Thermal Explosion Reaction in the Ti-C System under Air Atmosphere
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Combustion synthesis (CS) of titanium and carbon powders to produce TiC has been widely investigated as a typical system. Considerable efforts have been made to investigate the dynamics of the reaction-front propagation in CS. Numerous analytical and experimental investigations have also been performed to achieve a consistent agreement between experimental observations and theoretical predictions.[1] Experimentally, a CS reaction can be started either by igniting the sample at one end (plane wave propagation (PWP)) or by uniformly heating the sample to the ignition temperature (thermal explosion (TE)). Compared with the PWP mode, only a few studies have been focused on the TE process. However, it could be more amenable for preparing dense composites under external pressure application than the PWP mode.[2] The reason is that the TE reaction completes instantaneously without the propagation of combustion wave, which helps to implement fast densification under external pressure. However, the continuous propagation of the combustion wave increases the reaction completion time, which delays the quick implementation of external pressure and certainly weakens the densification. Nevertheless, for combustion-synthesized TiC, almost exclusive use of the PWP mode was carried out under the vacuum or Ar protective atmosphere. With regard to the TE mode, relatively limited work has been carried
Y.F. YANG, Doctor, and H.Y. WANG, J.G. WANG, and Q.C. JIANG, Professors, are with the Key Laboratory of Automobile Materials of Ministry of Education and Department of Materials Science and Engineering, Jilin University, Changchun 130025, People’s Republic of China. Contact e-mail: [email protected] Manuscript submitted March 19, 2009. Article published online August 20, 2009 2514—VOLUME 40A, NOVEMBER 2009
out. The reason for this is the fact that the ignition temperature (reaching the melting point of Ti) for the thermal explosion reaction under the vacuum or Ar protective atmosphere is so high that the conventional furnace hardly supplies enough heat to initiate the reaction. A possible solution to these problems could be the incorporation of a second metal such as Ni, Fe, or Cu into the Ti and C reactants for the formation of a low melting point eutectic, facilitating an ignition temperature well below the melting point of Ti.[3–7] Inevitably, the additions of metals with high contents may produce some intermediate intermetallic compounds to lower the product purity. On the other hand, the ignition temperatures for the system with the addition of metals are still relatively high. Therefore, the realization for initiating the TE reaction from the Ti-C system at a low temperature can be significant in promoting the development and practical application of TiC ceramic matrix composites. In the present study, an attempt is performed to verify whether the TE reaction from the Ti-C system can be initiated at a low temperature under air. Moreover, the principal ignition mechanism and reaction mechanism of the Ti-C system under the incorporation of
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