Synthesis, microstructure and physical properties of celsian Ba1−xCaxAl2Si2O8

Monoclinic barium aluminosilicate (celsian) shows application potential owing to its high-temperature resistance, low thermal conductivity, and excellent oxidative reduction properties. Hexacelsian can easily undergo nucleation because of its favorably symmetric crystal structure, resulting in faster precipitation compared to than in the case of celsian. Celsian can only be formed through the sluggish transformation of hexacelsian at high temperatures. In this study, celsian doped with different contents of CaO was synthesized through a simple one-step solid-state reaction process at lower temperatures and in a shorter time and investigated using differential thermal analysis, phase characterization, microstructural observation, and FactSage thermodynamic calculations. Results showed that the addition of CaO could promote the solid-state reaction, affording products such as barium silicate, hexacelsian, and celsian at lower temperatures. Moreover, CaO could promote the synthesis of celsian in the form of solid solution, affording fully monoclinic celsian Ba_0.7Ca_0.3Al₂Si₂O₈ with only 3 h of holding time at 1400 °C. The optimal addition of CaO showed a decreasing trend with the increase in heat treatment temperature. An optimum CaO level of 0.1 ≤ x ≤ 0.3 was recommended to stabilize celsian. The effects of CaO addition and temperature on the physical, mechanical and thermal conductivity properties of Ba_1-xCa_xAl₂Si₂O₈ were investigated, and Ba_1-xCa_xAl₂Si₂O₈ also exhibited excellent antioxidant reduction properties.