Improvement of the atmospheric corrosion resistance of materials used in connectics. Surface treatments by ion implantation

Tests of corrosion of a material, constituted of brass covered with an elec trochemical nickel coating (thickness approximate to 5 mu m) and with a gol d coating (thickness approximate to 0.4 mu m or approximate to 1 mu m), use d in electrical contact applications, have been carried out in humid synthe tic air with low contents of NO2 (0.2 vpm), SO2 (0.2 vpm) and Cl-2 (0.01 vp m). The results obtained show that the corrosion products are well localise d on the surface. The aggregates formed are principally constituted of basi c nitrate, sulphate and chloride of nickel and zinc. These studies showed t hat the corrosion of the material is due to the presence of porosities in t he gold and nickel layers. X-ray analysis (SEM/EDS) revealed the presence o f carbon in these porosities, probably related to the presence of organic c ompounds in the electrolytic coating baths. During the galvanic corrosion o f nickel and zinc, the carbon is rejected to the periphery of the aggregate s. The amount of carbon was determined by Van De Graaff analysis, by (d,p) nuclear reaction. Some treatments of the material by ion implantation (tita nium or titanium and nitrogen or helium) have been realised in order to sup press the porosities of the gold layer. These treatments lead to a remarkab le improvement of the corrosion resistance of the material. (C) 2000 Academ ie des sciences / Editions scientifiques et medicales Elsevier SAS.