Applying a Mono-Octadecanethiol Film on Silver and Gold Coin Products

Abstract

Monomolecular anti-tarnish and lubricant layer was utilized in the coining industry for more than ten years, saving millions of dollars each year. However, the benzotriazole (BTA) that formed the monolayer on cupronickel did not react with silver. In recent years, many chemicals were screened for evaluating the bonding strength on silver surfaces. Finally, a mono-octadecanethiol (ODT) film was solidly bonded with silver surfaces in the laboratory utilizing an ultrasonic bath. To apply this technology for industry, the process must be tested in a real production environment, since many unexpected issues needed to be solved just like applying BTA on cupronickel years ago. In this work, several bench tests were conducted on the silver production line at Sunshine Mint. The results illustrated that the mono-ODT film could be applied on silver surfaces with different processes and parameters according to the production conditions. The processes are simple, reliable, and low cost. Based on the test data, the process can soon be fully implemented on the production line.