Lithium compatibility of insulator coatings fabricated by RF sputtering method

The development of insulating coatings is one of the most important subjects in fusion reactor liquid lithium blankets. AlN, Y2O3 and Er2O3 are thought to be potential candidate materials for ceramic coatings because of their high electrical resistivity and high compatibility with liquid lithium. In this study, the coatings of Er2O3, Y2O3 and AlN were fabricated by RF sputtering method. After fabrication, some of the coated specimens were annealed or immersed in liquid lithium. In the case of Y2O3 or Er2O3, coatings had many circular pits on the surface after annealing at 673 and 773 K. The coatings which were immersed in liquid lithium were peeled off from the substrates. It is considered that the circular pits were formed by the heat of liquid lithium and the coatings were peeled off from the substrates. In the case of AlN coatings, specimens which were annealed at 673 and 773 K formed no pit or crack on the surfaces, but the coatings which were immersed in liquid lithium were almost lost. The AlN coatings contain 5–10 at% of oxygen as aluminum oxide. It is suggested that this aluminum oxide formed pits and cracks on the surfaces by reacting with lithium and the coatings peeled off from the substrates.