ACID DEPOSITION EFFECTS ON MATERIALS - EVALUATION OF NICKEL AFTER 4 YEARS OF EXPOSURE

The atmospheric corrosion of nickel after 4 years of exposure inside a sheltered box has been investigated. Quantitative evaluation of corro sion attack resulted in a linear relation between the weight increase of nickel and the sulfur dioxide concentration. Analysis of corrosion products by x-ray photoelectron spectroscopy combined with diffuse ref lectance infrared Fourier transform spectroscopy and x-ray powder diff raction agreed with previous conclusions and suggested the initial for mation of an amorphous basic-nickel sulfate with less protective abili ty and subsequent formation of a crystalline basic nickel sulfate with higher protective ability. A carbonate was also detected, more abunda nt at lower weight increases. Conductivity of precipitation correlated with the weight increase of nickel but not SO much as SO2. High level s of this parameter are related to high concentrations of the differen t ions in precipitation. A complementary exposure program was performe d to compare actual exposure conditions inside and outside the sample box. It was concluded that the SO2 deposition outside and inside the s ample box differ approximately by a factor of 10. This difference coul d be separated into air flow conditions (a factor of 2) and concentrat ions (a factor of 5).