The self-diffusivity of 18O in monocrystals and polycrystals was studied by using ion implantation, thick-film and isotopic exchange methods. The resultant diffusion profiles were measured by means of secondary ion mass spectrometry, and the diffusion coefficients were calculated by using the Whipple-LeClaire solution for type-B intergranular diffusion. Bulk diffusivities were deduced from a solution of Fick's equation which took account of evaporation and surface exchanges. It was found that the diffusion coefficients were lower than published values, and did not seem to depend upon the O pressure (table 59).

A.C.S.Sabioni, A.M.Huntz, J.Philibert, B.Lesage, C.Monty: Journal of Materials Science, 1992, 27[17], 4782-90. See also: Philosophical Magazine A, 1992, 66[3], 361-74

Table 57

Grain-Boundary Diffusion (PO2 = 10-4atm) of Fe

in a Cr2O3 Film on Ni70Cr30