Microstructure and phase formation of mullite-Pr6O11 composite prepared by spark plasma sintering
The present work investigates the effect of high praseodymium oxide (Pr6O11) content on the microstructure and phase formation of mullite (3Al2O3·2SiO2) precursor by means of the spark plasma sintering process. 30 wt% Pr6O11 was added to a mullite precursor consinting of aluminum nitrate nonahydrate and tetraethyl orthosilicate through a high energy mixer mill in ethanol media. The spark plasma sintering was performed at a temperature of 1200 °C under 23 Pa vacuum conditions by applying initial and final pressure of 10 and 30 MPa, respectively. XRD analysis confirmed the existence of mullite, alumina, Pr6O11, Pr2O3 and quartz as the only crystalline phases. FESEM images reveal an interesting deposition of hexagonal-shaped Al2O3 particles on polished surfaces and complex oxide phases of the fiber network adhering to alumina particles in the form of tails seen on the fracture surfaces. Moreover, the bending strength of 213±21 MPa, Vickers hardness of 9.3±0.1 MPa and fracture toughness of 6.21±0.12 MPa·m1/2 are obtained for the prepared composite.