Monitoring of the conductivity properties with respect to the development of geopolymer network

Abstract

In this work, we focused on the chemical and (micro)structural changes that occur during curing at different temperatures of geopolymers (GP) prepared with a mullite-based precursor obtained by sol-gel synthesis. Several factors, such as the Si-to-Al ratio in the precursors and the curing temperatures, affect geopolymerisation. While potassium, sodium and even lithium are the most commonly studied cations, for this study, we examined geopolymers with sodium cations only. The H2O:Na2O ratio was set high at 22.80 to allow good workability of the paste having in mind the intended thin film application, i.e. the water-to-geopolymer binder ratio was set at 0.64. We performed extensive structural (diffraction and vibrational spectroscopy), morphological (electron microscopy) and electrical (impedance spectroscopy) characterisation, to facilitate an understanding of the conditions behind the optimal geopolymerisation. Particular attention was paid to the study of the evolution of the GP system as a function of curing temperature using solid-state magic angle spinning nuclear magnetic resonance. This allowed us to better understand the influence of the chemical composition of the constituents and their homogeneity, on the evolution of the organizational domains and electrical properties of the GP samples. We have explored the feasibility of moving from a relatively porous bulk to a thin film configuration, highlighting the applicability of geopolymers as constituents in photovoltaic facade systems.