COLLOIDAL PROCESSING FOR LAMINATED COMPOSITES OF MULLITE ALUMINA WOVEN FABRICS

A sol-gel-processed mullite powder and alumina woven fabrics were for- med into laminated composites (5 vol% alumina fabrics) by filtration o f the aqueous mullite suspensions containing polyacrylic ammonium at p H = 8.8 which were poured into the spaces separated with alumina fabri cs. The mullite suspensions with 30-55 vol% solids showed a Newtonian flow and formed high-density green compacts of 60-63% of the theoretic al density (TD). The green composites were densified to near full dens ity by hot-pressing at 1650-degrees-C for 1 h at 39 MPa in N2 atmosphe re. The mechanical properties (strength, hardness and fracture toughne ss) of the dense composites (> 99% TD) were measured at room temperatu re. However, no significant improvements of strength and fracture toug hness were obtained due to the formation of large cracks (> 100 mum) a cross the alumina fabrics and disappearance of long fiber characterist ics after sintering.