Showing papers on "Friction sensitivity published in 2012"

Effect of Different Polymeric Matrices on Some Properties of Plastic Bonded Explosives

Abstract: Matrices based on polyisobutylene (PIB), polymethyl-methacrylate (PA), Viton A 200, Dyneon FT 2481 (Fluorel), and polydimethyl-siloxane binders were studied as desensitizers. A series of plastic explosives (PBXs) were prepared, based on four different nitramines, namely RDX (1,3,5-trinitro-1,3,5-triazinane), β-HMX (β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane), BCHMX (cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole) and e-HNIW (e-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, e-CL-20), bonded by the matrices mentioned. For comparison, pentaerythritol tetranitrate and certain commercial explosives based on it, Semtex 1A, Semtex 10 and Sprangdeg m/46, were used. Detonation velocities, sensitivities to impact and friction, and peak temperatures of thermal decomposition by differential thermal analysis technique (DTA) for all the explosives studied were determined. Heat of detonation was calculated by means of a thermodynamic calculation program (EXPLO 5 code). Fluoroelastomers have a neutral to positive effect on the thermal stability of nitramines and they have a significant effect on decreasing the friction sensitivity. However, their anti-impact efficiency is the lowest in this study although they have a positive effect on performance of the corresponding PBXs. PA and PIB matrices markedly decrease thermal stability of nitramines, the anti-impact influences of PIB-binders are better than those of PA-binders, while PA-binders have a higher anti-friction effect and slightly less negative influence on the performance of the PBXs in comparison with PIB mixtures. The polydimethyl-siloxane matrix has a neutral effect on thermal stability of the nitramines studied, it has an influence on the volume thermochemistry of detonation comparable with that of fluoroelastomers although it does not provide comparable performance, and its corresponding PBXs have optimum sensitivity parameters.

Friction Sensitivity of Nitramines. Part I: Comparison with Impact Sensitivity and Heat of Fusion（英）

Abstract: Fractions of β-HMX(β-1,3,5,7-tetranitro-1,3,5,7-tetrazocane) have been used to demonstrate the mutual relationship between friction and impact sensitivities.Inclusion of an additional twelve nitramines into this scenario resulted in a series of partial relationships,which were determined from the molecular structure of these substances.It was also found that there is a relation between increasing heats of fusion of the nitramines studied and their decreasing friction sensitivities.Comparison of friction sensitivity with heats of fusion,ΔHm,tr of the studied nitramines shows that the increase in ΔHm,tr values is more or less connected with a decrease in friction sensitivity.

Effect of Tungsten on Aluminized Melt Cast High Explosive Formulations

Abstract: Aluminized 2,4,6-trinitrotoluene (TNT) based, melt-cast, high explosive compositions are widely used in warheads. These compositions offer a blast effect over a larger period due to the secondary combustion of aluminum. During recent times tungsten based explosives have been reported for lethality at close range to avoid collateral damage in low intensity conflicts (LIC) and find application in shaped charges to enhance their penetration capability. This paper reports findings on tungsten-based, melt-cast, explosive formulations. The compositions were prepared by substituting aluminum with tungsten in the reference aluminized, high explosive formulation. The compositions were characterized for their sensitivity to mechanical/shock stimuli, velocity of detonation (VOD) and blast performance. The study reveals that the impact sensitivity remains comparable on incorporating 10% tungsten at the cost of aluminum whereas an increase in tungsten content to 20% leads to an increase in impact sensitivity. However friction sensitivity and shock sensitivity remained more or less unchanged. The velocity of detonation (VOD) of tungsten-loaded, aluminized formulations is found to be comparable to the standard aluminized formulation. The peak over pressure of tungsten-based formulations is lower than the reference, aluminized composition at close range but is almost unchanged at long range. The impulse of tungsten-based formulations is also lower than the reference, aluminized composition. The reduction in impulse at close range is substantial on replacing 10% aluminum with inert tungsten.

Mechanical Pulverization for Nano HMX and Study on Its Mechanical Sensitivities

Abstract: Nano HMX was prepared by mechanical pulverization.The particle size and size distribution were studied by the employment of the nano laser particle size analyzer.The particle size and the morphology were characterized through the use of FESEM.The friction,impact and shock sensitivity of raw HMX and nano HMX were tested.It was found that the average size of the pulverized particles was mainly under 100 nm.Compared with raw HMX,the friction sensitivity of nano HMX was shown an apparently reduction,particularly the impact and the shock sensitivity,decreased 107.0% and 62.1% respectively.

Study of TATP: Mass Loss and Friction Sensitivity During Ageing

Abstract: Triacetone triperoxide (3,3,6,6,9,9-hexamethyl-1,2,4,5,7,8-hexoxonane; TATP) is one of the most frequently used improvised explosives, often misused worldwide. In our previous studies, we had observed that the kind of acid used to catalyse its formation has a significant influence on TATP’s properties. TATP was prepared using five different acids that are often used in improvised conditions. All of the samples were subjected to natural ageing in both open and closed vials at laboratory temperature. During ageing, TATP sublimes and decomposes. The changes in crystal size and shape after ageing were documented by optical microscopy. The mass loss was monitored about every third day during ageing. Samples prepared using sulphuric and perchloric acids lose weight more quickly than the others due to chemical decomposition. The friction sensitivity was determined for all samples before and after ageing. Neither the type of acid used nor the influence of closing the vials had any significant influence on the friction sensitivity after ageing. The friction sensitivity of all tested samples of TATP was about the same − between that of lead azide and that of mercury fulminate.

Desensitizing Technology of High Quality HMX by Coating

Abstract: The desensitizing technology of high-quality HMX were studied by coated with wax(W) or thermoplastic polyurethane(TPU) as insensitive coating additiveThe feasibility study of high-quality HMX coated by W and TPU were proved through contact angle and surface energiesThen the samples were characterized by using SEM and XPSThe mechanical sensitivity of HMX samples before and after coating was measured and comparedThe coating integrality and desensitizing effect of D-HMX coated by W in water and non-agueous media(Novec 7200),respectivelyThe results show that the high-quality HMX are coated entirely by W and TPU and the impact and friction sensitivity of high-quality HMX coated by W decreases significantly from 88% to 16%,from 92% to 4%,respectivelyIt indicats that D-HMX is coated entirely and more insensitive which the impact sensitivity fall to 0% while coated in non-aqueous media(Novec 7200) than in water

Process Intensification in Crystallization: Submicron Particle Generation Using Alternative Energy Forms

Abstract: Crystallization is one of the oldest separation and product formation techniques that continues to be in use today. Despite its long history, it only started to develop significantly in the past few decades. In this thesis, the application of Process Intensification in crystallization is investigated. Process Intensification is a set of often radically innovative principles in process and equipment design, which can bring significant benefits in terms of process and chain efficiency, capital and operating expenses, quality, wastes, process safety, etc. Alternative energy forms as basic elements of Process Intensification are investigated by applying electric fields and plasma technology in crystallization processes. Three main topics are discussed in this thesis: a) Submicron-sized and nano-sized particles can have beneficial product properties compared to conventionally sized crystalline products. Electrospray Crystallization, an advanced crystallization technique can serve as a tool to produce such submicron-sized particles. In this thesis, it was investigated whether electrospray crystallization can be used to produce 1. energetic materials with a reduced sensitivity and 2. submicron-sized pharmaceutical compounds for improved dissolution and absorption. Electrospray crystallization of a solution is an integrated process of spraying and crystallization that uses a high voltage to produce a fine aerosol of droplets in the micron-size range. During the process, the emitted solvent droplets evaporate and a droplet disruption process (Coulomb-fission) occurs, which creates even smaller droplets. Due to solvent evaporation, eventually supersaturation is achieved and crystals of submicron particles can commence. Electrospray crystallization is an efficient, cost-effective and simple method for the production of submicron-sized crystals, but it suffers from a low production rate and it could be challenging to scale up. In this thesis, the process parameters for establishing a stable jet for producing submicron-sized particles were determined. The operation window to establish a continuous jet and produce submicron-sized crystals is relatively narrow, but experimentally feasible to maintain. Energetic crystals of RDX and HMX were produced with a mean size of around 500 nm by electrospray crystallization. The produced explosive crystals were tested for impact and friction sensitivity. The samples were remarkably insensitive to friction stimuli, while an insignificant difference for the impact sensitivity was observed. With similar process parameters, submicron-sized crystals of a poorly water-soluble active pharmaceutical ingredient, niflumic acid, were produced. In the absence of excipients, for the case of the submicron-sized niflumic acid, no significant difference was shown in the dissolution profile compared to the conventional one. However, upon mixing the excipients, D-Mannitol and Poloxamer 188, with the submicron-sized niflumic acid, the dissolution rate of the drug was enhanced. Thus, it is possible to increase the bioavailability of drugs by drastically reducing the crystal size, while preventing their aggregation by using the proper excipients. b) Plasma Crystallization is a new crystallization technique, in which an atmospheric pressure cold ionized gas is used to generate submicron-sized crystals. This novel type of plasma, the Surface Dielectric Barrier Discharge (SDBD), is a plasma made by several self-terminating microdischarges on a surface. A nebulizer system sprays the solution aerosol into the plasma with the help of a carrier gas. The plasma charges and heats the droplets. Upon evaporation Coulomb-fission occurs, supersaturation increases, and nucleation and crystal growth take place within the small, confined volume offered by the small droplets. Compared to the electrospray crystallization, much higher production rates can be achieved. The energetic material, RDX, and the active pharmaceutical ingredient, niflumic acid, and its excipient, Poloxamer 188, were produced by plasma crystallization with a significant size reduction compared to the conventional products. While there was no measurable change in the sensitivity of RDX, a substantial increase in the dissolution rate of the submicron niflumic acid crystals was observed in the presence of the plasma-made excipient. c) The effect of a constant high electric field was investigated during the cooling crystallization of isonicotinamide in 1,4-dioxane (Electrostatic Crystallization). Two experimental setups were built in order to examine the electric field effect, with a focus on crystal polymorphism control. An inhomogeneous electric field was generated in a controlled crystallization environment. A Crystalline station with an on-board camera system offered in situ investigation of the experiments. A more homogeneous electric field was generated in a different setup, but without a precise temperature control. Image analysis from the Crystalline station experiments showed that the applied electric field induced fluid motion of the solution due to the Lorentz-force acting on the isonicotinamide molecules in solution. This induced fluid dynamics was further visualized by using a suspension of the isonicotinamide-1,4-dioxane system. Image analysis also showed that the nucleation was localized to the anode, and crystals were formed only on the anode surface. The electric field generated a concentration gradient, with the highest solution concentration around the anode. The crystal growth rate was also measured with the help of the on-board camera system. It was found that in the presence of the electric field, the growth rate of the isonicotinamide crystals formed on the anode is 15 times higher than in the absence of the electric field. From this crystal growth rate increase, the local supersaturation ratio increase was estimated at the anode, and found to be at least 2.5 times higher in the presence of the electric field, than in the absence. In the absence of the electric field, the metastable, chain-like form I isonicotinamide was crystallized in both experimental setups. In the inhomogeneous electric field, both form I and form II of isonicotinamide were crystallized. By applying a more or less homogeneous, constant electric field during the crystallization, only the stable form II was formed. In addition, concerns regarding the reliability of standard small-scale sensitivity tests methods for submicron-sized explosives were discussed in this thesis, since the obtained results for the produced explosive materials are questionable. In order to test the quality of the produced submicron-sized energetic materials, a series of small-scale sensitivity tests were carried out. Impact and friction sensitivity tests and ballistic impact chamber test were performed to determine the product sensitivity. Concerns were found with the standard friction and ballistic impact chamber sensitivity test methods, and suggestions were made to improve these tests. The friction sensitivity for all submicron-sized crystals showed no ignition even at the highest possible load. The ballistic impact chamber tests showed also no or only partial ignition with all the submicron-sized explosives. The submicron-sized crystals were distributed among the grooves of the porcelain plate used in the friction test or among the sand grains of the sandpaper used in the ballistic impact chamber test. There is a need to revisit the ignition mechanism of these sensitivity test methods, and make suggestions for accurate measurement methods for the sensitivity of nano-sized explosives. Recommendations have been suggested to develop new tests that only rely on the interactions between the particles making them applicable to conduct the sensitivity tests for submicron/nano-sized energetic materials. A friction initiation setup as developed at TNO more than 30 years ago, might be a technique that could provide a more reliable measurement of the friction sensitivity of submicron- or nano-sized energetic materials by allowing only the frictional heating between the sample particles and exclude any other sources of frictional heating, allowing more reliable results.

Experimental Study of PTFE Powder Size Impact to Mg/PTFE Pyrotechnic Composition

Abstract: To discover the polytetrafluoroethylene (PTFE) powder size impact to Mg/PTFE pyrotechnic composition, hot compatibility of various particle sizes of PTFE powder with spherical superfine Mg powder was studied. Safety performance of Mg/PTFE pyrotechnic composition was also researched by parameters of friction and impact sensitivity. Burning temperature and velocity were recorded and analysed. The result shows that the Mg/PTFE exothermic temperature peak floats =0.8~2.2°C, apparent activation energy alter ratio (AAEAR) =12.5%~17.8%, ignition probability due to friction sensitivity =0.32~0.48 and to impact sensitivity =0. It indicates that PTFE powder size will not inflect the safety of Mg/PTFE composition, which burns more stable with PTFE size great than 400μm. Once mass combustion velocity 2.09~3.87 g•cm-2•s-1 and linearcombustion velocity 5.02~8.13 mm•s-1, the combustion velocity will increase much by following with PTFE particle sizes decrease.

Influence of Nano Al on Mechanical Sensitivity and Flame Sensitivity of RDX-based Explosive

Abstract: The RDX-based composite explosive with nano Al were prepared by the mixed mechanically method.The mechanical sensitivity and flame sensitivity of composite explosive were measured.The morphologies of nano Al and explosives were characterized and the cause of the sensitivity changes was analyzed.Results showed that adding nano Al to RDX-based explosives made the impact sensitivity,friction sensitivity and flame sensitivity of explosives increase.With increasing the content of nano Al,the impact sensitivity of explosive showed a increased tendency,and both friction sensitivity and flame sensitivity had also remarkably increased.The impact sensitivity,friction sensitivity and flame sensitivity of composite explosive containing nano Al were higher than explosive containing micron Al,Both nano Al and nano Al explosives had a small amount of aggregation,this phenomena influenced the sensitivity of nano Al explosives to some extent.

Preparation and Properties of Lowest Eutectic Mixture TNAZ/ANTA

Abstract: A phase diagram of 1,3,3-trinitroazetidine(TNAZ) and 3-amino-2,4,6-trinitroanisole (ANTA) was draw by origin software and the sensitivity, thermal stability, and detonation performance of the eutectic mixture were tested in order to design a potential TNT replacement for melt-cast explosive The results show that when the weight percent of 3-methoxy-2,4,6-trinitrobenzenamine is 40%, the mixture has the lowest melting point, 84 ℃ The eutectic mixture has good thermal stability and its friction sensitivity, impact sensitivity, electrostatics sensitivity are comparable to TNT The working capability of the mixture is 148% equivalent to TNT and 114% equivalent to CompB Furthermore, another advantage of eutectic mixture is that there is no permeability oil at 70 ℃ for 6 h These results indicate that the eutectic mixture is a potential replacement of TNT for melt-cast explosive

The Green Crystallization of RDX

Abstract: High quality RDX crystals are prepared with cyclohexanone by cooling crystallization method,based on the analysis of the recrystallization process of RDX.Experimental results indicated that,the crystal surface of high quality RDX crystals is smoothy and transparent,the crystal density is up to 1.810g/cm3,the impact sensitivity is reduced to 48%,the friction sensitivity is also reduced to 64%,and the packing density is up to1.28 g/cm3.It showed that the cooling recrystallization method can realize green crystallization for RDX,and obtain high quality RDX crystals.