# US 4,392,920 A · Method of forming oxide coatings

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- Number: US 4,392,920 A
- Document ID: US4392920A
- Status: Granted
- Kind: A
- Application number: 06/272,152
- Filed: 1981-06-10
- Granted: 1983-07-12
- Earliest claimed: 1981-06-10
- Assignees: The United States of America as represented by the Administrator of the National Aeronautics and Space Administration
- Inventors: Glen E. McDonald
- Web page: https://patentgrep.com/patent/US4392920A

## CPC

- C25D 9/08: by cathodic processes
- C25D 5/48: After-treatment of electroplated surfaces
- F24S 70/25: Coatings made of metallic material
- Y02E 10/40: Solar thermal energy, e.g. solar towers
- C25D: PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- F24S: SOLAR HEAT COLLECTORS; SOLAR HEAT SYSTEMS (for producing mechanical power from solar energy F03G6/00)
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

This invention is concerned with an improved plating process for covering a substrate with a black metal oxide film. The invention is particularly directed to making a heating panel for a solar collector. A compound is electrodeposited from an aqueous solution containing cobalt metal salts onto a metal substrate. This compound is converted during plating into a black, highly absorbing oxide coating which contains hydrated oxides. This is achieved by the inclusion of an oxidizing agent in the plating bath. The inclusion of an oxidizing agent in the plating bath is contrary to standard electroplating practice. The hydrated oxides are converted to oxides by treatment in a hot bath, such as boiling water. An oxidizing agent may be added to the hot liquid treating bath.

## Claims

### Claim 1

In a method of covering a substrate with a black metal oxide film from an electroplating bath containing about 270 grams per liter of cobalt sulfate, about 37 grams per liter of cobalt chloride, and about 30 grams per liter of boric acid having a pH in the range between about 1.5 and about 4.5 at a temperature between about 45.degree. C. and about 60.degree. C. to form a coating that is highly absorbing, the improvement comprising the steps of
adding an oxidizing agent to said bath,
placing a metal substrate in said electroplating bath to form a cathode,
electrodepositing a compound of cobalt from said bath onto said substrate at said cathode by passing a current of about 400 amps per square meter of substrate therethrough in the presence of said oxidizing agent thereby forming an oxide coating containing hydrated cobalt oxides, and
contacting said coated substrate with water having a temperature substantially at the boiling point.

### Claim 2 (depends on 1)

A method of covering a substrate as claimed in claim 1 wherein the oxidizing agent added to the electroplating bath is hydrogen peroxide.

### Claim 3 (depends on 2)

A method of covering a substrate as claimed in claim 2 wherein the electroplating bath contains about 100 ml/liter of 30 percent H.sub.2 O.sub.2.

### Claim 4 (depends on 1)

A method of covering a substrate as claimed in claim 1 wherein the coated substrate is immersed in boiling water for about two minutes.

### Claim 5 (depends on 1)

A method of covering a substrate as claimed in claim 1 wherein the coated substrate is contacted with a solution of ammonium persulfate in water.

### Claim 6 (depends on 5)

A method of covering a substrate as claimed in claim 5 wherein the solution contains sodium hydroxide thereby making the solution alkaline.

### Claim 7 (depends on 1)

A method of covering a substrate as claimed in claim 1 wherein the coated substrate is contacted with a solution of sodium peroxide in water.