Ignition and Combustion of Condensed Systems with Energy Fillers

This paper describes the results of an experimental study of ignition and combustion of condensed systems, containing energy fillers, i.e., powders of aluminum, boron, aluminum borides, and titanium. Compositions on a hydrocarbon or active fuel binder with a combined oxidizer (ammonium perchlorate and/or ammonium nitrate) are considered. Thermodynamic estimates for the ballistic characteristics of the compositions under study are given. It is shown that a unit pulse increases by 3.5% with the replacement of aluminum by boron in the compositions considered. It is experimentally determined that the time delay of ignition of boron-containing compositions decreases in conductive and radiant heat transfer and that the stationary burning rate of boron and aluminum boride containing compositions increases. The efficiency of the impact of energy fillers on the characteristics of condensed systems as a function of the composition of a combined oxidizer is determined.     

Some Experiments on Model Composite Solid Propellants

Experiments on two-dimensional model propellants using cylindrical oxidizer (ammonium perchlorate) pellets in a fuel matrix (CTPB) are described. Measurements show that burning rate of AP in the fuel environment is lower than of pure AP. The oxidizer-to-fuel ratio seems to be fuel-rich when the oxidizer particles are imbedded in contact with the fuel and it becomes oxidizer-rich for a non-zero separation between oxidizer particle and the fuel.     

Ammonium Perchlorate,Friend or Foe? Part 1: The Influence of this Oxidizer on the Aging Behavior of Propellant Compositions

Propellants containing nitroglycerine and ammonium perchlorate have been reported to have comparatively shorter shelf lives than analogous energetic materials without this oxidizer. However, investigation into the aging behavior of three compositions containing polyethylene glycol and nitroglycerine revealed that the propellant which included ammonium perchlorate degraded at a slower rate compared with the other materials. It was suggested that ammonium perchlorate might act as an oxygen inhibitor reducing the oxidation rate of the polyethylene glycol binder so decreasing the rate of the propellant decomposition. In addition, at temperatures of 80 °C or lower, ammonium perchlorate initially appears to hinder acid hydrolysis of nitroglycerine which also slows down the degradation of polyethylene glycol based propellant.     

Approximate Method for Calculating the Impact Sensitivity Indices of Solid Explosive Mixtures

An approximate method is proposed to calculate the impact sensitivity indices (critical initiation pressure and critical charge thickness) for solid explosive mixtures (explosive compositions and mixtures of an oxidizer with a fuel). The calculation is based on some model concepts of the physicochemical and explosive properties of reactive mixtures. Test calculations of the sensitivity indices were performed for mixtures of HMX and TNT and mixtures of ammonium perchlorate with polymethylmethacrylate (PMMA) and TNT, and the results are compared with data of laboratory experiments on an impactor.     

Mechanical and burning properties of highly loaded composite propellants

An improvement in the performance of solid rocket motors was achieved by increasing the oxidizer content of HTPB-based solid propellants. To minimize the adverse changes in the mechanical and rheological properties due to the increased amount of hard solid particles in the soft polymeric binder matrix, the optimum combination of the particle sizes and volume fractions of the bimodal ammonium perchlorate and the aluminum powder in the solid load was obtained from the results of testing a series of propellant samples prepared by using ammonium perchlorate in four different average particle sizes, 9.22, 31.4, 171, and 323 μm. The maximum packing density of solids in the binder matrix was determined by changing the sizes and the volume fractions of fine and coarse ammonium perchlorate at constant solid loading. The average size (10.4 μm) and concentration of aluminum powder used as metallic fuel were maintained constant for ballistic requirements. Optimum sizes and fine-to-coarse ratio of ammonium perchlorate particles were determined to be at mean diameters of 31.4 and 323 μm and fine-to-coarse ratio of 35/65. Solid content of the propellant was then increased from 75 to 85.6% by volume by using the predetermined optimum sizes and fine to coarse ratio of ammonium perchlorate. Mechanical properties of the propellant samples were measured by using an Instron tester with a crosshead speed of 50 mm/min at 25°C. The effect of oxidizer content and fine-to-coarse ratio of oxidizer on the burning rate of the propellant was also investigated by using a strand burner at various pressures. From experiments in which the size and the fine-to-coarse ratio of ammonium perchlorate were changed at constant solid loading, a minimum value of initial modulus was obtained for each fine-to-coarse ratio, indicating that the solids packing fraction is maximum at this ratio. The tensile strength and the burning rate increase, while the elongation at maximum stress decreases with increasing fine-to-coarse ratio of ammonium perchlorate. Experiments in which the total solid loading was increased at constant fine-to-coarse ratio of ammonium perchlorate show that the modulus, the tensile strength and the burning rate increase, while the elongation at maximum stress decreases with increasing solid loading. Propellants having solid loading of up to 82% exhibit acceptable mechanical properties and improved burning properties suitable for rocket applications. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1457–1464, 1998     

二硝酰胺铵在火炸药中的应用

综述了新一代氧化剂二硝酰胺铵盐(ADN)在固体推进剂、炸药及发射药中的应用研究进展,认为ADN是替代推进剂中过氯酸铵氧化剂的最佳侯选物。提出了优化工艺、降低成本、改进ADN稳定化和球形化技术以及ADN应用方面的建议。     

Burning Behavior of Composite Solid Propellant containing porous ammonium perchlorate

A pilot scale fluidized bed process was developed for preparing porous ammonium perchlorate (PAP) in various particle sizes. The oxidizer, ammonium perchlorate (AP), of composite solid propellant was partially replaced by PAP which was obtained by the fluidization process. The burning rate of propellants containing PAP was found to increase as compared with that of propellants without PAP. In the present study, the effects of percentage content and particle size of PAP incorporated in propellant compositions, on the burning rate were investigated. The results showed that the burning rate increases with increasing of PAP content and with decreasing of PAP particle size for trimodal oxidizer propellants.     

Combustion mechanism of RDX and HMX and possibilities of controlling the combustion characteristics of systems based on them

Modeling of the combustion of cyclic nitramines (CNAs) has shown that their combustion proceeds by the same mechanism with the joint effect of the processes in the condensed and gas phases. The combustion characteristics of the pure substances can be changed only at low pressures by using catalysts acting in the condensed phase, and at high pressures, this problem is difficult to solve. The combustion of binary compositions [CNA + fuel (F) and CNA + ammonium perchlorate (AP)] and ternary compositions (AP + CNA + F) is considered. It is shown that the combustion mechanism and characteristics are determined by the chemical interaction and heat exchange between the reactants, which depend on the characteristic particle size in the system.     

Mechanism of combustion catalysis by ferrocene derivatives. 2. Combustion of ammonium perchlorate-Based propellants with ferrocene derivatives

Combustion of mixtures of a narrow fraction of ammonium perchlorate (AP) with hydrocarbon binders and combustion catalysts diethylferrocene and 1,1′-bis(dimethyloctyloxysilyl)ferrocene, as well as nano-sized Fe₂O₃ is studied. It is shown that the efficiency of ferrocene compounds from the viewpoint of increasing the burning rate depends on the oxidizer/fuel ratio in the propellant and on the place of the leading reaction of combustion. In composites with a high oxidizer/fuel ratio whose combustion follows the gas-phase model, the catalyst efficiency is rather low. In systems with a low oxidizer/fuel ratio where the contribution of condensed-phase reactions to the burning rate of the system is rather large, the catalyst efficiency is noticeably greater, and it is directly related to the possibility of formation of a soot skeleton during combustion. The close values of the catalytic activity of ferrocenes and Fe₂O₃ in the case of their small concentrations in such compositions testify that the main contribution to the increase in the propellant burning rate is made by Fe₂O₃ formed due to rapid oxidation of ferrocene on the AP surface and accumulated on the soot skeleton. Thermocouple measurements of propellants with a low oxidizer/fuel ratio are performed, and it is shown that the temperature of their surface is determined by plasticizer evaporation. A phenomenological model of combustion of the examined propellants is proposed.     

Reducing Agglomeration of Ammonium Perchlorate Using Activated Charcoal

Ammonium perchlorate is the most widely employed oxidizer for composite solid propellants. When exposed to atmosphere, it absorbs moisture and agglomerates. It is usually vacuum dried in order to avoid this agglomeration. When ammonium perchlorate that has been exposed to atmosphere for a certain period of time, is used in making a composite solid propellant, the burning rate is different because of the change in particle size distribution due to its agglomeration. This change in burning rate will change the thrust‐time profile from that of what it is designed for. As one goes to a finer ammonium perchlorate particle size this problem becomes more evident. Experimental studies aimed at reducing the agglomeration of ammonium perchlorate by coating it with activated charcoal. Ammonium perchlorate coated with 1 % activated charcoal showed almost no agglomeration, even when the particle size of ammonium perchlorate is approx. 1 μm. The burning rates also remained unchanged when ammonium perchlorate coated with 1 % activated charcoal was employed in propellant composition, after it has been exposed to the atmosphere for a period of 1 h.     

Pyrolysis and thermo‐oxidative degradation of polycyclopentadiene

Thermal degradation of polycyclopentadiene polymer (PCPD) was investigated by pyrolysis gas chromatography (PGC) in the temperature range of 500–950°C. The nature and composition of the pyrolyzates at various temperatures are presented, and the mechanism of degradation is explained. The activation energy of decomposition (E_a) was obtained from an Arrhenius‐type plot using the concentration of the product ethylene (C₂) at different pyrolysis temperatures and the value was found to be 138 kJ mol⁻¹. Thermo‐oxidative degradation of PCPD in the presence of ammonium perchlorate (AP), the most commonly used oxidizer for polymeric fuel binders, was studied at a pyrolysis temperature of 700°C. The compositions of the products with varying amounts of AP are given, and the exothermicity of oxidative decomposition reactions is evaluated. The energetics of the degradation processes are compared with those of polybutadiene type polymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 635–641, 2000     

Ion Chromatographic Analysis of Ammonium Dinitramide–Oxidizer for Propellant and Pyrotechnic Applications

Analysis of ammonium dinitramide (ADN), the advance rocket propellant oxidizer, in pure form as well as in mixtures was carried out by ion chromatography (IC). The purity of ammonium dinitramide was directly determined by estimating the dinitramide ions and indirectly by estimating the impurities. Both methods gave results comparable with those determined by Differential Scanning Calorimetry and UV spectroscopy. The chemical composition of ADN in mixtures containing nitrate, chromate, chlorate, perchlorate, and thiocyanate ions was quantitatively estimated in the same solution without any interferences or prior separation of analyte ions. The newly developed ion chromatographic methods for the analysis of ADN are simple and fast with good accuracy and precision when compared to other analytical techniques. The IC methods are found to be highly suitable for quality control analysis of ADN containing compositions and for the online process monitoring of the formation of ADN in the reaction mixture.     

Combustion of model compositions based on furazanotetrazine dioxide and dinitrodiazapentane. I. Binary systems

The combustion behavior of high-energy systems based on furazano[3,4-e]tetrazine-4,6-dioxide and 2,4-dinitro-2,4-diazapentane with metal and energetic additives (Al, AlH₃ ammonium perchlorate, ammonium dinitramide, and HMX) has been studied. The burning rate, combustion stability, and characteristic combustion temperatures with pressure variation are estimated. It is found that there is a critical burning rate above which a deflagration-to-explosion transition occurs. The critical conditions depend on the formulation of the compositions.     

An experimental study on the hypergolic ignition of hydrogen peroxide and ethanolamine

This paper presents the hypergolic ignition test results of a potential environmentally friendly liquid propellant consisting of hydrogen peroxide oxidizer (with a concentration of 85%) and ethanolamine fuel for use in rocket engines. Open cup drop tests were conducted to study the effect of amount of metal salt catalyst in fuel and the initial temperatures of fuel and oxidizer on the ignition delay time. To test the hypergolic ignition of bipropellant formulation in a real rocket engine environment, a pressure-fed liquid propellant rocket engine (LPRE) was designed and developed. During the tests it was found that the amount of catalyst and the initial temperature of the fuel had a significant effect on the ignition delay of hypergolic bipropellant. However, the oxidizer temperature seemed to have almost no affect on the ignition delay. There was also significant difference between the ignition delay times from open cup tests and those from rocket engine static firings.     

Thermochemical Calculations for Potassium Ferrate(VI), K2FeO4, as a Green Oxidizer in Pyrotechnic Formulations

This paper documents the first‐time assessment of a novel oxidizer, potassium ferrate(VI), as an alternative to perchlorate and hazardous metal‐containing oxidizers in energetic formulations, using thermochemical calculations. Calculations were performed for several different types of pyrotechnic formulations using the NASA Chemical Equilibria with Applications (NASA‐CEA) program. Formulations used in devices including smokes, illuminants, signals, igniters, delays, and flashes were evaluated to determine the feasibility of using potassium ferrate(VI) as an alternative oxidizer. The calculated adiabatic flame temperatures and equilibrium combustion products for the proposed formulations were compared to those of common baseline formulations for different pyrotechnic applications to determine the likelihood of functional success of potassium ferrate(VI)‐based formulations. Based on these initial data, it is highly probable that formulations incorporating potassium ferrate(VI) will result in reactive compositions for a variety of pyrotechnic applications. This material could address environmental concerns about perchlorate and heavy metal contamination by offering an environmentally‐friendly alternative oxidizer.     

铝镁贫氧推进剂的点火性能

为研究镁铝富燃料固体推进剂组分对点火性能的影响,采用改进的靶线法燃速测试系统对多种含镁铝富燃料固体推进剂在常压和加压下进行了通电金属丝点火性能的对比实验。被测试推进剂的镁铝合金含量为20%～40%,或者同时含镁铝合金及硼,氧化剂含量为30%～53%。实验表明,在固定外界输入热源的情况下,推进剂的点火性能主要与氧化剂含量和粒度有关;金属的含量和种类也有一定的影响;催化剂对点火延迟时间影响很小;压强对此种点火方式几乎无影响。该点火延迟测试方法简单易行,并具有一定的可靠度,适于配方调试。     

Combustion of Propellants with Ammonium Dinitramide

This paper reports a series of experiments involving ammonium dinitramide (ADN), a new energetic oxidizer of potential use in composite solid propellants. The experiments include (a) self‐deflagration of pressed pellets of ADN; (b) combustion of sandwiches with ADN laminae on both sides of a binder lamina that is either “pure” or filled with particulate oxidizer and other additives; and, (c) combustion of propellants with a bimodal oxidizer size distribution, wherein, combustion of coarse ADN and fine AP (ammonium perchlorate) and vice versa were used, in addition to mixtures of coarse ADN and AP, fine ADN and AP, and all‐ADN or all‐AP formulations.     

Effect of the physical state of the activators on the combustion of composite rocket propellants. I. The applied catalysts

The effects on the burning and thermal decomposition of composite rocket propellants, based on ammonium perchlorate and butyl rubber, of oxide coated catalysts applied to tge surface of the ammonium perchlorate crystals and introduced into the propellant in the form of a colloidal suspension are investigated. It is shown that the possibility of changing the burning rate by means of applying the catalyst on the oxidizer crystal surface is determined by the chemical nature, the content of the compounds deposited on the oxidizer surface, and by the structure of the coating formed on the ammonium perchlorate surface. Excluding the agglomeration of the catalytic additives using the developed methods, the variation in their dispersivity and the nature of localization in the propellant are the indicators of the propellant's performance efficiency within the region of small additive concentrations (up to 0.5%) in the propellant. Scientific Research Institute for Physicochemical Problems, Belorus State Univ., 220050 Minsk. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 6, pp. 82–88, November–December, 1995.     

Microwave sintering of mullite–cordierite precursors prepared from solution combustion synthesis

Mullite–cordierite composite was synthesized using the solution combustion synthesis method and glycine as a fuel and aluminum nitrate, magnesium nitrate and colloidal silica as the reagents. The effect of fuel to oxidizer ratio on the combustion behavior, as well as chemical composition and morphology of the formed powders was investigated. All synthesized powders were amorphous with submicron particle size. It was found that the change of fuel to oxidizer ratio had no effect on synthesis of this composite without heat treatment. The smallest particle size of composite powder was obtained as 302 nm for ratio less than 1 (rich of fuel). Mullite, cordierite and spinel were detected after microwave heating at 1200 and 1400 °C. Mullite and cordierite were detected as the only crystalline phases when the stoichiometric ratio of fuel to oxidizer was chosen and this composite obtained the highest density of 2.61 g/cm³.     

Is ammonium perchlorate in composite solid propellant under strain?

Thermal decomposition of ammonium perchlorate-polystyrene propellant as a function of oxidizer loading has been found to behave in a fashion analogous to the thermal decomposition of ammonium perchlorate as a function of precompression pressure. It has been argued that the above behaviour of the propellant is due to the strain caused by the binder film on ammonium perchlorate contained in the propellant matrix. The presence of strain has been demonstrated independently by x-ray diffraction peak and infrared peak broadening and strain energy measurements.