IN-SITU WHISKER-REINFORCED ALPO4-MODIFIED BETA-EUCRYPTITE GLASS-CERAMIC .1. MORPHOLOGY AND CRYSTALLIZATION KINETICS

A whisker-reinforced glass-ceramic composite in the Li2O-Al2O3-SiO2-P2 O5 system has been fabricated by a single-stage process that simultane ously forms the glass-ceramic material and whiskers of TiO2 in situ. T he method utilizes typical glass-ceramic processing techniques and req uires precise addition of a TiO, nucleation agent during the glass-mel ting operation, followed by controlled nucleation and crystallization. The maximum nucleation temperature, 740 degrees C, was determined by differential thermal analysis (DTA), and the result was confirmed by s canning electron microscopy (SEM) of the microstructures formed by nuc leation/isothermal crystallization heat treatments. The apparent activ ation energy for crystallization of the material was determined to be 285 +/- 3 kJ/mol, The average aspect ratio of the TiO, whiskers depend s on temperature and time during crystallization. The X-ray diffractio n patterns of the in situ composite show that eucryptite(ss) and rutil e exist as two different phases; no additional phases were observed, E lemental X-ray mapping by electron microprobe indicates that these hig hly crystallized composites consist of modified beta-eucryptite glass- ceramic matrix and acicular grains of TiO2.