document: The dashed curve represents the PuO2 molar fraction on the sample surface. It shows that, following the UO2–PuO2 phase boundaries, rather well established in this compositional range (see Section 4.3 below), the newly formed liquid surface is initially enriched in plutonium dioxide. Subsequently, due to fast diffusion in the liquid phase, the initial sample composition (x(PuO2)=0.25) tends to be rapidly restored. It is however clear, from the simulation, that the fast cooling occurring after the end of the laser pulse leads to onset of solidification before the initial composition is fully recovered in the liquid. A surface solid crust forms then upon freezing before the total liquid mass has crystallised (see insets in Fig. 4). The double inflection during cooling in this case corresponds to the solidification onset on the sample surface (first inflection) and to the disappearance of the last liquid inside the material (second inflection). The highest recalescence temperature represents the solidification point of a composition very close to the initial one (approximately ±0.01 on x(PuO2) in the current example), except for small segregation effects. These latter have been studied also experimentally in the present research, by post-melting material characterisation.
extractive_keyphrases: cooling enriched in plutonium dioxide freezing laser pulse liquid puo2 sample surface simulation small segregation effects solidification surface solid crust uo2–puo2 phase boundaries
abstractive_keyphrases: liquid surface plutonium dioxide post-melting material characterisation