فصلنامه مواد پر انرژی
سال دوم شماره 1 (پیاپی 3، بهار و تابستان 1386)

Gelled propellants are improved propellants that can be considered as the final extension of liquid propellants. High specific impulse, good density, a safety better than that of both solid and liquid propellants and thrust management ability are some of the advantages of these propellants compared with common solid and liquid propellants. In early decades, an extensive research has been carried out on making, quality control, combustion and application of these propellants. Gelled propellants can be used in air breathing systems, pilot seat ejection systems, smart propulsion missiles, advanced launch-vehicle boosters, etc. In this research a review of the papers on making gelled propellants was carried out, on the basis of which,the basic properties and characteristics of gelled propellants are described. Then methods for making important gel fuels and oxidizers such as, hydrazine, mono methyl hydrazine (MMH), unsymmetrical dimethyl hydrazine (UDMH), kerosene, inhibited red fuming nitric acid (IRFNA) and nitrogen tetroxide are presented. Next gelled simulants, their applications and preparation methods as a background for making main gelled propellants are described. In order to study the possibility of making MC-UDMH gelled propellants, MC-H2O gelled simulant was made in the laboratory and the rheological behavior of this simulant was investigated. Results showed that the prepared MC-H2O gel has good rheological behavior and can be used as a simulant for UDMH gelled propellants.

Because of their excellent properties such as extremely high hardness, wear resistance, low specific weight, high cross section for neutron absorption and resistance to chemical attacks, boron carbide based ceramics have great potential for industrial applications such as armor sheets, rocket nozzles, cutting tools, high temperature resistant coating, neutron-absorbing materials, etc. In spite of its unique properties, boron carbide has some disadvantages like relatively low strength (200-400MPa), low sinterability and low fracture toughness which have restricted its applications. Due to the presence of strong covalent bond and low diffusion rate, densification of boron carbide above 80% of theoretical density is very difficult. To reduce these problems, a number of secondary phases were added to B4C as sintering aids. It this paper, the effect of SiB6 additive on the sintering behavior and mechanical properties of boron carbide was investigated. It was found that the addition of 0-10% of SiB6 to B4C led to a remarkable improvement in the sinterability and density of boron carbide. The maximum theoretical density of 98% was obtained by 5% SiB6 addition. The mechanical properties such as microhardness, bending strength and fracture toughness were also increased with SiB6 increasing up to 5%. As the amount of SiB6 was increased further, the mechanical properties were reduced.

Extensive experimental tests have been carried out in order to investigate the behavior of Impulse meter (Ballistic Pendulum) subjected to blast loading. Explosives were situated at a given stand-off distance in front of Impulse meter plates, which were attached to the bob of the Impulse meter. Using these test set-ups, the maximum swing angle of the plates of Impulse meter after each test was used to calculate the energy and impulse to be transfer from the blast loading. Tests were carried out by varying the plate and charge mass as well as the stand-off distance. In order to investigate impulse phenomenon, an analytical solution based on shock wave theory and dynamic equations was proposed to describe the behavior of pendulum plates swing angle under blast loading. Finally, experimental results were compared with theoretical results.

The design of future weapons systems requires the use of explosive and propellant formulations having enhanced performance (energy output) and reduced vulnerability during storage and transportation. Apart from the additional energy of the azido group containing compounds, they are also interesting because of their high gas production rate (nitrogen release). This can increase the burning rate and intensify the effect of the blast waves of high explosives.In this article, general methods of preparation of energetic azide compounds (II) from cellulose or nitrocellulose (I) and the experimental method of preparation of azidodeoxycellulose nitrate from nitrocellulose, metal azide in aprotic solvents have been discussed. The presence of azido groups and the enhancement of nitrogen percent were confirmed by IR spectroscopy and elemental analysis. Heat of explosion and the value of gases were measured by calorimetry and gasometry.

Octogen or HMX is one of the most powerful explosives which produced in large scale. Crystallization is one of the most critical steps in production of HMX. This paper is related to an invention to produce crystalline HMX with 1 micron average particle size, when the particle size of explosive reaches the grade of sub-micron, it impact sensitivity reduces sharply. In this research all affecting parameters such as solvent and antisolvent, mixing speed, concentration are optimized. Easy to adjust parameters affecting on particle size, short operation time are the main special characteristics of this method. Other advantages are easy to nucleation, continually super saturation condition during particle growth and improving the crystal defects. In this method ultrafine HMX is produced due to decreasing of HMX solubility with addition of HMX solution to an antisolvent.

Potassium perchlorate is an important energetic material. In this study, the thermal properties of this material were investigated by differential thermal analysis (DTA). The results show that the transition phase and the melting point of KClO4 occur at 305 and 588°C respectively and KClO4 decomposes at a higher temperature the activation energy of KClO4 decomposition was measured by Kissinger type isoconversional method. Activation energy obtains 215kj/mol that has a good agreement with that measured via other methods. It was seen that at a high heating rate of 15°C/min critical temperatures decreased with particle size from nearly 300μm and reached equilibrium temperatures when the particle size was~ 50nm.

To avoid the repetition of experimental tests, the process of explosive forming for two nonhomogenous plates withe plastic deformation was investigated both theoretically and numerically. Then the analytic model was developed based on the principle of energy conservation, obuerving boandary conditions and considering the critical amount of impact and deformation. The maximum deformation of plate and the possibility of rupture were predicted with depending on the mechanical properties of plates. ANSYS and LS-DYNA software were used due to the dynamic nature the loads and the numerical results were compared with the analytic values and a fairly good similarity was obsereved.