# US 4,397,721 A · Pickling of aluminum

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- Number: US 4,397,721 A
- Document ID: US4397721A
- Status: Granted
- Kind: A
- Application number: 06/347,974
- Filed: 1982-02-11
- Granted: 1983-08-09
- Earliest claimed: 1982-02-11
- Assignees: Fokker B.V.
- Inventors: Robertus Exalto; Adriaan Kwakernaak
- Web page: https://patentgrep.com/patent/US4397721A

## CPC

- C23G 1/125: {aluminium}
- C25F 1/04: in solution
- C23G: CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C25F: PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR

## Abstract

Articles of aluminum are pickled by placing them as anodes into a sulfuric acid bath in the absence of chromic acid or bichromate and connecting them by a short-circuit connection to a carbon cathode placed in the same bath. The process also excludes the application of an anodic control voltage.

## Claims

### Claim 1

A pickling process for aluminum articles, comprising the steps of:
(a) providing a pickling bath consisting essentially of sulfuric acid;
(b) positioning two electrodes, viz. an anode and a cathode, into said pickling bath, said anode comprising an aluminum article to be pickled and said cathode comprising at least one carbon body;
(c) interconnecting said anode and said cathode by means of an external short-circuit connection; and
(d) maintaining said short-circuit connection during a period of time sufficient to cause complete pickling of said aluminum article.

### Claim 2 (depends on 1)

The process as claimed in claim 1, wherein said article is an aluminum alloy article.

### Claim 3 (depends on 1)

The process as claimed in claim 1, wherein said article is an article of a non-aluminum metal coated with a layer of aluminum.

### Claim 4 (depends on 1)

The process as claimed in claim 1, wherein said cathode has a surface area exceeding the surface area of said anode.

### Claim 5 (depends on 1)

The process of claim 1, wherein said cathode has a surface area of more than 6 times the surface area of said anode.

### Claim 6 (depends on 1)

The process as claimed in claim 1, wherein said bath has a temperature of between 40.degree. and 60.degree. C. at a sulfuric acid concentration of about 100 g/dm.sup.3 in said bath.

### Claim 7 (depends on 1)

The process as claimed in claim 1, wherein said bath has a temperature of about 40.degree. C. at a sulfuric acid concentration of about 200 g/dm.sup.3 in said bath.

### Claim 8

A pickling process for aluminum articles, comprising the steps of:
(a) providing a pickling bath consisting essentially of sulfuric acid in a concentration of about 100 g/l said bath having a temperature between 40.degree. and 60.degree. C.;
(b) positioning two electrodes, viz. an anode and a cathode, into said pickling bath, said anode comprising an aluminum article to be pickled and having a surface area ratio of about 6 to said cathode, and said cathode comprising at least one carbon body;
(c) interconnecting said anode and said cathode by means of an external short-circuit connection, and
(d) maintaining said short-circuit connection during a period of time sufficient to achieve a complete pickling of said aluminum article.

### Claim 9 (depends on 8)

The pickling process of claim 8, wherein said article is an aluminum alloy article.

### Claim 10

A pickling process for aluminium articles, comprising the steps of:
(a) providing a pickling bath consisting essentially of sulfuric acid in a concentration of about 200 g/dm.sup.3, said bath having a temperature of about 40.degree. C.;
(b) positioning two elelctrodes, viz. an anode and a cathode, into said pickling bath, said anode comprising an aluminium article to be pickled and having a surface area ratio of more than 6 to said cathode, said cathode comprising at least one carbon body;
(c) interconnecting said anode and said cathode by means of an external short-circuit connection; and
(d) maintaining said short-circuit connection during a period of time sufficient to achieve complete pickling of said aluminium article.

### Claim 11 (depends on 10)

The process as claimed in claim 10, wherein said article is an aluminum alloy article.