Solid Propellants for Rockets: A Methodology to Obtain High Purity Kno3 From an Inexpensive Source

Abstract

Solid propellants are mainly used in rocket propulsion applications. The performance of a rocket is directly affected by the design of the solid propellant used. The presence of impurities in the propellant formulation can reduce the average thrust, specific impulse and characteristic velocity of a rocket. Oxidizers are the main compounds in propellants formulation, which produce the high energy on combustion. One the most commonly used oxidizers in amateur rocketry is potassium nitrate. KNO 3 is normally used because of its good characteristics that include compatibility with others ingredients and availability at low cost in fertilizer formulation. The main objective of this work is to propose a methodology to obtain higher purity potassium nitrate from a fertilizer, an available and inexpensive source that can be used as oxidizer in a solid rocket propellant formulation. The KNO 3 crystals were obtained by recrystallization process using a commercial fertilizer. The properties of purified fertilizer were compared with the properties of KNO 3 analytical. The fertilizer, purified and analytical grade KNO 3 samples were evaluated by means of morphology, pH of saturated solution, Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC). The results demonstrated that recrystallization process effectively remove impurities from the fertilizer. The purified KNO 3 crystals were optically transparent with a planar shape, similar to higher purity KNO 3. The FTIR and DSC results showed that some impurities, such as, sulfur and alkaline compounds were removed after recrystallization and the purified KNO 3 presented a similar behavior than higher purity KNO 3. The recrystallization process used in this work can successfully used to obtain KNO 3 crystals with high purity that can be used as oxidizer in solid propellants for rockets.