Ternary carbides such as Ti3AlC2 and Ti3SiC2 are nano-layered ceramics with the general formula Mn+1AXn (n=1-3), where M is an early transition metal, A is a group A element, and X is either carbon and/or nitrogen. These ceramics exhibit a unique combination of mechanical, electrical, thermal and physical properties such as good high-temperature strength, and excellent corrosion and damage resistance. For instance, the electrical and thermal conductivities of Ti3SiC2 are greater than that of titanium and its machinability is similar to graphite. However, these ceramics are susceptible to thermal dissociation at ~1400°C in inert environments (e.g., vacuum or argon) to form TiC and Ti5Si3C. The chemistry and kinetics of the dissociation processes involved are not yet fully understood. Surprisingly, the study of thermal stability in ternary carbides has received relatively little attention despite its importance in applications such as heating elements or the feasibility of designing functionally-graded Ti3SiC2-TiC with unique wear resistance and damage tolerance. In this paper, we present the thermochemical processes, phase relations and air-oxidised of Ti3SiC2 from 25-1500°C as revealed by neutron diffraction (ND), secondary-ions mass spectroscopy (SIMS).