Molecular-topological structure of γ-irradiated ftorlon polytetrafluoroethylene

Six topological structures (an amorphous and five crystalline blocks) have been detected in a polytetrafluoroethylene film with a pseudo-network structure. During the Γ-irradiation of the polymer in air, the crystalline fractions degrade and gradually convert into amorphous and cluster states with the increasing radiation dose. After irradiation at a dose of 90 kGy, the polymer loses its capability for crystallization and forms a completely amorphous topological structure. However, regardless of dose in the range of 3–90 kGy, the topological structure of the polymer irradiated in a vacuum remains unchanged and consists of amorphous, cluster, and crystalline blocks.     

Thermal Stability of γ-irradiated Tolbutamide

The thermal stability of tolbutamide before and after exposure to various γ-radiation doses was investigated. The data were followed by studying DTA, X-ray diffraction, IR, and UV absorption spectra before and after γ-irradiation. The results obtained were promising, and were explained, and discussed on the basis of γ-enhanced stabilization through recombination of free radicals. This revised version was published online in August 2006 with corrections to the Cover Date.     

Luminescent properties of γ-irradiated NaCl

Exposure of alkali halide crystals to high-energy radiation makes the crystals coloured and also causes them to glow. The luminescent behaviour of γ-irradiated NaCl crystals at room temperature is studied and results are presented on the correlation of known types of colour centres to the afterglow.     

Isothermal decomposition of γ-irradiated indium acetate

The isothermal decomposition of un-irradiated (pristine) and pre-γ-irradiated indium acetate was studied in the temperature range (298–1273 K) and in air using isothermal thermogravimetric technique. The data were analyzed using various solid-state reaction models. The results showed that the kinetic of isothermal decomposition of indium acetate was governed by random nucleation reaction (Erof’ev equation A₃). The kinetics and thermodynamic parameters of the main decomposition process for un-irradiated and γ-irradiated samples were calculated and evaluated.     

Characterization of γ-irradiated polychlorotrifluoroethylene by thermomechanical spectrometry

Three topological blocks (low- and high-temperature amorphous and crystalline) have been detected for the first time in polychlorotrifluoroethylene with a pseudo-network structure. The molecular weight of the polymer decreases and the crystalline and high-temperature amorphous fractions degrade with an increase in γ-radiation dose. Thermal annealing at 493 K leads to amorphization of the polymer, as well as its radiolysis. However, slow recrystallization of the thermally annealed polymer has been observed during storage at 300 K.     

Prevention of degradation of γ-irradiated EPDM using phenolic antioxidants

The mitigation of oxidative degradation under γ-irradiation promoted by eight commercial antioxidants: Ethanox 330, Hostanox O3, Irganox 1010, Topanol OC, Ionox 220, Santonox R, Santowhite, Cyanox 2246 loaded onto ethylene-propylene terpolymer at the concentration of 0.5 phr in respect of a pristine polymer was studied. The polymer samples were exposed to various doses up to 500 kGy. The kinetic parameters of oxidations: oxidation induction times, onset oxidation temperature, oxidation rates were evaluated by CL measurements. They validated the differences in the stabilisa-tion activities by limitation of the oxidation gradient. The high efficiency of some of the antioxidants studied, such as Ionox 220 and Santowhite, ensured the delay in degradation even at a high irradiation dose (500 kGy). For the environments with γ-radiation exposure, a relevant sequence in the increasing protection efficiency could be established: Topanol OC; Hostanox O3; Irganox 1010; Cyanox 2246; Santonox R; Ionox 220; Santowhite. The FT-IR spectra were recorded for the calculation of the radiochemical yields resulting from the modifications occuring in the concentrations of oxygenated structures. The accumulations of hydroxyl- and carbonyl-containing products were calculated to evaluate the irradiation effects in EPDM-based products during a severe accident. The options for EPDM stabilisation are discussed based on chemiluminescence and FTIR analyses.     

Degradation of γ-irradiated linear perfluoroalkanes at high dosage

The effects of the carbon backbone chain length on the EPR spectra of linear perfluoro-n-alkanes (PFAs) γ-irradiated at 77 K was studied for the short chain n-C₆F₁₄, n-C₈F₁₆, n-C₁₂F₂₆, and n-C₁₆F₃₄ molecules as well as the polymer polytetrafluoroethylene (PTFE). The experimental data show that the processes occurring during radiolysis of perfluoro-n-alkanes and polytetrafluoroethylene are very similar. EPR spectra of irradiated perfluoro-n-alkanes at low radiation dose show superimposed signals from three radicals: -F₂CCFCF₂-, -CF₂CF₂ and F₃C. The signal intensity decreases with perfluoro-n-alkanes chain length. At doses above 2.0 MGy, a constant increase in concentration of the radicals -F₂CCFCF₂- and -CF₂CF₂ is observed with decreasing chain length. The concentration of these radicals formed during radiolysis of PFA is described by the ratio: [-CF₂CF₂]/[-F₂CCFCF₂-] ≈3/(n − 2), where n is the number of carbon atoms in the linear perfluoroalkanes. Density functional theory was used to calculate the structures of the radicals and C-F bond energies in model perfluoro-n-alkanes as well as the EPR spectra of the associated radicals. This data is used to provide further insight into the radiation stability of PTFE. Four topographical structures of polytetrafluoroethylene, one amorphous and three crystalline, were identified by thermomechanical analysis. In the crystal phase, γ-irradiation results in their transformation to the amorphous form. The helical structure of individual perfluroalkanes readily distorts on removal of a fluorine and this will have an impact on the overall structure of the material. Such structural reorganization can lead to loss of the mechanical stability of polytetrafluoroethylene.     

Molecular-topology of powder of the γ-irradiated tetrafluoroethylene/ethylene copolymer

The molecular-topological structure of γ-irradiated commercial copolymers of tetrafluoroethylene with ethylene (CTE) were explored in the coaxial mode, which has the vectors of CTE loading and compression pressure in the same plane, and in the perpendicular mode with the two vectors perpendicular to each other. Instead of the amorphous-crystal structure observed with the coaxial orientation of the vectors, the CTEs are completely amorphous in their perpendicular orientation. Radiolysis with a dose of 140 kGy leads to the formation of a crosslinked structure for the CTEs. On irradiation, the crystals are transformed to an amorphous state and CTE can form a fully amorphous structure after 600 kGy of irradiation.     

Differential thermal analysis of γ-irradiated linear polyesters of terephthalic acid

Linear polyesters of terephthalic acid of general formula OCOC₆H₄COO(CH₂)_n (where n varied from 2 to 10) were irradiated with ⁶⁰Co γ-rays. Irradiations were carried out at room temperature at a dose rate of 1·5 Mrad/hr to give a total dose of 1000 Mrad. DTA analysis showed that the number of CH₂ groups within the aliphatic part of the polymer chain influences both the enthalpy of melting of the original polymers and also the change in ΔH caused by irradiation. Polyterephthalates which contain an even number of CH₂ groups (even polymers) exhibit a higher value of ΔH, but radiation affects this value to a lesser extent than for odd polymers, especially in the range 4 ⩽ n ⩽ 9. In the presence of air, the decrease in ΔH for irradiated polymers is more pronounced. Irradiation also leads to a decrease in the melting temperature, the change being greater for even polyterephthalates for 3 ⩽ n ⩽ 10 when irradiated in vacuum. In the presence of air, the change of melting temperature is more distinct for odd polymers for 4 ⩽ n ⩽ 9.     

Analysis of the ESR spectra of the ~ CF2CFCF2~ macroradical trapped in a γ-irradiated polytetrafluoroethylene matrix at 77 K

The Β-fluorine atoms in the ~CF₂CFCF₂~ radical trapped in γ-irradiated polytetrafluoroethylene (PTFE) were found to be nonequivalent and, hence, responsible for a doublet-triplet-triplet ESR spectral pattern. The conformational angle between the axis of the unpaired-electron orbital and the projection of C_Β-C_γ bond is equal to 60‡. The hyperfine coupling constants for α- and Β-fluorine atoms were determined. The hyper-fine splitting constants for two equivalent Β-fluorine atoms were found to be 7.2 mT. The corresponding value for the two other equivalent fluorine atoms is 1.8 mT, whereas the hyperfine splitting due to α-fluorine atom is 23.8 mT.     

Photoconductivity in γ-irradiated alkali halides

γ-irradiated alkali halides undergo bleaching under prolonged light illumination, hence the photocurrent decreases with time. We studied the kinetics of photocurrent decay of γ-irradiated alkali halides under steady-state illumination, and the spectral response of the photocurrent for various alkali halides. From the data on the variation of the photocurrent with applied electric field and intensity of F light employed for illumination, the value of the product of quantum efficiency and mean electron range per unit field is calculated at room temperature.     

Generation of hydrogen by hydroreactive compositions with γ-irradiated aluminum

The kinetics of hydrogen generation by heterogeneous hydroreactive compositions with aluminum, which was preliminarily γ-irradiated in air, held in aqueous solutions at room temperature, and annealed at a high temperature, was studied. Changes in the hydrogen generation kinetics depending on the γ-radiation dose, the composition of aqueous solution, and the temperature are caused by the conversion of aluminum oxide coatings, which should be taken into account in the prediction of the corrosion resistance of structural materials under the conditions of exposures at nuclear power plants.     

Features of the molecular–topological structure of γ-irradiated powdered tetrafluoroethylene–perfluoro(propyl vinyl ether) copolymer

With the use of thermomechanical spectrometry in two modes, coaxial, when the load application vector is coplanar with the compacting pressure vector (semicrystalline copolymer) during the measurement of the deformation of a copolymer of tetrafluoroethylene with perfluoro(propyl vinyl ether), and mutually perpendicular (completely amorphous copolymer), it has been established that the axial compression of the copolymer brought its topological structure to an absolutely anisotropic state. After γ-irradiation, the semicrystalline structure of the copolymer was retained regardless of the radiation dose. The minimum values of the glass transition temperature of the amorphous block and the degree of crystallinity were observed in the copolymer irradiated to a dose of 150 kGy. The molecular weight distribution functions of interjunction chains in the networks of the amorphous blocks of the initial copolymer and its γ-irradiated analogs are bimodal.     

Kinetics of thermal decomposition of γ-irradiated and unirradiated complexes of mandelhydroxamic acid

The thermal decomposition of -irradiated and unirradiated complexes of mandel-hydroxamic acid (HMA), Co(HMA)₂.1/2H₂O, Mn(HMA)₂.2H₂O, Ba(HMA)₂.2H₂O and Cd(HMA)₂.2H₂O have been studied thermogravimetrically (under isothermal conditions). The thermal dehydration of each complex occurred in one step, while the decomposition of dehydrated complexes occurred in two steps. The kinetic parameters for dehydration were computed by different models. The thermal dehydration is regulated by random nucleation A₃ for Co-, Mn-, and Cd-complexes and by phase-boundary (R₃) for Ba-complex. The effect of -irradiation on the kinetic parameters of thermal decomposition is discussed. Radiation did not modify the mechanism of the reaction but accelarated the dehydration steps in the case of Mn- and Co-complexes.     

Density and refractive index of some γ-irradiated alkali silicate glasses

The densities and refractive indices of some sodalime-silica glasses with replacements of CaO by either BaO or ZnO have been studied before and after being subjected to varying doses of -irradiation. Also, the effect of varying the Na₂O or Al₂O₃ content was investigated. The experimental results show that -irradiation produces a slight change in the density but a remarkable increase in the refractive index. These data are correlated with the way of housing of the cation introduced into the glass and its response on the compactness and flexibility of the glassy network. Also the effect of interaction of -rays with the glass and the creation of new induced defects in the glass network, which might affect the properties investigated, is considered.     

ESR spectra of γ-irradiated samples of iron(iii) binuclear complexes

-Irradiation of -oxo-bridged binuclear iron complexes Fe^III ₂OL _n in a glycerol or dimethylformamide matrix at 77 K affords unstable mixed-valence Fe^IIF^III forms resulting from the transfer of a mobile electron generated by the ionizing radiation. These nonequilibrium forms retain the ligand environment of the original complexes, and their ESR spectra at 77–200 K are characterized by an asymmetric signal with an axially anisotropicg-factor, which is in agreement with the spectra of the Fe^IIFe syu forms obtained by chemical reduction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 869–871, April, 1996.     

EPR evaluation of absorbed doses in γ-irradiated animal bone tissues

The accumulation of CO ₂ ^- radicals in γ-irradiated porcine, chicken, bovine, walleye pollack, and navaga bone tissues and chicken eggshells was studied by EPR spectroscopy for the purpose of detecting irradiated food and evaluating the dose absorbed during its radiation processing. It was found that, in the dose range 0–10 kGy, the concentration of radicals is a linear function of dose, and the variation coefficient of the radiationchemical yield of radicals is no higher than 30% for bone tissues from various biological species. The applicability of the additive dose method to the EPR dosimetry of irradiated beef was examined. A linear regression model used in the additive dose method was found to give overestimated results, as compared with an exponential fitting model.