Small angle scattering of Ag-1 wt.% Mg alloys internally oxidized at high temperatures: a model of interacting spherical clusters

Strong interference effects in the X-ray small angle scattering (SAXS) intensity vs. scattering-angle plot are shown to appear in foil specimens of a relatively concentrated Ag-Mg alloy (1 wt.% Mg corresponding to 4.3 at.% Mg) treated in air under two very different high temperature conditions. Such interference effects are ascribed to MgOv clusters formed during an internal oxidation process and are quantitatively evaluated applying a special theoretical approach based on a model of interacting spherical particles. It is found that, in the sample oxidised at 1023 K for 2 min, particles with a surface-weighted average diameter of 1.4 nm are present and occupy 5.4% of the sample volume. In the sample oxidised at 1123 K for 6 h, the particles are larger (3.3 nm) and represent a 3.8% volume fraction. The clusters formed at lower temperatures for a few minutes are much richer in oxygen (v=1.6) than those formed at higher temperatures for some hours, which are composed of stoichiometric (v=1) magnesium oxide.