HETEROGENEITY, NUCLEATION, SHRINKAGE AND BLOATING IN SOL-GEL GLASS-CERAMICS (THE CASE OF LITHIUM ALUMINOSILICATE COMPOSITIONS)

Sintering of sol-gel powders often leads to porous samples despite the high reactivity of such powders. The influence of heterogeneity comin g firstly from the use of different reagents as gel formers (Si and Al alkoxides) or of a mixed nature (Si-Al ester) and secondly from the h ydro lysis-polycondensation route (mixing in anhydrous condition or pr ehydrolysis of the reagents) was studied for a lithium aluminum silica te composition using differential thermal analysis, expansion-shrinkag e measurements and X-ray diffraction. The effects of the synthesis con ditions on the microstructures is discussed from optical microscopy, s canning electron microscopy and metallurgical observations.