Maximum Incorporation of Oxygen Radicals, O^- and O₂^-, into 12CaO·7Al₂O₃ with a Nanoporous Structure

The effects of oxygen partial pressure ( p O 2 ) up to 400 atm on the generation of active oxygen radicals in 12CaO·7Al 2 O 3 (C12A7) was examined using a hot isostatic pressing technique. Concentrations of superoxide (O 2 - ) and oxygen anion radicals (O - ), which were analyzed from a combination of electron paramagnetic spin resonance (EPR) and Raman spectroscopy, increased with p O 2 . The total concentration of the radicals reached 1.7 × 10 21 cm 3, which is comparable to the theoretical maximum, confirmed that dominant radical incorporation process is O 2 - (cage) + O 2 (atmosphere) → O - (cage) + O 2 - (cage). The radical incorporated C12A7 has a large magnetic susceptibility that obeys Curie's law down to 2.5 K without magnetic ordering, although a weak exchange interaction was suggested by the line narrowing of the EPR signal.