Absorption of molecular radioiodine from the water vapor-air flow

Sorption of ¹³¹I₂ from the water vapor-air medium on inorganic nanocomposite materials was studied. All the nanocomposite materials synthesized, containing 1, 2, 4, and 8 wt % Ag in various chemical forms, remove ¹³¹I₂ from the water vapor-air flow with more than 99% efficiency.     

Sorption of CH3 131I from a water vapor-air flow onto inorganic sorbents containing Ag and nonferrous metals (Cu,Ni, Zn)

Sorption of CH₃ ¹³¹I from a water vapor-air medium onto Fizkhimin inorganic sorbents containing Ag and nonferrous metals (Cu, Ni, Zn) was studied. Ag-free Fizkhimin inorganic sorbents exhibit poor ability to take up CH₃ ¹³¹I. No more than 51% of the initial 10-mg portion of CH₃ ¹³¹I is taken up by the sorbents heated to 350°C. The sorbents containing 1.4–2 wt % Ag and 5.6–8 wt % nonferrous metal (Cu, Ni, Zn) show high ability to take up CH₃ ¹³¹I (>99.8% uptake), with the performance of the Ni-containing sorbents remaining very high (>99.9%) with variation of various parameters of both the sorbents and the medium. The Cu- and Zn-containing analogs do not exhibit such properties.     

Localization of CH<Subscript>3</Subscript><Superscript>131</Superscript>I from Water vapor–Air flow on granulated sorbents containing nanoparticles of Ag and Ni compounds

Sorption of CH₃ ¹³¹I from the water vapor–air medium onto Fizkhimin inorganic sorbents containing nanoparticles of Ag and Ni compounds was studied. The developed solvents containing 2 wt % Ag and 4–10 wt % Ni exhibit high performance in CH₃ ¹³¹I sorption (>99.9% uptake). The sorption efficiency remains very high (>99.9%) as characteristics of the sorbents and the medium are varied.     

Removal of volatile radioactive iodine compounds from water vapor–air medium

Sorption of CH₃ ¹³¹I and ¹³¹I₂ from water vapor–air medium onto SiO₂–C (2 wt %) composite material and a mixture of SKT-3I with SiO₂–Cu⁰ (10 wt %) was studied. SKT-3I shows high performance in sorption of ¹³¹I₂ and CH₃ ¹³¹I. The degree of localization of ¹³¹I₂ and CH₃ ¹³¹I exceeds 99.99% at ~60°С and gas phase–sorbent contact time τ of ~0.45 s. The degree of sorption of ¹³¹I₂ and CH₃ ¹³¹I onto the SiO₂–C (2 wt %) composite material under similar conditions does not exceed ~87 and ~8%, respectively. Experiments on ¹³¹I₂ and CH₃ ¹³¹I sorption onto mechanical mixtures of SiO₂–Cu⁰ and SKT-3I in the weight ratio varied from 1: 4 to 1: 1 showed that the degree of the ¹³¹I₂ and CH₃ ¹³¹I sorption at ~60°С and τ ~0.45 s exceeded 99.95 and 99.0%, respectively. The scheme of layer-by-layer arrangement of SiO₂–Cu⁰ and SKT-3I in the column was examined. It shows promise for use in AUI-1500VM filters in ventilation systems of nuclear power plants.     

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.     

Behavior of 131I and 137Cs in the oil-water and oil-gas phase systems

The behavior of ¹³¹I and ¹³⁷Cs in various chemical forms in the oil-water and oil-gas phase systems and the sorption of these radionuclides from radioactive transformer oil onto various inorganic and organic sorbents was studied. The degree of the ¹³⁷Cs extraction depends neither on the time of contact of the oil with aqueous solutions nor on the ¹³⁷CsI concentration in the solution. Under all the experimental conditions, the degree of extraction of ¹³⁷Cs did not exceed 5%. The degree of ¹³¹I extraction from water by the oil depends on the chemical form of the radionuclide: ¹³¹I^?, ³¹IO ₃ ^? , or ¹³¹I₂. The maximal extraction (～70%) is observed for K¹³¹IO₃, and the minimal (～25%), for ¹³¹I₂. Granulated nanocomposites containing particles of carbon or NaX zeolite and Fizkhimin sorbents based on coarsely porous silica gel and containing Ag and Ni in 1: 4 ratio allow efficient removal of ¹³⁷Cs and ¹³¹I from spent transformer oil of GK grade.     

Sorption of 131I2 and CH3 131I from gas-water vapor medium with porous inorganic sorbents containing d elements

Sorption of ¹³¹I₂ and CH₃ ¹³¹I from gas-water vapor medium on porous inorganic sorbents based on silica gel of the MSKG type, containing d elements, was studied. Sorbents containing Zn, Ni, Cu, and Co ammoniates show a low degree of recovery of ¹³¹I₂ and CH₃ ¹³¹I from the gas-water vapor flow (less than 30%); their calcination at a temperature above 250°C does not noticeably affect the sorption power of the sorbent. The sorbents containing Zn, Ni, and Cu nitrates, both unmodified and modified, show a low degree of recovery of CH₃ ¹³¹I from the gas-water vapor medium (less than 1%). At the same time, whereas for unmodified sorbents the degree of recovery of ¹³¹I₂ from the gas-water vapor phase does not exceed 70%, their modified analogs have higher degree of absorption of ¹³¹I₂ (more than 99%), comparable with the similar data for Ag-containing sorbents based on silica gel of the MSKG type.     

Gas-Phase UV Photolysis of CH<Subscript>3</Subscript><Superscript>131</Superscript>I

Gas-phase UV photolysis of ¹³¹I-labeled CH₃I was studied. CH₃ ¹³¹I (228 mg) is completely photolyzed within 5 min under the static conditions at room temperature in an argon atmosphere. The final radioiodine compound formed under these conditions is ¹³¹I₂. The chemical composition of the final products of CH₃I photolysis in air is more complex. Agglomeration corcystallization of the CH₃I photolysis products with NH₄Cl in the gas phase was studied. The results of this study suggest that the main final product of CH₃I photolysis in air is a fine I_xO_y aerosol. In the presence of NH₄Cl, formation of NH₄ ¹³¹I aerosols is possible.__________Translated from Radiokhimiya, Vol. 47, No. 3, 2005, pp. 269–273.Original Russian Text Copyright © 2005 by Kulyukhin, Kulemin, Rumer, Konovalova.     

Sorption of CH3131I from the Gas Phase on Modified Metal-Substituted Zeolites Containing Copper and Silver Ions

Sorption of CH₃ ¹³¹I from vapor-gas flow with acetylene-modified Cu⁺- or Ag⁺-containing zeolites in argon atmosphere was studied. The decontamination factor of the gas flow from radioiodine with the sorbent containing 7% of Ag⁺ is considerably higher than that of the Cu⁺-containing zeolite and reaches more than 10⁴ at the bed height of 6.5 cm and contact time of 3.4 s. The sorbent capacity is more than 9 mg of CH₃I per 1 g of the sorbent. In treatment of the sorbent with water after absorption of CH₃I, ¹³¹I is not noticeably desorbed to aqueous phase.     

Sorbents for treatment of water vapor-air flows to remove volatile organic compounds of radioactive iodine

Sorption of CH₃ ¹³¹I from water vapor-air medium on Fizkhimin and Siloksid inorganic sorbents and on SKT-3I activated carbon was studied. The sorption power of Fizkhimin, Siloksid, and SKT-3I sorbents toward CH₃ ¹³¹I was examined (1) after their 20-h contract with water, followed by removal of the liquid phase and drying at 110°C; (2) after 4-h treatment with steam (95–98°C), followed by drying at 25°C; (3) after keeping for 9 months in 100% humid air at ambient temperature of 10 to 45°C; and (4) after treatment with a water vapor-air flow (95–98°C, 60–80 vol % water vapor) for 2 h. In most cases, Fizkhimin sorbent and SKT-3I activated carbon preserve high sorption efficiency toward CH₃ ¹³¹I from water vapor-air flow.     

Recovery of <Superscript>131</Superscript>I and <Superscript>137</Superscript>Cs from a solution simulating NPP trap waters

Sorption of ¹³¹I and ¹³⁷Cs from a solution simulating NPP trap waters on various inorganic and organic sorbents was studied. The highest degree of ¹³¹I recovery (>99%) can be attained with Fizkhimin granulated sorbents based on coarsely porous silica gel containing Ag and Ni in 1: 4 ratio, with K _d for ¹³¹I exceeding 10⁵ ml g⁻¹ at V/m = 10³ ml g⁻¹ and contract time of the solid and liquid phases of 120 min. Elevation of the solution temperature to 40°C does not affect the degree of ¹³¹I and ¹³⁷Cs recovery. The degree of ¹³⁷Cs recovery in all the experiments did not exceed 35%. The degree of ¹³¹I recovery by coprecipitation with AgCl and Ag₄[Fe(CN)₆] was about ∼96% and only 65%, respectively.     

Sorption of CH<Subscript>3</Subscript><Superscript>131</Superscript>I from water vapor-air medium on porous inorganic sorbents containing triethylenediamine and <Emphasis Type="Italic">d</Emphasis> element nitrates

Sorption of CH₃ ¹³¹I from a water vapor-air medium on porous inorganic sorbents based on silica gel of KSKG grade and containing triethylenediamine (CH₂-CH₂)₃N₂ and d element nitrates was studied. The sorbents prepared by impregnation with (CH₂-CH₂)₃N₂ and Zn, Ni, and Cu nitrates from aqueous solution recover CH₃ ¹³¹I from a water vapor-air flow poorly (degree of recovery <10%). Calcination of the sorbents at temperatures exceeding 250°C does not noticeably affect their sorption power. Heating of the complex Ag(NO₃)(OH)·(CH₂-CH₂)₃N₂H to 160°C causes its exothermic decomposition with a large heat release and formation of metallic silver. Thermal decomposition of the complex of Cu²⁺ with (CH₂-CH₂)₃N₂, synthesized from an aqueous solution at the molar ratio Cu(NO₃)₂: (CH₂-CH₂)₃N₂ = 1: 2, occurs similarly.     

Recovery of iodine and cesium radionuclides localized on granulated sorbent Fizkhimin from air-vapor phase

A procedure for recovery of ¹³¹I and ¹³⁷Cs radionuclides from Fizkhimin sorbent containing ¹³⁷Cs¹³¹I and ¹³⁷CsOH radioaerosols and also of Ag¹³¹I formed in the sorbent matrix during chemisorption of gaseous ¹³¹I₂ and CH₃ ¹³¹I was developed. Sequential treatment of the sorbent with 6.0 M HNO₃ and then 10.0 M N₂H₄·nH₂O allows practically complete (more than 99%) removal of ¹³⁷Cs and noticeable decrease of the ¹³¹I content in the sorbent matrix (in some cases, by a factor of more than 10).     

Microstructure and tribological behaviour of super-hard Ti-Si-C-N nanocomposite coatings deposited by plasma enhanced chemical vapour deposition

In this study, a series of new quaternary Ti-Si-C-N nanocomposite coatings have been deposited on HSS substrate at 550 °C using an industrial set-up of pulsed direct circuit plasma enhanced chemical vapour deposition (PECVD) equipment with a gas mixture of TiCl₄/SiCl₄/H₂/N₂/CH₄/Ar. The composition of the coatings can be controlled through the adjustment of CH₄ flow rate and the mixing ratio of the chlorides. Detailed structural and chemical characterisations using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) suggest the formation of a Ti (C, N)/a-C/a-Si₃N₄ nanocomposite structure. Ti (C, N) films show a (200) texture, which change to random orientation of the crystallites when the silicon content reaches about 9 at.%. The tribological behaviour of these coatings was investigated at room and elevated temperature. The results show that the nanocomposite Ti-Si-C-N coatings with low Si and high C contents have a lower friction coefficient of 0.17-0.35 at room temperature. The Ti-Si-C-N nanocomposite coating containing 12 at.% Si and 30 at.% C shows excellent tribological properties with a low friction coefficient of 0.30 and a low wear rate of 4.5 × 10⁵ mm³ N^− 1m^− 1 at 550 °C.     

Sorption of I2 and CH3 131I on ion-exchange materials from aqueous solutions at 20°C

Sorption of I₂ and CH₃ ¹³¹I from aqueous solutions at 20°C on the materials obtained by modification of KU-2 cation-exchange resin was studied. It was found that these materials are able to absorb I₂ both from distilled water and from a solution whose composition corresponds to the composition of aqueous coolant of the primary circuit of NPPs equipped with reactors of the WWER type, with the distribution coefficients K _d higher than 10³ ml g^?1 at the ratio V/m = 100 ml g^?1. Practically complete absorption of I₂ (>95%) is reached in 15 min. It was shown that AV-18 anion-exchange resin extracts CH₃ ¹³¹ I from aqueous solution with a distribution coefficient K _d exceeding 300 ml mg^?1 at the ratio V/m = 100 ml g^?1.     

Improved photocatalytic degradation of organic dye using Ag<Subscript>3</Subscript>PO<Subscript>4</Subscript>/MoS<Subscript>2</Subscript> nanocomposite

Highly efficient Ag₃PO₄/MoS₂ nanocomposite photocatalyst was synthesized using a wet chemical route with a low weight percentage of highly exfoliated MoS₂ (0.1 wt.%) and monodispersed Ag₃PO₄ nanoparticles (~5.4 nm). The structural and optical properties of the nanocomposite were studied using various characterization techniques, such as XRD, TEM, Raman and absorption spectroscopy. The composite exhibits markedly enhanced photocatalytic activity with a low lamp power (60 W). Using this composite, a high kinetic rate constant (k) value of 0.244 min^-1 was found. It was observed that ~97.6% of dye degrade over the surface of nanocomposite catalyst within 15 min of illumination. The improved photocatalytic activity of Ag₃PO₄/MoS₂ nanocomposite is attributed to the efficient interfacial charge separation, which was supported by the PL results. Large surface area of MoS₂ nanosheets incorporated with well dispersed Ag₃PO₄ nanoparticles further increases charge separation, contributing to enhanced degradation efficiency. A possible mechanism for charge separation is also discussed.     

Synthesis of nanostructured M/Fe3O4 (M = Ag,Cu) composites using hexamethylentetramine and their electrocatalytic properties

Nanoscaled Ag/Fe₃O₄ hybrids with different Ag contents and Cu/Fe₃O₄ nanoshpere and microsphere were successfully synthesized with assistance of sodium citrate and (CH₂)₆N₄ via a hydrothermal process. The as-prepared samples were identified and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS), respectively. All samples were used as electrocatalysts modified on a glassy carbon electrode for p-nitrophenol reduction in a basic solution. The catalytic activity of Ag/Fe₃O₄ samples increased first and then decreased by increasing Ag content from 0% to 8%, and the one with 6% Ag displayed the highest catalytic activity. All the Cu/Fe₃O₄ samples exhibited enhanced catalytic activity by comparison with a glassy carbon electrode, and the one prepared with the molar ratio of Cu²⁺, Fe³⁺, citrate anion, and (CH₂)₆N₄ with 1:1:3:5 exhibited the highest catalytic activity.     

Effect of annealing on mechanical properties of self-reinforced alpha-silicon carbide

Alpha-SIC powder containing 7.2 wt % Y₃Al₅O₁₂ (YAG, yttrium aluminum garnet) and 4.8 wt % SiO₂ as sintering aids were hot-pressed (SC0) at 1820°C for 1 h and subsequently annealed at 1920°C for 2 h (SC2), 4 h (SC4) and 8 h (SC8). When the annealing time was increased, the microstructure changed from equiaxed to elongated grains and resulted in self-reinforced microstructure consisted of large elongated grains and small equiaxed grains. Development of self-reinforced microstructure, consisted of mostly 6H phase, resulted in significant improvements in toughness. However, the improved toughness was offset by a significant reduction in strength as in the materials consisted of 4H originated from -SiC. The fracture toughness and strength of the 8-h annealed materials were 5.5MPa · m^1/2 and 490 MPa, respectively.     

Microwave plasma enhanced chemical vapor deposition diamond synthesis from high carbon content source

To synthesize diamond films by microwave plasma enhanced chemical vapor deposition (MPECVD), the methane concentration (CH₄/H₂)plays a crucial role. It is well-known that there always exists a critical methane concentration (≤0.6%) only below which a good quality diamond film can be obtained. In this study, however, the phenomena of diamond synthesis resulting from high carbon concentration conditions were observed. The molten metals, e.g., Ag, Cu, were used as the deposition substrates on which crystalline diamonds can be achieved from a methane content of CH₄/H₂≥6% or even from solid carbon sources. These results suggest that there may exist a low methane content boundary layer (<0.6%) in the proximity of molten metal surface on which suitable species, CH, CH⁺, H_α and H_β are composed for the diamond nucleation and growth similar to the condition as in the conventional low methane contents. The molten metal inclines to dissolve other forms of carbonaceous materials other than diamond, and thus keeps a much higher steady supply of carbon atoms that enhances the quality as well as the growth rate of the forming diamonds. Received: 23 June 2001 / Accepted: 23 July 2001     

Silver(I)–3,6-bis(pyridin-3-yl)-1,2,4,5-tetrazine coordination polymers: a diversity of chain motifs

The influence of solvent and anion on the formation of coordination polymers between silver(I) and 3,6-bis(pyridin-3-yl)-1,2,4,5-tetrazine (3,3′-pytz), a bridging ligand that can adopt both cisoid and transoidconformations, is reported. Reaction of AgPF₆ in MeCN with 3,3′-pytz in CH₂Cl₂ gives ([{Ag(NCMe)₂}(μ-3,3′-pytz)][PF₆]·MeCN)_∞, 1, of AgPF₆ in MeNO₂ and 3,3′-pytz in CH₂Cl₂ gives ([{Ag₂(μ-3,3′-pytz)₂}(μ-3,3′-pytz)][PF₆]₂·4MeNO₂)_∞, 2, and of AgCF₃SO₃ in MeCN and 3,3′-pytz in CH₂Cl₂ gives {[Ag(μ-3,3′-pytz)]CF₃SO₃}_∞, 3. These cationic coordination polymers exclusively form chain structural motifs. That in 1, ([{Ag(NCMe)₂}(μ-3,3′-pytz)]⁺)_∞, has a castellated construction with each tetrahedral silver(I) center coordinated by two solvent molecules as well as two linking transoid-oriented 3,3′-pytz bridges (Ag⋯Ag 13.210 Å) in a 1:1 polymeric chain. That in 2, ([{Ag₂(μ-3,3′-pytz)₂}(μ-3,3′-pytz)]²⁺)_∞, is novel. It is the first coordination polymer to exhibit both cisoid and transoid conformations of a bridging ligand coordinated to the same metal center. Pairs of silver(I) centers are linked by pairs of cisoid-oriented 3,3′-pytz molecules (Ag⋯Ag = 11.695 Å) to form [Ag₂(μ-3,3′-pytz)₂] motifs, which are bridged, in turn, by transoid-oriented 3,3′-pytz molecules (Ag⋯Ag = 13.318 Å) to form a 3:2 ligand:metal infinite polymeric zigzag chain. That in 3, {[Ag(μ-3,3′-pytz)]⁺}_∞, has a zigzag architecture despite being based on linear silver(I) centers. Transoid-oriented 3,3′-pytz molecules link silver(I) centers (Ag⋯Ag 13.225 Å) to give a 1:1 ligand:metal infinite polymeric zigzag chain. The chains aggregate in parallel pairs linked by weak Ag⋯Ag contacts (Ag⋯Ag = 3.220 Å), which are supported by (μ₂-κO,κO′) bridging CF₃SO₃⁻ anions.