Investigation of hydrolysis of lithium oxide by thermogravimetry, calorimetry and in situ FTIR spectroscopy

The mechanism of hydrolysis of lithium oxide (Li2O) was studied by thermogravimetry, calorimetry and in situ infrared spectroscopy under water (H2O) vapor pressure at 298 K. Additional infrared measurements were also performed with heavy water (D2O) to go deeper in the understanding of the mechanism. First, this study showed that the pristine oxide is composed of micrometric particles of lithium oxide core surrounded by a thin protective layer of lithium hydroxide (LiOH). When exposed to a pressure below 5 hPa, the hydrolysis of the particles proceeds mainly through the adsorption of water molecules on the external surface of the lithium hydroxide layer and to a lesser extent to the formation of lithium hydroxide for the smallest particles. By increasing the pressure, the reaction proceeds through the alternative formation of lithium hydroxide monohydrate (LiOH·H2O) and lithium hydroxide. The kinetics of this reaction is controlled by water diffusion through the lithium hydroxide layer. In such a process, the formation of the monohydrate starts when the LiOH layer reaches some critical thickness.