Synthesis, characterization and combined kinetic analysis of thermal decomposition of hydrotalcite (Mg6Al2(OH)16CO3·4H2O)

• Published in: Thermochimica acta Vol. 667; pp. 177 - 184
• Main Authors: Yahyaoui, Raoudha, Jimenez, Pedro Enrique Sanchez, Maqueda, Luis Allan Pérez, Nahdi, Kais, Luque, Jose Manuel Criado
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 10.09.2018
• Subjects: Activation energy; Combined kinetic analysis; Hydrotalcite; Hydrotalcite; TG; Combined kinetic analysis; Activation energy
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2018.07.025

•Hydrotalcite (Mg6Al2CO3(OH)16·4H2O) is synthesized by coprecipitation.•The thermal decomposition comprises dehydration, dehydroxilation and decarbonation.•The last two processes strongly overlap and needs to be separated by deconvolution.•The Kinetics of resolved stages are studied by combined and isoconversional analysis.•The kinetic model is based on the diffusion of species out of the laminar structure. Here, a kinetic study of the thermal decomposition of synthesized hydrotalcite, Mg6 Al2 CO3 (OH)16·4H2O, has been carried out using thermogravimetric experiments in air atmosphere. It is shown that the thermal decomposition occurs in two well differentiated stages. The first one is a single-step dehydration process that comprises the release of four water molecules. On the other hand, the second stage is complex and corresponds to both dehydroxylation and decarbonation processes which occur simultaneously. The kinetic parameters describing all processes were calculated by means of a combined approach comprising isoconversional, model-fitting and deconvolution methods. It was concluded that dehydroxilation and decarbonization cannot be separated by TG experiments and the two stages contributing to the complex process do not apparently match the expected stoichiometry of the process. Therefore, it is proposed that such stages mark a change on the reaction mechanism due to the structural collapse of the laminar double hydroxide.