Friction Sensitivity Test Research Articles

Friction-induced temperature rise at energetic β-HMX crystal interfaces: Part II. Simulation of HMX rough surface under dry friction conditions

In this study, the frictional temperature rise of HMX/HMX is investigated with a rough surface sliding on a flat surface by finite element method. The simulation model on the frictional temperature on HMX surface is validated by the in-situ temperature monitoring at moderate friction conditions by tribological experiments and friction-induced ignition of HMX at extreme conditions by friction sensitivity tests. Simulation results reveal that the significance order of frictional parameter that determine the maximum temperature on the asperity of HMX is: friction coefficient > sliding speed > contact pressure. Surface roughness of HMX surface can also affect the frictional temperature rise. Furthermore, a frictional power density of ∼10.8 W/mm2 is determined as the critical security boundary of the friction system when the critical temperature is set to 220 ℃. These findings can provide deep insights into the microscale hot-spot formation and frictional safety mechanisms of explosives.

Friction Sensitivity Test Experiment and Desensitization Mechanism of Nitrocellulose-Coated DNTF Explosive Crystals

In response to the problem of the high friction sensitivity of 3,4-bis(3-nitrofurazan-4-yl) furoxan (DNTF) in solid propellants, the inherent component of solid propellants, nitrocellulose (NC), was used to coat DNTF explosives via the water suspension method. The coated samples were characterized by scanning electron microscopy (SEM) and friction sensitivity tests at a fixed 66° swing angle, and molecular dynamics calculations were performed to study the friction sensitivity and desensitization mechanism of NC-based DNTF coatings. The results show that NC, when used as a coating layer, can form a white gel on the surface of DNTF crystals, which can effectively reduce the friction sensitivity of DNTF. The coating effect becomes more obvious as the NC content increases. When the NC content is 5%, the friction sensitivity decreases by 72%, and a prediction formula for the exponential decay of DNTF friction sensitivity is obtained. MD calculation data show that NC can weaken the stiffness, enhance the elastic-plastic properties, increase the ductility and toughness of DNTF materials, and effectively improve the mechanical properties of DNTF. By combining experiments and simulation calculations, while considering the compatibility of new components and changes in propellant energy and other unpredictable new issues, NC can be referred to as a better coating layer for DNTF, as it has a certain feasibility for improving the friction sensitivity of DNTF.

“Green” PBX Formulations Based on High Explosives (RDX and HMX) and Water-Soluble pH-Sensitive Polymeric Binders

The increasingly harsher and more complex international and European environmental legislation drives the current development of "greener" energetics materials and munitions. The aerospace and defense industries rely on extensive research in the formulation and scale-up production of polymer-bonded explosives (PBX). In this context, this paper aims to present a versatile method for obtaining "green" PBX formulations based on two high explosives (hexogen (RDX) and octogen (HMX)) and acrylic acid-ethyl acrylate copolymeric binders. This study developed an innovative "eco-friendly" technology for coating the RDX and HMX crystals, allowing straightforward and safer manufacture of PBX, avoiding the use of traditional organic solvents. At the same time, these polymeric binders are soluble in water at a slightly alkaline pH and insoluble at acidic or neutral pH, thus ensuring a safer manipulation of the energetic materials during their entire life cycle and a facile recovery of the explosive in its original shape and morphology in demilitarization. The PBX formulations were characterized via specific analytical tools to evaluate the influence of their composition on the safety and performance characteristics: scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), alkaline pH solubility tests, differential thermal analysis (DTA), impact sensitivity test (BAM Fall Hammer Test), friction sensitivity test (BAM Friction Test), electrostatic sensitivity test (ESD), vacuum stability test, small scale shock reactivity test (SSRT), detonation velocity test. The "green" PBX formulations obtained through a simple and innovative coating method, based on the polymeric binders' adjustable water solubility, demonstrated remarkable energetic performances and a facile recovery of the explosive crystals by the dissolution of the polymeric binder at pH 11 and 30 °C.

Crystal structure and explosive performance of a new CL-20/benzaldehyde cocrystal

A new cocrystal of 2,4,6,8,10,12-hexanitrohexaazaiso-wurtzitane (CL-20) and benzaldehyde with a molar ratio of 1:2 was prepared by a slow solvent evaporation method. The crystal structure of the CL-20/benzaldehyde cocrystal characterized by single-crystal X-ray diffraction (SXRD) reveals that the cocrystal is formed by intermolecular hydrogen bond interactions and belongs to the triclinic system. Moreover, impact sensitivity and friction sensitivity tests of CL-20/benzaldehyde cocrystal were conducted to evaluate its security. The detonation velocity of the CL-20/benzaldehyde cocrystal is 7455 m/s, lower than that of CL-20 and similar to that of TNT.

Facile Preparation and Properties Study of CL-20/TATB/VitonA Composite Microspheres by a Spray-Drying Process

To improve the safety of ammonium nitrate explosives, a one-step method involving the formation of CL-20/TATB/VitonA composite microspheres using spray drying is presented. The crystal morphology, particle size, crystal structure, thermal properties, and sensitivity of raw materials of CL-20 and TATB, CL-20/VitonA particles, and CL-20/TATB/VitonA microspheres were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and impact and friction sensitivity tests. The SEM results show that the prepared CL-20/TATB/VitonA composites with micro-/nanoscale grain size have a good spherical shape. Thermal analysis data show that TATB coating enhances the thermal stability of CL-20/VitonA. The impact and friction sensitivity results show that superior mechanical properties of these composite microspheres could be maintained. Obviously, this approach is an effective desensitization technique to prepare composite microspheres for explosives.

Pyrazol-triazole energetic hybrid with high thermal stability and decreased sensitivity: facile synthesis, characterization and promising performance

The barrier in the development of energetic material is the material design and performance improvement based on it. Currently, creative design and preparation of novel nitrogen-rich compounds are significant for new generation of green energetic materials. At the present work, organic heterocyclic hybrid pyrazol-triazole was constructed, synthesized and applied as building blocks in the development of versatile thermally stable high-energy materials. All derivatives were fully characterized by vibrational infrared spectroscopy (IR), multinuclear NMR (1H, 13C) spectroscopy, elemental analysis, differential scanning calorimetry (DSC), impact and friction-sensitivity test. Additionally, the structures of 4–8 and 10–13 were further confirmed by single-crystal X-ray diffraction and their crystal packing characteristics were thoroughly analyzed. Compound 2 not only enchanced physical properties of its ionic derivatives obviously, but also showed good detonation performance (D: 9075 m s−1) exceeding that of RDX, excellent insensitivity (IS > 80 J, FS > 360 N) comparable to that of TATB and superior thermal stability (331 °C) to that of HNS. Its ionic salts (compounds 4–14) also exhibit reasonable properties, such as good experimental densities (1.75–2.10 g cm−3), high thermal stability (174289 °C), good safety properties, excellent detionation performance (Dv: 7745–8952 m s−1, P: 23.830.6 GPa), suggesting this new pyrazol-triazole hybrid is beneficial for improving their physical performance. This work is helpful for accelerating the discovery of insensitive, thermostable and high-energy green energetic materials.

Thermal Safety of a Gun‐Launched Missile's Solid Rocket Motor Under Conditions of High Environm. Temp. and Overloaded Forces

AbstractTo verify a hypothetical failure cause of a gun‐launched missile's solid rocket motor (SRM) under conditions of high environmental temperatures and overloaded forces of up to 6000∼12000 g, experiments and simulations were conducted and a new criterion variable was proposed. Uniaxial compression tests of the composite modified double base (CMDB) propellant used in the gun‐launched missile were carried out at low and intermediate strain rates at 50 °C to characterize the CMDB propellant's dynamic properties. The Schapery nonlinear viscoelastic constitutive model was employed and applied in finite element analyses. Contact and an oscillating frictional direction between the grain and the case were observed when the overload curve oscillated with time. Three key variables of the process were researched: the contact pressure, the relative velocity, and the total contact time. Based on these, a new criterion variable q is proposed for judgements regarding the SRM's thermal safety. By comparing the results with those from friction sensitivity tests, it was discovered that the grain had a possibility of self‐ignition that cannot be ignored. Meanwhile, the gap width between the case and the grain was determined to be a key influencing factor.

Mechanochemical fabrication and properties of CL-20/RDX nano co/mixed crystals.

By milling 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) together, a nano CL-20/RDX co/mixed crystal explosive with a mean particle size of 141.6 nm is prepared from the raw materials, and the co/mixed crystals are characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC) and thermal-infrared spectrometry online (DSC-IR) technology; furthermore, the impact, friction and thermal sensitivity of the samples are tested. The results show that after milling, the morphology of the co/mixed crystal explosive is near-spherical, and the particle size reveals a normal distribution. The milled sample showed the same molecular structure and surface elements as the raw materials, but the XRD test shows that CL-20/RDX has a new crystal phase and the Raman and IR spectra gave a supplementary confirmation for the existence of a cocrystal phase in the milled sample. The activation energy of the thermal decomposition of CL-20/RDX is 206.49 kJ mol−1 higher than that of raw RDX. DSC-IR analysis showed that the thermolysis of CL-20/RDX produces a large amount of CO2 and N2O and a small amount of H2O, NO2 and NO. The mechanical sensitivity of CL-20/RDX is very low. In impact sensitivity tests with a 5 kg hammer, the special height (H50) is 51.43 cm, which is higher than the values of 36.43 cm for raw CL-20 and 9.78 cm for raw RDX. In the friction sensitivity tests, the explosion probability (P) is 56%; however, the thermal sensitivity of CL-20/RDX is higher than that of the raw materials, with its 5 s burst point being only 243.51 °C.

5-Amino-1H-1,2,4-triazole-3-carbohydrazide and its applications in the synthesis of energetic salts: a new strategy for constructing the nitrogen-rich cation based on the energetic moiety combination.

Nitrogen-rich cation 5-amino-1H-1,2,4-triazole-3-carbohydrazide and its derivatives were synthesized by a new molecular design strategy based on the energetic moiety combination. All derivatives were fully characterized by vibrational spectroscopy (IR), multinuclear (1H, 13C) NMR spectroscopy, elemental analysis, differential scanning calorimetry (DSC), and impact and friction-sensitivity tests. The structures of compounds 1-4, 7 and 8 were further confirmed by single-crystal X-ray diffraction and six different types of crystal packing were surprisingly discovered. The results show that the extensive hydrogen bonding interactions between the cations and anions lead to a complex 3D network, which contribute greatly to the high density, insensitivity and thermal stability of the 5-amino-1H-1,2,4-triazole-3-carbohydrazide salts. It is also found that the cationic form of 5-amino-1H-1,2,4-triazole-3-carbohydrazide can decrease the sensitivity and elevate the nitrogen content of the target salts effectively. Some of these salts exhibit reasonable physical properties, such as good thermal stability (up to 407 °C) and reasonable impact sensitivities (IS = 5-80 J). In addition, theoretical detonation properties of the energetic salts obtained with EXPLO 5 (version 6.02) confirm them as competitively energetic compounds comparable to those of RDX or HMX.

Crystal structure and thermal behaviour of pyridinium styphnate.

In the crystal structure of the title mol-ecular salt, C5H6N(+)·C6H2N3O8 (-) (systematic name: pyridinium 3-hy-droxy-2,4,6-tri-nitro-phenolate), the pyridin-ium cation and the 3-hy-droxy-2,4,6-tri-nitro-phenolate anion are linked through bifurcated N-H⋯(O,O) hydrogen bonds, forming an R 1 (2)(6) ring motif. The nitro group para with respect to phenolate ion forms an intra-molecular hydrogen bond with the adjacent phenolic -OH group, which results in an S(6) ring motif. The nitro group flanked by the phenolate ion and the phenolic -OH group deviates noticeably from the benzene ring, subtending a dihedral angle of 89.2 (4)°. The other two nitro groups deviate only slightly from the plane of the benzene ring, making dihedral angles of 2.8 (4) and 3.4 (3)°. In the crystal, the 3-hy-droxy-2,4,6-tri-nitro-phenolate anions are linked through O-H⋯O hydrogen bonds, forming chains along [100]. These anionic chains, to which the cations are attached, are linked via C-H⋯O hydrogen bonds, forming a three-dimensional structure. Impact friction sensitivity tests and TGA/DTA studies on the title mol-ecular salt imply that it is an insensitive high-energy-density material.

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

AbstractSubmicrometer‐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.

Electrospray Crystallization for High‐Quality Submicron‐Sized Crystals

AbstractNano‐ and submicron‐sized crystals are too small to contain inclusions and are, therefore, expected to have a higher internal quality compared to conventionally sized particles (several tens to hundreds of microns). Using electrospray crystallization, nano‐ and submicron‐sized crystals can be easily produced. With the aid of electrospray crystallization, a mist of ultrafine solution droplets is generated and subsequent solvent evaporation leads to crystallization of submicron‐sized crystals. Using cyclotrimethylene trinitramine (RDX) solutions in acetone, the conditions for a stable and continuous jet were established. At relatively small nozzle diameters and relatively low potential differences, hollow spheres of RDX crystals were observed. At a higher nozzle diameter and potential difference and in the region of a continuous jet, RDX crystals with an average size of around 400 nm could be produced. In order to test the quality of the submicron‐sized energetic material, impact and friction sensitivity tests were carried out. The test results indicate that the submicron‐sized product had reduced friction sensitivity, indicating a higher internal quality of the crystalline product.

Development of a biodegradable ethylene glycol dinitrate-based explosive

Bacteria capable of degrading ethylene glycol dinitrate (EGDN) were isolated under aerobic and, carbon and nitrogen-limiting conditions from EGDN contaminated soil and rivers. EGDN degradation was monitored using HPLC and UV–Vis spectrometer. Among the isolated strains Bacillus subtilis GN was the best, completely degrading 6.6 mM EGDN with the concomitant release of nitrite and EGMN within 72 h. Furthermore, the level of toxicity of EGDN as measured by the bioluminescent bacteria, Vibrio fischeri was reduced by 80% when 100% of the 6.6 mM EGDN was degraded. An environmentally friendly “biodegradable explosives”, was achieved by adsorbing B. subtilis GN spores onto the wood flour, an ingredient of the explosive. The incorporation of B. subtilis GN spores into the explosive formulation did not affect the quality of the explosive as confirmed by the almost unchanged detonation velocity (3410 ms −1 compared to 3500 ms −1 of the control), autoignition temperature, Abel test, shock and friction sensitivity test. It was also possible to achieve rapid degradation of the residues after detonation upon exposure to air and moisture.

COMBUSTION AND IGNITION PROPERTIES OF AMMONIUM NITRATE AND ACTIVATED CARBON MIXTURES

In order to obtain a better understanding of combustion and ignition properties of ammonium nitrate (AN) and activated carbon (AC) mixtures, friction test, thermal analysis, and 200-mL closed vessel combustion test were carried out and the influence of the mixing ratio on the combustion and ignition properties of various compositions of AN/AC mixtures was investigated. As a result of the BAM friction sensitivity test, all mixtures showed negative results. From differential scanning calorimetry (DSC) test results, each AN mixed with more than 4 wt% of AC mixtures showed violent exotherm after the melting of AN and some of the mixtures exploded in a SUS crucible. The largest heat of reaction was observed at a higher concentration than the stoichiometric composition. The results of 200-mL closed vessel test showed that the powdered AN and the phase stabilized AN (PSAN) mixed with AC showed a fast reaction and a high pressure due to the large amount of gas release and the maximum pressure, and the maximum rate of pressure rise showed the maximum values at a higher concentration than the stoichiometric composition.

Synthesis and characterization of some new acid salts of 8H-2,6,8,9,10-Pentaazabicyclo[5,2,1]-deca-2,5,9,10-tetraene

Some new acid salts of 8H-2,6,8,9,10-pentaazabicyclo[5,2,1]-deca-2,5,9,10-tetraene were prepared and characterised by spectral data (IR, 1H-NMR and Mass) and elemental analysis. The purity of these compounds was confirmed by HPLC and was found to be > 95% pure. In addition, the compounds were subjected to impact and friction sensitivity tests and were found very safe.

Bismuth Chromate in Delay Compositions

Barium chromate is used as a secondary oxidiser in delay compositions which slows down the rate of the reaction. The composition containing barium chromate potassium perchlorate and sulphur along with the binder, gives inverse burning rates up to 4.5 s/cm. If barium chromate is substituted by bismuth chromate hydrate, the rate of reaction is slowed down further to 11.8 s/cm. Various compositions were prepared by changing the percentage of barium chromate and bismuth chromate. The energy of activation was determined to be 14.5 kcal/mole for the composition with 40 per cent bismuth chromate. The explosion temperature for a delay of 5 s was observed as 480 degree centigrade. These compositions were subjected to impact and friction sensitivity tests to determine the safety aspects. This paper presents the results of burning rate calorimetry, explosion temperature and the sensitivity data of some delay compositions containing bismuth chromate.

Friction sensitivity mechanism of Ammonium Perchlorate Composite Propellants

AbstractFriction sensitivity of ammonium perchlorate (AP) composite propellants has been studied experimentally by means of thermal analysis and micro‐thermocouple techniques. Several types of catalysts were mixed with AP in order to examine the effect of the reactivity on the sensitivity. The results of friction sensitivity test show that the samples are sensitized when the concentration of catalysis which are used for high burning rate propellants is increased. Metal contents within the catalysts tend to give some effects on the friction sensitivity. Based on the results of the temperature profile measurements in combustion waves, it is found that the friction sensitivity is correlated with the burning surface temperature of the propellants. The catalysts which accclerate the AP decomposition are responsible for the friction sensitivity but not for the fallhammer sensitivity.

The effect of high energy X-rays and pile radiation on the thermal decomposition and thermal explosion of α -lead azide

α -lead azide has been irradiated in air with the X-rays from a 1 MV generator and with pile radiation. At dosages below 10 4 r the thermal decomposition and thermal explosion characteristics of the X-irradiated material are indistinguishable from those of the unirradiated material. At higher dosages decomposition rates are changed and explosion times reduced. Pile radiation gives very similar results for the same energy deposition. Samples irradiated at 10 4 and 10 7 r showed no difference from unirradiated material on a friction sensitivity test.