Question 17:

(a) Inert Al₂O₃ powder is sprinkled over the surface of iron before it is oxidized under conditions that yield FeO. Where will the alumina particles (i.e. Al2O3) be located after oxidation if D_Fe >> D_o in FeO?

(b) The diffusion coefficients of several organic molecules in natural rubber are plotted as a function of temperature in the figure below. In a brief one sentence explanation provide a rationalization for the ranking of the diffusivities.

(c) NiO is an ionic compound with a rocksalt structure. Identify an impurity dopant that could be used to decrease the diffusivity of Ni and hence slow oxidation.