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    Spinodal Decomposition

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    Rudrang Chauhan
    Spinodal decomposition is a process where a homogeneous mixture of two phases spontaneously separates without nucleation due to certain fluctuations that reduce the free energy of the system. When the two phases emerge in equal proportions, they form intertwined structures that gradually coarsen over time. Spinodal decomposition occurs when a homogeneous phase becomes thermodynamically unstable and lies at a maximum in free energy, unlike nucleation which occurs when a phase is metastable. Recent research has studied spinodal decomposition in nanocrystalline alloys, polymeric materials, and using characterization techniques like 3D NMR to analyze evolving microstructures.

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    Spinodal Decomposition

    Uploaded by

    Rudrang Chauhan
    48 views13 pages
    Spinodal decomposition is a process where a homogeneous mixture of two phases spontaneously separates without nucleation due to certain fluctuations that reduce the free energy of the system. When the two phases emerge in equal proportions, they form intertwined structures that gradually coarsen over time. Spinodal decomposition occurs when a homogeneous phase becomes thermodynamically unstable and lies at a maximum in free energy, unlike nucleation which occurs when a phase is metastable. Recent research has studied spinodal decomposition in nanocrystalline alloys, polymeric materials, and using characterization techniques like 3D NMR to analyze evolving microstructures.

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    Spinodal decomposition is a process where a homogeneous mixture of two phases spontaneously separates without nucleation due to certain fluctuations that reduce the free energy of the system. When the two phases emerge in equal proportions, they form intertwined structures that gradually coarsen over time. Spinodal decomposition occurs when a homogeneous phase becomes thermodynamically unstable and lies at a maximum in free energy, unlike nucleation which occurs when a phase is metastable. Recent research has studied spinodal decomposition in nanocrystalline alloys, polymeric materials, and using characterization techniques like 3D NMR to analyze evolving microstructures.

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    48 views13 pages

    Spinodal Decomposition

    Uploaded by

    Rudrang Chauhan
    Spinodal decomposition is a process where a homogeneous mixture of two phases spontaneously separates without nucleation due to certain fluctuations that reduce the free energy of the system. When the two phases emerge in equal proportions, they form intertwined structures that gradually coarsen over time. Spinodal decomposition occurs when a homogeneous phase becomes thermodynamically unstable and lies at a maximum in free energy, unlike nucleation which occurs when a phase is metastable. Recent research has studied spinodal decomposition in nanocrystalline alloys, polymeric materials, and using characterization techniques like 3D NMR to analyze evolving microstructures.

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    of 13

    Seminar

    SPINODAL DECOMPOSITION
    Made by
    Rudrang Chauhan
    PRN- 347
    HISTORY OF SPINODAL DECOMPOSITION
    • 1937- earliest observation were made where it was noted that diffusivities becomes negative inside spinodal
    regime, Bradley reported first experimental evidence.

    • 1940’s- Daniel and Lipson did extensive studies on Cu-Ni-Fe alloy systems. There are compositional
    modulations specifically along 100 direction in these alloys with wavelength of about 100 angstroms.

    • 1943-44- Becker and Dellinger gave their postulations.

    • 1951- regular solution model and discrete lattice based theories, 100 angstrom wavelength is expected under
    certain circumstances given by Hilliard.

    • 1961- Cahn developed the continuum model based on Hilliard’s model which gave rise to Cahn-Hilliard
    equation.
    WHAT IS SPINODAL DECOMPOSITION

    A spinodal decomposition occurs when one phase spontaneously (without nucleation) separates
    into two phases.

    Decomposition occurs in the absence of nucleation because certain fluctuations in the system
    reduce the free energy.

    When the two phases emerge in approximately equal proportion (each occupying about the same
    volume or area), they form characteristic intertwined structures that gradually coarsen .The
    dynamics of spinodal decomposition are commonly modelled using the Cahn–Hilliard equation.

    It is fundamentally different from nucleation. Where is nucleation large fluctuation are needed for
    phase transformation, here only small fluctuations can start transformation.

    Nucleation proceeds with grain growth and happens at discrete locations in the system, while here
    there is uniform and instant transformation throughout the region under consideration. Figure 1: Dynamics of spinodal
    Spinodal decomposition occurs when a homogenous phase becomes thermodynamically unstable. decomposition.
    An unstable phase lies at a maximum in free energy.
    WHAT IS SPINODAL DECOMPOSITION

    • In contrast, nucleation and growth occurs when a homogenous phase becomes metastable. that is, another new phase becomes lower in
    free energy but the homogenous phase remains at a local minimum in free energy, and so is resistant to small fluctuations
    • Nucleation proceeds with grain growth and happens at discrete locations in the system, while here there is uniform and instant
    transformation throughout the region under consideration.
    • Spinodal decomposition occurs when a homogenous phase becomes thermodynamically unstable. an unstable phase lies at a maximum
    in free energy. in contrast, nucleation and growth occurs when a homogenous phase becomes metastable. that is, another new phase
    becomes lower in free energy but the homogenous phase remains at a local minimum in free energy, and so is resistant to small
    fluctuations.

    • Spinodal decomposition involves uphill diffusion, whereas diffusion is always down a concentration gradient for nucleation and growth .
    UNDERSTANDING SPINODAL DECOMPOSITION
    Suppose that a very small fluctuation occurs
    Consider a part of the free energy and consider what happens to the free energy
    curve where the curvature is negative. for the small fluctuation:

    Suppose that a material is manufactured with a composition


    Xo that is function of some partial coordinate Z.
    UNDERSTANDING SPINODAL TRANSFORMATION

    Apparently, the free-energy charge is negative for an arbitrarily small fluctuation in composition such that one part of the system gets more concentrated
    at the expense of another. The system is inherently unstable and phase separation will proceed as illustrated:

    This process is called spinodal decomposition and it occurs spontaneously when there is compositional modulation in miscibility gap.
    UNDERSTANDING SPINODAL TRANSFORMATION

    Consider the part of the curve where the curvature is positive This kinetic information is shown graphically in the
    but inside the miscibility gap (miscibility gap is another way of phase diagram below.
    saying the two-phase region).

    Figure 2: Free energy Vs composition phase diagram


    showing miscibility gap. Figure 3: Temperature vs composition phase diagram showing miscibility gap
    SOME RESEARCH RESULTS
    Explaining figure 4 and 5: Three-dimensional evolution of spinodally decomposed liquid (polymer). The modelling is provided using a "hyperbolic" model for phase separation.
    Snapshots for the decomposed (blue) phase are shown for various computational times. 3D modelling of spinodal decomposition in Fe-45-Cr alloys is shown on the image in right.
    EVOLUTION OF SPINODAL STRUCTURES
    Explanation for figure 6 and 7: The analysis of spinodal decomposition in the Zn 1−x CdxO ternary alloy was carried out by means of the nonlinear Cahn Hilliard equation. The morphological patterns
    for the ternary alloys with dierent Cd content (x = 5, 10, 50%) were experimentally obtained using the semi-implicit Fourier-spectral method. The microstructure having a form of bicontinuous worm-
    like network is evolved with the progress of aging. Below figure also shows spinodal decomposition in alloys.
    RECENT RESEARCH AREAS

    Spinodal decomposition in Nanocrystalline alloys:


    The most lucrative aspect for spinodal decomposition is
    the low barrier for transformation pathway. There is
    negligence of grain boundary and other defects effect on
    the process. Nevertheless, in nanocrystalline alloys, with
    a high population of grain boundaries with diverse
    characters, the structurally heterogeneous landscape can
    greatly influence the chemical decomposition behavior.
    The research conducted on Pt-11Au alloy proved that
    grain boundaries posses their own miscibility gaps and Figure 8 : 3D simulation results of temporal
    evolution of solute redistribution revealing
    profound effect on spinodal decomposition. density dependent segregation and interfacial
    spinodal behaviour.
    RECENT RESEARCH AREAS

    Polymeric materials:
    Studies of bicontinuous structures
    developed via spinodal decomposition
    have been a research theme for those
    dealing with binary mixtures of molecular
    fluids and polymer blends. A great deal of
    information on the time evolution of the
    phase-separated structures has been
    obtained. Characterization techniques like
    laser scanning confocal microscopy
    (LSCM), X-ray computed tomography (X-
    Ray CT) and 3D NMR have been used for Figure 9 : Evolution of structures seen in 3D by reconstructing 2d NMR
    accurate results. images of PMMA rich and PS-Br-rich domains observed.
    REFERENCE

    • https://pf.jitin.xyzspinodal-decompostion-in-3d/
    • https://en.wikipedia.org/wiki/spinodal_decomposition
    • http://pruffle.mit.edu/3.00/lecture_32_web/node3.html
    • http://www.lnsm.eu/modelling/spinodal
    • https://wxiong.weebly.com/microstructure-design.htm
    • https://www.researchgate.net/figure/morphological-patterns-during-the-spinodal-decomposition-and-the-subsequent-coarsening_fig2_
    269313717
    • https://doi.org/10.1016/j.actamat.2021.117054
    • https://doi.org/10.1016/s0066-4103(10)70002-8
    Thanks for your kind attention

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