Preparation of Mg and Al phosphate coatings on ferritic steel by wet-chemical method as tritium permeation barrier

Layers of Mg or Al phosphate were prepared on type 430 ferritic stainless steel (SS430) by wet-chemical methods as tritium permeation barrier. Disk-type specimens of SS430 were first coated with ZrO₂/ZrO₂ or ZrO₂/Al₂O₃ layers (100 nm) by sol-gel and electrolytic deposition techniques. Then, the phosphate layers were prepared by dip-coating method; the total thickness of coating was 200 nm. The permeation rate of hydrogen was measured at 300-600°C under driving pressure of 0.1 MPa. The Mg or Al phosphate layers provided significant barrier effects, and the permeation reduction factor observed under the present conditions was 200-3000 against that of Pd coated 430 specimen. Further investigation, however, was required to improve the stability at high temperatures.