Effect of temperature on mullite synthesis from attrition-milled pyrophyllite and α-alumina by spark plasma sintering

Abstract This paper addresses the effects of processing technique on the synthesis of mullite from pyrophyllite and alpha-alumina powder. The influence of firing temperatures were examined in order to optimize the fabrication process to achieved a suitable mechanical properties. Feedstock powders, with stoichiometric composition, were wet milled in an Attritor mill. The dried powders were consolidated using spark plasma sintering (SPS) in the temperatures range 1400 °C to 1700 °C under pressure of 50 MPa, with a heating rate of 100 °C/min at different holding times. Densities of 3.25 g/cm3 and 3.17 g/cm3 were obtained for the samples sintered at 1400 °C and 1600 °C respectively, with a 10-min holding time. The XRD and SEM/EDS were employed to characterize the firing transformation and microstructure of the samples. The SEM micrograph of samples, sintered at 1600 °C with 10 min holding times, revealed that the sample retained its equiaxed grain structure. The XRD results show a reduction in alpha-alumina content after the sample was fired. Hardness and fracture toughness values up to 11.73 GPa and 1.99 MPa•m1/2 respectively were obtained.