Answered: 4. Compare salient features of spinodal…

Physical Chemistry

2nd Edition

ISBN:9781133958437

Author:Ball, David W. (david Warren), BAER, Tomas

Publisher:Ball, David W. (david Warren), BAER, Tomas

Chapter21: The Solid State: Crystals

Section: Chapter Questions

Problem 21.57E

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Transcribed Image Text:4. Compare salient features of spinodal vs nucleation and growth (use table 4.3 and figure 4.9 given in Sperling) Table 4.3 Mechanisms of phase separation 1. Nucleation and growth (a) Initial fragment of more stable phase forms. (b) Two contributions to free energy: (i) work spent in forming the surface and (ii) work gained in forming the interior. (c) Concentration in immediate vicinity of nucleus is reduced; hence diffusion into this region is downhill. (Diffusion coefficient is positive.) (d) Droplet size increases by growth initially. (e) Requires activation energy. 2. Spinodal decomposition (a) Initial small-amplitude composition fluctuations. (b) Amplitude of wavelike composition fluctuations increases with time. (c) Diffusion is uphill from the low concentration region into the domain. (Diffusion coefficient is negative.) (d) Unstable process: no activation energy required. (e) Phases tend to be interconnected. positive diffusion coefficient (a) Distance t1 negative diffusion coefficient t2 (b) M. t3 Distance Figure 4.9 A schematic of concentration profiles during phase separation (34), for (a) nucleation and growth and (b) spinodal decomposition. Concentration Profile Concentration Profile

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