Advanced HfC-TaC Oxidation Resistant Composite Rocket Thruster

Several compositions of HfC-TaC codeposited by chemical vapor deposition were evaluated for oxidation protection of graphite substrates. Oxyacetylene torch ablation tests with an O₂, C₂, H₂, ratio of 4:1 were used to test the adherence and composition of the coating and resulting oxides, which were subsequently characterized by x-ray diffraction and scanning electron microscopy. The preferred HfC-TaC composition of 70:30 was used to fabricate a 25 lbf graphite fiber reinforced rocket thruster with a unique structural design. Thruster testing at NASA Lewis was performed at 0.520 MPa chamber pressure and 1650°C (3000°F) using a 6 to 7:1,0₂,:H₂ fuel mixture; a uniform, adherent oxide layer was observed on the internal surface of the combustion chamber following the test.