Evaluation of some thermal,mechanical and explosive properties of plastic bonded explosives based on epoxy resin

Abstract

RDX/HMX based Plastic Bonded Explosives (PBXs) with epoxy resin as a binder have been formulated and studied in detail for their explosive, mechanical and thermal properties. The effect of pressure on the moulding powder has also been optimized to achieve maximum loading density and compression strength. Further, these PBXs have been analysed for homogeneity and coating of binder over RDX/HMX crystals. The data suggest that epoxy resin based PBXs have higher loading density, higher mechanical strength and higher velocity of detonation (VOD) as compared to polyurethane based PBXs.     

Quantitative evidence for nitroso compound formation in drop-weight impacted RDX crystals

Abstract

Quantitative results are presented for the formation of two nitroso compounds during the drop-weight impact of Holston production-grade Class D RDX explosive crystals. Gas chromatography, using a sensitive Ni-63 electron capture detector, was employed to analyze “RDX residues” recovered from impact tests involving a 5 kg mass dropped from 10, 12, and 14 cm heights. The compounds, 1,3,5-trinitroso-1,3,5-triazacyclohexane (R) and 1,3-dinitroso-5-nitro-1,3,5-triazacyclohexane (RO) were detected at levels of (0·80 to 9·3) × 10^?10 percent and (1·3 to 560) × 10^?10 percent, respectively. More RO than R was formed at the 14 cm drop height. This appears to be the first time that nitroso compounds structurally similar to RDX have been observed in impacted RDX crystals.     

Thermokinetic decomposition and sensitivity studies of 4,4ˊ-diamino-3,3ˊ-azoxy furazan (DAAF)-based melt cast explosive formulations

4,4ˊ-diamino-3,3ˊ-azoxy furazan (DAAF) is an insensitive high explosive. DAAF has safety characteristics (impact, friction) similar to triaminotrinitrobenzene and shock sensitivity similar to HMX. The present article describes the thermal analysis and sensitivity study of DAAF with RDX and 2,4,6-trinitrotoluene (TNT). DAAF has been evaluated as a possible replacement for RDX in TNT-based, aluminized as well as nonaluminized melt cast formulation. DAAF-based melt cast formulations were characterized for their sensitivity to mechanical stimuli, bomb calorimetric analysis, and thermal decomposition behavior. The thermal analysis reveals the compatibility of DAAF with benchmark explosives like RDX and TNT in explosive formulations. The composition DT (DAAF + TNT) and DTA (DAAF + TNT+ Al) is more friction and impact insensitive as compared to RT (RDX + TNT) and RTA (RDX + TNT+ Al) compositions. The bomb calorimetric values of DT composition as well as DTA composition are higher than RT and RTA compositions. The result shows that DAAF can be effectively used as a RDX replacement in melt cast explosive formulations. DT-based aluminized composition showed more thermal stability than RT- and RTA-based control compositions, which clearly revealed the usefulness of DAAF for enhanced blast effect.     

Evaluation studies on partial replacement of RDX by spherical NTO in HTPB-based insensitive sheet explosive formulation

ABSTRACT

Hydroxyl terminated polybutadiene (HTPB)-based sheet explosive incorporating spherical 3-nitro-1,2,4-triazol-5-one (NTO) as a partial replacement of 1,3,5-trinitro-1,3,5-triazinane (RDX) was investigated. The effect of incorporation of NTO on mechanical properties, sensitivity behavior, and velocity of detonation (VOD) was studied in comparison with a sheet explosive formulation containing 82 wt% RDX, both based on an HTPB-binder system. The replacement of 22 wt% of RDX by spherical NTO resulted in reduced vulnerability to shock as well as impact stimuli. The data demonstrated that the NTO-added formulation was found to be higher shock insensitive compared to the RDX-only formulation. However, ~5% decrease in VOD was observed on incorporation of NTO. Further, the sheet explosive formulations were found insensitive toward friction up to 360 N. Also, molecular dynamics simulations were performed to predict the elastic constants of RDX and NTO and the results revealed that the predicted trend correlated with the experimentally obtained mechanical properties of the formulations.     

Thermal characterization of mixtures of nitrotriazolone with HMX and RDX

Abstract

Thermal characterization of mixtures of nitrotria-zolone (NTO) with octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) has been carried out by means of differential scanning calorimetry and thermogravimetric analysis. It has been found that HMX decomposition temperature remains constant through the whole composition range. However NTO decomposition temperature decreases as the NTO/HMX ratio decreases. The RDX decomposition temperature keeps constant in all compositions studied. The RDX melting temperature decreases few degrees. The NTO decomposition appears at lower temperatures as the RDX content increases.     

Reversal of particle size/shock sensitivity relationship at small particle size for pressed heterogeneous explosives under sustained shock loading

Abstract

Shock initiation of pressed heterogeneous explosives has been reviewed. The key processes of ignition and buildup and their relative importance under sustained and short duration shock are described. Particle size effects on shock sensitivity are shown to depend on both density (ZTMD) and shock duration. A series of RDX samples of narrow particle size range were subjected to sustained shock (gap test). Sensitivity increased over the series 250 < 138 < 100.0 < 21.2 μm median particle size but decreased for a 3.9 μm sample. These results combined with earlier published data support published modelling studies which predict decreased shock sensitivity at small particle size.     

Microstructure and performance of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystal clusters obtained by the solvation-desolvation process

ABSTRACT

The microstructure and performance of HMX were adjusted by a solvation-desolvation process. HMX solvates were prepared by recrystallization in N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP), respectively. Specific microstructures of HMX with microcrystal clusters were obtained by the desolvation of HMX solvates through anti-solvent extraction and vacuum pyrolysis. With different solvents and desolvation methods, the HMX crystals show a variety of morphologies, particle size, and polymorphic stability. The microcrystalline HMX clusters can be easily broken into superfine crystals by ultrasonic dispersion system and have higher β→δ polymorphic transformation temperature than the raw β-HMX. Moreover, microcrystalline HMX clusters have reduced impact and friction sensitivity and are expected to enhance the reliability of small booster charges and improve the overall performance of the HMX-based booster.     

Studies on thermoplastic elastomers based RDX-propellant compositions

Abstract

This paper presents the results obtained during studies on 80% RDX propellant systems based on thermoplastic elastomers (TPEs) namely ethylene-vinyl acetate (EVA), triblock copolymers of styrene-butadiene/styrene-isoprene (Kraton), poly-urethane-ester-MDI (Estane) and copolymer of polybutylene terephthalate - polyether glycol (Hytrel) as binders, Dioctyl phthalate (DOP), triacetin (TA) and glycidyl azide polymer (GAP) were incorporated as plasticizers in the formulations. An attempt has been made to correlate structural features of TPEs with mechanical properties as well as glass transition temperature (Tg). Results obtained suggest that TPE-based RDX-propellants have the advantage of high insensitivity to impact and friction stimuli vis-à-vis nitrte ester based conventional propellants. EVA based propellents gave the best results in this regard. Ignition temperature for all the compositions was >200°C. EVA, Hytrel and Estane based formulations were found to be more energetic than Kraton based formulations. Incorporation of GAP resulted in the improvement in ballistics (Impetus and burn rates) as compared to DOP plasticised formulations. TA based compositions gave an intermediate value. Thermal decomposition pattern was determined by applying Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC). An attempt has been made to explain the trends observed on the basis of the evidences generated during this study and theories proposed by other researchers.     

Pourability enhancement of petn explosive powders

Manufacture of precision detonators requires the pelletizing of very fine, organic, crystalline explosive powders. Production of pellets in automatic machines within critical dimensional and weight tolerances requires that the powders pour uniformly into die cavities. The pellets must be able to be initiated with low energy and have a predictable energy output. Modifications to needle-like crystalline PETN explosive powders to make them pourable were introduced by the application of about 80 A thick polymeric coatings to the individual crystals, followed by a controlled agglomeration into a spherical prill. Microencapsulation techniques provided the key to achieving the result using less than 0.5 wt. % coating (an order of magnitude less coating than in usual PBX systems). These coatings did not appreciably alter the energy required to initiate and significantly increased the strength of the pellets. A key point demonstrated, which may be translated to other applications, was that powders that exhibit performance based on physical characteristics could have their handling and strength properties tailored with little change in their primary function.     

Microstructure effects on the detonation velocity of a heterogeneous high-explosive

ABSTRACT

Although numerous methods exist for the theoretical calculation of detonation parameters of explosives, few thermodynamic-hydrodynamic-based theoretical codes take into account particle size. The basis for their computational analysis is primarily focused on the equation of state of the detonation products, heat of formation, and density of the explosive composition. This study utilized regression analysis to model the relationship between the microstructure characteristics and detonation velocity of a heterogeneous high-explosive composition containing cyclotrimethylene-trinitrmaine (RDX). The principal characteristics examined were the average particle size of RDX, amount of HMX impurity within the RDX particles, method of RDX manufacture, and compositional density. Statistical analysis demonstrated the relevancy of the microstructure influence on the detonation velocity of the developed experimental compositions of 73 wt. % solids and 27 wt. % polyurethane binder. An equation is developed that accurately predicts detonation velocity based on average particle size, density, and manufacturing process for RDX. The model underscores the significance of the relationship between the average particle size and detonation velocity. Compositions containing smaller average particle sizes of RDX generate higher detonation velocities. A 100 micron increase in the average particle size was shown to decrease detonation velocity by 161 m/s for the monomodal polyurethane compositions used in this study. The relevance of using statistical models for selecting characteristics that result in optimum explosive performance is addressed.     

An Investigation into the Effects of Additives on Crystal Characteristics and Impact Sensitivity of RDX

Additives are one of the most important factors that greatly affect the crystal characteristics of the high energy compound hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX, C₃H₆N₆O₆) and they have an influence on impact sensitivity. In this article, a growth morphology method was applied to obtain the crystal habit of RDX in a vacuum as well as the morphologically important faces, and molecular dynamics simulations were applied to calculate the interaction energy between these crystal faces and additive molecules for prediction of the additive-effect crystal habits of RDX. On this basis, crystal characteristics including crystal morphology, aspect ratio, and total surface charge were investigated. Then the particle size and surface electrostatic voltage of the samples from recrystallization were analyzed experimentally. The impact sensitivity test indicated that acrylamide, which could enhance the regularity and degree of sphericity of RDX crystals and effectively reduce the surface static electricity of RDX, was successful in reducing the impact sensitivity of RDX as an additive for crystallization. The above experimental results were in good agreement with the conclusions based on the theoretical calculations.     

Preparation and characterization of RDX/BAMO-THF energetic nanocomposites

ABSTRACT

Novel 1,3,5-trinitro-1,3,5-triazine/3,3-bis (azidomethyl) oxetane-tetrahydrofuran copolymer (RDX/BAMO-THF) energetic nanocomposites were successfully prepared by a facile sol–gel freezing–drying method. The as-prepared RDX/BAMO-THF energetic nanocomposites were characterized by Raman and Fourier transform infrared spectroscopy, which revealed that RDX particles were incorporated into BAMO-THF gel matrix. Scanning electron microscopy was used to characterize the morphology and the particle size of the as-obtained samples. The results showed that RDX particles were trapped in the BAMO-THF gel matrix and the particle sizes were in nanoscale. Differential thermal analyzer (DTA) was performed to determine the thermal decomposition behaviors of BAMO-THF, raw RDX and RDX/BAMO-THF nanocomposites. The results indicated that the thermal decomposition process of RDX/BAMO-THF nanocomposites was enhanced compared with that of BAMO-THF and RDX. The kinetic, thermodynamic and thermal stability parameters were calculated according to DTA analysis. The calculated results revealed that RDX/BAMO-THF nanocomposites presented high thermal reactivity. The results of impact sensitivities for RDX/BAMO-THF nanocomposites indicated the sensitivity was effectively reduced compared to raw RDX.     

Shock Initiation Characteristics of an Aluminized DNAN/RDX Melt-Cast Explosive

Shock sensitivity is one of the key parameters for newly developed, 2,4-dinitroanisole (DNAN)-based, melt-cast explosives. For this paper, a series of shock initiation experiments were conducted using a one-dimensional Lagrangian system with a manganin piezoresistive pressure gauge technique to evaluate the shock sensitivity of an aluminized DNAN/cyclotrimethylenetrinitramine (RDX) melt-cast explosive. This study fully investigated the effects of particle size distributions in both RDX and aluminum, as well as the RDX’s crystal quality on the shock sensitivity of the aluminized DNAN/RDX melt-cast explosive. Ultimately, the shock sensitivity of the aluminized DNAN/RDX melt-cast explosives increases when the particle size decreases in both RDX and aluminum. Additionally, shock sensitivity increases when the RDX’s crystal quality decreases. In order to simulate these effects, an Ignition and Growth (I&G) reactive flow model was calibrated. This calibrated I&G model was able to predict the shock initiation characteristics of the aluminized DNAN/RDX melt-cast explosive.     

Particle size reduction of RDX by sequential application of solvent–antisolvent recrystallization and mechanical methods

ABSTRACT

Solvent–antisolvent recrystallization produced ~8 µm average size RDX particles (UF-RDX) that were subsequently subjected to mechanical methods of ultrasonication and ball-milling to find further achievable reduction in particle size. Long duration ultrasonication for 20 h and 300 rpm ball milling for 4 h of UF-RDX decreased its average particle size to ~2 µm. RDX produced by all the three processes (solvent–antisolvent recrystallization, ultrasonication and ball-milling) was similar to coarser RDX in structure and thermal decomposition behavior. However, UF-RDX produced by solvent–antisolvent recrystallization was significantly less impact sensitive than that produced by ball-milling and ultrasonication. The issues of residual solvent and the metal contamination during RDX processing were addressed by process parameter optimization. Solvent–antisolvent recrystallization and mechanical methods even when used sequentially could not bring average particle size of RDX to nano-scale.     

Preparation and Safety of Well-Dispersed RDX Particles Coated with Cured HTPB

HTPB/IPDI (hydroxyl terminated polybutadiene & Isophorone diisocyanate) and TNT (2,4,6-trinitrotoluene) were successively coated on RDX (hexogen) particles by solvent evaporation and aqueous slurry melting, respectively. When HTPB coated on RDX particles cured completely, TNT was removed by solvent dissolution and the well-dispersed RDX particles coated with cured HTPB were obtained successfully. SEM (scanning electron microscopy), TEM (transmission electron microscopy), XPS (X-ray photoelectron spectrometry), and laser granularity measurement were employed to characterize the coated samples, and the mechanical sensitivity and thermal stability were measured and analyzed. Results show that TNT on the outer layer effectively hinders the adhesion among the particles resulting from the curing of inner layer (i.e., HTPB and IPDI). The final coating particles disperse well and their mechanical sensitivity decreases significantly. When the covering amount of HTPB is 2 wt.%, drop height (H₅₀) of RDX increases from 37.2 to 66.5 cm and explosion probability (P) decreases from 92 to 16%. Compared with that of uncoated samples, the activation energy and self-ignition temperature of coated samples do not vary.     

A comparison of the shock and static compression curves for four solid explosives

Abstract

For the four explosives, PETN, RDX, HMX, and TATB, comparison is made between published data for Hugoniot curves generated from shock-wave experiments and Hugoniot curves generated from isothermal static compression measurements to 10 GPa. For PETN, the static and shock Hugoniot curves in the pressure-volume plane are in agreement. From this agreement, one can conclude that the shock data for PETN determine the Hugoniot curve for unreacted material. The same conclusion can be drawn for RDX, although there is a phase transition between 4 and 5 GPa. Also for TATB the two types of data agree over their common range (0 to 7 GPa). For HMX the comparison is not as conclusive, but may indicate the presence of a phase transition in HMX above 10 GPa.     

Evaluation of small-scale combustion of an insensitive high explosive formulation containing 3-nitro-1,2,4-triazol-5-one (NTO), 2,4-dinitroanisole (DNAN), and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX)

ABSTRACT

Energetic materials are often disposed by open-burning or open-detonation as it is a cost-effective and efficient means of destroying explosive material, and often minimizes the need to transport hazardous explosives to treatment facilities. This practice is often scrutinized for the negative environmental impact of the odorous and unsightly toxic gaseous emissions as well as the resulting deposition residues, which often contain unburned energetic materials. With the increasing use of Insensitive High Explosive compositions in munitions, it is essential that the potential environmental impact of their disposal is assessed before their extensive use to prevent the kind of contamination incidents experienced with legacy explosives. Therefore, the aim of this work was to develop a controlled laboratory experiment to identify the gaseous emissions and the energetic material residues that are generated through the combustion of the IHE components 3-nitro-1,2,4-triazol-5-one (NTO), 2,4-dinitroanisole (DNAN), and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX). A sealed vial containing small (mg) quantities of energetic material was heated until the energetic material combusted. Gas chromatography/mass spectrometry (GCMS) was used to calculate the oxygen consumption and to identify the gases that were generated. The solid residues were analyzed by high-performance liquid chromatography (HPLC) to quantify unburned energetic material. Results showed that DNAN was the most resistant to burning, thus leaving significant quantities of unreacted starting material in the vial. An interesting observation for the IHE formulation was that DNAN also inhibited the combustion of NTO and RDX. The gases emitted during the open burning of IHE components and mixtures included CO, CO₂, and N₂O as expected, but the proportions differed when the components and mixture were compared, reflecting the influence of DNAN on the burning behavior. From our data, we concluded that open-burning DNAN-based formulations is an environmentally unfavorable waste-management practice for the disposal of IHEs mainly due to generation of solid residues as well as unburnt DNAN.     

Properties and impact sensitiveness of cyclic nitramine explosives containing nitroguanidine groups

Abstract

Some properties of hexahydro-5-nitro-2-(nitroimino)-1,3,5-triazine 1, octahydro-1,3-dinitro-5-(nitroimino)imidazo[4,5-d]imidazole 2, dodecahydro-4,8-dinitro-2,6-bis(nitroimino)diimidazo[4,5-b:4′,5′-e]pyrazine 3 and octahydro-2,5-bis(nitroimino)imidazo[4,5-d]imidazole 4 have been determined. They have acceptable thermal and hydrolytic stability. Compound 3 has greater friction sensitiveness than RDX, however the others are much less sensitive. Rotter impact test data indicate that the cyclic nitroguanidines 1–4 are more easy to initiate than RDX; however, the extent of propagation is less and depends on oxygen balance. Consideration of Hazard Index and Average Powder Explosiveness data indicates that US drop-weight tests, which measure a combination of ease of initiation and extent of propagation, would rank the cyclic nitroguanidines and references explosives in the following order of increasing impact sensitiveness: NQ < 4 < NTO < 1 < RDX, 3 < 2.     

超高分子聚合物性能评价及微观结构研究

为了进一步提高聚合物驱的驱油效果,评价了相对分子质量在3 500万以上的超高分子聚合物的性能,并观察了超高分子聚合物溶液的结构。在70 ℃、矿化度11 200 mg/L的试验条件,利用安东帕流变仪评价了超高分子聚合物和常用聚合物的增黏性、耐温性、抗盐性、剪切流变性及黏弹性,采用物理模拟试验方法分析了2种聚合物的驱油效果,并通过冷冻蚀刻扫描电镜对比了常用聚合物与超高分子聚合物溶液的微观结构。结果表明,超高分子聚合物在水溶液中能够形成更致密的网络结构,相对于常用聚合物,它的增黏性和抗盐性高30%以上,耐温性高40%以上,威森伯格数是其2倍,采收率提高率高6.5%。研究表明,超高分子聚合物是一种性能更优的驱油剂,可以显著改善驱油效果。      

The Characterization of Natural Surfactant and Polymer and Their Use in Enhanced Recovery of Oil

Abstract

Studies have been done to examine the applicability of natural surfactant and polymer for enhanced oil recovery. A detailed investigation has been made on interfacial and rheological properties of natural guar gum polymer and surfactant obtained from extracted soapnut shell. Based on the physicochemical properties of the surfactant and polymer solutions, optimum compositions were designed for flooding experiments. Three sets of experiments were performed to study enhanced oil recovery by injecting the same pore volume of polymer, surfactant–polymer, and alkaline–surfactant–polymer slug after brine flooding. Significantly higher additional recovery (~24% original oil in place) was obtained by alkaline–surfactant–polymer flooding compared to the other two methods over waterflooding (~50% original oil in place).