Solvent free sol-gel based synthesis of soft magnesium silicate

Abstract

In this study, soft magnesium silicates were prepared via sol-gel method starting from diethylphosphatoethyltriethoxysilane (SiP), magnesium ethoxide and magnesium acetate. The thermal reaction of the different systems without any solvent was studied by a thermogravimetric analysis coupled to gas chromatography and mass spectroscopy in order to identify the volatile by-products and then suggest a reaction mechanism. The identification of several by-products formed during the reactions evidenced a non-hydrolytic sol-gel based route between the ethoxy and acetoxy groups of magnesium ethoxide and magnesium acetate respectively with the ethoxy groups of SiP. In addition, X-ray photoelectron spectroscopy analyses highlighted the creation of Mg–O–Si bonds. The viscoelastic behavior of the reactive systems allowed to confirm the formation of the network but also the determination of the gelation time. It corresponded respectively to 2150 and 1020 s for the reaction between magnesium ethoxide and SiP and magnesium acetate and SiP carried out at 170 °C. All these data confirm the formation of a “soft” inorganic network in that range of temperature. The graphical abstract represents first a schematic view of the studied reactions. The graph on the bottom-left corner shows the deconvolution of high resolution XPS spectra in the Mg (1s) region of MgOEt + SiP system treated at 450 °C. On the bottom-right corner, the evolution of tan (δ) at 170 °C under air during time sweeps at 1, 2, 3, and 5 rad/s for MgOEt + SiP system is presented.