Comparison of two-step and one-step sintering: Synthesis, microstructure, and 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 in the case of celsian. This study successfully synthesized celsian Ba 1− x Ca x Al 2 Si 2 O 8 using a two-step sintering method. Ca 2+ doping significantly promoted celsian formation, with each 5% increase in CaO content reducing synthesis temperature by ∼50°C. A nearly pure monoclinic celsian phase (Ba 0.7 Ca 0.3 Al 2 Si 2 O 8 ) was obtained after 3 h of heat treatment at 1300°C, achieving a ∼100°C reduction compared to conventional one-step sintering. Meanwhile, the celsian Ba 1− x Ca x Al 2 Si 2 O 8 prepared by the two-step sintering method exhibits higher bulk density and thermal conductivity compared to the one-step sintering method. And the thermal conductivity decreased progressively with both increasing heat treatment temperature and CaO content, primarily influenced by phase composition and crystalline defects.