Phase transition and thermal expansion coefficient of leucite ceramics with addition of SiO₂

Abstract

In this work, the influence of SiO2 additions in leucite ceramics on the bulk linear thermal expansion coefficient (TEC) especially during the phase transition, has been studied. Thermal expansion and x-ray diffraction measurements at high temperatures were carried out to characterize the tetragonal-cubic phase transition. TEC for reference and SiO2-added leucite samples exhibited similar behavior as a function of temperature. Before and after the phase transition, the TEC values were similar to those observed in non-SiO2-added samples, whereas during the phase transition, a maximum TEC value was observed and it tends to decrease as the SiO2 addition increases. This behavior could be caused by the formation of an intermediate phase with an extremely high TEC (70 × 10–6 °C−1) during the phase transformation. Furthermore, the results suggest that as the intermediate phase is partially suppressed via SiO2 addition, the cubic phase can be partially stabilized at temperatures as low as 200 °C.

Fabrication of Structural Leucite Glass–Ceramics from Potassium‐Based Geopolymer Precursors

“…Geopolymer precursors based on metakaolin therefore can be used to form high‐purity, leucite‐based ceramics. It is also possible to tailor the thermal expansion of the ceramic by varying the alkali 21,22 (e.g., Cs produces a lower thermal expansion, while K produces a higher thermal expansion) or silica concentration 23 …”

“…It is also possible to tailor the thermal expansion of the ceramic by varying the alkali 21,22 (e.g., Cs produces a lower thermal expansion, while K produces a higher thermal expansion) or silica concentration. 23 In this investigation, leucite ceramic disks were fabricated by grinding K 2 O Á Al 2 O 3 Á 4SiO 2 Á 11H 2 O geopolymer to a powder, followed by drying, isostatic pressing, and firing under different heating conditions in air. Die pressing of dried geopolymer successfully prevented cracking on heating, which is commonly observed in as-cast geopolymer due to capillary stresses created from the evaporation of water.…”

Tailorable thermal expansion in leucite‐pollucite materials derived from geopolymers for environmental barrier coatings

“…These minerals consist of a framework of mostly Q 4 ‐bonded aluminate and silicate tetrahedra which form cages that enclose alkali cations and water molecules. The cages are aligned along certain crystallographic directions to form “pore channels.” The local structure of geopolymers, within 1‐2 nearest neighbor atoms, is identical to that of framework zeolites of equivalent compositions 18‐22 …”

“…The local structure of geopolymers, within 1-2 nearest neighbor atoms, is identical to that of framework zeolites of equivalent compositions. [18][19][20][21][22] In this work, materials of the analcime family, having the formula…”

“…The local structure of geopolymers, within 1-2 nearest neighbor atoms, is identical to that of framework zeolites of equivalent compositions. [18][19][20][21][22] In this work, materials of the analcime family, having the formulawere studied. The exact temperature at which crystallization occurs increases with the ionic radius of the interframework cation due to the dependence of diffusive mobility on cation size.…”