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Non equilibrium systems

Non equilibrium systems. Advanced material and technologies, MSc 2017. What is the meaning of „ equilibrium state "?. phenomenology. thermodynamic consideration. The water-ice system is popular example. 1 atm is 0 o C , T 0: supercooled liquid ( metastable ).

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Non equilibrium systems

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  1. Non equilibrium systems Advanced material and technologies, MSc 2017

  2. What is the meaning of „equilibrium state"? phenomenology thermodynamic consideration The water-ice system is popular example 1 atm is 0 oC, T 0:supercooledliquid (metastable) Supersaturated solution: metastable. How metastability evolves generally? Atomic rearangements do not be able to succeed the cooling rate.

  3. Fundamental terms: - stability • - unstability • - metastability Unstable materials are avoided by engineering practice, metastable states are often used. Examples: - unstable: highly deformed, high purity materials - metastability: diamond, martensite

  4. Characters of metastable statesThey have a role in strength-enhancing.

  5. Kinetic consideration for the metastability formation Basic concept: • relation between the rate of the energy subtraction and time-scale necessary for the atomic rearrangements • in the case of delay Gm state will be frozen

  6. Formation of metastable structure by melt quenching:

  7. Property modification by grain size: Hall―Petch-equation:

  8. Morphological metastability: nanostructured materials

  9. Morphological metastability: clusters in condensed materials Materials with high specific surfaces • Cluster: a set of small number of atoms that permanently or temporarily coincide during an observation process. • Binding strength depends significantly on the number of atoms that form the cluster. • The “size-related”propertiesbetween the individual properties of constituentatoms and the thermodynamically stablemacroscopicproperties. • All properties are valid (in the thermodynamic sense) only for the macroscopic material!

  10. Sintering (example for morphological metastability and technology based on it)

  11. Tsintering 2/3 Tmelting The driving force behind the sintering process is to reduce surface energy: For example: in the case of Al2O3 powder with particle size of1μ, the surface of 10 cm3 material ≈ 1000 m2, and the interfacial energy is approx. 1 kJ. The change of density as a function of time and temperature: a: particle size C: constant Q: activation energy

  12. Compositional metastability: k0: compositional partition coefficient in equilibrium state v: cooling rate

  13. How does freeenthalpy change during phase transition?(amorphous-crystalline, liquid-crystalline, crystallization from supersaturated solid solution) Assumed free enthalpy diagram for depicting the formation conditions of amorphous and crystalline states (am – amorphous phase,  – solid solution,  – compound) [21]

  14. Slope of T0 curves and maximum supersaturation, solidification without compositional partition, phenomenon of glass forming • What are the boundary conditions? • Forming of supersaturated, crystalline solid solutions. • Forming of metallic amorphous states (glassy alloys)

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