关键词：柠檬酸;耐腐蚀;硝酸;被动;污染控制;不锈钢
摘 要：John F. Kennedy Space Center (KSC) has equipment and processes which require the passivation of stainless steel. The standard practice for passivation uses nitric acid. While nitric acid exhibits excellent performance, there are a number of environmental and safety issues: nitrogen oxide (NOx) emissions are considered greenhouse gases, NOx are volatile organic compounds that contribute to smog, NOx increase nitrogen loading (oxygen depletion) in bodies of water, nitric acid can remove beneficial heavy metals (nickel, chromium, etc) from surfaces, and worker safety issues. The longtime military specification for passivation of stainless steel was Federal Specification QQ-P-35 (Passivation Treatments for Corrosion-resistant Steel), but that has been cancelled in favor of American Society for Testing and Materials (ASTM) A 967 (Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts) and Aerospace Material Specifications (AMS) 2700 (Passivation Treatments for Corrosion-resistant Steel). Both of the new specifications allow for the use of citric acid in place of nitric acid. In addition, KSC also uses NASA-STD-5005 (Standard for the Design and Fabrication of Ground Support Equipment) and ASTM A 380 (Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment, and Systems). The primary objective of this effort is to demonstrate and validate citric acid as an alternative to nitric acid for the passivation of stainless steels. Citric acid offers a variety of benefits: it is naturally occurring and biodegradable; upon disposal, it is rarely classified as a hazardous waste; it does not remove beneficial heavy metals from surfaces; and there are no toxic fumes created during the passivation process. This project is follow-on to United Space Alliance (USA) work to optimize the parameters for the use of citric acid and verify effectiveness. USA evaluated the following parameters during their effort: concentration, temperature, and dwell time. This project will use the results from that testing to determine what process parameters will be used in the preparation of test coupons. This Test Protocol contains the critical requirements and tests necessary to qualify citric acid as an alternative to nitric acid for use at KSC. These tests were derived from engineering, performance, and operational impact (supportability) requirements defined by KSC participants. A Test Report will document the results of the testing as well as any test modifications made during the execution of the testing. The Test Report will be made available as a reference for future pollution prevention endeavors by other NASA centers, the Department of Defense, and commercial users to minimize duplication of effort. Users of this Test Protocol should check the project's Test Report for additional test details or minor modifications that may have been necessary in the execution of the testing. The technical stakeholders will have agreed upon test procedures modifications documented in the Test Report.