The effects of moisture on LiD single crystals studied by temperature-programmed decomposition

Temperature-programmed decomposition (TPD) technique was performed on LiOH powders and LiD single crystals previously exposed to different moisture le vels. Our results show that the LiOH decomposition process is rate-limited by an inward moving reaction front mechanism with an activation energy barr ier of similar to 122-149 kJ/mol. The LiOH structure is stable even if kept at 320 K. However, LIOH structures formed on the surface of LiD single cry stals during moisture exposure at low dosages may have multiple activation energy barriers, some of which may be much lower than 122 kJ/mol. The rate- limiting mechanism for the decomposition of LIOH structures with reduced ac tivation energy barriers is consistent with a unimolecular nucleation model . We attribute the lowering of the activation energy barrier for the LiOH d ecomposition to the existence of sub-stoichiometric Li(OH), with x < 1 and cracks, broken bonds, and other disorders in the LIOH structures formed at low levels of moisture exposure. These defective LiOH structures may decomp ose significantly over many years of storage even at room temperature. At h igh moisture exposure levels, LiOH .H2O formation is observed. The release of H2O molecules from LiOH .H2O structure has small activation energy barri ers in the range of 48-69 kJ/mol ann follows a unimolecular nucleation proc ess. The loosely bonded H2O molecules in the LiOH .H2O structure can be eas ily pumped away at room temperature in a reasonable amount of time. Our exp eriments also suggest that handling LID single crystals at an elevated temp erature of 340 K or more reduces the growth rate of LiOH and LiOH .H2O sign ificantly. (C) 2001 Elsevier Science B.V. All rights reserved.