Preparation of MgO-doped mullite by sol-gel method, powder characteristics and sintering

Abstract

Mullite doped with MgO in quantities ranging from 0.01 to 1.5 wt% were prepared by the sol-gel method. The mullitization temperature decreases with increased MgO dopant content. The XRD patterns of the MgO-doped mullite calcined at temperatures up to 1600° C for durations ranging from 1 to 10 h did not show the presence of any other phase except mullite. The IR spectrum shows a broadening of the Al-O absorbance band at 1175cm−1 with MgO content, indicating the solid solution of MgO. Sintering temperature decreases with increased MgO dopant content. The microstructure observed consisted of equiaxed grains. The TEM observation of the microstructure showed the presence of glassy pockets at the triple grain junctions. The thermal coefficient of expansion and dielectric constant were not changed up to 0.75wt% MgO dopant concentration. The three-point bend strength observed for 0.3wt% MgO-doped mullite at room temperature was 300 MPa and decreased below 200 MPa at 1400° C.