Synthesis, thermal properties and electrical conductivity of phosphoric acid-based geopolymer with metakaolin

In this work, kaolin was used to prepare a geopolymer from a phosphoric acid solution. Microstructural properties were investigated by X-ray powder diffraction, while thermal properties were evaluated by differential thermal analysis and thermogravimetry. Finally, the electrical conductivity of the geopolymer and its dielectric properties were investigated.The results showed that the onset temperature of crystallization of the zeolite phase occurred at 180 °C. This phase was converted into phosphocristobalite phase at 300 °C and persisted until 1400 °C. From the temperature of 700 °C, a new crystalline phase was observed: the tridymite SiO2.The amount of phosphocristobalite and tridymite crystals reached a maximum at approximately 1100 °C, then, at 1400 °C, the X-ray diagram showed that the peak presented a weak intensity due to the partial dissolution of two solid crystalline phases: tridymite and cristobalite. The electrical conduction properties of the geopolymer indicated first a very low solid-state conductivity (σ ≈ 10−10 S.cm−1), and then above 625 °C, the conductivity began to rise rapidly, reaching 10−7 S.cm−1.