Synthesis and thermal behaviour of potassium sialate geopolymers

摘要

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℃, its amorphous structure being replaced by the crystalline feldspars leucite and kalsilite at 1000℃. ~(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℃, 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℃.