Sintering of silica gel derived from the alkoxysilane solution containing N,N-dimethylformamide

The sintering of three kinds of dried gels with different microstructures prepared from the tetramethoxysilane (TMOS) solutions containing N,N-dimethylformamide (DMF) with varying H₂O]/TMOS] mole ratios and different catalysts was investigated by measuring the pore size distribution, the Vickers hardness, the linear shrinkage and the apparent density of the gels heated to various temperatures. The marked shrinkage of the pores started at temperatures above 900 °C. The temperature required for the conversion of a gel to a pore-free silica glass depended on the average size of the pores contained in the dried gels; the average pore sizes of about 50 Å, 75 Å and 100 Å corresponded to 1040 °C, 1060°C and 1080°C, respectively. The Vickers hardness, the linear shrinkage and the density of the gel showed a corresponding change with a change in heating temperature.