Di Fonzo, Fabio. Alumina-stabilized coatings under irradiations: towards future generation nuclear systems

Principal Investigator
First Name:
Last Name:
Di Fonzo
Istituto Italiano di Tecnologia
Technologist-Group Leader
Team Members:
Name: Institution: Expertise: Status:
Matteo Vanazzi Center for Nano Science and Technology (CNST) - IIT Design of radiation experiments Graduate Student
Meimei Li Argonne National Laboratory Radiation Effects, Material Characterization Post Doc
WEIYING CHEN Argonne National Laboratory TEM Graduate Student
Experiment Details:
Experiment Title:
Alumina-stabilized coatings under irradiations: towards future generation nuclear systems
Describe the work that you are proposing in detail. Please include as many specifics as possible (e.g., dose, dose rate, ion energy, types of ions, beam line x-ray energy, irradiation temperature, analysis temperature, atmosphere, etc.):
In the present study, different types of coating will be considered: - pure Al2O3 coatings on TEM grids - doped Al2O3 coatings (specifically, SiO2, Y2O3, ZrO2 or La2O3 doped-Al2O3) on TEM grids The chemical composition of the doped samples will be tailored according to the relative solubility limits and the physical interactions between the elements inserted in the alumina matrix. Dopant concentration will be settled from 3 to 20 wt.% for each dopant. Single element and multiple elements doping (i.e. co-doping) will be used to enhance further the stabilizing effect. For each materials - either pure or doped alumina - films will be firstly deposited on monocrystalline salt substrates, then detached and moved to TEM grids. An ideal mesh around 2000 will be used, to maximize the TEM resolution. Cu- and Mo-based grids will be selected, to investigate the middle and high temperature regimes, respectively. Samples (ten to twenty samples) will be sent ready for testing, thus no further preparation will be required. We are planning to use different ions, but with similar nuclear properties. This will be crucial to confirm our previous data and produce a comprehensive picture of ion-induced phenomena in amorphous/nano-crystalline alumina. Particularly, Kr ions will be used, due to the long expertize accumulated in IVEM with this specific element. Specimens will be irradiated with a dose rate in the range of 1012 ions/cm2/sec, up to 10-20 dpa per sample. Thus, each irradiation test will take from half to one day to be completed. Background temperature will be tuned from 600 to 1100°C, depending on the specific application and the available beam time. A major concern will be devoted to the high-temperature range, to study the evolution of alumina-based systems in the operative conditions (800°C) and accidental scenarios (1100°C). A more detailed test matrix will be produced later, in collaboration with the IVEM staff. Real time recording of defect nucleation and evolution will be captured on the high speed CCD camera with 200 frames/second, so is their number density and size distribution. 3D reconstruction of all the sample defects will be generated using a rotating holder which will give a comprehensive visualisation of the coating structure and second phases distribution. Irradiated samples will be analysed also using RAMAN, XRD and XRR, FTIR, and EDX, at the IIT facilities. We will examine the crystalline size and fraction, the formation and evolution of crystalline phases and, locally, the chemistry of the different doped compounds.
Technical Abstract
Next generation nuclear power plants are meant to outperform current ones in terms of efficiency, fuel utilization, safety and waste production. Different fission reactor concepts have been proposed as GIV candidates. Lead-cooled Fast Reactors (LFRs) are particularly interesting due to the intrinsic safety features brought about by lead as coolant. However, the development of LFRs is linked to the availability of suitable materials solutions. The greatest challenges in this sense arise from the extremely corrosive environment: at the foreseen temperature - above 500°C - typical corrosion rates produced on bare steels are not acceptable and protective methods are required. In this framework, some of the most interesting solutions are based on the use of bulk alloys, surface-alloying techniques or coatings. In the last years, researches of the IIT have studied an amorphous/nano-crystalline Al2O3 coating produced by Pulsed Laser Deposition (PLD) for liquid metal-cooled nuclear systems. Up to now, the results indicate that the PLD-grown Al2O3 is a suitable candidate for protecting steels in lead and Pb-alloys, at temperatures up to 600°C. Moreover, the alumina coatings have already been irradiated with heavy ions in previous campaigns. The positive outcome of these tests has granted ceramic coatings developed by IIT a special mention as one of the most enabling technologies for LFRs by the DOE report “Research and Development Roadmaps for LFRs”. The main feature behind these promising evidences have been identified in the amorphous/nano-crystalline structure of alumina films, which confers a unique assemble of strong adhesion, metal-like mechanical properties and radiation-tolerance. However, because these properties depend strictly on the amorphousness, further studies are required to evaluate the amorphous to crystalline transition under irradiation, and how to control it. The stabilization of the pristine alumina seems even more relevant now since industrial companies such as Westinghouse aim to increase further the operation temperature, up to 800°C. In order to allow these economic advantages and push forward the technological development, new solutions are demanded. In this framework, we propose chemical doping as a valid strategy to tune the crystallization kinetic of Al2O3-based protective coatings. Different compounds have been added to the pure alumina: Cr2O3 and Y2O3 have been selected to anticipate or retard, respectively, the crystallization threshold. In December 2018, doped alumina has been irradiated for the first time, at the IVEM-tandem facility. The most relevant result has been accomplished at 800°C, above the crystallization temperature of standard alumina. Here, Y2O3 dopant is able to preserve partially the amorphous matrix, increasing also the overall radiation-tolerance. Thanks to the stabilization effect at elevated temperatures, doping prevents the formation of the brittle alumina structure, tackling traditional phenomena under irradiation such as voids formation and intergranular swelling. This project represents a continuation of the work started last year at the IVEM facility. New types and concentrations of dopant will be compared, to find the best performer in stabilizing the alumina amorphous matrix. Tests will be focused to the higher temperature levels (up to 1100°C) to assess the feasibility of Al2O3-based coatings for high-temperature nuclear power plants
Conference Publications
Name Title
Fabio Di Fonzo Kinetic study on the evolution of nanoceramic coatings under heavy ions irradiation
Fabio Di Fonzo Kinetic study on the evolution of nanoceramic coatings under heavy ions irradiation
Fabio Di Fonzo Radiation tolerance of stabilized alumina coatings: an in situ irradiation study