MATS 3011 Lecture Notes - Gibbs Free Energy, Tinn
Document Summary
Phase transformation can be broken into 2 steps: nucleation, growth. Start with some type of phase, let"s say liquid consider first a phase change like nucleation of a spherical solid particle in liquid volume of particle = (4/3)pi*r 3 solid-liquid interface area = 4*pi*r2. Total change in gibbs free energy = (4/3)pi*r 3*deltagv + 4*pi*r2*(gamma) Deltagv = free energy difference between the 2 phases (will be negative) gamma --> surface energy first term in eqn is negative, 2nd is positive total gibbs free energy. The barrier for nucleation: the maximum total gibbs free energy, after which energy decreases; growth happens after it max g = deltag* and corresponding r = r* Deltag* --> activation free energy for nucleation r* --> critical nucleus size (nucleation will not start at r value less than this) Nucleation is like a democracy (particles on inside = happy, but ones in surface aren"t happy)if too small, unhappy ones windoesn"t grow.
