(a) Nickel has melting temperature of 1455C and often does not nucleate until 1136C. Find the critical radius (r) and activation free energy (AG) for the solidification of nickel. Nickel has a latent heat of fusion is -2.53 x 10" J/m and the surface tension energy is 0.255 J/m. (b) Now let's figure out the number of Ni atoms are in that r". At these temperatures Ni has lattice parameter of 0.360 nm and is FCC. (c) Joules is a less common unit used for activation energy in materials science, so let's convert AG to eV. 1 eV = 96 kJ/mol.