D. Mendeleev University of Chemical Technology of Russia, Moscow, Russia

A. V. Makarov, Associate Professor at the Department of General Technology of Silicates, Candidate of Technical Sciences, e-mail: makarov.a.v@muctr.ru
S. V. Kirsanova, Associate Professor at the Department of General Technology of Silicates, Candidate of Technical Sciences, e-mail: kirsanova.s.v@muctr.ru
I. N. Tikhomirova, Associate Professor at the Department of General Technology of Silicates, Candidate of Technical Sciences, e-mail: tikhomirova.i.n@muctr.ru
M. O. Senina, Associate Professor at the Department of Chemical Technology of Ceramics and Refractories, Candidate of Technical Sciences, e-mail: senina.m.o@muctr.ru

This paper describes a study that looked at the phase transformations taking place in an inorganic binder based on aqueous solutions of lithium silicates when it is being heated up. The application scope includes diffusion thermal control coatings applied to surfaces of complex geometry parts made of light aluminum-magnesium alloys. The paper considers the processes of structuring of silicon-oxygen patterns during transition from an amorphous glassy state to a crystalline state when heated to 1,000 ^оC. The sequence of phase formation was established and the key role of chemically bound water as a stabilizing component of the system, which keeps it from crystallization, is demonstrated. It is shown that the decreased internal energy is associated with the formation of a crystalline phase and an increased connectivity of the amorphous component of the composition, due to the formation of long polysilicate chains of various structures and the precipitation of excess silica in the form of low-temperature quartz. It was established that the phase transformations occur in steps in the temperature range of 350 to 950 °C, and they begin immediately after a complete dehydration of the silicate binder with the separation of lithium metasilicate and the low-temperature form of tridymite into separate phases. As the heating process develops, a polymerization of the silicon-oxygen framework is observed due to the formation of chain- and ribbon-like polysilicate structures and the transition of tridymite into quartz.
The research was carried out using the equipment of the D. I. Mendeleev Center for Collective Use within the framework of project No. 075-15-2021-688.

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