Transport Properties of the Pd-H2 System

Formula (74) yields an averaged description of the mean energy of the Pd-H2 system, which refers to local uniform regions of the membrane. Based on the averaged version of the atomistic model for the Pd-H2 system, 

To reduce the number of unknown parameters of the model, it was assumed [203] that the dependence (Jmm( h) can be determined from existing experimental data [200,212]. Fig. 8.13 compares the shear modulus for two limiting states of the membrane matrix equilibrium (rj) and nonequilibrium (77 ). The model proposed qualitatively agrees with few reliable experimental data on the effect of dissolved hydrogen on the mechanical modules. It correctly predicts the decrease in both Young s modulus and sheer modulus during the saturation of the metal with hydrogen in a wide 

Theoretical formulas show that the self-diffusivity of interstitial metal atoms decreases with an increase in the concentration of included hydrogen, which blocks free interstitial sites. A calculation of the coefficient of self-diffusion in the QCA is presented in Fig. 8.14. To calculate concentration dependences of the self-diffusivity, authors used eHh = 0-6 kcal/mol [217]. The curves are normalized to a self-diffusivity of 2.9 x 1CT3 sm/sec at 0H = 0 [218]. As can be seen, the character of curves 1-3 and 5 substantially depends on the value of an = hh/shh, which reflects the difference between 

changes in the phase composition of a membrane as a result of its operation may substantially alter local mechanical characteristics, a process that should be taken into account and controlled when analyzing experiments in which intense flows of hydrogen pass through a palladium membrane. The model also makes it possible to relate independent experimental data on equilibrium, transport, and mechanical properties of palladium membranes. The estimates obtained are in close agreement with a large numbers of experimental data [200-202] on the behavior of various characteristics of palladium membranes with different prehistories and under different condition of hydrogen transport. 

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