An in-situ real-time synchrotron-based grazing incidence X-ray diffraction was systematically used to investigate the crystal structural evolution of carbon fiber reinforced carbon matrix (C/C) composite impregnated with FLiNaK molten salt during the heat-treatment process. It was found that the crystallographic thermal expansion and contraction rate of interlayer spacing d
002 in C/C composite with FLiNaK salt impregnation is smaller than that in the virgin sample, indicating the suppression on interlayer spacing from FLiNaK salt impregnated. Meanwhile the crystallite size L
C002 of C/C composite with FLiNaK salt impregnation is larger than the virgin one after whole heat treatment process, indicating that FLiNaK salt impregnation could facilitate the crystallization of C/C composite after heat treatment process. This improved crystallization in C/C composite with FLiNaK salt impregnation suggests the synthetic action of the salt squeeze effect on crooked carbon layer and the release of internal residual stress after heating-cooling process. Thus, the present study not only contribute to reveal the interaction mechanism between C/C composite and FLiNaK salt in high temperature environment, but also promote the design of safer and more reliable C/C composite materials for the next generation molten salt reactor.
Yiyang Liu,Rongshan Lan,Changwu Dong,Kun Wang,Xiaobin Fu,Hongtao Liu,Yuan Qian,Jianqiang Wang
The new salt heating magic-angle spin (MAS) system for high-temperature nuclear magnetic resonance (HT-NMR) is achieved by a laser heating beam coupled with optical fiber. The formation of a sodium ion-doped crystal KF phase is revealed in FLiNaK ternary eutectic salt (46.5%LiF–11.5%NaF–42.0%KF), which is considered unable to exist at room temperature according to its phase diagram. Density functional theory (DFT) simulation proved that Na+ ion-doped crystal is clearly ascertained to develop with the solidification of the melt. Temperature dependence, relaxation, and variable contact time cross-polarization NMR studies provide insights into the unique dynamics and the spatial scale of the doped Na+ ions in KF crystals, which exhibit faster ionic vibration due to the weakening of coordinated interactions from the ambient F– ions.
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