Thesis - Oztek_Muzaffer_T_200508_MA

The dehydriding procedure was initiated immediately after the system reached
ambient temperature at the end of hydriding process. For this procedure, the exit valves
were opened to release hydrogen and a minimal argon flow was established using the
needle valves. The system was purged with argon for 15 minutes after which the inlet
valves were closed followed very quickly by closing the exit valves to maintain
atmospheric pressure argon within the system. Dehydriding was accomplished by holding
the furnace at the initial temperature for 180 seconds and then heating to T 2 with a ramp
rate of 5 °C/min. The furnace was held at T 2 for 180 seconds and then cooled at a rate of
10 °C/min. Dehydriding in a closed system allowed quantization of the H 2 given off by
the sample. Hydriding and dehydriding cycles were repeated without removing the
sample from the DSC.
Because LaNi 5 and LaNi 5 Al x will absorb and release H 2 at ambient temperatures,
their dehydriding characteristics were determined using a slightly modified procedure.
For these samples, excess H 2 pressure after the hydriding experiment was reduced to 1
atm. Then pressure and thermal data acquisition were started immediately. The system
was heated to 150 ºC with no delay period.
2.2.1.2. Thermal Activation Procedure
Some samples were not sufficiently activated by ball milling alone. The activation
of these samples was accomplished by a thermal cycle in the DSC following milling.
This was done by placing the sample in the DSC in a hydrogen atmosphere at
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