Análise de bates propelentes KNSU produzidos utilizando compactação a frio e sinterização

Abstract

Solid propellants consist of a mixture of reducing and oxidizing compounds. The development of new propellants takes place primarily on a laboratory scale, with analysis of the repeatability of the manufacturing process and energy efficiency of the proposed formulations. The main characteristics for propellants used in experimental rocket competitions are: resource availability; ease of fabrication; repeatability; and secure processes. Such characteristics are found in the KNSU propellant, produced from potassium nitrate and sucrose. The production of this propellant is divided into three stages: milling; melting of the grains; and drying/compacting. The grain melting step is seen as the most critical, due to the low repeatability of the process, difficulty in molding into the desired shape (due to the high viscosity) and safety factors. Sintering is the process of heating below the melting temperature a certain compacted material, a technique widely used to produce materials with high density and better mechanical properties. The present work aims to study the replacement of the grain melting step by a compacted powder sintering step, analyzing different sintering times and temperatures, mechanical characteristics, process repeatability and the hygroscopicity of the sintered propellant. This production process obtained an average standard deviation of 0.013 g/cm3 in the 72 samples produced. Mechanical tests of stress-strain and diametrical compression were performed. For the first, the samples were submitted to a gradual temperature scale at the beginning of the sintering. In the second test, the sintering process started already at the desired temperature. In the stress-strain test, a maximum stress 589% higher was obtained with sintering at 137 °C and 4.5 hours. In the diametrical compression test, samples sintered for 1.5 hours and 110 °C supported 40% more stress. It is supposed that the lower performance of the samples from the second test is due to the change in the initial sintering process.As for hygroscopicity, there were no significant changes between the compacted powder and the sintered compacted powder.