Degradation behaviour of a composite material for thermal protection systems - Part III - Char characterization

In the former parts of this work (J. Mat. Sci. 33 (1998) pp. 3137 and 3145) the kinetic characterisation and the mathematical modelling of the behavio ur of an ablative material subjected to high heat fluxes were analysed. In this work the structure and morphology of the char produced from the degrad ation of the same ablative material, occurring as a consequence of plasma t orch exposure, are evaluated in order to improve the ablative behaviour of an active protection. Usually the char produced from the degradation of pol ymeric ablators is weak and brittle, and therefore is susceptible of rapid removal by the mechanical stresses due to the high vehicle speed, this phen omena provokes a reduction of the thermal insulation. Reinforcing fibres an d other inorganic fillers must be therefore included in the ablative formul ation in order to improve the char stability. One of the roles of the char, which is very important, is to limit oxygen diffusion from the boundary la yer to the bulk to prevent the exothermic degradation reactions of the poly meric matrix. Therefore, the mechanical characteristics and the physic-chem ical properties of the char are of fundamental importance to ensure good qu ality of an ablative material. In this paper Scanning Electron Microscopy ( SEM) elemental microanalysis (EDAX) and wide angle X-ray diffraction (WAXD) are used to provide respectively the morphological characteristics of the char and further insight on the crystalline structure resulting after quenc hing at room temperature. (C) 2000 Kluwer Academic Publishers.