OSTWALD RIPENING IN IONIC CRYSTALS

S. Jain , A. Hughes

The Lifshitz-Slezov-Wagner (LSW) theory of Ostwald ripening, limited by bulk diffusion or surface reaction rates, is extended to the case of dislocation or grain-boundary diffusion. The theory predicts a universal particle size distribution, F(R/Rc), where Rc is the critical radius i.e. the radius of a particle which is instantaneously in equilibrium with the solute concentration in the matrix. Some of the approximations used in the theory are critically examined. The approximation eα/R ≈ 1 + α/R, used in applying Thomson's equation to the theory, is not always valid and can cause a significant error in the shape of the size distribution function for small values of R. Inhomogeneities in the distribution of interparticle separation can cause different groups of particles in the same solid to ripen independently, thus giving an observed size distribution which does not agree with the simple theory. A comparison of the theory with recent experiments on alkali halides and glass supports the above findings and explains a variety of observations satisfactorily. The observed size distribution of Ag particles in glass is described by two overlapping distributions for the bulk diffusion case. Ag particles in KCl are described by the narrow distribution obtained for the dislocation diffusion case and the distribution of MnCl2. 6NaCl (Suzuki phase) in NaCl by the surface reaction case when allowance is made for the errors due to the approximations discussed above.

Domaines: Articles anciens

S. Jain, A. Hughes. OSTWALD RIPENING IN IONIC CRYSTALS. Journal de Physique Colloques, 1976, 37 (C7), pp.C7-463-C7-469. ⟨10.1051/jphyscol:19767103⟩. ⟨jpa-00216824⟩