A study by in situ techniques of the thermal evolution of the structure of a Mg-Al-CO3 layered double hydroxide

Several in situ techniques have been used to investigate the thermal evolution of the structure of a Mg-Al-CO3 layered double hydroxide (LDH) under an inert atmosphere. Based on the results of the study, a model is proposed to describe the structural evolution of the Mg-Al-CO3 LDH. According to this model as the temperature is increased, loosely held interlayer water is lost in the temperature range of 70-190degreesC, but the LDH structure still remains intact. The OH- group, likely in a Al-(OH)-Mg configuration, begins to disappear at 190degreesC, and is completely lost at 280degreesC; a gradual transformation of the LDH structure begins in the same range of temperatures. The OH- group, likely in a Mg-(OH)-Mg configuration, begins to disappear at 280degreesC and is completely lost at 405degreesC; a gradual degradation of the LDH structure is observed in the same range. Although some CO2- loss is observed at lower temperatures, its substantial loss 3 begins at 410degreesC, and is completed at 580degreesC. At these temperatures the material becomes an amorphous metastable, mixed solid oxide solution. (C) 2002 Elsevier Science Ltd. All rights reserved.