Thin-film sulfuric acid anodizing as a replacement for chromic acid anodizing

Conference · Wed Mar 01 04:00:00 EST 1995

OSTI ID:102019

Kallenborn, K J; Emmons, J R

Chromic acid has long been used to produce a thin, corrosion resistant (Type I) coating on aluminum. Following anodizing, the hardware was sealed using a sodium dichromate solution. Sealing closes up pores inherent in the anodized coating, thus improving corrosion resistance. The thinness of the brittle coating is desirable from a fatigue standpoint, and chromium was absorbed by the coating during the sealing process, further improving corrosion resistance. Unfortunately, both chromic acid and sodium dichromate contain carcinogenic hexavalent chromium. Sulfuric acid is being considered as a replacement for chromic acid. Sulfuric acid of 10-20 percent concentration has traditionally been used to produce relatively thick (Types II and III) or abrasion resistant (Type III) coatings. A more dilute, that is five weight percent, sulfuric acid anodizing process, which produces a thinner coating than Type II or III, with nickel acetate as the sealant has been developed. The process was evaluated in regard to corrosion resistance, throwing power, fatigue life, and processing variable sensitivity, and shows promise as a replacement for the chromic acid process.

• Research Organization: National Aeronautics and Space Administration, Huntsville, AL (United States). George C. Marshall Space Flight Center
• OSTI ID: 102019
• Report Number(s): N--95-31746; NASA-CP--3298; M--775; NAS--1.55:3298; CONF-9408174--
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
54 ENVIRONMENTAL SCIENCES
ALUMINIUM
ANODIZATION
BRITTLENESS
CHROMIC ACID
CORROSION PROTECTION
CORROSION RESISTANCE
POROSITY
PROTECTIVE COATINGS
SULFURIC ACID