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Title: New insights into water's phase diagram using ammonium fluoride
Author: Sharif, Zainab
ISNI:       0000 0004 9359 7693
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2020
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Ice is a complex, yet highly relevant material and has been a rife area of research since the beginning of the 20th century.1-5 Understanding ice is expected to have consequences not just for furthering our appreciation of the different states of water, but also general chemistry, physics and geology.2, 6, 7 It has often been found that properties first observed in ice (e.g. stacking disorder) are also present in other materials.2, 6, 8, 9 This thesis largely builds on work performed by Shephard et al. which explored the effect of 2.5 mol% NH4F in ice, and astoundingly fully prevented ice II formation.10 Initially, the thesis focuses on the effect of adding NH4F to ice at ambient pressure, which is demonstrated to produce a denser material than pure ice. At 0.5 GPa, NH4F-ice solid solutions (≥ 12 mol%) surprisingly produce stable ice XII-type structures. Additionally, upon the mapping of the 2.5 mol% NH4F phase diagram to 1.7 GPa, it was found that phase-pure ice XII could be quenched at 1.1 GPa. Both ice XIItype structures did not require an amorphous precursor. The influence of NH4F in ice is explored in mixtures that are subjected to the compression conditions that yield high-density amorphous ice ‘pressure-induced amorphised’ upon their compression to 1.4 GPa at 77 K. Unexpectedly, the crossover of PIA to recrystallisation is determined as beginning on the water-rich side (35 mol% NH4F) of the solid solutions. Stacking disorder from the heating of NH4F II and III at ambient pressure is quantified. The materials reach a maximum cubicity of 77%, yet the stacking disorder obtained from each material is unique. Remarkably NH4F III did not transform to an amorphous phase upon heating. The final standalone chapter focuses on the ordering of ices V/XIII and IX with 0.01 M HCl doping.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available