Establishing a quantifiable tarnish timeline for comparison of anti-tarnish processes in metals

Brass samples were controllably tarnished using the thioacetamide accelerated corrosion (ISO 4538:1995) and synthetic sweat (ISO 3160–2:2003) methods. Spectrophotometry, energy dispersive X-ray spectroscopy (EDX) and electrochemical impedance spectroscopy (EIS) were performed on samples tarnished for set exposure times over seven days. Synthetic sweat produced a loose surface corrosion layer, which limited the use of EIS and spectrophotometry, but for the thioacetamide method both measurements produced a continuous change over the time period. EDX was able to observe a continuous change in the surface layer chemistry for both methods over the whole timescale and represents the best characterisation method to establish an equivalent tarnish timeline against which anti-tarnish treated samples can be compared. The current study was conducted using brass, however the method can be used for quantifying tarnish on other metallic systems.


H.N.S. Yousef1, R.J. Cobley2, H.M. Davies1, D.M. James3, S. Mehmood1, E. Sackett1 and J. Sienz1

1. Advanced Sustainable Manufacturing Technologies (ASTUTE), College of Engineering, Swansea University, Swansea SA2 8PP, (UK)
2. Multidisciplinary Nanotechnology Centre, College of Engineering, Swansea University, Swansea SA2 8PP, (UK)
3. The Royal Mint, Pontyclun CF72 8YT, (UK)

Materials and Corrosion, 2015 Vol. 66(10), Pages 1120-1124, doi:10.1002/maco.201407969