Composite Propellant Formulations Research Articles

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.

Shear and combustion characterization of printable ammonium perchlorate composite propellant formulations

AbstractSeven formulations of ammonium perchlorate composite propellant (APCP) are developed and their properties relevant for successful additive manufacture are characterized. Extrusion in a custom‐built 3D printing system and spindle viscometry are used to collect viscosity measurements of curing primary and non‐curing secondary versions of the formulations. The formulations that behave similarly to a Bingham plastic, with apparent viscosities between 4 and 8 thousand Pa*s at 30 minutes post‐mix, are determined to be most suitable for printing applications. Measurements of one material show a yield stress of 1 kPa. Ambient pressure burn rates of 2.0–2.9 mm/s were measured for the compositions tested. All measured burn rates were comparable to the lower end of typical burn rates for APCP. The results of the characterization demonstrate a propellant suitable for use in a 3D printing system.

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.

Synthesis of multifunctional additives for solid propellants: Structure, properties and mechanism

To simplify the composite propellant formulation and address the current issue of the single-functionality present in existing additives, the multi-cyano, amine-based polybutadiene (AEHTPB-CN) was prepared based on AEHTPB by adopting appropriate synthesis strategies. By replacing 10% of HTPB binder in the propellant formulation, it can effectively enhance the interfacial bond strength between the propellant binder matrix and solid fillers (AP (ammonium perchlorate) and RDX (cyclotrimethylene-trinitramine)), the mechanical properties of the HTPB/AP/RDX/Al propellant were superior to blank control propellant with an improvement of 35.4% in tensile strength, 62.0% enhancement in elongation at break, and reduce the propellant burn rate by 10.7% with any energy loss. The function mechanism of AEHTPB-CN was systematically elucidated through experiments and computer simulation techniques. The results show that the tertiary amine group in AEHTPB-CN can react with AP to form ammonium ionic bonds, and the hydroxyl and cyano groups can form hydrogen bonding interactions with AP, which enables AEHTPB-CN to be firmly adsorbed on the AP surface through chemical and physical interactions. For RDX, the interfacial bonding effect of AEHTPB-CN is attributed to their ability to form C–H⋅⋅⋅NC weak hydrogen bonding interaction between the cyano group and RDX methylene group.

Manufacturing superfine AP by milling in a lab-scale resonant acoustic mixer (LabRAM)

ABSTRACT A common practice to deisgn composite propellants with high burning rates is to use several sizes of the oxidizer (e.g., ammonium perchlorate, AP) to increase the total amount of solids that can be packed into the composite propellant system. Small AP particles (≤15 μm) are difficult to obtain from commercial vendors due to restrictions derived from increased explosion hazards for superfine AP (SFAP). An in-house SFAP manufacturing process was devised herein using resonant acoustic mixing (RAM). A 90-μm AP feedstock was utilized to produce SFAP batches with average particle sizes of approximately 2 μm. Scanning electron microscopy (SEM) was used to characterize particle size distributions. Ballistic testing was conducted with an 80% SFAP composite propellant formulation was burned over a pressure range of 500 to 3,000 psi (3.45 to 20.68 MPa) and a burning rate of 1 in/s (25 mm/s) at 1,000 psi (6.89 MPa) was achieved without optimizing the propellant with additives.

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.

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.

On the Question of the Energetic Performance of TKX‐50

AbstractAn analysis of the experimental data available to date shows that the explosive TKX‐50 has really high explosive performance characteristics, although not as outstanding as claimed previously, due to the overestimation of the enthalpy of formation. The obtained experimental data on the dependence of the detonation velocity on the density of TKX‐50 samples agree with the results of calculations, in which the experimentally determined enthalpy of formation 194.1 kJ mol−1 is used. The energetic performance of TKX‐50 surpasses the parameters of nitramines RDX, HMX, and even CL‐20, determined at the same densities. However, the calculated detonation velocity of TKX‐50 at theoretical maximum density is 9287 m s−1, which is slightly lower than the detonation velocity of CL‐20 at maximum density. It is worth noting that the detonation velocity of the TKX‐50 at the experimentally attainable density (1.8 g cm−3) is 9037 m s−1. Calculations using the experimentally determined enthalpy of formation show that high‐energy composite propellant formulations containing TKX‐50 are inferior in a specific impulse to compositions based on CL‐20 and HMX.

Rocket Propellant Comparison: Conventional Planetary Mixing and Resonant Acoustic Mixing

AbstractA standard HTPB/AP/Al composite rocket propellant formulation was prepared with a conventional vertical planetary action mixer and resonant acoustic mixer (RAM). Ingredients and process conditions were standardised as much as possible to facilitate a direct comparison of the two process regimes. Cured propellant specimens were characterised for sensitiveness, ballistic properties and mechanical properties at 3 temperatures (−54 °C, 25 °C and 74 °C). No significant differences were noted for sensitiveness between the planetary and RAM mixes. A slightly lower burn rate at 1000 psi (6.89 MPa) was noted for the RAM mixes. Maximum stress results at 25 °C were similar but significant differences in maximum strain and modulus were recorded. Maximum strain for the 1 Pint, 2 Gallon and RAM were 7.4 %, 9.1 % and 17.6 %, respectively. Modulus results were 26.0 MPa, 19.3 MPa and 11.1 MPa, respectively. Similar improvements in strain capability for the RAM propellant were recorded at −54 °C and 74 °C, with increases of 66 % and 117 %, respectively. A greater strain capability results from stronger interfacial adhesion between the solid fill and the binder, which is in turn generally a result of improved wetting of solid particles. This result, therefore, indicates more thorough mixing in the case of the RAM process but this requires confirmation through a more direct examination of the underlying mechanism.

Thermal Decomposition of Ammonium Perchlorate in the Presence of Copper Tungsten Oxide (CuWO4)

AbstractThe catalytic effect of copper tungsten oxide (CuWO4) was investigated on the thermal decomposition of ammonium perchlorate (AP) using differential scanning calorimetry. A lowering of the high‐temperature decomposition peak temperature of AP was observed due to catalytic effect of copper tungsten oxide particles, now referred to as CTO in this paper henceforth. The kinetic parameters were evaluated using the Kissinger method. The decrease in the activation energy confirmed the catalytic activity of CTO. Further, CTO was evaluated in a standard composite propellant formulation having 86 % solid loading. Propellant performance and processing parameters such as the end of mix (EOM) viscosity, density, burning rate, pressure exponent (n‐value), etc. were measured for standard as well as a composition containing 1 % CTO. The results revealed that at 1 % level CTO causes more than 36 % increase in propellant burning rate compared to the standard propellant composition at 6.86 MPa pressure. The pressure exponent also increased to 0.48, whereas the standard composition was having its value of 0.41.

(3-Nitro-1H-1,2,4-triazol-1-yl)-NNO-azoxy]furazans: energetic materials containing an N(O)[double bond, length as m-dash]N-N fragment.

The strategy for the synthesis of substituted [(3-nitro-1H-1,2,4-triazol-1-yl)-NNO-azoxy]furazans 4–7, in which the distal nitrogen of the azoxy group is bonded to the nitrogen atom of the azole ring, includes, firstly, the reaction of 1-amino-3-nitro-1H-1,2,4-triazole with 2,2,2-trifluoro-N-(4-nitrosofurazan-3-yl)acetamide in the presence of dibromisocyanuric acid followed by removing of the trifluoroacetyl protecting group to afford aminofurazan (4). Transformation of the amino group in the latter made it possible to synthesize the corresponding nitro (5), azo (6), and methylene dinitramine (7) substituted furazans. The compounds synthesized are thermally stable (decomposition onset temperatures 147–228 °C), exhibit acceptable densities (1.77–1.80 g cm−3) and optimal oxygen balance (the oxidizer excess coefficients α = 0.42–0.71). Their standard enthalpies of formation (576–747 kcal kg−1) were determined experimentally by combustion calorimetry and these compounds have been estimated as potential components of solid composite propellants. In terms of the specific impulse level, model solid composite propellant formulations based on nitro and methylene dinitramine substituted furazans 5 and 7 outperform similar formulations based on CL-20 by 1–4 s, and formulations based on HMX and RDX by 5–8 s.

Composite Propellant Formulation of Poly (16-, 32- and 64-) Azido Dendritic Esters as Energetic Plasticizer and Evaluation of Properties

Composite Propellant Formulation of Poly (16-, 32- and 64-) Azido Dendritic Esters as Energetic Plasticizer and Evaluation of Properties

Synthesis, characterization and thermal decomposition behavior of a novel HNTO/AN co-crystal as a promising rocket propellant oxidizer

• A new energetic-co-crystal HNTO/AN is successfully prepared. • The FTIR/XRD/DSC analyses confirm the development of new co-crystal. • The manufactured co-crystal exhibits excellent performance. • The prepared co-crystal displays good stability and low sensitivity. A novel energetic co-crystal composed of hydrazine 3-nitro-1,2,4-triazol-5-one (HNTO) and ammonium nitrate (AN) was successfully synthesized by solvent evaporation method. The formation of the co-crystal was confirmed by using scanning electron microscopy (SEM), powder X-ray diffraction (XRD), infrared and Raman spectroscopies. Compared to pure HNTO and AN, the manufactured highly dense energetic co-crystal crystalized into a new polymorphic form and exhibited a reduced sensitivity to friction and impact. Furthermore, the differential scanning calorimetry (DSC) analysis showed the absence of all temperature-dependent phases of AN in the new co-crystal. The kinetic investigation carried out by the isoconversional methods revealed that the apparent activation energy of decomposition of the HNTO/AN co-crystal is situated between those of its pure components. Compared to AN, the known propellant oxidizer, the obtained energetic co-crystal may be considered as a potential oxidizer for composite solid propellant formulations.

An experimental study on mechanical and ballistic characteristics of different HTPB composite propellant formulations

The main goal of this paper is to investigate the changing in the tensile behavior and the burning rate characteristics of hydroxyl-terminated polybutadiene (HTPB) propellantunder the variations of the crosslinking density, which was predominantly determined by the equivalent ratio of diisocyanate to total hydroxyl (NCO/OH ratio), which known as the curing ratio. Four variousbatches with different curing ratios (NCO/OH) percentage were produced in which the production processes were fixed. Uniaxial tensile tests were conducted at different temperatures (-40, 20 and 55°C), and different strain rates (0.000656 1/s, 0.0328 1/s) using a Zwick universal test machine. In order to measure the burning rate, cured solid propellant strands were tested using the acoustic wave emission method under different pressure ranging from 4 to 10 MPa. The experimental results indicate that the tensile behavior of HTPB propellant is remarkably influenced by curing ratio, strain rate, and temperature. It was observed that a great change on stress-strain curves affected various curing ratios and temperatures on the mechanical behavior of propellant composition. The results showed that high curing ratio leads to increase theultimatestress and decrease the strainat maximum stress, but higher temperatures lead to decrease theultimate stress and the strain at maximum stress.The curing ratios (NCO/OH) have an intense impact on mechanical characteristics, but slightly impact on ballistic characteristics for propellant. Furthermore, careful measurements of these parameters are important to control the production quality and to provide a reliable comparison between different propellant batches.

Novel evaluation enhancement role of poly (1-(3-nitrophenyl)-1H-1,2,3-triazol-4-yl) acrylate materials for propellant composite formulation

The performance of solid propellants is often tailored by incorporating energetic materials such as novel oxidizers, energetic binders and ballistic modifiers. Metal oxide nanoparticles are known for their persuasivenature to modify burning rate ofammonium perchlorate based composite propellants. In the present work, nano iron oxide and poly (1-(3-nitrophenyl)-1H-1,2,3-triazol-4-yl) acrylate are incorporated in the composite propellant formulation by partly replacing coarse ammonium perchorate (AP) as well as hydroxy terminatined polybutadiene (HTPB), respectively, and different properties were evaluated. The mechanical properties data revealed that on increasing the percentage of polymer in the composition by partly replacing HTPB, there is an increase in tensile strength while decreasing elongation percentage. Thedata of ballistic properties revealed that on incorporation of nano iron oxide in the composition enhances the burning rate while on partial replacement of HTPB with polymer there is a decrease in burning rate from 11.95 mm s−1 to 8.75 mm s−1, respectively was observed.

ADN Recrystallization and Microencapsulation with HTPB by Simple Coacervation

AbstractAmmonium dinitramide (ADN) has been considered the potential substitute for ammonium perchlorate in solid green propellants. However, it has also some drawbacks due to its high hygroscopicity and chemical incompatibility with some of the components present in composite propellant formulations. On the other hand, ADN melts at temperatures below degradation, which makes emulsion crystallization an important method to prepare spherical ADN particles that benefit both propellant slurry processing and casting. Spherical ADN particles were prepared by emulsion crystallization to be used for the microencapsulation studies, and whose method was assessed to better understand which parameters may affect the ADN particles formation. Microencapsulation protects ADN particles as it addresses hygroscopicity besides the given protection from chemical incompatibility. Polyurethane made of hydroxyl‐terminated polybutadiene was selected as a coating material because of its common use in propellants as a binder. Also, the good performance of methylene diphenyl diisocyanate as a curing agent was such that it was used in the whole study. The number of layers and the processing time played important roles in the formation of the capsule as seen in the impermeability tests. Besides, drying at 50 °C for 168 h showed to be even more beneficial on average for the capsule protective property. Chemical compatibility between the capsule and ADN was confirmed at 60 °C which allows it to be used as a protective coating. However, the obtained average coating thickness of ten microns has to be reduced yet with more efficient protective coating materials.

Design of new energetic materials based on derivatives of 1,3,5-trinitrobenzenes: A theoretical and computational prediction of detonation properties, blast impulse and combustion parameters

This paper reports the design of some of the new ionic based high energy materials derived from the anion of picric acid (2,4,6-trinitrobenzene-1-ol), styphnic acid (2,4,6-trinitrobenzene-1,3-diol) and 2,4,6-trinitrophloroglucinol (2,4,6-trinitrobenzene-1,3,5-triol) and cation derived from the key synthon molecules such as 5-trifluoromethyl-1H-tetrazole, 5-dinitromethyl-1H-tetrazole and 5-azido-1H–tetrazole-1-carbonitrile. The detonation properties of these newly proposed compounds are predicted by using software such as EXPLO-5, EXTEC and LOTUSES and Keshvarz method. Moreover, other explosive parameters such as density, gurney velocity, and oxygen balance and decomposition products of the newly designed molecules have also been predicted and reported for the first time in this manuscript. The predicted detonation parameters of some of the newly designed compounds exhibit higher velocity of detonation (VOD) and detonation pressure in comparison to other well-known benchmark explosives such as 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-triazinane (RDX). Further, the peak over pressure (POP) and the blast impulse parameters of the newly designed compounds are predicted by using Shock physics explicit eulerian dynamics (SPEED) software, and the same is reported for the first time in this work. The work also reports the theoretical prediction of impact and electrostatic spark sensitivity parameters for the newly designed molecules. The ballistic performance parameters of the newly designed ionic energetic materials are also predicted by incorporating them into model composite rocket propellant formulations. The predicted ballistic parameters indicate that the proposed materials may find an application in the propellant formulation as an energetic additive.

Effect of Long-Chain Bonding Agent on the Combustion of Composite Propellant and Modification of Combustion Performance Using Nano Additives

ABSTRACT Novel long-chain bonding agent MST was synthesised and introduced into the bonding agent matrix in order to enhance the mechanical properties of composite propellant by improving the interfacial interactions between the bonding agent and solid particles, in order to withstand stresses produced due to combustion loading conditions, changes in environmental condition, transportation and handling without effecting on the ballistic performance. In this work, the replacement of the long-chain MST bonding agent instead of the most famous reference MAPO bonding agent has improved the mechanical properties especially strain value corresponding to stress value which doubling the maximum strain value with an acceptable value of maximum stress with a good value with Young’s modulus in propellant formulations. Different compositions of composite propellant were carried, in order to measure the linear burning rate and to study the effect of the replacing MST bonding agent instead of tradition bonding agent MAPO. Due to the presence of a bonding agent, the burning process of the composite propellant should become more regular and stable burning but it reduces slightly the burning rate as in formulation F2 in which the pressure exponent (n) value reached .067. It should be modifying the reduction in burning rate due to the presence of MST in order to achieve promising burning properties. By using nano-aluminum it was secured improving performance and achieved a high burning rate of the propellant formulations based on MST bonding agent as well as the composite propellant formulations based on MAPO bonding agent. And by using nano-copper chromite the values of the burning rate of composite propellant formulations became greater than those values of formulations based on nano-aluminum with the same weight ratio and particle size, due to the nature of copper chromite and its effect on the binder and the ammonium perchlorate.

Organically-Capped, Nanoscale Alkali Metal Hydride and Aluminum Particles as Solid Propellant Additives

This Paper reports on organometallic composites, containing nanoscale aluminum and lithium-based hydride fuel particles, as solid propellant additives. Theoretical performance is evaluated for bimodal metal propellant formulations containing capped fuel additives (nanoMetallix LLC) and aluminum. Replacing aluminum with nanoMetallix capped fuel additives reduces specific impulse, adiabatic flame temperature, condensed-phase products, and hydrochloric acid. Combustion behavior is investigated using high-speed video techniques, including flame emission, laser backlit configurations, and a two-camera ratiometric bandpass emission technique used to detect lithium. Agglomeration behavior of the nanoMetallix particles at atmospheric pressure is similar to nanoaluminum (nAl), producing large aggregates that ignite quickly, increasing radiative heat feedback. Spectrally filtered video identifies lithium vapor around the nanoMetallix particles on and above the burning surface, suggesting lithium vapor is released close to the surface. Pressurized burning rate measurements indicate nanoMetallix-based propellant burning rates are up to approximately 14% higher than similar nAl-based propellants at and below 6.89 MPa. Above this pressure, nanoMetallix propellants exhibit plateau pressure dependence, likely an effect of the different capping agents used. This Paper shows organically-capped nanoscale particles are a promising alternative to nano/microaluminum in composite solid propellant formulations.