164 Annual Report 1999 PL0001581

9.3 Ion Assisted Palladium Treatments for Improved Corrosion Resistance of Titanium 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 vacuum 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 oxide 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 Nuclear Chemistry 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 DEPARTMENT OF RADIATION DETECTORS 165 anticipated high corrosion resistance provided by the and extensive fine pitting are similar to those found coating. Elsewhere, loss of palladium at different on untreated titanium exposed to the same compo- stages of the test allowed corrosion of the foil by the sition of flue gas. At locations where palladium flue gas. In the worst case, corrosion was similar to remains on the surface for the duration of the test, that of untreated titanium. In other areas, intergranular the underlying foil is free of significant corrosion. corrosion, general corrosion and pitting were in 3. Among the treatments employed, plasma source evidence, although the surface damage was less. A ion assisted deposition, with a high pulse bias, PSIAD coating deposited with a high pulse bias provided the best performance, with about 60% of provided the best performance, with an estimated 60% the coated region being free from corrosion at the of the surface remaining relatively free of corrosion. end of the test period. Main results may be concluded as follows: Further improvements are necessary to the coating 1. The main factor determining the corrosion beha- procedures to provide the required adhesion of the viour of the present palladium-coated window, pre- coatings for windows in commercial plant. pared by IBAD and PSIAD, in the electron beam dry scrubber process is adhesion of the palladium !) Corrosion and Protection Centre, University of coating. The adhesion of the present coatings redu- Manchester Institute of Science and Technology, ces significantly during exposure to the flue gas, P.O. Box 88, Manchester M60 1QD, U.K. with pieces of the coating becoming detached and 2) Institute of Nuclear Chemistry and Technology, the flue gas attacking the revealed titanium. 16 Dorodna str., 03-195 Warszawa, Poland 2. Pitting, intergranular and general corrosion occur at 3> Forschungszentrum Rossendorf e.V., Institute of the locally revealed titanium, the extent and types Ion Beam Physics and Materials Research, P.F. of corrosion being dependent upon the particular 510119, 01314 Dresden, Germany region of the surface. In places, general corrosion

9.5 Thermoelectrically Cooled HRSi Detector of X-Ray Radiation by W.Czarnacki, E.Belcarz, A.Kotlarski, B.Sawicka, T.Sworobowicz PL0001583

A model of the thermoelectrically cooled HRSi The detector energy resolution was tested for silicon detector of X-ray radiation has been developed. radiation of energies in the range 5-60 keV, and for se- Optical feedback was used in the detector. The HRSi veral amplifier shaping time constants (2, 4, 8, 16, and silicon detector consists of: 24 us). Stability of the resolution was verified in mea- 1. Detection device (structure) made of high- surements lasting 8 hours. During tests the HRSi de- resistivity p-type silicon of specific resistivity vice and the first stage of the preamplifier (consisting greater than 40 000 Ohm-cm. In view of poor of the FET and the LED) assembled in vacuum were homogeneity of the available HRSi Si monocrystal cooled down to about -60°C. The best energy resolu- (inhomogeneous distribution of specific resistivity tion was obtained at 4 us shaping time. It amounted to around 40 kOhm-cm across the crystal), 40 356 eV FWHM for the energy 5.9 keV (Fe-55 source), detecting devices have been manufactured in order 391 eV FWHM for the energy 16 keV (Mo-93 sour- to select the best one. The device active area is ce), and to 356 eV FWHM for the energy 59.5 keV about 14 mm2, its active layer thickness - about (Am-241 source). Stability of the energy resolution 2.3 mm. was better than ±15 eV FWHM in 8 hours. The obtained results confirm that the grant objec- 2. Miniature header that houses the HRSi device, a tives (active area surface 10-30 mm2, active layer structure of the 2N4416 Field Effect Transistor FET thickness about 3 mm, energy resolution below removed from its package, a Light Emitting Diode 800 eV FWHM for 5.9 keV line) have been attained. LED, and a temperature-controlling thermistor. The developed model of the thermoelectrically cooled HRSi detector of X-ray radiation and the obtained 3. Charge preamplifier with optical feedback. results of its testing will be used for developing a pro- totype of a HRSi detector with a higher bias voltage 4. Two-stage thermoelectrical cooler and a water- (above 100) and a better energy resolution. cooled radiator made of electrolytic copper.

5. Vacuum chamber equipped with a beryllium win- dow of thickness of about 20 urn