Investigation of ion assisted palladium treatments for improved corrosion resistance of titanium foil in the electron beam dry scrubber process

Titanium foil windows have been employed in the dry scrubbing of flue gases by electron beam irradiation, with the window lifetime limited by corrosio n. As part of a programme aimed at improving the lifetime of windows, the c orrosion resistance of titanium foil has been assessed following palladium surface treatments applied by vacuum evaporation, ion beam mixing, ion beam assisted deposition and plasma source ion assisted deposition, with produc tion of palladium layers up to approximately 400 nm thick. For evaluation o f corrosion behaviours, immersion tests and potential-time and potentio-dyn amic polarization measurements were carried out, mainly in 0.1 M H2SO4 and 0.1 M HNO3 environments at 80 degrees C, which approximates the possible co nditions in a plant. The foil surfaces were examined by scanning electron m icroscopy, Auger electron spectroscopy, Rutherford backscattering spectrosc opy and nuclear reaction analysis to determine the nature of surface degrad ation and changes in surface compositions. The results indicated major impr ovements in the corrosion resistance of the titanium foil from all palladiu m treatments, with surfaces undergoing relatively minor or negligible corro sion following immersion testing for up to 2000 h. However, the coatings of ten suffered loss of adhesion with extended periods of immersion in H2SO4, either locally or generally, possibly associated with the presence of a thi n oxide layer at the interface between the coating and the substrate. The o ptimum performance was found for coatings produced by ion beam assisted dep osition and plasma source ion assisted deposition. The coated foil revealed significantly increased open-circuit potentials compared with untreated ti tanium, which assists protection of the titanium foil when the coating is d etached locally from the substrate. (C) 2000 Published by Elsevier Science S.A. All rights reserved.