Examination of Non-Hexavalent Chromium, Low-Volatile Organic Compound (VOC) Alternative Sealers for MIL-DTL-13924D Black Oxide Coatings on Ferrous Substrates

Report No. ARL-TR-8809
Authors: Thomas Considine, Jack Kelley, Thomas Braswell
Date/Pages: September 2019; 31 pages
Abstract: Military specification MIL-DTL-13924, Detailed Specification: Coating, Oxide, Black, for Ferrous Metals, is the mainstay for finishing unpainted ferrous and stainless steel components for firearms, fasteners, tooling, and other mechanical components for the military. Black oxide coatings provide mild corrosion resistance and minimize light reflection. A chromic acid (Cr(VI)) post rinse is required for enhancing corrosion resistance of the coating. It has been known for quite some time that hexavalent chromium is a risk to both human health and the environment. In April 2009, a memo was released from the Office of the Secretary of Defense that specifically directed the military to approve the use of alternatives to Cr(VI) where they can perform adequately for the intended application and operating environment. This effort examines the efficacy of non-hexavalent chrome sealers and passivating rinses to replace the required chromic acid. A total of 11 candidates along with the baseline were tested. Four candidates demonstrated excellent overall performance and exceeded that of the baseline Cr(VI) rinse.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2019