ZINC COATINGS FOR PROTECTION OF COLUMBIUM FROM OXIDATION AT ELEVATED TEMPERATURES

摘要

Zinc coatings may be applied to columbium by vacuum distillation at 1450 F, hot dipping at 1000 to 1300 F, aqueous electroplating, or cladding. A conditioning treatment consisting of about 16 hours at 1600 F in air is required to obtain maximum protection at higher temperatures. The service life of a properly conditioned 6-mil coating is about 1000 hours at 1800 F and 70 hours at 2000 F. The columbium-zinc intermetallics, which form during application and conditioning of the coating, decompose between 1892 and 2048 F.nZinc coatings exhibit remarkable self-repair properties and re?duce or eliminate contamination hardening of the columbium substrate. The ability to repair relatively large defects is associated with the high zinc vapor pressure over the intermetallics. Zinc vapor oxidizes to ZnO over the defect, arresting the columbium-oxidation reaction. The vapor also reforms intermetallic layers under the oxide. Contamination hardening of the sub?strate is eliminated for 1000 hours at 180Q F by a 10- to 12-mil coating.