Sol-gel processing of high-yield, dense alumina bioceramics

Advanced sol-gel processing technologies were used to develop pre-ceramic inorganic polymeric precursors to alumina ceramics. These inorganic polymers were tailored for use as reactive liquid phase binders for alumina powder processing. These gels were prepared via the transesterification of aluminum sec-butoxide and glacial acetic acid [0.50 mole%] in tetrahydrofuran solvent [25.0 vol.%]. This gelation reaction, driven by the evaporation of sec-butyl acetate [T/sub b/=112/spl deg/C], results in complete solvent and reaction by-product elimination for improved ceramic yields. Thermogravimetric (TGA) and differential thermal analysis (DTA) indicate that the alumina gels endothermically transform [T=400/spl deg/C] in O/sub 2/ to form a high-yield product [/spl sim/70 wt.%]. FTIR and XRD confirm that the decomposition product is amorphous Al/sub 2/O/sub 3/, with subsequent heat treatment to 1100/spl deg/C resulting in the crystallization of /spl gamma/-Al/sub 2/O/sub 3/. 25-30 vol.% of the inorganic binder with optimal viscosity (/spl sim/1 cP) was mixed with commercially pure alumina and mechanically pressed into high-density bars. Optimal thermal sintering conditions were evaluated in a controlled atmosphere (oxidizing, reducing) high temperature to produce high-density tiles [/spl sim/4.0 g/cc]. This novel processing technique is being used to develop near net-shape, high quality alumina bioceramics with the improved properties required for advanced ceramic dental restorations.