Ti / Ti-Al Alloys / Implant Alloys / Passivity / Passive FilmsThe stability of passive films on titanium and Ti-Al alloys (Ti-6Al-4V, Ti-6Al-7Nb implant alloys and Ti-50Al intermetallic compound) were studied in 0.5 M H 2 SO 4 electrolyte. Upon exposure to the acidic solution, fast open-circuit activation of native passive films on Ti-Al-V, Ti-Al-Nb and Ti-50Al takes place, whereas pure Ti remains in the passive state. Passivation in an acidic solution leads to a higher protectiveness of the passive films, as well as to a higher stability against open-circuit activation. Surface analytical experiments suggest that the stability of the passive films is related to the amount of oxidized Al in the film. No sites of high-Al content on the surface could be detected after active dissolution, which may indirectly indicate that selective dissolution of Al takes place out of the higher-Al containing phases.
Two experimental loops for operation in research reactor LVR-15 in ÚJV Řež are
recently under preparation: High Temperature Helium Loop (HTHL) and SuperCritical Water Loop
(SCWL). Pure helium will be used as working medium in HTHL and its main physical parameters
are: operating pressure 7MPa, max. temperature in the test section 900°C and flow rate 36kg/h.
HTHL will include helium purification system, system for dosage of impurities (e.g. CO2, H2, H2O,
O2, N2 etc.) and helium sampling. Helium purification experiments and testing of materials in
simulated HTR conditions will take place in HTHL in the future. Main parameters of the SCWL are
25MPa, max. temperature in the test section 600°C, flow rate max. 200kg/h. SCWL will be used for
corrosion tests of candidate materials, studies of water radiolysis at supercritical conditions and for
testing of water chemistry suitable for operation. Both loops possess an irradiation channel with
quite complicated internals design, whose complexity is imposed by current constraints on
constructional materials of nuclear experimental devices, which limit the choice and maximum
surface temperature of material of construction to 500°C for austenitic stainless steel. The working
temperature will thus be attained only in a restricted volume of the test section. The channel
internals will be briefly described. The mentioned loops will represent novel experimental devices,
whose objective is to gain and extend knowledge on materials and environment performance under
the influence of radiation.
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