RDX and HMX with Reduced Sensitivity Towards Shock Initiation–RS‐RDX and RS‐HMX

Reduced Sensitivity RDX (RS‐RDX) has received a lot of attention and interest from the explosive community in the recent years. There are several producers of RS‐RDX, most of them using a direct nitration (Woolwich process) for the RDX synthesis, while Chemring Nobel uses the Bachmann process. The processes for obtaining the RS properties probably differ between the various producers. Chemring Nobel has also developed an HMX quality that shows Reduced Sensitivity (RS‐HMX) of different particle size distributions. The shock sensitivity is at the same level as for RS‐RDX in comparable compositions. Reduced shock sensitivity has been obtained for RS‐RDX and Reduced Sensitivity (RS‐HMX) in both pressable and cast‐cured compositions. By using a pressable composition, it is possible to get the results from a BICT gap test faster than from a cast‐cured composition that has to go through a curing process. Chemring Nobel in cooperation with FFI have performed an extensive accelerated ageing testing of RS‐RDX produced by the Bachmann process. The samples have been aged at 60 and 70 °C and the shock sensitivity tested by two different gap tests. The results demonstrate that the Chemring Nobel RS‐RDX retain the insensitivity towards shock during ageing and show no degradation at all. Accelerated ageing testing of RS‐HMX has also been performed and shows no degradation in the shock sensitivity.     

Relationship Between RDX Properties and Sensitivity

An interlaboratory comparison of seven lots of commercially available RDX was conducted to determine what properties of the nitramine particles can be used to assess whether the RDX has relatively high or relatively low sensitivity. The materials chosen for the study were selected to give a range of HMX content, manufacturing process and reported shock sensitivity. The results of two different shock sensitivity tests conducted on a PBX made with the RDX lots in the study showed that there are measurable differences in the shock sensitivity of the PBXs, but the impact sensitivity for all of the lots is essentially the same. Impact sensitivity is not a good predictor of shock sensitivity for these types of RDX. Although most RDX that exhibits RS has low HMX content, that characteristic alone is not sufficient to guarantee low sensitivity. A range of additional analytical chemistry tests were conducted on the material; two of these (HPLC and DSC) are discussed within.     

Reduced Sensitivity RDX (RS‐RDX) in Pressed Formulations: Respective Effects of Intra‐Granular Pores,Extra‐Granular Pores and Pore Sizes

Reduced sensitivity RDX (RS‐RDX) particles are now available from several manufacturers. But a clear understanding of this reduced sensitivity behavior is not yet available. RS‐RDX particles are usually employed in cast formulations to reduce their shock sensitivity. The use of RS‐RDX in pressed formulations is more recent and does not always give reduced sensitivity formulations.     

Divergent Detonation Wave Processes in PBX Based on RDX

In order to characterize the initial phase of the divergent detonation wave in PBX, a hemispheric explosive sample was initiated by a long cylindrical charge of the same explosive. The tested PBX is composed of 85 wt% of RDX and 15 wt% of binder based on HTPB. This PBX‐RDX presents an effective density of 1.57 g/cm³, and a detonation velocity of 7.90 mm/μs.     

超细HMX和RDX撞击感度的研究

利用爆炸概率法对超细奥克托今（ＨＭＸ）和黑索今（ＲＤＸ）的撞击感度进行了研究。试验结果表明：超细ＨＭＸ和ＲＤＸ的爆炸分数相比军用标准样品的值有较大幅度下降。文章分析了撞击感度降低的原因,并展望了超细炸药在高能量、低感度炸药研制中的重要意义。     

Production of Nanocrystalline RDX by Rapid Expansion of Supercritical Solutions

Nanoscale crystals of cyclotrimethylenetrinitramine (RDX) were produced by Rapid Expansion of Supercritical Solutions (RESS). The experiments were performed by expansion of supercritical solutions of RDX in carbon dioxide through sapphire nozzles (ID: 100 and 150 μm) at pressures of 15.0–29.5 MPa and temperatures of 343–348 K. Recrystallized particles were characterized by Field Emission Scanning Electron Microscopy (FESEM), X‐ray diffraction, HPLC and melting point analysis. The process produced particles with a mean size in the range 110–220 nm and a narrow size distribution. The product was crystalline as determined by X‐ray diffraction. The effect of process conditions (T, P, nozzle diameter) on the crystal size distribution was determined.     

Hexamethylenetetramine Dinitrate (HDN): The Precursor for RDX Production by Bachmann Process

Hexamethylenetetramine dinitrate (HDN) is a rather weak explosive but is used as a precursor for the synthesis of RDX, one of the most important secondary nitramine explosives. HDN has limited application because of its hygroscopic character. This paper reports on the synthesis and characterization of HDN in high yield and purity by the reaction of hexamine with nitric acid at temperatures below 15 °C. It was characterized by FTIR and ¹H NMR spectroscopy, Scanning Electron Microscopy (SEM) and Liquid Chromatography/Mass Spectrometry (LC/MS) measurements. The thermal characteristics of HDN were determined by DSC and TG/DTA. The DSC curve of HDN shows an endothermic peak at 170.5 °C corresponding to the melting point of HDN, followed by two exothermic peaks at 174.0 °C and 200.5 °C due to the decomposition. The differences in the thermal behavior of HDN samples, which were thermally aged at 50 °C, 100 °C, and 150 °C in a nitrogen atmosphere were examined. Additionally, some quantum chemical properties of the nitration of hexamethylenetetramine were calculated.     

HMX as an Impurity in RDX Particles: Effect on the Shock Sensitivity of Formulations Based on RDX

Two main kinds of heterogeneities are pointed out in RDX particles in using optical microscopy with matching refractive index and scanning electron microscopy. These are HMX impurities and solvent inclusions.     

Characterization of Granular and Polymer‐Embedded RDX Grades: Floret Tests

In an attempt to further contribute to the characterization of explosive compositions, small scale Floret tests were performed using four RDX grades, differing in product quality. A Floret test provides a measure – by indentation of a copper block – of detonation spreading or the initiability and shock wave divergence and is applied in particular to explosives used in initiation trains. Both as‐received RDX and PBXs (based on the AFX‐757 composition, a hard target penetrator explosive) containing these RDX grades were tested in the Floret test set‐up. It was found that the Floret test method, when applied to granular, as‐received RDX, was not able to discriminate between the overall RDX product qualities on the basis of the resulting volume of the indentation in the copper block. For the Floret test data of the PBX samples, a division into two parts, where one of the RDX lots shows a lower dent volume compared to the other RDX lots tested. Based on the results presented in this paper with granular RDX and a PBX composition and earlier results with a different type of PBX (based on PBXN‐109, an insensitive high explosive used in a wide range of munitions), the Floret test could be developed into a screening test for shock sensitivity and product quality, without the need for complex and large volume casting of specific PBX compositions.     

重结晶降低RDX感度研究

采用N-甲基吡咯烷酮、二甲基甲酰胺、二甲基亚砜作溶剂,对普通RDX进行重结晶.研究了不同溶剂对RDX晶体形貌、晶体内空穴、位错、残存溶剂的影响,通过扫描电镜和光学显微镜,分析了重结晶RDX晶体的结晶形貌和内部质量,用密度瓶法测试了晶体密度,用10kg落锤测定了撞击感度.结果表明,用二甲基亚砜重结晶制备的RDX有较好的晶体质量,撞击感度最低(54%),晶体密度达1.823g/cm3.     

RDX粒度对机械感度的影响

系统研究了RDX粒度对撞击感度和摩擦感度的影响．实验测试的RDX平均粒径为1．5～124μm,并在此粒度范围内分为5个粒度等级。其中撞击感度用特性落高法表示,摩擦感度用特性正压力表示。结果表明：炸药的撞击感度、摩擦感度均随粒度的减小而降低。从理论上分析了炸药粒度变化对机械感度影响的机理。     

Evaluation of Plastic Bonded Explosive (PBX) Formulations Based on RDX,Aluminum, and HTPB for Underwater Applications

Aluminized high explosives are known to give better underwater performance. All explosive formulations for underwater targets are filled into warheads and shells by casting method. TNT, a high explosive is used as casting medium due to its lower melting point. Plastic bonded explosives are fast replacing TNT‐based high explosive formulations for the reasons that they are more insensitive and low vulnerable explosives with better shelf life. Few aluminized plastic bonded explosive formulations based on RDX, aluminum, and HTPB have been processed, varying the aluminum content from 0 to 35% and evaluated underwater. The present paper discusses the experimental methodology adopted to evaluate the above formulations for their ballistic parameters, viz., peak over pressure and impulse. Explosion bulge tests have been conducted with each explosive formulation and extent of bulge in test plates is presented and compared with a standard underwater explosive, viz., HBX‐3.     

Micro Videographic Analysis of the Melt Layer of Self‐Deflagrating HMX and RDX

Micro videographic analysis of the thin molten layer on the surface of HMX (Octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine) and RDX (Hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine) during self deflagration were performed. This was done to gain a better understanding of the physical structure present in this 100–300 μm layer and give a visual picture for the development of computational models. During steady‐state combustion, RDX had a consistent melt layer with vigorous bubble formation. There was a continuous liquid layer throughout combustion and no foam was formed. The surface of HMX during steady‐state combustion at ambient initial temperatures was an uneven layer of foam. Foam appeared to convect across the surface in undulating waves. At elevated initial temperatures, the HMX molten layer was a consistent foam layer in both time and space. Micro videography was also done with a diagnostic laser sheet as illumination to measure the melt layer thickness. The RDX bubbling layer was about 217±30 μm thick. The HMX foam thickness varied from almost nothing to 660 μm, with an average value of about 234±106 μm.     

氧化石墨烯对RDX/PMMA安全性能及力学性能影响

为改善RDX的安全性能和力学性能,采用乳液聚合法制备RDX/聚甲基丙烯酸甲酯/氧化石墨烯(RDX/PMMA/GO)微球,并用相同方法制备了RDX/PMMA复合粒子进行对比;通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FT-IR)和差示扫描热量仪(DSC)对样品进行表征,并测试其撞击感度和药柱的静态力学性能。结果表明,包覆后RDX/PMMA微球形貌趋于球形,RDX/PMMA/GO粒子存在明显的层状皱褶;RDX晶型均未发生改变;与原料RDX和RDX/PMMA相比,RDX/PMMA/GO微球的表观活化能分别提高22.16kJ/mol和15.17kJ/mol,升温速率趋近于0时的峰温和热爆炸临界温度与原料RDX相比分别提升6.45℃和6.23℃;特性落高由包覆前的26.74cm分别提至62.95cm和78.52cm,撞击感度明显降低。RDX/PMMA/GO抗压强度比RDX/PMMA增加了7.5MPa,表明GO的加入对复合材料的力学性能提升明显。     

硬脂酸包覆超细RDX及其撞击感度

为改善超细RDX的性能,采用硬脂酸(SA)为钝感添加剂,获得了以超细RDX为基的钝感混合炸药.通过测试接触角、计算表面能验证其包覆可行性,SA能够包覆UFRDX.用扫描电镜对包覆后的样品进行表征验证,并测试了SA包覆后的超细RDX的撞击感度.结果表明,其表面形貌得到明显改善,SA可降低其撞击感度,说明钝感剂SA的加入是降低炸药撞击感度的有效方法.     

Research on the Size of Defects inside RDX/HMX Crystal and Shock Sensitivity

Intragranular defects inside RDX/HMX were studied by optical microscopy with matching refractive (OMS), sink‐float method (SFM), and micro‐focus CT (μCT) techniques. OMS results revealed the phenomenon that RDX/HMX had more defects and cracks than RS‐RDX/RS‐HMX. μCT results indicated that RDX/HMX had more defects with larger volume than RS‐RDX/RS‐HMX. The gap test showed that critical shock pressure/gap thickness was 6.4 GPa/19.4 mm for PBX based on RDX, while they were 7.5 GPa/17.5 mm and 8.6 GPa/16.2 mm for PBX based on M‐RDX and RS‐RDX, respectively. Meanwhile, an analysis of the relationship between defects inside RDX/HMX crystal and shock sensitivity was made. Finally, the shock pressure response under impact loading was investigated by discrete element method.     

Production and Sensitivity Evaluation of Nanocrystalline RDX‐based Explosive Compositions

The initiation sensitivity of cyclotrimethylenetrinitramine (RDX) was investigated as a function of crystal size. For this study, RDX powders with mean crystal sizes of ca. 200 and 500 nm were prepared by rapid expansion of supercritical solutions (RESS) with carbon dioxide as the solvent. Initiation sensitivity testing to impact, sustained shock, and electrostatic discharge stimuli was performed on uncoated as well as wax‐coated specimens. The test data revealed that in a direct comparison to coarser grades the nanocrystalline RDX‐based samples were substantially less sensitive to shock and impact stimuli. Furthermore, the 500 nm RDX‐based specimens exhibited the lowest sensitivity values, an indication that minima in shock and impact sensitivities with respect to crystal size exist.     

HMX/TATB基PBX的感度与表面形态的关系探索

报道了以HMX/TATB基的PBX中,蜡的加入量和加入方式对配方的机械感度如撞击感度、摩擦感度、特性落高有明显的影响,但对配方的热感度如5s爆发点、1000s热爆炸临界温度影响不大。同时结合扫描时局镜（SEM）和光电子能谱（XPS）的测试结果分析了造型粉的表面包覆形态和感度之间的关系。     

Shock Sensitivity of Pressed RDX‐Based Plastic Bonded Explosives under Short‐Duration and High‐Pressure Impact Tests

The shock sensitivities of plastic bonded explosives were studied with a thin flyer impact test by using two types of pressed RDX. The thin flyer, driven by an electrically exploding plasma, exerts a short‐duration, high‐pressure pulse to the samples to trigger a shock‐to‐detonation process. It was found that the duration and magnitude of the incident shock strongly influence the dominant mode of hot‐spot formation, promoting a fast pore collapsing mechanism while suppressing other slower shear or friction mechanisms, as proposed by Chakravarty et al. [1]. The pressed PBX based on reduced sensitivity RDX had higher shock threshold pressure, compared to the pressed PBX based on commercial RDX. The difference was observed even with a certain portion of external extragranular defects. It is postulated that the internal crystal defects are more efficient than the external porosity in terms of the rapid reaction of hot spots.     

On the Reliability of Sensitivity Test Methods for Submicrometer‐Sized RDX and HMX Particles

Submicrometer‐sized RDX and HMX crystals were produced by electrospray crystallization and submicrometer‐sized RDX crystals were produced by plasma‐assisted crystallization. Impact and friction sensitivity tests and ballistic impact chamber tests were performed to determine the product sensitivity. Rather than reflecting the quality of the particles, we found the sensitivity tests to be unreliable for submicrometer particles. The used impact test was not accurate enough, while in the friction and ballistic impact chamber tests the submicrometer‐sized crystals were distributed among the grooves of the porcelain plate or among the grains of the sandpaper used in these tests. These observations stress the need for revisiting the current standards used for determining the hazardous properties like friction and impact sensitivity of energetic materials in the case, where the sample consists of submicrometer‐sized crystals. Recommendations were suggested to develop new test methods that only use the interactions between the particles and therefore allow the application of sensitivity tests for submicrometer/nano‐sized energetic materials.