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Dense Sic-whisker-reinforced mullite composites with up to 50 vol% whiskers can be obtained by tape casting and hot pressing. The tape casting process results in high degrees of S i c whisker orientation as determined visually and by X-ray diffraction. The ability to achieve dense composites with as much as 50 vol% whiskers is attributed to the higher percolation threshold of aligned whiskers. The factors affecting the degree of whisker orientation during tape casting are described using a fluid dynamics model derived from Jeffery's equations and show that the orientation of anisometric particles is enhanced primarily by the casting rate and particle aspect ratio.

Fabrication of lightweight, cellular ceramic composites by foaming sol-gels is presented. Foams of ZO-vol%-Sic-whisker-reinforced Si02 can be tailored with relative densities as low as lo%, with either open or closed cell structures. In addition to reducing drying shrinkage and thus gel cracking, whisker reinforcement significantly increases the strength of the composite foams relative to pure silica foams. [

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