Published online by Cambridge University Press: 21 February 2011
Results obtained with small angle neutron and X-ray scattering will bepresented of systems with various silica concentrations. Silica gels withlow silica concentration exhibit uniform mass fractal behaviour and afterprolonged aging, dual mass fractal behaviour. A zeolite (silicalite)synthesis precursor gel with a high silica concentration was alsoinvestigated and was found to exhibit surface fractal behaviour. A model ispresented, explaining the occurrence of dual fractality after prolongedaging. The change-over from mass fractal behaviour to surface fractalbehaviour is explained, supported by scattering spectra calculated fromsimulated aggregate structures.