Thesis - Oztek_Muzaffer_T_200508_MA

3. RESULTS AND DISCUSSIONS
3.1. Hydride Formers
The small scale testing of hydride forming materials was done in the differential
scanning calorimeter (DSC). Hydrogen uptake capacity and onset temperature were
determined quantitatively. Qualitative data about the rate of reactions were obtained by
observation of the rate of pressure change. The materials selection was based on the
literature review, which emphasized factors such as hydrogen capacity, hydriding
conditions, as well as safety and availability. The materials subjected to initial
experiments were Mg 2 Ni, VTiNi, LaNi 5 and LaNi 5 Al x where 0.05 < x < 5.67.
During the course of the experiments, heat flow, in milliwatts, into or out of the
DSC sample cell and sample temperature, in ºC, were recorded. The output of the
instrument, a thermogram, is a plot of differential heat flow and sample temperature
versus time. In this plot, an upward peak represented an exothermic event and named an
exotherm; a downward peak represented an endothermic event and is named an
endotherm. The design of the pressure cells utilized with the DSC incorporated pressure
transducers, and thus, allowed for simultaneous thermal and pressure measurements. The
pressure transducer mV output was collected at a sampling rate of one point per second.
Then, using the appropriate transform in the SigmaPlot software, the output was
converted to pressure in atmospheres and then to percent hydrogen by weight using the
number of moles, calculated from the ideal gas law
35