M.Sc Thesis


M.Sc StudentGelena Stepura
SubjectExperimental Investigation of Combustion Synthesis of Metal
Hydrides
DepartmentDepartment of Aerospace Engineering
Supervisors Professor Emeritus Gany Alon
Dr. Valery Rozenband
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Titanium hydride is a relatively stable metal hydride that may be useful for pyrotechnics, hydrogen storage and other applications. This work investigates the production of titanium hydride by self-propagating high-temperature synthesis (SHS). The method consists of an exothermic reaction between a solid component, cold pressed pellet of titanium powder, and a surrounding gas, hydrogen, where the reaction propagates as a combustion wave through the pellet without the need for external energy (heating). The synthesis allows to get a pure hydride product, since the volatile impurities evaporate in high temperatures. The process proceeds at a rate of a few mm per second. Experiments have been conducted using a constant pressure bomb with hydrogen supply. The pellet was ignited by an electrically heated coil attached to its upper surface. The process of hydrogenation includes two stages: first,  hydrogen absorption during the reaction wave, lasting for 1-10 seconds; the second stage resulting in complete hydrogenation takes place during cooling and lasts for a few minutes. The work investigated the dependence of absorbed hydrogen quantity on different parameters such as hydrogen pressure, argon addition, porosity of the pellet, and titanium particle size. Other process characteristics such as rate of reaction wave propagation and temperature change during the synthesis have been recorded as well. Measuring of pressure variation and mass addition before and after the synthesis indicated hydrogen absorption; x-ray analysis showed that the product is pure titanium hydride. Thermo-analytical investigation (simultaneous TGA and DTA) of the product revealed the main characteristics of the dehydrogenation process of titanium hydride during controlled heating, including an apparent activation energy.  Comparison of titanium hydride made by standard high pressure furnace technology and titanium hydride generated by the SHS method of the present research revealed that hydrogen release from the latter is easier. Another part of the work has studied the hydrogenation of nanoparticles of titanium and its differences compared to standard micrometer- range titanium powder. Last subject of the work is hydridization of titanium by thermal explosion mechanism. In this method the entire material is heated to a temperature where a very fast reaction takes place over the entire volume. It was revealed that the thermal explosion method is able to produce titanium hydride from metal powder without pressing, simplifying the process and anabling a larger scale production at a time.