Thermophysical Properties of Boron Carbide Irradiated by Ionizing Radiation

Resumo

Differential-scanning calorimetry is used to study the thermophysical properties of boron carbide irradiated by the ionizing radiation from the ⁶⁰Co source. With increased temperature, the heat capacity and entropy values of nonirradiated and irradiated B₄C specimens increase. At high temperatures (723–1300 K), the character of variation of the enthalpy and the Gibbs’ potential of the irradiated B₄C 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 B₄C crystal structure, and B₄C 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 (B₂O₃) in B⁴C specimens irradiated by the absorbed dose of 194 Gy is observed; that process continued until the transformation of ~26% of crystal structure into the amorphous phase at 1300 K.