1,271 research outputs found
CCDC 980693: Experimental Crystal Structure Determination
No full textRelated Article: Francesca P. A. Fabbiani, Colin R. Pulham, John E. Warre|2014|Z.Kristallogr.|229|667|doi:10.1515/zkri-2014-172
CCDC 980692: Experimental Crystal Structure Determination
No full textRelated Article: Francesca P. A. Fabbiani, Colin R. Pulham, John E. Warre|2014|Z.Kristallogr.|229|667|doi:10.1515/zkri-2014-172
CCDC 980691: Experimental Crystal Structure Determination
No full textRelated Article: Francesca P. A. Fabbiani, Colin R. Pulham, John E. Warre|2014|Z.Kristallogr.|229|667|doi:10.1515/zkri-2014-172
CCDC 980690: Experimental Crystal Structure Determination
No full textRelated Article: Francesca P. A. Fabbiani, Colin R. Pulham, John E. Warre|2014|Z.Kristallogr.|229|667|doi:10.1515/zkri-2014-172
Colin Humphris
No full text"Colin Humphris 2 Sqdrn. RAAF. 1941 - 1942 Author of - 'Trapped on Timor' (as a result of bombing of Darwin Feb. 19, 1942)".Colin Humphris. 2 Squadron, Royal Australian Air Force 1941 - 1942. Author of - 'Trapped on Timor' (as a result of bombing of Darwin February 19, 1942)
A high-pressure polymorph of propionamide from in situ high-pressure crystallisation from solution
No full textThe structure of a high-pressure polymorph of propionamide is reported from synchrotron single-crystal X-ray diffraction data. The polymorph was obtained by in situ high-pressure crystallisation from solution in a diamond-anvil cell at 0.9 GPa; its structure is 23% denser than that of the ambient-pressure polymorph at STP. PIXEL lattice and dimer energies calculations indicate that the ambient-and high-pressure polymorphs are energetically competitive. Together with acetamide and formamide, this is the third high-pressure polymorph of an aliphatic amide crystallising as a Z'=2 structure; the H-bonded network is however significantly different from the ones reported for the other two compounds. This study highlights the power of in situ high-pressure crystallisation techniques for accessing novel polymorphic forms of molecular compounds
Applications of liquid cathode electrochemistry towards the nuclear industry
Full text linkProjections of the World Energy Council indicate a significant increase in global energy
consumption in the medium and long term due to a growing world population and rising
prosperity whilst global fossil fuel reserves are in decline. Eighty percent of the world’s
energy consumption is generated from fossil fuels and this is unlikely to change in the
short and medium term inevitably leading to energy shortfalls. The CO2-less energy of
nuclear fuel shows strong potential to meet the future energy demands. However
economic, politic and environmental requirements mean that the nuclear industry must
adapt its current technology and present fuel usage. A pyroelectrochemical reprocessing
system utilising liquid cathode technology could provide an efficient and secure
reprocessing cycle essential for reduction in volume and toxicity of nuclear waste and
extension of natural nuclear resources.
The electrochemistry of aqueous copper(II) and zinc(II) chloride was studied upon a
liquid mercury cathode using cyclic voltammetry. Bulk deposition of the Cu upon the
liquid mercury cathode was studied using both amperometry and Electrochemical
Impedance Spectroscopy. The surface deposits formed by copper deposition upon the
mercury liquid cathode were analysed using x-ray powder diffraction and determined to
be the rare naturally occurring mineral Belendorffite, Cu7Hg6.
Electrochemical diagnostics for surface deposition upon the mercury liquid cathode
surface were investigated as a potential analogue system for high temperature liquid
cathode systems. Bulk deposition investigation of lanthanum upon the high temperature
bismuth system demonstrated transfer of EIS diagnostics for surface growth, with the
system demonstrating a similarity to the zinc-mercury ambient system.
An electrochemical technique for purifying LiCl/KCl molten salt using an electrolysis
technique was demonstrated. The electrochemical cleaning method forgoes the standard
chemical treatments that can leave contaminants within the treated salt and results in a
cleaner less oxidising molten salt eutectic
Structural studies on nitrocellulose: direct investigation and structural model
No full textNitrocellulose (NC) is a structurally important material with applications ranging from biomedical test membranes to propellants. As a polymer binder for double base propellants (DBPs), NC gives mechanical strength to solid formulations together with excellent combustion characteristics. The mechanical and chemical properties of NC make DBPs a versatile propellant system found in both rocket motors and gun propellants. Despite the widespread use of NC as a propellant, there is only limited and empirical understanding of how its structure affects mechanical properties. This is exacerbated further by the properties of cellulose - its precursor, a natural product that is subject to many variations. Poor understanding of why current DBP formulations perform well mechanically, combined with difficulties reliably producing these formulations, illustrates the need for better characterisation of their structure. Despite the relatively high crystallinity found in NC compared to other polymers, there remains no credible atomistic crystal structure for NC. This research therefore explores a selection of approaches to gain reliable structural information about NC through two general approaches: direct diffraction experiments and small molecule models.
First, fibre X-ray diffraction (FXRD) was used to probe NC directly. To achieve this, samples were optimised for high crystallinity and uniaxial orientation to give a high signal-to-noise ratio and strong well-defined diffraction signals. Various nitration methods, cellulose sources and annealing methods were evaluated through diffraction experiments to obtain optimal samples for FXRD. Meridional diffraction signals on the 7th, 10th and 15th lines of the fibre diffraction patterns were found, however a missing signal on the 5th line remains unexplained and casts doubt upon the previously proposed helical structure for cellulose making the possibility of simple 5- or 2-fold helical structures unlikely. The shortest repeat fitting the fibre XRD data determined here is now a 7-fold helical structure suggesting this as a plausible alternative worthy of investigation. This is the first reported evidence that the helical structure of cellulose does not take on the widely reported simple helical structures with low numbers of repeats. The overall fibre repeat, c-axis, length was found to be close to literature reported values at 25.6 Å.
The second approach looks to reduce NC chain length to increase crystallinity. The influence of NC polymer chain length on crystallinity of NC was first evaluated, utilising simultaneous hydrolysis and nitration of cellulose. The selectivity of hydrolysis was investigated finding that hydrolysis preferentially occurred in amorphous regions to give high crystallinity NC of short chain length. With short chain lengths, recrystallisation of this material revealed additional Bragg peaks in diffraction experiments. Based on this, small-molecule analogues of NC were prepared, starting with cellobiose octanitrate (CON), the dimer of NC. The structure of the dimer is structurally characterised using single crystal X-ray diffraction and compared with published unit cell dimensions for NC, finding significant similarities. Packing and intermolecular interactions were investigated through non-covalent interaction plots and Hirschfeld surfaces. The dominant interaction was found to be non-classical H-bonding at C-H…O-N; this contrasts with the strong classical H-bonding seen for the non-nitrated dimer. Further crystal structures for isomers of CON: maltose octanitrate (MON), lactose octanitrate (LON) and trehalose octanitrate (TON) were obtained. Comparison of these structures highlights the influence of the polysaccharide structural features on molecular structure and packing.
This thesis builds up a more comprehensive structural understanding of NC and rationalises the properties of NC through this structural model. Experiments presented here, especially the initial FXRD results and determination of NC dimer crystal structure, provide a foundation to determine a fully atomistic crystal structure of NC. Ultimately, reliable structural models for NC could enable better control of NC material properties. Through such models the characterisation of individual NC samples would be possible, along with the development of structure property relationships. This could potentially provide a route to NC without the variability found in naturally derived materials
Towards understanding the catalytic properties of lead-based ballistic modifiers in double-base propellants
Full text linkDouble-base propellants, derived from nitrocellulose and nitroglycerin, are a
combined solid fuel and oxidiser system. They present smokeless combustion, and are
typically utilised for small rocket motor applications. In order to provide stability in
combustion performance, ballistic modifiers, which modify the burn-rate properties
in three distinct ways, are added to the formulation. However, these additives are
lead-based, which poses personal and environmental safety concerns. Moreover,
impending European legislation will soon ban their use. Despite years of experimental
research, no viable alternative currently exists, and so the impending ban presents a
considerable challenge for our defence industries. For this reason, the main aim of this
thesis is to develop a better understanding of the fundamental role played by lead as
a ballistic modifier.
Catalysis with the lead-based ballistic modifier is known to occur at the solid/gas-phase boundary of the propellant, which is known as the burning surface. It is
assumed throughout this work that the lead additives, presented as metal salts in the
propellant formulation, will decompose to lead oxide in the high temperatures (> 300
C) of the propellant flame. This is taken as the baseline catalytic model. As such, in
this work two computational models have been employed; one to investigate catalysis
in the solid-state, the other in the gas-phase. The lead additives are known to generate
(i) super-rate, (ii) plateau-burn and (iii) mesa-burning effects, and it is known that
carbon-soot, which builds up and is subsequently lost from the burning surface, plays
an essential (but unknown) role in these burn-rate phenomena. Thus the interaction
of carbon with lead oxide is a recurring theme throughout this work.
Looking first to the solid-state, Chapter 3 documents a comparative study of the
properties of several metal oxides, namely lead, tin and bismuth oxide. Tin and
bismuth oxide are ballistic modifiers which demonstrate super-rate burning, but fail
to produce plateau- and mesa-rate burning. This chapter examines the chemical
reactivities of each metal oxide through computation of their electronic band gaps,
surface energies and surface work functions, to deduce any unique properties that
separates the behaviour of lead oxide from the other metal oxides. A layer of
amorphous carbon is also bound to the stable surfaces of each metal oxide to ascertain
whether any significant differences in bond strength and surface integrity arise.
Chapter 4 turns its attention to investigate the formulation of industry-standard
ballistic modifiers, which are derived from a blend of lead and copper salts. Here the
structures of stable small metal oxide clusters which could form in the gas-phase
above the burning surface are investigated with respect to their interaction with
carbon. The individual roles of each metal in terms of the burn-rate effects are
accounted for, and a phenomenological model is proposed that accounts for the three
burn-rate effects. Finally, Chapter 5 presents a continuation of the narrative from
Chapter 4, and widens the gas-phase discussion to include tin and bismuth oxide. The
results obtained further validate the catalytic model presented in Chapter 4. Thus
overall, the work reported in this thesis provides an atomistic interpretation of ballistic
modifiers in double-base propellants, routed in first principles simulation, that
provides a new platform for the continued search for lead-free additives
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