Exchange of hydrogen isotopes in oxide ceramics at room temperature

The decay curves of D and up-take curves of H on the exchange of D implante d into Li2TiO3 for H in H2O vapor caused by exposure to normal-air at room temperature have been measured as a function of exposure time at different implantation concentrations by means of the elastic recoil detection techni que. The re-emission curves of D retained and H up-taken in a specimen by i sochronal annealing for 10 min have been also measured. It is found that th e thermal re-emission of D and H takes place uniformly over the whole speci men due to local molecular recombination in the bulk and that the re-emissi on rates of H and D in the near-surface layers are slower than those in the deeper layers. It is also found that the decay of D caused by the D-H exch ange takes place rapidly in the beginning and the retained amount of D atta ins at a constant level and the retained fraction of D are higher as the in itial implantation concentrations of D are lower. The decay curves of D and the up-take curves of H have been analysed using the mass balance equation s, in which the elementary processes are taken into account according to th e exchange model of one way diffusion from the surface into the bulk. It is shown that the solution of the mass balance equations reproduces well the experimental data. The rate constants of the elementary processes determine d are discussed.