Effect of RDX and HMX on the Efficiency of Catalysts for Double–Base Propellant Combustion

High explosives (RDX or HMX) are added to double–base propellant formulations to improve their energy characteristics. The influence of these HE on the catalysis of propellant combustion practically has not been discussed in the literature. The present paper considers the role of RDX and HMX in the catalysis of double–base propellant combustion. Propellants having various compositions and energy characteristics were studied experimentally. It is established that RDX and HMX decrease the burning rate of double–base propellants (without catalysts) with moderate and high calorific values irrespective of their effect on the energy and combustion characteristic of the propellants. It is shown that if the burning rate of a propellant is affected by catalysts, the addition of RDX or HMX to this propellant (in excess of 100%) does not decrease the relative efficiency of catalysis but even increases it somewhat.     

Combustion Effects of Nitrofulleropyrrolidine on RDX‐CMDB Propellants

The effect of N‐methyl‐2‐(3‐nitrophenyl)pyrrolidino[3′,4′:1,2]fullerene (mNPF) on the decomposition characteristics of hexogen (RDX) was investigated using differential scanning calorimetry (DSC). The results show that mNPF can accelerate the decomposition of RDX, the peak temperature (T_p) of the exothermal decomposition is reduced by 6.4 K, and the corresponding apparent activation energy (E_a) is decreased by 8.7 kJ mol⁻¹. N‐methyl‐2‐(3‐nitrophenyl)pyrrolidino[3′,4′:1,2]fullerene (mNPF), carbon black (CB), and C₆₀ were used as combustion catalysts to improve the combustion performance of a composite modified double‐base propellant containing RDX (RDX‐CMDB). The burning rate experimental results show that mNPF has a stronger catalytic effect than C₆₀ and CB. The magnitude of the effect of the three carbon substances on the enhancement of the burning rate is as follows: mNPF>C₆₀>CB. The catalytic effects of different contents of mNPF on the burning rates of RDX‐CMDB propellants were also studied, and the results show that the burning rates of RDX‐CMDB propellants are improved with increasing mNPF content. The plateau burning rate of a RDX‐CMDB propellant can be increased to 19.6 mm s⁻¹ when 1.0 % mNPF is added, and the corresponding plateau combustion region occurs at 8–22 MPa.     

GAP-ETPE基发射药配方的能量特性分析

采用内能法计算了GAP含能热塑性弹性体(ETPE)为基的多个发射药配方的能量特性参数.结果表明,RDX/ETPE/A3发射药的火药力约为1 170 kJ/kg,用CL-20、TNAZ等替代配方中的RDX,火药力呈线性规律变化,并且能够得到1 300 kJ/kg以上的火药力.不同的含能增塑剂对配方的能量有很大的影响,含BTTN、BuNENA发射药配方具有很高的能量,RDX/ETPE/NC/BTTN(ETPE与NC的质量比为70∶30)发射药配方的火药力在较宽的范围内都可以达到1 200 kJ/kg.     

Analysis for Decomposition Characteristics and Piecewise Thermokinetics of Nitramine Modified Double‐base Propellant with High Solid Content

The thermal stability and decomposition characteristic of nitramine modified double‐base propellant (RDX‐CMDB propellant) with high solid content and its components were investigated under dynamic and isothermal conditions by differential scanning calorimetry (DSC). It was found that the mixture of nitrocellulose (NC) and nitroglycerin (NG) had a promote effect on the decomposition of RDX. The activation energy (E ) and the pre‐exponential factor (A ) of two obviously exothermic processes were obtained by Friedman iso‐conversional method. The screening method suggested by ICTAC was used to determine the most probable mechanism functions and kinetic parameters of the two processes which are corresponding to the deceleration model and the autocatalytic model. The theoretical value was consistent with the experiment result.     

含1,1–二氨基–2,2–二硝基乙烯推进剂的能量特性参数计算研究

利用国军标方法及CAD系统软件,在标准条件(pc∶p0=70∶1)下,计算了含1,1-二氨基-2,2-二硝基乙烯(FOX-7)的各类推进剂的能量特性参数,分析了氧化剂(AP、RDX、CL-20)及黏合剂(HTPB、PET、GAP、PBAMO)等成分对FOX-7推进剂能量特性的影响。结果表明,将AP加入HTPB/FOX-7推进剂配方中取代FOX-7可有效改善氧条件,有利于推进剂能量的提高。在黏合剂含量较低(质量分数<8%)的推进剂体系中,使用惰性黏合剂有利于提高推进剂的能量;而在黏合剂含量较高(质量分数>10%)的推进剂体系中,使用含能黏合剂提高推进剂能量的幅度优于惰性黏合剂,且GAP优于PBAMO。用FOX-7取代NEPE推进剂中的AP,推进剂最大理论比冲可达2 567 N.s/kg。由GAP/FOX-7/RDX组成的无烟推进剂,在很宽的范围内都可以达到2 400 N.s/kg以上的理论比冲值。     

Multiscale Simulation on the Influence of Dimethyl Hydantoin on Mechanical Properties of GAP/RDX Propellants

The influence of dimethyl hydantoin (DMH) on the mechanical properties of GAP/RDX propellant was studied by molecular dynamics (MD) and dissipative particle dynamics (DPD) simulation. The results showed that the binding energies (E_binding) between GAP and different surfaces of RDX were in the order of (010)>(001)>(100). Compared to GAP/RDX, GAP grafted with DMH (GAP‐DMH) exhibits higher binding energies with RDX, and the sequence of E_binding turns to (001)>(010)>(100). Radial distribution simulations demonstrated that GAP‐DMH is more close to the surfaces of RDX, increasing the van der Waals energies between GAP‐DMH and RDX. The stress and strain of GAP‐DMH/RDX excel those of GAP/RDX. DPD simulations showed that GAP‐DMH was able to restrain the agglomeration of RDX, to improve the dispersibility and to enlarge the contact surface with RDX, which also increased the mechanical properties of GAP/RDX propellant.     

Preparation and Properties of a nRDX‐based Propellant

The incorporation of nano‐scaled cyclotrimethylene trinitramine (nRDX) in nitrocellulose (NC)‐based propellants poses processing problems when following conventional methods. Hence, a new preparation method containing a pre‐dispersion process was developed, by which 30 mass % RDX (290 nm) was incorporated in the propellant. Meanwhile, the corresponding 290 nm, 12.85 μm and 97.76 μm RDX‐based propellants were prepared for comparison using a conventional method. The morphology, structure, ballistic and mechanical properties of the prepared propellants were characterized by scanning electron microscopy (SEM), density analyzer, closed vessel (CV), uniaxial tensile tester and impact tester. The results indicate that the nRDX particles were uniformly dispersed in the NC/NG/TEGDN matrix using the novel method, while agglomerated and recrystallized into large particles with the conventional method. The propellant density increased with decreasing RDX particle size. In particular, the 290 nm RDX‐based propellant exhibited a higher burning rate and lower average pressure exponent (α =0.958) compared to the 12.85 μm RDX‐based propellant (α =1.043). The tensile strength, elongation at break and impact strength of the RDX‐based propellant at −40 °C, 20 °C and 50 °C were dramatically improved by using 290 nm RDX with the novel method.     

Application of Nitramines Coated with Nitrocellulose in Minimum Signature Isocyanate‐Cured Propellants

Cyclotrimethylenetrinitramine (RDX) coated with nitrocellulose (NC‐RDX) is prepared by an internal solution method and applied in a minimum signature isocyanate‐cured propellant. It was found that RDX was coated or bonded by NC to form NC‐RDX particles; the median particle diameter (d₅₀) and specific surface area of NC‐RDX are in the range from 150 to 240 μm and 0.03 to 0.04 m²⋅g⁻¹, respectively. The NC‐RDX particles could swell in nitrate ester plasticizers with relatively low swelling rate compared with NC added directly in the plasticizers. Different types of ballistic modifiers can be effectively added to NC‐RDX. It was experimentally shown that NC‐RDX can increase the content of NC in the propellant with viscosities in the range from 371 to 394 Pa s and improve the mechanical characteristics of the propellant with maximum tensile strength (σ_m) between 0.48 MPa<σ_m<1.92 MPa, elongation at maximum tensile strength (ε_m) between 28.0%<ε_m<37.3%, and elastic modulus between 3.18 MPa<E<8.68 MPa in the temperature range from −40 to +50 °C.     

Effects of an Organic‐inorganic Nanocomposite Additive on the Combustion and Erosion Performance of High Energy Propellants Containing RDX

A nanocomposite microsphere consisting of solid paraffin, nano‐TiO₂, nano‐BN, zeolitic imidazolate framework‐67 particles and polymethyl methacrylate was prepared and applied as a functional additive for high energy propellants (with about 23 wt % RDX) to reduce the barrel erosion and improve its combustion performance as well. High energy propellants modified with the nanocomposite were manufactured by a solvent extrusion technique. According to the scanning electron microscope and differential scanning calorimetry results, there exists a good compatibility between the nanocomposite and propellant matrix. The energy and combustion performance as well as erosion of the modified propellants were studied by a closed bomb test and an erosion tube device, respectively. Results showed that compared with the unmodified propellant, both the erosion and energy performance of modified high energy propellant gradually decreased with the increase of nanocomposites contents. When the content of nanocomposites was 5.1 %, the erosion mass of the modified propellant reduced to 37.0 % while the propellant force only decreased 5.7 %, indicating that the nanocomposite has enormous ability to improve gun erosion resistance while barely affect energy performance of propellant. Furthermore, the closed bomb burning curves of the samples showed that addition of nanocomposites to propellant matrix could prolong the combustion time, efficiently inhibit the initial generation rate of combustion gas, and further achieve the progressive burning of the propellants.     

An Interphasic Region between Nitrocellulose and Nitroguanidine in triple base propellant

Evidence for the existence of an interphasic region in the nitroglycerin-nitrocellulose matrix immediately surrounding the crystalline nitroguanidine filler in triple base propellant is presented for the first time. This interphasic region displays anomalous thermal expansion and mechanical relaxation behaviour compared to the bulk nitroglycerin-nitrocellulose matrix in the propellant. The interphasic region accounts for the highly unusual thermal expansion behaviour of triple base propellants containing long needlelike nitroguanidine crystals. An interphasic region does not occur in similar propellant when the nitroguanidine filler is replaced by crystalline RDX. Thus the interphase region is thought to be a manifestation of a significant bindernitroguanidine interaction. Implications for munition survivability stemming from the existence of a separate polymeric interphase are discussed in terms of the thermal and relaxation behaviour of the interphasic binder-crystalline filler interface.     

Studies on RDX Particle Size in LOVA Gun Propellant Formulations

This paper presents the results of systematic studies carried out on the role of fine RDX in determining the burning rate and ballistics of LOVA gun propellants. Propellant formulations containing fine RDX particles with a size of 4.5, 6, 13 and 32 µm as energetic ingredient, cellulose acetate as inert binder, triacetin as inert plasticizer, nitrocellulose of lower percentage nitrogen content as energetic binder and carbamite as stabilizer were made. The evaluation of the propellant batches has been carried out by static firing using closed vessel technique. It indicates the linear relation between the burning rate of the propellant and the fine RDX particle size used in this formulation. The results of the present studies revealed that fine RDX of 4.5 to 6 µm size may be the most suitable for LOVA gun propellant to meet the desired burning rate for satisfactory ballistics.     

Study on the Synthesis and Interfacial Interaction Performance of Novel Dodecylamine‐Based Bonding Agents Used for Composite Solid Propellants

An effective pathway was explored to design and select proper bonding agents that could effectively improve the interfacial interactions between bonding agents and solid particles, with three novel synthesized alkyl bonding agents, dodecylamine‐N,N‐di‐2‐hydroxypropyl‐acetate (DIHPA), dodecylamine‐N,N‐di‐2‐hydroxypropyl‐hydroxy‐acetate (DIHPHA) and dodecylamine‐N,N‐di‐2‐hydroxypropyl‐cyano‐acetate (DIHPCA), as examples. Molecular dynamics simulation was applied to compare unit bond energies of these bonding agents with the [110] crystal face of ammonium perchlorate (AP) and the [120] crystal face of hexogen (RDX). The infrared test was used to characterize the interfacial interactions of these bonding agents with AP or RDX. XPS test was applied to calculate the adhesion percentage of the bonding agents on the surface of precoated AP or RDX particles. All of the above results indicated that these three bonding agents have strong interfacial interactions with AP or RDX in the order of DIHPCA>DIHPHA>DIHPA. The prepared three bonding agents were used in HTPB/AP/RDX/Al propellants, and their effects on tensile strength (σ), elongation under maximum tensile strength (ε_m), elongation at breaking point of the propellant (ε_b) and adhesion index (Φ) of the propellant were studied. The results show that the bonding agents improve the mechanical properties of the propellant in the order of DIHPCA>DIHPHA>DIHPA. The methods found from theoretical design, materials synthesis, and mechanistics studies up to practical application show effective guiding significance for choosing the proper bonding agent and improving the interfacial interactions between the solid particles and binder matrix.     

典型高能硝胺发射药的摩擦静电起电特性

为了研究高能硝胺发射药的摩擦静电起电特性,采用斜槽模拟高能硝胺发射药制造和使用过程中的摩擦行为,并利用法拉第筒测量了发射药摩擦后的静电带电量,系统研究了滑槽长度、接触介质、湿度、药体形貌以及配方组成对高能硝胺发射药摩擦静电起电特性的影响。结果表明,高能硝胺粒状发射药与不锈钢滑槽摩擦分离后带负电;环境湿度从28%增至68%,药粒静电积累量降低近50%;发射药静电积累量按接触介质排序为:不锈钢﹥导电橡胶﹥铝合金,均质叠氮硝胺发射药与接触介质的摩擦起电规律与高能硝胺发射药基本相同;药粒与滑槽接触面积越大,静电积累量越高;高固含量硝胺发射药药粒表面易产生RDX颗粒的剥离,与介质摩擦后静电积累量比均质叠氮硝胺发射药高35%;质量分数0.1%的石墨光泽可将高能硝胺发射药静电积累量降低至接近于0,而配方中添加质量分数0.75%的CNT,高能硝胺发射药静电积累量仅降低34%。     

Thermal and Sensitivity Study of Dihydroxyl Ammonium 5,5′‐Bistetrazole‐1,1′‐diolate (TKX‐50)‐based Melt Cast Explosive Formulations

Dihydroxyl ammonium 5,5′‐bistetrazole‐1,1′‐diolate (TKX‐50) is a promising energetic material with predicted performance similar to RDX as well as to CL‐20. In the present study, TKX‐50 was evaluated as a possible replacement for RDX in TNT‐based, aluminized as well as non‐aluminized melt cast formulations. Thermal analysis reveals the compatibility of TKX‐50 with benchmark explosives like RDX and TNT in explosive formulations. This paper describes the thermal and sensitivity study of TKX‐50 with RDX and TNT‐based melt cast explosives. The result indicated that TKX‐50 can be effectively used as a RDX replacement in melt cast explosive formulations. TKX‐50/TNT‐based aluminized composition shows more thermal stability than RDX/TNT based composition, which clearly indicated the usefulness of TKX‐50 in melt cast explosive formulations.     

Applying modified hyperbranched polyester in hydroxyl‐terminated polyether/ammonium perchlorate/aluminium/cyclotrimethylenetrinitramine (HTPE/AP/Al/RDX) composite solid propellant

Composite solid propellants demand fine and stable mechanical properties, creep resistance and stress relaxation performance during their long storage and usage time. In this study, modified hyperbranched polyester (MHBPE) was prepared and introduced into HTPE/AP/Al/RDX (HTPE, hydroxyl‐terminated polyether; AP, ammonium perchlorate; RDX, cyclotrimethylenetrinitramine) solid propellant as an effective additive. The static tensile and dynamic mechanical properties of this propellant before and after the introduction of MHBPE were evaluated. The elevated interfacial interaction by using MHBPE between the binder and RDX fillers improved the toughness and elasticity of the propellant. The enhancement mechanisms were also confirmed by the influence on the fracture surface morphology of the binder which was investigated by SEM. In addition, some influence on the dynamic mechanical properties of HTPE/AP/Al/RDX propellant caused by MHBPE was investigated by dynamic mechanical analysis. The creep behaviors of the HTPE/AP/Al/RDX propellants with and without MHBPE were also investigated at different stresses and temperatures. Reduced creep strain rate and strain were obtained for the modified propellant, implying enhanced creep resistance performance. The creep properties were quantitatively evaluated using a six‐element model and the long‐term creep performance of the propellant was predicted using the time–temperature superposition principle. A creep behavior of nearly 10⁶ s at 30 °C could be acquired in a short‐term experiment (800 s) at 30–70 °C. Moreover, the stress relaxation investigation of the propellants with and without MHBPE at ?40 °C, 20 °C and 70 °C suggested that MHBPE/HTPE/AP/Al/RDX propellant possessed better response ability to deformation. Thus, the application of MHBPE provides an efficient route of reinforcement to enhance the creep resistance and stress relaxation properties. © 2020 Society of Chemical Industry     

Synthesis,Characterization, and Combustion Catalytic Activities of Copper(II) and Lead(II) Salts of p‐Nitrocalix[n]arenes (n=4, 6, 8)

Six copper(II) and lead(II) salts of p‐nitrocalix[n]arene (n=4, 6, 8) were synthsized and characterized. The DSC curves of all salts showed exothermic decomposition. Sensitivity studies revealed that all the salts with the exception of the lead salt of p‐nitrocalix[6]arene (NCPb6) are relatively insensitive materials. Investigations of the catalytic activities showed that most of the salts displayed high activities in thermal decomposition of NC‐NG and RDX. As evaluated in this work, the salts enhanced the burning rates of both double base (DB) and RDX‐component modified double base propellants. The best catalytic effect was obtained with NCPb6, which increased the burning rate of the DB propellant to the order of about 200 % (2–6 MPa) and 103–198 % (8–20 MPa) while decreasing the pressure index (n) to 0.22 (20–22 MPa).     

Formation and Characterization of Nano‐sized RDX Particles Produced Using the RESS‐AS Process

It has been shown that nano‐sized particles of secondary explosives are less sensitive to impact and can alter the energetic performance of a propellant or explosive. In this work the Rapid Expansion of a Supercritical Solution into an Aqueous Solution (RESS‐AS) process was used to produce nano‐sized RDX (cyclo‐1,3,5‐trimethylene‐2,4,6‐trinitramine) particles. When a saturated supercritical carbon dioxide/RDX solution was expanded into neat water, RDX particles produced from the RESS‐AS process agglomerated quickly and coarsened through Ostwald ripening. However, if the pH level of the suspension was changed to 7, particles were metastably dispersed with a diameter of 30 nm. When the supercritical solution was expanded into air under the same pre‐expansion conditions using the similar RESS process, RDX particles were agglomerated and had an average size of approximately 100 nm. Another advantage of using a liquid receiving solution is the possibility for coating energetic particles with a thin layer of polymer. Dispersed particles were formed by coating the RDX particles with the water soluble polymers polyvinylpyrrolidone (PVP) or polyethylenimine (PEI) in the RESS‐AS process. Both PVP and PEI were used because they have an affinity to the RDX surface. Small and well‐dispersed particles were created for both cases with both PVP and PEI‐coated RDX particles shown to be stable for a year afterward. Several benefits are expected from these small polymer coated RDX particles such as decreased sensitivity, controlled reactivity, and enhanced compatibility with other binders for fabrication of bulk‐sized propellants and/or explosives.     

Synthesis of Three Novel Laurylamine‐Derived Long‐Chain Alkyl Bonding Agents and Their Interactions with RDX

Three novel long‐chain alkyl bonding agents including 1,1′‐dodecylimino‐bis[3‐[bis(2‐hydroxyethyl)amino]‐2‐propanol (DHAP), 1‐acetyl‐5‐dodecyl‐octahydro‐1,5‐diazocine‐3,7‐diol (ADODD) and 1,3‐bis(dodecylimino)‐5,5‐dimethyl‐2,4‐imidazolidinedione (DDID) were synthesized by modification of laurylamine. Interaction energies between bonding agents and RDX were calculated and compared using the molecular dynamics method. Effects of coating by different bonding agents on characteristic absorption peaks of RDX were analyzed by micro‐infrared spectroscopy. The adhesion degrees of different bonding agents on the surface of RDX solid particles were calculated by XPS methods. The three prepared bonding agents were added to the HTPB/RDX/Al propellant and their effects on σ, ε_m, ε_b and Φ (the adhesion index between filling particles and binder matrix) value of propellant were studied. Simulation and experimental results showed that those three types of long‐chain alkyl bonding agents exhibit a strong interaction with RDX, with highest interaction potencial observed for DHAP, followed by DDID and ADODD. In addition, the current study demonstrated that results obtained by molecular dynamics simulation were in very good agreement with the experimental data.     

Energetic-material combustion experiments on propellant formulations containing prilled ammonium dinitramide

Energetic material combustion experiments were performed on propellant formulations containing ammonium dinitramide prills. The overall performance of the formulation was found to be sensitive to the prill microstructure. The combustion experiments show that the performance of the composition could be further improved by “tailoring” the microstructural characteristics of the prills. These parameters are not revealed by strand burning-rate measurements, which represent an average or overall measurement and pick up on the localized rate variations as “noise,” averaging them out. Microstructural characterization (such as filming of the propellant combustion at the highest magnifications and examination of quenched samples) of propellant formulations may thus provide some of the complementary data to the standard propellant characterization measurements to reduce or eliminate measurement errors. Furthermore, with prilling the errors are reduced and the performance is improved. Translated fromFizika Goreniya i Vzryva, Vol. 36, No. 1, pp. 131–137, January–February, 2000. This work was supported by ONR.     

Comparative Studies of Pressure Sensitization of Zirconium Carbide and Zirconium Silicate on Burning Rates in a RDX‐AP based Composite Propellant

In a systematic study to compare the effects of the values of burning rate and pressure exponent in RDX‐AP based composite propellant, various compositions with varying percentages of zirconium carbide (ZrC) and zirconium silicate (ZrSiO₄) were formulated to select a suitable candidate. Various rocket parameters of each formulation were theoretically predicted by the NASA CEC‐71 program and the burning rate was evaluated in pressure range of 3–11 MPa. In addition, density, sensitivity, and thermal properties of compositions having maximum effects on pressure exponent’s values were also evaluated. It was concluded that ZrSiO₄ enhances the pressure exponent “n” value substantially, whereas ZrC doesn’t have significant effects on it as compared to base composition and also provides higher density values of composite propellant formulated.