Novel aspects for thermal stability studies and shelf life assessment of modified double-base propellants

Modified DB propellants, based on energetic nitramine(RDX) were manufactured by solventless extrusion process. Thermal stability and shelf life assessment of modified DB propellant were investigated. Shelf life assessment was evaluated using Van’t Hoff’s formula and artificial aging at 70℃ up to120 days. Quantification of total heat released and heat flow with aging time was conducted using differential scanning calorimetry(DSC) and thermal activity monitoring(TAMIII) respectively. Modified DB formulation based on 20 wt % RDX demonstrated enhanced thermal stability in terms of controlled heat flow, and slow decomposition reactions at elevated temperature. This formulation demonstrated extended service life up to 56 years compared with reference formulation. These novel finding was ascribed to the high thermal stability of RDX and its compatibility with DB constituents. This manuscript shaded the light on novel and effective approach for thermal stability via monitoring thermal activity with aging.

Novel approach to quantify the chemical stability and shelf life of modified double-base propellants

Double-base(DB) propellant is vulnerable to auto-catalytic decomposition reactions during storing with the evolution of nitrogen oxides. Modified DB propellant based on energetic nitramines(RDX) can offer enhanced thrust and action time. This study is devoted to evaluate the impact of RDX on chemical stability and shelf life of DB propellant. Extruded modified DB propellant based on RDX was manufactured by solventless extrusion process. Shelf life assessment was performed using an artificial aging at70 ℃ up to 120 days and employing Van't Hoffs formula. Quantification of evolved NOx gases and stabilizer depletion with aging time was conducted using Bergmann-Junk test and HPLC respectively.Modified DB formulation based on RDX 20 wt % demonstrated enhanced chemical stability and extended service life up to 46 years compared with reference formulation. This finding was ascribed to the high chemical and thermal stability of RDX as well as its compatibility with DB constituents; no side chemical reactions could take place during storing. This manuscript shaded the light on RDX as effective energetic constituent that offered DB propellants with enhanced performance, good chemical stability, and extended service life.

Combustion Properties of Metal Particles as Components of Modified Double-Base Propellants

Metal particles such as aluminum（ Al）,magnesium（ Mg）,boron（ B） and nickel（ Ni）,as well as Mg/Al alloy（ Mg/Al = 3/4） are currently the most widely used ingredients in modified doublebase propellants. In this contribution,the combustion properties of the metal species are studied by means of the high-speed photography technique and the non-contact wavelet-based measurement of flame temperature distribution. The combustion process of the Al,Mg and Mg/Al samples shows both gas phase reaction and surface oxidation,which yield volatile and nonvolatile products,corresponding to the oxide and suboxide respectively. However,the combustion of B and Ni shows only gas phase reaction,due to their high melting point as well as high enthalpy of vaporization. In addition to the experiments,a hypothetical combustion model has been proposed to clarify the combustion characteristics of metal species in modified double-base propellants.

Experimental study of Al agglomeration on solid propellant burning surface and condensed combustion products

Aluminum(Al) particles are commonly added to energetic materials including propellants,explosives and pyrotechnics to increase the overall energy density of the composite,but aluminum agglomeration on the combustion surface may lower the combustion efficiency of propellants,resulting in a loss in twophase flow.Therefore,it is necessary to understand the agglomeration mechanism of aluminum particles on the combustion surface.In this paper,a high-pressure sealed combustion chamber is constructed,and high-speed camera is used to capture the whole process of aluminum accumulation,aggregation and agglomeration on the combustion surface,and the secondary agglomeration process near the combustion surface.The microscopic morphology and chemical composition of the condensed combustion products(CCPs) are then studied by using scanning electron microscopy coupled with energy dispersive(SEM-EDS) method.Results show that there are three main types of condensed combustion products:small smoke oxide particles oxidized by aluminum vapor,usually less than 1 μm;typical agglomerates formed by the combustion of aluminum agglomerates;carbonized agglomerates that are widely distributed,usually formed by irregular movements of aluminum agglomerates.The particle size of condensed combustion products is measured by laser particle size meter.As the pressure increases from 0.5 MPa to 1.0 MPa in nitrogen,the mass average particle size of aluminum agglomerates decreases by 49.7%.As the ambient gas is changed from 0.5 MPa nitrogen to 0.5 MPa air,the mass average particle size of aluminum agglomerates decreases by 67.3%.Results show that as the ambient pressure increases,the higher oxygen content can improve combustion efficiency and reduce the average agglomeration size of aluminum particles.

Strength criterion of composite solid propellants under dynamic loading

Based on the dynamic loading(1-100 s^(-1)) experiments under different temperatures(223-298 K) and stress states, uniaxial and biaxial strength criterion of a Hydroxyl-terminated polybutadiene(HTPB)based composite solid propellant were further investigated. These experiments were conducted through the use of a new uniaxial INSTRON testing machine, different new designed gripping apparatus and samples with different configurations. According to the test results, dynamic uniaxial tensile strength criterion of the propellant was directly constructed with the master curve of the uniaxial maximum tensile stress. Whereas, a new method was proposed to determine the dynamic uniaxial compressive strength of the propellant in this study. Then uniaxial compressive strength criterion of the propellant was constructed based on the related master curve. Moreover, it found that the uniaxial tensilecompressive strength ratio of the propellant is more sensitive to loading temperature under the test conditions. The value of this parameter is about 0.4 at room temperature, and it reduces to 0.2-0.3 at low temperatures. Finally, the theoretical biaxial strength criterion of HTPB propellant under dynamic loading was constructed with the unified strength theory, the uniaxial strength and the typical biaxial tensile strength. In addition, the theoretical limit lines of the principal stress plane for the propellant under dynamic loading at different temperatures were further plotted, and the scope of the limit line increases with decreasing temperature.

Recent advances in catalytic combustion of AP-based composite solid propellants

Composite solid propellants(CSPs) have widely been used as main energy source for propelling the rockets in both space and military applications. Internal ballistic parameters of rockets like characteristic exhaust velocity, specific impulse, thrust, burning rate etc., are measured to assess and control the performance of rocket motors. The burn rate of solid propellants has been considered as most vital parameter for design of solid rocket motors to meet specific mission requirements. The burning rate of solid propellants can be tailored by using different constituents, extent of oxidizer loading and its particle size and more commonly by incorporating suitable combustion catalysts. Various metal oxides(MOs),complexes, metal powders and metal alloys have shown positive catalytic behaviour during the combustion of CSPs. These are usually solid-state catalysts that play multiple roles in combustion of CSPs such as reduction in activation energy, enhancement of rate of reaction, modification of sequences in reaction-phase, influence on condensed-phase combustion and participation in combustion process in gas-phase reactions. The application of nanoscale catalysts in CSPs has increased considerably in recent past due to their superior catalytic properties as compared to their bulk-sized counterparts. A large surface-to-volume ratio and quantum size effect of nanocatalysts are considered to be plausible reasons for improving the combustion characteristics of propellants. Several efforts have been made to produce nanoscale combustion catalysts for advanced propellant formulations to improve their energetics. The work done so far is largely scattered. In this review, an effort has been made to introduce various combustion catalysts having at least a metallic entity. Recent developments of nanoscale combustion catalysts with their specific merits are discussed. The combustion chemistry of a typical CSP is briefly discussed for providing a better understanding on role of combustion catalysts in burning rate enhancement. Available information on different types of combustion nanocatalysts is also presented with critical comments.

Cu–Co–O nano-catalysts as a burn rate modifier for composite solid propellants

Nano-catalysts containing copper–cobalt oxides(Cu–Co–O) have been synthesized by the citric acid(CA) complexing method. Copper(II) nitrate and Cobalt(II) nitrate were employed in different molar ratios as the starting reactants to prepare three types of nano-catalysts. Well crystalline nano-catalysts were produced after a period of 3 hours by the calcination of CA–Cu–Co–O precursors at 550 °C. The phase morphologies and crystal composition of synthesized nano-catalysts were examined using Scanning Electron Microscope(SEM), Energy Dispersive Spectroscopy(EDS) and Fourier Transform Infrared Spectroscopy(FTIR) methods. The particle size of nano-catalysts was observed in the range of 90 nm–200 nm. The prepared nano-catalysts were used to formulate propellant samples of various compositions which showed high reactivity toward the combustion of HTPB/AP-based composite solid propellants. The catalytic effects on the decomposition of propellant samples were found to be significant at higher temperatures. The combustion characteristics of composite solid propellants were significantly improved by the incorporation of nano-catalysts. Out of the three catalysts studied in the present work, Cu Co-I was found to be the better catalyst in regard to thermal decomposition and burning nature of composite solid propellants. The improved performance of composite solid propellant can be attributed to the high crystallinity, low agglomeration and lowering the decomposition temperature of oxidizer by the addition of Cu Co-I nano-catalyst.

Estimation of the Ballistic Effectiveness of 3,4-and 3,5-Dinitro-1-(trinitromethyl)-1H-Pyrazoles as Oxidizers for Composite Solid Propellants

The experimental values of the enthalpy of formation of two isomeric 3,4-and 3,5-dinitro-1-(trinitromethyl)-1H-pyrazoles have been obtained(261.5±5.0and 246.4±6.7kJ/mol for crystalline 3,4-and 3,5-dinitro-1-(trinitromethyl)-1H-pyrazoles,respectively).The ballistic effectiveness of these potential oxidizers in composite solid propellants was studied.It is shown that these two oxidizers may be successfully applied in metal-free compositions or with a small content of metal.For the bottom stage 3,4-dinitro-1-(trinitromethyl)-1H-pyrazole is a bit better than 3,5-dinitro-1-(trinitromethyl)-1H-pyrazole,for the upper stage the both oxidizers show the equal ballistic parameters.These oxidizers allow to create metal-free solid composite propellants with the binder percentage not lower than 19%(volume fraction),with I3spequal to 256.5-257.0sat density equal to 1.72-1.74g/cm^3.

A Study of Estimating the Safe Storage Life, Self-accelerating Decomposition Temperature and Critical Temperature of Thermal Explosion of Double-base Propellant Using Isothermal and Non-isothermal Decomposition Behaviours

A method of estimating the safe storage life （τ）, self-accelerating decomposition temperature （TsADT） and critical temperature of thermal explosion （Tb） of double-base propellant using isothermal and non-isothermal decomposition behaviours is presented. For double-base propellant composed of 56±1wt% of nitrocellulose （NC）, 27±0.5wt% of nitroglycerine （NG）, 8.15±0.15wt% of dinitrotoluene （DNT）, 2.5±0.1wt% of methyl centralite, 5.0±0.15wt% of catalyst and 1.0±0.1wt% of other, the values of r of 49.4 years at 40℃, of TSAOT of 151.35℃ and of Tb of 163.01℃ were obtained.

Effect of neutral polymeric bonding agent on tensile mechanical properties and damage evolution of NEPE propellant

Introducing Neutral Polymeric bonding agents(NPBA) into the Nitrate Ester Plasticized Polyether(NEPE)propellant could improve the adhesion between filler/matrix interface, thereby contributing to the development of new generations of the NEPE propellant with better mechanical properties. Therefore,understanding the effects of NPBA on the deformation and damage evolution of the NEPE propellant is fundamental to material design and applications. This paper studies the uniaxial tensile and stress relaxation responses of the NEPE propellant with different amounts of NPBA. The damage evolution in terms of interface debonding is further investigated using a cohesive-zone model(CZM). Experimental results show that the initial modulus and strength of the NEPE propellant increase with the increasing amount of NPBA while the elongation decreases. Meanwhile, the relaxation rate slows down and a higher long-term equilibrium modulus is reached. Experimental and numerical analyses indicate that interface debonding and crack propagation along filler-matrix interface are the dominant damage mechanism for the samples with a low amount of NPBA, while damage localization and crack advancement through the matrix are predominant for the ones with a high amount of NPBA. Finally, crosslinking density tests and simulation results also show that the effect of the bonding agent is interfacial rather than due to the overall crosslinking density change of the binder.

Energetic Abilities of Solid Composite Propellants Based on 3,4,5-Trinitropyrazole and Ammonium Dinitramide

The investigation aims at the expansion of the basis of formulations of solid composite propellants by introducing new compositions with lower sensitivity to mechanic impact and improved thermal stability.The formulations based on trinitropyrazole(TNP)contains a binder(a hydrocarbon or active one),aluminum and inorganic oxidizer ADN.The results show that a binary formulation TNP+active binder(18%-19%)(volume fraction)with no metal is well designed which would achieve high specific impulse(at Pc∶Pa=40∶1)of 248s,high density of 1.80g/cm3 and combustion temperature Tcabout 3 450K.In terms of energy,metal-free compositions with TNP lose a bit to those with HMX,only if HMX fraction in formulation is higher than 45%-50%.

Study on the Detonation Danger of Solid Propellants

A measurement system to study shock initiation behavior of solid propellants was established experimentally. By using this system, the study on shock initiation to the recovered solid propellants with micro damage was performed, especially on the deflagration to denonation transition (DDT) process of solid propellants under both the strong and weak conditions of restriction. The experimental results show that there is a fully compression region in DDT process..

Energetic Opportunities of Solid Composite Propellants Containing Some Hypothetic Furazano-[3,4-d]-pyridazine-based Derivatives

Six furazano-[3,4-d]-pyridazine-based derivatives as main compounds in solid composite propellants have been investigated.It was shown that the use of some furazano-[3,4-d]-pyridazine-based derivatives as main compounds in solid composite propellants can considerably increase ballistic parameters compared with HMX if the compounds under consideration contain difluoramine groups.And the use of the compounds under consideration may be successful only in the presence of an active binder and 10%-30% of AP or ADN as additional oxidizers.

Multiscale modeling of heterogeneous propellants from particle packing tograin failure using a surface-based cohesive approach

In the present work, a computational frame- work is established for multiscale modeling and analysis of solid propellants. A packing algorithm, considering the am- monium perchlorate （AP） and aluminum （A1） particles as spheres or discs is developed to match the size distribution and volume fraction of solid propellants. A homogenization theory is employed to compute the mean stress and strain of a representative volume element （RVE）. Using the mean results, a suitable size of RVE is decided. Without consider- ing the interfaces between particles and matrix, several nu- merical simulations of the relaxation of propellants are per- formed. The relaxation effect and the nonlinear mechanical behavior of propellants which are dependent on the applied loads are discussed. A new technology named surface-based cohesive behavior is proposed to describe the phenomenon of particle dewetting consisting of two ingredients： a damage initiation criterion and a damage evolution law. Several ex- amples considering contact damage behavior are computed and also nonlinear behavior caused by damaged interfaces is discussed in this paper. Furthermore the effects of the criti- cal contact stress, initial contact stiffness and contact failure distance on the damaged interface model have been studied.

Improvement in Time Efficiency in Numerical Simulation for Solid Propellant Rocket Motors(SPRM)

The main purpose of the present work is to study the possibilities of reducing calculation time while maintaining the validity in the numerical simulation of the combustion product flow in SPRM chamber.Three ways of decreasing the calculation time-the use of numerical methods of high accuracy order,the reduction in spatial dimension of the problem,and the use of physical features of the processes in SPRM chamber while constructing a calculation model-were considered.Presented calculation data show that the use of these approaches makes it possible to reduce the time for solving the problems of SPRM simulation significantly(up to 100times).Also conclusions about the applicability of the mentioned above approaches in SPRM design were made.

Controllable combustion behaviors of the laser-controlled solid propellant

Microsatellites have been widely applied in the fields of communication,remote sensing,navigation and science exploration due to its characteristics of low cost,flexible launch mode and short development period.However,conventional solid-propellant have difficulties in starting and interrupting combustion because combustion is autonomously sustained after ignition Herein,we proposed a new type of solid-propellant named laser-controlled solid propellant,which is sensitive to laser irradiation and can be started or interrupted by switching on/off the continuous wave laser.To demonstrate the feasibility and investigate the controllable combustion behaviors under different laser on/off conditions,the combus tion parameters including burning rate,ignition delay time and platform pressure were tested using pressure sensor,high-speed camera and thermographic camera.The results showed that the increase of laser-on or laser-off duration both will lead to the decrease of propellant combustion performance during re-ignition and re-combustion process.This is mainly attributed to the laser attenuation caused by the accumulation of combustion residue and the change of chamber ambient temperature.Simultaneously the multiple ignition tests revealed that the increased chamber ambient temperature after combustion can make up for the energy loss of laser attenuation and expansion of chamber cavity.However,the laser-controlled combustion performance of solid propellant displayed a decrease trend with the addi-tion of ignition times.Nevertheless,the results still exchibited good laser-controlled agility of laser-controlled solid propellant and manifested its inspiring potential in many aspects of space missions.

The properties of Sn-Zn-Al-La fusible alloy for mitigation devices of solid propellant rocket motors

The Al and La elements are added to the Sn9Zn alloy to obtain the fusible alloy for the mitigation devices of solid propellant rocket motors. Differential scanning calorimetry(DSC), metallographic analysis,scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), tensile testing and fracture analysis were used to study the effect of Al and La elements on the microstructure, melting characteristics, and mechanical properties of the Sn9Zn alloy. Whether the fusible diaphragm can effectively relieve pressure was investigated by the hydrostatic pressure at high-temperature test. Experimental results show that the melting point of the Sn9Zn-0.8Al0·2La and Sn9Zn-3Al0·2La fusible alloys can meet the predetermined working temperature of ventilation. The mechanical properties of those are more than 35% higher than that of the Sn9Zn alloy at-50°C-70°C, and the mechanical strength is reduced by 80% at 175°C. It is proven by the hydrostatic pressure at high-temperature test that the fusible diaphragm can relieve pressure effectively and can be used for the design of the mitigation devices of solid propellant rocket motors.

Application of transient burning rate model of solid propellant in electrothermal-chemical launch simulation

A 30 mm electrothermal-chemical(ETC) gun experimental system is employed to research the burning rate characteristics of 4/7 high-nitrogen solid propellant. Enhanced gas generation rates(EGGR) of propellants during and after electrical discharges are verified in the experiments. A modified 0D internal ballistic model is established to simulate the ETC launch. According to the measured pressure and electrical parameters, a transient burning rate law including the influence of EGGR coefficient by electric power and pressure gradient(dp/dt) is added into the model. The EGGR coefficient of 4/7 high-nitrogen solid propellant is equal to 0.005 MW-1. Both simulated breech pressure and projectile muzzle velocity accord with the experimental results well. Compared with Woodley's modified burning rate law, the breech pressure curves acquired by the transient burning rate law are more consistent with test results. Based on the parameters calculated in the model, the relationship among propellant burning rate, pressure gradient(dp/dt) and electric power is analyzed. Depending on the transient burning rate law and experimental data, the burning of solid propellant under the condition of plasma is described more accurately.

Effects of Metal and Composite Metal Nanopowders on the Thermal Decomposition of Ammonium Perchlorate (AP) and the Ammonium Perchlorate/Hydroxyterminated Polybutadiene (AP/HTPB) Composite Solid Propellant

Effects of metal (Ni, Cu, Al) and composite metal (NiB, NiCu, NiCuB) nanopowders on the thermal decomposition of ammonium perchlorate (AP) and composite solid propellant ammonium perchlorate/hydroxyterminated polybutadiene (AP/HTPB) were studied by thermal analysis (DTA). The results show that metal and composite metal nanopowders all have good catalytic effects on the thermal decomposition of AP and AP/HTPB composite solid propellant. The effects of metal nanopowders on the thermal decomposition of AP are less than those of the composite metal nanopowders. The effects of metal and composite metal nanopowders on the thermal decomposition of AP are different from those on the thermal decomposition of the AP/HTPB composite solid propellant.

Investigation on the foaming behaviors of NC-based gun propellants

To prepare the porous NC-based(nitrocellulose-based) gun propellants,the batch foaming process of using supercritical CO_2 as the physical blowing agent is used.The solubilities of CO_2 in the single-base propellants and TEGDN(trimethyleneglycol dinitrate) propellants are measured by the gravimetric method,and SEM(scanning electron microscope) is used to observe the morphology of foamed propellants.The result shows that a large amount of CO_2 could be dissolved in NC-based propellants.The experimental results also reveal that the energetic plasticizer TEGDN exerts an important influence on the pore structure.The triaxial tensile failure mechanism for solid-state nucleation is used to explain the nucleation of NC-based propellants in the sol id state.Since some specific foaming behaviors of NC-based propellants can not be explained by the failure mechanism,a solid-state nucleation mechanism which revises the triaxial tensile failure mechanism is proposed and discussed.