Examination of codeposited a-C:D-layers in oxygen

In continuation of development work on a method for tritium removal from codeposited layers with carbon the oxidation of diamond like laboratory created DIARC specimen (D/C=0.1, thickness 3.5 μm) is studied in detail in oxygen; it is shown by SIMS, that C-oxidation and D-release proceed parallel. Furtheron, flakes from TEXTOR with thick a-C:D-layers (D/C≈0.04, thickness≈20±5 μm, total boron and metal content 15 weight-%) were oxidised in O2 (21 kPa), showing a stepwise process: At 573 K a weight-loss of 25% was found before rate drops; temperature increase to 623 K leads to gasification of additional 35% with a maximum layer reduction rate of 0.25 μm/h. Complete gasification of the carbon remaining in the ash requires temperatures of up to 773 K. a-C:D-layers are compared with nuclear graphites, indicating, that the latter react much slower in oxygen but not in ozone. Different a-C:D-specimen examined up to now are discussed and for a tritium removal method in oxygen/air a temperature of at least 673 K (160 K higher than the ITER reference value) is proposed.