Formation of Ceramics from Metakaolin‐Based Geopolymers: Part I—Cs‐Based Geopolymer

Abstract

The structural evolution and crystallization of a cesium-based geopolymer (Cs 2 O . Al 2 O 3 . 4SiO 2 . 11H 2 O) on heating was studied by a variety of techniques including X-ray diffraction, thermal analysis, dilatometry, pycnometry, specific surface area, and microstructural investigation. The Cs geopolymer gradually crystallized into pollucite (Cs 2 O . Al 2 O 3 . 4SiO 2 ) on heating above 9001C. Its low crystallization temperature is believed to be due to the presence of nuclei in the geopolymer precursor, which are formed after curing at 501C for 24 h. The Cs-based geopolymer was found to be more refractory compared with K-and Na-based geopolymers. Significant shrinkage, due primarily to viscous sintering, did not occur until the samples were heated to above 12001C. The microstructure of unheated geopolymer had B20-30 nm-sized precipitates that coarsened on heating above 10001C. By 13501C, the geopolymer surface had a smooth, glassy texture, although large macropores and closed pores remained. After heating to 16001C, the closed pores were removed, and the geopolymer reached B98% of the theoretical density of pollucite. Higher than expected levels of Cs were found near large voids, as seen by scanning electron microscopy and transmission electron microscopy analysis. The presence of this extra Cs was due to Cs left behind in pore water, which was not bound within the geopolymer structure.

Preparation of macroporous ceramic from metakaolinite-based geopolymer by calcination

“…When treated at 1400°C, those composites tend to fracture in a very brittle manner owing to the seriously degraded carbon fibers together with matrix melting and crystal phases dissolve. Bell et al [15] prepared Cs-based geopolymer through cesium silicate solution and found Cs geopolymer gradually crystallized into pollucite on heating above 900°C. These studies help us obtained some important information on geopolymer at higher temperature.…”

Production of nepheline/quartz ceramics from geopolymer mortars

“…This route to ceramic production has advantages associated with high green (unfired) strength and increased dimensional stability during the sintering process when compared to conventional ceramic production involving powder pressing and sintering. 3 Previous work on the effect of high temperatures on geopolymers has examined phase changes using XRD and NMR [15][16][17][18][19][20]. Different charge balancing cations (Na, K and Cs)…”

Other Potential Applications for Alkali-Activated Materials

“…Other utilisation of alkali-activation in the area of radioactive or nuclear fuel cycle-related waste treatment has included the solidifi cation of spent ion exchange resins [ 125 ], and S/S treatment of radioisotopes including 152 Eu, 60 Co and 59 Fe [ 196 ] 99 Tc [ 197 , 198 ] and 129 I [ 198 ]. This does appear to be an area in which the versatility of alkali-activation chemistry, in developing matrices based either on calcium-silicate chemistry or alkali-aluminosilicate chemistry, or a mixture of the two gel types, can provide advantages over purely calcium silicate-based systems, particularly if water removal (by moderate-temperature heat treatment) to prevent radiolytic hydrogen generation is desired.…”