Ternary Ceramics Ti₃SiC₂: Combustion Synthesis and the Reaction Mechanism

Abstract

In this study, Ti3SiC2 was successfully synthesized by the combustion of green samples with a composition formula: (3-x)Ti/Si/(2-x)C/xTiC, where x ranged from 1.0 to 1.8. First, the Ti3SiC2 yield monotonically increased with x, but the maximal yield was less than 50%. The most important factor to increase the Ti3SiC2 yield was found to be the post-combustion heating. The yield dramatically increased to about 90% when a 150-second post-combustion heating time was provided. Furthermore, the yield was proportional to the post-heating time, and linearly increased with the amount of applied post-combustion heating energy. Next, excess Si in the starting reactant powders can further increase the extent of Ti3SiC2. When the mole of Si increased from 1.0 to 1.1, the resulted yield was more than 99%. For the study of reaction mechanism, analyses of sequential layers of quenched samples resulted in the following proposed mechanism. First, TiC, TiSi2, Ti5Si3 were formed from the reactions of Ti, Si and C powders. Next, the eutectic liquids (Ti-Ti5Si3 and Si-TiSi2) covered the TiC particles at the elevated temperature. In the final stage, product Ti3SiC2 was resulted from heating the eutectics and TiC. It is noted that the last two steps required large energy, indicating the post-combustion heating was crucial to produce high-purity Ti3SiC2 product.

Self‐Propagating High‐Temperature Synthesis of Ti3SiC2: Study of the Reaction Mechanisms by Time‐Resolved X‐Ray Diffraction and Infrared Thermography

“…Moreover, Lis et al 15,29 and Khoptiar and Gotman 18 have shown that, for high heating rates of the reactants (500 K/s in their case), metallic reactants rapidly melt and form a Ti-Si liquid phase. Such a Ti-Si liquid phase is also supported by the work of Huang and Chen 27 and is the base of the so-called temperature fluctuation procedure developed by Zhang et al 30 The absence of a liquid signature in our TR-XRD analysis likely results from the low penetration depth of the Xray beam (beam energy is about 4.9 keV to avoid the Ti fluorescence), from the flow of the liquid phase through the pores of the medium or from the low volume fraction of the liquid phase.…”

“…Such a first step of the reaction between Ti-Si-C reactant mixtures is in very good agreement with different observations previously performed by other authors. 14,27,28 During the heating of the (3Ti1Si12C) powder blend up to t 2 , TR-XRD analyses do not indicate any other solid state reaction; neither Ti 5 Si 3 18 nor Ti 5 Si 3 C x 17 intermediate phases were detected. To our knowledge, Ti 5 Si 3 C x is always formed as an intermediate phase when SiC is used as silicon source.…”

“…Such a result is in good agreement with the phases obtained by other groups. 14,15,18,27,28 Consequently, TiC x solid particles are assumed to coexist with a Ti-Si liquid at t 3 . As the Ti 3 SiC 2 amount increases and the TiC x content decreases while the Ti-Si liquid phase is present, nucleation of the MAX phase is heterogeneous in nature and not homogeneous as discussed in Khoptiar and Gotman 18 and Lis et al 29 Such a heterogeneous nucleation is moreover supported by the results of Huang and Chen which show that Ti 3 SiC 2 is likely formed from solid TiC x and Ti-Si liquid phase.…”

“…As the Ti 3 SiC 2 amount increases and the TiC x content decreases while the Ti-Si liquid phase is present, nucleation of the MAX phase is heterogeneous in nature and not homogeneous as discussed in Khoptiar and Gotman 18 and Lis et al 29 Such a heterogeneous nucleation is moreover supported by the results of Huang and Chen which show that Ti 3 SiC 2 is likely formed from solid TiC x and Ti-Si liquid phase. 27 Finally, the Ti-Si liquid phase and solid TiC x reorganize into the final product of Ti 3 SiC 2 . Such a formation mechanism is similar to the ones proposed by Huang and Chen 27 and by Zhang et al 30 By decreasing the fluctuation rate, Zhang et al have indeed shown that the TiC x amount decreases which implies that very stable TiC x decomposes in the presence of a Ti-Si liquid phase.…”

“…27 Finally, the Ti-Si liquid phase and solid TiC x reorganize into the final product of Ti 3 SiC 2 . Such a formation mechanism is similar to the ones proposed by Huang and Chen 27 and by Zhang et al 30 By decreasing the fluctuation rate, Zhang et al have indeed shown that the TiC x amount decreases which implies that very stable TiC x decomposes in the presence of a Ti-Si liquid phase. More work is needed in order to have a better understanding of the interaction between solid TiC x and Ti-Si liquid phase.…”