A markedly rapid Brownian movement of He bubbles, in material which contained a very small concentration of Pb or In, as studied by means of hot-stage transmission electron microscopy. Bubble diffusion was enhanced because the impurity coated the bubble surfaces at annealing temperatures which were above the melting point of the impurity. Upon assuming that bubble migration occurred via the self-diffusion of Al atoms at the bubble surfaces, it was found that the corresponding surface diffusion coefficients (table 22) were some orders of magnitude higher than the diffusion coefficients which were deduced from He bubble growth data for pure Al.

C.D.Van Siclen, R.N.Wright, S.G.Usmar: Physical Review Letters, 1992, 68[26], 3892-5

Table 22

Diffusion at 823K of Al on He Bubble Surfaces in Al Alloys