Thesis Defense: A Theoretical Analysis of Interstitial Hydrogen: Pressure-Composition-Temperature, Chemical Potential, Enthalpy and Entropy

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Event Speaker: 

Peter Omondi Orondo

Event Location: 

32-D451

Event Date/Time: 

Thursday, June 21, 2012 - 2:30pm

Research Area: 

 

We provide a first principles analysis of the physics and thermodynamics of interstitial hydrogen in metal. By utilizing recent advances in Density Functional Theory (DFT) to get state energies of the metal-hydrogen system, we are able to model the absorption process fairly accurately. A connection to experiment is made via Pressure-Composition-Temperature (PCT) isotherms, and thermodynamic molar quantities.

 

In the model, we understand the excess entropy of absorbed hydrogen in terms of the change in its accessible microstates. A connection is also made between the entropy and electronic states of interstitial hydrogen. However, our model indicates that this connection is too small to account for experimental results. Therefore, a conclusion is made that the entropy of absorbed hydrogen is mostly (non-ideal) configurational in nature.

 

To model the latter in a manner consistent with experiment, we have explored a new model that posits a weak binding between clusters of hydrogen atoms at neighboring sites. We have developed a formulation and fitted the results to experimental data. We find a least squares fitting of the model to the entropy and enthalpy results in model parameters which seem physically reasonable. The resulting model appears to provide a natural physical explanation for the dependence of the excess entropy on loading.

 

Thesis Supervisor: Prof. Peter Hagelstein