LiAlH hydrogen desorption

Fig. 3.34 Hydrogen desorption curves under continuous heating up to 300°C (quasi-TPD) imder 0.1 MPa hydrogen pressure of composites (MgH + LiAlH ) synthesized by ball milling for 20 h (corrected for increasing pressure due to hydrogen temperature change)...

Furthermore, Fig. 3.35 shows the desorption cnrves of the ball-milled (MgH h-50 wt%LiAlH ) composite dnring continuous heating np to 250,260,275 and 300°C under 0.1 MPa hydrogen atmosphere. Under these conditions the composite desorbs 4.3 and 4.9 wt%H2 at 250 and 260°C, respectively. The pnrity-corrected amonnt of hydrogen which conld be desorbed from the 50 wt%LiAlH constitnent in a composite at these temperatnres which are higher than the temperatnres of the solid state reaction (Rib) of (3.12) and (R2) of (3.13) in Fig. 3.30b, is 3.8 wt%. Experimentally observed values are larger by about 0.5-1.0 wt% than the theoretical one. This excess could only be desorbed from MgH. That means that MgH is able to desorb at temperatnres 250 and 260°C, which are lower than its eqnilibrinm temperature of desorption nnder 0.1 MPa equal to 275°C. Apparently, MgH is thermodynamically destabilized by the second composite constituent LiAlH. Additional evidence that MgH is, indeed, destabilized is provided by the shape of the desorption cnrves at 250 and 260°C in Fig. 3.35 in which one can see a clearly discernible third... 

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