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Title: The ammonia, carbon dioxide and water ternary system
Author: Howard, Christopher
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2019
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Interactions between simple molecules are of fundamental interest across diverse areas of the physical sciences, and the ternary system NH3 +CO2 H2O is no exception. In the outer solar system, interaction of CO2 with aqueous ammonia is likely to occur, synthesising 'rock-forming' minerals, with CO2 perhaps playing a role in ammoniawater oceans and cryomagmas inside icy planetary bodies. In the same context, ammonium carbonates may have some astrobiological relevance, since removal of water leads to the formation of urea. On Earth, combination of CO2 with aqueous ammonia has relevance to carbon capture schemes, and there is interest in using such materials for hydrogen storage in fuel cells. Consequently, from earthly matters of climate change to the study of extraterrestrial ices, understanding the structures and properties of ammonium carbonates are important. Despite this, our knowledge of ammonium carbonates is limited, even under ambient conditions of pressure and temperature, and is entirely absent at the higher pressures, severely limiting our ability to model the behaviour of NH3 +CO2 H2O solids and fluids in planetary environments. This work reports the results of several experiments using variable pressure and temperature neutron diffraction work on ammonium bicarbonate [NH4HCO3] and ammonium carbamate [[NH4]+[NH2CO2] - ], with complementary Density Functional Theory (DFT) calculations. The excellent agreement between experiments and DFT calculations obtained so far adds weight to the accuracy of calculated material properties of ammonium carbonate monohydrate [(NH4)2CO2 H2O], ammonium sesquicarbonate monohydrate [(NH4)4(H2(CO3)3) H2O] and several polymorphs of urea [CO(NH2)2] where little empirical data exists. These experimental and computational studies provide the structural and thermoelastic information required for accurate planetary modelling and remote identification of these material on planetary surfaces.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available