A MODEL OF DIFFUSION VISCOUS MASS-TRANSPORT IN SILICATES DURING LIQUID-PHASE SINTERING

The model of capillary transport of liquid metals driven by shear stre ss resulting from the displacement of menisci [J. W. Nowok, Scripta Me tall. Mater. 29, 931 (1993); Acta Metall. Mater. 42, 4025 (1994)] is a pplicable to liquid-phase sintering of silicate/aluminosilicate glasse s. The movement of a liquid phase between adjacent particles is compar ed with that in capillaries. It appears that the transport property of intergranular melt may be expressed by the viscosity (eta) and volume diffusion (D) parameters if mean displacement of menisci is compared with the mean diffusive jump lengths of atoms/molecules (L). This lead s to the following relation: (gamma/eta)L alpha = D-cap, where alpha a nd D-cap are a specific permeability and volume diffusion coefficient. The use of this model requires the assumption that the diffusing spec ies are also the viscous flow units, and they can be either atoms or s tructural units. This assumption seems to be applicable for depolymeri zed silicate melts if the dominant mass transport is initiated by the diffusion of both nonbridging oxygen and silicon atoms.