Cellular anorthite glass-ceramics: Synthesis, microstructure and properties

Highly permeable cellular anorthite glass ceramics with porosity of ∼95% were obtained by a simple replication technique using near-stoichiometric glass powders and a polymeric foam as sacrificial template material. Impacts of sintering conditions and additions of minor constituents, respectively, on microstructural evolution and resulting macroscopic properties of the derived foams were investigated by X-ray diffraction, scanning electron microscopy (SEM), differential thermal analysis and X-ray microcomputer tomography. Apparent activation energies of crystallization and the Avrami coefficient were estimated from nonisothermal crystallization experiments to evaluate the impact of titania and zirconia, respectively, as potential nucleation agents. Consistent with SEM analyses, it was found that crystal growth occurs in two dimensions. While TiO₂ primarily acts on the viscosity of the precursor glass and, thus, on the process of sintering by viscous flow, ZrO₂ is found to exhibit at least some nucleation efficiency. As compared with sintering of ceramic powders and solid-state reactions in general, the glass ceramic route enables significant reduction in sintering time and temperature.