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 HO even at ppm levels, forming oxide (LiO) and hydroxide (LiOH) corrosion layers while outgassing H. An effective means to eliminate unwanted outgassing is vacuum-heating to convert LiOH into LiO, although subsequent re-exposure to moisture during transport/handling reconverts some LiO 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/LiO and LiO/LiH interfaces, is validated experimentally by subjecting a previously vacuum-baked polycrystalline LiH sample to 35 ppm of HO 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.