Synthesis and thermal behaviour of potassium sialate geopolymers

The geopolymers potassium polysialate (K-PS) and potassium sialate disiloxo (K-PSDS) have been found to possess extremely good thermal stability. K-PS shows little sign of melting up to 1400 degreesC, its amorphous structure being replaced by the crystalline feldspars leucite and kalsilite at 1000 degreesC. (27)Al and (29)Si MAS NMR confirm the ease of this thermal reaction which involves only slight changes to the tetrahedral Al environment. Silica-rich K-PSDS becomes friable and porous at >1200 degreesC, with less complete crystallisation of K-feldspar, the formation of some cristobalite and the retention of a degree of amorphous geopolymer. (39)K NMR suggests that the charge-balancing alkali ions in the K-PS and K-PSDS geopolymer networks behave similarly to those of Na geopolymers, dehydrating on heating and moving into the feldspar lattice >1000 degreesC. (C) 2002 Elsevier Science B.V. All rights reserved.