A series of low-toxicity gelcasting systems has been developed. The reagents used in these systems have very low acute toxicity. The new systems perform at least as well as, and in some cases better than, the original acrylamidebased system. The development of these systems is described herein, including the search for new gel compositions, the study of suspensions made with the new gel precursor solutions, and pyrolysis of the dried gels and gelcast parts. Applications of the new gelcasting systems include complex silicon nitride parts, large-diameter rings, rapid prototyping by green machining, and metal-powder gel casting.

Gelcasting, a ceramic forming process, was developed to overcome some of the limitations of current complex-shape forming techniques such as injection molding and slip casting while reducing the costs of shaping advanced ceramics. Gelcasting is based on the separation of the mold filling step from the setting step in these forming processes by utilizing the polvmerization of organic monomers into a chemical gel which holds the ceramic powder in place after the mold is filled. The simplicity of the process has attracted industrial partners and by collaboration between them and the developers, the process is being advanced from the laboratory toward industrial production.

Gelcasting, a ceramic forming process, was developed to overcome some of the limitations of current complex-shape forming techniques such as injection molding and slip casting while reducing the costs of shaping advanced ceramics. Gelcasting is based on the separation of the mold filling step from the setting step in these forming processes by utilizing the polvmerization of organic monomers into a chemical gel which holds the ceramic powder in place after the mold is filled. The simplicity of the process has attracted industrial partners and by collaboration between them and the developers, the process is being advanced from the laboratory toward industrial production. IntroductionThe advantages of advanced ceramics over metals in harsh environments have lead to extensive research in the last three decades to improve their reliability. Although the research resulted in the development of toughened, more reliable

Ceramic green bodies prepared by gelcasting were shown to be readily machinable using WC cutting tools. Samples of alumina and silicon nitride were examined. It was found that a gelcasting formulation which uses a high molecular weight crosslinking agent produces a green body having superior machining characteristics. Samples fabricated with a lower molecular weight cross-linker exhibited a poor machined surface finish due to chipping. Machining tests showed that using a 3.2 m (0.125 in.) diameter cutting tool at a cutting speed of 162.5 c d s e c (64 ft./sec.) to machine a flat-bottomed groove 3.2 mm wide and 9.5 mm deep (0.125 x 0.375 in.) using three passes, feed rates ranging from 0.85 to 6.35 c d s e c (0.33 to 2.50 in./sec.) could be used without damaging the sample.