THE SOLUBILITY OF ALUMINUM IN RARE-EARTH NITROGEN MELILITE PHASES

The incorporation of Al into nitrogen (N-)melilite phases has recently been reported [Cheng and Thompson, J. Am. Ceram. Sec., 77, 143-48 (19 94)]. This occurrence allows simultaneous substitution of Al and O thr ough replacement of Al-O for Si-N bonds and therefore, may offer poten tial improvement to the oxidation resistance properties of original N- melilite, which in the past was a problem that deterred the utilizatio n of N-melilite as a grain boundary phase for Si3N4-based ceramics. In this work, the techniques of X-ray diffraction, scanning electron mic roscopy with quantitative energy dispersive X-ray spectroscopy and sol id state Al-27 and Si-29 nuclear magnetic resonance spectroscopy with magic angle spinning have been used to study the solubility of Al in t he structure of neodymium and samarium N-melilite phases.