One surface was then polished and cleaned using a protocol designed to eliminate as much preparation-related contamination as possible. This is as follows: The lead surface was polished by hand using a damp abrasive disc (BuehlerMet II ®) to remove visible surface defects and to expose a fresh metal surface. Coupons were then polished using a sequence of diamond polishes with decreasing particle sizes (6μm, 3μm, 1μm Buehler MetaDi ® polycrystalline diamond suspension). A polishing cloth (Buehler MicroCloth ®) was saturated with the appropriate diamond suspension. A custom-made jig fitted to an automatic polisher (Buehler Minimet ® 1000) was used to hold the coupons in place during automated polishing. Coupons were polished for 15min using each diamond suspension followed by rinsing with 2-propanol (99.5%, reagent grade) and cleaning in 2-propanol for 5min in an ultrasonic bath. After polishing with the 1μm diamond suspension, the coupons were ultrasonically cleaned in 2-propanol for 3×5min, with fresh propanol for each cleaning cycle. Polished coupons were stored in 2-propanol until required.
