American Institute of Aeronautics and Astronautics 092407 1 Graphite Nitridation in Lower Surface Temperature Regime Toshiyuki Suzuki * and Kazuhisa Fujita † Japan Aerospace Exploration Agency, Tokyo, 182-8522, Japan and Takeharu Sakai ‡ Nagoya University, Aichi, 464-8602, Japan The rate of nitridation reaction at graphite surface is evaluated in an inductively coupled plasma heated wind tunnel, especially focusing on lower surface temperature regime. In the tests, graphite test pieces are exposed to pure nitrogen test flow. By enlarging the diameter and cooling test piece by water, the surface temperature becomes 500K lower than that measured in our previous study. The rate of nitridation is deduced from the measured mass loss and the surface temperature of graphite test piece. The obtained result varies from 0.0014 to 0.0024 for the surface temperature ranging from 1351 to 1723K. The numerical model of the nitridation rate is also developed based on the obtained results. Using the developed nitridation model, the effect of nitridation on the amount of mass loss of ablative heatshield for HAYABUSA capsule is calculated. In the method, the thermal response of ablator is calculated along flight trajectory by loosely coupling a shock layer flowfield calculation and a thermal response analysis of ablator. It is found from the study that the surface recession calculated by using the present nitridation model becomes 25% larger than that calculated without nitridation, while no significant differences in surface temperature are seen between with and without nitridation. Nomenclature J s = mass flux of species s, kg/(m 2 ⋅s) k = surface reaction velocity, m/s M s = molecular weight of species s, kg/mol p = pressure, Pa R = universal gas constant, 8.314 J/(mol⋅K) r = mass loss rate, m/s S = recession, m T = temperature, K t = time, s α = reaction probability ρ s = density of species s, kg/m 3 subscript c = char nit = nitridation reaction oxi = oxidation reaction sub = sublimation reaction * Researcher, Aerospace Research and Development Directorate, 7-44-1 Jindaiji-higashi-machi, Chofu, Member AIAA. † Senior Researcher, Aerospace Research and Development Directorate, 7-44-1 Jindaiji-higashi-machi, Chofu, Senior Member AIAA. ‡ Assistant Professor, Department of Aerospace Engineering, Furo-cho, Chikusa-ku, Nagoya, Member AIAA. 47th AIAA Aerospace Sciences Meeting Including The New Horizons Forum and Aerospace Exposition 5 - 8 January 2009, Orlando, Florida AIAA 2009-260 Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.