Promotion of oxidation in the powder compact: effect of nitrate as raw material on the solid-state reaction forming hexacelsian probed with europium ion

This study presented an investigation into the oxidation promotion within the powder compact of hexacelsian (BaAl2Si2O8), a stable layered inorganic solid during heat treatment, utilizing Eu ion as a probe. Specifically, the solid-state reaction of kaolinite with barium nitrate (Ba(NO3)2) was compared wiht that of kaolinite (Al2Si2O5(OH)4) with barium carbonate (BaCO3) under the presence of Eu ion in the resulting powder compacts. X-ray diffraction pattern revealed that the single-phase hexacelsian was evident in the nitrate-based compact, whereas hexcelsian was slightly converted into celsian in the carbonate-based compact. Despite the higher density of the nitrate-based compact compared to the carbonate-based one, the former exhibited Eu3+ red luminescence, but the latter appeared Eu3+ red and Eu2+ blue luminescence. Therefore, these results indicated that the use of nitrate as a raw material promoted oxidation and the formation of hexacelsian within the powder compact. Therefore, this study developed the method for oxidizing within the reductive inner part of a powder compact.