The structure of pumice by neutron diffraction

Small-angle neutron scattering (SANS) and wide-angle neutron scattering (WANS) measurements on pumice, an amorphous natural aluminosilicate used as support for metals in the preparation of catalysts, are reported. The SANS spectrum indicates the presence of a broad size distribution of pores and the absence of volume fractality. Surface fractality, however, cannot be ruled out. The structure of pumice, suggested by the pair-correlation function derived from the WANS spectrum and simulated by a random-network structure model, is very similar to that of vitreous silica, consisting mainly of SiO^4-₄ tetrahedra interconnected by bridging O atoms with additional local disorder generated by the replacement, on average, of one in ten Si atoms by aluminium.