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- Author or Editor: K. Das x
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Differential scanning calorimeter (DSC) has been used to study the dehydration characteristics of hydrated calcium aluminates such as CA, CA2 and C12A7 where C and A stand for CaO and Al2O3 respectively. Dehydration of CAH10 and C2AH8 (whereH=H2O) occur ∼ at 160–180°C and 200–280°C respectively. These two phases are unstable and ultimately get transformed to AH3 and C3AH6. Dehydration of AH3 and C3AH6 occur between 290 and 350°C and overlap at lower scanning rate. The activation energy for dehydration of the stable AH3 and C2AH6 phases has been found to be 107.16 and 35.58 kJ mol−1 respectively. The compressive strength of the hydrated calcium aluminates has been determined. The result shows that in the case of CA, almost 90% of ultimate strength has been attained in 1 day whereas in CA2, ultimate strength has been attained in 14 days and in C12A7 in 1 day. DSC results have been correlated with the rate of strength developments.
Abstract
The main result of this paper is a fixed point theorem of self-mappings in Menger spaces which satisfy certain inequality. This inequality involves a class of real functions which we call Φ-functions. As a corollary we obtain a result in the corresponding metric spaces. The result is supported by an example. The class of real functions we have used is the conceptual extension of altering distance functions used in metric fixed point theory.
Abstract
Trace level tantalum and rhenium, 182Ta and 186,188Re, have been separated with liquid anion exchanger, TOA from HNO3 medium. The feasibility of the separation process has also been verified for the separation of trace level rhenium from bulk or macro quantity of tantalum. The developed radiochemical scheme will be useful for the separation of carrier-free rhenium radionuclides produced in 
-particle activated matrix target.
Abstract
Carrier-free radionuclides of mercury and gold192,193Hg and192,193Au have been produced by heavy ion activation of tantalum target with 95 MeV16O5+ beam obtained from an ECR ion source. An effective radiochemical separation scheme has been developed to isolate gold and mercury radionuclides from the tantalum target matrix.
Pomelo fruit juice is concentrated using two different techniques, i.e. block freeze concentration (BFC) and thermal concentration (TC), and both concentrates were spray dried separately to observe the effects of two different concentration techniques on the physicochemical properties of the spray dried powder. BFC juice had comparatively better values of retention of acidity, colour, vitamin C, DPPH● scavenging activity, total phenolic content (TPC), and total sugar content than TC juice. The powder obtained from the combination of BFC and spray drying had better retention of vitamin C (121.17 mg/100 g), colour, and exhibited higher DPPH● scavenging activity than TC spray dried powder. The physical parameters including solubility index, bulk density, and hygroscopicity were significantly higher in BFC spray dried powder. BFC was observed as an efficient concentration technique in comparison to TC as a pretreatment to produce spray dried powder with a better retention of bioactive components and powder flow properties.
Abstract
The k 0 based internal monostandard neutron activation analysis was used to analyze 41 ancient pottery samples from three major locations of Andhra Pradesh state, India, belonging to two different age groups namely Megalithic and Buddhist periods. Samples were irradiated with neutron flux obtained from CIRUS reactor and radioactive assay was carried out using a 40% relative efficiency HPGe detector coupled to 8 k MCA. Concentration ratios of 21 elements were calculated with respect to internal monostandard Sc. Absolute concentrations for six (three each from both Megalithic and Buddhist periods) representative samples along with a modern pottery were obtained for comparison. Elemental concentration ratios with respect to Sc were used for grouping of these archaeological samples. Preliminary grouping of these artifacts was done using La/Ce values, and the grouping was confirmed by statistical cluster analysis using eleven selected trace elements. The IAEA RM SL-3 sample was analysed for validation of the method, where in both concentration ratios and absolute concentrations were calculated.
Abstract
The k 0-based internal monostandard neutron activation analysis (IM-NAA) method was used for the analysis of 30 large and non-standard geometry ancient pottery samples obtained from Buddhist sites of Andhra Pradesh, India. One freshly finished pottery and a sun-drenched pottery were also analyzed for comparison. Samples were irradiated in thermal column facility of Apsara reactor and also in graphite reflector position of critical facility of Bhabha Atomic Research Centre. Radioactive assay was carried out using a 40% relative efficiency HPGe detector coupled to MCA. Concentration ratios of 15 elements with respect to Sc were determined. The La/Ce values as well as statistical cluster analysis utilizing concentration ratios of elements were used for grouping/provenance of the potteries.
The activation energy for the transformation of silica gel to cristobalite, a partial reaction of first order, was determined from a single DTA curve by the methods available in the literature. The values obtained were not in agreement with those obtained by the isothermal method. This suggested that the methods were not applicable to reactions which are partial. A modified equation was derived which could be utilized for the determination of the activation energy of first-order reactions from a single DTA curve, if the fraction transformed during the reaction was known.
