To optimize the diopside synthesis process, it is necessary to study the phase transformations that occur as a result of the interaction of rice husk ash and dolomite at different stages of firing. Target. Study of phase transformations in the process of solid-phase synthesis of diopside to ensure its maximum yield. Methods. Complex differential thermal analysis (DTA), X-ray quantitative phase analysis (XQFA). Results. Using the DTA method, it was discovered that the DTA curve in the region of 621-761 °С shows an endothermic effect, with a maximum at a temperature of 740°C, associated with the decomposition of calcium-magnesium carbonate (dolomite) and the formation of calcium and magnesium oxides, with the release of carbon dioxide. Two exothermic effects are observed in the temperature ranges 982–1281°C and 1281–1345 °C, with corresponding maxima at 1152 and 1301 °C, characteristic of the transformation of calcium, magnesium and silicon oxides into calcium-magnesium silicate - diopside. The XRD method has shown that, indeed, when the initial components are fired at 1000 °С, the monticellite phase is mainly formed, a certain amount of unreacted silicon oxide remains, and the process of formation of diopside and ackermanite begins. When the firing temperature increases from 1100 to 1150 0C (the first exothermic peak on the DTA curve), not only the recrystallization of monticellite into diopside occurs, but also the separation of forsterite as a separate phase. The firing temperature of the initial components at 1300 °C (the second exothermic peak on the DTA curve) corresponds to the final transition of all silicates to diopside. Conclusions. The process of synthesis of diopside from rice husk ash and dolomite goes through the stages of dolomite decomposition with the formation of calcium and magnesium oxides, then the appearance of the monticellite phase, then the separation of forsterite as a separate phase. At a temperature of 1300°C, all previously formed silicates finally transform into diopside.

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