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Abstract  

[NiL3]X2 (where L=N-phenylethane-1,2-diamine and X=I and ClO4 ), [NiL2X2] (X is Cl, Br, NCS, 0.5SO4 2− or 0.5SeO4 2−) and [NiL2(H2O)2](NO3)2 have been synthesized from solution and their thermal study has been carried out in the solid phase. [NiL2Cl2] upon heating undergoes irreversible endothermic phase transition (142–152C, ΔH=0.35 kJ mol−1) without showing any visual colour change. This phase transition is assumed to be due to conformation changes of the diamine chelate rings. NiLCl2 and NiL2.5I2 have been prepared pyrolytically from [NiL2Cl2] and [NiL3]I2 respectively in the solid state. [NiL2(H2O)2](NO3)2 upon heating undergoes deaquation-anation reaction without showing any visual colour change. [NiL2X2] (X is Cl, Br, NCS), [NiL2(H2O)2](NO3)2 and [NiL2(NO3)2] possess trans-octahedral configuration, whereas, [NiL2X2] (X is 0.5SO4 2− or 0.5SeO4 2−) are having cis-octahedral configuration. Amongst the complexes, only NiLCl2 shows unusually high (5.1 BM at 27C) magnetic susceptibility value.

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Abstract  

Literature data on the stability constants of the fluoride complexes of the actinides in different oxidation states have been compiled. In order to have a reasonable inter-comparison, the stability constant (β1) values obtained in diverse ionic strength media are converted to so called thermodynamic stability constants, β 1 0 using the DAVIES equation (a modification of Debye-Huckel equation). A correlation of the β 1 0 values with the fundamental properties of the actinide ions using various models available in the literature has been attempted. Using the values of inonic radii and best available values of the stability constants of a large number of metal ions from recent compilations a comparative study of the various models or relations available in the literature has been tried. For metal ions in general, the semi-empirical relation recently developed by BROWN, SYLVA and ELLIS (BSE equation)_gives the best correlation. In an attempt to accommodate the unusual trend in the stability constants of the tetravalent actinides a modification in a parameter of the BSE equation has been proposed. Good agreement between the theoretically calculated and experimentally determined values for actinides in different oxidation states is obtained in most of the cases. Further improvements in theoretical relation as well as experimental data are required for better correlation.

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Abstract  

Extraction of U(IV) by an organic phase containing 30% tri-n-butyl phosphate (TBP) in dodecane from aqueous nitric acid solution containing large amount of U(VI), relevant to nuclear fuel reprocessing by PUREX process, was studied. While acquiring distribution data, an argon atmosphere was maintained. A potentiometric method was used for the determination of U(IV) in the two phases after equilibration. Hydrazine used as stabiliser of U(IV) in the stock solution was destroyed and sulphamic acid was added just before equilibration to avoid the interference due to hydrazine in the subsequent determination of U(IV). Uranium(IV) distribution data between 30% TBP in dodecane and aqueous solution of uranium(VI) and nitric acid of varying concentrations have been presented and compared with available literature data.

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Abstract  

Determinations of hexamethylene tetramine (HMTA) and urea in the process solutions are required to optimize their concentrations for obtaining high quality ceramic oxide microspheres, for monitoring the washing procedure and for their subsequent recovery, recycling or waste disposal. Determination of urea in the feed solution by conventional procedures is difficult as it contains HMTA. It is more so in the effluent as it contains hydrolytic products like formaldehyde, methylol derivatives of urea, ammonium nitrate and ammonium hydroxide used for washing the gel microspheres. This work describes a derivative potentiometric method using a microprocessor-based autotitrator. Peaks on the first derivative of the titration plot corresponded to constituents of different basicities. Urea was selectively hydrolyzed at room temperature by the catalytic action of urease enzyme leaving HMTA unaffected. Ammonium hydroxide and ammonium bicarbonate produced from urea and HMTA were sequentially titrated for the analysis of the feed solution to obtain the three corresponding peaks respectively. Two separate titrations were required for the analysis of the effluent solution, which contained free ammonia also. One aliquot was first titrated directly without adding urease (for free ammonia and HMTA) and another aliquot was titrated after treatment with urease. The end points due to the ammonia used for washing and that from urea hydrolysis merged resulting in the appearance of three peaks again. Using this sequential method the relative standard deviations were found to be 0.81% and 1.38% for urea and HMTA, respectively, in eight determinations when the aliquots contained 50 to 75 mg of urea and 75 to 125 mg of HMTA. Feed and effluent solutions of the process stream were analyzed.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
N. Chaudhuri
,
R. Sampathkumar
, and
R. Iyer

Abstract  

Analysis of fissile materials in solution by fission track registration technique has been extended to plutonium in solution of its alloys. In these estimations, the results agreed within 1–4% with the average of those obtained by other chemical and instrumental methods like potentiometry, mass-spectrometry and X-ray fluorescence. Some special practical problems encountered in the analysis of plutonium solutions are noted. Various factors affecting the results have been investigated and the necessary precautions for reducing these errors have been indicated. The advantages of the method over some other conventional methods have also been discussed. It is suggested that a source of about 10 μg of252Cf corresponding to a neutron flux of about 107 n·cm−2·sec−1 is ideal for these experiments.

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Abstract  

A method based on the back-extraction of Th(IV) from its TTA complex in benzene by aqueous F followed by spectrophotometric measurement of Th(IV), for the determination of fluoride has been developed. The coefficients of variation obtained are 2.4% and 1.4% in 11 determinations at F concentration levels of 1.0 g ml–1, respectively.

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Abstract  

Complex formation of Th(IV), U(IV), Np(IV), and Pu(IV) with fluoride ions in aqueous perchloric acid solution of 1M ionic strength has been studied potentiometrically, using a fluoride ion selective electrode. A highly acidic medium was essential to prevent hydrolysis and disproportionation of the tetravalent actinide ions. A procedure developed earlier in this laboratory for studying the fluoride complexes of hexavalent actinides was successfully extended to this work. The 1 values follow the trend Th(IV)<U(IV)>Np(IV)>Pu(IV), and 2 values the trend Th(IV)<U(IV)>Np(IV)<Pu(IV), while 3 and 4 values followed an increasing order.

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