SANS study of sintering of rough surfaces

Small-angle scattering has been used to follow the heat-induced smoothing of rough fumed silica particles by viscous sintering. When analyzed by a fractal surface model, the surfaces evolved from a fractal dimension of 2.5–2.7 to 2.0. The specific surface area σ(r) for a given resolution r could be described by the simple law σ(r) = σ₀(r/r*)^2−D, where σ₀ is the specific surface area for smooth particles and r* is a characteristic length that is the same for all the fumed silicas studied and is comparable to the primary particle size. This is the first indication of a universal relation between fractal surfaces, albeit within a closely related class of materials.