جستجوی مقالات مرتبط با کلیدواژه « composite solid propellant » در نشریات گروه « مواد و متالورژی »

Using antioxidants in the composite propellants' formulations is inevitable. These materials are added to the propellant in order to increasing its stability during the storage and maintenance. In this paper, a simple, new and efficient method for the synthesis of some phenolic antioxidants from the reaction of 2-tert-butyl-4-methyl phenol with a variety of aliphatic and aromatic aldehydes in the presence of Lewis acids has been described. Phenolic products have been synthesized in mild, simple and safe method. The products have been characterized by their melting points as well as IR, 1HNMR and 13CNMR spectroscopies. In addition to high purity and high yields of the products, not needing to use of common corrosive, inorganic acids and the surfactant (generally sodium dodecyl sulfate) are as advantages of the present method.

The storage time of propellants is one of the important issues, the determination of which requires a precise analysis of the kinetic parameters of the decomposition reaction. One of the methods of investigating the decomposition reaction and determining the kinetic parameters of the thermal decomposition reaction is the use of thermal analysis. in this thesis, the thermal degradation reaction in a composite solid propellant sample based on PDEGA was investigated at several heating rates 5,10,15○C/min using differential scanning calorimetry (DSC). Then, using the model-free method of Kissinger and Ozawa, the average activation energy was determined at about 136 kJ/mol, then using a vacuum thermal stability test (VST), parameters of pressure and time in 3% degradation were obtained as 0.07563 bar and 91 hours, respectively and finally The shelf life of 38 years was calculated with Arrhenius mathematical equation.

In this research, the effect of dual curing agent TDI:DDI with different ratios on properties such as mechanical strength, elongation percentage, elastic modulus, hardness, burning rate and pressure exponent (n) has been investigated. Dimeryl diisocyanate (DDI) is a diisocyanate with long carbon chain, high molecular weight, low toxicity and low reactivity. In order to investigate the effect of the TDI: DDI double curing agent on propellant properties, five propellant formulations with the same loading rate and R value were produced and the prepared samples were tested for mechanical properties and burning rate. The results of the tensile test on the seventh day of the propellant curing process showed that with the increase in the ratio of DDI to TDI in the propellant formulation, the amount of elongation increases, the tensile strength decreases and the modulus decreases with the passage of time. The results of the burning rate test showed that with the increase in the ratio of DDI to TDI in the propellant formulation, the burning rate decreases. Comparing the propellants with different ratios of dual TDI:DDI curing agents with the propellant that is the only TDI curing agent, shows that as the amount of DDI in the formula increases, the pressure exponent (n) will decrease.

Iron oxide as a burning rate catalyst is commonly used in many of solid composite propellants. As the particle size of this component decreased, the final properties of the propellant change. In this research, effects of using 1 percent by weight of nano hematite iron oxide (α-Fe2O3) on the properties of an HTPB/AP/Al formulation is investigated and is is compared with the properties of same propellant containing micronized iron oxide. Nano Fe2O3 has a rod shape with a diameter of 40 nm and a length of about 150 nm. The test performed on the propellant slurry showed that applying nano particles instead of micronized powder increase the viscosity from 4.1 to 6.3 kp. Tensile strength and hardness of cured sample were also increased (22 and 5%, respectively). While strain was reduced (56 to 45%). This replacement enhanced the burning rate of propellant by an average of about 20%. Also, the pressure index (n) changed from 0.3927 to 0.3517.

Viscosity is one of the important parameters in design and production of composite solid propellants. Propellants with low end of mix (EoM) viscosity and longer pot-life have suitable condition for casting process. Several factors control the rheology behavior of propellants. In some cases, it may be necessary to apply some additives in order to optimize the rheology of the formulation. In this research, the effect of adding 0.013 to 0.029% by weight of maleic anhydride (MA), as a pot-life extender, was investigated on rheological properties of a HTPB/DDI based composite solid propellant containing 88% solid loading. Results showed that the formulation containing 0.025% by weight of MA compared to other samples showed lower EoM viscosity. EoM viscosity enhanced by either increase or decrease in MA concentration related to this formulation. The viscosity of samples decreased due to shear stress and rotational motion of the viscometer spindle until a specific time and then will increase by progress in cure reaction in binder system. Furthermore, viscosity reached to ascendant step in relatively longer time by adding MA concentration. Furthermore, having increased amount of MA, the viscosity increases over a relatively longer period of time.

Hydroxyl terminated polybutadiene (HTPB) is the most commonly used binder in composite solid propellants. However, due to its non-energetic characteristic, it is recognized as a dead weight in practice. Therefore, replacing HTPB with an energetic polymer is essential. In this research,
nitrated hydroxyl terminated polybutadiene resin (NHTPB) with 12.2% nitration rate, in combination with HTPB resin was used as binder . Thus, the HTPB propellant base formulation (HB) was prepared as a reference sample and its physical-mechanical properties, burning rate, and sensitivity were compared with two other cured formulations: the propellant formulation with binder ratio of 5% NHTPB and 95% HTPB (NH5) and the other with binder ratio of 10% NHTPB and 90% HTPB (NH 10). The results showed that, with increasing NHTPB to HTPB ratio from 5% to 10%, Young's modulus, burning rate, impact, and friction sensitivities were increased in comparison to reference propellant. In addition, the cross-linking density, hardness, and tension were decreased

The success of the composite solid propellant motordepends on mechanical propertiesof the propellant grainagainst tensile, compression and shearstressesand intensivechanges in gravity during launch. In this paper, the effect of formulation components and other parameters affecting mechanical properties (tensile strength, elongation and elastic modulus), andtheir effectsAP/Al/HTPB basedcompositesolid propellants have been investigated.The main objective of the paper is to obtain a comprehensive understanding of how to influence and provide a way to improve the mechanical properties of composite solid propellantMicrostructure (cis, trans, vinyl), molecular weight, hydroxyl groups andHTPB pre-polymerfunctionality,type of curing agents,ratio of curing agentsNCOvalueto pre-polymerand chain extenderOH value(NCO / OH), use of plasticizer ,chain extenderand cross-linkingagent,size, shape, distribution and solidloadingare one of the most important parametersaffecting mechanical properties of solid propellant.Investigations showed that changes in the distribution of AP particle size, theratio of curing agentsNCO valueto pre-polymerand chainextenderOH value(NCO / OH), use of chain extenderand cross-linkingagentare the most operational parameters for upgradethe propellant mechanical properties.

In this work, thermal degradation behavior of a solid composite propellant containing Epoxy/Ammonium perchlorate\Strontium nitrate\Anthracene was studied by simultaneous thrmogravimetric analysis and differential scanning calorimetry under dynamic nitrogen atmosphere at different heating rates. Variation curves of the thermal degradation activation energy of Epoxy\Ammonium perchlorate\Strontium nitrate, Epoxy\Ammonium perchlorate\Anthracene and Epoxy\Ammonium perchlorate\Strontium nitrate\Anthracene calculated were evaluated by differential and integral isoconversional methods and AKTS software package. Self-accelerating decomposition temperature and explosion critical temperature of the composites has been determined to evaluate their thermal stability. Thermal degradation activation energy and pre-exponential factor of the composites were determined by Kissinger method. Finally, life-time prediction of the composites was done by AKTS software.

in order to aging study of the compsite solid propellants, usually the changes in propellant properties during warehousing and storage are measured, and then the shelf life of them estimated. In this regard, by applying the common methods based on mechanical tests, chemical and thermal analysis, the propellant properties due to aging and time lapse are measured. In this paper, first we remark to conventional methods such as stress/strain test, and differential scanning calorimetery, differential thermal analysis and thermogravimetric analysis, and then some of new methods and tests including NMR and IR spectroscopy, determination the amount of dilatation, oxygen consumption, the sensitivity (BAM test), crack growth rate, ballistic properties, and microscopic study are presented that by applying these tests, it is possible to measure the changes of propellant properties over the time and realized the aging of compsite solid propellants and predicting their shelf life

By comparing the empirical and predicted performance diagrams of the composite solid propellants, it appears that there is a discrepancy between these two graphs .This deviation has been attributed to spatial burning rate variation which is related to burning rate fluctuation or hump effect. The most important reasons for this spatial burning rate variation are casting process. In order to approve the effects of propellant flow during casting, on burning rate, the ballistic model include measuring burning rate of casted sample based on flow analysis may be used. In this paper, there are two assumptions which affect the burning rate deviation, the first one is based on the influence of oxidizer orientation on linear burning rate and the second one is based on the effect of casting method and slurry flow line on burning rate deviation and local burning behavior of propellant in grain. Hump effect is related to the spatial variation in burning rate which is result of rheology process of propellant slurry.

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.

Concentrated suspension of binders in composite propellant causes a complex phenomena so that controlling of rheology properties is difficult due to high percentage of fillers. Composite solid propellant contains paste suspension of mixtures of different components, e.g. oxidizer, fuel and binder. Increasing the percentage of solid phase without increment of viscosity is an important subject in the production of solid propellant. This problem can be solved using two different particle sizes distribution. Five samples of composite solid propellants on the basis of hydroxyl terminated polybutadiene (HTPB) with 85% of solid phase containing dual sizes of ammonium perchlorate (AP) have been prepared. These samples have different coarse/fine ratios between 80/20 to 60/40. It was found that optimum temperature for casting of propellant is greater than 40C. The best ratio for obtaining the least viscosity is 70/30 coarse/fine ratio.

Investigation shows that the some complex and expanded parameters are effective on the burning rate. In this paper we evaluate the effect of particles dispersion, size of AP particle, the size of Al particles, Fe2O3, viscosity, shape factor, the size of mixer and the mechanical parameters such as tensile and stress on the burning rate. These studies show that the decrease of AP particles, size distribution, using nano-size Al particles, decreasing the mixer size and adding burning rate catalysts such as Fe2O3 can increase the burning rate of composite propellant. Also loaded stress and strain can increase this parameter.

The formulation of the composite propellant is constituted of solid particles of (ammonium perchlorate) as well as metal fuel such as aluminum particles which are all dispersed homogenously within the Binder matrix. The availability of these solid particles affects the combustion mechanism of the composite propellant and causes the betterment in the performance parameters of rocket such as: increasing in specific impulse and burning time. The very accentuation of this paper is upon the acceleration effect and the derived phenomena of its (including agglomeration, pit formation by means of solid particles within propellant matrix, heat feedback, heat transferring -made of agglomerates- unto the surface of propellant which is being burnt) on the combustion mechanism of composite solid fuels which is conducive to increase in the burning rate of propellant. The rest of the paper is devoted to effects of miscellanies of factors such as pressure, static burning rate, and Al content upon increasing the burning rate of propellant.