Tracer self-diffusion of Ni in 2 bicrystals, and in a polycrystalline specimen, at 700C was studied using sectioning and autoradiography (table 155). The 2 bicrystal boundaries were <110> symmetrical tilt boundaries with misorientations of 39.5° and 99.5°, respectively. The tracer penetration profiles were analysed in terms of lattice diffusion and diffusion along low-angle boundaries composed of dislocation arrays introduced by mechanical polishing. The coefficients for lattice and low angle boundary diffusion were in acceptable agreement with previous determinations. Diffusion along high-angle

boundaries could not be detected by profiling, but could be detected by autoradiography in some boundaries after annealing at 1400C before diffusion annealing. Autoradiography revealed that the boundary diffusion was not homogeneous and was sensitive to both thermal history and boundary geometry. The bicrystal boundaries were found to be extensively contaminated by Ca and Si compounds. It was concluded that the high-angle boundary diffusion is dominated by these impurities and their distribution.

Tracer Diffusion Studies in NiO Bicrystals and Polycrystals. A.Atkinson, D.P.Moon, D.W.Smart, R.I.Taylor: Journal of Materials Science, 1986, 21[5], 1747-57

Table 156

Diffusion of O in NiO at PO2 = 0.0001atm