Abstract

Ablative materials are used to protect vehicles from atmospheric reentry, to protect rocket nozzles and ship hulls from propellant gas erosion, as protection from laser beams, and to protect land-based structures from high heat environments. Ablative heatshield materials protect a vehicle from excessive heating, and can also act as a structural component. Thermophysically, ablation involves the elimination of thermal energy by sacrifice of surface material. Some principles of this heat and mass transfer process are melting, conduction and storage of heat in the material substrate, absorption of heat by gases, and exothermic and endothermic chemical reactions. The three groups of ablative materials are subliming or melting ablators, charring ablators, and intumescent ablators. Subliming ablators, eg, Teflon, carbon and composites, act as heat sinks until the surface reaches the sublimation or melting temperature, then removing heat from the insulation material. In the charring ablator, the surface material acts as a heat sink, up to the reaction temperature, where endothermic chemical decomposition into charred material and gaseous products occurs. As the charred surface is eroded, more char forms. Intumescent ablators form a foamlike region on exposure to heat, resulting in improved insulation performance.