Desorption kinetics curves at various temperatures

Fig. 2.6 (a) Desorption kinetic curves at various temperatures under initial hydrogen pressure of 0.1 MPa of the as-received, nonactivated, commercial MgH powder Tego Magnan and (b) the Arrhenius plot of the desorption rate for the estimate of the apparent activation energy, fi, using kinetics data for four temperatures 350, 375, 400, and 420°C (fi -120 kJ/mol). Coefficient of fit = 0.996... 

Fig. 2.53 Desorption kinetic curves at various temperatures obtained in a Sieverts-type apparatus under 0.1 MPa of hydrogen pressure of (a) ABCR MgH + n-Ni (SSA = 14.5 mVg) baU-miUed for 15 min and (b) Tego Magnan MgH + m-Ni ball-milled for 20 h...

Most often, the primary experimental desorption data [[mainly the P(t) or P(T) function] represent, after due corrections, the temperature dependence of the desorption rate, —dnjdt = Nt vs T. The resulting curves exhibit peaks and their most reliable point is the maximum at the temperature Tm, corresponding to the maximum desorption rate Nm. Its location on the temperature scale under various conditions is essential for estimating the kinetic parameters of the desorption process. 

Thermal desorption techniques have gained great popularity owing to their comparatively easy operation. Various different mathematical analyses of the thermodesorption profiles have been proposed by different authors to provide kinetic information about the distribution of the surface acid strength [22]. A simple approach is based on the analysis of thermodesorption curves collected at different heating rates ( 3). The shift of the temperature of the maximum rate of desorption (Tmax) as a function of P can be exploited to derive activation parameters (i.e. TJ... 

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