Application of Compositionally Diphasic Xerogels for Enhanced Densification: The System Al₂O₃‐SiO₂

Stoichiometric mullite (71.38 wt% Al₂O₃‐28.17 wt% SiO₂) and 80 wt% Al₂O₃‐20 wt% SiO₂ gels were prepared by the single‐phase and/or diphasic routes. Dense sintered bodies were prepared from both sets of gels in the Al₂O₃‐SiO₂ system. Apparent densities of 96% and 97% of theoretical density were measured for the diphasic (using two sols) mullite samples sintered at 1200° and 1300°C for 100 min, respectively; this compared with 85% and 94% for the single‐phase xerogels under the same conditions, and to much lower values for mullite prepared from conventional mixed powders. The microstructure of the mullite pellets from diphasic xerogel precursors is also considerably finer.