The Influence of Gravity on the Precise Measurement of Solute Diffusion Coefficients in Dilute Liquid Metals and Metalloids

A bstract : It is now well known that the diffusion coefficient ( D ) measured in a laboratory in low earth orbit (LEO) is less than the corresponding value measured in a terrestrial laboratory. However, all LEO laboratories are subject to transient accelerations ( g ‐jitter) superimposed on the steady reduced gravity environment of the space platform. In measurements of the diffusion coefficients for dilute binary alloys of Pb‐(Ag, Au,Sb), Sb‐(Ga,In), Bi‐(Ag,Au,Sb), Sn‐(Au,Sb), Al‐(Fe, Ni,Si), and In‐Sb in which g ‐jitter was suppressed, it was found that D ∝ T (temperature) if g ‐jitter was suppressed, rather than D ∝ T 2 as observed by earlier workers with g ‐jitter present. Furthermore, when a forced g ‐jitter was applied to a diffusion couple, the value measured for D increased. The significance of these results is reviewed in the light of recent work in which ab initio molecular dynamics simulations predicted a D ∝ T relationship.