6) Briefly describe the possible outcomes of adding impurity atoms to a metal. 7) In your own words, explain what a grain boundary is, and draw a simple sketch to illustrate your explanation. 8) What type(s) of microscope(s) can be used to view individual atoms in a material? 9) (a) Compare interstitial and vacancy atomic mechanisms for diffusion. (b) Cite two reasons why interstitial diffusion is normally more rapid than vacancy diffusion