جستجوی مقالات مرتبط با کلیدواژه « پیشرانه » در نشریات گروه « مواد و متالورژی »

The design and synthesis of energetic ionic liquids has provided a new method in the development of a new type of hypergolic propellants. These compounds, having characteristics such as low vapor pressure, high chemical and thermal stability,wide range of liquidity and having environmental requirements, are proposed as fuel substitutes in common liquid propellants that mainly contain hydrazine and its toxic derivatives. In this research, the synthesis of some new symmetric and asymmetric dimidazolium ionic liquids based on the energetic nitrocyanamide anion has been investigated. 1HNMR and FT-IR spectroscopic methods have been used to identify and characterize the synthesized ionic liquids. The viscosity analysis data of these ionic liquids show that in terms of viscosity, they can be used as hypergolic fuels in propellants (viscosity less than 63cP). Among the synthesized energetic ionic liquids, 1-(2-propenyl)-1’-methyl-3,3’-(1,3-propan-di-yl)diimidazolium dinitrocyanamide has the lowest viscosity (42cP). The thermal gravimetric analysis (TGA) of this compound shows its high thermal stability (around 250ºC). Differential scanning calorimetry (DSC) analysis of this material showed a good agreement with TGA analysis data. In addition, the hypergolic properties of the synthesized ionic liquids were investigated in the presence of concentrated nitric acid and it was shown that upon contact with the oxidizer, these materials ignited spontaneously (ID<48ms).

Polycaprolactone is a polyester binder that has a polar structure and is compatible with polar plasticizer. Also, due to ester structure, oxygen balance of this polymer is more suitable than HTPB, therefore, by combining these two binders as a copolymer, the disadvantages of HTPB are eliminated and its advantages are preserved. In this research work, triblock copolymer of PCL-HTPB-PCL is made by ring opening polymerization of caprolactone by HTPB (1000 g.mol -1 ) molecular weight as a initiator and 69% yield. This copolymer was characterized by (FT-IR) and 1H-NMR spectroscopy. The investigation of the curing conditions showed that the copolymer with IPDI and N100 isocyanate in a ratio of 80: 20 were properly cured. Finally, the compatibility of cured copolymer with high energy plasticizers was investigated using swelling test and it was found that PCL-HTPB-PCL copolymer is more compatible with Bu-NENA and TEGDN plasticizers than BTTN and TMETN.

Binders are one of the most key components of solid composite propellants used in the military and space research industries. In present research, a PPG-PTHF-PPG triblock copolymer was synthesized as a binder using polytetrahydrofuran as an initiator and propylene oxide monomer through the cationic ring-opening mechanism with suitable molecular weight and high efficiency. The synthesized copolymer was investigated and identified with tools such as IR, NMR, GPC, and DSC. In the next, the optimal conditions for copolymer synthesis, including the choice of solvent type, the amount of solvent and catalyst, and the duration of the reaction, were investigated. After taking steps of copolymer synthesis, the curing of the copolymer was tested by different isocyanate curing agents, so the optimal amounts of curing catalyst, chain extender, and R ( mixture of N-100 and IPDI isocyanate agents) were obtained. The mechanical properties of elastomers were also evaluated through preparing dumbbell-shaped elastomers, which showed an 80% increase in elongation compared to the HTPB sample.

Cracking is the breaking of bonds in a part of the propellant polymer due to the existing stresses that change the structure of the propellant polymer and they are classified into two general categories: macrocrack and microcrack. The service life of rocket engines is largely a function of the mechanical properties of the solid rocket propellant, the aging characteristics of the rocket propulsion, the grain design, and the environmental conditions that it undergoes during operation. The mechanical properties of solid rocket propellants are critical to the good performance of rocket engines. Increased combustion of propellant grains due to the presence of undesirable cracks and cavities can cause improper performance. This article reviews the causes of cracks due to heat stress, mechanical fatigue, humidity, temperature, corrosion, light, as well as crack detection methods such as radiography, mechanical waves, microscopy and infrared waves

the most part of the propellants,containig the oxidant and ammonium perchlorate is the most applicable oxidizer in composite solid propellants. Therefore, its thermal decomposition and safety properties have been a great effect on the propellants properties. The using of polymeric additives is one of the proper methods for improving the thermal and immunological properties of ammonium perchlorate. The types of additive are usually selected based on the applicable purpose. This paper reviews, the effects of polymeric additives to improve the sensitivity, the increase of thermal and chemical stability, and also the prevention of ammonium perchlorate particle agglomeration.

Chain extenders are diols or small diamines that enter the polyurethane hard parts through chemical reactions. N, N -bis(2- hydroxypropyl) aniline (Isonol C100) and bis (2-hydroxyethyl) aniline as the most important chain-extender in the curing of propellant solids composite, stabilizers and plasticizers in the propellants system double and also as a co-plasticizers in ethyl cellulose. It can be said that the most important application of this compounds is in polyurethanes. In the synthesis of rubber-like polyurethanes (sticky), it is used to strengthen, and extend the length of the chain. In the structure of these compounds, there is a benzene ring that increases the strength of the product. On the other hand, there is also a third type of amine in the skeleton, which increases the mechanical properties of the polyurethane. In this study will investigate the synthesis methods of bis (2-hydroxypropyl) aniline (Isonol C100) and bis (2-hydroxyethyl) aniline. Many of the methods have used aniline, ethylene oxide or 2-chloroethanol to synthesize bis (2-hydroxyethyl) aniline and propylene oxide and aniline to synthesize Isonol C100.

Several parameters affect the rheological and mechanical properties of solid composite propellants. Among them, the molar ratio of isocyanate (NCO) to hydroxyl (OH) groups (i.e. R value) is one of the important factors. In this research, the effects of changing the weight ratio of dimeryl diisocyanate (DDI) curing agent related to hydroxyl terminated polybutadiene on different properties of a HTPB based solid composite propellant such as end of mix viscosity, time depending behavior of viscosity, tensile stress, elongation, elastic modulus and hardness is investigated. For this purpose, five propellant formulations were prepared with various R value in the range of 0.755 to 0.815. Results showed that as the R value increased, end of mix viscosity is reduced at the first due to the wetting effect resulting from DDI addition and then is increased because of progressing of curing process. Furthermore, the mechanical properties are enhanced by increasing the R value, whereas elongation at maximum stress is reduced about 20%.

2- Azido N, N-Dimethyl Ethane-1-Amine, well-known as a DMAZ, is considered as a new green liquid fuel and a good alternative to hydrazine fuels because of its high performance while being non-carcinogenic. But no DMAZ energetic complex has been synthesized and reported yet. In this study, a new energetic complex of copper(II) nitrate and DMAZ ligand was synthesized for the purpose of increasing the density of this ligand by metal-coordinating at two nano and bulk scales (with the medium particle size, 54.6 nanometers, and 45.33 micrometers, respectively). These synthesized complexes were characterized by FT-IR, UV-Vis, and fluorescence spectroscopy methods and the molar ligand-to-metal ratio was obtained by Job and Mole fraction methods. Their thermal decomposition behaviour have also been investigated. The results showed that changes in particle size led to changes in thermal behavior and energy released from these complexes (480 J/gr).

Considering the role of plasticizers in the processability of solidpropellants, recentlymany researcheshave been carried out on the development and investigation of the role of these plasticizersonthe improvement of the propellants’ properties. These compounds are used in the formulation of double base and composite propellants to improve processability during propellantpreparation and thus to improve the mechanical properties of propellant. Energetic plasticizers, in addition to improving mechanical properties, increase energy and improve the explosive performance of the propellant. Although a lot of studies have been carried out in the field of plasticizers in recent years, but due to the complex structure of solid propellantsand the various mechanismsofplasticization, the need to design new plasticizers with high energy and the ability to interact with various polymeric structuresof propellantis tangible. Recently, ionic liquids and energeticionicliquids have been studied for this purpose. Ionic liquids with good properties such as structural designability, low vapor pressure, miscibility with various compounds, and the ability to make covalent bond with polymer, have the requirementsas desirable alternatives forcommonplasticizers.

Use of energetic plasticizer, N-Butyl-N-(2-Nitroxyethyl) Nitramine (BuNENA), in the propellants’ formulations, has some advantages such as not migration in the fuel, high thermal stability, low sensitivity of the propellant formulation, improvement in mechanical properties and raising the impulse due to light molecular weight of combustion gases. In this study two acidic ionic liquids ([(Ph)3P(CH2)4SO3H][PTSA] and [(Ph)3P(CH2)4SO3H][HSO4]) were synthesized, characterized and used in the synthesis of BuNENA energetic plasticizer, as green and reusable catalysts. These catalysts have efficiently catalyzed the synthesis reaction of BuNENA via the nitration of n-butyl ethanol amine in the presence of nitric acid 65% or nitric acid 100%. Use of these ionic liquids in the synthesis of BuNENA has some benefits such as high yield of the product, short reaction time, use of green, non corrosive, non toxic and reusable catalyst and finally economic procedure.

Determinations of lifetime for propellants require exact evaluation of thermal decomposition kinetic parameters. Thermal analysis is one of the tools for investigation of thermal decomposition reaction and its kinetic parameters. In this article, thermal decomposition process for a single-base propellant is investigated under 1, 2 and 3 K/min heating rates. Then by using Friedman isoconversionalmodel free method, average activation energy is determined about 185 kJ/mol. In continuous by using Ma’lek combined kinetic analysis and plotting master curves, kinetic model (f(α)) and pre-exponential factor (A) are determined. Results are: f (α) = (1-α) 2.2, A=2.75×10 s-1. Finally predicted lifetime for 250C and 5% degree of conversion are about 22.4 years.It is necessary to said that all calculation steps from start up to end are programming in MATLAB software.

The purpose of this paper is to review the effect of polymer additives on the final viscosity of PBX slurry and viscosity reduction mechanism. Variables related to the formulation and manufacturing process affects PBX viscosity. PBX viscosity directly affects the process of mixing and charging of these materials and hence it is necessary that the viscosity values to be low in order to facilitate the mixing and casting these materials. In this study, a summary of the performance of polymer additives to reduce viscosity is studied. So the effect of additives on the experimental values of viscosity is investigated. Additives are divided into two groups: The first group contain materials such as lecithin and silane by reducing surface tension binder leading to complete wetting of solid particles and the viscosity decreases. The second group is compounds such as phosphate oxides, aziridines and blocking agents of curing reaction leading to increase pot life and decrease viscosity.

Because of high toxicity of hydrazine and its derivatives, many efforts are conducted to finding alternative for hydrazine in hypergolic fuels which meanwhile can do spontaneous ignition, has a low environment risk. Due to high reducing ability of hydrazine, usage of powerful conducing agents’ idea was interested. These conducting agents required to improvement in order to use as a hypergolic fuel, so considering to low toxicity, environment consistency, high thermal-chemical stability and designable physic-chemical properties, synthesis of aluminum- and boron-based ionic liquids are considered. Aluminum-based ionic liquids aren’t success results as hypergolic fuels and in rare cases are suitable as monopropellant. But boron-based ionic liquids have desirable results and in some cases are better than hydrazine. In this paper, conducted efforts and their results, which done in this course, were briefly investigated.

One of the most important required additives in production of composite solid propellants are bonding agents. These compounds are used in order to increase the adhesion between the polymer resin and the oxidizer and also to enhance the physical and mechanical properties and to improve the solids loading of propellants. In some cases, the bonding agents also play a role as a curing agent by crosslinking with the polymer matrix (resin). Aziridines are used as an intermediate in different industries and one of the compounds that recently has attracted many attentions in order to reduce its production cost. This compoundes are mainly applied in the defence industries as solid fuel missiles. In this study, bonding agents and different methods for synthesis of aziridines as main component of aziridine bonding agents, HX-752 and MAPO, are investigated.

Because of the suitable characteristics such as having desirable burning rate, easily manufacture and high purity and yield, pay attention to Ferrocene compounds as commonly burning rate catalysts of composite propellants. Migration of this compound in during shelf time is their main disadvantage. This process can be caused reduction of propellant efficiency and creation of secondary hazards. Though their migration mechanism is vague, nevertheless various methods are suggested to resolving of this defect, such as adding of active groups and formation of massive compounds or reinforce of intermolecular bonding, polymerization, hyper branching and etc. due to high importance of effective migration on efficiency of composite propellants, in this paper, Ferrocene-based burning rate catalysts are introduced and methods of prevention their migration are investigated briefly.

Propellants are decomposed slowly during storage. So each propellant has useful life time which more than that time propellant is not safe and cannot used. Tracing of propellant stabilizer consumption is one of the important methods for determination of storage life time period of a propellant. In this article by accelerated aging on a double-base propellant and then chemical extraction of stabilizer, Tracing of propellant stabilizer consumption is done. Kinetic models which used are zero order, First order, Second order, NATO method and Bertholet. Then kinetic parameters of aging reaction and storage life time of propellant for 50% consumption of stabilizer by different methods are estimated Finally predicted lifetime for Zero order, First order, Second order, NATO method and Bertholet are 58, 45, 35, 31 and 14 years respectively.

Liquid hydrogen is used as a powerful and efficient propellant in spacecraft industries. This paper first presents the main principles of hydrogen liquefaction. Then, different methods for hydrogen liquefaction, including four general categories: precooled Linde-Hampson process, Claude process, helium-precooled Claude process and liquefaction by small cryo-coolers, are expressed along with their advantages and disadvantages. Considering native technology, the precooled Linde-Hampson process for small scale hydrogen liquefaction has been selected.

Conventional propellants (single base, double base and triple base) due to accidental initiation cause to catastrophic disasters for crews and lose of costly equipments. During recent times, for reducing sensitivity of ammunitions, It have been efforts for development of LOVA propellants. The concept of LOVA gun propellant is evolved by formulation a propellant which is least sensitive to impact friction and heat stimuli and meeting the ballistic requirements satisfactorily. LOVA propellant are developed using a reduced amount of nitric ester (which are highly sensitive constituents).in their propellant formulation as well as, using newer ingredients such as inert binders. In order to replace, nitroglycerine (containing nitric ester) and a part of nitrocellulose, we can use micronized RDX as an energetic factor. In this paper, we have considered formulation, ballistic parameters, mechanical characteristics, process technology, erosion and aging phenomena of this kind of novel propellant.