Nucleation and Growth

Nucleation and Growth - Nucleation and Growth Chapter 8 How...

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Unformatted text preview: Nucleation and Growth Chapter 8 How Do Materials Solidify? We dont usually spend a lot of time thinking about the solidification process As you cool off a metal ( or water or any material) the average kinetic energy drops Boltzman Distribution Formation of Nucleii Molecules are always bumping into each other sometimes they stick At lower kinetic energies more stick Why Does Anything Solidify? The energy of the crystal structure is less than that of the liquid The difference is the volume free energy G v As the solid grows in size, the magnitude of the total volume free energy increases But it is a negative value But When solids form in a liquid there is an interface created The surface free energy, is associated with this interface As the solid grows, the total surface free energy increases, and. Its a positive value That means The total change in free energy for the system is the sum of the two factors. G = 4/3 r 3 G v + 4 r 2 The volume free energy goes up as the cube of the radius The surface free energy goes up as the square of the radius Total Free Energy of a Solid Liquid System Surface Energy Volume Energy Critical Radius What Does It All Mean ? If just a few molecules stick together, they will redissolve If enough molecules stick together, the embryo will grow Supersaturated Solutions If the liquid is just at the freezing point,...
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Nucleation and Growth - Nucleation and Growth Chapter 8 How...

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