Structural Characterization of Phosphate-Based Geopolymer

Abstract

Geopolymers obtained following acidic activation represent a promising future material with their different advantages, namely high mechanical strength, excellent dielectric properties and important chemical stability. In the present research, Phosphate-based geopolymer was prepared from metakaolin, as the aluminosilicate precursor and commercial phosphoric acid H₃PO₄, as the activator precursor. These reagents were mixed with (Al/P) molar ratio and solid/liquid (S/L) volume ratio equal to 1. To investigate the obtained material structure, different techniques were used as Fourier Transform Infrared spectroscopy (FTIR), magic angle spinning nuclear magnetic resonance (MAS-NMR) spectra of ²⁹Si, ²⁷Al and ³¹P, X-ray diffraction powder (XRD) and scanning electron microscopy (SEM). As well, the same techniques were used to characterize the used aluminosilicate precursor, which is metakaolin. As a result, the formation of a first aluminum phosphate geopolymeric network dispersed in a second one based on (Si–O–T) units was proven, with T=Si, Al and P. The XRD analyze shows the formation of an amorphous material. In fact, any crystalline phases were observed. Accordingly, the Phosphate-based geopolymer was considered as a composite material composed from two amorphous networks: the aluminum phosphate geopolymeric network which plays the role of reinforcement and the silicate network which represents the matrix.