In Situ Whisker-Reinforced AlPO4-Modified β-Eucryptite Glass-Ceramic: I, Morphology and Crystallization Kinetics

Abstract

A whisker-reinforced glass-ceramic composite in the Li2O-Al2O3-SiO2-P2O5 system has been fabricated by a single-stage process that simultaneously forms the glass-ceramic material and whiskers of TiO2in situ. The method utilizes typical glass-ceramic processing techniques and requires precise addition of a TiO2 nucleation agent during the glass-melting operation, followed by controlled nucleation and crystallization. The maximum nucleation temperature, 740°C, was determined by differential thermal analysis (DTA), and the result was confirmed by scanning electron microscopy (SEM) of the microstructures formed by nucleation/isothermal crystallization heat treatments. The apparent activation energy for crystallization of the material was determined to be 285 ± 3 kj/mol. The average aspect ratio of the TiO2 whiskers depends on temperature and time during crystallization. The X-ray diffraction patterns of the in situ composite show that eucryptite(ss) and rutile exist as two different phases; no additional phases were observed. Elemental X-ray mapping by electron microprobe indicates that these highly crystallized composites consist of modified β-eucryptite glass-ceramic matrix and acicular grains of TiO2.