Preflight Diffusion Experiments on Liquid Metals Under 1g Conditions for the FOTON-M2 Mission

: We measured diffusion of up to 5% Ag in liquid Pb, using the Foton shear cell (designed and used for the FOTON‐M2 mission). Since the density change of the alloy with composition has been reported to be very small but is not reliably known, we performed two arrangements of layering: (a) with PbAg on top and Pb below and (b) with Pb on top and PbAg below. The Berlin group did interdiffusion experiments from a “thick layer” of PbAg into “semi‐infinite” Pb and the Karlsruhe group did the typical “interdiffusion” experiments with a diffusion couple of PbAg versus Pb. The results of both groups were equivalent, showing much lower D values for arrangement (b) than for (a). The lower values were even definitely lower than reference microgravity values from MIR/MIM and could be fitted by D=ATn with n about 2.2. We discuss the stability/instability by density layering depending on the arrangement.