Structural, Textural and Mechanical Properties of Products Obtained by Interaction of Metakaolin-phosphoric Acid at High Temperature

The various molar ratios of P/Si + Al (0.1, 0.2, 0.4, and 1.4), based on metakaolin and phosphoric acid, have been investigated at two temperatures 750 and 1000°C. The characterization results by 27Al, 31P, 29Si MASNMR and X-ray powder diffraction show that the H3PO4 reacts with metakaolin to form an AlPO4 phase for the three ratios (0.1, 0.2, and 0.4), while with P/(Si + Al) ratio = 1.4 two phases have been formed: Al(PO3)3 at 750°C and AlSi2(PO4)3 at 1000°C. The fl exural strength tests of obtained ceramics increases from 0.75 to 15.53 MPa at 750°C and from 4.55 to 9.03 MPa at 1000°C compared with those made with only metakaolin. Water absorption reached 30.36%, bulk densities varied from 1.79 to 1.37 g cm–3 at 750°C and between 1.71–1.42 g cm–3 at 1000°C while the porosity decreases from 43.25 to 30.36%.