Crystalisation#

Introduction

Intro paragraph

Plan


  • Summary

Page

  • Status: flag alt >

  • Reviewed: ❌

  • Updated: 04/02/2023

Notes

To Do

  • Think about coherent plan

  • Implement

Colaboration

Star formation is not my expertise so if you want to help, feel free to comment the contribution you could make

Key Review to read !!#

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Science of crystalisation#

‣ Avrami equation #

‣ Avrami equation #

Also known as the Johnson–Mehl–Avrami–Kolmogorov (JMAK) equation. Describe how solids evolve from one phase to another at a constant temperature. transformation of α into β will proceed by the nucleation of new particles at a rate N per unit volume, which grow at a rate G into spherical particles and only stop growing when they impinge upon each other.
../../_images/287px-Avrami_equation.png

Fig. 12 Source#


../../_images/Avrami_transformation_plot.svg

Fig. 13 Source#

ASW Crystalisation …#

From an Astrochemist point of view

ASW crystalisation is often described as a single event occuring throughout the whole sample

Even though that may be correct within certain laboratory condition, particulary those using high rate of annealing like for example DSC, the picture is probably much more complex than that

Phase transition#

Glass to liquid transition#

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Experimental investigation#

Positron beam spectroscopy#

Note

Technique to describe

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Crystalisation Proceses#

Separating nucleation & growth in amorphous ice

  • Crystallisation temperature: Tx
  • Crystallization rate: RJG

General mechanism: Amorphous ices turning into an ultraviscous deeply supercooled liquid prior to nucleation.

Note

To investigate

Nucleation#

Homogeneous#

Thickness dependence#

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Heterogeneous#

Growth#

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Models#

Decoupling of simultaneous nucleation and growth processes as well as the quantification of their kinetics []. Growth is isolated from nucleation by dividing a phase transition into two isothermal stages:

  • prenucleation, where product crystallites nucleate and grow concurrently
  • growth, in which transformation is completed essentially entirely by the expansion of these seed grains

Isothermal transformation kinetics can usually be described by the Kolmogorov–Johnson–Mehl–Avrami equation:

In depth explanation
../../_images/Avrami_transformation_plot.svg

Fig. 14 Source#

  • Review []

Molecular Dynamics#

{cite:p}`Martelli 2018

Surface#

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Substrate#

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Crystalisation kinetics of ASW#

The overall kinetics of an isothermal phase transition is usually determined by the time dependence of a specimen’s converted fraction, which is often determined using calorimetry, spectroscopy, or diffraction

Studies that state that ASW crystalises from the surface: []

  • insert BD Kay article

ASW vs HGW#

  • []: Porosity, SSA & Crystallisation of ASW & HGW: 14 – 150 K, CH4 adsorption -> SSA = 280 ± 30 m2 g-1 ( ASW) and SSA = 40 ± 12 m2 g-1 (HGW), crystallisation rate constant (≈ 7 x 10-4 s-1) independent of deposition T (14, 40, 90 K), hints towards different ASW structure at very low (14 K) T

Operando measurment in order to resolve the ASW crystalisation.

In the intermediate pressure regime#

ie other forms of amorphous ices

  • Review: []

Geometrical vs statistical model#

  • []

Glass Transition#

  • Modern computational studies of the glass transition Nature Review (not accessible)

Transition between different forms of amorphous ice#

  • []: Liquid-liquid transition (TIP4P-Ew model water), 150 – 360 K, low/high/very high density transformations.