| The ultrahigh speed torpedo is a new concept in underwater weaponry and it is currently an active area of research. These types of weapons utilize high energy density reaction between metal and water to provide them with superior speed and increased range. However, the high metal content adversely affects the ignition and combustion characteristics of the propellant which are the most important properties of the propellant. This work focuses on the modification of aluminium and magnesium powders and their application in metal/water propellants.As a first step in this research, magnesium pellets were modified using vapour and liquid deposition and the technics to improve the reactivity of magnesium with water, as well as the shelf life. The structure of the modified magnesium powder was characterized utilizing scanning electron microscope. It was found that the modified magnesium power had three distinct layers. The modification led to improvement in the control of the magnesium and water reactions under certain conditions. The modified magnesium pellets had little effect on the energy density of the reaction but increased the hydrogen generating ability by 2.7 times.The second objective of this project is to improve the ignition and combustion properties of the propellant by incorporating aluminium powder. Aluminium flakes, as well as aluminium/magnesium alloy with variable proportions of magnesium were obtained from spherical aluminium powder using a new type of mill. The modification of these metal powders decreased the ignition temperature of the propellant and improved the oxidation performance. The analysis of the various powders using DSC-TG showed that the weight of the spherical aluminium powder was increased by 23.3% due to the oxidation. Under same oxidation conditions the weight of superfine aluminium flakes and Al/Mg alloy was increased by 44.5% and 60%, respectively.The third outcome of this project was that the modification of the metal powder can affect the thermal decomposition temperature of the propellants. Based on the DSC-TG analysis results, the modification of magnesium by the addition of HTPB and double-base propellant decreased the thermal decomposition temperature by 16℃and 10℃, respectively. Similarly, by modifying spherical aluminium to superfine aluminium flakes and aluminium/magnesium alloy (contains 20% magnesium by weight), the thermal decomposition temperature decreased by 26℃and 37℃, respectively. This resulted in more favourable ignition and improved the decomposition characteristics of the propellants. Other experimental results indicated that the addition of the oxidizer ADN and a catalyst deceased the thermal decomposition temperature.The combustion energy and products of the Al/H2O and Mg/H2O propellants were systematically calculated and analysed. Results showed that the temperature of the first stage of combustion enhanced with increasing AP content. Under 7MPa the combustion temperature of Mg/H2O propellant was between 1600K and 2600K, which resulted in the vaporization of the magnesium; while for Al/H2O propellant, the combustion temperature was between 2000K and 2500K, the aluminium existed in the combustion products mainly as the condensed phase. The specific impulse (Isp) can be improved by increasing the proportions of the metal powder in the propellants, or the ratio between water and propellant (W/F). However, if the W/F value is too low, it will result in the incomplete combustion of the metal. Very high W/F ratios result in the formation of metal hydroxide and lower combustion temperatures. The optimized formulas for two propellants were determined to be: Mg/AP/HTPB≈55/30/15, W/F≈3, Isp≈3994N·s·kg-1 with the second stage combustion temperature of 683K; Al/AP/HTPB≈55/30/15, W/F≈3.5, Isp≈4547N·s·kg-1 with the second stage combustion temperature of 684K. The second stage combustion temperatures above 600K ensured that the water produced by the propellant was completely vaporized.The mechanism of Al/Mg and water reaction was explored as part of this project. The results suggested that additive Tec accelerated the reaction under lower temperature mainly by changing the pH of the reaction systems. The water vapour concentration and the metallic powder size are the dominant factors that affect the high temperature combustion reaction time. Under certain conditions, the combustion reaction can be controlled and the propellants combustion characteristics can be improved by the modification of the metal powders. |
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