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

The model of capillary transport of liquid metals driven by shear stress resulting from the displacement of menisci [J. W. Nowok, Scripta Metall. Mater. 29, 931 (1993); Acta Metall. Mater. 42, 4025 (1994)] is applicable to liquid-phase sintering of silicate/aluminosilicate glasses. The movement of a liquid phase between adjacent particles is compared 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 leads to the following relation: (gamma/eta)L alpha = D-cap, where alpha and D-cap are a specific permeability and volume diffusion coefficient. The use of this model requires the assumption that the diffusing species are also the viscous flow units, and they can be either atoms or structural units. This assumption seems to be applicable for depolymerized silicate melts if the dominant mass transport is initiated by the diffusion of both nonbridging oxygen and silicon atoms.