Raman Centre for Applied and Interdisciplinary Sciences, 16A, Jheel Road, Kolkata-700 075, India E-mail: cv@rcais.res.in, ritabratabhowmick@gmail.com, kghoshcu@gmail.com Present address: Department of Chemistry, Techno India-Batanagar, Kolkata-700 141, India Manuscript received 16 May 2018, revised 25 May 2018, accepted 26 May 2018 Boron carbide, an extremely hard material that is used in lightweight body armour and nuclear reactors, requires to be sintered at high temperature to form appropriate shapes. The quality and hardness of the product is affected by oxidative processes and reaction with traces of nitrogen in air. Information on the thermodynamics of such processes is quite limited. In this work, computational study of the thermodynamics of reactions of B4C with oxygen and nitrogen has been undertaken. This includes derivation of equilibrium constant (log k)-temperature relations and equilibrium O2/N2 activities-temperature relations in the region 273–2300 K, for all possible reactions with O2 and N2. Reaction phase diagrams were then derived to depict the reaction that is thermodynamically most favourable under the T-PO2/N2 conditions. All computations were done with a program in Mathematica, developed for this purpose. Results reveal that log k values for all oxidative reactions are positive and those producing the trioxide (B2O3) are energetically most favoured. Reaction phase diagrams show that B4C is stable only at extremely low O2 pressures and under high concentrations of gaseous components; the B moiety is more susceptible to oxidisation compared to C moiety. When heated, initially B2O3 is formed regardless of concentration of gases. Similar behaviour is observed in N2, where BN is produced at the lowest temperatures but is stable at higher temperatures. It is concluded that a surface layer of B2O3 produced initially serves as a protective shield against catastrophic oxidation of B4C