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111.
S. D. Dogmane R. K. Singh D. D. Bajpai J. N. Mathur 《Journal of Radioanalytical and Nuclear Chemistry》2002,253(3):477-482
Extraction of U(VI) from HNO3, HCl and HClO4 media using cyanex-272 (bis[2,4,4 trimethyl pentyl] phosphinic acid)/n-dodecane has been carried out. In the case of HNO3 and HClO4 media, the distribution ratio (D) value first decreases and then increases, whereas from HCl medium it first decreases and then remains constant with increase in H+ ion concentration. At lower acidities, U(VI) was extracted as UO2(HA2)2 by an ion exchange mechanism, whereas at higher acidities as UO2(NO3)2
.2(H2A2) following a solvation mechanism. The D for U(VI) by cyanex-272, PC-88A and DEHPA at low acidities follows the order cyanex-272 > PC-88A > DEHPA. Also, cyanex-272 was found to extract U(VI) more efficiently than TBP at 2M HNO3. The effect of diluents on the extraction of U(VI) by cyanex-272 followed the order cyclohexane > n-dodecane > CCl4 > benzene. The loading of U(VI) into cyanex-272/n-dodecane from 2M HNO3 has shown that at saturation point, cyanex-272 was 78% loaded. No third phase was observed at the saturation level. The stripping of U(VI) from the loaded organic phase was not possible with water, it was poor with acetic acid and sodium acetate but quantitative with oxalic acid, ammonium carbonate and sodium carbonate. 相似文献
112.
P. B. Ruikar M. S. Nagar M. S. Subramanian K. K. Gupta N. Varadarajan R. K. Singh 《Journal of Radioanalytical and Nuclear Chemistry》1995,201(2):125-134
The extraction of plutonium(IV), uranium(VI), zirconium(IV), europium(III) and ruthenium(III) with -pre-irradiated n-dodecane solutions of methylbutyl substituted hexanamide (MBHA), octanamide (MBOA) and decanamide (MBDA) from 3.5M HNO3 has been studied as a function of absorbed dose up to 184×104 Gray. The distribution ratios (Kd) of uranium(VI) decreased gradually up to a dose of 50×104 Gray and became almost constant thereafter, while ruthenium(III) and europium(III) were not extracted in the entire dose range studied. The Kd values of Pu(IV) decreased gradually up to 10×104 Gray, for MBOA, and 30×104 Gray for MBHA and MBDA and then increased up to a dose of 72×104 Gray, indicating the synergistic effect of radiolytic products at higher doses. The extraction of zirconium(IV) was found to increase gradually up to 72×104 Gray. However, the steep fall in Kd values of plutonium(IV), zirconium(IV) beyond a dose of 72×104 Gray was atrributed to third phase formation. The radiolytic degradation of amides was monitored by quantitative IR spectroscopy and was found to follow the order MBOA>MBDA>MBHA at 184×104 Gray having the amines and carboxylic acids as the main radiolytic products. 相似文献
113.
Yu K Singh S Patrito N Chu V 《Langmuir : the ACS journal of surfaces and colloids》2004,20(25):11161-11168
Using cadium oxide (CdO) as the Cd precursor and tri-n-octylphosphine selenide (TOPSe) as the Se source, TOP-capped and TOP/tri-n-octylphosphine oxide (TOPO)-capped CdSe nanocrystals were synthesized without the use of an acid. The synthetic approach involved the addition of a TOPSe/TOP solution into a CdO/TOP solution with or without TOPO at one temperature and subsequent growth at a lower temperature. The temporal evolution of the optical properties, namely, absorption and luminescence, of the growing nanocrystals was monitored in detail. A comprehensive examination on the control of the photoluminescence (PL) properties was performed by systematically varying the TOP/TOPO weight ratio of the reaction media. Surprisingly, a rational choice of 100% TOP or 80% TOP was found to produce "quality" nanocrystals when monitored under the present experimental conditions and growth-time scale. The term "quality" is mainly based on the sharp features and rich substructure exhibited in the absorption spectra of the growing nanocrystals, as well as the sharp features in the emission spectra with narrow full width at half-maximum (fwhm). There are two distinguishable stages of growth: an early stage (<5 min) and a later stage. TOP plays a major role in the control of a slow growth rate in the early stage, while TOPO controls slow growth in the later stage. The optical sensitivity of the growing nanocrystals when dispersed in nonpolar or polar solvents was studied, including two size-dependent parameters, namely, the solvent sensitivity (PL intensity) and nonresonant Stokes shift (NRSS). The insights gained from the present study enable a synthetic approach in which high-quality CdSe nanocrystals are achieved with high synthetic reproducibility. 相似文献
114.
The stabilization of polyolefins against γ-sterilization has been studied with single or binary additive system. The present attempt is to utilize synergistic mixtures of stabilizers which are approved for food contact applications. Ethylene-propylene (EP) copolymer has been melt-mixed with hindered amine stabilizers (HAS), phenolic antioxidants and organo-phosphites (hydroperoxide decomposer). Samples were sterilized with different doses of γ-radiation. Stabilization was characterized in terms of changes in the functional groups (oxidation products), tensile properties, yellowing and surface morphology by FTIR spectroscopy, Instron, colorimetry (reflectance) and scanning electron microscopy (SEM), respectively. Results were discussed by comparing the stabilizing efficiency of mixtures with and without phenol system. Among phenol containing systems, where we mostly observe discoloration due to the oxidation of hindered phenol and the combination of secondary HAS, tertiary HAS, organo-phosphite and hindered phenol exhibited improved stabilization efficiency than single or binary additive systems. The mixture of secondary HAS and tertiary HAS, has shown antagonistic effect of stabilization whereas their combination with organo-phosphite has exhibited synergistic effect of stabilization even at higher doses of γ-sterilization. The effects have been explained through the interaction between the stabilizers. 相似文献
115.
Darian E Hnizdo V Fedorowicz A Singh H Demchuk E 《Journal of computational chemistry》2005,26(7):651-660
A method of statistical estimation is applied to the problem of evaluating the absolute entropy of internal rotation in a molecule with two torsional degrees of freedom. The configurational part of the entropy is obtained as that of the joint probability density of an arbitrary form represented by a two-dimensional Fourier series, the coefficients of which are statistically estimated using a sample of the torsional angles of the molecule obtained by a stochastic simulation. The internal rotors in the molecule are assumed to be attached to a common frame, and their reduced moments of inertia are initially calculated as functions of the two torsional angles, but averaged over all the remaining internal degrees of freedom using the stochastic-simulation sample of the atomic configurations of the molecule. The torsional-angle dependence of the reduced moments of inertia can be also averaged out, and the absolute internal-rotation entropy of the molecule is obtained in a good approximation as the sum of the configurational entropy and a kinetic contribution fully determined by the averaged reduced moments of inertia. The method is illustrated using Monte Carlo simulations of isomers of stilbene and halogenated derivatives of propane. The two torsional angles in cis-stilbene are found to be much more strongly correlated than those in trans-stilbene, while the degree of the angular correlation in propane increases strongly on substitution of hydrogen atoms with chlorine. 相似文献
116.
Room temperature ionic liquid (DMOImTf) based upon 2,3-dimethyl-1-octylimidazolium cation and trifluoromethanesulfonate or triflate (CF(3)SO(3))(-) anion has been synthesized and shows conductivity of 5.68 mS/cm and viscosity of 26.4 cP at 25 degrees C. Ion conducting polymer electrolytes based on polymers (poly(ethylene oxide) (PEO) and polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP)) and ionic liquid (DMOImTf) were prepared in film form by the casting technique. The conductivity of polymer electrolytes containing 0.5 M LiCF(3)SO(3) in PEO:DMOImTf taken in equal weight ratio increases with the addition of propylene carbonate (PC) while its mechanical stability improved by dispersing nanosize fumed silica. However, polymer electrolytes containing PVdF-HFP and ionic liquid show a high value of conductivity (10(-4)-10(-3) S/cm) alongwith better mechanical stability. 相似文献
117.
Complexes of the types (C5H5)2TiClL, (C5H5)TiClL2 and [(C5H4)TiL2]2 (L is a monofunctional bidentate ligand) have been made by reactions of titanocene dichioride with the substituted pyrazolones, RCOCH3 (where R = CH3, C2H6, C6H5 and p-ClC6H4) in the presence of triethylamine in refluxing THF. A possible mechanism for the formation of [(C5H4)TiL2]2 is suggested. 相似文献
118.
The diffusion length of charge carriers in the active layer of a perovskite solar cell (PSC) of the structure Glass/PEDOT: PSS/CH3NH3PbI3/PC60BM/Al is modelled. It is found that the diffusion length depends on the position x in the active layer measured from the PEDOT: PSS interface, Urbach energy and temperature. By varying the voltage in the range from zero to , it is shown that the dependence of diffusion length on the position x in the active layer reduces at higher voltage. The combined influence of applied voltage and temperature on the diffusion length of charge carriers is investigated and it is found that in the low voltage range the diffusion length is temperature independent, but it becomes significantly temperature dependent at higher voltages. Also, it is found that the diffusion length decreases as the applied voltage increases and this reduction becomes much more significant at higher voltage and temperatures. The combined influence of applied voltage and Urbach energy on diffusion length of charge carriers reveals that the diffusion length decreases when both the applied voltage and Urbach energy increase. However, the reduction in the diffusion length due to the increase in Urbach energy becomes less significant at higher voltage. 相似文献
119.
MgAl2O4:Mn phosphors have been prepared at 500 °C by combustion route. Powder X-ray diffraction (XRD) indicated the presence of mono-MgAl2O4 phase. Scanning electron microscopy showed that the powder particle crystallites are mostly angular. Fourier transform infrared spectroscopy confirmed the presence of AlO6 group which makes up the MgAl2O4 spinel. Photoluminescence studies showed green/red emission indicating that two independent luminescence channels in this phosphor. The green emission at 518 nm is due to 4T1 → 6A1 transition of Mn2+ ions. The emission at 650 nm is due to the charge-transfer deexcitation associated with the Mn ion. EPR spectrum exhibits allowed and forbidden hyperfine structure at g=2.003. The g≈2.00 is due to Mn2+ ion in an environment close to tetrahedral symmetry. It is observed that N and χ increase with decrease of temperature obeying the Boltzmann law. The variation of zero-field splitting parameter (D) with temperature is evaluated and discussed. 相似文献
120.
An extract of crystal violet-tetrachloroferrate(III) in nitrobenzene was used to prepare a tetrachloroferrate(III)-selective liquid membrane electrode with a poly(vinyl chloride) support. The optimal conditions to determine 2.5 × 10–5 – 5.0 × 10–2
M iron(III) as tetrachloroferrate(III) (anionic slope 56 mV/decade, detection limit 7.9 × 10–6
M) were found to be 4.0–5.5.M total chloride in 0.75–1.5M hydrochloric acid. The electrode was reliably applied to determine iron in human blood, haematite and mineralized vitamin syrup by direct potentiometry, standard and sample additions as well as standard subtraction techniques. 相似文献