Search

Physico-chemical behavior of vanadium in chloride melts was studied using high temperature electronic absorption spectroscopy and spectroelectrochemistry. Dissolution of VCl3 in molten chloride leads to the formation V(III) species, VCl63-. Vanadium(II) complex ions VCl64- are formed during electroreduction of vanadium(III)-containing melts and vanadium metal anodic dissolution. V(II) chloro-species slowly react with silica to form an oxygen-containing insoluble phase. Due to high volatility of VCl4 oxygen-containing vanadyl species, VOCl42-, is the only stable form of V(IV) in fused chlorides. It is formed when V2O5, V2O4 or V2O3 react with HCl. Electroreduction of vanadyl complexes leads to the formation of insoluble oxygen-containing vanadium(III)species, whereas electrochemical oxidation has no effect on vanadium speciation, VO3+/VO2+ red-ox potential is more positive than Cl2/Cl-. Further oxidation VO2+ species gives vanadate anions. The electronic absorption spectra of soluble vanadium species were measured in 3LiCl-2KCl, NaCl-KCl and NaCl-2CsCl mixtures at 450-750 0C.

The corrosion resistance of nickel, molybdenum and two types of stainless steel (12H18N10T (analog of AISI321) and AISI316L) were investigated in molten salt media. Corrosion tests were carried out in NaCl-KCl equimolar mixture and niobium-containing mixture NaCl-KCl-NbCln employing gravimetric analysis, metallography, potentiometry, polarization and voltametry. It was shown that molybdenum metal is most stable material both in pure alkali chloride and in niobium-containing electrolytes. The corrosion processes of studied materials under inert atmosphere have electrochemical nature.

The process of vanadium electrolytic refining in NaCl-KCl melt was performed in the specially designed semi-industrial scale electrolyser. The method of experiments mathematic planning was used to determine the electrolysis optimal conditions. In a special series of industrial experiments distribution of metallic and non-metallic impurities during vanadium electrorefining was investigated. The optimal parameters of the electrolysis for producing 99.5% pure vanadium were determined and the requirements for purity of crude materials formulated.

The article presents a discussion of "These Are the Times," a screen biography of British revolutionary and intellectual Thomas Paine. It highlights Paine's participation in the American Revolution and his influence on the French Revolution. It also contains excerpts from the screenplay written by Trevor Griffiths.

The formation of phosphates of the lighter lanthanides Ln  La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy by reaction with alkali metal phosphates has been studied in a LiCl–KCl eutectic melt between 450 and 650 °C and in a NaCl–KCl equimolar melt at 750 °C and under an inert atmosphere. Alkali metal ortho-, meta- and pyrophosphate precursors have been employed. The reaction results in the formation of single lanthanide or double alkali metal–lanthanide orthophosphates, the former favoured in LiCl–KCl melts and the latter in NaCl–KCl melts. The mean crystallite size of precipitated phosphates was evaluated from X-ray powder diffraction patterns, and found to be within 300–450 Å. Increasing the melt temperature results in increasing the crystallite size of phosphate phases. This technique offers an attractive means of removing lanthanide fission products from chloride melts arising from pyrochemical reprocessing of spent nuclear fuels. LiCl–KCl based melts are recommended because the bulk of phosphate waste precipitated is smaller since normal rather than double phosphates are formed therein.

A detailed investigation of the dissolution of alkali metal uranates in carbonate melts has been performed for the first time. The solubilities are reported for three alkali metal (Li, Na and K) mono- and diuranates, between 723 and 1073 K in alkali metal carbonate mixtures, and ranged from 20 to 275 wt ppm. The solvents used were the carbonate eutectics Li–Na, Li–K and Li–Na–K, and the low melting carbonate liquid Na–K. The well-known V-shaped behaviour of the solubilities of binary oxides in molten sulfates and carbonates with basicity increase was here observed for mono- and diuranates(VI). The explanation in terms of acid–base behaviour holds, the acidity and solubilities decreasing initially with temperature increase and then reversing as the melt becomes more basic. Uranate dissolution is thus both a physical and chemical process and hence from these data the solubilisation enthalpy in both acidic and basic melts was obtained for all six uranates(VI) in the four melts. Further, the oxidation of UO2 to form uranates in molten carbonates must proceed by mass transfer of an oxidising species through a layer of uranates formed on the urania surface.

The problem of the uniqueness of parameters obtained during fitting of experimental spectra containing closely overlapping bands has been evaluated, since conventional methods of fitting do not produce reliable results. It is here shown that, despite the difficulties inherent in both the formal mathematical problem and its numerical solutions, typical and representative spectra can be resolved unambiguously within a reasonably chosen theoretical model. Reliable values of the parameters of the model, including parameters of band shape, can also be obtained. A random search method of global minimisation of a function with a significant number of arguments is derived. A program and algorithm to implement this method for spectra decomposition have been developed. The program allows the microdynamics of liquids to be obtained directly upon performing numerical Fourier transformations on a model (theoretical) time correlation function together with using model spectra obtained thereby in each fitting step. A model spectrum for any desired accuracy and frequency range can hence be generated without the unavoidable errors inherent in conventional methods. The apparatus function of the spectrophotometer is also now readily incorporated. Using the algorithm, the parameters of the microdynamics of acetonitrile molecules are obtainable for the first time upon decomposition of its ν2 Raman vibration, and a value of 0.069 was obtained for the dimensionless modulation speed in liquid acetonitrile. This method has also enabled for the first time the detection of molecules in the second solvation shell around Li+ in acetonitrile, from within its Raman spectrum.

The optical absorption spectrum of the octahedral moiety CoCl4(H2O)2 in single crystal [(CH3)3NH]CoCl3·2H2O has been studied at room and liquidair temperatures. The observed ambient bands at 6800, 16,300, and 19,000 cm-1 have been assigned, respectively, to the transitions4T1(F) ?4T2(F),4A2(F), and4T1 (P). The crystal field parameters evaluated areDq=B=850 cm-1, andC=4.63B. At liquid-air temperatures the4T1(P) band is seen to split into the expected four componentsG7,G8,G8, andG6, due to spin-orbit coupling, and the coupling coefficient? was computed to be 525 cm-1.

The optical absorption spectrum of Ni2+ doped in NH4Br single crystals has been studied at room and liquid-air temperatures. The observed ambient bands at 6300, 11,600, 13,400, 18,500, and 20,000 cm-1 have been assigned, respectively, to the transitions3A2(F) ?3T2(F),3T1(F),1E(D),1T2(D and3T1(P). The crystal field parameters evaluated areDq=630 cm-1,B=850 cm-1, andC=3600 cm-1. In assigning the location of Ni2+ ions within the lattice, evaluations are made of the (limited) extant comparable data. It is then concluded that Ni2+ enters an octahedral interstitial, rather than a substitutional, site. It is surrounded by four bromide ions, in a plane, with two polarized water molecules at the opposing fifth and sixth positions.

Claims have been made that aqueous sodium sulfate solutions exhibit an anomalous temperature dependence close to the transition point of the solid decahydrate (Na2SO4·10H2O), viz., 32.38°C. In studies of dilute solutions these claims have been queried. Concentrated solutions, where this effect might be more readily detected, have not been investigated. A very accurate analysis of the shift of the charge transfer to solvent spectrum of iodide, a sensitive probe of its environment, (6×10-5 M) in concentrated (1 and 2 M) sodium sulfate solutions, as a function of temperature has not evinced any support for a structural change in solution on traversing the transition point temperature.

An excerpt from the play "Thatcher's Children" by Trevor Griffiths that was first performed at the Old Vic in Great Britain on May 19, 1993 by Giles Thomas, is presented.

The plain films of the skull of 625 patients with verified intracranial tumours have been reviewed. It is clear that the examination of such films continues to form an indispensable preliminary to any further radiological examination which may be necessary. Some of the abnormalities seen have been considered at length, their incidence assessed and compared with that noted in other series of cases. Attention has been drawn to the classification of gliomas devised by Kernohan and Sayre (1952), and which has received wide clinical acceptance.