Moisture Corrosion of LiH: A Kinetic Investigation by DRIFT Spectroscopy

Lithium hydride (LiH) is a unique, ionic compound with applications in a variety of industries. Unfortunately, LiH is very reactive toward H₂O even at ppm levels, forming oxide (Li₂O) and hydroxide (LiOH) corrosion layers while outgassing H₂. An effective means to eliminate unwanted outgassing is vacuum-heating to convert LiOH into Li₂O, although subsequent re-exposure to moisture during transport/handling reconverts some Li₂O back to LiOH. A corrosion growth model for previously vacuum-baked LiH is necessary for long-term prediction of the hydrolysis of LiH. In this work, a para-linear hydroxide corrosion growth model is proposed for the reaction of previously vacuum-baked LiH samples with moisture. This model, composed of two competing diffusion reaction fronts at the LiOH/Li₂O and Li₂O/LiH interfaces, is validated experimentally by subjecting a previously vacuum-baked polycrystalline LiH sample to 35 ppm of H₂O at room temperature while monitoring the corrosion growth as a function of time with diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy. The para-linear growth model for the hydrolysis of previously vacuum-baked LiH proposed in this report can also serve as a template for the hydrolysis of other hygroscopic oxides grown on metal or metal hydride substrates.