Behaviour of the fluoroplastic-4 effected by nitrogen tetroxide and gamma-radiation

The kinetics of teflon swelling in nitrogen tetroxide has been studied both without irradiation and under irradiation, and the changes in its physico-mechanical properties (tensile strength, compression strength, relative elongation) under the same conditions. The tests have been made of standard samples in the form of plates (to determine the extent of swelling), blades and cubes (for mechanical measurements). The samples sealed in glass ampoules in nitrogen tetroxide medium, are exposed to gamma radiation (60Co) on the RKHM-gamma-20 irradiation installation. The dosemetry is conducted by the ferrosulfate method. The Fe2+/Fe3+ concentration change is determined by spectrophotometry. The irradiation is performed at 27 deg C, the pressure corresponds to the tension of N2O4 saturated vapours at the given temperature. The absorbed dose varies in the range of 0.1 to 10 Mrad. The swelling of teflon at room temperature makes up on the average 3.16 to 3.26%. At 50 deg C the equilibrium swelling is achieved on the 18-th to 20-th day and makes up 3.6 to 3.7%. The swelling is somewhat higher in the liquid phase. The data obtained give evidence that the gamma-irradiation practically does not influence the extent of the teflon swelling in nitrogen tetroxide. The tensile properties of teflon in N2O4 medium, as well as in vacuum or in air, vary under gamma radiation effect even at low absorbed doses - to 0.1 Mrad, and then with the absorbed dose increase to 10 Mrad they vary negligibly, while the deformation properties decrease considerably. The permissible dose of teflon irradiation in N2O4, when 50% of strength and plasticity is lost, is equal to 0.3 to 0.4 Mrad