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164 Annual Report 1999 PL0001581

9.3 Ion Assisted Palladium Treatments for Improved Corrosion Resistance of Window in the Electron Beam Dry Scrubber Process by S.D.Barson0, P.Skeldon", G.E.Thompson0, A.Kolitsch2), E.Richter2', E.Wieser2>, J.Piekoszewski, A.Chmielewski3), Z.Werner

Titanium foil windows have been employed in the Main results may be concluded as follows: dry scrubbing of flue gases by electron beam irradia- 1. Palladium coatings, of up to 415 nm thickness, tion, with the window lifetime limited by corrosion. deposited upon titanium foil by evaporation, As part of a programme aimed at improving the life- ion beam mixing, ion beam assisted deposition and time of windows, the corrosion resistance of titanium plasma source ion assisted deposition result in foil has been assessed following palladium surface significant improvements in the corrosion resistance treatments applied by vacuum evaporation, ion beam of the foil in 0.1M H2SO4 and 0.1M HNO3 at 80°C. mixing, ion beam assisted deposition and plasma source ion assisted deposition, with production of pal- 2. Corrosion of the coated foil is negligible during ladium layers up to about 400 nm thick. For evalua- immersion in 0.1M H2SO4 and 0.1M HNO3 at 80°C tion of corrosion behaviours, immersion tests and po- for times up to at least 2000 h. The loss of palladium, tential-time and potentiodynamic polarization measu- as determined by EDX and RBS analysis, is rements were carried out, mainly in 0.1M H2SO4 and negligible. 0.1M HNO3 environments at 80°C which approximate 3. The adhesion of the coatings to the titanium sub- possible conditions in plant. The foil surfaces were strate is weakened during immersion in 0.1M H2SO4 examined by scanning electron microscopy, Ruther- at 80°C, with detachment of the coating occurring in ford backscattering spectroscopy and nuclear reaction removal of specimens from the acid after 1000 h analysis to determine the nature of surface degradation immersion. However, there was no significant and changes in surface compositions. corrosion of the titanium substrate at sites where the coating had detached. The results indicated major improvements in the 4. The detachment of the coating proceeds by attack corrosion resistance of the titanium foil from all palla- at or close to the coating/substrate interface, which dium treatments, with surfaces undergoing relatively may be facilitated by stresses in the coating and minor or negligible corrosion following immersion substrate and the presence of an film at the testing for up to 2000 h. However, the coatings often suffered loss of adhesion with extended periods of interface. immersion in H2SO4 either locally or generally, pos- 1} sibly associated with the presence of a thin oxide layer Corrosion and Protection Centre, University of at the interface between the coating and the substrate. Manchester Institute of Science and Technology, P. O. Box 88, Manchester M60 1QD, U.K. The optimum performance was found for coatings 2) produced by ion beam assisted deposition and plasma Forschungszentrum Rossendorf e.V., Institute of source assisted deposition. The coated foil revealed Ion Beam Physics and Materials Research, P.F. 510119, 01314 Dresden, Germany significantly increased open-circuit potentials 3) compared with untreated titanium, which assists pro- Institute of and Technology, tection of the titanium foil when the coating is deta- 16 Dorodna str., 03-195 Warszawa, Poland ched locally from the substrate.

9.4 On the Laboratory-Unit Field Test of Palladium-treated Titanium Foil for Dry CM CO Scrubber Application by S.D.Barson", P.Skeldon0, G.E.Thompson1', J.Piekoszewski, A.Chmielewski2', J.Licki2), O B.Sartowska2), Z.Werner, E.Richter3', E.Wieser3) o 13 Titanium foil of about 50 um thickness is The palladium was deposited on the foil by ion Q_ smployed for electron transparent windows in the beam assisted deposition (IBAD) and plasma source slectron beam dry scrubber process. The electrons ion assisted deposition (PSIAD), with deposition con- induce reactions in the flue gas leading to reduced ditions selected to provide five types of coating in levels of SOT and NOX. The window suffers corrosion total. Untreated titanium windows were also exposed during operation of the process. Previous laboratory to similar flue gas conditions. The untreated titanium studies demonstrated enhanced corrosion resistance of suffered general corrosion and extensive fine pitting. the foil by palladium coating. Here, the results of The performance of the coated foil was influenced examination of a palladium-coated titanium window greatly by the adhesion of the coating, which was following service in a laboratory set-up electron beam reduced during exposure to flue gas. In places where dry scrubber plant are reported. the coating remained attached to the foil, the titanium surface was unaffected by corrosion, confirming the