a factor of 100 in 3.5% NaCl solution.

13. An improved solar selective coating as claimed in claim 1 , wherein the coating deposited on stainless steel substrates qualifies tape adhesion test and demonstrates high adhesion strength while scratching using a 5 rim diamond tip.

14. A process for the deposition of improved solar selective coating of claim 1 on a substrate, comprising the following steps:
[a] metallographic or buff cleaning of substrate;
[b] chemical cleaning of the substrate as obtained in step [a];
[c] degassing of the substrate as obtained in step [b] in vacuum using a substrate heater;
[d] etching of the substrate as obtained in step [c] in Argon plasma to remove the impurities;
[e] depositing a Titanium/Chrome interlayer on the substrate as obtained in step [d] in argon plasma by maintaining the substrate temperature in the range 100-350° C. and bias voltage in the range −50 to −200 V;
[f] depositing a first absorber layer comprising aluminum titanium nitride (AlTiN) on the substrate as obtained in step [e] by sputtering two Titanium and two Aluminium targets in argon-nitrogen plasma by maintaining the substrate temperature in the range 100-350° C. and bias voltage in the range −50 to −200 V;
[g] depositing a second absorber layer comprising aluminum-titanium oxy-nitride (AlTiON) on the substrate as obtained in step [f] by sputtering two Titanium and two Aluminium targets in argon-nitrogen-oxygen plasma by maintaining the substrate temperature in the range 100-350° C. and bias voltage in the range −50 to −200 V;
[h] depositing a third antireflection layer comprising aluminum-titanium oxide (AlTiO) on the substrate as obtained in step [g] by sputtering two Titanium and two Aluminium targets in argon-oxygen plasma by maintaining the substrate temperature in the range of 100-350° C.; and
[i] etching of the antireflection layer as obtained in step [h] in argon-oxygen plasma for a duration of 20-60 min by maintaining substrate temperature in the range 100-350° C. and bias voltage in the range −500 to −1200 V to obtain the substrate deposited with desired solar selective coating.

15. A process as claimed in claim 14 , wherein the substrate used is selected from the group consisting of copper, nickel, stainless steel 304, glass nimonic, nickel coated stainless steel (SS), mild steel (MS) and aluminum.

16. A process as claimed in claim 14 , wherein deposition of all the layers is done in a single sputtering chamber on flat and tubular metal and non-metal substrates.

17. A process as claimed in claim 14 , wherein the solar selective coating is deposited at a sputtering power density of 2.75-3.5 watts/cm 2 for Aluminium and Titanium targets.

18. A process as claimed in claim 14 , wherein compositions of the first, second and third layers are independently controlled by controlling the sputtering power to the Aluminium and Titanium targets and the flow rates of N 2 and O 2 .

19. A process as claimed in claim 14 , wherein vacuum chamber is maintained at a base pressure of 3.0-6.0×10 −4 Pa before deposition of the coating.

20. A process as claimed in claim 14 , wherein the solar selective coating is deposited in the pressure range of 0.1-0.5 Pa.

Assignees

• Barshilia Harish Chandra
• Council Scient Ind Res

Inventors

• Barshilia Harish Chandra

Classifications

• C23C14/022

  by means of bombardment with energetic particles or radiation · CPC title

• C23C14/021 Primary

  Cleaning or etching treatments · CPC title

• Y02P80/24

  Cross-Sectional Technologies · mapped topic

• C23C28/345

  with at least one oxide layer · CPC title

• Y02E10/40

  Solar thermal energy, e.g. solar towers · CPC title