High performance ceramic coating for DEMO Breeding Blankets

This Ph.D work focuses the characterization of alumina (Al2O3) ceramic coating as barrier against hydrogen permeation and corrosion in heavy liquid metals as well as the development of custom made Atomic Layer Deposition facility. The study is of particular relevance on the development of the advanced nuclear fusion DEMO reactor. One of the major bottleneck for the development of DEMO breeding blanket is the degradation of candidate structural steels (ferritic-martensitic eurofer97) at high temperature by means of corrosion and tritium permeation. The most promising route available for an attempt to reduce hydrogen permeation and mitigate corrosion attack is the application of surface ceramic coatings. Al2O3 is considered from the seventies the major barrier candidate, thanks to its chemical inertia in heavy liquid metal and stability even at high temperature. In order to meet requirements, a room temperature PLD process is proposed along with a custom made ALD facility, according to a bottom-up approach. Eurofer97 disks are covered starting with di erent morphologies and nally focused on compact and dense amorphous alumina. Performances as hydrogen permeation barrier are tested in PERI II facility up to 923K obtaining a promising PRF result close to 105. Short-term (1000h) corrosion tests in static eutectic Pb-16Li at 873K are performed at ENEA Brasimone. SEM analysis reveal that compact amorphous alumina performs as barrier against corrosion-dissolution by heavy liquid metals. Characterization of the PLD-grown coating is also performed by SEM and AFM analysis. Also, development of a custom made ALD is carried out. Set up of fundamental parameters in order to de ne the so called ALD regime are de ned for the most common metal oxides, namely alumina and titania. A rst of kind thermal cycle tests in air demonstrate the adhesion and barrier potential of alumina grown by ALD. This thesis is structured as follow: Chapter 1 introduces fusion reactors design with a focus on breeding blanket materials challenge. Chapter 2 details the main relevant phenoma in breeding blankets such as gaseous permeation and corrosion by heavy liquid metals. Chapter 3 is devoted to describe the Ph.D. work results for the ceramic coating on eurofer97 steels and the development of the ALD facility. In Chapter 4 conclusions and remarks. Chapter 5 describes materials and method used in this Ph.D work.