Low-Cost, Lightweight Rocket Nozzle Materials For Tactical Missle

Current tactical missile rocket nozzles provide adequate performance, but it is expected that significant improvements can be realized if the present generation nozzles are replaced with composite nozzles composed of carbon fibers and hafnium or zirconium-based ceramic matrix materials. Present development of advanced composite nozzles has focused on costly chemical vapor infiltration (CVI) as the method of fabrication. An alternate fabrication method based on liquid impregnation and pyrolysis is proposed here as a potentially low- cost replacement or enhancement for CVI. A survey of appropriate liquid or liquefiable precursors for hafnium and zirconium ceramics showed that the use of relatively inexpensive acetates, chlorides, alkoxides, and colloids has the potential for reducing the cost of the composites. Processing involves repeated cycles of vacuum impregnation of the liquid precursor into a carbon fiber preform, drying or gelation to form a solid, and pyrolysis at high temperatures in inert gas. Hybrid processes combining CVI and liquid impregnation and pyrolysis may also be more cost-effective than CVI alone. A 6 month Phase I program to be performed in three sequential tasks is proposed to prove the feasibility and demonstrate the potential of the liquid impregnation and pyrolysis approach. In Task I pyrolysis experiments will be conducted to determine the yield, chemical composition, and phase constitution of ceramic products obtained from the various precursors and important precursor mixtures. A reduced list of precursors selected on the basis of the Task 1 results will be used to fabricate small composite samples by impregnation and pyrolysis in Task 2. The nature of the matrix materials and matrix-fiber characteristics will be evaluated in Task 2 and the most promising precursors will be used to fabricate samples for mechanical testing in Task 3. An optional Task 4 is proposed for the fabrication and matrix-fiber characteristics will be evaluated in Task 2 and the most promising precursors will be used sponsor for evaluation. Demonstrating effective and efficient processing using precursors of reasonable cost to fabricate composites of acceptable tensile