Grain-Boundary and Lattice Permeation

Photo-micrographs may illustrate both the mosaic structure of metals, and a concentration of impurity between crystal blocks. If diffusion occurs mainly down these boundaries, the permeability of a metal would be governed by their number and nature. The mere fact that oxide is found concentrated in these boundaries does not, however, necessarily imply that diffusion of oxygen occurs along them, since the oxide may be formed within the lattice and then be thrown out of solution in the zones between crystallites. That grain-boundary diffusion plays an important part in diffusion processes such 

The permeability of hydrogen-iron systems has received considerable attention at low as well as at high temperatures. Ham and Rast (loo) studied the permeability from 55 to 920° C. In addition to discontinuities in permeability at every 

Much more evidence of this kind is necessary before any generalisation concerning the relative importance of grainboundary, slip-plane, or isotropic lattice diffusions may be made. 

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