Atomic Layer Deposited Boron Nitride Films Act As High Temperature Hydrogen Barriers

Nuclear thermal propulsion (NTP), which can produce twice the specific impulse as chemical propulsion, is limited by hydrogen diffusion. Elemental hydrogen can diffuse into the nuclear fuel elements and cause hydrogen embrittlement through the formation of hydrides, which exert pressure on the surface and cause cracking. Atomic layer deposition (ALD) was used to coat surfaces with thin films of boron nitride of thicknesses ranging from 6-15 nm. Differential thermal analysis was used to prove stability and resistance to hydrogen embrittlement of these coated surfaces in hot (up to 1713 K) hydrogen environments. A high activation energy of hydrogen diffusion through hexagonal boron nitride was calculated to be 3.25 eV. Compared to activation energies of hydrogen diffusion calculated for other thin film materials, it was proven that boron nitride was the most effective material to protect a surface against hydrogen embrittlement.