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.

Keywords:

• Chemically bonded ceramics
• Aluminophosphate (AlPO₄)
• Young's modulus
• Transverse rupture strength
• Hardness