Wustite-induced formation of sp³-rich faceted carbon foam: The key role of cooling rate on sp³-abundance (and oxide crystal-habit) control

We report the formation of a novel faceted carbon-foam (CFM) phase by re-crystallization of recently discovered sp³-rich α−Fe filled CFM. The formation of this novel carbon material is found by increasing the cooling-rate factor after the annealing stage. High cooling rates can therefore create the right thermodynamic conditions for FeO crystallization with consequent modification of the carbon-surface-characteristics and sharp increase in the sp³-carbon content. In addition a possible dependence of the sp³ content on the crystal-habit of the encapsulated oxide is found. This observation is confirmed by additional measurements in CFM-samples filled with variable quantities of maghemite/hematite phases obtained with slow cooling experiments. This method has a crucial importance since it can allow the control of surface-carbon-characteristics by modification of the encapsulated oxide crystal-habit phases.