Abstract:
Oxidizers are the key ingredients used in the propellants. Ammonium Nitrate (AN) is cheap, easily available and vital component especially in the fields of explosives and agriculture. It is being used widely as an oxidizer in the propellants and as fertilizers. However, the key element of propellants is limiting its use especially in the rocket motors because of its solid state phase transition at 32°C coupled with formation of cracks leading to volumetric changes. Moreover, it is dangerous when exposed to storage conditions. Number of experiments has been carried out for the phase stabilization incorporating different phase stabilizers in the propellants composition including metal oxides. Nickel oxide being one such ingredient was incorporated as phase stabilizer.
This study investigates thermal and kinetic studies of raw ammonium nitrate and the effect of addition of nickel oxide employing simultaneous thermal analysis technique. Thermal behavior of individual components and mixture were analyzed by making use of Thermogravimetry and Differential Thermal Analysis (TG/DTA). The kinetics are calculated by using Horowitz and Metzger method. Whereas, SEM analysis of the mixture containing raw ammonium nitrate and nickel oxide was carried out to ascertain the physical microstructure, porosity, mixing and the particle size range. The structure was found mesoporous and it does not have any significant effect on the oxidizing potential.
During the course of experiments, it was found that addition of 0.25% nickel oxide in raw ammonium nitrate shifted phase transformation temperature from 32oC to 56oC. The second peak at 84.2oC shifted to 125.2oC, hence another phase transformation. It is pertinent to mention that increase in the percentage of nickel oxide has also increased the decomposition temperature which was observed in TG profiles. Moreover, addition of nickel oxide in raw ammonium nitrate has a profound effect on the activation energy which has increased manifolds in case of mixture containing 0.25% nickel oxide. The experiments were also performed with higher percentages and similar changes were observed as for the mixture containing 0.25% nickel oxide. The upshot of the present work is that 0.25% addition of nickel oxide in ammonium nitrate based composite propellants renders them safe under thermal stability limits for storage at -40oC to +55oC (55oC being the highest temperature generally reached in Pakistan) for subsequent safe functioning of the motor on firing.
