Structural Characterizations and Mechanical Behavior of Activated Clay-Based Si5(PO4)6O and SiP2O7 Compounds

Well-crystalline and low-cost silico-phosphate materials were prepared by a simple procedure, different from that previously reported by sol-gel method. In this case, the Si5(PO4)6O and SiP2O7 compound have been synthesized from the mixtures of activated clay –H3PO4 (70 wt% H3PO4 and 80 wt% H3PO4). The structural changes induced by thermal treatment, have been studied by X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, 31P, 29Si MAS-NMR techniques and by the mechanical Brazilian test. The XRD results showed that the well-crystalline Si5(PO4)6O material has been synthesized from a heat treatment at 800 °C. Meanwhile, the well- crystalline SiP2O7 material has been obtained after a heat treatment at 500 °C. These results were confirmed by 31P and 29Si MAS-NMR. the mechanical Brazilian test results showed that the silicophosphates SiP2O7 has high mechanical properties compared to Si5(PO4)6O. At 900 °C, the mechanical strength has increased from 6.58 for Si5O(PO4)6 to 21.02 MPa for SiP2O7.