Patent ID: 6099714
Filing Date: 2000-08-08
Classification: C25D

Abstract:
A method of electrocating a tin or tin plated article with a non-hexavalent trivalent chromium oxide and/or trivalent chromium hydroxide protective coating comprising:cleaning the tin or tin plated article,making the cleaned article a cathode of an electrolytic cell having a dilute sodium carbonate solution to provide a clean reactive surface tin or tin plated article,rinsing the clean reactive surface tin or tin plated article,placing the rinsed clean reactive surface tin or tin plated article as a cathode in an electrolytic trivalent chromium electrolyte which is a trivalent chromium composition free of chromium complexing agents and said trivalent chromium composition having a pH of about 2.25 to about 2.40 and comprises a trivalent chromium compound selected from the group consisting of potassium chromium sulfate, chromium sulfate chromium chloride and hydrates thereof; andapplying electrical current to the cathode for about 2 to 10 seconds to provide a trivalent chromium oxide and/or hydroxide protective coated tin or tin plated article.