The reactive sintering of 3Ti/SiC/C to form the layered ternary carbide Ti3SiC2 was studied in situ by time-resolved neutron powder diffraction. A number of intermediate processes occur during the synthesis beginning with the alpha-beta transition in Ti. Concurrent with the alpha-beta transition, two intermediate phases, TiCx and Ti5Si3Cx (x less than or equal to 1), form. These phases account for almost the entire sample in the range 1500-1600degreesC beyond which they react with each other and a small amount of free C to form the product phase Ti3SiC2.