Ceramics-Silikáty 53, (2) 88 - 97 (2009)

In this paper, a total of 9 Na-PSDS Geopolymeric matrices with different molar ratio of SiO₂/Al₂O₃, Na₂O/Al₂O₃, H2O/Na2O is designated to investigate the influence of the three key ratios on mechanical properties and microstructure in accordance with orthogonal design principle. The experimental results show that Na₂O/Al₂O₃ and H₂O/Na₂O have the most significant effect on compressive strength amongst the three ratios. The highest compressive strength (34.9 MPa) can be achieved when SiO₂/Al₂O₃ = 5.5, Na₂O/Al₂O₃ = 1.0 and H₂O/Na₂O = 7.0. Comparing the IR spectra of 9 Na-PSDS Geopolymeric matrices also indicates that Geopolymeric matrix with the highest strength is the most fully reacted one and possesses the largest amount of Geopolymeric products. Subsequently XRD, ESEM-EDXA and MAS-NMR techniques are employed to further characterize the microstructure of the fully reacted Geopolymeric matrix. The microscopic analysis reveals that the fully reacted Na-PSDS Geopolymeric matrix possesses structural characteristics similar to gel substances in having a wide range of Si endowments, but predominantly the framework molecular chains of Si partially replaced by 4-coordinated Al tetrahedral. A 3D molecular structural model is also proposed based on the decomposition of MAS-NMR spectrum of the fully reacted Na-PSDS Geopolymeric matrix.