Comparative study of the initial stage sintering behaviour of micro- and nano-size dense spherical silica particles

The initial stage sintering behaviour of dense spherical silica particles as a function of particle size in the range of 100-370-nm has been studied. Three powders of dense spherical silica particles (average size 370, 150 and 100-nm) with a sharp size distribution were synthesised by controlled hydrolysis of a tetraethylorthosilicate precursor. Sintering was performed in a conventional electrical furnace and the initial compact was not put under any forming mechanical pressure. The shrinkage was monitored indirectly by measuring the specific surface area of the samples using nitrogen adsorption at 77-K. As the size approaches 100-nm, the activation energy decreases ca. one order of magnitude (125-140-kcal-mol^-1 for d ≥ 150 ≥ nm and 11 ≥ 13 ≥ kcal ≥ mol^-1 for d ≃ 100 ≃ nm). The authors propose that a densifying sintering mechanism, lattice diffusion from grain boundary or/and grain boundary diffusion, prevails throughout the particle size range under investigation.