**5.2 Combustion rate of C/C-composite**

Figure 6(a) shows the combustion rate as a function of the surface temperature with the velocity gradient taken as a parameter. Use has been made of a test specimen of C/Ccomposite with rectangular cross section (5 mm width; 8 mm thickness). The velocity gradient used here is defined as *a* = 2*V*/, where is the width; the maximum velocity gradient is limited to be 1300 s-1, because of air-supply system. Other experimental conditions are the same as those in Figs. 1(a) and/or 3(a). An abrupt decrease in the combustion rate, as well as the general combustion response can be observed in the same manner as that of a graphite rod, reported in the previous Sections. Figure 6(b) is a similar plot with the airflow temperature taken as a parameter, presenting the same trend as that in Fig. 3(a).

Fig. 6. Combustion rate of C/C-composite (Makino, et al., 2006) as a function of the surface temperature; (a) with the velocity gradient of airflow taken as a parameter; (b) with the airflow temperature taken as a parameter.

Theoretical results are also shown in Figs. 6(a) and 6(b). In obtaining these results, use has been made of kinetic parameters for the artificial graphite with higher density (C = 1.82103 kg/m3), after confirming the experimental fact that there appears no remarkable difference in the combustion rates in different graphite densities, because of the prevalence of combustion behavior in the diffusionally controlled regime in the present experimental conditions. As far as the trend and approximate magnitude are concerned, fair agreement is demonstrated, including the ignition surface-temperature. It should be noted that the combustion rate of the C/C-composite is nearly the same as that of artificial graphite when there is no surface coating for protecting oxidation.
