AMS-QQ-P-35 (which replaced federal specification QQ-P-35) is an SAE standard used in the aerospace industry to passivate stainless steel parts. AMS-QQ-P-35 recommends the use of different concentrations of nitric acid (with and without chromates), and these solutions are used either at ambient temperatures or heated. The type of stainless steel that is being passivated dictates the nitric acid solution that should be used. In addition, the aerospace industry also has their specific list of preferred nitric acid passivation solutions that are variations of the AMS-QQ-P-35 solutions. Basically, this requires aerospace metal finishing job shops to maintain several passivation tanks (as many as four or more) in order to meet all of their aerospace customers' requirements. ASTM (American Society for Testing and Materials) has issued a specification for stainless steel passivation that allows the use of citric acid solutions as an alternative to nitric acid solutions (ASTM A967-99). This paper describes the results of an evaluation of citric acid solutions used to passivate stainless steel alloys for aerospace applications. The evaluation includes sample preparation of stainless steel for conducting passivation tests, design of experiment studies to determine optimum operating range for nitric and citric acid solutions, and comparison of AMS-QQ-P-35 nitric acid passivation solutions with citric acid solutions. Conclusions state the effectiveness of citric acid to passivate stainless steel, and the potential to have citric acid replace nitric acid passivation solutions that are currently being used in the aerospace industry.
Passivation of aerospace stainless steel parts with citric acid solutions
2002
13 Seiten, 8 Bilder, 5 Tabellen, 5 Quellen
Conference paper
Storage medium
English
ASTM-Norm , Betriebsbereich , Chromoxid , Eisen , experimentelle Untersuchung , Flugzeugbau , Korrosionsbeständigkeit , Korrosionsprüfung , Korrosionsschutzschicht , nichtrostender Stahl , Oberflächenveredlung , Passivierung , Raumfahrtindustrie , SAE-Norm , Salpetersäure , Salzsprühprüfung , Zitronensäure
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