Double Base Rocket Propellants Research Articles

Modified Arrhenius kinetics for double base propellant decomposition: Effect of water

Numerous studies have been conducted on the decomposition mechanisms of cellulose nitrate (NC), a polymer employed in double base (DB) rocket propellants. It is well known that storage temperature affects the lifetime of these energetic formulations. However, less studies have been published on the influence of water. This research examined the role of water on the stabiliser consumption rate during accelerated ageing of a DB rocket propellant, as well as the impact on the shelf life prediction of the energetic formulation. Different volumes of water (0.8, 1.6, 2 and 4 µl/g) were added to the propellant in sealed vials, which were then isothermally aged (70, 80, 90, 100 °C). Analyses of the stabiliser consumption showed a faster decomposition kinetics in presence of water which is indirectly linked to the shortening of the storage life of the NC based propellant by 35 %. For the conditions, an activation energy of 133 ± 4 kJ/mol was reported for the water catalytic decomposition mechanism. A numerical model that included water as a variable was reported to reduce the uncertainty in the determination of the service life of NC based propellant. International standards such as Allied Ordnance Publication 48 should not overlook the effect of water/moisture on the safety of ammunition containing NC and should implement a modified Arrhenius equation.

Influence of humidity on the decomposition process of double base rocket propellant

The decomposition mechanisms of the polymer cellulose nitrate (NC) which is used in double base (DB) rocket propellants, have been extensively studied, and the influence of storage temperature on the lifetime of these energetic formulations is well known. However, the impact of humidity and water on the polymer decomposition process is poorly understood. This paper studies the influence of humidity on the decomposition chemistry of NC and its impact on shelf life. Stabiliser consumption was first analysed by ageing the propellant in sealed vials at different humidity levels for 7 days at an isothermal temperature of 90 °C. Samples were also analysed using heat flow calorimetry (HFC) at isothermal temperatures of 80 °C, 90 °C, and 100 °C. The results indicates that stabiliser depletion increases with increasing water content. Life assessment calculations (AOP 48 ed2) show that increasing the absolute humidity from 6 to 22 g m-3 will decrease the propellant life from 11 to 6 years (25 °C equivalents). The HFC results follow the same trend as the stabiliser depletion where greater absolute humidity increases the heat flow by up to 400 %. Unlike the pass/fail criteria for stabiliser depletion, the HFC samples passed the 10-year (25 °C equivalent) life criteria (STANAG 4582). A multi-temperature (80, 90, 100 °C) kinetic analysis of the initial heat flow showed that the heat flow rate increased with increasing humidity, but the activation energy for all humidity levels remained at 131 (± 3) kJ mol−1.

Review of the Application Progress of 2,6-diamino-3,5-dinitropyrazine-1-oxide

Since the first synthesis of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) in Lawrence Livermore National Laboratory (LLNL) of America in 1993, efforts of investigation into LLM-105 have never ended due to its premium performance. Therefore, with the goal to further emphasize the importance of this material and to provide reference to the application of LLM-105 in propellants and explosives, the properties and performance of LLM-105 are briefly introduced at first and then the application of LLM-105 is reviewed in various areas, including polymer bonded explosives, double-base rocket propellants with low signature and low sensitivity, propellants for perforating cartridges in oil and gas fields and gun propellants.

Research on Mechanical Properties and Sensitivity of a Novel Modified Double-Base Rocket Propellant Plasticized by Bu-NENA.

The research and development of rocket propellants with a high solid content and superior mechanical and security performance is urgently needed. In this paper, a novel extruded modified double-base (EMDB) rocket propellant plasticized by N-butyl-N-nitratoethyl nitramine (Bu-NENA) was prepared to overcome this challenge. The results indicated that Bu-NENA decreased the mechanical sensitivity successfully, contributing to the mechanical properties against traditional nitroglycerin (NG) based EMDB propellants, while hexogen (RDX), which is beneficial to propellant energy, was not conducive to the elongation and sensitivity of the propellants. By contrast with the blank group (NG-based EMDB propellant, R0), the elongation of the optimized propellant at −40 °C was promoted by 100% from 3.54% to 7.09%. Moreover, the β-transition temperature decreased from −33.8 °C to −38.1 °C due to superior plasticization by Bu-NENA, which represents a better toughness. The friction sensitivity dropped by 100% from 46% to 0%. Simultaneously, the height for 50% probability of explosion (H50) increased by 87.2% from 17.2 cm to 32.2 cm. The results of this research could be used to predict a potential prospect in tactical weapons.

Principal Component Analysis of FTIR Data to Accurately Assess the Real/Equivalent In‐Service‐Times of Homogenous Solid Propellant

AbstractThis study was devoted to setting up new methodologies for an accurate assessment of both real and equivalent in‐service‐times (RIST/EIST) of homogenous solid propellants (HSP) through a combination of principal component analysis (PCA) and Fourier transform infrared (FTIR) spectroscopy. Four double‐base rocket propellants (DBRP) have been artificially aged at T=338.65 K for 4 months with sampling every 20 days. FTIR showed that the homolytic scission of the O‐NO2 bonds and the hydrocarbon chains of the nitrate esters are the main processes occurring during the chemical decomposition. The scatter plot from PCA of FTIR spectra shows that over 93 % of the variance was described by the first principal component. Moreover, the loading plot designated the three characteristic FTIR bands from the nitro (NO2) group as the most influenced by aging. A new PCA/FTIR experimental way was set to accurately assess the RIST of HSPs. The relative deviation associated with the RIST evaluated by the present procedure and those from the PCA/VST experimental way, recently developed, was found to range from 4.0 % to 6.7 %. Subsequently, a PCA/FTIR prediction model of the EIST is established. The predictions present a relative deviation of less than 7.1 % compared to the recent PCA/VST model. The accuracy of the model was further confirmed using similar DBRPs artificially aged for 6, 8, 10, and 12 months. The relative variation between the RIST provided by the PCA/FTIR procedure and the prediction model was found less than 5 %, thus confirming the highest accuracy of such combination.

A new experimental way for the monitoring of the real/equivalent in-service-time of double base rocket propellant by coupling VST and PCA

The assessment of the real in-service-time (RIST) and the equivalent in-service-time (EIST) of double base rocket propellants (DBRPs) is of utmost importance for the safe storage and use of weapon systems as well as the efficiency of the accelerated aging plans. In this work, four DBRPs with similar chemical composition and different natural aging have been artificially aged at T = 338.65 K for 4 months with sampling every 30 days. The unaged and artificially aged samples have been investigated by vacuum stability test (VST) at five isothermal temperatures (T = 333.15 K, 343.15 K, 353.15 K, 363.15 K, and 373.15 K). The volume of the evolved gases in VST was found to decrease with natural/artificial aging. Furthermore, the VST data were treated and subjected to principal component analysis (PCA). The results showed excellent discrimination of the DBRP samples according to their stability thermal properties. Most of the variance was described by the first principal component (PC1) whose scores were linearly correlated with the natural aging durations when PCA is applied on VST data obtained at T = 363.15 K. In light of the obtained results, a new experimental way for the estimation of the real/equivalent IST was proposed, which takes into account the impact of the natural aging of the sample. The approach predicts successfully the RIST of two similar DBRPs with a relative deviation of less than 2%. At the specific heating temperature T = 338.65 K, the developed model provides more conceivable EIST values, with asymptotic behavior against artificial aging duration evolution, thus overcoming some shortcomings of the common generalized van’t Hoff formula (GvH).

Performance, mechanical and thermal properties of double base rocket propellant including copper oxide as burning rate modifier

In this work, different percentages of Copper oxide have been added to double base rocket propellant (DBRP) as burning rate modifier. A conventional DBRP has been prepared and studied for comparison. The mechanical properties at different temperatures were studied. The heat of combustion and ignition temperature of the samples were measured. The performance represented by the operating pressure and the burning rate were evaluated at 8mm throat diameters. The thermal behavior of the traditional DBRP in comparison with a selected composition containing copper oxide was discussed. It was concluded that the addition of copper oxide in DBRP has positive effect on the mechanical properties of the traditional DBRP while slight increase in the performance properties was observed.

Nitroglycerine migration to polyurethane used for inhibition of double-base propellants through thermal analysis techniques

Nitroglycerine (NG) migration in polyurethane (PU) inhibitor, which leads to ballistic malfunctions or tearing-down of the rockets for double-base rocket propellants, is investigated by thermal analysis–thermogravimetry/quadrupole mass spectrometer (TG/QMS) after accelerating migration at 65 °C. NG content increases before 48 h and then decreases dramatically till 84 h, after that it tends to stabilize and reaches 4.5 %. The thermal stability of PU is affected by NG migration, which brings down the onset temperature of PU at low-temperature zone, and accelerates the break of C–O bond in the main chain of polymer. In order to minimize the NG migration, the isolation coating consisting of 3-aminopropyltriethoxysilane (KH-550), phenolic resin (PF), and polyvinyl butyral (PVB) was designed and reduced the NG content to 0.48 %.

Dynamic mechanical analysis of double base rocket propellants

Dynamic mechanical analysis of double base rocket propellants

The Effect of Different Copper Salts on the Mechanical and Ballistic Characteristics of Double Base Rocket Propellants

The Effect of Different Copper Salts on the Mechanical and Ballistic Characteristics of Double Base Rocket Propellants

Determination of Glass Transition Temperature of Double-base Rocket Propellants with the Use of Dynamic Mechanical Analysis

The paper presents results of Dynamic Mechanical Analysis (DMA) of double-base (DB) solid rocket propellant with special attention paid to determining the glass transition temperature. The presented experiments were carried out with the use of Netzsch DMA 242C analyzer with the dual cantilever operation mode. Advantages and drawbacks of the DMA method, measured values, as well as important characteristics of solid double-base rocket propellants were briefly described. Obtained values of the storage modulus E', the loss modulus E, and tanδ were represented in dependence on temperature. The glass transition temperature of the tested propellant was determined according to NATO standard 4540 [7] at the peak of the loss modulus curve.

Bioremediation of Glycerol Trinitrate (GTN) Explosive

Bioremediation using living organisms, primarily microorganisms, offers the possibility to degrade or detoxify substances hazardous to human health and/or the environment. Explosives or ‘explosive waste’ fall into the category of energetic materials and are susceptible to initiation or self-sustained energy release, when present in sufficient quantities and exposed to stimuli such as heat, shock, friction, chemical incompatibility or electrostatic discharge. Explosives are classified as primary or secondary based on their susceptibility to initiation. The nitrate esters are classified as secondary explosives, as they are formulated to detonate only under certain conditions. Nitroglycerin or glycerol trinitrate (GTN) is manufactured for use as an explosive in the double-base gun and rocket propellants and as a pharmaceutical vasodilator. For most of its industrial history, GTN was considered either recalcitrant to microbial biodegradation or even inherently non-biodegradable and high concentrations of the ester (>900 ppm) were inhibitory to bacterial growth. Physicochemical methods of GTN destruction involve adsorption on activated carbon followed by reduction with inorganic chemicals or by alkaline hydrolysis, yielding glycerol and nitrite or nitrate. However, these techniques suffer from high operational costs, the presence of excess reactants that remain dissolved in the effluent and the necessity for secondary treatment to remove nitrogenous products. This review paper describes biotransformation and biodegradation of GTN using bacteria and fungi, which may offer a means of removal of GTN from waste streams and bioremediation of contaminated land sites. Possibilities of developing transgenic plants carrying microbial genes capable of metabolising GTN, and problems that can occur during the bioremediation of GTN, from the bacteria and fungi unable to adapt to the extreme anaerobic or anaerobic environment are also discussed in the paper.

Mechanism study of stabilization of double-base propellants by using zeolite stabilizers (nano- and micro-clinoptilolite)

The mechanism of stabilization of double-base rocket propellants (DBPs) using inorganic stabilizer (nano- and micro-clinoptilolite) was investigated. The surface structures of the stabilizers, the double-base propellants containing the new stabilizers and the effect of the stabilizers on the surface behavior of propellants and vice versa were checked using XRD and Electron Microscope (AFM and TEM techniques). The results obtained from XRD suggested that the crystalline structure of the new inorganic stabilizers was completely changed when it was introduced into the propellants which may be attributed to the pressing processes of DBPs with stabilizers under very high pressure during their mixture preparation. The results obtained from Atomic Force Electron Microscope (AFM) and TEM indicated that nano-clinoptilolite particles become more regularly arranged on the propellant surface than micro-clinoptilolite which gives the stabilizer a higher ability to absorb more nitrogen oxide. The work aimed chiefly to use zeolite stabilizers for DBPs instead of classically used organic compounds; in order to avoid the harmful and carcinogenic organic products coming from the reaction of NOx gases with these organic stabilizers. This is achieved by studying the thermal behavior of these zeolites via investigation of their surface interaction with NOx gases obtained during stabilization process and suggesting possible interaction mechanism.

Fabrication and characterisation of 2NDPA-loaded poly(lactide-co-glycolide) (PLG) microspheres for explosive safety

We demonstrate the microencapsulation of a double-base (DB) rocket propellant stabiliser, 2-nitrodiphenylamine (2-NDPA), that can potentially increase the shelf life of DB rocket propellants. Poly(lactide-co-glycolide) (PLG) microspheres loaded with 2-NDPA were prepared using the oil-in-water emulsion technique. The microsphere size was found to be inversely related to the mixing rate. It was also found that a higher theoretical loading of 2-NDPA resulted in larger microspheres. In addition, a Rosin Rammler distribution function gave an accurate representation of the microsphere size distribution, and the release rate 2-NDPA from PLG microspheres was found to be size dependent. We show that parameters such as the stirring speed and the percent loading of 2-NDPA can be varied to tailor the release of 2-NDPA from PLG microspheres. In addition, we have shown that temperature has a dramatic effect on the release of 2-NDPA from PLG microcapsules.

Evaluating the Thermal Hazard of Double‐Base Propellant SQ‐2 by Using Microcalorimetry Method

AbstractThe thermal decomposition behavior of double‐base rocket propellant SQ‐2 was studied by a Calvet microcalorimeter at four different heating rates. The kinetic and thermodynamic parameters were obtained from the analysis of the heat flow curves. The critical temperature of thermal explosion (Tb), the self acceleration decomposition temperature (TSADT), the adiabatic decomposition temperature rise (ΔTad), the time‐to‐explosion of adiabatic system (t), critical temperature of hot‐spot initiation (Tcr), critical thermal explosion ambient temperature (Tacr), safety degree (SD) and thermal explosive probability (PTE) were presented to evaluate the thermal hazard of SQ‐2.

Kinetics and enthalpy of nitroglycerin evaporation from double base propellants by isothermal thermogravimetry

Double base propellants are composed of two basic components: nitrocellulose as a matrix and nitroglycerin as a plasticizer and blasting oil at the same time, and of additives such as stabilizers, burning catalysts, modifiers of ballistic properties, etc. In the course of time, a number of chemical and physical processes (e.g. stabilizer consumption, migration and evaporation of nitroglycerin, decomposition of nitroglycerin and nitrocellulose, etc.) take place in a propellant grain. The result is a change of propellants’ physical, chemical, thermal, ballistic and mechanical properties. The final consequence is reduction of performances and decrease of safe service lifetime of propellants. Reduction of mechanical properties of a propellant grain during ageing can be the factor that limits rockets safe service time. On the other hand, the change in amount of nitroglycerin significantly affects mechanical properties. This is the reason why the evaporation of nitroglycerin from double base propellants is a subject of great importance. In this work we have studied a very early stage of evaporation of nitroglycerin from a double base rocket propellant applying isothermal thermogravimetry experiments. The experiments were done with a propellant containing 27% nitroglycerin, using thin plate samples having a thickness of 0.2–0.4 mm and weighing ∼4 mg. It was found that at a very early stage the evaporation can be described by the zero-order reaction model, while the entire process is characterized by power law decrees of the evaporation rate with time. The Langmuir vaporization equation, and equations proposed by Pieterse and Focke, and by Beverley et al. are used to relate nitroglycerin mass loss data and the vapor pressure. The activation energy of nitroglycerin evaporation was calculated to be 81.9 kJ mol −1 and the pre-exponential factor 5.6 × 10 7 s −1, while calculated enthalpy of nitroglycerin evaporation at 298.15 K lies between 80.0 and 90.5 kJ mol −1, depending on the calculation method applied.

Numerical modelling of sample–furnace thermal lag in dynamic mechanical analyser

Due to dynamic nature of processes taking place during the experiment (chemical reaction and physical processes, heat flow, gas flow, etc.) the results obtained by thermal methods may considerably depend on the condi- tions used during the experiment. Therefore, whenever the results of thermal analysis are reported, the experimental conditions used should be stated. In this paper we have studied the heat transfer from the furnace to the sample and through the sample during dynamic mechanical analysis measurements. Numerical modelling of the heat transfer was done using an own computer program based on the heat conduction equation, solved numerically applying the finite difference methods. The calculated values of the thermal lag between the furnace and the sample were compared with the values experimentally determined on samples of a com- posite polymeric energetic material (double-base rocket propellant). Also, the temperature distribution within the sample as a function of the heating rate was analysed using the same numerical model. It was found out that using this model and temperature dependent heat transfer coefficient, experimentally obtained values of the thermal lag between the furnace and the sample can be satisfactory described. It was also shown that even at slow heating rates, such is, e.g. 2 C min -1 , the thermal lag between the furnace and the sample can reach several degrees, while the thermal gradient within 3-mm thick rectangular sample can reach 0.4 C.

Artificial ageing of double base rocket propellant

The ageing of double base rocket propellants (DB rocket propellants), which is a consequence of chemical reactions and physical processes that take place over time, has significant effect on their relevant properties (e.g. chemical composition, mechanical properties, ballistic properties, etc.). The changes of relevant properties limit the safe and reliable service life of DB rocket propellants. This is the reason why numerous research efforts are devoted to finding out reliable methods to measure the changes caused by ageing, to assess the quality at a given moment of time, and to predict remaining life-time of DB rocket propellants.

Nonisothermal Thermal Decomposition Reaction Kinetics of Double-base Propellant Catalyzed with Lanthanum Citrate

The decomposition reaction kinetics of the double-base (DB) rocket propellant composed of the mixed ester of triethyleneglycol dinitrate (TEGDN) and nitroglycerin (NG), and nitrocellulose (NC) with lanthanum citrate as a combustion catalyst was investigated by thermogravimetry and differential thermogravimetry (TG-DTG), and differential scanning calorimetry (DSC) under atmospheric pressure and flowing nitrogen gas conditions. The results showed that the thermal decomposition processes of DB propellant had two mass loss stages: volatilization and decomposition of the mixed ester in the first-stage and exothermic decomposition reaction in the second-stage. The exothermic decomposition reaction mechanism obeyed the third-order chemical reaction rule. The kinetic parameters of the reaction were: E a=231.14 kJ·mol –1, A=10 23.29 s –1. The kinetic equation can be expressed as: d α/d t=10 22.99(1– α) 3e –2.78×10 4/ T . The critical temperatures of the thermal explosion of the DB propellant obtained from the onset temperature ( T e) and the peak temperature ( T p) were: T be=463.62 K, T bp=477.88 K. The entropy of activation (Δ S ≠), enthalpy of activation (Δ H ≠), and free energy of activation (Δ G ≠) of the reaction were 219.75 J·mol –1·K –1, 239.23 kJ·mol –1, and 135.96 kJ·mol –1, respectively.

Tailoring of unsaturated polyesters for inhibition of double-base and composite modified double-base rocket propellants†

Unsaturated polyesters have proved their potential for inhibition of double-base (DB) and composite modified double-base (CMDB) rocket propellants but usually suffer from slightly higher nitroglycerine (NG) absorption andlower flame retardant characteristics. This requires tailoring of their properties through different techniques. This review summarizes different techniques for this purpose and presents the data generated. The present status of these tailored/modified systems is also discussed in detail followed by future scope of research in this field.