Treatment of spent NTA-based decontamination solutions

This study deals with potential treatment of spent NTA-containing decontamination solutions for final disposal. The method proposed is based on the degradation of organic substances followed by the separation of radionuclides. The influence of various parameters (pH value, irradiation time, temperature, catalyst amount, type and various combinations of catalysts) on photocatalytic degradation of NTA has been studied. Photo-Fenton reagent (Fe³⁺/H₂O₂) as a homogenous catalyst was found to be much more efficient than the TiO₂-based heterogeneous catalyst Degussa P25. Under optimum conditions NTA in a simulant of a spent decontamination solution without or with hydrazine could be degraded within 5 or 9 hours, respectively. The study of sorption properties of a series of absorbers revealed that radiostrontium and radiosilver can be effectively removed from the simulant of a spent decontamination solution even in the presence of NTA, while total NTA degradation is necessary for effective radiocobalt separation.     

High-performance liquid chromatographic/ion-trap mass spectrometric speciation of aquatic mercury as its pyrrolidinedithiocarbamate complexes

Mercury-pyrrolidinedithiocarbamate complexes are first time used for speciation of aquatic mercury with high-performance liquid chromatographic/ion trap-mass spectrometric method utilizing atmospheric pressure chemical ionization (APCI). The separation of the four mercury species was achieved in less than 5 min with a linear gradient profile of aqueous methanol from 70 up to 100% (v/v) in 4th min, isocratic elution at 100% up to 5th min and followed by a negative gradient to 70% in 6th min. The best separation was achieved on a reverse phase Zorbax Eclipse XDB C18 column (50 mm × 2.1 mm i.d., 1.8 μm particle size). The on-column limits of detection (injection volume 1 μL) were 370 pg for methylmercury (MeHg⁺), 280 pg for ethylmercury (EtHg⁺), 250 pg for phenylmercury (PhHg⁺) and 90 pg for inorganic mercury (Hg²⁺) when the data were collected in selective ion monitoring (SIM) mode. A method of isolation and preconcentration of the mercury species using a “home-made” C18 solid phase extraction (SPE) microcolumns was developed to enhance sensitivity of the method. The preconcentration factor as much as 2500 was achieved with on-column complex formation of mercury-pyrrolidinedithiocarbamate. Methanol (100%) was chosen for elution of preconcentrated mercury species. The method was applied for the determination of mercury species in river water samples.     

Combined isolation and purification procedures prior to the high-performance liquid chromatographic-ion-trap tandem mass spectrometric determination of estrogens and their conjugates in river sediments

A fast and sensitive analytical procedure has been developed for the simultaneous separation and determination of alpha-estradiol, beta-estradiol, estriol, estrone and ethynylestradiol and their sulfate, glucuronide and acetate conjugates in river sediments. The procedure includes a microwave-assisted extraction (MAE) with aqueous methanol (25:75, v/v) at 100 degrees C in 10 min, a clean-up on Oasis WAX cartridge and a high-performance liquid chromatography-ion-trap tandem mass spectrometry (HPLC-IT-MS/MS) with electrospray ionization. The recovery for each compounds ranged from 83 to 107% and the repeatability represented as RSDs ranged from 4.9 to 9.6%. The limits of detection (LODs) were down to 1 ng g(-1). The analytical performance of the method was evaluated using determination of free and conjugated estrogens in river sediments.     

High-Temperature Corrosion Behavior of Superalloys in Molten Salts – A Review

The use of molten salts based on fluorides/chlorides/nitrates/sulfates or carbonates is now an accepted practice in energy conversion technologies and many other industrial processes. However, compatibility of molten salts with the structural alloys and materials corrosion has been of real concern at such temperatures (600–900°C). Hence, the material development and corrosion studies turn out to be an essential part of research. The results of recent studies are reviewed to understand the developments that have occurred in the latter part of the last decade. The corrosion kinetics of modern materials in variety of molten salts with focus on reaction mechanisms and corrosion products is investigated by scientists around the globe. Emphasis has also been given on the composition of the oxide films/corrosion products on alloys of interest in wide a range of melts. By and large, molten salt corrosion has been predominantly studied by gravimetric, electrochemical techniques and, morphology and chemical analysis of corrosion products by means of XRD, SEM/EDX, ICP/AAS, etc. This article gives in-depth insight into the composition of materials, the molten salt mixtures, and various aggressive environments mainly high temperatures and long exposures.     

On the Complexity of Cover-Incomparability Graphs of Posets

In this paper we show that the recognition problem for C-I graphs of posets is NP-complete. On the other hand, we prove that induced subgraphs of C-I graphs are exactly complements of comparability graphs, and hence the recognition problem for induced subgraphs of C-I graphs of posets is polynomial.     

Electronic structure and elasticity of Z-phases in the Cr-Nb-V-N system

Structural properties and energetics of Cr-based Z-phases (CrNbN, Cr(Nb,V)N and CrVN) were investigated using the Vienna ab?initio simulation package (VASP) code employing the projector augmented wave (PAW) pseudopotentials by means of both local density approximation (LDA) and generalized gradient approximation (GGA) for the exchange and correlation term. The geometry of all studied phases including NbN, VN and elemental constituents (nonmagnetic bcc Nb and V and antiferromagnetic bcc Cr) was fully relaxed, providing the equilibrium structure parameters and total energies. The calculated lattice parameters of Z-phases correspond very well to the experimental data and decrease with increasing molar fraction of vanadium. Enthalpies of formation show that all three Z-phases are stable at T?=?0?K. The electronic structures of Z-phases including densities of states and charge densities were analysed. The calculated bulk moduli and elastic constants were used to evaluate stability conditions and elastic anisotropy ratios. It was confirmed that Z-phases are mechanically stable. Additional information on ductility was obtained from Cauchy pressures, Pugh ratios, Young moduli, and Poisson ratios. The ductility evaluated using the Pugh ratio decreases with number of vanadium atoms.     

Dimerisation Process of Silybin‐Type Flavonolignans: Insights from Theory

Natural polyphenols are known to be oxidized by free radicals, which partially explains the antioxidant properties of a number of these compounds. This oxidation may also be used to synthesise new compounds of biological interest, for example, dimers. The present theoretical study describes the existing experimental evidence showing that silybin and dehydrosilybin [natural polyphenols isolated from milk thistle (Silybum marianum)] form dimers regioselectively. Based on DFT calculations, thermodynamic and kinetic values were computed in order to better understand the physicochemical behaviour of these dimerisation processes. Calculations showed that after H‐atom transfer (from polyphenol to radical), dimerisation could proceed in two steps: 1) bond formation and, when possible, 2) tautomerisation reorganisation. The former step is the limiting step, while the latter is crucial for the process to be thermodynamically favourable (ΔG<0). If this rearrangement is impossible then dimerisation is not feasible, or at least becomes a minor process (e.g., dehydrosilybin dimerisation after H‐atom abstraction from the 3‐OH group). This explains the regioselectivity of polyphenol dimerisation.     

Monte Carlo calculation of penetration of electrons into poly(methylmethacrylate)

Monte-Carlo method is applied to the problem of penetration of 20 keV and 30 keV electrons to polymethylmethacrylate. In this paper the ranges and backscattering yields are calculated and a comparison with the results obtained by different methods is made. Depth-dose functions are depicted as well.The authors wish to thank Mr. J. Kae of the Research Institute of Mathematical Machines for a valuable help in programming.