NIU Yan;F.GESMUNDO;WU Weitao;ZENG Chaoliu;F.VIANI;(State Key Laboratory for Corrosion and Protection,Institute of Corrosion and Protection of Metals,Chinese Academy of Sciences,Shenyang.110015,China)(Istituto di Chimica,Facolta'di Ingegneria,Universita'di Genova,Fiera del Mare,Pad.D,16129 Genova,Italy)Manuscript received 3 July 1995