Thermophysical properties of boron carbide irradiated by ionizing radiation

Differential-scanning calorimetry is used to study the thermophysical properties of boron carbide irradiated by the ionizing radiation from the $^{60}\rm Co$ source. With increased temperature, the heat capacity and entropy values of nonirradiated and irradiated $\rm B_4 \rm C$ specimens increase. At high temperatures $(723$–$1300$ K$)$, the character of variation of the enthalpy and the Gibbs' potential of the irradiated $\rm B_4 \rm C$ specimen depends on the presence of oxygen. The values of the thermodynamic functions vary due to the formation of excited atoms, active centers, defects of the $\rm B_4 \rm C$ crystal structure, and $\rm B_4\rm C$ oxidation in the presence of the air oxygen after the ampoule opening. Also possible is an increase, at $723$–$1300$ K, in the rate of oxidation of the boron carbide surface (contacting with the air oxygen), where the defects that form upon irradiation are distributed. At temperatures above $723$ K, melting of the oxygenated part $(\rm B_2\rm O_3)$ in $\rm B_4\rm C$ specimens irradiated by the absorbed dose of $194$ Gy is observed; that process continued until the transformation of $\sim 26\%$ of crystal structure into the amorphous phase at $1300$ K.