Masking material and a thickening agent preserve limited unanodized areas when aluminum surfaces are anodized with chromic acid. For protection of large areas it combines well with a certain self-adhesive plastic tape

Crawford, G. B.

Thompson, R. E.

English

NASA Technical Reports Server

September 1969
	 Brief 69-10335 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Masking of Aluminum Surfaces Against Anodizing 
The problem: 
Development of a method of preserving limited 
unanodized areas when aluminum surfaces are an-
odized with chromic acid. Such areas, from which the 
coating is normally etched subsequently with acid, 
are required for such purposes as electrical contacts. 
The solution; 
Masking of the areas with a mixture of two com-
mercial materials: a "maskant" (masking material) 
and a thickening agent. The mixture consists of 
(parts by weight) 98 parts maskant and 8 parts of a 
1:3 solution of thickening agent in toluene. 
How it's done: 
Used alone, this mixture is successful when a heavy 
coat is dried for 16 hours before the anodizing. For 
protection of large areas it combines well with a cer-
tain self-adhesive plastic tape. The tape is rolled on 
the metal's surface, and a thick coating of the mix-
ture is applied to the edges of the tape and over 
0.5 inch of the adjacent metal before being dried for 
16 hours. When used alone, the tape permits anodiz-
ing under its edges. Both protectants are easily 
stripped after the anodizing. 
All test specimens anodized were immersed for 
from 10 to 30 minutes in an alkaline solution at 
71 0C; rinsed with a water spray before a 30-second 
dip in water; immersed for from 10 to 30 minutes 
at 21°C in a bath containing, per liter of water,
120.4 ml of nitric acid, 48 g of chromic acid, and 
10 ml of hydrofluoric acid; and rinsed with a water 
spray before a 30-second dip in water. 
They were then placed in water containing chromic 
acid at 60 g/liter and maintained between 32 11
 and 
38°C; a voltage was applied and gradually increased, 
to maintain constant current in the specimens, until 
the level reached 40 v. After 60 minutes of such 
treatment the specimens were withdrawn and allowed 
to drain briefly. They were then immersed for 5 min-
utes in a rinse tank maintained between 82 0
 and 
100°C, and at a pH between 5.0 and 7.0 with 
chromic acid, before drying under ambient conditions. 
Notes: 
Anodizers or electroplaters may be interested. 
Documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: TSP69-1 0335 
Patent status: 
No patent action is contemplated by NASA. 
Source: R. E. Thompson and G. B. Crawford of 
Douglas Aircraft Company 
under contract to 
Marshall Space Flight Center 
(MFS-12964) 
Category 05 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
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Masking of aluminum surface against anodizing

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