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 coming 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 hydrolysis–polycondensation route (mixing in anhydrous condition or pre-hydrolysis of the reagents) was studied for a lithium aluminum silicate composition using differential thermal analysis, expansion-shrinkage measurements and X-ray diffraction. The effects of the synthesis conditions on the microstructures is discussed from optical microscopy, scanning electron microscopy and metallurgical observations.