Thesis - Oztek_Muzaffer_T_200508_MA

solid solution of hydrogen rather than a covalent or metallic hydride as in the case of
Mg 2 Ni, which required a considerable energy input to initiate the reaction with hydrogen.
The LaNi 5 used in the first part of this study was obtained from Ergenics Inc.
Unfortunately, Ergenics, Inc. stopped supplying the material and so the remainder of the
work was done with alloy obtained from Alfa Aesar. The LaNi 5 obtained from Ergenics
Inc. was shown to have a higher hydrogen capacity than the alloy obtained from Alfa
Aesar but was otherwise a comparable material.
Samples were activated for hydrogen uptake by ball milling and subsequent
thermal treatment in a hydrogen atmosphere. The effects of ball to powder ratio and the
type of mill on the activation of the alloy were studied.
3.1.3.1. Effect of Ball Milling
Approximately 200 mg of LaNi 5 were directly transferred to the DSC sample boat
without any treatment. The sample was subjected to thermal activation then was
pressurized again with 5 atm H 2 and pressure was monitored at constant temperature. As
no change in pressure, it is assumed that the sample did not react with hydrogen
significantly. A second activation cycle was performed followed by the second constant
temperature hydriding; however, the sample still did not react with hydrogen. In both of
the constant temperature experiments, the non-milled sample took up only 0.05% H.
The next LaNi 5 sample was prepared by ball milling in Spex8000 Mixer Mill for
10 minutes with a ball to powder ratio (BPR) of 10:1. Approximately 200 mg of sample
45