Novel determination of surface temperature of lithium hydride hydrolysis using DRIFT spectroscopy

Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy has been used to show how increasing temperature causes the hydroxyl band of LiOH to shift linearly and reversibly towards lower wavenumbers. The band shift with temperature was used to determine the surface temperature of LiH when exposed to water vapour at 158, 317, 793 and >1900 Pa (5%, 10%, 25% and >60% relative humidity), the exothermic hydrolysis reaction resulting in surface temperature increases of up to 50 °C. The rate of surface heating was found to increase slightly with increasing water vapour exposures up to 793 Pa, demonstrating that the LiH hydrolysis reaction rate was dependent upon the partial pressure of water vapour. The growth of surface LiOH appeared to significantly slow down further reaction until the water vapour exposure was increased beyond 1900 Pa, when formation of hydrated LiOH occurred. The effect of temperature on detectors was also investigated showing that baselines shifted towards higher intensities with increasing temperature when measured with a DTGS detector and towards lower intensities with an MCT detector, over the temperature range 25–450 °C.