Browsing by Author "Akhavan, Jacqueline"
Now showing 1 - 14 of 14
Results Per Page
Sort Options
Item Open Access Cross-linking of hydroxyl-terminated polyols with triethyleneglycol diglycidyl ether: an alternative to toxic isocyanates(Wiley, 2018-01-16) Dossi, Eleftheria; Akhavan, Jacqueline; Gaulter, Sally E.; Williams, Richard G.; Doe, William J.Isocyanates are highly reactive and toxic substances with severe health effects. Certain diisocyanates are restricted under REACH – The European Regulation on Registration, Evaluation, Authorisation and Restriction of Chemicals. Triethyleneglycol diglycidyl ether (TEGDGE) was used as an alternative to toxic isocyanates for the cross-linking of hydroxyl-terminated pre-polymers at 70oC. The effect of three curing accelerators was determined while following the reaction kinetics by 1H-NMR spectroscopy and differential scanning calorimetry (DSC). Polybutadiene (Poly BD R45HT-LO) and acrylic ester (HyTemp 4454) successfully cross-linked in 7–10 days to produce thermally stable networks with low glass transition temperatures, as observed by DSC. Pre-aging the polybutadiene resin promoted cross-linking with TEGDGE. Four energetic compositions were then prepared using cyclotrimethylenetrinitramine (RDX) and pentaerythritoltetranitrate (PETN) as fillers, and polybutadiene (Poly BD R45HT-LO) and acrylic ester (HyTemp 4454) as binders. Both binders successfully cross-linked with TEGDGE in the presence of RDX and PETN, but only PETN was found to be chemically compatible with the cross-linked polymers. These results show that TEGDGE is suitable as a replacement for toxic isocyanates for the cross-linking of hydroxyl-terminated polyols.Item Open Access The development of a laser detonator system(2015-06-26) Bowden, M.; Akhavan, Jacqueline; Drake, R. C.Laser detonators offer several advantages over traditional electrical detonators, such as exploding bridgewire and slapper detonators, in terms of both safety and performance. Laser detonators remove the electrical conduction path to the energetic material, providing immunity from threats such as electrostatic discharge and lightning. A larger separation between the initiating energy source and the explosive devices is possible, up to several tens of metres, compared to a few metres for electrical slapper detonators. A laser detonator system has been developed, with laser-driven flyer plates used to shock initiate the explosive. All aspects of the system, including coupling into an optical fibre, used to transmit the laser energy to the detonator, the optical fibre, the flyer plate launch and acceleration and subsquent shock into the explosive, and the explosive initiation have been investigated, with an understanding of the underlying principles and processes developed. Shock initiation of two secondary explosives, hexanitrostilbene and pentaerythritol tetranitrate, has been studied at extremely high shock pressures, comparable to the detonation pressure, and the critical energy fluence required for initiation established. The laser detonator system is robust and optimised, with design tools developed to enable efficient design of future systemItem Open Access The Development of explosives competencies, training and education in the UK(2009-03-30T00:00:00Z) Wallace, Ian G.; Akhavan, Jacqueline; Murray, S. G.; Hooper, G.Competent explosives workers in the Armed Forces and in the civil sector are critical to the safe production, testing and use of explosives. Moreover we need competent explosives specialists to combat the challenge from terrorism and clean up the planet from the explosive hazards that are the legacy of past conflicts. Unfortunately many countries are witnessing a significant loss of capability in this area and are looking at ways of replenishing vital expertise. This paper describes the work done in recent years by the authors and others in the UK to establish numbers of people working in the sector and to consider the skills and knowledge required to carry out their work. It outlines the concept of national occupational standards and the framework of professional and vocational qualifications that are available or are being developed for explosives specialists. It also describes some of the educational and e-learning programmes designed to support this initiative. Ultimately the aim is to address the professionalism of all personnel who deal with explosives in order to reduce the incidence and consequence of accidents and maintain national capability.Item Open Access The development of Novel, Low Sensitivity, Gas-generating Formulations for Hotwire Ignited Devices(2013-04) McAteer, Daniel; Akhavan, Jacqueline; Contini, AlessandroA novel, low sensitivity, gas-generating composition was developed to replace an existing primary explosive, potassium picrate, for use in a generic squib device. The novel composition was based on energetic materials researched from the open literature. The chosen materials were synthesised or purchased and combined in order to produce formulations which would reproducibly ignite when contacted with a hotwire. The formulations were assessed for their chemical compatibility and homogeneity by small-scale hazard testing, differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) spectroscopy. The compositions were test fired within squibs coupled to a pressure bomb and the pressure generation and rise time was measured using a piezoelectric gauge.Item Open Access The effect of ionising radiation on the explosives: TATB, HMX and PETN(Cranfield University, 2019) Lewis, D. A.; Akhavan, Jacqueline; Cook, M.; Wilson, I; Stennett, C.The effect ionizing radiation, specifically gamma, has on three of the most well known explosive materials; HMX, PETN and TATB, has been studied experimentally and computationally. Samples of these explosives that had been irradiated in vacuum to a total dose (equivalent to water) of 200 kGy by an average incident energy of 1.25 MeV, showed changes to their explosive and physical properties to varying degrees, with sensitivity to impact being most notably changed for PETN and HMX. Changes to the thermal properties of HMX and TATB, alongside the detection of long lived radicals for TATB and PETN, suggests alterations to each material’s chemistry. Changes were only detectable in solid state analytical methods, indicating that alterations to these materials are isolated within this state. Through comparison with other data, these changes appear to be highly dependant on the gaseous environment in which they are irradiated, with vacuum having the most significant effect. The widely reported greening of TATB under the influence of gamma (and ultraviolet and x-Ray) irradiation was found to be reversible upon re-crystallisation, with the process also appearing to remove the long lived radical that had existed in the material for over eight years. Radical concentration appears to correlate with total absorbed dose along with the level of green within the material. Computational investigation attributes the discolouration of TATB to the cationic radical derivative of TATB, which is stabilised by de-localised pi-bonding resonance of the constitutive aromatic ring, it is also suggested that this is the source of the radical signal observed in ESR analysis.Further computational investigation suggests that purported decomposition products of TATB such as the mono-furazan, mono-nitroso and phenoxyl radical are not the source of the discolouration and are also not thermodynamically favourable, unless the monofurazan or phenoxyl derivatives are in a cationic form. Thermodynamic evaluation of potential decomposition pathways for PETN and HMX yield a selection of energetically favourable products, however the significant majority are, like TATB, in the cationic radical form. Simulated ESR spectra for purported HMX decomposition products did not agree with those observed in literature, attributed to their short lived nature. However a measured long lived radical in TATB is attributed to the cationic radical form of TATB, the purported source of the discolouration. A long lived radical in PETN was also measured and assigned to the cation derivative of PETN by comparison with computational predictions.Item Open Access The effects of Gamma radiation on a PBX containing TATB and the fluoropolymer FK-800(2014-06-10) Connors, S. C.; Akhavan, Jacqueline; Padfield, JamesThe polymer bonded explosive TCV is analogous to PBX compositions used in some nuclear weapons where the PBX will be exposed to high energy ionising gamma radiation. It is therefore important to study how gamma radiation affects the mechanical and chemical properties of the PBX. In this study 60Co was used to irradiate samples of the TCV, its FK-800 binder and TATB explosive filler, at 37.5 °C, to total doses up to 200 kGy in air and under vacuum. Post irradiation analysis consisted of mechanical, thermal and chemical analysis of the irradiated materials. Results from the radiolysis of the FK-800 showed predominant main chain scission taking place, these results in the release of volatile fluorine containing products and an increase in the polymer’s crystallinity. The changes to the FK-800’s structural properties result in an increase in Young’s modulus and yield stress whilst reducing both ultimate tensile strength and elongation at maximum stress. Dynamic mechanical analysis shows the material softening initially upon irradiation, then stiffening as crystallinity increased. TATB was found to turn green and have increased sensitiveness to impact and electric spark discharge with gamma radiation. Analysis by HPLC and LC-MS identified a decomposition product with a mass of 240 g mol-1. No significant changes to the mechanical properties of TCV were identified; however, its sensitiveness to impact and electric spark discharge were found to increase similar to TATB’s. In conclusion, gamma irradiation of TCV has identified significant changes to the mechanical and chemical properties of the FK-800 binder, have little to no effect on mechanical properties of PBX up to 100 kGy. The predominant radiolytic effects on TCV were to its hazard characteristics caused by changes in the TATB. A mono-furazan derivative of TATB has been suggested as the decomposition product identified, and as a possible cause for the increase in sensitiveness of TATB upon gamma irradiation.Item Open Access An estimate of the TNT-equivalent net explosive quantity (NEQ) of the Beirut port explosion using publicly-available tools and data(Wiley, 2020-10-21) Stennett, Chris; Gaulter, Sally; Akhavan, JacquelinePublicly available video recordings of the explosion in Beirut on August 4, 2020, were examined and from them it was possible, in conjunction with the well‐known Google Maps website, to obtain estimates for the locations of the observers’ cameras with respect to the blast, and estimates for the blast wave arrival time. A publicly‐available blast wave calculator was then used to estimate the size of the explosion in terms of the equivalent quantity of TNT that would produce the same blast wave arrival time at the observers’ distance. This work estimates the Beirut explosion to have been equivalent to 637 tons TNT, with a lower bound estimate of 407 tons and an upper bound estimate of 936 tonsItem Open Access Further insights into the discoloration of TATB under ionizing radiation(Taylor and Francis, 2020-02-26) Lewis, Dan; Padfield, James; Connors, Scott; Wilson, Ian; Akhavan, JacquelineTo determine degradation products formed by exposure of TATB to ionizing radiation, a computational and experimental study is presented. Thermochemical and spectral data have been calculated using DFT at the MH06-HF/aug-cc-pVTZ level which suggest the formation of the cation radical derivative of TATB. Irradiated TATB samples showed the widely reported yellow-to-green discoloration, with measured CIE L*, a*, b* and RGB values correlating with total dose. Trace quantities of a mono-furazan derivative were detected by HPLC-MS; the discoloration is not attributed to this, but rather to the presence of a paramagnetic species (i.e., the cation), as detected by ESR measurements. Recrystallized irradiated TATB samples reverted to their original color, further suggesting it is the cation radical that is responsible for color change.Item Open Access The Ignition Behaviour of Energetic Materials Under Confined Cookoff(2018-09) Stennett, Christopher; Akhavan, JacquelineIn a series of experiments and theoretical work, the process of ignition in confined energetic materials has been explored and understanding gained. Early work focused on the direct observation of the cook-off process but was hampered by the available technology. In more recent work, dynamic measurements of the deformation of the confinement have been explored, and refinements to the direct observation method have been made that make use of recent advances in camera technology. We have observed, for the first time, complex melting and development of gas spaces within which the early stages of ignition take place, and propose a new mechanism by which violent cook-off responses might develop in certain explosivesItem Open Access Low hazard small-scale synthesis and chemical analysis of high purity nitroglycerine (NG)(Royal Society of Chemistry, 2015-10-06) Contini, Alessandro E.; Flood, Nathan; McAteer, Daniel; Mai, Nathalie; Akhavan, JacquelineA previously reported two-phase (99.5% fuming nitric acid/dichloromethane) batch method to prepare high purity 1,2,3-propanetriyl trinitrate (nitroglycerine, NG) was evaluated, simplified and adapted specifically for low hazard small-scale synthesis. The purity of the product, as determined by NMR spectroscopy, HPLC and IR spectroscopic analysis was found to be greater than 99%. The quick synthetic method is highly recommended when small amounts of highly pure NG are required for analytical and related purposes in the absence of a microreactor.Item Open Access Material strength evolution of FCC metals under high strain rates(2020-12) Gilroy-Hirst, Caitlin; Hazael, Rachael; Wood, David; Akhavan, JacquelineCopper and stainless steel 21-6-9, two face-centred cubic (FCC) materials, were shock loaded in partially recovered uniaxial strain flyer-plate impact experiments at varying impact pressures (6 GPa - 16 GPa). These samples were collected post impact via three differing recovery configurations: (1) standard or ‘free boundary’; (2) partial shock recovery, i.e. using both ‘momentum trapping’ and ‘soft recovery’ techniques but with a flyer plate thickness of 10 mm to see the effects on partial tensile release in the rear spall plates of an established recovery target design; finally (3) a traditional full recovery comparison with a 2 mm flyer impact. These samples were then analysed using a suite of analytical techniques including X ray diffraction, optical microscopy, hardness testing and compression after impact testing, to observe the material deformation characteristics in the simplified partially recovered shock and release condition compared to the more complex ‘standard’ release wave situation. A control sample of a ‘ fully recovered’ sample was also carried out for comparative purposes. The rear spall plates were modified on these partially recovered samples to see the effect that this had on the tensile release waves and how this changed the material deformation properties overall. Results for the stainless steel 21-6-9 demonstrated the ability of the partial shock recovery technique (hereafter called ‘partial-recovery’) to mitigate the reverberations compared to that of the standard samples. Upon analysis of the targets, it was observed that the dislocation density was generally lower for the partially recovered samples but varied with impact pressure for both the standard and recovered configuration. For the stainless steel recovery experiments an increasing dislocation density from 4 x 1015 m-2 at 6 GPa to 6.5 x 1015 m-2 at 12 GPa was observed which then decreased to 5.5 x 1015 m-2 at 16 GPa. The twinning density to grain ratio obtained from optical microscopy showed a linear increase (y= 1.5345x - 8.3508) with an R2 value of 0.8295 from 7 GPa at 4 twins per grain to 17 twins per grain at 16 GPa. Twinning density is indicative of a successful recovery, where a successful recovery is a reduction in reverberations in the sample and in a full recovery is a 1D shock. The dataset both verifies the use and success of the recovery technique as well as demonstrating the materials characteristics under partial-recovery, while observing reverberation effects.Item Open Access Nitrogen-14 NMR spectroscopic detection of explosophores in solution(Wiley, 2016-12-02) McAteer, Daniel; Akhavan, JacquelineNitrogen‐14 (14N) quadrupolar nuclear magnetic resonance (NMR) spectroscopy was used to detect and measure the chemical environment of various nitrogen nuclei located within the explosophore of many commonly studied explosives in solution (Figure 1). The values are presented here as a resource for researchers in the field who may find use in this non‐destructive and convenient analytical technique.Item Open Access The shock Hugoniot of hydroxy-terminated polybutadiene(AIP, 2004-08-04) Meziere, Y.; Akhavan, Jacqueline; Stevens, G. S.; Millett, Jeremy C. F.; Bourne, Neil K.The response of polymers to shock loading is becoming of increasing importance, both as binder systems in plastic-bonded explosives (PBXs) and as structural materials in their own right. In this paper, we report on the shock Hugoniot of hydroxy-terminated polybutadiene (HTPB), which is commonly used as a binder system in PBXs, but whose shock response has yet to be presented in the open literature. Results indicate that the shock velocity --- particle velocity relationship is linear, similar to some but not all polymer-based materials.Item Open Access Understanding the explosion risk presented by ammonium nitrate and aluminium home-made explosives detonated as surface charges in hexahedral main charge containers(Springer, 2024-07-15) Collett, Gareth; Akhavan, Jacqueline; Critchley, RichardAmmonium nitrate and aluminium (AN–Al) has been used as a typical homemade explosive (HME) by non-state actors since the turn of the century. Despite the regulation applied to ammonium nitrate above 16% nitrogen content and an aluminium particle size below 200 µm, their use has been widespread in Afghanistan, Columbia, Iraq, Syria and Yemen. Containers used to utilise AN–Al as a man-portable improvised explosive device (IED) are typically hexahedral in shape, not the spherical or hemispherical geometries used to theorise risk mitigation. This is particularly important in post-blast investigation where explosives of a non-ideal nature are often used in non-spherical containers. Given the breadth of HME available to criminals, the explosion performance of forty hexahedral containers filled with AN–Al of unknown manufacture is examined. Performance of the AN–Al is determined through the surface detonation of these containers on alluvial soil, with apparent crater volume compared to theoretical calculations for spherical charges of TNT detonated in that same medium. A conversion factor for hexahedral main charges to spherical charges is then established to achieve more accurate predictions of the explosion risk using Kingery-Bulmash and Bowen curves. The paper provides worked examples for practical application and a methodology by which predictions of charge mass in other mediums such as asphalt can be determined.