Environmental Engineering Reference
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Pure MgH 2
MgH 2 +Ni
Fig. 8 Thermal desorption mass spectra of hydrogen under various heating rates 1, 5, 10, 20 C/
min (a), (b), (c), and (d), respectively, for the pure MgH 2 milled for 15 min at 200 rpm and the
2 mol% Ni catalyzed MgH 2 composite prepared by milling for 15 min at 200 rpm. The
intensities of the longitudinal axes indicate the amount of hydrogen desorption per unit time.
Adapted with permission from Hanada 2005
Fig. 9 Residual fraction versus temperature for three different rates of heating (left). Log (b)
versus 1/T for different degrees of conversion, C. Adapted with permission from Flynn 1966
3.2 Isothermal Methods
Both GCI and PCI techniques require a reaction chamber that can be evacuated
and highly pressurized, as well as a sample holder that can be thermally regulated.
In order to calculate the activation energies using these methods, kinetics rate
constants are used in association with the Arrhenius equation. However, to find the
kinetic rate constant, the sorption curves must be fit to the modeled function, f(a),
of the appropriate kinetic mechanism. As will be explained, the GCI and PCI
methods differ by the manner in which the fraction of completion, a, is determined.
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