Authors:P. Dimotakis, B. Symeopoulos, and M. Demetriou
The monotonic kinetics of isothermal yield of51Cr(VI) in51Cr(III)-doped potassium chromate reveals a common mechanistic scheme with that of neutron irradiated K2CrO4, including two first order processes during the examined first hour. One of them is fast and the other very slow, but both seem to be controlled by two thermal coefficients.
monotonically toward higher temperatures. Using the T g and T p obtained at various heating rates, following Eqs. 1 and 2 , the ln q vs. 1/ T g and ln ( q/T p 2 ) vs. 1/ T p plots are found to be linear with slope giving the E s and E c
The kinetics of homogeneous electron exchange Eu3+/Eu2+ has been investigated in 1M HClO4, water+dimethylformamide (DMF) mixed solvent by using labeled europium. Non-monotonic variations of the electron exchange rate constants as a function of the solvent composition was observed.
The thermodynamics of protonation of the lanthanide(III) chelates of trans-1,2-diaminocyclohexanetetraacetic acid (LnDCTA−) was studied by potentiometric titration at the ionic strength of 1 (KCl). The protonation constants determined change monotonically
and the double-double effect in the log K against Z variation is manifested in all four segments of the lanthanide series.
The variations of the protonation enthalpy and entropy with Z are estimated to be also monotonical. The direction of the double-double
effect observed indicates that the coordination number in the protonated chelates is higher by 1 in the entire series than
in non-protonated chelates i. e. the protonation is accompanied by the coordination of the additional water molecule. The
coordination number 10 is expected for the HLnDCTA chelates at least at the beginning of the series. Presumably the present
conclusions are valid also for the LnEDTA− system.
In lithium borate glasses RLi2OB2O3 (0
R<0.4), the following experimental results were obtained: 1. The density increases monotonically with increasing R.2. Both velocities of longitudinal and transverse ultrasonic waves increase monotonically with increasing R.3. The elastic constants such as bulk modulus and Young's modulus increase monotonically with increasing R.4. The linear expansion coefficient shows a broad minimum at around R=0.25. 5. The Poisson ratio shows a minimum at around R=0.10 and a maximum at around R=0.20. 6. Each of the temperature coefficients of velocities for longitudinal and transverse ultrasonic waves shows a sharp minimum at R=0.10 and a sharp change in slope at R=0.20. The experimental results 1, 2 and 3 can be ascribed to a change in short-range order groups. The experimental result 4 is ascribable to the most compact configuration at around R=0.25. The experimental results 5 and 6 are ascribable to a change in crosslink between six-membered borate rings.
The anion exchange behaviour of transplutonium elements, Am, Cm and Cf, has been studied in 0.3–1.3M hydrochloric acid solutions containing methyl alcohol 85% or more at elevated temperature. The distribution coefficients of the elements were increased monotonically with increasing concentration of hydrochloric acid and/or that of methyl alcohol at 90°C by forming anionic chloride complexes. Californium was separated by anion exchange within several drops of effluent from the trace amounts of americium, curium and fission products and macro amounts of aluminium and uranium, and samples for alpha-ray spectrometry were immediately prepared by directly evaporating the eluent drops on a counting disk.
Extraction of cesium by the nitrobenzene solution of bis-1,2-dicarbollylcobaltate in the presence of dibenzo-18-crown-6 (DB18C6, L) was investigated. It was found, that besides hydrated cesium ion Cs
the complexes CsL
were extracted to nitrobenzene phase. No maximums on dependencies of the cesium distribution ratio (D) on the concentration of crown in the systemcL was found andD increased monotony withcL. Values of extraction constants and stability constants of extracted species in nitrobenzene have been determined.
Authors:I. Varga, E. Kuzmann, M. Káldor, and A. Vértes
Mössbauer spectroscopy was used in order to get information about the anomalous austenite formation1 taking place between 450–600 °C in steel containing 12%Cr and 4%Ni. Even below the equilibrium transition temperature (640 °C) of
transformation a monotonic increase of the relative spectral area of the line belonging to austenite was observed in the Mössbauer spectra of the steel isothermally aged at 550 °C with increasing ageing time. At the same time, the Cr content of the ferrite phase decreases. Time dependence of the quantity of austenite formed during the isothermal ageing follows the Avrami-kinetics with an exponent n=0.3.
Authors:P. Lavrenko, O. Okatova, K. Andreeva, and B. Schulz
Translational diffusion of poly-2,5-(1,3-phenylene)-1,3,4-oxadiazole (PMOD) in solution in 96% sulphuric acid was studied,
and intrinsic viscosity was measured at different stages of thermal degradation. Polymer solution has previously been subjected
to heating at temperature ranging from 75 to 104C and then investigated at 26C. A monotonic decrease in intrinsic viscosity
and the molecular mass, M, of degraded products with increasing degradation temperature was detected. The rate constant of the degradation process
has been obtained from the change in M of the degradation products with time at a fixed solution temperature, and the activation energy of the process was calculated
by using the temperature dependence of the rate constant. The activation energy (E =1028 kJ–1 ) is close to that obtained previously for the hydrolysis of poly-2,5-(1,4-phenylene)-1,3,4-oxadiazole (PPOD) in sulphuric
acid (106 kJ–1 ), the rate constant being approximately twice in the value.
Authors:M. Reddy, A. Damodaran, J. Mathur, M. Murali, and R. Iyer
Mixed-ligand chelate extraction of trivalent lanthanides such as La, Eu and Lu and a trivalent actinide, Am into xylene with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP) and dihexyl-N,N-diethylcarbamoylmethylphosphonate (CMP) has been studied by tracertechniques. These trivalent metal ions are found to be extracted from 0.01 mol/dm3 chloroacetate buffer solutions as M(PMBP)3·HPMBP type self adducts with HPMBP alone and in the presence of CMP as M(PMBP)3·CMP (where M=La, Eu, Lu and Am) into the organic phase. The equilibrium constants of the above species are deduced by non-linear regression analysis. The synergistic constants of trivalent lanthanides do not increase monotonically with atomic number but have a maximum at Eu and that of Am was found to lie between that of La and Eu.