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  • Author or Editor: A. Mathur x
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The thermal behaviours of polystyrene (PS), polymethylacrylate (PMA), polyacrylonitrile (PAN), polystyrene-co-methylacrylate [P(S: MA)](alternate and random), polystyrene-co-acrylonitrile [P(S: AN)] (alternate) and a terpolymer of styrene, methylacrylate and acrylonitrile [P(S: MA: AN)] are discussed on the basis of non-isothermal thermogravimetric studies. The thermal stabilities of the copolymers have been found to be intermediate between of those of the individual homopolymers. The stability of the [P(S: AN)] copolymer is higher than those of the individual homopolymers. The activation energy values are also in accordance with the thermal behaviours of these polymers.

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The effect of In impurity on the crystallization kinetics and the changes taking place in the structure of (Se7Te3) have been studied by DTA measurements at different heating rates (α=5 deg·min−1, 10 deg·min−1, 15 deg·min−1 and 20 deg·min−1). From the heating rate dependence of the values ofT g,T c andT p, the glass transition activation energy (E t) and the crystallization activation energy (E c) have been obtained for different compositions of (Se7Te3)100−xInx (0≤×≤20). The variation of viscosity as a function of temperature has been evaluated using Vogel-Tamman-Fulcher equation. The crystallization data are analysed using Kissinger's and Matusita's approach for nonisothermic crystallization. It has been found that for samples containing In=0, 10, 15, 20 at%, three dimensional nucleation is predominant whereas for samples containing In=5 at%, two dimensional nucleation is the dominant mechanism. The compositional dependence ofT g and crystallization kinetics are discussed in terms of the modification of the structure of the Se−Te system.

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The physical state of benzoic acid (BA) and its interaction with ethyl cellulose (EC) were examined in ethyl cellulose—benzoic acid matrices by Differential Scanning Calorimetry (DSC). The glass transition temperature (T g) of EC of various matrices having BA in solid solution form (upto 27.7%) was reduced. The BA in matrices containing more than 38.9% drug exhibited distinct melting endotherms due to crystalline form. The peak temperatures of these endotherms were lowered and they broadened as the concentration was lowered. The solubility of BA increased at its melting point as compared to ambient temperature. The melting enthalpy of BA, when plotted as a function of its concentration yielded a straight line with intercept of 330 mg g–1 of matrix. This is the solubility of BA in EC at its melting temperature. Fourier Transform Infra Red Spectroscopy (FTIR) investigations confirmed that hydrogen bonding occurred between EC and BA through hydroxyl groups.

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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.

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The sorption of 241Am, 233U and 137Cs from nitric acid solutions on a synthesized sodium potassium fluoro-phlogopite (SPFP) gel, structurally close to the fluorine mica mineral, has been studied. The synthesized gel was characterized by energy dispersive spectrometry, X-ray powder diffraction pattern, FTIR and thermogravimetric analysis and has a composition of Na0.5K0.5Mg3(Si3AlO10)F2.6H2O. Different parameters like contact time, acid concentration, amount of SPFP, metal ion concentrations, effect of competing cations, desorption of the nuclides from the loaded SPFP gel etc., were studied using batch technique. Also, the SPFP gel was loaded with Eu(III), U(VI) and Cs(I) and the amounts sorbed on the gel has been estimated by difference from the concentrations in the original solution and those remaining in the solution after loading. Na, K, Mg, Eu and U were estimated by ICP-AES and Cs by electrothermal atomization atomic absorption spectrometry. The exchange of Na, K and Mg with the loaded cations has been evaluated and discussed in the light of ion exchange and surface precipitate sorption mechanisms.

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The separation of uranium and plutonium from oxalate supernatant, obtained after precipitating plutonium oxalate, containing ~10 g/l uranium and 30–100 mg/l plutonium in 3M HNO3 and 0.10–0.18M oxalic acid solution has been carried out. In one extraction step with 30% TBP in dodecane: ~92% of uranium and ~7% of Pu is extracted. The raffinate containing the remaining U and Pu is extracted with 0.2M CMPO+1.2 M TBP in dodecane and near complete extraction of both the metal ions is achieved. The metal ions are back extracted from organic phases using suitable stripping agents. The recovery of both the metal ions separately is >99%. The uranium species extracted into the TBP phase from the HNO3+oxalic acid medium was identified as UO2(NO3)2·2TBP.

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A chemical separation procedure has been developed for the extraction of uranium from some of the crucially important rare earths using a novel extractant viz. Cyanex-272 (2,4,4-trimethyl pentyl phosphinic acid). The near total extraction of uranium and quantitative separation of rare earth elements has been validated using inductively coupled argon plasma - atomic emission spectrometry (ICP-AES). The recovery of some of the representative elements has been confirmed by radioactive tracer studies. The back extraction of uranium from the organic phase was carried out using a solution of 0.5M Na2CO3 which resulted in a near total recovery of uranium into the organic phase. These studies have enabled determination of sub ppm amounts of the analyte elements with a precision of 5% RSD utilizing prior chemical separation of rare earths from 1 g uranium samples in just three extractions with Cyanex-272.

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