2019, 33(2): 17-22, 101.
doi: 10.11729/syltlx20180128
Abstract:
Based upon our previous research on the single/dual platforms theory for carbon-based material oxidation, it has been found that the generally accepted "slow" reaction model which was presented by Scala in 1962 and has been widely used till now for over fifty years does not exist, while the deserted "fast" reaction model really exists and is of great value in application. Theoretical analysis shows that the "slow" reaction appears only at the boundary-layer-diffusion-rate controlled regime, In this regime, the ablation rate has no business with the chemical reaction rates, so it is a fictitious reaction model and has no physical meanings, although the results from it may be in agreement well with test results. The products of the heterogeneous reactions of carbon with oxygen are CO and CO2, but CO2 is usually neglected when the surface temperature is higher than 1000K in many literatures. However, from theoretical analysis, author find that CO2 plays an important role in spanning the reaction range from the reaction-rate controlled regime to the diffusion controlled oxidation regime, and can't be ignored. It has been shown that for the ablation of carbon-based materials in a high speed stream of dissociated air, the "fast" reaction must be used with both products of CO2 and CO at the same time. There are two different platforms in the diffusion controlled regime. The first platform results from reactions of the predominant CO2 product, and the other is due to the predominant CO product reactions. With the increases of the surface temperature, the ratio of the mass fraction of CO to CO2 at the surface rises rapidly from zero to infinity, which causes the oxidation process to change automatically from the nominated "fast" reaction to the so called "slow" reaction lines. The dual platform theory has been confirmed by several experimental results.
