Application of alumoxane nanoparticles as precursors for 3D alumina features

Acetate- and methoxy(ethoxyethoxy)acetate-functionalized alumina nanoparticles (A-alumoxane and MEEA-alumoxane, respectively) have been investigated as processable, water soluble precursors to 3-dimensional (3D) ceramic features. The ceramic features were formed by slip-casting aqueous solutions of the alumoxanes into polydimethylsiloxane molds, into which negative images of the desired features were molded. The features ranged from 50 to 450 μm in width and approximately 70 μm in depth. Drying the aqueous solution, and removal from the molds revealed free-standing thin film ‘green bodies’ on which are the positive images of the features, which upon firing (1200◦C) resulted in their conversion to α-alumina. The formation of the ‘green body’ upon drying of the alumoxane solution and its sintering to ceramic was studied with regard to shrinkage and cracking. Ceramic 3D features formed from A-alumoxane faithfully reproduced the dimensions of the green body. However, shrinkage and cracking during the drying phase was observed. In contrast, MEEA-alumoxane was found to remain ‘plastic’ in its green body state, allowing for the retention of large features, but the shrinkage upon sintering (due to MEEA-alumoxane’s lower ceramic yield) was often accompanied by cracking of features. Physical mixtures of the two alumoxanes were investigated to determine optimum conditions for the controlled fabrication of ceramic features. The best combination of properties was obtained for a 2:1 mixture of A-alumoxane and MEEA-alumoxane. If metal-doped MEEA-alumoxane was employed, the appropriate aluminate ceramic was formed. Green body and ceramic samples were characterized by SEM, XRD, BET, and Vickers hardness measurements. C 2006 Springer Science + Business Media, Inc.