Chrome(VI)-free black passivates for surfaces containing zinc

摘要

Treatment solution contains first carboxylic acids with 1-8 carbon atoms and having no polar groups with the exception of the carboxyl group, second carboxylic acids with 1-8 carbon atoms having polar groups, 2-400 mmol/l chromium ions and 50-2000 mmol/l nitrate ions. The total concentration of carboxyl groups in the first carboxylic acids is 5-150 mmol/l. The total concentration of carboxyl groups in the second carboxylic acids is 5-150 mmol/l. The ratio of concentration of nitrate ions to chromium ions is at least 1. Independent claims are also included for the following: (1) Composition producing the above treatment solution by diluting with water; and (2) Method for the black passivation of zinc-containing surfaces using the treatment solution.