Flexible fluorinated graphite foils with high content of (C2F)n phase for slow neutron reflector
Résumé
In order to prepare self-standing and flexible slow neutrons reflectors made with graphite fluoride (GF) of high content of (C2F)n structural phase, graphite foils of different thicknesses were used as starting material for the gas (F2)/solid fluorination. The maximal interlayer distance for GF was obtained with this phase thanks to a stacking sequence FCCF/FCCF; this is mandatory for the efficient reflection of slow neutrons. 71 and 77 % of (C2F)n phase were achieved for graphite foils with thicknesses of 1.0 and 0.1 mm, respectively. The interlayer distances were then of 8.6 Å as expected. The fluorination conditions (static mode, long duration of 24 h and annealing in pure F2 gas for 24 h, temperatures in the 390-460 °C range) were adapted to large pieces of graphite foils (7x7 cm2) in order to both avoid the exfoliation and achieve a homogenous dispersion of fluorine atoms. This process was also efficient for thinner (0.01 mm of thickness) graphitized graphene oxide foil. 56 % of (C2F)n phase and interlayer of 8.6 Å were achieved for this foil when the fluorination was performed at 430°C. Whatever the nature and the thickness of the foil, their flexibilities are maintained.
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