Effect of Process Parameters and Binder Concentration on Mechanical Properties of Phosphate Bonded Alumina

Abstract

Alumina and alumina matrix composites typically require sintering temperature in excess of 1550°C. Utilization of aluminium phosphate bonding provides process flexibility and significantly lowers sintering temperature (500° to 1280°C). While phosphate bonded alumina (PBA) may have a lower sintering temperature, its limitations include the presence of porosity in pressure less sintered samples leading to lowered strength and phase instability above approximately 1200°C. The present study describes the effect of processing routes and binder concentration on density, hardness, Young's modulus and transverse rupture strength (TRS) of PBA. In this study, ultra fine Al2O3 (particle size ≈0.5 µm) was reacted with H3PO4 to yield phosphate bond in a matrix of tabular Al2O3 (particle size ≈0.5 µm) after final sintering at 1280°C for 6 h. Green samples were compacted at pressures in the range of 96-290 MPa. The effect of aluminium phosphate binder concentration on mechanical properties of the PBA samples was measured at optimized pressure. The presence of different polymorphs of AlPO4 in the sintered product was confirmed by XRD.