Solid Propellant Formulations Research Articles

Thermal structural damage and thermal decomposition characterization of GAP propellants with nitrate ester plasticizers

AbstractGAP and nitrate ester compounds are introduced into the solid propellant formulation as energetic binders and energetic plasticizing agents, respectively, to further enhance the energy level of solid propellants. However, under abnormal thermal conditions, various components within GAP propellants, especially nitrate ester plasticizers, can collectively result in the generation of a large number of voids within the propellant due to factors such as thermal stress and slow component decomposition. This phenomenon can impact the safety of solid rocket engines, necessitating research into their thermal decomposition processes and thermal damage structures. In this study, the thermal decomposition characteristics and gas products of GAP propellants with different nitrate ester plasticizer formulations were investigated using DSC‐TG and FT‐IR. The damage structure of GAP propellants heated under unignited conditions was studied through Micro‐CT, examining the influence of heating conditions and nitrate ester plasticizers on the thermal damage structure of GAP propellants. During heating, the thermal damage structure of GAP propellants was found to include voids generated within the GAP binder and cracks at the interface between the GAP binder and particles, with nitroglycerin as a plasticizer exacerbating the thermal damage of GAP propellants (about 2.2–2.9 times).

Synergistic effect of nitrocellulose coating on structural and reactivity stabilization of ammonium nitrate oxidizer

The present work aims to stabilize the room temperature allotropic transition of ammonium nitrate (AN) particles utilizing a microencapsulation technique, which involves solvent/non-solvent in which nitrocellulose (NC) has been employed as a coating agent. The SEM micrographs revealed distinct features of both pure AN and NC, contrasting with the irregular granular surface topography of the coated AN particles, demonstrating the adherence of NC on the AN surface. Structural analysis via infrared spectroscopy (IR) demonstrated a successful association of AN and NC, with slight shifts observed in IR bands indicating interfacial interactions. Powder X-ray Diffraction (PXRD) analysis further elucidated the structural changes induced by the coating process, revealing that the NC coating altered the crystallization pattern of its pure form. Thermal analysis demonstrates distinct profiles for pure and coated AN, for which the coated sample exhibits a temperature increase and an enthalpy decrease of the room temperature allotropic transition by 6 °C, and 36%, respectively. Furthermore, the presence of NC coating alters the intermolecular forces within the composite system, leading to a reduction in melting enthalpy of coated AN by ∼39% compared to pure AN. The thermal decomposition analysis shows a two-step thermolysis process for coated AN, with a significant increase in the released heat by about 78% accompanied by an increase in the activation barrier of NC and AN thermolysis, demonstrating a stabilized reactivity of the AN-NC particles. These findings highlight the synergistic effect of NC coating on AN particles, which contributed to a structural and reactive stabilization of both AN and NC, proving the potential application of NC-coated AN as a strategically advantageous oxidizer in composite solid propellant formulations.

Titanium a novel catalyst and high energy dense material: an opportunity for composite propellants with enhanced performance

ABSTRACT Whereas aluminum with combustion enthalpy of 32 KJ/g is the universal reactive metal particles, its passive protective oxide layer could encounter its efficient combustion. While titanium can offer low combustion enthalpy (20 KJ/g), it does not expose passive oxide layer. The impact of both reactive particles on ammonium perchlorate (AP) decomposition enthalpy was investigated via DSC. Aluminum and titanium particles secured an increase in AP decomposition enthalpy by 46.9%, and 80.7% respectively. This significant impact of titanium particles was ascribed to full exploitation of metal energy content. The impact of titanium particles on AP decomposition kinetics was assessed via Kissinger, KAS, and FWO models using TGA. Whereas virgin AP demonstrated average apparent activation energy of 155 KJ/mol, Ti/AP demonstrated average apparent activation energy of 141.2 KJ/mol. Solid rocket propellant formulations based on 17 wt % metal (Al or Ti) were developed via mixing and vacuum casting. Ballistic performance was investigated using small-scale ballistic evaluation rocket motor. Ti-based formulation offered an increase in propellant burning rate, average operating pressure, average thrust by 18.2%, 26.5%, and 19.7% respectively. It was concluded that titanium particles have a dual effect as efficient high energy dense material and as a catalyst.

The significant role of passive oxide layer on reactive metal combustion: insights into composite solid propellant with superior performance

ABSTRACT Passive oxide layer could expose a significant impact on reactive metal combustion. Boron and aluminum experience combustion enthalpy of 59.3 and 31.1 KJ/g and passive oxide layer of 200 and 7 nm, respectively. In this study, surface oxygen of born and aluminum particles (10 µm) was quantified via EDAX analysis. Boron and aluminum demonstrated surface oxygen content of 14.6 and 7.2 wt %, respectively. Reactive particles were integrated into ammonium perchlorate (AP) oxidizer. While boron demonstrated decrease in AP decomposition enthalpy by −14.8%; aluminum offered an increase in AP decomposition enthalpy by 60.8% using DSC. Whereas, aluminum oxide layer could be pealed out more effectively; boron passive oxide layer could melt with the evolution of an insulating barrier. Aluminum particles offered decrease in AP apparent activation energy by 68%, 105%, and 76% using Kissinger, Kissinger-Akahira-Sunose (KAS), and Flyn and Wall (FWO) models, respectively. Solid propellant formulations were developed; ballistic performance was assessed using small-scale rocket motor. Aluminum particles demonstrated stable combustion process with enhanced specific impulse and total pressure impulse compared with boron. Additionally, aluminum particles demonstrated stable burning with pressure exponent of 0.19 compared with 0.4 for boron particles.

An aldehyde-group-containing energetic ZIF with unprecedented “negative” catalytic properties for seven different energetic materials

Energetic materials possessing high energy content, exceptional heat resistance, and insensitivity have long been recognized as a significant and prominent subject of academic debate. In this study, the necessity for high-energy explosives in both military and civilian domains prompted the introduction of the concept of an “energetic negative-burning rate catalyst” in heat-resistant and insensitive energetic materials. Therefore, a typical and effective catalyst (ZIF-90) was discovered. ZIF-90, which can be easily synthesized and features a large specific surface area and regular pore structure, contributes to molecular-scale changes in the pyrolysis process of energetic materials. Additionally, the presence of surface aldehyde groups facilitates the partial absorption of heat, thereby collectively contributing to the augmentation of pyrolysis peak temperatures for seven distinct energetic materials (RDX, HMX, CL-20, LLM-105, LLM-126, AlH3, and DAP-4). Specifically, the pyrolysis peak temperatures were elevated by 6.6 ​°C, 1.7 ​°C, 1.6 ​°C, 6.4 ​°C, 1.4 ​°C, 13.1 ​°C, and 7.0 ​°C, respectively. Moreover, the highly stable ZIF-90, functioning as an intrinsically insensitive Energetic Metal-Organic Framework (EMOF), not only effectively mitigates the sensitivity of energetic materials but also ensures minimal energy loss. Notably, the incorporation of a mere 5 ​wt% of ZIF-90 resulted in a significant enhancement of over one-fold in the heat resistance of LLM-105-based explosive cylinders, thereby validating the practical applicability of ZIF-90 in energetic materials. Moreover, the efficacy of ZIF-90 in solid propellant formulations was corroborated through flame experiments conducted on solid propellants. The development of such a pragmatic and universally applicable energetic negative-burning rate catalyst presents a promising strategy for the future advancement of high-performance, heat-resistant, and insensitive energetic materials.

Propulsion theoretical and experimental analysis of composite propellants motors

Rockets have revolutionized space technology and human space exploration. Most rockets and missiles are both propelled by rocket motors that use composite solid propellants. The ICT code and the NSAS CEA code are two programs that can be used to forecast theoretical propulsion parameters for composite solid rocket propellant. Rocket propellant performance is governed by a specific impulse factor, which is calculated theoretical and experiment. In this paper, the theoretical specific impulse for different composite solid propellant formulations at 70 bar combustion pressure and an adapted nozzle (optimum expansion) were calculated by the NASA-CEA code and the ICT code. Meanwhile, a static firing test was performed on a small scale test motor to experimentally determine the actual specific impulse. The objective is to verify theoretical calculations from two codes with experimental data, via the determination of the specific impulse deviation co-efficient.

Energetic hydrogen-bonded open-framework as promising green combustion catalyst for nitramine-based solid propellants

The development of halogen-free nitramine-based green solid propellants has attracted a significant interest due to their application in rapidly developing aerospace technologies. However, relatively low burn rates, and generation of high pressure in the combustion chamber limit applications of such propellants. The alleviation of these problems could be achieved by using suitable combustion catalysts. Herein, a new energetic nitrogen-rich open framework compound 1 was prepared and evaluated as an efficient Pb-free combustion catalyst for HMX-nitrocellulose-nitroglycerin solid composite propellant formulation. Compound 1 was synthesized by a straightforward one-step process, its structure was comprehensively characterized by x-ray crystallography, and it was found to be thermostable (decomposition at 289 °C), insensitive to mechanical impact and friction (60 J, 360 N), and showed high hydrolytic stability. A propellant formulation containing 3.0 wt.% of 1 exhibited 45% increase in its burning rate (under 6.0 MPa) versus catalyst-free reference propellant. In the pressure range of 3–10 MPa, the pressure exponent was calculated to be 0.32, which is more than two times lower than of the reference propellant. These impressive properties of catalyst 1 suggest that it has a great potential to be further used in the development of future highly energetic green solid propellants.

Kinetic Parameters Governing the Rapid Pyrolysis Of Ammonium Perchlorate

Ammonium Perchlorate (AP) has been in use in many solid propellant formulations since decades. However, data regarding the chemical reactions taking place in the condensed phase during combustion of AP and their associated kinetic parameters are sparse. This data is crucial in modelling the combustion of AP. To mimic the behaviour of AP in condensed phase during its combustion, it is necessary to isolate the condensed phase reactions and study pyrolysis of AP at heating rates similar to those observed during combustion (~105K.s-1). In the current study, an electrical fast pyrolyser coupled to a Fourier Transform Infrared (FTIR) spectrometer was used to study the fast pyrolysis of AP. Activation energy (Ea) of the global pyrolysis reaction was extracted from the variation of mole fraction with time of the observed pyrolysis products. An activation energy of 48 kJ.mol-1 was obtained along with a pre-exponential factor (A) of 4039 s-1. The value of activation energy obtained in the current study is significantly different than that obtained from Thermo-Gravimetric Analysis (TGA) studies. This signifies that the mechanism of decomposition during rapid pyrolysis maybe different from that occurring during slow pyrolysis.

Combustion performance of nano Si powder with molecular perovskite energetic materials DAP-4 as oxidant

Nano Silicon (Si) powder has become a new type of solid fuel in recent years because of its high energy density, large gas production, and low agglomeration behavior. Optimizing and improving its energy release performance is an important challenge. In this paper, DAP-4, an energetic molecular perovskite material with high energy and strong oxidation, was introduced as the oxidant to prepare DAP-4/Si composites, and its combustion properties were studied. The thermal decomposition, combustion performance, as well as their combustion product properties, were studied. The results showed the thermal decomposition properties of DAP-4/Si composites still keep stable (>370 °C), and the combustion properties of DAP-4/Si composites first increase with Si content and then reduced. It was confirmed that DAP-4/Si with the ratio of 6.5:3.5–6:4 had a better burning intensity than the other ratios. The combustion mechanism of DAP-4/Si composites was proposed based on the ignition and combustion characteristics of DAP-4/Si composites. This work may provide a further reference for the application of DAP-4 into solid propellant formulation.

Studies of Energetic and Non‐Energetic Plasticizers for Nitrile Butadiene Rubber based CSP

AbstractBinders with energetic plasticizers besides boosting energy also enhance the structural integrity of the propellant composition. In recent energetic compositions, energetic plasticizers such as NG, BTTN, DEGDN and TEGDN replace conventional plasticizers as they possess positive heat of the explosion and energetic groups in the same molecule. Energetic groups impart enhanced potential for delivering superior performance. In the present paper, a comparative study is done between NBR based composite solid propellant formulations with energetic (DEGDN and TEGDN) and non‐energetic (DAP and DBP) plasticizers. The predicted theoretical performance of non‐aluminized and aluminized propellants shows that DEGDN/TEGDN based propellants are more energetic than that of DAP/DBP propellants. The viscosity (768 Pa.s), density (1748 kg/m3), cal‐val (5426.64 J/g), burning rate (4.21 mm/s) of DBP and DAP based propellants are on the lower side than DEGDN and TEGDN based propellants. End of mix viscosity and burning rate of energetic plasticizer based compositions is approximately twice of the inert plasticizer based compositions. There is up to 60 % increase in TS and modulus while elongation is reduced by 20 %. Pressure index increases from 0.159 to 0.310 for DBP to DEGDN based propellant. The study shows that high performance high burning rate propellant can be designed with DEGDN.

Thermal decomposition and kinetic modeling of HNTO/AN-based composite solid propellant in the presence of GO-based nanocatalyst

The present study has been conducted to investigate the characteristics of composite solid propellant (CSP) based on hydrazinium 3-nitro-1,2,4-triazol-5-one and ammonium nitrate (HNTO/AN) cocrystal as an oxidizer and hydroxyl-terminated polybutadiene (HTPB) as a binder, supplemented with or without nanocatalyst (triaminoguanidine-transition iron, containing graphene oxide). NASA Lewis Code, Chemical Equilibrium with Application (CEA), has been used to select the optimal formulation through the evaluation of the theoretical performance. Compared to the AP/HTPB baseline formulation, the developed one presents promising properties since it may deliver an interesting specific impulse value (231 s−1). On the other hand, based on the DSC data, the kinetic triplet of the studied samples was determined using four model-free integral methods, namely, it-KAS, it-FWO, VYA, and TAS. It was observed that the decomposition peak temperature (Tp) and the activation energy (Ea) decreased obviously after the addition of the nanocatalyst. This study will certainly motivate further researches in the field of energetic cocrystals and graphene-based materials expected to be used in solid rocket propellant formulations.

Polyethylene Glycol Propargyl Ethers Based Curing Agents for Glycidyl Azide Polymer

Three polyethylene glycol propargyl ethers (PGPEs), namely 4,7,10-trioxatrideca-1,12-diyne (TOTDY), 4,7,10,13-tetraoxahexadeca-1,15-diyne (TOHDY) and 4,7,10,13,16-pentaoxanonadeca-1,18-diyne (TONDY) were designed and successfully synthesized as curing agents for glycidyl azide polymer (GAP). Their structures were characterized by FT-IR, 1H NMR, 13C NMR and elemental analysis, and their glass transition temperatures (Tg) were measured by DSC. The films of GAP cured by the title compounds were prepared via 1,3 dipolar cycloaddition, and then the influences of PGPEs on the Tg, decomposition temperature (Td) and mechanical properties of the films were studied accordingly. The results showed that the Tg of GAP cured by TOTDY and TOHDY were-38.1 oC and-38.2 oC, respectively. The Td of GAP cured by PGPEs was in the range of 235.5 oC - 241.0 oC. The results of tensile tests showed that the maximum stress of GAP films cured with PGPEs were in the range of 0.11 MPa to 0.52 MPa at elongation from 29% to 48%. These results indicated that PGPEs would have potential application in GAP based high energy solid propellant formulations.

Making progress towards promising energetic cellulosic microcrystals developed from alternative lignocellulosic biomasses

ABSTRACT This study reported the valorization of various alternative lignocellulosic feedstocks including giant reed (GR), palm fronds (PF) and esparto grass (EG) for the development of promising nitrated structurally modified cellulosic biopolymers (NNCs). The extracted nanostructured cellulose precursors and their nitrated derivatives were analyzed for their physicochemical properties, chemical structure, crystallinity and thermal stability. Experimental findings confirmed the successful formation of the desired energetic NNCs polymers with increased densities (1.698–1.711 g/cm3) and high nitrogen contents (13.10–13.26%) followed the order NNC-EG>NNC-PF>NNC-GR, which are greater than those of the commonly used nitrocellulose (1.650–1.670 g/cm3 and 12.50–12.70%). Furthermore, isoconversional integral models (TAS, it-KAS and VYA/CE) were exploited based on non-isothermal DSC data to investigate their thermal decomposition kinetics. The predicted kinetic parameters displayed that the synthesized energy-rich NNCs presented close values of Arrhenius parameters within the range of 156 ≤ Eα (kJ/mol) ≤163 and 14.7 ≤ Log(A(s−1) ≤ 15.6, and decomposed following diverse reaction mechanisms. Consequently, the explored lignocellulosic biomasses could be considered as valuable alternative non-woody resources for the production of advanced high-energy dense cellulosic biopolymers for potential application in the next generation of solid propellant formulations and composite explosives.

Valorization of Esparto Grass Cellulosic Derivatives for the Development of Promising Energetic Azidodeoxy Biopolymers: Synthesis, Characterization and Isoconversional Thermal Kinetic Analysis

AbstractIn the frame of developing new high‐energy materials from bioresources, emergent cellulose and microcrystalline cellulose functionalized with explosophoric azides were successfully synthesized from a prominent alternative esparto grass fibres. The designed insensitive nitrogen‐rich cellulosic biopolymers, namely, azidodeoxy esparto grass cellulose (AEGC) and azidodeoxy esparto grass microcrystalline cellulose (AEGMCC), displayed outstanding features, such as nitrogen content (w/w) of 18.24–18.68 %, the density of 1.601–1.626 g/cm3, and thermal decomposition of 203–218 °C. Their kinetic triplet was also determined under non‐isothermal DSC conditions employing isonversional integral approaches. Interestingly, the apparent activation energy and the decimal logarithm of a pre‐exponential factor of the developed AEGC and AEGMCC were found to be better than those of the common nitrocellulose. In addition, the reaction model examination based on Trache‐Abdelaziz‐Siwani (TAS) approach revealed that the produced AEGC and AEGMCC were accurately presented by an autocatalytic Avrami‐Erofeev decomposition process. These results established that esparto grass fibres could be considered as a valuable alternative feedstock for the synthesis of outstanding energetic cellulose‐rich polymers for potential applications in solid propellant formulations.

Constructing α-AlH3@polymer composites with high safety and excellent stability properties via in situ polymerization

The in situ polymerization of encapsulated α-AlH3 has promising applications in aerospace and weapon fields, and the resulting α-AlH3@PVP has potential applications in solid propellant formulations.

Exploration of palm fronds as a prominent alternative resource for the production of energetic cellulose-rich biopolymers

This study deals with the valorization of Algerian date palm fronds (DPF) as a prominent alternative biomass for the synthesis of energy-rich cellulosic biopolymers through electrophilic nitration of the isolated pristine cellulose and cellulose microcrystals (OCN and MCCN). The successful chemical structure of the designed energetic biopolymers and their cellulosic precursors was confirmed by Fourier trans-form infrared spectroscopy (FTIR) analysis. Furthermore, differential scanning calorimetry (DSC) indicated that the new produced MCCN present slightly lower thermal stability than the common OCN. In addition, elevated density and great nitrogen content were obtained for MCCN compared to the conventional OCN. Consequently, the explored DPF could be considered as a valuable alternative non-woody biomass for the production of advanced high-energy cellulosic biopolymers for potential application in the next generation of solid propellant formulations.

Solid Propellant Formulations: A Review of Recent Progress and Utilized Components.

The latest developments in solid propellants and their components are summarized. Particular attention is given to emerging energetic binders and novel, ‘green’ oxidizing agents and their use in propellant formulations. A brief overview of the latest reports on fuel additives is included. Finally, a summary of the state of the art and challenges in its development are speculated on.

Novel energetic aminofurazans with a nitro-NNO-azoxy group

Novel energetic azoxy- and azofurazans bearing nitro-NNO- azoxy and amino groups were synthesized using the ammonolysis of some known (nitro-NNO-azoxy)furazans. 3-Amino-4-{[4′-(nitro-NNO-azoxy)f urazan-3′-yl]-NNO- azoxy}furazan displays the highest melting point (114 °C, decomp.) among the known (nitro-NNO-azoxy)furazans, optimal density (1.80 g cm−3), high experimental enthalpy of formation (639 kcal kg−1) and mechanical sensitivity on the level of PETN. In terms of the specific impulse level, the model solid composite propellant formulations based on this compound outperform similar formulations based on RDX, HMX or CL-20 by 7–12 s.

Modelling of the formulated solid rocket propellant characteristics

This study is a mathematical model to obtain the characteristics performance of magnesium metal (powder) and carbon on a potassium nitrate-sucrose (KNSU) solid propellant formulation. Characterization of propellant is, as a general rule, important to determine its performance before it can be suitable for use for a rocket flight or any mission. Method of ballistic load cell evaluation was used to validate results and a mathematical model using the combustion exhaust products was solved to obtain the characteristics performance parameters of the propellant. The carbon constituent which acts as an opacifier and coolant was kept constant at 2% in order to arrest some of the heat during the combustion process and helped to lower the combustion temperature, because high combustion temperature could lead to combustion chamber rupture or failure. The effect of addition of magnesium which was optimized for 3% in the formulation contributed significantly in improving the overall performance of the propellant. The utilization of magnesium in KNSU propellant provided higher values parameters and better performance compared to when not included. This was confirmed with the model equations. The propellant combustion products equation was used to model and obtain the characteristics performance parameters. This gave propellant specific impulse (122.9s), combustion temperature (1821K), heat ratio (1.1592), molecular weight (36.89g/mole), propellant density (1912.5kg/m3) and characteristics velocity (1000m/s) result while maintaining the same chamber pressure.

Effect of magnesium metal in the characteristics performance of a sucrose-based solid rocket propellant

This research work aimed at investigating the effects of magnesium metal (powder) and carbon on a potassium nitrate-sucrose (KNSU) solid propellant formulation. Characterization of propellant is very important to determine its performance before it can be suitable for use for a rocket flight or any mission. Ballistic loadcell method was used. The ballistic load cell instrumentation measured the thrust generated by the propellant, the propellant burn time and the exit temperature of the burning hot propellant gases. The carbon constituent which acts as an opacifier and coolant was kept constant at 2% in order to arrest some of the heat during the combustion process and helped to lower the combustion temperature, because high combustion temperature could lead to combustion chamber rupture or failure. Also, carbon was not increased beyond 2%, so as not to make the propellant excessively smoky because of presence of magnesium oxide and other solids in the combustion products that can cause air pollution, and could be harmful to human lives and the environment. The propellant specific impulse (117.9s), combustion temperature (1818K), heat ratio (1.1508), propellant molecular weight (38.88g/mole), propellant density (1874.6kg/m3), characteristics velocity (997.2m/s) and burn rate (0.00906m/s) were obtained. The effect of addition of magnesium which was optimized for 3% in the formulation contributed significantly in improving the overall performance of the propellant as parameters such as the specific impulse, chamber temperature, characteristics velocity and heat ratio were found to have higher values as compare to the KNSU propellant when magnesium was not present in the formulation. Basically, higher values of these parameters suggest better propellant performance. Also, in this case, when carbon was increased beyond 2%, the propellant was excessively smoky because of presence of magnesium oxide and other solids in the combustion products that can cause air pollution, and could be harmful to human lives and the environment.