Textural, Structural, and CO2 Chemisorption Effects Produced on the Lithium Orthosilicate by Its Doping with Sodium (Li_(4-x)Na_xSiO4)

摘要

Solid solutions of lithium and sodium orthosilicate (Li_(4-x)Na_xSiO4) were synthesized by coprecipitation. Samples were characterized by powder X-ray diffraction, scanning electron microscopy, N2 adsorption, and thermogravimetric analyses (dynamic and isothermically). Results showed that the solubility limit of sodium into Li4SiO4 is 0.1, Li_(3.9)Na_(0.1)SiO4. Sodium additions, higher than 0.1, produced the formation of secondary phases. Thermal analyses into a CO2 flux showed that Li_(4-x)Na_xSiO4 solid solutions present a much better CO2 absorption than that observed for pure Li4SiO4. Isothermal analyses were performed to the samples in order to obtain kinetic information. These data were adjusted to double exponential model as there are two different processes taking place, the CO2 absorption and diffusion processes. Nevertheless, in some cases, it was detected the presence of a third process, desorption. Those experiments were fitted to a triple exponential model. Finally the enthalpy activation energies for the different processes were calculated using the Eyring's model.