Celsian formation from barium-exchanged geopolymer precursor: Thermal evolution

In this paper, thermal evolution, including element & phase composition and microstructure, of Ba²⁺ exchanged K-based geopolymer precursor (BaGP) were systematically investigated during high-temperature treatment. The results proved that celsian precursor with lower residual alkaline cation content were obtained through amorphous geopolymer than traditional ion-exchanged celsian through crystallized zeolite. With the increase in temperature, weight loss of BaGP was due to evaporation of –OH groups and decomposition of BaCO₃. Similar to K-based geopolymer, BaGP showed amorphous structure, and nanometer-sized celsian nucleuses first crystallized from the amorphous BaGP matrix after it was treated at 900 °C. In the treatment temperature range from 1000 to 1400 °C, hexagonal celsian became the main phase. After being treated at 1400 °C, hexagonal celsian grains were clearly noticeable with extra SiO₂ locating between celsian grains. It was therefore concluded that geopolymer precursor technique provides an alternative route for the preparation of celsian ceramics.