High-temperature synthesis of finely dispersed oxide materials and C12A7:e electrides in carbon nanoreactor conditions

Solid-state transformations of the oxide core in core-shell structures Oxide@C consisting of oxide nanoparticles covered with a carbon coating were studied at temperatures of up to 1500$^\circ$ C. It is shown that such coating can stabilize the size of the oxide core nanoparticles for alumina, zirconia, calcium and lanthanum aluminates and act as a shell of a nanoreactor where phase and chemical transformation can take place. For ZrO$_2$@C and Al$_2$O$_3$@C it is demonstrated that it is the preservation of the small particle size that accounts for the preservation of cubic ZrO$_2$ and $\delta$-Al$_2$O$_3$ until the carbothermal reduction temperatures of the corresponding oxides (above 1400$^\circ$ C for Al$_2$O$_3$). The electride state C12A7:e is shown to be formed in C12A7@C material at temperatures above its melting point. The surface of activated C12A7 was found to have a significant concentration of active OH radicals capable of converting diphenylamine into stable nitroxyl radicals.