Composition of a solid phase growing under nonequilibrium conditions

The composition of a binary solid phase is predicted in a multiphase enviro nment during phase formation by a steady-state process in linear growth geo metry characterized by planar interfaces. In this situation, Gibbs free ene rgy is also dissipated at the opposite interfaces of the forming phase whic h is not in thermodynamic equilibrium with its surroundings. Although the c ommon tangent rule of an equilibrium situation cannot be applied to the ste ady-state process, the composition is derived here from the free energy cur ves of the equilibrium phase by a self-consistent, iterative solution of a new model that combines thermodynamic and diffusional considerations. Accur ate composition-as proven experimentally-is predicted for the amorphous Al- Pt phase using a reasonable assumption for the ratio of chemical potential drops at the opposite interfaces of the forming phase. Although our numeric al example is the amorphous Al-Pt system, the model can also be applied to other amorphous or solid solution phases which exist in a wide compositiona l range. (C) 2000 American Institute of Physics. [S0021-8979(00)07010-9].