White anodize is applied to aluminum alloy surfaces by specific surface preparation, anodizing, pigmentation, and sealing techniques. The development techniques resulted in alloys, which are used in space vehicles, with good reflectance values and excellent corrosive resistance

Dale, K. H.

English

NASA Technical Reports Server

May 1969
	
Brief 69-10144 
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. 
Advances in Aluminum Anodizing 
Three aluminum alloys, 2014, 2219 and 7006, were 
considered in the development of techniques for ap-
plying white anodize to aluminum alloy surfaces. The 
techniques developed have resulted in alloys with 
good reflectance values and excellent corrosive resist-
ance. 
The solution: 
The application of white anodize to aluminum alloy 
surfaces can be considered in four parts: surface prep-
aration, anodizing process, pigmentation and sealing. 
1. Surface preparation. A method of mechanical and 
chemical pre-treatment of the aluminum surface 
was developed to obtain a surface reflectance of 
82-86 percent. The treatment consists of clean-
ing, chemical etching, abrasive blasting with alu-
minum oxide, cleaning, alkaline etching, acid de-
oxidizing, fluoride etching, and acid deoxidizing. 
2. Anodizing process. The anodizing process that 
produced the best result used 26 percent sulfuric 
acid electrolyte containing glycerol, lactic acid, 
and titanium ammonium lactate. While the electro-
lyte at low anodic film thickness (.0001 inch—
.00012 inch) gave absolute reflectance values be-
tween 70 and 80 percent, the corrosion resistant re-
quirements of 1000 hours salt spray could not be
met at this thickness. An anodic film thickness of 
.0008 inch to .0010 inch was necessary to meet 
the corrosion requirements; however, absolute re-
flectance values at this thickness were in only 
the mid-forty to low fifty percent range. 
3. Pigmentation. The best pigmentation results were 
obtained with the induced precipitation of lead 
sulfate from a complexed acetate solution with 
soluble barium, strontium, or calcium salts. The 
lead sulfate is dissolved in an acetic acid solution 
of ammonium acetate, and when the anodic film 
containing a soluble barium ion such as the ace-
tate is immersed, a dense fine precipitate is formed. 
This precipitation proceeds slowly but steadily and 
impregnates deeply. 
4. Sealing. The corrosion resistance of the anodic 
film was increased by a further sealing treatment 
in a polyorganosiloxane after boiling water seal-
ing. The polyorganosiloxane provides such a good 
paint base that even after 1250 hours of exposure 
in the salt spray, the surface can be painted with 
the NASA white enamel with excellent results. 
Notes: 
1. Another sealing material based upon a benzyl 
alcohol solution of fluorochemical surfactants and 
carboxylic acids gave excellent results in salt spray 
testing. 
2. Neither the polyorganosiloxane seal nor the fluoro-
chemical seal was affected by welding at a dis-
tance of one inch from the center of the bead. 
Both materials materially increased the dielectric 
breakdown voltage of the anodic film, with the 
siloxane being better in this respect. 
The problem: 
• To develop a white anodize for the aluminum sur- 
face of a space vehicle that would have the surface 
reflectance equivalent to the white enameled surface 
now in use, would meet high corrosive resistance 
requirements and would result in a weight reduction 
over previous methods.
(continued overleaf) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000144 2020-03-16T17:57:39+00:00Z
3. Documentation is available from: 	 Patent status: 
Clearinghouse for Federal Scientific 	 Inquiries about obtaining rights for the commer-
and Technical Information 	 cial use of this invention may be made to NASA, 
Springfield, Virginia 22151	 Code GP, Washington, D.C. 20546. 
Reference: TSP69-10144	 Source: K. H. Dale 
of Reynolds Metals Co. 
under contract to 
Marshall Space Flight Center 
(MFS-14600) 
Brief 69-10144
	
:	 Category 05


Advances in aluminum anodizing

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