Journal
APPLIED SURFACE SCIENCE
Volume 565, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.apsusc.2021.150428
Keywords
Hydrogen diffusion; Atomic layer deposition; Environmental barrier coatings; Thin films; Density functional theory
Categories
Funding
- NASA ESI [80NSSC18K0254]
- Office of Nuclear Energy of the U.S. Department of Energy
- Nuclear Science User Facilities [DE-AC07-05ID14517]
- National Science Foundation [ACI-1532235, ACI-1532236]
- University of Colorado Boulder
- Colorado State University
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In this study, atomic layer deposition was used to coat substrates with boron nitride films, providing resistance to hydrogen reaction. Computational and experimental analyses confirmed the stability and hydrogen diffusion resistance of the coatings.
Hydrogen environmental barrier coatings reduce hydrogen diffusion and concomitant hydrogen embrittlement of materials such as those used in nuclear and fuel cell applications where hydrogen is used as a fuel source. In this work, atomic layer deposition (ALD) was used to coat substrates with boron nitride (BN) films of approximately 6, 8, and 15 nm thicknesses. Differential thermal analysis of the coated samples in hydrogen gas showed resistance to reaction with hydrogen to at least 1713 K. Diffusion of atomic hydrogen into the hexagonal BN (001) surface and between sheets as well as material stability were computationally studied using density functional theory. A high activation energy of 3.25 eV was calculated for atomic hydrogen diffusion into the (001) hexagonal BN surface through a sheet. However, lower activation energies of 1.35 eV, 1.11 eV, and 0.12 eV were computed for unique hydrogen diffusion pathways between sheets, suggesting that sheet orientation parallel to the substrate surface is vital for attaining desirable barrier film properties. A predicted positive nitrogen vacancy formation energy of 4.3 eV at 2773 K suggests that hexagonal BN is stable at nuclear thermal propulsion operating temperatures, and stability was confirmed experimentally up to 1773 K.
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