关键词: 地聚物;高岭土;LaF3;YF3;抗压强度

Abstract: Geopolymers has been a research hotspot in recent years due to its excellent mechanical property and durability.The kaolinite mixed with different amount of LaF3 and YF3 were employed to prepare a series of geopolymers, and the mechanical properties of the geopolymers were evaluated by testing the compressive strength at different ages.The phase and microstructure of the geopolymers were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray energy spectrum (EDS), infrared spectroscopy (FTIR) and nuclear magnetic resonance (MAS-NMR).The results show that the addition of LaF3 and YF3 led to the evident decrease in the compressive strength of the geopolymers, and the decreasing range is more significant with the increase of the dosage.At the same conditions, the effect of YF3 on the decrease amplitude of compressive strength of the geopolymers is more obvious than LaF3.Analysis of Fourier transform infrared spectroscopy (FTIR) reveal that the bending vibration peak of geopolymers mixed with LaF3 and YF3 in 950-1250 cm-1 is moved to the high velocity, which make the geopolymers structure become looser because of the decrease of Si-O-Si bonds.27Al magnetic resonance (MAS-NMR) results show that the coordination number of Al in geopolymers is not changed.The pattern of XRD illustrates that rare earth fluoride has been transformed into rare earth fluoride oxide after calcination of kaolinite.The microstructure analysis of the geopolymers by SEM and EDS shows that rare earth fluoride oxide is segregated apparently at the cracks, the stress concentration in the two-phase grain boundary makes the mechanical weakness,which would be the primary cause of strength decreased significantly of geopolymers mixed with LaF3 and YF3.

Key words: geopolymers;kaolinite;LaF3;YF3;compressive strength