Hydrolysis of lithium hydride under low relative humidity

• The first step of hydrolysis of LiH is the adsorption of water on the surface.
• The formation of Li2O or LiOH depends on the ratio amount of water/amount of LiH.
• Hydrolysis kinetics is predicted by the model of core shrinking limited by diffusion.
• Under 0.04% of humidity there is no major risk to form LiOH in significant amount.

Hydrolysis of LiH at room temperature and under low relative humidity (RH < 2%) is studied by manometry working with heavy water either in closed (variable water vapor pressure) or open (constant water vapor pressure) system. Products of the reaction are characterized by XRD and FTIR. It is shown for the first time that the hydrolysis reaction occurs in two steps: first water is adsorbed on the LiH surface and then the hydrolysis reaction starts. In open system, for relative humidity lower than 0.04% only the formation of Li2O is observed while for higher moisture the reaction continues with the production of LiOD. The reaction rate is however extremely low and only a very small amount of LiH is transformed. The kinetic can be well predicted by the model of core shrinking limited by the diffusion through the layer of Li2O and/or LiOD surrounded LiH particles. For practical application, it is concluded that if LiH is stored under controlled humidity lower than 0.04% (40 ppm) there is no major risk to form LiOH in significant amount.

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