(Digital Presentation) Multiscale Understanding of Local Structure-Dependent Hydrogen Incorporation in TiO₂

Hydrogen interaction with metal oxides is an important phenomenon that affects all vital areas of industry such as aerospace, transportation, and commercial applications. The metal oxide provides a naturally forming protective layer against dissolution of the underlying metal. It has been reported that hydrogen is still able to percolate through this protective layer traveling all the way to the metal to form a corrosive brittle metal hydride. There have been many studies looking to understand the interaction of hydrogen at the surface but an in depth look at the surface to bulk transition of hydrogen through a metal oxide for all representative phases of an oxide is minimally represented in the literature. For the focus of our study, we employed a multi-scale approach combined with experimental studies to explore the different phases of titania (TiO2) which includes rutile, anatase, and an amorphous phase. A thermodynamic analysis of the stability for hydrogen was considered using density functional theory (DFT) starting at the low energy surface facets to the bulk. For the amorphous phase, the binding energy was analyzed as a function of the hydrogen content and oxygen coordination environment. Temperature programmed desorption (TPD) experiments provided a direct comparison with theory. Additionally, NMR simulations validified the generated amorphous phase which agreed well with experimental data. The material properties computed using DFT were used in combination with experimental results to parameterize a mesoscale model. Several environmental conditions were analyzed consisting of grain size, temperature, and grain boundary properties. Further work investigated crystalline titanium (Ti) in the bulk and at several grain boundaries to elucidate possible initiation stages of hydride formation. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.