Tesis doctoral de Roger Doménech Ferrer
The aim of this work is to study hydrogen storage properties of thin film materials by means of novel combinatorial approaches on a large spread of compositions. in the preliminary study, we checked out the positive effect that thin film nanostructured mgh2 has in its kinetic properties compared with the bulk system. A significant decrease in the desorption temperature has been observed from 425°c down to 150°c for bulk and mg thin films respectively. two different approaches were developed to study combinatorial hydride systems. On one hand, we developed u-xrd combinatorial characterisation on discrete combinatorial samples. In this approach, 4 identical libraries can be deposited simultaneously by means of 2 u-shape masks with e-beam deposition technique. By moving these two masks in the x and y directions sequentially we can prepare 4 identical arrays of nxm different compositions. In this work 4×4 and 7×7 arrays were prepared. Afterwards, different thermal treatments in h2 atmosphere were performed and theses samples were analyzed by performing u-xrd measurements in each cell of these arrays. This technique has been applied to mg-al system. On the other hand, thermography technique was applied to measure absorption and desorption of hydrogen. This technique measures the change radiated power that any metal has when absorbs/desorbs hydrogen. When hydrogen is absorbed, the emissivity increases and the radiated power become higher, according to stefan boltzman law. Also, when hydrogen is desorbed, emissivity decreases and the radiated power decreases. Measuring the changes of radiated power versus temperature, we can monitor the absorption and desorption of hydrogen in discrete and graded combinatorial samples and therefore to analyze a continuous range of compositions in a single experiment. This technique has been applied to discrete mg-al combinatorial samples and to graded mg-ti and mg-fe-cu samples covered with pd in all cases. The last two set of samples were deposited by sputtering dc. in the mg-al system, we concluded that thin layers of al between the mg ones improve significantly the absorption properties of mg, since the al layers act as a free pathway for hydrogen diffusion inside of the hydride phase. However, there is no improvement in desorption properties because hydrogen is desorbed from top to bottom of the layers and therefore, hydrogen does not cross the hydride phase in anyway. Also we found out some results that pointed out to the formation of magnesium alanate by the direct hydrogenation of the pure elements. in mg-ti co-deposited system, has been found out that ti improves the absorption and desorption properties of mg, since these reactions were observed at much lower temperature than for single mg layers. Two different behaviours of the decomposition temperature versus ti concentration were observed indicating the two different roles that ti plays in the mg-ti system. in the mg-fe-cu system we just made a preliminary study by means of thermography in the ternary combinatorial graded sample that pointed out to the positive effect in desorption kinetics when cu and fe are co-deposited with mg.
Datos académicos de la tesis doctoral «Combinatorial approaches applied to preparation and characterisation of hydrogen storage thin films«
- Título de la tesis: Combinatorial approaches applied to preparation and characterisation of hydrogen storage thin films
- Autor: Roger Doménech Ferrer
- Universidad: Autónoma de barcelona
- Fecha de lectura de la tesis: 08/01/2010
Dirección y tribunal
- Director de la tesis
- Javier Rodriguez Viejo
- Tribunal
- Presidente del tribunal: María teresa Mora aznar
- José Santiso lópez (vocal)
- Marta Gonzalez silveira (vocal)
- José ramón Ares fernández (vocal)