Desorption Destabilization

Destabilization of High Desorption Temperature Hydrides by (Nano)Compositing 253... 

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... 

In the (NaBH + MgH ) composite system the MgH constituent has much lower desorption temperature than NaBH and decomposes first which may have a destabilizing effect on the NaBH constituent. This was the underlying factor why we decided to examine the ROM for this specific system. As shown in Fig. 3.17b pure NaBH undergoes melting first at 500°C and finally decomposes at 580°C to the elemental Na, B and as shown by (3.39). 

Caution should be taken regarding the disposition of the material treated by thermal desorption because the treatment process may alter the physical properties of the material. For example, the matrix material could be susceptible to such destabilizing forces as liquefication, where pore pressures are able to weaken the material on sloped areas or places where materials must support a load (i.e., roads for vehicles, subsurfaces of structures, etc.). 

Our previous study [130] on the adsorption and desorption behavior of bovine IgG has shown that the protein adsorbed to HA surface would be eluted quantitatively by 0.1 M PBS (phosphoric buffer solution) as shown in Table 11. Presumably, IgG molecules had been trapped in the destabilized network of water molecules on the surface of the HA copolymer. 

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