SINTERING OF MASS FRACTALS BY SURFACE-DIFFUSION OR BY VISCOUS-FLOW - NUMERICAL AND SCALING APPROACHES IN D=2

Numerical methods are used to model two kinds of sintering processes, by Surface Diffusion (SD) or by Viscous Flow (VF), and are applied to deterministic and random two-dimensional ''mass fractals'' with variou s fractal dimensions. In the SD case the relevant partial differential equation is discretized and the evolution of the contour is numerical ly studied. In the case of viscous how, a recently introduced approxim ate ''dressing'' method is used. In both cases it is shown that the ge ometrical characteristics which are the perimeter length L, the size x i and the lower cut-off a, vary as some powers of time t (L similar to t(-alpha)) xi similar to t(-beta) a similar to t(gamma)). The exponen ts alpha, beta, gamma, and their dependence on the fractal dimension D , are estimated from scaling arguments and are found to be different i n the SD and VF cases. The SD case is particular in the sense that bet a similar or equal to O (no shrinkage) and that, if the initial fracta l is too large, it breaks into separate pieces.