Liquid Metals: Crystal and Glass Formation in Supercooled Liquids Close to Revolution?
A special issue of Metals (ISSN 2075-4701).
Deadline for manuscript submissions: closed (31 October 2017) | Viewed by 4394
Special Issue Editor
Interests: low temperature physics; amorphous materials; glasses; vitrification; homogeneous nucleation; spin glasses; superconducting materials; melt memory; overheating
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Special Issue Information
Dear Colleagues,
Liquid transformation is based, up to now, on the classical equation of nucleation. Tiny crystals, acting as growth nuclei, do not exist in melts above the melting temperature Tm. Crystal nuclei do not have the time to condense below Tm by homogeneous nucleation in quenched liquids. The vitreous state is frozen at Tg and there is no expected Gibbs free energy change, leading to a first or second-order thermodynamic transition.
Many observations are in contradiction with these views. Magnetic texturing experiments show that intrinsic nuclei govern the crystallization of liquid elements and compounds. These growth nuclei disappear after a strong superheating. Experiments and calculations show that liquids undergo a thermodynamic transition at Tg leading to percolating or interpenetrating icosahedral-like tiny superclusters. The new ultra-stable glass state is obtained at the thin film deposition temperature after recovery of a liquid enthalpy fraction. Liquid He-4 confined in nanoporous media under pressure undergoes a first-order glass transition. The new ultrastable glass state would correspond to an equilibrium phase between those of liquid and crystal. Numerous hyperquenched or vapor-deposited substances, such as pure metals, are amorphous. Their glass transitions are masked by the occurrence of crystallization. This temperature of homogeneous nucleation could be equal to Tg.
All these findings could be explained by the formation of icosahedral-like superclusters, submitted to complementary Laplace pressures, depending on their formation temperature, giving rise to glasses by quenching melts below Tg and to crystals by heating the glass above Tg. The condensation of superclusters of radius R and their growth critical radius would depend on a critical enthalpy saving \( \epsilon_{ls}\times\Delta H_{m} \) Its introduction in the classical nucleation equation as shown below is now in agreement with Lindemann rule at Tm:
\( \Delta G_{ls} = 4\pi R^{3}3^{-1}\Delta H_{m} \times (\theta - \epsilon_{ls}) + 4\pi R^{2}(1+\epsilon_{ls})\sigma_{ls}\Delta H_{m} \)A fraction of such nuclei could survive above Tm and limit the supercooling rate of melts. This Special Issue of Metals is devoted to the following fields, in order to clarify whether the critical radius of nuclei is finite at Tm instead of being infinite, and whether the glass transition occurs at the homogeneous nucleation temperature of crystals in the glass state:
- Existence of intrinsic growth nuclei in liquid metals:
- Texturing of metals and alloys (mainly with a congruent melting) in a high magnetic field and dependence of the magnetic alignment with the liquid superheating temperature above Tm.
- Grain size of hyperquenched crystallized metals as a function on the superheating rate applied to the melt.
- Dependence of the supercooling rate with the duration and the temperature of isothermal overheating.
- Formation temperature of metallic glasses by hyperquenching liquids or thin film deposition at temperatures below Tm/2 down to low temperatures (Tg < Tm/2).
- Devitrification temperature of amorphous metals by spontaneous crystallization.
- Nanostructured and Nanocrystallized metallic glasses having Tg < Tm/2.
- Formation of superclusters in supercooled metallic liquids.
Dr. Robert F. Tournier
Guest Editor
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