ФАЗОУТВОРЕННЯ ФУНКЦІОНАЛЬНИХ КЕРАМІЧНИХ МАТЕРІАЛІВ ДЛЯ АНТЕННО-ХВИЛЬОВОДНИХ СИСТЕМ

Functional ceramic materials based on oxide systems retain their leading positions among technical materials due to the combination of wide availability of raw materials, high chemical inertness, thermal stability, and the ability to form complex multiphase structures. Among such systems, oxide three-component systems, in which aluminosilicate compounds play the main role, attract special attention. The paper presents a comprehensive study of phase formation processes during the synthesis of barium and strontium aluminosilicates from stoichiometric mixtures based on technical raw materials. Thermal analysis methods (DTA, TG, DTG) in combination with X-ray phase analysis were used to establish the temperature ranges of stability of intermediate phases and the sequence of phase transformations within the range of 40…1500 °C. For the BaO – Al2O3 – SiO2 system, it was found that the formation of primary barium silicates (Ba2Si3O8, Ba5Si8O21) occurs at temperatures of 270 – 390°C, while the formation of celsian is recorded from 990°C with a transition to hexacelsian at 1180–1190°C. The role of intermediate phases – barium aluminates and polymorphic modifications of quartz and barium carbonate – in the synthesis mechanism is described. In the SrO – Al2O3 – SiO2 system, the synthesis of slavsonite occurs through the sequential formation of the phases SrSiO3, Sr2SiO4, Sr3Al2O6, SrAl2O4 and Sr2Al2SiO7. The main stage of slavsonite synthesis is realized within 1070 – 1200°C. Under conditions of SiO₂ deficiency, an alternative mechanism through the decomposition of Sr2Al2SiO7 has been described. It was found that due to the formation of Sr-helenite, further heating to 1500°C does not ensure complete synthesis of the target phase. Experimental data fully correspond to thermodynamic calculations and confirm the complex multi-stage nature of the formation of celsian and slavsonite phases, in which both thermochemical processes and polymorphic transformations are of significant importance. The results obtained allow us to determine the optimal temperature regimes, reaction mechanisms and the influence of the charge composition on the synthesis, which is important for improving the technologies for obtaining functional celsian and slavsonite ceramics.