ELSEVIER Physica A 224 (1996) 128-139 PHYSICA Nucleation in binary mixtures Gangasharan, Deepak Kumar School of Physical Sciences, Jawaharlal Nehru University, New Delhi, 110067, India Abstract The nucleation kinetics of a binary mixture is studied using a Gibbs free energy function that we have recently used to obtain a range of generic phase diagrams when liquid mixtures are cooled to solid state. This allows us to compute analytically all the quantifies related to the free energy barrier that occur in the nucleation kinetic equation. This equation is solved using the general procedure due to Langer. The variation of the nucleation rate and other related quantities are calculated as functions of undercooling and composition for a representative phase diagram. 1. Introduction The nucleation kinetics of freezing of binary mixtures is a problem of great theo- retical and practical interest. The basic principles of metastability, nucleation barriers and associated rates of nucleation in one-component systems were already laid down in full glory by the forties [ 1,4]. The application of these principles to binary mixtures has also been vigorously pursued both from vapour to liquid state transition, and from liquid state to solid state transition in the past fifty years [5-13]. The latter transition, being a key interest area in metallurgy, has been text-book material for several decades. Though this work has clarified the basic qualitative principles, we find that several issues connected with binary mixtures have not been addressed. Binary mixtures exhibit a very rich variety of phase diagrams, and thus offer opportunity to study nucleation processes in a variety of conditions. The early work of Reiss [5] did establish the appropriate theoretical framework on the lines of Becker-Doring theory. However, the explicit cal- culation of the nucleation rates could be done only in the vapour phase and in the dilute limit. The work of Thompson and Spaepen [ 11 ] addressed itself to nucleation in metal- lic melts and obtained results that could be compared with the undercooling data (i.e., maximum undercooling achievable in binary mixtures as a function of composition). This work achieved a successful explanation of the data of Refs. [8,9], even though it was based on dilute or ideal solution approximation for the solid phase. 0378-4371/96/$15.00 @ 1996Elsevier Science B.V. All rights reserved SSDI 0378-4371 (95) 00358-4