3. The grain boundary diffusivity of a ceramic material is given by Dgb = 100exp(- 40kJ kT and the bulk diffusion coefficient is 50kJ Dlattice 300exp(- kT) (a) Determine whether grain boundary diffusion or lattice diffusion will dominate at 900K. (b) Determine whether grain boundary diffusion or lattice diffusion will dominate at 1300K. (c) At which temperature will they be equally important?