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Abstract  

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.

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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

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Abstract  

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.

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Double-double effect and the coordination number

I. Protonated and non-protonated lanthanide(III) chelates of trans-1,2-diaminocyclohexanetetraacetic acid

Journal of Radioanalytical and Nuclear Chemistry
Author: T. Mioduski

Abstract  

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.

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Abstract  

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.

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Abstract  

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.

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Abstract  

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 org + the complexes CsL org + and CsL 2,org + were extracted to nitrobenzene phase. No maximums on dependencies of the cesium distribution ratio (D) on the concentration of crown in the systemc L was found andD increased monotony withc L. Values of extraction constants and stability constants of extracted species in nitrobenzene have been determined.

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Abstract  

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.

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Abstract  

New polyurethanes with mesogenic units in the main chain due to the use of a liquid crystalline chain extender were synthesized from 4,4'-methylenebis(cyclohexyl isocyanate) (HMDI)using diisocyanates of different trans, trans isomer content, a low molecular diol4,4'-bis(6-hydroxyhexoxy)biphenyl (BHHBP) and a high molecular poly(hexyleneadipate)diol (PHA). The growth of trans, trans isomer content in HMDI used to syntheses of PU induces monotonic growth of melting point, rectilinear growth of crystallization temperatures and the growth of crystallization enthalpy, both for hard segment polyurethanes and block polyurethanes. The increase of trans, trans isomer content in HMDI increases also glass transition temperatures and dynamic storage modulus of the polyurethanes.

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Abstract  

Differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and dynamic mechanical analysis (DMA) of the blends ofepoxy cresol novolac (ECN) resin toughened with liquid carboxy terminated butadiene-co-acrylonitrile (CTBN) rubber have been carried out. Exothermal heat of reaction (ΔH) due to crosslinking of the resin in presence of diaminodiphenyl methane(DDM, as amine hardener) showed a decreasing trend with increasing rubber concentration. Enhancements of thermal stability as well as lower percentage mass loss of the epoxy-rubber blends with increasing rubber concentration have been observed in TG. Dynamic mechanical properties reflected a monotonic decrease in the storage modulus (E′) with increasing rubber content in the blends. The loss modulus (E″) and the loss tangent(tanδ) values, however, showed an increasing trend with rise of the temperature up to a maximum (peak) followed by a gradual fall in both cases. Addition of 10 mass% of CTBN resulted maximum E″ and tanδ.

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