Energetic Materials Round Up
Introduction
As in previous year’s we have attended and presented information at a number of energetics related meetings, these included 48th ICT in Germany, the 8th KISHEM in South Korea and the Pyrotechnics workshop in Germany. We were unable to attend or be present at all meetings, such as the annual seminar NTREM held in the Czech Republic.
Both ICT and KISHEM were well attended with an increase in the number of participants from previous years and a good quality in the presented work. ICT had 296 people registered to attend the meeting with 27 countries were represented, and of those 12 were MSIAC member nations. KISHEM had 17 countries represented (7 MSIAC nations) and over 100 submitted abstracts; 52 oral papers were delivered and 56 posters were presented over the 3 days.
Pyrotechnic Workshop (26-Jun-17)
The pyrotechnic workshop was held in conjunction with ICT and was entitled Combustion Mechanisms: Thermites – Versatile Energetic Materials. This workshop is usually held in association with the International Pyrotechnic Symposium.
The workshop was chaired by Dr Knapp (ICT) and Dr Koch (Lutradyn) and the day allowed for several presentations and discussion surrounding thermite processes. The first presentation touched upon the potential explanation as to why, after high temperature reactions, low concentrations of elements not present in reactants are present (Prof Gromov; Tomsk University, RUS). These reactions were described as Kervran-Bolotov transmutation reactions whereby elements such as Ca, K and Na can be found after thermitic reaction of Al with Fe2O3. Discussion within the group stated that similar ‘impurities’ have been seen in detonations and explosive bridge wires reactions but that the impurity answer has always been the easy explanation. This will no doubt be a topic for further and future discussions.
Doorenbos (LLC; USA) provided an overview of Fe-based solid state combustion emitters with the addition of multiwall carbon nano tubes. Resodyn Acoustic Mixing (RAM) was used for manufacture of the Fe-MWNT with a range of oxidisers. Good results were observed using Al2SiO5 but the project remained at the research level.
Comet (ISL; FRA) described their work on nanothermites and the ability to use them as initiators. DDT reactions were possible using mixtures of Bi2O3/nAl/nRDX giving reaction velocities of 2700 m s-1 in 6-8 mm. Tests were able to shock initiate secondary explosives within 50 µs. A good understanding of density effects and sensitiveness could lead to these materials being used in detonators.
Catoire (ENSTA Paris Tech; FRA) provided detailed chemical kinetic models for nanothermite combustion and highlighted the detailed work required to capture the experimental parameters such as elementary kinetics for these reactions.
Weinhold (Schott, DEU) gave an interesting presentation on the variety of glass based thermites from bullet-proof glass to shaped charge jet (SCJ) liners. Fabrication of the SCJ liners required multiple steps, selection of three powdered materials at the correct particle size distribution; addition of polymer matrix and the use of a LabRAM to mix high viscosity material. Subsequent step included sintered and/or passivation in inert atmosphere to produce the final product.
Weiser (ICT; DEU) provided a systematic comparison of theoretical and performance data for thermite systems. Of these reactions, a matrix of 6 (metals) by 18 (oxides) were tested for burn rate, particle release, temperature of reaction (in N2 & air) and compared against the EVKI adiabatic temperature code. The correlation between actual temperature measurements against models was lower than expected. The sources of errors or understanding of the thermite materials would improve the correlation.
Finally Proud (ISP; GBR) provided an overview of shock and ignition properties of thermites that Cavendish and ISP had performed over the last 40-50 on the topic. One of the take away points was thermites were more sensitive to shock impact when in pressed disc form compared to loose powder.
48th ICT (27 – 30-Jun-17)
The topic of this year’s conference was energetic materials: reactivity and modelling, which attracted 39 oral presentations and 125 posters. The opening address was given by Dr. Stella Oldenbürger (German MoD) in which she referred to the development of a toolbox to aid the German government to make responsible decisions. Responsibility means choosing the right option, options are needed and that is where scientists come in to provide the options/advice.
Some of the highlights of the meeting are included plus the winners of the poster competition.
Poster winners
- 1st - P80, Wenchao Zhang, PRC. Template-directed construction of three dimensionally ordered macroporous materials for nanothermites
- 2nd - P59, A. Mitchell, GB. The development of a time resolved initiation characterization test
- 3rd - P108, A. Provatas, AUS. Development, characterization and ageing of an alternative plastic explosive
- 1st (ICT) - P126, S. Hafner, ICT-Poster Award. Synthesis of copolyethers for energetic binder systems
Synthesis
Of main interest was the high output of ammonium dinitramide (ADN) based research. Heil (ICT; DEU) provide some information on stabilising ADN, whilst Heintz (ICT, DEU) showed the effect of prilled particle properties on sensitivity. A number of propellant papers also provided results of combustion behaviour (Imiolek, ICT; DEU), ballistic modifiers (Tagliaue, ICT; DEU) and decomposition behaviour (Freudenmann, DLR; DEU).
Processing and Formulations
Doorenbos (LLC; USA) provided characterisation of a DBX-1 based composite energetic material for percussion primer applications. This work was looking to replace lead styphnate in primers.
Provatas (DST Group; AUS) provided an excellent review on the hazard and performance properties of ARX-2045. This material was investigated as a replacement for PE-4, and used RS-RDX, polydimethylsiloxane (PDMS) binder and taggant. ARX-2045’s performance matched that of PE-4, had a larger critical diameter and showed promising ageing characteristics.
Propellants & Pyrotechnics
An interesting 3-D printed propellant grain using a helical grain geometry showed an increase in performance properties (Zhou, National University of Defense Technology; PRC). Griffiths (Qinetiq; GBR) gave a presentation on pyrotechnic delay formulations containing 1,2,4-trihydroxyanthraquinone; a naturally occurring dye from the madder plant. Both the method of manufacture and ingredient particle size were found to influence the burning rates of the compositions.
Testing
A redesign and evaluation for the method to determine the erosivity of gun propellant led to a standard model that was independent of experimental conditions and propellant type (Langlotz, Diehl; DEU)
Hobbs (Sandia; USA) presented working using their SITI test apparatus to understand the binder effects during cookoff of HMX formulations. 12 HMX-based explosives were tested with different binders. The employed model was able to describe the cookoff process using either HMX kinetics or HMX and a binder kinetics irrespective of the binder type. This, along with the experimental data, highlighted when the binder was involved in the reaction which was related to density-dependent thermal conductivity.
4th KISHEM (29-Aug – 01-Sep-17)
This was the 4th iteration of the Republic of Korea’s symposium on energetic materials. It was, however, the first time that it was held jointly with the Chinese International Autumn Seminar on Propellants, Explosives and Pyrotechnics (IASPEP). The topics covered in the plenary sessions included synthesis, mechanical behaviour of binders, modelling of SDT/DDT, environmental aspects, propellants, and pyrotechnics. Similar topics, including storage, were covered in the parallel sessions.
Synthesis
Plugged flow microfluidics for the synthesis of primary explosives, lead styphnate, was presented by Shen, R (Nanjing; CHN). This is one of many recent papers now referring to this technique for energetic materials manufacture. The continued work on the synthesis of nitroazapropellanes was reported by Lee, B (Seoul National University; ROK). The target compound of 2,4,6,8,9,11-hexanitro-2,4,6,8,9,11-hexaaza[3.3.3]propellane has still not been achieved, but results were however presented on the formation of 2,6-dinitro-3,7,9,11-tetraoxo--2,4,6,8,10-pentaaza[3.3.3]propellane (DNTOPAP).
A number of papers, but mainly posters, presented work on azoles (pyrazoles, triazole, tetrazoles, bis-compounds….) and their derivatives. By example two bis(dinitropyrazole)methane compounds, bis(3,4-dinitropyrazole)methane & bis(3,5-dinitropyrazole)methane, were synthesised by Kim, N (Seoul National University; ROK) and co-workers. Both materials exhibited properties similar to RDX but, due to their lower densities, did not achieve high performance characteristics.
Processing and Formulations
Large scale manufacture of VI-RDX was reported by Eurenco [Eck, G. (Eurenco; FRA)], which has commericalised the work carried out by ISL. Formulations of VI-RDX have shown an increase in the threshold for shock initiation. A novel plastic explosive based on cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (bicyclo-HMX; BCHMX), FOX-7 and polydimethylsiloxane (PDMS) binder (44, 44, 12 wt %) was presented by Hussein, A. K. (University of Pardubice, CZE). Detonation velocity and pressure was quoted as being higher than SEMTEX-10 and this is the second formulation reported this year using PDMS as a binder system.
Propellants
Interesting monopropellants work investigating replacements for hydrazine focused on 4-amino-1-methyl-1,2,4-triazolium nitrate; C1N [Schaller, U. (ICT; DEU)]. Synthesis of C1N used microfluidics to produce kg quantities for research; this highlights the flexibility of this technology to the research community. Mixtures of C1N with nitromethane exhibited desirable properties for sensitiveness, shock and Isp. Rocket research by ADD has focused on non-isocyanate curing reaction mechanisms for the polymeric binder systems [Min, B. S. (ADD; ROK)] such as the 3+2 cycloaddition chemistry of azide moieties (N3) reacting with alkynes to generate triazoles.
Pyrotechnics
Flare igniters and their ignition process, under temperature & pressure extremes, was presented by Woodley, C (Qinteiq, GBR). Critical material parameters were collated and used in a number of models to aid simulation of the burning processes. Presentation on lithium-based red light emitting, chlorine-free pyrotechnics (Glück, J; LMU, DEU) as Sr has to be withdrawn from use (US EPA) due to adsorption into the human body; can replace Ca in bone calcification, affect children bone growth. The work used a high nitrogen-Li salt (bis-lithium 5,5’-diamino-4,4’-dinitramino-3,3’-bi-1,2,4-triazolate) that produced the correct frequency, and high spectral purity as Sr/PVC composition but the intensity was low. 5-Aminotetrazole was employed as an additional gas generator for improved efficiency coloured smokes [Glück, J. (LMU, DEU)].
