Electrical conductivity of iodine adducts of nylon 6 and other non-conjugated polymers

Iodine-nylon 6 adducts containing 70 to 90wt% iodine have been prepared by heating iodine and nylon 6 at 115 and 145° C. The electrical conductivity () of the adduct increases with increase in the iodine content and the iodine-nylon 6 adduct containing 90wt% iodine and prepared at 145° C gives = 10^–3 S cm^–1 at 25° C. Infrared, nuclear magnetic resonance (¹H and¹³C{1 H}), and powder X-ray diffraction analysis of the adduct show a profound change of the structure around the amide group of nylon 6 and suggest the formation of a-C=NH⁺-group in the reaction of nylon 6 with iodine. The temperature dependences of of the idoinenylon 6 adducts prepared at 115° C give activation energies of 51 to 92 kJ mol^–1 depending on the iodine content. Addition of carbon powder to the iodine-nylon 6 adduct causes an increase in electrical conductivity. Other polymers (aliphatic and aromatic nylons, poly(vinyl alcohol), poly (tetrahydrofuran), poly(N-vinylpyrrolidone), poly (4-vi nylpyridine), and poly(acrylonitrile)) which have lone pair or -electrons also form iodine adducts containing 70 to 95 wt % iodine and the adducts show an electrical conductivity in the range of 10^–5 to 10^–2 S cm^–1. Among the iodine adducts, those of poly(vinyl alcohol) and poly (tetra hydrofuran) show electrical conductivities as high as 1.5 X 10^–2 S cm^–1 when the adducts contain about 90 wt% iodine.     

Thermal decomposition of CH3 131I in a gas flow

Thermal decomposition of a volatile organic compound of radioactive iodine, methyl iodide CH₃ ¹³¹I, in a gas flow in the presence of various modifications of granulated materials based on KSKG silica gel impregnated with d elements was studied. Under comparable experimental conditions, 97–99% decomposition of CH₃ ¹³¹I is achieved at 770 ± 15°C without sorbents and at 540 ± 10 and 465 ± 20°C in the presence of straight KSKG silica gel and of the material based on it, impregnated with compounds of Ni or its mixture with Cu (8–10 wt %), respectively.     

Radiation resistance of a composite ferrocyanide-silica gel sorbent

The radiolytic behavior of FNS composite ferrocyanide sorbent based on potassium nickel ferrocyanide and silica gel was studied. γ-Irradiation of the sorbent results in formation of hydrogen due to radiolytic decomposition of water in the solid phase. The hydrogen yield (molecules/100 eV) is 0.02 for the dry sorbent and 0.07 for the wet sorbent. The amount of hydrogen formed in the course of storage of the sorbent saturated with ¹³⁷Cs was calculated. On irradiation of the dry sorbent in the potassium form to a dose of 4 MGy, the ¹³⁷Cs distribution coefficient K _d decreases by a factor of 2.5. However, K _d of ¹³⁷Cs on irradiated sorbents remains sufficiently high (>10⁴), i.e., the FNS ferrocyanide sorbent shows high functional resistance to radiation. γ-Irradiation of dry and wet samples of the ferrocyanide sorbent to a dose of 4 MGy does not lead to oxidation of Fe(II) to Fe(III) in [Fe(CN)₆] groups. Thus, FNS ferrocyanide sorbent is a radiation-resistant material suitable for recovery of cesium radionuclides from liquid radioactive wastes and the subsequent long-term and safe storage.     

Preparation of Exfoliated Graphite Modified with Magnesium Ferrite

A magnetic sorbent based on exfoliated graphite modified with magnesium ferrite has been prepared by impregnating oxidized graphite in a mixed solution of FeCl₃ and Mg(NO₃)₂, followed by heat treatment of the impregnated oxidized graphite in air. X-ray diffraction and Mössbauer spectroscopy results demonstrate that the structure of the magnesium ferrite is an inverse spinel with a degree of inversion of 0.59. The saturation magnetization of the magnesium ferrite-containing exfoliated graphite is 16.1 emu/g, whereas its oil sorption capacity is as high as 54 g/g. Compaction of the exfoliated graphite to a density of 0.03 g/cm³ reduced its sorption capacity to 26 g/g. Further increasing the density of the material led to a considerable decrease in its sorption capacity.     

Crystallisation of selenium thin films doped with iodine after evaporation

Amorphous selenium thin films deposited under vacuum have been doped with iodine either during or after crystallisation. It is shown that when the films are first crystallised at 363 K for 6 h and then submitted to iodine atmosphere at 363 K for 1 h, the structural properties of the films are not modified while their conductivity increases by a factor of 8. Iodine atmosphere induces post crystallisation of amorphous selenium films even at room temperature by increasing the selenium atom mobility at the surface of the films, which induces growth of crystalline spherulites. With annealing, when the heating rate is high (>15 K/min), constraints appear in the films, the density of spherulites increases and the films are inhomogeneous. When the heating rate is small and constant (1 K/min) the interaction between iodine and selenium takes place all over the sample and there is only a small density of small spherulites, while the crystallisation of the whole sample is more homogeneous. XPS and microprobe analysis that the iodine is equally repartitioned in the selenium film show it. Moreover there is a mixture of neutral iodine andS I₃ ^– as shown by XPS and Raman studies. The high crystalline quality of the films can explain the high conductivity (>10^{–3 –1} cm^–1) of these selenium doped films     

Sorption of Iodine,Cesium, and Strontium Radionuclides on Alkaline-Earth Hydroxyphosphates from Aqueous Solutions

Sorption of ¹³¹I⁻, ¹³¹IO ₃ ⁻ , ¹³⁷Cs⁺, ⁸⁵Sr²⁺, and F⁻ ions on synthesized alkaline-earth (AE) (calcium, strontium, and barium) hydroxyphosphates was studied. These hydroxyphosphates were prepared by the reactions MCl₂ +Na₃PO₄ + NaOH = M₅(PO₄)₃OH; MCl₂ + NH₄OH + (NH₄)₂HPO₄ = M₅(PO₄)₃OH; and MCl₂ + NaOH + (NH₄)₂HPO₄ = M₅(PO₄)₃OH (M = Ca, Sr, Ba). All the tested AE hydroxyphosphates do not sorb ionic species of radioactive iodine from aqueous solutions. The highest sorption power with respect to fluoride ion is exhibited by calcium hydroxyphosphate. The degree of ¹³⁷Cs and ⁸⁵Sr sorption recovery from aqueous solutions upon their 120-min contact with AE hydroxyphosphates is ∼5–25 and ∼15–80%, respectively.__________Translated from Radiokhimiya, Vol. 47, No. 1, 2005, pp. 80–84.Original Russian Text Copyright © 2005 by Kulyukhin, Krasavina, Mizina, Rumer, Tanashchuk, Konovalova.     

Sorption of Radioactive Iodine on Polymeric Sorbents from Aqueous Solutions and Gas Phase

Sorption of various species of radioactive iodine from aqueous and gas phases on polymeric sorbents Styrosorb and Polysorb-1 was studied. These sorbents do not take up ionic species of radioactive iodine (¹³¹I^- and ¹³¹IO₃ ^-) from aqueous solutions. At the same time, both sorbents take up ¹³¹I₂ from aqueous solutions at 25°C. At V/m = 500 ml g^{- 1}, the distribution factors K _d are 1350 and 590 ml g^{- 1} with Styrosorb and Polysorb-1, respectively. These sorbents efficiently recover ¹³¹I₂ from an air flow at 25°C and flow velocity of 0.33 cm s^{- 1}. The sorption capacity of Styrosorb is approximately four times higher than that of Polysorb-1 and amounts to 97.0 mg of I₂ per gram of sorbent. These data are consistent with the specific surface areas of the sorbents.     

Optical and electrical properties of soluble copolymers of pyrrole-thiophene-3-decylthiophene

Three novel soluble copolymers of pyrrole(P)-thiophene(T)-3-decylthiophene (D) at different molar ratio of comonomers 4 : 1 : 5, 1 : 4 : 5 and 1 : 1 : 2 have been synthesized. NMR, FTIR, UV, emission spectroscopy, GPC, DSC, TGA and conductivity measurements were used to characterize these copolymers. The dark electrical conductivity increases from 3–7 × 10^–6 S/m for undoped samples to 10^–1–10^–2 S/m for samples doped with 4% of iodine, and to 10–10² S/m for 16% of iodine in a form of I₃ ^–.     

Carbon fibre-reinforced silicon nitride composite

The processing of silicon nitride reinforced with carbon fibre was studied. The problems of physical and chemical incompatibility between carbon fibre and the silicon nitride matrix were solved by addition of a small amount of zirconia to the matrix and by low-temperature hot-pressing. The composite material possesses a much higher toughness than hot-pressed silicon nitride. Its work of fracture increased from 19.3 J m^–2 for unreinforced Si₃N₄, to 4770 J m^–2; its fracture toughness,K _lc , increased from 3.7 MN m^–3/2 for unreinforced material, to 15.6 MN m^–3/2. The strength remains about the same as unreinforced Si₃N₄ and the thermal expansion coefficient is only 2.51×10^–6 ° C^–1 (RT to 1000° C). It is anticipated that this composite may be promising because of its mechanical and good thermal shock-resistance properties.     

Electrocal,thermal, thermoelectric and related properties of magnesium silicide semiconductor prepared from rice husk

Polycrystalline, 10m size magnesium silicide was prepared by alloying 99.9% purity polycrystalline silicon obtained from rice husk ash and high-purity magnesium powder. The material in sintered pellet form was characterized for its structural, electrical, thermal, thermoelectric and other properties. A typical sintered pellet exhibited a room-temperature (30°C) thermoelectric power of 565 V K^–1 and an electrical resistivity of 35 cm. On the other hand, the material was found to be thermally quite stable up to 650°C with a room-temperature thermal conductivity of 6.3×10^–3cals^–1cm^–1K^–1 (2.6 J s^–1 m^–1 K^–1). These properties of the material indicate that the material can find potential applications as a thermoelectric generator and in other semiconductor devices. Furthermore, an indigenous technology for large-scale production of silanes (SiH₄) can be developed using this Mg₂Si which could be prepared in large quantities by a simple and low-cost process.     

Simulated strength and structure of carbon–carbon reinforced composite

The atomistic simulations of carbon nanotube (CNT) – carbon reinforced composite material are reported. The studied composite samples are obtained by impregnating certain amounts of CNTs (3,3) and (6,6) into a pristine graphite matrix. The addition of CNTs is found to be of significant usefulness for the CNT–reinforced composites, since it allows to achieve extreme lightness and strength. Being impregnated into graphite matrix, CNTs are able to increase the critical component of its initially highly anisotropic Young modulus by 2–8 times. The linear thermal expansion coefficients do not exceed 10⁻⁶ to 10⁻⁵ K⁻¹, making this material applicable for novel aviation and space vehicles. The degree of dispersion of CNTs within graphite matrix is found to drastically influence composite properties.     

A study of the crystallization process of Na1.6Zn0.8Si1.2O4 glass and the ionic conductivity properties of partially crystallized samples

The crystallization process of Na_1.6Zn_0.8Si_1.2O₄ glass was studied by means of differential scanning calorimetry, X-ray powder diffraction and the platinum/carbon replication technique. Partially crystallized samples were made by rapidly cooling samples from elevated temperatures using the DSC apparatus, and the ionic conductivity of the materials was determined by means of impedance measurements conducted at lower temperatures where the crystallization rate was negligible. The glass was found to crystallize at 830 K by precipitation and three-dimensional grain-growth of a crystobalite-type phase with the same composition as the glass. The overall activation energy for the crystallization process was determined from isothermal DSC measurements to be 340 kJ mol^–1. The bulk ionic conductivity for partially crystallized samples increases smoothly from 9.3 x 10^–5( cm)^–1 at 600 K for the glass to 2.4 x 10^–3( cm)^–1 for the crystallized material.     

Poly(3-nonylthiophene-co-methylthiophene)s: New soluble conductive copolymers

New conductive soluble copolymers of 3-nonylthiophene (3NT) and 3-methylthiophene (3MT) were chemically synthetized using FeCl₃ in chloroform solution as a catalyst at room temperature and a N₂ atmosphere. The structural properties of the undoped and iodine doped 3NT-co-3MT have been studied by UV-Vis, FTIR, 1H- and ¹³C-NMR, GPC, DSC, TGA, WAXD, magnetic susceptibility and charge transfer measurements. The results show that copolymers (3NT-co-3MT) have a random arrangement. These copolymers have good thermal stability dependent on the 3NT. 3MT content and low magnetic susceptibility (typical for compounds of this class) which decreases with increasing temperature. The conductivity of the iodine doped copolymer (3NT-co-3MT) (measured in the dark at room temperature) increases distinctly in comparison to the undoped samples (2–8×10^–9 Sm^–1).     

Corrosion-cracking resistance of austenitic stainless steel under stress in an iodine medium

The critical iodine concentration (C_cr) is determined for steel KhNS-4 (steel OKH16N15M3B after vacuum remelting and and microalloying with Sc) at 923°K to assess the feasibility of its use as a jacket material for the fuel cells of fast reactors. The value of C_cr is established from criteria of residual deformation at failure, longevity, and creep rate under a given stress. Experiments are conducted under ordinary and in reactor conditions. It is noted that creep rate is the most sensitive criterion. It increases sharply as the iodine concentration reaches values of 10–15 mg/cm², depending on the stress level, whose growth is accompanied by an increase in the value of C_cr It is demonstrated that radiation damage improves resistance to corrosion cracking. It is concluded that the C_cr values obtained exceed the corrodent concentration actually obtained by many times.Translated from Problemy Prochnosti, No. 12, pp. 12–17, December, 1993.     

Diamond Crystallization in the System B4C–C

Superhard polycrystalline diamond material consisting of crystallites less than 20 m in size and containing less than 5 wt % B₄C is synthesized in the graphite–B₄C system at 2600–2800 K and 8–9 GPa. In the Raman spectrum of this material, the main band (1332 cm^–1) is shifted to lower frequencies by 40 cm^–1, typical of heavily boron-doped diamond films. Based on experimental data, a mechanism is proposed for the transformation of graphite into polycrystalline diamond at temperatures between the melting points of the B₄C–diamond and B₄C–graphite eutectics.     

Sorption properties of silicate materials based on Ca<Subscript>2</Subscript>SiO<Subscript>4</Subscript>

Sorption studies showed that a silicate material formed in the course of metallurgical slag reprocessing, containing dicalcium silicate as the major component, exhibits high affinity (logK _d [ml g⁻¹] > 4) for U(VI), Pu(IV), REE(III), and Th(IV) cations and for simple anions and appreciable affinity (logK _d [ml g⁻¹] > 2) for Cs(I) and Sr(II) cations in their sorption from river water. The sorbent can be of practical interest for separation, preconcentration, neutralization, and recovery of harmful chemical elements and radioactive substances from aqueous solutions, followed by their cementation (solidification) and safe disposal.     

Thermodynamic Modeling of the Vacuum Synthesis of Transition-Metal Borides

Thermodynamic analysis of the Ti–B–C–O and V–B–C–O systems was carried out with the aim of establishing the conditions of TiB, TiB₂, VB, VB₂, and V₃B₄formation at temperatures from 673 to 1813 K and total pressures in the system from 10⁵to 10^–3Pa. The results indicate that B and B₄C are more suitable boronizing agents than B₂O₃and that the formation of the borides in stoichiometric mixtures is preceded by the formation of carbides and lower borides. The calculations point to a carbon deficiency in the starting mixtures, which can be compensated by introducing free carbon. Preliminary results of electron-beam boronizing demonstrate the feasibility of producing refractory-metal boride coatings on the surface of carbon steels in a vacuum of 10^–2to 10^–3Pa. The thickness of the TiB₂, VB₂, and W₂B₅coatings thus produced is 80–100, 50, and 15–20 m, respectively. A part of the boronizing paste was found to convert into single-phase powder borides.     

Phase distribution of iodine in the course of production of <Superscript>99</Superscript>Mo concentrate

A novel procedure was suggested for studying the phase distribution of radioactive iodine in the liquid–gas system. Without redox reactions, the degree of iodine transfer into the gas phase is maximal for sulfuric and nitric acid solutions at pH ≤ 1.5. In weakly acidic, neutral, and alkaline solutions, the iodine transfer into the gas phase is insignificant (degree of transfer <0.05). Conditions for stabilization of iodine species (presence of redox reagents, solution acidity) were found. The most efficient purification of ⁹⁹Мо to remove iodine radionuclides is observed in sulfuric acid solutions, where the probability of formation of IО₃ ^– anions, exhibiting the highest affinity for titanium hydroxide, is minimal. Silver-modified Termoxid sorbents are suitable for selective sorption of iodine only from alkaline solutions (0.3–0.5 M NaOH), with the best result obtained for Т-5(Ag) (iodine distribution coefficient 2000–3000 mL g^–1). An additional step of purification of alkaline molybdenum concentrates to remove iodine on Т-5(Ag) sorbent was suggested; it allows the residual iodine content of the molybdenum concentrate to be decreased by a factor of 20.     

Electrical conductivity,TEP and dielectric studies on mol% 66.6 Agl-22.2 Ag2O-11.1 (0.8 V2O5-0.2 P2O5) electrolyte material for solid state batteries

In the superionic conducting quarternary system Agl-Ag₂O-V₂O₅-P₂O₅, the best ionic conductivity was obtained for the composition 66.6% Agl-33.3% (2Ag₂O-1 (V₂O₅-P₂O₅)), when the GF/GM ratio was varied from 0.20 to 5.0. Then fixing the GF/GM ratio at 0.50, the ratio of the glass formers V₂O₅ and P₂O₅ were varied and the highest conducting composition was obtained as 66.6% Agl-22.2 Ag₂O-11.1% (0.8 V₂O₅-0.2 P₂O₅). A preliminary investigation using this material in the form of an electrolyte in a solid state electrochemical cell is reported. The polycrystalline and amorphous compounds were prepared from the same melt, by open air crucible melting and the rapid quenching technique. The ionic conductivity for the best conducting polycrystalline (hence referred as 66VP82P) and amorphous (66VP82G) samples was obtained as 8.3 × 10^–3 and 4.2 × 10^{–2 –1} cm^–1 respectively. The electronic conductivity of the order 10^{–10 –1} cm^–1 was observed for 66VP82G and 10^{–8 –1} cm^–1 for 66VP82P samples. Thermoelectric power studies revealed that the charge carriers are the Ag⁺ ions, with an activation energy of 0.288eV for 66VP82G, which correlated well with the activation energy obtained from the conductivity measurements. The dielectric constant, dielectric loss and the loss tangent were calculated for both polycrystalline and glassy 66VP82 material. It was observed that the dielectric loss is more for the glassy material than the polycrystalline material. Solid state galvanic cells with 66.6% Agl-22.2% Ag₂O-11.1% V₂O₅, 66.6% Agl-22.2%-Ag₂O-11.1% P₂O₅ and 66.6% Agl-22.2% Ag₂O-11.1% (0.8 V₂O₅-0.2 P₂O₅) (coded as 66V, 66P and 66VP82 respectively) electrolytes were constructed. Both polycrystalline and amorphous electrolyte cells were fabricated for a comparative study and the polarization effects were observed to be negligible in amorphous cells. The variation of open circuit voltage with temperature was reported and the current discharge curves indicate that the 66VP82 material has higher current capacity with high current drain when compared to 66V and 66P cells.     

Sorption of cesium iodide radioactive aerosols on metal felt during oxidative hydrolysis in steam gas-system

The behavior of ¹³⁷Cs ¹³¹I radioactive aerosols at sorption in a column packed with Bekipor WB metal felt from argon, air, and steam-gas flow was studied to assess the possibility of formation of CsI CsOH and CsI₃ in the course of CsI oxidative hydrolysis. The layer distribution of radionuclides in the column was analyzed as influenced by temperature (405–560 K), carrier gas humidity (up to 60 vol %), flow velocity (2–6 cm s¹), and amount of cesium iodide sorbed on the felt (0.7–65.0 mg). It was found that the oxidative hydrolysis under certain conditions yields CsI CsOH and CsI₃ aerosols. Although under the experimental conditions studied the sorption of radionuclides on the metal felt is nearly quantitative (97–99%), escape of the radionuclides from the column upon prolonged passing of steam-gas mixtures cannot be excluded.Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 449–453.Original Russian Text Copyright © 2004 by Kulyukhin, Mikheev, Kamenskaya, Rumer, Konovalova, Novichenko.