Reaction kinetics in Ti3SiC2 synthesis studied by time-resolved neutron diffraction

The reactive sintering of 3Ti/SiC/C to form the ternary carbide Ti3SiC2, previously found to involve the intermediate phases TiCx and Ti5Si3Cx, was investigated by time-resolved neutron powder diffraction. The kinetics of Ti3SiC2 formation from the intermediate phases TiCx Ti5Si3Cx (x <= 1) and a small amount of free C was determined. The crystallization rate of the Ti3SiC2 phase was determined through quantitative analyses of the diffraction patterns collected at different temperatures and is initially well-described by the Mehl-Avrami-Johnson equation. The activation energy was found to be 380 +/- 10 kj/mol and the Avrami exponent 3.0 +/- 0.2. The Avrami exponent decreases to close to I when more than half of the crystallization process was completed. This indicates a change in the mechanism of Ti3SiC2 crystal growth from unrestricted two or three-dimensional growth in the a-b planes to one-dimensional growth only, due to interaction of the growing,disk-like crystals and cessation of growth in the preferred direction