Tetrafluoroethylene telomerization initiated by benzoyl peroxide

The radical telomerization of tetrafluoroethylene initiated by benzoyl peroxide (BP) photolysis at λ ≥ 365 nm is studied in acetone, dichloromethane, carbon tetrachloride, and Freon 114B2 at 25°C. The products of synthesis are a mixture of telomers of different molar masses, segregated into soluble and insoluble fractions. To characterize the radicals initiating telomerization, crystalline BP and its solution in ethanol are subjected to low-temperature (77 K) photolysis, with the liquid system serving as a model for BP behavior in solutions of telogens. It is established that radicals are not only initiators but also participate in chain termination reactions, lowering the telomers’ molar mass and thus raising the proportion of the soluble fraction. Telomerization initiated by an initiator compound versus initiation by gamma radiation are compared and discussed.     

Kinetics and mechanism of radiation telomerization of tetrafluoroethylene in hexafluoropropan-2-ol and trifluoroethanol

The kinetics of radiation telomerization of tetrafluoroethylene (TFE) in trifluoroethanol and hexafluoropropan-2-ol (HFIP) has been investigated by method of kinetic calorimetry. The nature of active centers initiating the process of telomerization of tetrafluoroethylene in hexafluoroisopropanol in the temperature range of 77—300 K was investigated by ESR spectroscopy. The molecular structure and properties of the obtained telomeres were studied by IR spectroscopy and TGA.     

Thermoluminescence measurements of ceramic samples from accidentally polluted territory of southern urals

During 1949–1956, the plutonium production facility Mayak released large quantities of radioactive waste into the Techa river. As a result, a contamination of the river system occurred, and the population of the riverside villages was exposed to external and internal irradiation. Currently, the problem of dose assessment must be solved to make correct risk estimations using the information on long-term epidemiological observations from the URCRM database. TL measurements are an important part of this work. The method of TL dating of ancient pottery and geological objects originally developed in the late 1960s was modified for retrospective dosimetry using environmental materials such as bricks, from procedures developed at Moscow State University. Special investigations were carried out for correct dose estimations in quartz extracted from different layers of brick samples. A number of brick samples were collected from a few buildings that remained in the village of Metlino which was situated 7 km below the point of release and was demolished in 1956. The accrued doses in quartz extracted from the outer centimeter of the bricks ranged from 0.76 to 5.28 Gy. The highest doses were measured in the samples from a wall of the mill located near the river bank.     

Spontaneous polymerization of acrylamide in glycerol: Active centers and specific features

The nature of active centers and the specific features of the spontaneous polymerization of acrylamide in glycerol in the range 300-77 K have been studied. Glycerol activation is needed for polymerization. At this stage, active intermediate species are formed and stabilized under the action of photo-and γ radiation. Intermediate species are hydroperoxide compounds resulting from the sensitized (through technical traces) photolysis (or radiolysis) of glycerol. The decomposition of hydroperoxides into radicals on addition of finely dispersed acrylamide powder into the activated glycerol yields primary acrylamide radicals that initiate the growth of polymer chains.     

Incommensurate structural correlations in the disordered spin-dimer state induced by X-Ray and electron irradiation in CuIr2S4

Irradiation with approximately 10 keV x rays or medium-energy electrons destroys long-range order of Ir spin dimers in CuIr2S4 while preserving the dimers locally. We find that as the order is destroyed, a new type of incommensurate structural correlations appears. This represents an intriguing example of order from disorder phenomenon, in which a previously unknown incommensurate order appears in the radiation-induced disordered state. These results suggest that two competing instabilities, one of which can be suppressed by radiation, are present in the system. Otherwise unrealized structural or electronic states can, therefore, be revealed in correlated systems by x-ray or electron irradiation.     

Ferroelectricity in an ising chain magnet

We report discovery of collinear-magnetism-driven ferroelectricity in the Ising chain magnet Ca3Co2-xMn(x)O6 (x approximately 0.96). Neutron diffraction shows that Co2+ and Mn4+ ions alternating along the chains exhibit an up-up-down-down ( upward arrow upward arrow downward arrow downward arrow) magnetic order. The ferroelectricity results from the inversion symmetry breaking in the upward arrow upward arrow downward arrow downward arrow spin chain with an alternating charge order. Unlike in spiral magnetoelectrics where antisymmetric exchange coupling is active, the symmetry breaking in Ca3(Co,Mn)2O6 occurs through exchange striction associated with symmetric superexchange.     

Formation of pancakelike Ising domains and giant magnetic coercivity in ferrimagnetic LuFe2O4

We have studied quasi-two-dimensional multiferroic LuFe2O4 with strong charge-spin-lattice coupling, in which low-temperature coercivity approaches an extraordinary value of 9 T in single crystals. The enhancement of the coercivity is connected to the collective freezing of nanoscale pancakelike ferrimagnetic domains with large uniaxial magnetic anisotropy ("Ising pancakes"). Our results suggest that collective freezing in low-dimensional magnets with large uniaxial anisotropy provides an effective mechanism to achieve enhanced coercivity. This observation may help identify novel approaches for synthesis of magnets with enhanced properties.     

A monopole mass filter with a hyperbolic V-shaped electrode

In this article we compare the classical monopole mass filter of von Zahn and the monopole mass filter with a hyperbolic V-shaped electrode. The experimental results and those of computer simulation for both mass spectrometers are presented. We show that the replacement of a conventional 90 degrees V-shaped electrode by an electrode with a hyperbolic profile substantially improves the peak shape of any given mass, and increases the mass resolution by a factor of 3-4 and the abundance sensitivity by a factor of 100. The potential of high analytical performance combined with electroforming techniques for electrode manufacture indicate future practical uses of such instruments. Copyright 1999 John Wiley & Sons, Ltd.