Energetics of AMMO

The thermal decomposition process and combustion wave structure of azide polymer were studied to determine the parameters which control the burning rate. The azide polymer studied was 3-azidomethyl-3-methyl oxetane (AMMO) which contains energetic –N₃ groups. From the experiments, it was found that the thermal decomposition process of AMMO consists of a two-stage weight loss process: the first-stage corresponds to an exothermic reaction which is caused by the scission of N-N₂ bond, and the second-stage corresponds to the decomposition of the remaining fragments. The burning rate of AMMO is approximately 50% of the burning rate of GAP propellant and is as high as that of conventional double base propellant. The heat feedback from gas phase to the burning surface increase with increasing pressure. The burning surface temperature and the heat of reaction at the surface decrease with increasing pressure.     

Glycidyl Azide Polymer Crosslinked Through Triazoles by Click Chemistry: Curing,Mechanical and Thermal Properties

Glycidyl azide polymer (GAP) was cured through “click chemistry” by reaction of the azide group with bispropargyl succinate (BPS) through a 1,3‐dipolar cycloaddition reaction to form 1,2,3‐triazole network. The properties of GAP‐based triazole networks are compared with the urethane cured GAP‐systems. The glass transition temperature (T_g), tensile strength, and modulus of the system increased with crosslink density, controlled by the azide to propargyl ratio. The triazole incorporation has a higher T_g in comparison to the GAP‐urethane system (T_g−20 °C) and the networks exhibit biphasic transitions at 61 and 88 °C. The triazole curing was studied using Differential Scanning Calorimetry (DSC) and the related kinetic parameters were helpful for predicting the cure profile at a given temperature. Density functional theory (DFT)‐based theoretical calculations implied marginal preference for 1,5‐addition over 1,4‐addition for the cycloaddition between azide and propargyl group. Thermogravimetic analysis (TG) showed better thermal stability for the GAP‐triazole and the mechanism of decomposition was elucidated using pyrolysis GC‐MS studies. The higher heat of exothermic decomposition of triazole adduct (418 kJ ⋅ mol⁻¹) against that of azide (317 kJ ⋅ mol⁻¹) and better mechanical properties of the GAP‐triazole renders it a better propellant binder than the GAP‐urethane system.     

Combustion of GAP Based Energetic Pyrolants

Glycidyl azide polymer (GAP) is a high energy material used as a fuel component and binder of propellants and gas generators. High temperature products are formed by the scission of the chemical bond N₃ when GAP is decomposed. The major decomposition products are N₂, CO, and C. Though GAP contains no oxidizer fragments in its products, an addition of metal particles increases the energy of GAP. A mixture of GAP and metal particles forms a high energy metal based GAP pyrolant, i.e. GAP/metal pyrolant. The metals examined are Al, Mg, B, Ti, and Zr. The results indicate that the thermal decomposition and burning rate are dependent on the type of metals mixed.     

Combustion Mechanism of Glycidyl Azide Polymer

A combustion model of glycidyl azide polymer (GAP) is presented. Linear burning rate and temperature profile measurements of model samples led us to the conclusion that linear burning rate is controlled by N₂ liberation process below the pressure exponent break point (2.3 MPa). Further, scanning electron microscope (SEM) photographs and Fourier transform infrared (FTIR) spectra of quenched samples by rapid depressurization of the combustor show that the N₂ liberation process is strongly limited to the melt layer at the combustion surface and the profile of the heat release rate is probably δ-function like. This fact enables the application of an asymptotic analysis to this phenomenon.     

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.     

Thermal characterization of glycidyl azide polymer (GAP) and GAP‐based binders for composite propellants

Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) were used to investigate the thermal behavior of glycidyl azide polymer (GAP) and GAP‐based binders, which are of potential interest for the development of high‐performance energetic propellants. The glass transition temperature (T_g) and decomposition temperature (T_d) of pure GAP were found to be −45 and 242°C, respectively. The energy released during decomposition (ΔH_d) was measured as 485 cal/g. The effect of the heating rate on these properties was also investigated. Then, to decrease its T_g, GAP was mixed with the plasticizers dioctiladipate (DOA) and bis‐2,2‐dinitropropyl acetal formal (BDNPA/F). The thermal characterization results showed that BDNPA/F is a suitable plasticiser for GAP‐based propellants. Later, GAP was crosslinked by using the curing agent triisocyanate N‐100 and a curing catalyst dibuthyltin dilaurate (DBTDL). The thermal characterization showed that crosslinking increases the T_g and decreases the T_d of GAP. The T_g of cured GAP was decreased to sufficiently low temperatures (−45°C) by using BDNPA/F. The decomposition reaction‐rate constants were calculated. It can be concluded that the binder developed by using GAP/N‐100/BDNPA/F/DBTDL may meet the requirements of the properties that makes it useful for future propellant formulations. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 538–546, 2000     

Synthesis of Carbon‐Rich Hybrid Foam from GAP‐Modified Polyurethane

4,4′‐Diisocyanato diphenylmethane (MDI)‐based polyurethanes melt and start to burn at 150–200 °C. Mainly H₂O, CO₂, CO, HCN, and N₂ are formed. The new modified polyurethane shows a different pyrolysis behavior. GAP‐diol (glycidyl azide polymer), which was used as a modifying agent, is a well‐known energetic binder with a high burning velocity and a very low adiabatic flame temperature. The modified polyurethane starts to burn at approximately 190 °C because of the emitted burnable gases, but it does not melt. The PU foam shrinks slightly and a black, solid, carbon‐rich hybrid foam remains. TGA and EGA‐FTIR revealed a three‐step decomposition mechanism of pure GAP‐diol, the isocyanate‐GAP‐diol, and PU‐GAP‐diol formulations. The first decomposition step is caused by an exothermic reaction of the azido group of the GAP‐diol. This decomposition reaction is independent of the oxygen content in the atmosphere. In the range of 190–240 °C the azido group spontaneously decomposes to nitrogen and ammonia. This decomposition is assumed to take place partly via the intermediate hydrogen azide that decomposes spontaneously to nitrogen and ammonia in the range of 190–240 °C. The second decomposition step was attributed to the depolymerization of the urethane and bisubstituted urea groups. The third decomposition step in the range of 500–750 °C was attributed to the carbonization process of the polymer backbone, which yielded solid, carbon‐rich hybrid foams at 900 °C. In air, the second and the third decomposition step shifted to lower temperatures while no solid carbon hybrid foam was left. Samples of PU‐GAP‐diol, which were not heated by a temperature program but ignited by a bunsen burner, formed a similar carbon‐rich hybrid foam. It was therefore concluded that the decomposition products of the hydrogen azide, ammonia and mainly nitrogen act as an inert atmosphere. FTIR, solid‐state ¹³C‐NMR, XRD, and heat conductivity measurements revealed a high content of sp²‐hybridized, aromatic structures in the hybrid foam. The carbon‐rich foam shows a considerable hardness coupled with high temperature resistance and large specific surface area of 2.1 m²⋅g⁻¹.     

Energetics of BAMO

3,3-Bis(azidomethyl)oxetane (BAMO) is a typical energetic azide polymer containing two N₃, bonds in the molecular structure. Since BAMO is a solidified polymer at room temperature, a liquid BAMO copolymer with tetrahydrofuran (THF) was synthesized in order to gain energetic binders for solid propellants. Various types of experiments were carried out to elucidate the decomposition and combustion processes of BAMO polymer, BAMO/THF copolymer, and crosslinked BAMO/THF copolymer. The heat produced by the decomposition is caused by the bond breakage of -N₃ to produce N₂, gas. The burning rate characteristics of crosslinked BAMO/THF copolymer depend largely on the mole fraction ratio of BAMO and THF.     

Burning Rate Characterization of GAP/HMX Energetic Composite Materials

The burning rate of the energetic materials composed of glycidyl azide polymer (GAP) and HMX particles was characterized in order to elucidate the heat release process during burning. Since GAP is an energetic polymer and burns by itself, the addition of HMX increases the flame temperature and alters the burning rate characteristics. Experimental observations indicate that the gas phase structure consists of a two‐staged gas phase reaction: the burning rate is controlled by the first‐stage reaction zone and the final flame is formed at the second‐stage reaction zone. The heat flux transferred back from the first‐stage reaction zone to the burning surface increases as pressure increases and the heat released at the burning surface remains unchanged when pressure is increased.     

Plateau Burning Characteristics of AP Based Azide Composite Propellants

The site and mechanism by which iron oxide catalyst acted to enhance burning rate and produced plateau burning behavior at high pressure was studied. The condensed phase chemistry study was conducted by isothermal thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and rapid-scan FTIR spectroscopic technique. Uncatalyzed ammonium perchlorate (AP) based azide composite propellant showed unstable combustion at relatively lower pressure region. The heat balance at the buring surface would be unstable at these pressures. However, iron oxide altered the burning property of the propellant and enhanced the burning rate with the plateau-mesa burning characteristics. Such pressure insensitiveness of the burning rate indicated that the condensed phase chemistry played important role in the catalytic mechanism of action. According to the microrocket motor tests, physical effect, melted fuel binder covered the AP particles and prevented the further decomposition of AP, had not affected the plateau burning. Fe₂O₃ was more effective on the burning rate augmentation than Fe₃O₄. However, the pressure exponent of the burning rate point of view Fe₃O₄ was favored catalyst to the propellant used here.     

Combustion of GAP/HMX and GAP/TAGN Energetic Composite Materials

Energetic composite materials (ECM) have high thermodynamic potential and flexible design capability. Two types of ECM were formulated as mixtures of glycidyl azide polymer (GAP) and crystalline materials. The crystalline materials evaluated were cyclotetramethylene tetranitramine (HMX) and triaminoguanidine nitrate (TAGN). The thermochemical properties of HMX and TAGN were different to each other: HMX is a high energy material but the burning rate is lower than that of TAGN. TAGN produces hydrogen as a combustion product and the thermodynamic potential becomes high even though the flame temperature is low. The results of burning rate measurement tests indicate that the burning rates of both ECM are decreased significantly by the addition of HMX and TAGN even though the burning rates of GAP, HMX, and TAGN are higher than those of the ECM. The temperature sensitivity of burning rate of GAP is reduced significantly by the addition of HMX and remains unchanged by the addition of TAGN. The reduced burning rates of GAP/HMX and GAP/TAGN are caused by the reduced heat flux transferred back from the gas phase to the burning surface. The reduced heat release at the burning surface of GAP/HMX is responsible for the reduced temperature sensitivity.     

Thermal Decomposition of BAMO/HMX Propellants

Thermal decomposition of BAMO [bis(azidomethyl)oxetane/tetrahydrofuran copolymer]/HMX composite propellants was studied by isothermal TGA (thermogravimetric analysis) and DSC (differential scanning calorimetry) in helium atmosphere, which was showing overall two steps first-order kinetics. The effects of cross-link ratio on the accelerated aging of the BAMO/HMX propellants were also measured with infrared spectroscopy and gas chromatography. The accelerated aging was conducted at 347 K for several weeks. BAMO/HMX propellants for a very low cross-link ratio made the cavity between HMX and BAMO binder by N₂, CO₂, and H₂O evolutions during accelerated aging. An exotherm, generated by the decomposition of azide binder, initiated and accelerated the thermal decomposition of HMX. The burning rate of BAMO/HMX propellant was larger than those of BAMO binder and HMX, respectively. However, the propellant could not maintain the combustion at low pressure, at which its burning rate was equal to that of BAMO binder.     

铅盐催化剂对GAP少烟推进剂燃烧性能的影响

采用DSC研究了不同形貌的铅盐催化剂CH-Ⅰ和CH-Ⅱ对AP热分解行为的影响,获得了其热分解反应的动力学参数,并考察了催化剂对GAP少烟推进剂燃烧性能的影响。结果表明,铅盐催化剂能够降低AP的低温分解反应活化能,提高高温分解反应速率。在GAP少烟推进剂中,加入铅盐催化剂CH-Ⅰ和CH-Ⅱ,能够显著提高其高压下的燃速,15~25MPa内的压强指数分别由不加催化剂时的0.46降至0.35和0.34。AP的热分解行为与GAP少烟推进剂燃烧紧密相关。AP热分解反应的加快是推进剂燃速提升的主要原因,催化剂的催化活性与其形貌和粒度有关。催化剂CH-Ⅱ的催化效果优于催化剂CH-Ⅰ。     

Temperature sensitivity of Burning Rate of Ammonium Perchlorate Propellants

The temperature sensitivity of burning rate of ammonium perchlorate (AP) composite propellants was studied as a function of AP particle size and a burning rate catalyst. A simplified temperature sensitivity model was presented in order to discriminate the effect of the gas phase and solid phase reactions on the initial propellant temperature (T₀). The temperature sensitivity was decreased by the addition of small sized AP particles and/or 2,2-bis(ethylferrocenyl)propane (BEFP). This is caused by the insensitive burning surface temperature to T₀. Thus, the gas phase reaction rate becomes little dependent on T₀, and the temperature sensitivity decreases.     

Energetics of Nitro/Azide Propellants

A new type of double-base propellant which contains GAP was studied in order to elucidate the burning rate characteristics and combustion wave structure. This class of propellants is termed “nitro/azide propellants”. Experimental results revealed that the burning rate and temperature sensitivity are increased when 12.5% DEP is replaced with 12.5% GAP. The reaction rate in the dark zone is increased by the replacement of DEPo with GAP. However, the gas phase structure of NG/NC/GAP propellant is fundamentally the same as that of NG/NC/DEP propellant and the basic chemical reaction mechanism in the gas phase zone remains unchanged for both propellants.     

An Advanced GAP/AN/TAGN Propellant. Part I: Ballistic Properties

A solid rocket propellant based on glycidyl azide polymer (GAP) binder plasticized with nitrate esters and oxidized with a mixture of ammonium nitrate (AN) and triaminoguanidine nitrate (TAGN) was formulated and characterized. Non‐lead ballistic modifiers were also included in order to obtain a propellant with non‐acidic and non‐toxic exhaust. This propellant was found to exhibit a burning rate approximately twice that of standard GAP/AN propellants. The exponent of the propellant is high compared to commonly used composite propellants but is still in the useable range at pressures below 13.8 MPa. This propellant may present a good compromise for applications requiring intermediate burn rate and impulse combined with low‐smoke and non‐toxic exhaust.     

Curing characteristics of glycidyl azide polymer‐based binders

The curing of a glycidyl azide polymer (GAP) with a triisocyanate, Desmodur N‐100, was followed by measuring the hardness and viscosity. The thermal behavior of the cured samples were investigated by a differential scanning calorimeter (DSC) and thermal gravimetric analysis (TGA). Curing causes an increase in the glass transition temperature of GAP. The T_g of gumstocks also increases with an increasing NCO/OH ratio while the decomposition temperature remains practically unchanged. The ultimate hardness of the cured samples increases with an increasing NCO/OH ratio. The binder with a NCO/OH ratio of 0.8 was found to provide the most suitable thermal and physical characteristics for composite propellant applications. The increase in the glass transition temperature of gumstocks upon curing can be compensated by using a 1:1 mixture of bis‐2,2‐dinitropropyl acetal and formal as the plasticizer. The T_g value of gumstocks can be decreased to −46.7°C by adding 25% b.w. of a plasticizer which does not have any significant effect on the decomposition properties of the gumstocks. Furthermore, a remarkable decrease in the ultimate hardness of the gumstocks is achieved upon addition of a plasticizer, while the curing time remains almost unaffected. The addition of dibuthyltin dilaurate as a catalyst reduces the curing time of the gumstocks from 3 weeks to 5–6 days at 60°C. Use of the curing catalyst also results in the hardening of the gumstocks. The decomposition properties of the gumstocks remain practically unchanged while a noticeable increase is observed in the glass transition temperature with an increasing concentration of the catalyst. This can also be compensated by a reverse effect of the plasticizer. The gel time, an important parameter which determines the pot life of a propellant material, can be measured by monitoring the viscosity of the mixture, which shows a sharp increase when gelation starts. The addition of a curing catalyst shortens the gel time remarkably. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 65–70, 2001     

Temperature profile in the combustion wave of low calorific value propellants

Combustion wave temperature profiles are determined for two low calorific value propellants (Q _c = 2189 and 2518 kJ/kg). It is shown that the structure and parameters of the combustion wave differ significantly from those for previously studied propellants of medium (propellant N) and high (propellant NB) calorific values. At a relatively short distance from the burning surface, the temperature is significantly (180–270 K) higher than the calculated value due to fact the combustion products contain carbon black from the decomposition of heat-resistant dibutyl dinitrotoluene and dibutyl phthalate. Then, part of carbon black reacts endothermically with CO₂ and H₂O, leading to a decrease in temperature, which for the first sample is nevertheless 100–140 K higher than the thermodynamic value. For the investigated propellants, the activation energy of the leading reaction is the same as for the previously studied propellants, suggesting a common decomposition kinetics of the condensed phase regardless of the propellant composition. However, a uniform dependence of the burning rate on surface temperature is not observed. For low calorific value propellants, the surface temperatures are close to those for propellant N although their burning rate is significantly (2–2.2 times) lower. The causes of this fact are considered.     

Effects of crosslinking degree and carbon nanotubes as filler on composites based on glycidyl azide polymer and propargyl‐terminated polyether for potential solid propellant application

Triazole crosslinked polymers were prepared by reacting glycidyl azide polymer (GAP) with the propargyl ‐ terminated poly(tetramethylene oxide) (PTMP) at different molar ratios of azide versus alkyne. Based on the optimum mechanical properties of the GAP/PTMP ‐ 2.5, a series of GAP/PTMP nanocomposites reinforced by either multi ‐ walled carbon nanotubes (MWCNTs) or carboxy ‐ functionalized multiwalled carbon nanotubes (MWCNTs ‐ COOH) were prepared with different mass ratios. The glass transition temperatures (T_{g, PTMP}) assigned to PTMP of the GAP/PTMP composites almost kept at a constant range when the molar ratio of azide versus alkyne was from 1.0 to 2.5. When the loading MWCNTs was 1.0 wt %, the tensile strength and elongation at break achieved a maximum of 1.77 MPa and 36.3%, respectively. The nanocomposites with nearly similar T_{g, PTMP} indicated no phase separation in the crosslinked polymers. The results revealed that the improved properties of GAP ‐ based materials could be achieved by changing the molar ratio of azide versus alkyne and the nanofillers content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45359.     

Combustion of Energetic Fuel for Ducted Rockets (I)

Energetic solid fuels composed of modified GAP (glycidyl azide polymer) propellants were formulated in order to obtain optimized combustion characteristics for variable flow ducted rockets. Burning rate in a primary combustor and the combustion efficiency in a secondary combustor were studied and evaluated as a function of the mixture ration of fuel and air. The energetic fuels consisting of – N₃ groups in its chemical structure burned very rapidly even though the combustion temperature was low when compared with conventional solid propellants for rockets. The pressure exponent of the burning rate was optimized to gain wide range of mass generation rate. The combustion gases generated in the primary combustor burned very efficiently in a secondary combustor. The effective specific impulse of the ducted rockets was obtained to be about 780 s.