Sol–gel prepared Al2O3 coatings for the application as tritium permeation barrier

One of the critical issues in test blanket module (TBM) system is to reduce tritium permeation from Pb–Li into the water/helium coolant. Use of alumina coating is one of the most promising methods to solve this problem. In the present study, well-adhered alumina coatings on ferritic steel substrates were prepared by the sol–gel method. X-ray diffraction (XRD) and field-emission scanning electron microscope (FSEM) were employed to identify the phase and examine the microstructure of the coating. The coating prepared at 500 °C is amorphous, while that prepared at 650 °C is γ-Al2O3. When calcination temperature is elevated to 1100 °C, α-Al2O3 is formed. The surface of the well-adhered coating was smooth and uniform. No spallations and cracks were observed in the coating or at the scale/alloy interface. The grain size of the coating remains very small even at 1100 °C (in the range 30–40 nm for 1100 °C). The thickness of the coating can be controlled by changing aging time and the number of dipping cycles. The flexibility to coat complex geometries by this method, even inside tubes, is guaranteed.