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Time-resolved crystallization of deeply cooled liquid hydrogen isotopes

Abstract

This thesis serves two main purposes: 1. The introduction of a novel experimental method to investigate phase change dynamics of supercooled liquids 2. First-time measurements for the crystallization behaviour for hydrogen isotopes under various conditions (1) The new method is established by the synergy of a liquid microjet of ∼ 5 μm diameter and a scattering technique with high spatial resolution, here linear Raman spectroscopy. Due to the high directional stability and the known velocity of the liquid filament, its traveling axis corresponds to a time axis static in space. Utilizing evaporative cooling in a vacuum environment, the propagating liquid cools down rapidly and eventually experiences a phase transition to the crystalline state. This temporal evolution is probed along the filament axis, ultimately resulting in a time resolution of 10 ns. The feasibility of this approach is proven successfully within the following experiments. (2) A main object of study are para-hydrogen liquid filaments. Raman spectra reveal a temperature gradient of the liquid across the filament. This behaviour can quantitatively be reconstructed by numerical simulations using a layered model and is rooted in the effectiveness of evaporative cooling on the surface and a finite thermal conductivity. The deepest supercoolings achieved are  More>>
Publication Date:
Feb 15, 2014
Product Type:
Thesis/Dissertation
Resource Relation:
Other Information: Diss. (Dr.rer.nat.)
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; COMPUTERIZED SIMULATION; CRYSTAL GROWTH; CRYSTAL STRUCTURE; CRYSTALLIZATION; EVAPORATIVE COOLING; HYDROGEN ISOTOPES; INTERFACES; LIQUIDS; MELTING POINTS; MIXTURES; NUMERICAL ANALYSIS; RAMAN SPECTRA; SPATIAL RESOLUTION; SUPERCOOLING; THERMAL CONDUCTIVITY; TIME RESOLUTION
OSTI ID:
22260411
Research Organizations:
Frankfurt Univ. (Germany). Fachbereich 13 - Physik
Country of Origin:
Germany
Language:
English
Other Identifying Numbers:
TRN: DE14F3375081626
Availability:
Available from: http://www.atom.uni-frankfurt.de/publications/files/Matthias_K%C3%BChnel.pdf
Submitting Site:
DE
Size:
263 page(s)
Announcement Date:
Sep 09, 2014

Citation Formats

Kuehnel, Matthias. Time-resolved crystallization of deeply cooled liquid hydrogen isotopes. Germany: N. p., 2014. Web.
Kuehnel, Matthias. Time-resolved crystallization of deeply cooled liquid hydrogen isotopes. Germany.
Kuehnel, Matthias. 2014. "Time-resolved crystallization of deeply cooled liquid hydrogen isotopes." Germany.
@misc{etde_22260411,
title = {Time-resolved crystallization of deeply cooled liquid hydrogen isotopes}
author = {Kuehnel, Matthias}
abstractNote = {This thesis serves two main purposes: 1. The introduction of a novel experimental method to investigate phase change dynamics of supercooled liquids 2. First-time measurements for the crystallization behaviour for hydrogen isotopes under various conditions (1) The new method is established by the synergy of a liquid microjet of ∼ 5 μm diameter and a scattering technique with high spatial resolution, here linear Raman spectroscopy. Due to the high directional stability and the known velocity of the liquid filament, its traveling axis corresponds to a time axis static in space. Utilizing evaporative cooling in a vacuum environment, the propagating liquid cools down rapidly and eventually experiences a phase transition to the crystalline state. This temporal evolution is probed along the filament axis, ultimately resulting in a time resolution of 10 ns. The feasibility of this approach is proven successfully within the following experiments. (2) A main object of study are para-hydrogen liquid filaments. Raman spectra reveal a temperature gradient of the liquid across the filament. This behaviour can quantitatively be reconstructed by numerical simulations using a layered model and is rooted in the effectiveness of evaporative cooling on the surface and a finite thermal conductivity. The deepest supercoolings achieved are ∼ 30% below the melting point, at which the filament starts to solidify from the surface towards the core. With a crystal growth velocity extracted from the data the appropriate growth mechanism is identified. The crystal structure that initially forms is metastable and probably the result of Ostwald's rule of stages. Indications for a transition within the solid towards the stable equilibrium phase support this interpretation. The analog isotope ortho-deuterium is evidenced to behave qualitatively similar with quantitative differences being mass related. In further measurements, isotopic mixtures of para-hydrogen and ortho-deuterium are investigated. It is found that the crystallization process starts earlier and lasts significantly longer compared to the pure substances with the maximum values between 20-50% ortho-deuterium content. A solely temperature based explanation for this effect can be excluded. The difference in the quantum character and hence effective size of the isotopes suggests a strong influence of the progressing liquid-solid-interface. Small dilutions of each para-hydrogen and ortho-deuterium with neon show an even more extended crystallization process compared to above isotopic mixtures. Additionally, the crystal is strongly altered in favor of the equilibrium lattice structure of neon.}
place = {Germany}
year = {2014}
month = {Feb}
}