6 January, 2010

The Influence of Liquid and Glass Structures on Phase Transitions

Lecture 1: Amorphous structure

Lecture 2: Nucleation

Abstract

In two lectures the influence of amorphous structure in liquids and glasses on crystal nucleation, glass formation and the glass transition will be discussed. In the first lecture, containerless processing techniques will be reviewed, focusing on electromagnetic and electrostatic levitation methods. The techniques used to measure properties such as the density, surface tension, viscosity, and specific heat and liquid structure will be presented. Case studies will (i) demonstrate the development of icosahedral short-range order (ISRO) in transition metal and alloy liquids, (ii) suggest chemical ordering in Cu-Zr, possibly explaining easy glass formation, (iii) show medium-range ordering in a Zr-Pt liquid, even at temperatures above the melting temperature, (iv) raise questions about a proposed liquid/liquid phase transition in silicon, (v) suggest an ordering-related phase transition in a quasicrystal-forming liquid, and (vi) indicate a dynamical phase transition in a bulk metal glass forming liquid, possibly related to mode-coupling or a fragile-to-strong transition. The second lecture will focus on nucleation, and the coupling of amorphous structure to crystallization and other phase transitions. The classical theory of nucleation (CNT) will be developed and predictions of steady-state nucleation rates will be compared with experimental nucleation data in liquids and glasses. Limitations of the thermodynamic model for CNT will be highlighted and other models that address these, such as diffuse-interface and density functional models, will be introduced. As one example of coupled processes in nucleation, a new model that couples the stochastic processes of diffusion and interfacial-attachment, will be discussed. Other examples will show that ordering in a supercooled Ti-Zr-Ni liquid lowers the nucleation barrier for a metastable quasicrystal, blurring the distinction between heterogeneous and homogeneous nucleation, and show a case where the Curie transition in supercooled Co-Pd liquids couples with the crystal nucleation barrier. CNT predictions of time-dependent nucleation will be compared with experimental data in silicate and metallic glasses. The combination of liquid structure data showing the growth of ISRO in a supercooled Zr-based liquid that forms a bulk glass, and time-dependent nucleation data for an icosahedral quasicrystal in the glass support a frustration model of the glass transition. Supported by the National Science Foundation (DMR-0606065 & DMR-08-56199) and NASA (NNX07AK27G).

References and suggested reading

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  4. K. F. Kelton, Acta Materialia, 48, 1967-1980 (2000)
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  6. Y. T. Shen, T. H. Kim, A. K. Gangopadhyay and K. F. Kelton Phys. Rev. Lett., 102¸ 057801/1-4 (2009)