Use of Infrared Spectroscopy to Study Geopolymerization of Heterogeneous Amorphous Aluminosilicates

Geopolymerization is a general term to describe all the chemical processes that are involved in reacting aluminosilicates with aqueous alkaline solutions to produce a new class of inorganic binders called geopolymers. In the present work, a novel analytical procedure is developed to study geopolymerization of amorphous aluminosilicates in real time. This procedure involves first conducting a series of well-designed leaching experiments, within which an aluminosilicate is alkali-activated with aqueous alkaline solutions of varying alkalinities and soluble silicate dosages. The leached solutions are diluted and analyzed using inductively coupled plasma equipped with optical emission spectroscopy (ICP−OES), and the activated solid particles are separated, washed, desiccated, and analyzed by Fourier transform infrared (FTIR) spectroscopy. By comparing the results obtained from the ICP−OES and the FTIR analyses, a linear calibration curve can be constructed to correlate the extent of the alkali-activation of the solid and its T−O−Si (T = Al and Si) asymmetric stretching vibration frequency. Using this calibration curve as a basis, the extent of alkali-activation of the aluminosilicate of interest within a geopolymer can then be approximated in real time with the aid of IR spectral deconvolution. This novel analytical procedure can be used to study the roles of alkalis and soluble silicates in alkali-activation and geopolymerization of a highly heterogeneous and amorphous aluminosilicate such as fly ash. It can also be used to understand the reaction mechanism of geopolymerization and to determine the reaction conditions (such as the SiO2/R2O ratio of the activating solution, where R = Na or K) that are critical in controlling the various reaction pathways, which in turn affect the products formed and the macroscopic (compressive) strengths of the products.