Atomic structure of a cesium aluminosilicate geopolymer: A pair distribution function study

The atomic pair distribution function (PDF) method was used to study the structure of cesium aluminosilicate geopolymer (Cs₂O·Al ₂O₃·4SiO₂·xH₂O, with x - 11). The geopolymer was prepared by reacting metakaolin with cesium silicate solution followed by curing at 50 °C for 24 h in a sealed container. Heating of Cs-geopolymer above 1000 °C resulted in formation of crystalline pollucite (CsAlSi₂O₆). PDF refinement of the pollucite phase formed displayed an excellent fit over the 10-30 Å range when compared with a cubic pollucite model. A poorer fit was attained from 1 -10 Å due to an additional amorphous phase present in the heated geopolymer. On the basis of PDF analysis, unheated Cs-geopolymer displayed structural ordering similar to pollucite up to a length scale of ∼9 Å, despite some differences. Our results suggest that hydrated Cs⁺ ions were an integral part of the Cs-geopolymer structure and that most of the water present was not associated with Al-OH or Si-OH bonds.