Fabrication of Zirconia-Mullite Composites by Liquid Infiltration

Zirconia-mullite composites were fabricated by infiltration of porous 3Y-TZP pellets with an ethanol solution of aluminum nitrate and tetraethyl orthosilicate (TEOS). The ratio of aluminium nitrate and TEOS in the ethanol was such that, upon pyrolysis, it would convert into mullite. The pellets were dried and pyrolyzed at 700 °C after each infiltration to decompose the infiltrant and to form amorphous mullite precursor. The infiltrated mullite precursor would increase with each infiltration-pyrolysis cycle and would eventually reach a saturation amount. The number of infiltration-pyrolysis cycle to reach saturation depended primarily on the initial porosity. The repeated infiltration-pyrolysis reduced more effectively the pore size than the total porosity of the green compacts. After sintering at 1500 °C for 2 hours, the infiltrated pellets became dense composites of tetragonal zirconia/mullite or tetragonal zirconia/SiC/mullite. From SEM and EDS analyses, it was found that the zirconia grain size appeared to be unaffected by the infiltration of mullite and the spatial distribution of mullite was not uniform throughout the pellets.