Temperature Effects on Fe(OH)₃ Gel Phase Nanostructures: Implications for the Performance Regulation and Application of Calcium Sulfoaluminate Cement

Temperature is one of the most important factors affecting the hydration process and the crystallinity of cement pastes, and its effect on the gel phase cannot be ignored. The Fe(OH) 3 phase is an indispensable gel phase in calcium sulfoaluminate cement, which significantly contributes to the desirable properties of CSA cement (especially ferric-rich calcium sulfoaluminate (FR-CSA) cement). In order to thoroughly study the influence of temperature on the nanostructure of the Fe(OH) 3 gel phase, XRD, TGA, FTIR, SEM, TEM and Mössbauer spectroscopy were used to investigate the nanostructure of the Fe(OH) 3 phase synthesized by the sol–gel method and Fe(OH) 3 phase in ferric phase hydration products prepared by solid-phase sintering at different temperatures. The results show that the chemically synthesized Fe(OH) 3 phase has a crystal structure, goethite/hematite is the main product of the Fe(OH) 3 phase, and temperature has a significant effect on the crystallinity and microstructure of Fe(OH) 3 . The increase of temperature leads to the gradual increase of the crystallinity of the Fe(OH) 3 phase, changes the crystallization path of the Fe(OH) 3 phase, and is conducive to the formation of a hematite crystal. At the same time, the microstructure changes from a needle-like structure of goethite to a flaky structure of hematite. In addition, Fe(OH) 3 has a significant crystal structure during hydration at different temperatures. As the temperature increases, the crystallinity of Fe(OH) 3 generated by hydration increases and the particle size gradually increases. The microscopic morphology of the Fe(OH) 3 phase formed by hydration is predominantly scaly with significantly smaller particle sizes and weaker crystallization compared to the chemically synthesized Fe(OH) 3 phase.