PECULIARITIES OF OBTAINING ELECTRORHEOLOGICAL ACTIVE FERROPHOSPHATE
The conditions of chemical deposition of x-ray amorphous iron orthophosphate of FePO<sub>4</sub>∙2,5H<sub>2</sub>O composition and hydrothermal crystallization of FePO<sub>4</sub>∙2H<sub>2</sub>O having a monoclinic structure are presented. The process and products of thermal dehydration of FePO<sub>4</sub>∙2,5H<sub>2</sub>O and FePO<sub>4</sub>∙2H<sub>2</sub>O were studied. The dependence of the amount of water removed on the temperature and duration of dehydration of crystalline FePO<sub>4</sub>∙2H<sub>2</sub>O is established. The influence of temperature on the phase composition of heat treatment products is shown. The scheme of phase transformations occurring during heat treatment of hydrated iron phosphates is given. Temperature intervals of formation and formation of crystalline anhydrous iron phosphates with the structure of tridimite and quartz, which were used as a dispersed phase in electrorheological suspensions, were established. The electrorheological activity (ER-activity) of electrorheological suspensions (ERS) containing anhydrous iron phosphate with the structure of tridimite and quartz was studied. The dependence of the electrorheological activity of suspensions on the structure and dispersion of anhydrous iron phosphate, the duration of its formation at a given temperature, and the nature of the initial iron phosphate hydrate is shown. The conditions for obtaining anhydrous iron phosphate as an electrosensitive filler of ERS are studied. It is noted that the value of the shear stress (τ, Pa) at the electric field strength E = 4 mV/mm reaches 340 Pa for ERS based on tridymite-like iron phosphate obtained by heat treatment at 550 °C for 90 minutes.