Evaluating Ceramic Materials as Alternatives to Graphite in Rocket Nozzles

Hybrid rocket nozzles face a critical challenge: traditional graphite materials suffer significant erosion during combustion, reducing thrust efficiency and limiting operational lifespan. Additionally, their manufacturing process generates conductive dust, posing risks to electronic equipment. This study investigates ceramic materials as potential replacements for graphite nozzles, to develop a durable, cost-effective alternative with safer manufacturing characteristics. The research progressed through multiple design iterations, beginning with fully cast Alumina and Zirconia nozzles, both with and without carbon fiber reinforcement. A series of high-temperature hybrid rocket static fire tests at a chamber pressure of 250 psi revealed that these cast ceramics, despite their promising thermal properties, experienced catastrophic thermal shock failure. The testing was then moved to an additively manufactured alumina resin-printed nozzle, which exhibited less surface erosion but failed due to severe structural cracking. To improve mechanical strength and reduce thermal stress concentrations, the study evaluated compressed ceramic throat inserts in alumina, zirconia, and silicon carbide, again with and without carbon fiber reinforcement. The final iteration tested a small-scale alumina resin-printed throat insert with a refined geometry to minimize stress concentrations; however, it exhibited similar cracking failures despite improved erosion resistance. Although alumina demonstrated superior erosion resistance among cast ceramics, all configurations did not meet the minimum burn time of 6 seconds due to progressive loss of material, melting, or structural cracking. These findings provide insight into the behavior of ceramic nozzles in hybrid rocket applications and highlight critical failure modes that must be addressed. Although ceramics offer theoretical advantages, further advancements in materials science and manufacturing processes are necessary before they can serve as viable, cost-effective replacements for graphite nozzles.