(350f) Computational Materials Screening and Experimental Validation of Hydrogen Environmental Barrier Coatings Via Atomic Layer Deposition
Hydrogen environmental barrier coatings can be used to reduce hydrogen embrittlement of structural materials by reducing diffusion into susceptible substrates. This protection is especially important in hydrogen pipelines and fields such as nuclear and fuel cell applications where hydrogen is used as a fuel source. The higher the operational temperature, though, the fewer options for material choice. A nanoscale film of the current state-of-the-art material for nuclear thermal propulsion (NTP), tungsten, was previously shown to increase the temperature at which hydrogen reacts with the substrate. However, the increase was still far from the operational temperature of these nuclear applications. In this work, density functional theory (DFT) calculations for energy barriers of atomic hydrogen diffusion were used to compare likelihood of various refractories in preventing hydrogen diffusion. The larger the energy barrier, the less likely hydrogen is to diffuse through the material. The bonding behavior of hydrogen as it diffuses into the surface of these materials and the rearrangement of atoms to accommodate it were also analyzed. To experimentally confirm these predictions, the material predicted to perform best, BN, was deposited via atomic layer deposition (ALD). The films were then characterized and the samples tested in a high temperature hydrogen environment using differential thermal analysis. Results showed that BN performed as predicted, preventing reaction of hydrogen with the coated sample above 1400°C.