SYNTHESIS OF SINTERACTIVE SINGLE-PHASE MICROSTRUCTURE YTTRIUM DISILICATE PRECURSOR POWDER USING HYDROTHERMAL PROCESSING

This paper is the first report of the synthesis of a sinteractive sing le-phase microstructure yttrium disilicate precursor powder using hydr othermal processing. The effect of the pH of the precursor chemicals o n the ease of formation of a single-phase material was investigated us ing x-ray diffraction, TEM, and SEM. Under very acidic conditions (pH 1), the formation of yttrium chloride, in addition to the yttrium disi licate precursors, produced a powder that absorbed moisture, did not s inter well, and produced a two-phase interpenetrating microstructure a fter sintering. At pH 6, yttrium chloride no longer formed, but the in terpenetrating network persisted after sintering. Only under basic con ditions (pH 10) did single-phase yttrium disilicate form after sinteri ng. This work is noteworthy because the calcination time of 1 h requir ed for the formation of this ceramic at 1050 degrees C is over an orde r of magnitude lower than the calcination times of over 100 h required when calcined in the temperature range 900 degrees C to 1150 degrees C, as reported previously by other workers.