|Ph.D Thesis||Department of Aerospace Engineering|
|Supervisors:||Prof. Emeritus Gany Alon|
|Dr. Valery Rozenband|
|Full Thesis text - in Hebrew|
An interesting application of metal hydrides is their inclusion in solid propellant and energetic material formulations. However, the theoretical understanding and modeling of metal hydride combustion are relatively incomplete. The main problem of such modeling arises from the complexity of the combination of several processes occurring almost simultaneously, such as hydrogen desorption as a result of heating, gas phase hydrogen combustion, and oxidation of the decomposing hydride particle. The objective of the present work is to conduct a comprehensive investigation of metal hydride particle decomposition and combustion consisting of both theoretical modeling and experimental effort. The model includes simultaneous condensed phase processes - metal hydride decomposition and oxidation, and gas phase combustion of desorbed hydrogen around the particle. One of the major assumptions made in the present model is that the decomposition rate is limited by hydrogen diffusion through the oxide layer around the particle, whose thickness grows due to the surrounding oxidizing gases. The model predictions of the decomposition and oxidation processes for three different metal hydrides, titanium hydride, zirconium hydride, and magnesium hydride, have demonstrated a good agreement with experimental results of a TGA-DTA thermal analysis.
The second part of this work focused on experimental investigation of a new application of metal hydrides: reduction of agglomeration in aluminized solid propellants by adding a small amount of metal hydride. It was revealed that small addition of titanium or zirconium hydrides results in a significant decrease of agglomerate size. The phenomena may be related to the influence of hydrogen desorption which disturbs contact among adjacent particles, early hydrogen combustion (which increases local heat transfer and promotes aluminum particle ignition), and surface combustion of transition metals (titanium and zirconium) that disturbs aluminum droplet coalescence.
The last part of the research investigated an alternative method for fast and low cost synthesis of titanium and zirconium hydrides. The method known as “Thermal Explosion” is based on heating a metal powder sample under hydrogen pressure, which leads to a fast exothermic volumetric reaction between the metal and hydrogen, indicated by a sharp increase of several hundred degrees in the sample temperature. The test results revealed the formation of good quality hydrides, favoring the practical application of this method.