Transitioning the phase composition of geopolymers: Effect of seed crystal size

Abstract

Geopolymers hold significant potential for applications in fireproof coatings owing to their excellent high-temperature resistance. However, their main hydration product, a gelatinous phase, undergoes dehydration at ∼500 °C, leading to a decline in performance. Moreover, the zeolite-like phase, a secondary byproduct of the hydration reaction, exhibits superior high-temperature resistance compared with the gelatinous products. Therefore, transitioning the phase composition of geopolymers to increase the zeolite-like phase is beneficial for improving high-temperature resistance. In this study, the seed-induced technique was employed as the transformation technique, and the effects of seed size on the composition and high-temperature resistance of the geopolymer were evaluated. The results showed that zeolite seeds promoted the transition of gelatinous products to zeolite. This effect increased with decreasing seed size. The zeolite content increased from 4.47 % to 11.75 % at a seed particle size of ∼250 nm. Moreover, the seed-induced technique mitigated the detrimental effects of gel dehydration on the microstructure. Newly generated zeolites filled the pores as aggregates after crystalline transformation at high temperatures. Additionally, the compressive strength of geopolymers decreased 20 % when adding the seeds after exposure at 800°C for 1 hour. Overall, this research offers a new approach for enhancing the high-temperature resistance of geopolymer materials.