8.13 Find the grain size of a polycrystalline solid for the same amount of material to be transported through (i) the grain and (ii) the grain boundary at 500°C. Assume that the grains are cube shaped and the grain boundaries are 5 Å thick. For lattice diffusion: D0 = 0.7 10–4 m2 s–1 Q = 188 kJ mol–l For grain boundary diffusion: D0 = 0.09 10–4 m2 s–1 Q = 90 kJ mol–l