Effect of niobia as an additive in phosphate-bonded alumina

In this work a study was carried out on the Al2O3/Nb2O5/H3PO4 system. A-2 alumina from Alcoa (Brazil) was used and the Al2O3/Nb2O5/H3PO4 system with an Al2O3P2O5 molar ratio of 20.3, pressed at 20 and 60 MPa and thermally treated at 110, 300, 500, 800, 1000, 1200, 1400 and 1600 °C, was studied. An attempt was made to relate mechanical properties with porosity as well as with the phases formed during thermically treatment. X-ray diffraction (XRD), infrared spectroscopy (IRS) and magic-angle spinning phosphorus nuclear magnetic resonance (31P MAS NMR) were used for phase detection. The amorphous AlPO4 was considered as the low temperature bonding phase. The system studied showed highest mechanical strength at 1400 °C.