STRUCTURAL CORRELATION AND STRUCTURAL RELAXATION AT THE FINAL STAGE OF GEL-TO-GLASS TRANSITION IN SILICA

In this work more detailed information is obtained about the final sta ge of the gel-to-glass transition and the interrelations between the g lass network structure and the mechanical properties of thr material a re revealed. The structural modification of silica xerogels was follow ed by measuring Vickers hardness and Young's modulus in parallel with measurements of the network structure by means of IR reflection and lo w-frequency Raman spectroscopies, Two correlations of material propert ies and scales have been found: (i) at annealing temperature, T-a= 100 0 degrees C, the relaxation of the silica. network produces a definite correlation sphere and an increase of Young's modulus to that for vit reous SiO2; (ii) at T-a= 1160 degrees C, a decrease of the mobility of glass-forming units causes a decrease of the correlation radius and a n increase of Vickers hardness to that specific for vitreous SiO2.