Showing papers in "Propellants, Explosives, Pyrotechnics in 1992"

Thermal expansion, transitions, sensitivities and burning rates of HMX

Abstract: The phases of HMX and their transitions were investigated by thermal analysis using X-ray diffraction. Series of diffraction pattern were measured, while the samples were heated and cooled. The thermal expansion coefficients and the colume changes at the transitions were extracted from the diffraction series. A contraction of β-HMX was found before changing into δ-HMX resulting in a high volume difference during the transition. On cooling, the reconversion of the high temperature phase requires days. It is further slowed down by decomposition products, which are formed at temperatures beyond 490 K. The final reconversion results in mixtures of α-and βHMX. The mechanical sensitivities and the buring rates of the HMX phase were determined. The high sensitivity of δ-HMX against impact together with its slow reconversion creates handling risks when the HMX is exposed to temperatures above 440 K.

Aging behavior of propellants investigated by heat generation, stabilizer consumption, and molar mass degradation

Abstract: Four double-base rocket propellants and a single-base gun propellant were tested to find out stabilizer consumption molar mass degradation, and heat generation between 50 °C and 90 °C and between 40 °C and 110 °C, respectively. Stabilizer depletion was measured by high performance liquid chromatography (HPLC), molar mass degradation by gel permeation chromatography (GPC), and heat generation by microcalorimetry. The conditioning times at different temperatures were determined with one of the rocket propellants, and the influence of the long-term storage on heat generation at 60 °C for 2191 dys was investigated. A correlated experiment between stabilizer consumption and heat generation showed that heat production does not increase substantially until the stabilizer has been consumed almost completely. The experimental data of molar mass degradation are described by a kinetic model based on statistical chain scission, and the stabilizer decrease by a first order reaction. For the gun propellant the Arrhenius plots of the reaction rate constants show two temperatures of teh stabilizer consumption, molar mass degradation and heat generation were determined.

Thermal Decomposition of Energetic Materials 56. On the fast thermolysis mechanism of ammonium nitrate and its mixtures with mangnesium and carbon

Abstract: Fast thermolysis studies of ammonium nitrate (AN) and its mixtures with magnesium and activated charcoal have been carried out by the Fourier transform infrared spectroscopy/temperature profiling technique. When subjected to rapid heating (ca. 80°C/s), AN Sublimes/decomposes around 300°. Sublimation dominates at ambient pressures. The IR-active products of decomposition are NH3, NO2, N2O and H2O. Reaction schemes accounting for the products are proposed which involve proton transfer leading to NH3 by the decomposition products of HNO3. The decomposition of AN is significantly enhanced when AN is mixed with magnesium powder or charcoal, and occurs at as low a temperature as 135°C. Whereas NH3 is the major product of decomposition of ANMg mixtures, no NH3 is observed from ANC mixtures. The results are explained by the reaction of HNO3 and NH3 with Mg or C.

Thermal Decomposition of Azide Polymers

Abstract: Thermal decomposition of polyglycidyl azide (GAP) and bis(azidomethyl)oxetane/tetrahydrofuran copolymer (BAMO/THF) was studied by TGA and DSC in helium atmosphere, which was showing overall first-order kinetics. The additional azide groups at terminal position in the molecular structure decomposed independently and increased the rate of decomposition. However, the decomposition kinetics was less affected by the additional azide groups in the main chain. The decomposition properties of aged polymer Samples were the same as those of untreated ones. Catocene significantly altered the decomposition temperatures of GAP and BAMO/THF. The speak temperature of DSC thermogram changed from 533 K to 494 K in GAP and from 535 K to 498 K in BAMO/THF. Like UV treatment, BAMO/THF with catocene was thermally cross-linked during the aging at 343 K. Although BAMO/THF with catocene produced rubbery solids from the initial viscous liquids, there was no significant difference between the rate of decomposition of treated sample and that of untreated one.

Energetics of BAMO

Abstract: 3,3-Bis(azidomethyl)oxetane (BAMO) is a typical energetic azide polymer containing two N3, bonds in the molecular structure. Since BAMO is a solidified polymer at room temperature, a liquid BAMO copolymer with tetrahydrofuran (THF) was synthesized in order to gain energetic binders for solid propellants. Various types of experiments were carried out to elucidate the decomposition and combustion processes of BAMO polymer, BAMO/THF copolymer, and crosslinked BAMO/THF copolymer. The heat produced by the decomposition is caused by the bond breakage of -N3 to produce N2, gas. The burning rate characteristics of crosslinked BAMO/THF copolymer depend largely on the mole fraction ratio of BAMO and THF.

Studies on the critical temperature of thermal explosion for 3‐Nitro‐1,2,4‐triazol‐5‐one (NTO) and its salts

Abstract: The critical temperature of thermal explosion for 3-nitro-1,2,4-triazol-5-one (NTO) and its ethylenediammonium salt (ENTO), potassium salt (KNTO), copper salt (CuNTO) and lead salt (PbNTO) were obtained using the stationary theory of thermal explosion, the calculation formula of estimating the critical temperature of thermal explosion under non-isothermal DSC condition, and the determination method for the critical temperature of thermal explosion of small-scale solid explosive and its data treatment method. The results of the four methods are agreeable to each other, whose differences are within 5%. The results indicate that the heat-resistance ability of NTO and its salts and of the common explosives, cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetrinitramine (RDX), pentaerythritoltetranitrate (PETN) and tetryl decreases in the order HMX > NTO > ENTO > KNTO > RDX > PETN > tetryl > PbNTO > CuNTO.

Developement of neutral polymeric bonding agents for propellants with polar composites filled with organic nitramine crystals

Abstract: Versatile neutral polymeric bonding agents (NBPA's) have been developed for energetic propellants in which polar HMX particles are dispersed in a polar binder matrix containing highly polar plasticizers (TMETN, NG, etc.). Using a semi-empirical approach through adjustment of solubility parameters and molecular weight, neutral acrylonitrile interpolymers were synthesized which mix uniformly with the submix and still have a high affinity for the HMX particles when they are added. Addition of about 0.2 % w/w of NPBA to HMX-filled PEG binders increases the strength by a factor of as high as five compared to samples with no NPBA, and also eliminates the sudden decrease in modulus (knee) which occurs at relatively low elongation. The degree of filler reinforcement achieved by our NPBA's in energetic propellants is far superior to that achieved by adding nitrocellulose or any other previously proposed bonding agents, and similar to the effect of precoating the HMX particles with polyurea shells.

The Mechanism of Filler Reinforcement from addition of neutral polymeric bonding agents to energetic polar propellants

Abstract: It has been demonstrated that addition of small amounts of the newly developed neutral polymeric bonding agents (NPBA's) to energetic propellants such as HMX/PEG/NG composites causes strong filler reinforcement. The mechanism of this reinforcement occurs through interfacial effects, and not because of an overall increase in the crosslink density of the binder. It has been demonstrated directly that the NPBA's have a favorable relative affinity for HMX and concentrate at the solid surface during mixing. All the experimental evidence supports the theory that highly crosslinked polymeric shells form around the HMX particles and chemically bond to the binder matrix during the cure, thus causing an increase in the initial modulus. Furthermore, these shells appear to eliminate the weak, soft layers around the particles, and hence filler reinforcement persists up to much higher elongation than without addition of NPBA. Based on the filler reinforcement observed, the simple one-step procedure of incorporating our NPBA is almost as effective as the more costly process of precoating the particles.

Use of Dynamic Mechanical Measurements to determine the aging behavior of solid propellant

Abstract: A process for determining the aging characteristics of solid rocket propellants by measuring their dynamic mechanical properties is described. Samples of rocket propellant are tested using a mechanical spectrometer at low strain levels and low frequencies. The change in the dynamic storage modulus of the propellant with aging time and temperature is used to determine the aging rate anf the likely mechanisms occuring during aging. The technique is advantageous is several respects: (1) because the tests are non-destructive and use small test specimens, and entire aging program can be conducted using much less propellant than is required ihn traditional aging programs (propellant requirements are reduced by more than an order of magnitude) (2) the technique can be applied to samples with unusual or unique geometries which cannot be tested using traditional methods; (3) test specimens can be obtained directly from live, operational solid rocket motors, and service life and mechanical property degradation can be determined.

Fuel Regression Mechanism in a Solid Fuel Ramjet

Abstract: A model relating the combustion characteristics, particularly the regression rate, to the fuel properties in a solid fuel ramjet (SFRJ), is presented. The analysis is based on inspecting the different phenomena (e.g., chemical kinetics and heat transfer) involved in the fuel decomposition process in order to determine the rate controlling steps, and modeling the important mechanisms. Model predictions were compared to experimental findings for four polymeric fuels, showing excellent qualitative agreement in classifying different fuels, as well as good quantitative predictions of the fuel regression rates. The model can serve as a useful tool for the selection of appropriate fuels, as well as for preliminary design of the engine and mission profile prior to static firings of the final SFRJ prototype.

New dependence of Activation Energies of Nitroesters Thermolysis and possibility of its application

Abstract: Relationship was found between activation energies E of low-temperature non-autocatalyzed thermolysis of the nitric acid esters, on the one hand and their oxygen balances OB100, on the other. By this relationship, molecular-structural dependence is evidenced of values E, at the same time existence is signalized of the direct relationship between the values E and the impact sensitivity of nitroesters.

Polymer Binder for High Performance Explosives

Abstract: An evaluation on coating HMX crystals with three different polymeric binders using the “solvent slurry process” was conducted. Three polymers employed were: –a thermoplastic copolymer [Kel-F 3700], –a thermoplastic elastomer [kraton-G 1650] and –a polyurethane [Impranil DLH]. Kel-F 3700 presented an electrostatic hazard and was too insoluble for application by the slurry process. Kraton-G 1650 presented a similar electrostatic hazard and its process yield was low. Impranil DLH produced a high yield using the batch slurry process.

High Rate Decomposition of Cyclotrimethylenetrinitramine (RDX)

Abstract: RDX products obtained at high heating rates are discussed. RDX was decomposed by combustion in pressurized bomb and by short laser pulse irradiation.

Thermal Behaviour of HMX/RDX Mixtures

Abstract: Thermal behaviour of HMS/RDX mixtures is studied by differential thermal analysis (DTA) and thermogravimetric analysis (TGA). It has been found that the temperature of polymorphic transformation of HMX shows an increase due to the presence of RDX. The enthalpies of the enothermic transformations depend on the composition of the mixture, and up to 30% RDX there is a linear relationship. The formation of an eutectic with a composition of 30/70 (HMX/RDX) is postulated to explain the melting processes.

Internal Shearing during Shaped Charge Jet Formation and Break-up

Abstract: During jet formation and elongation, the shaped charge linear material is subject to forces which vary extremely in both magnitude and direction. As a result, the direction in which the slip planes are formed in the material, changes so as to comply with the force direction and strength. By following the direction of the slip planes from the beginning of liner motion until the jet breaks up, it is possible to suggest a description of the internal changes occurring in the material during liner collapse, jet formation, and jet elongation. The mechanism obtained by this study may account for the slight systematical deviation by a jet from the original shaped charge axis of symmetry, such as has been measured very accurately using the orthogonal synchro-streak technique (OSST) developed by Held. The mechanism may also explain some jet details observed in OSST photographs and flash radiographs. The modeled mechanism identifies the possibility that some basic differences may exist between the break-up process occurring in expanding rings and shells and the break-up process occurring in shaped charge jets.

Synthesis of N‐2,4,6‐trinitrophenyl‐N'‐2,4‐dinitrobenzofuroxano‐3,5‐dinitro‐2,6‐diaminopyridine

Abstract: N-2,4,6-trinitrophenyl-N' -2,4-dinitrobenzofuroxano-3,5-dinitro2,6-diaminopyridine has been synthesied from 2,6-diaminopyridine and dinitrodichlorobenzene as well as 2,4,6-trinitrochlorobenzene. For this compound, the structure has been determined by elemental analysis, IR 1HNMR, and MS spectroscopies.

Stability Studies on Pentaerythritol Tetranitrate

Abstract: Tyhe influences of acidity and dipentaerythritol hexanitrate (DiPEHN) on the thermal sensitivity of pentaerythritol tetranitrate (PETN) was studied using differential scanning calorimetry (DSC). Decomposition kinetics of PETN with or without DiPEHN, acidic PETN and DiPEHN were also studied by SC to evaluate Arrhenius parameters. The presence of sulphuric acid impurity decreased the thermal stability as well as the activation energy, whereas the nitric acid influence was negligible. Thermal stability of PETN was not affected by the presence of DiPEHN. DiPEHN showed better thermal stability and higher decomposition energy compared to PETN.

Analysis of the Accidental Explosion at PEPCON, Henderson, Nevada, on May 4, 1988

Abstract: Several hours of fire and numerous explosions destroyed the Pacific Engineering Company plant in Henderson, Nevada, that manufactured ammonium perchlorate (AP) for rocket fuel. This incident began about 1130 PDT on May 4, 1988, with a fire in their Batch House that grew out of control and caused a first large explosion at about 1153 PDT. The final and largest explosion occurred about 1157 PDT. Damages to the surrounding community were surveyed and interpreted as airblast overpressures versus distances, which allowed an estimate of 1-kiloton nuclear free-air-burst for the equivalent explosion yield. This could be reproduced by 250-tons TNT burst on the ground surface. Weather reports were obtained from the National Weather Services which indicated somewhat enhanced airblast propagation downwind toward northerly directions and attenuated airblast propagations upwind in southerly directions. It was impossible, for lack of winds aloft information below about 500 m above ground, to determine whether there was any atmospheric acoustic airblast focusing. Several seismic recordings in Las Vegas showed the greatest ground motion resulted from the airblast wave passage, traveling at near acoustic speed. Ground wave arrival times were not sufficiently precise to allow seismic speed interpretations. Of the 4000 tons of AP apparently stored inmore » and around the plant, it appears that about 1500 tons detonated in the largest explosion. This leads to a conclusion that the TNT airblast equivalence factor for AP is near 1/6. An independent estimate, based on analysis of more ideal close-in structural deformations, suggested an equivalence factor of 1/3. 25 refs., 12 figs., 14 tabs.« less

Numerical Simulation of Casting Explosives in Shell

Abstract: Predicting interface position of solid-liquid phase change is important for the filling of explosives in the shell. The cooling process of casting charge is discussed analytically and experimentally. The basic equations describing this process are derived from a modified and extended equivalent heat capacity model. Numerical calculations are then performed to determine the solidification front distributions and temperature distributions. The experiments are performed using TNT as the phase change material. Comparison between practical experiments and computer simulation has shown that there is a good agreement. By using computer calculations, a better knowledge of important parameters for the casting process can be easily obtained.

The glass transition temprature measurement of nitrocellulose by torsional braid analysis

Abstract: The glass transition temperature of pure nitrocellulose is determined by torsional braid analysis. The reproducibility and reliability of the measured results are discussed.

Study on Thermal Decomposition of Pentolites by modified vacuum stability apparatus and differential scanning calorimetry

Abstract: A modified manometric vacuum stability test (VST) apparatus as well as a differential scanning calorimeter (DSC) were used to study the decomposition of pentolites (mixtures of PETN and TNT). The former operated isothermally at three heating temperatures (100°.C 110°C and 120°C), the latter with a constant heating rate. Various compositions of pontolites were examined. For the VST tests, heating periods were 40 hours except for experiments in which resulting pressures were higher than 760 mmHg. Using the ideal gas law, the volume of gaseous products was calculated from the pressure readings. The evolved gas volume from pentolites tested at 100°C is about as large as that from either pure PETN or pure TNT. However, the gas volumes released from pentolites heated at 110°C and 120°C are apparently larger than those from either PETN or TNT alone. In particular, a mixture of PETN and TNT with a 1:1 weight ratio releases a maximum volume of gas products. It is found by DSC analyses that decompositions temperature of TNT decreases as mixed with PETN.

Polymers with high-energy substituents: polyesters containing azidomethyl groups

Abstract: This paper describes the synthesis of linear azidopolyesters which appear suitable as high-energy binders in explosive systems. Preparation is carried out via a nucleophilic substitution reaction from the corresponding halogenic polyesters with sodium azide. In the polycondensation of the halogen derivates, the authors examined the influence of the intial compound ratio of dicarbonic acid and diol on the distribution of end groups and molecular weight. In this work it was found that the azido group could be introduced into the polyester backbone relatively easily. Some properties of polyesters are fundamentally changed through the introduction of the azido group. The changes as regards viscosity, thermal stability and glass transition temperature were documented and the friction and impact sensitivities recorded.

Am1 MO Study of Benzene Nitro Derivatives

Abstract: Molecular properties of benzene nitro derivatives were investigated by using semi-empirical MO calculations. As the results, the molecular structures and the rotational barrier of the nitro group calculated by AM1 showed a good agreement with the experimental values. The heats of formation in gaseous and condensed phases were obtained by considering isodesmic reactions. By this procedure, the heat of formation of hexanitrobenzene in solid phase was calculated to be +22.7 kcal/mol. The detonation parameters were also calculated by using four equations of state. The predicted detonation velocities showed a good agreement with the experimental values.

Molecular orbital studies of the thermal decomposition mechanism of dimethylnitramine

Abstract: The electronic structures of dimethylnitramine (DMNA) were calculated using ab initio Gaussian 80 program at the Hartree-Fock level with STO-3G and STO-4-21G basis set, respectively. The Mulliken bond order of the NNO2 bond is the least one in comparision with those of the other bonds in the DMNA molecule. Two potential energy curves along the NN bond splitting pathway (RNN) were obtained using MINDO/3 and MNDO methods, respectively. These curves have the same trend and are qualitatively consistent with the results obtained from the thermolysis of nitromethane (CH3NO2). It was found that the frontier MO levels and the net charges of groups are changed with RNN distance. The products of thermal decomposition and the energy changes were calculated by MINDO/3 method and are discussed in this paper.

Method for the Determination of the Critical Diameter of High Velocity Detonation by conical geometry

Abstract: A critical diameter exists for both high velocity (HVD) and low velocity detonation (LVD). No relationship exists between these two diameters, however they are both dependent upon the temperature, confinement, contaminants, type of detonation and, most importantly, geometry. In cylindrical geometry, the critical diameter is determined by go/no go tests which are relatively expensive and time consuming. In this respect, there is a need for a method by which the critical diameter can be determined quickly and reliably. A relatively simple procedure which can also be performed in the field is proposed in this article where the critical diameter is determined in principle by a single test through the application of conical geometry. However, on account of “overdrive”, the values always fall below those obtained by cylindrical geometry. Metal plating is proposed as a method of indication. The results are then compared simultaneously by optical and electrical measurements. The temperature dependence of the critical diameter of the HVD of pure nitromethane was also demonstrated by conical geometry and was compared to the values of cylindrical geometry. The method was originally proposed as a joint US/German effort between Dr. Mallory of NSWC, China Lake, and Dr. Leiber of BICT. Since Dr. Mallory has recently passed away, the question is therefore open as to whether or not this test can be approved internationally.

Tactical Solid Rocket Motors Response to Bullet Impact

Abstract: Vulnerability studies are very important for rocket motors development using high energy and minimum smoke solid propellant. Among the treated threats, the bullet impact is a well known test studied for many years. Nevertheless, during our experimentations against true rocket motor, the well-known scenarios failed. A new scenario has been identified and confirmed to take into account the new phenomenon. This scenario implied the solid propellant but also the geometry of the grain. The paper presents the experimental works and describes the physics of the phenomenon supported by the associated model studies.