Morphological and chemical changes in nuclear graphite target under vacuum and high-temperature conditions
Stefania De Rosa,
Elisabetta Colantoni,
Paolo Branchini,
Domizia Orestano,
Antonio Passeri,
Gianlorenzo Bussetti,
Lisa Centofante,
Stefano Corradetti,
Martina Marsotto,
Chiara Battocchio,
Cristina Riccucci,
Luca Tortora
Affiliations
Stefania De Rosa
LASR3 Surface Analysis Laboratory Roma Tre, via della Vasca Navale 84, Rome, Italy; INFN, Roma Tre, via della Vasca Navale 84, Rome, Italy
Elisabetta Colantoni
LASR3 Surface Analysis Laboratory Roma Tre, via della Vasca Navale 84, Rome, Italy; INFN, Roma Tre, via della Vasca Navale 84, Rome, Italy; Department of Mathematics and Physics, Roma Tre University, via della Vasca Navale 84, Rome, Italy
Paolo Branchini
LASR3 Surface Analysis Laboratory Roma Tre, via della Vasca Navale 84, Rome, Italy; INFN, Roma Tre, via della Vasca Navale 84, Rome, Italy
Domizia Orestano
INFN, Roma Tre, via della Vasca Navale 84, Rome, Italy; Department of Mathematics and Physics, Roma Tre University, via della Vasca Navale 84, Rome, Italy
Antonio Passeri
INFN, Roma Tre, via della Vasca Navale 84, Rome, Italy
Gianlorenzo Bussetti
Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy
Lisa Centofante
Legnaro National Laboratories (INFN-LNL), Viale dell’Università 2, Legnaro, Padova, Italy
Stefano Corradetti
Legnaro National Laboratories (INFN-LNL), Viale dell’Università 2, Legnaro, Padova, Italy
Martina Marsotto
Department of Sciences, Roma Tre University, Via della Vasca Navale 84, Rome, Italy
Chiara Battocchio
Department of Sciences, Roma Tre University, Via della Vasca Navale 84, Rome, Italy
Cristina Riccucci
CNR- ISMN, Institute for the Study of Nanostructured Materials, Via Salaria Km 29300, Montelibretti, Rome, Italy
Luca Tortora
LASR3 Surface Analysis Laboratory Roma Tre, via della Vasca Navale 84, Rome, Italy; INFN, Roma Tre, via della Vasca Navale 84, Rome, Italy; Department of Sciences, Roma Tre University, Via della Vasca Navale 84, Rome, Italy; Corresponding author. LASR3 Surface Analysis Laboratory Roma Tre, via della Vasca Navale 84, Rome, Italy.
Nuclear-grade graphite is a high-efficiency material, widely used for vacuum applications in nuclear reactors and accelerators as targets facing particle beams. In these contexts, graphite is often exposed to extreme thermal stresses altering its physical and chemical properties. The thermal-induced release of volatile contaminants from targets and the damage of structural components are critical issues that can affect the safety and operation efficiency of beamline facilities. Here, we provide for the first time a detailed picture of the chemical and morphological changes occurring in a nuclear-grade graphite target, obtained through Electrical Discharge Machining (EDM), when exposed in vacuum to high temperatures. The radial temperature gradient induced by the impact of a pulsed energetic (MeV- GeV range) focused particle beams was reproduced by cyclically heating, in the 1300–1800 K temperature range, a disc-shaped graphite target in a vacuum setup. An accurate surface and in-depth chemical analysis of the graphite target was obtained thanks to the high sensitivity (ppm/ppb) of the Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) technique. The chemical maps clearly show the presence of several metal oxides and impurities in the surface and subsurface regions of the untreated sample. Such contaminants were removed because of the thermal treatment in vacuum more or less efficiently, as demonstrated by Thermogravimetric analysis (TGA), X-ray Photoelectron Spectroscopy (XPS), and ToF-SIMS. However, Raman spectroscopy and SEM-EDS revealed that the high-temperature treatment induces a decrease in the crystallite size of the graphite as well as changes in the target surface porosity with the appearance of microvoids, leading the graphite target to be more prone to the breakage.