Effect of LiOH addition on dehydration reaction of Mg(OH) 2

Abstract

The dehydration behavior of LiOH-modified Mg(OH) 2 (LiOH/Mg(OH) 2 ), as a new chemical heat storage material, was investigated. Structural analysis of LiOH/Mg(OH) 2 was carried out using an X-ray diffraction (XRD) meter. The profile of the dehydration reaction of LiOH/Mg(OH) 2 was observed to analyze the dehydration kinetics of the LiOH/Mg(OH) 2 samples. The XRD patterns of the LiOH/Mg(OH) 2 samples shifted toward higher angles than that of Mg(OH) 2 . This indicated that the lattice parameter might have changed and lattice defects such as oxygen vacancies might have been generated on the surface of Mg(OH) 2 . The rate of the dehydration reaction increased as the amount of added LiOH increased; therefore, LiOH/Mg(OH) 2 could be a potential chemical heat storage material. We concluded that LO20 (Mg(OH) 2 containing 20 mol% LiOH) was the combination with the most optical mixing mole ratio. This result was determined by analyzing the dehydration activation energy values. When the dehydration reactions of the LiOH/Mg(OH) 2 samples were considered to be first-order reactions, the calculated mole fraction of Mg(OH) 2 could not be reproduced. However, the calculated mole fractions of Mg(OH) 2 were in agreement with those measured considering the reactions to be zero- and first-order reactions. Therefore, the kinetics of the dehydration reaction of the LiOH/Mg(OH) 2 samples included both zero- and first-order reactions.