Fabrication of ZrO ₂ coatings on ferritic steel by wet-chemical methods as a tritium permeation barrier

Layers of tetragonal ZrO ₂ (180 nm) were prepared on the surfaces of ferritic steel specimens by dip coating and electrolytic deposition techniques. These methods were selected because of their applicability to large and complicated structures. Hydrogen permeation tests were carried out at 300-550°C, and the results were compared with those obtained in the previous study for thinner ZrO ₂ coating (100 nm). Although the thickness of the present coatings was less than twice that of the previous coatings, the permeation reduction factor for the former was larger by an order of magnitude than that for the latter at/below 400°C. Tritium retention in the coatings was also measured after exposure to a deuterium-tritium mixture at 300°C. The obtained results suggest that the permeation rate was determined by transportation through defects in the coatings, and the density of defects penetrating into the coating/substrate interface was significantly reduced by an increase in coating thickness.