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Browsing Cranfield Defence and Security by Publisher "American Chemical Society"
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Item Open Access Catalytic effects on the nonisothermal oxidation of solid fuels by oxygen: an experimental study(American Chemical Society, 2019-09-24) Nyombi, Antony; Williams, Mike; Wessling, RolandThe role played by catalysts in solid fuel reactivity toward oxygen as a viable method for reducing toxic combustion emissions was studied. Catalyst (1 wt % Pd–Sn/alumina) treated and untreated solid fuels were analyzed using thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) coupled with a gas detection system at heating rates of 20–40 °C/min and airflow rates of 30–100 mL/min. The relative CO emission factors, NOx, CH4, energy output, and combustion efficiency were determined as well as values of the activation energy (Ea) and pre-exponential factor (A) for the oxidation of the solid fuels. Results showed that the catalyst treatment enhanced the energy output by more than 22% and reduced CO emission factors by up to 87%. The temperature for release of nitrogen compounds was considerably reduced; however, the amounts produced were not impacted. The combustion efficiency was also improved by up to 60%. In terms of reactivity, catalyst treatment lowered the Ea for oxidation especially at 0.2 ≤ α ≤ 0.8. Catalyst treated samples had more free active sites on their surfaces, which decreased at temperatures of >500 °C possibly due to thermal deactivation of the catalyst. This is a viable method for minimizing toxic emissions from solid fuel combustion and enhancing energy output for domestic and industrial applications.Item Open Access Elastic Deformation in Ceria Nanorods via a Fluorite-to-Rutile Phase Transition(American Chemical Society, 2010-02-28T00:00:00Z) Sayle, T.X.T.; Sayle, D.C.Atomistic simulations reveal that ceria nanorods, under uniaxial tension, can accommodate over 6% elastic deformation. Moreover, a reversible fluorite-to- rutile phase change occurs above 6% strain for a ceria nanorod that extends along [110]. We also observe that during unloading the stress increases with decreasing strain as the rutile reverts back to fluorite. Ceria nanorods may find possible application as vehicles for elastic energy storage.Item Open Access John N. Sherwood: studies of energetic materials(American Chemical Society, 2023-07-03) Vrcelj, Ranko; Gallagher, Hugh G.; Halfpenny, Peter J.The studies on the physico-mechanical properties of commonly used energetic materials (EMs) that were pursued by the group led by Professor John Sherwood are reviewed in this paper. The studies ranged from the growth of high quality single crystals and the characterisation of their defect and dislocation structures, mechanical testing, through to the study of polymorphism of EM crystals and fundamental aspects of crystallization processes generally. The work performed lead to the definition of good growth conditions for all the EMs studied and to the full characterization of the defect structure, slip systems and hardness properties of cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN). Partial characterization of the defect structures and hardness properties of cyclotetramethylene tetranitramine (HMX) and 2-4-6 trinitrotoluene (TNT) were also achieved. Additionally, fundamental crystal growth and polymorph information was defined, allowing a deeper understanding of the crystallization and crystal structure of TNT. In addition to the general review, some thoughts as to possible future routes for further study that could suitably utilize the complementary nature of established and modern techniques.Item Open Access Primary alkyl phosphine-borane polymers: Synthesis, low glass transition temperature, and a predictive capability thereof(American Chemical Society, 2017-11-30) Cavaye, H.; Clegg, F.; Gould, P. J.; Ladyman, Melissa K.; Temple, Tracey J.; Dossi, E.With a multitude of potential applications, poly(phosphine-borane)s are an interesting class of polymer comprising main-group elements within the inorganic polymer backbone. A new family of primary alkyl phosphine-borane polymers was synthesised by a solvent-free rhodium catalysed dehydrocoupling reaction and characterised by conventional chemico-physical techniques. The thermal stability of the polymers is strongly affected by the size and shape of the alkyl side chain with longer substituents imparting greater stability. The polymers show substantial stability towards UV illumination and immersion in water however they undergo a loss of alkyl phosphine units during thermal degradation. The polymers exhibit glass transition temperatures (Tg) as low as -70 °C. A group interaction model (GIM) framework was developed to allow the semi-quantitative prediction of Tg values and the properties of the materials in this study were used to validate the model.Item Open Access Reactivity and free radical chemistry of lilac (Syringa vulgaris) charcoal(American Chemical Society, 2019-01-28) Nyombi, Antony; Williams, Mike; Wessling, RolandThe reactivity, and surface chemistry of charcoal determine its combustion behaviour, and these properties depend on the source of the original wood, production conditions and treatment. Here we studied the properties of charcoal derived from lilac (Syringa vulgaris). Its reactivity was tested by isothermal and non-isothermal thermogravimetric analysis and differential scanning calorimetry in air and nitrogen. The free radical concentration was determined by measuring the electron spin resonance of fresh charcoal, after washing with HCl, and after degassing in air with or without nitrogen. We found that lilac is highly reactive, igniting at 250–300 oC with peak combustion at 320–520 oC. The quantity of oxygen consumed and heat released during oxidation increased with temperature. The free radical concentration in the untreated charcoal was 5.29 x 1018 spins/g, compared to 3.49 x 1019 spins/g after acid washing, 7.06 x 1019 spins/g after exposure to air, and 3.75 x 1017 spins/g after degassing with nitrogen before exposure to air. The line width of all the charcoal samples was 11.6–11.9 G. However, degassing the charcoal in nitrogen followed by exposure to air at low temperatures resulted in a four-fold increase in the line width to 41.8 G. The exposure of lilac charcoal to air alone at low temperatures resulted in the formation of persistent peroxyl radicals superimposed on the main peak. The g-values of charcoal samples that were untreated, acid washed, degassed in N2 + air, and degassed in air alone (main peak) were 2.00481, 2.00477, 2.00260 and 2.00483, respectively. The g-values of the peroxyl radicals superimposed on the main peak were 2.0155, 2.0138, 2.0020 and 2.0007, respectively. The reactivity, and free radical content suggest that lilac charcoal is particularly suitable for applications involving energetic materials, catalysis and co-firing.Item Open Access Seeded crystal growth of the acentric organic non-linear optical material Methyl-p-Hydroxybenzoate (MHB) from the vapour phase(American Chemical Society, 2023-06-06) Hou, Wenbo B.; Ristic, Radoljub I.; Sherwood, John N.; Vrcelj, RankoUsing in-situ differential interference contrast microscopy (DICM), growth morphology, structure, and step velocities of the vicinal hillocks on {110} and {111̅} faces of MHB crystal seeds growing from the vapour phase have been investigated over a supersaturation (σ) range of (0.2 < σ < 0.6). Under these conditions of supersaturation, a dislocation induced growth mechanism was identified. Ex-situ atomic force microscopy (AFM) shows that some dislocation induced hillocks exhibit hollow cores. The general observations of the {110} and {111̅} surfaces reveal that these faces follow a classical mode of layer growth, continuous generation of new layers by dislocation outcrops, which subsequently bunch and spread to cover the entire facets. A tangential step velocity of the slow and fast sides of {110} and {111̅} growth hillocks show a linear dependence with supersaturation in the region of (0.2 < σ < 0.4). Analysis of this dependence leads to the respective growth parameters for the identified growth mechanism: the activation energies for the slow and fast step motion of a growth hillock (EaS and EaF) and the corresponding kinetic coefficients (βaS and βaF), for both faces. The growth from physical vapour transport (PVT) shows that for the title material, as with a number of other polar materials, solvent poisoning is not the cause of the highly differential growth rates and is an intrinsic feature of the crystal. The results suggest that in terms of the production of large single crystals of high perfection by PVT, the supersaturation range for dislocation growth should be between 0.2 and 0.4. These findings provide a foundation for the rational design of large MHB crystals that may find applications utilizing their high optoelectronic potential.Item Open Access Ultrasonic studies of solid azobenzene decorated polymer thin films(American Chemical Society, 2018-12-19) Moniruzzaman, Mohammed; Christogianni, Paraskevi; Vrcelj, Ranko; Gill, Philip P.This work investigates the effect of ultrasound on switching of cis azobenzene isomers to their trans counterparts in solid films of methyl methacrylate and methacryloyloxyazobenzene copolymers [P(MMA/MOAB)]. UV/Vis and 1H NMR spectroscopy demonstrates that 46% of the cis isomer converts to the trans form purely by ultrasonic agitation and 46% converts to the trans isomer by localised ultrasound induced heating effects. Comparative studies of isomerisation by ultrasound wave, heat and visible irradiation shows that ultrasound exposure requires a longer time to switch the cis to trans conformation. The estimated activation energy for the cis to trans conversion in the solid polymer films is shown to be comparable to previous values of azobenzene isomerization, indicating that incorporation of the chromophore in a polymeric system affects the kinetics of transition, but not the barriers to conformational change.