Graphite is used in solid rocket propulsion nozzles due to its lightweight, high-temperature, and corrosion-resistant properties compared to materials like tungsten. Therefore, it is used in the most demanding heat-sensitive nozzles. Recently, to compensate for graphite's brittleness, multi-dimensional carbon-carbon composites, consisting of three-dimensional or multi-dimensional carbon fiber braids impregnated with pitch and then calcined, have been adopted.
In rocket propulsion nozzles, the throats are traditionally made of graphite, as the ultrasonic gas jet reaches temperatures of approximately 3000°C, while the backside temperature is relatively low. However, carbon-carbon composites offer lighter weight, higher strength, and improved resistance to thermal shock and burnout. Furthermore, because they can be made thinner, they can achieve higher opening ratios (nozzle outlet area/throat area) and mass ratios (propellant mass/total thruster mass), resulting in higher specific thrust.
For nozzle applications, carbon-carbon composites have been developed and applied both domestically and internationally, proving to be an ideal material. Research is underway into the use of carbon-carbon composite materials in liquid rocket engine components, aiming to achieve lightweight combustor materials and improve high-temperature properties for high-temperature combustion gases.
In addition, research is also underway into ramjets, the engines used in space shuttles. These engines experience turbine inlet temperatures exceeding 1750°C, so research and development of carbon-carbon composite components with oxidation-resistant coatings is underway as a promising future material for heat and oxidation resistance.