Phase transformation studies carried out on Mn−Al−C permanent magnet alloy employing DSC and electrical resistivity measurements,
are reported and discussed. The transformation of the hexagonal Mn−Al phase (disordered and non-magnetic) to the ferromagnetic
fct phase proceeds via the formation, in at least two stages, of the ordered orthorhombic phase. The activation energy for
the formation of the fct phase is ≈34.65 kcal/mol. Microstructural changes occurring at various stages of the transformation
are also studied.
Sorption of chromium radionuclide has been studied in the pH range of 1–10 on titanium dioxide from aqueous solutions. The adsorption isotherm obtained is of the Freundlich type. The kinetic study of adsorption and desorption of tagged chromate ions at different temperatures show that the adsorption process is exothermic innnature. Further, the feasibility of adsorption process is confirmed by calculating the thermodynamic parameters.
The kinetics of adsorption of chromate ions has been investigated radiometrically over a wide range of concentration of chromate ions (10–6–10–2M) and temperature (303–323 K). The kinetics of the process follows essentially a first order rate law with respect to adsorptive concentration and obeys the Freundlich adsorption isotherm in the concentration range studied. In addition, the kinetics of desorption of the preadsorbed species also follows a first order rate law and the activation energy for desorption is greater than that of the adsorption process. On the basis of an adsorption kinetic study, the thermodynamic parameters have been calculated. Infrared spectroscopy has shown the chemical interaction of chromate ions on the surface of MnO2.
Authors:Tapas Mitra, G. Sailakshmi, A. Gnanamani, and A. B. Mandal
This study emphasizes, cross-linking potential of a simple di-carboxylic acid, namely, oxalic acid with type I collagen for the preparation of collagen based biomaterial for clinical applications. Further the study discusses the characteristics features of the cross-linked material in comparison with the standard cross-linker. In addition, the study also demonstrates the role of ionic interactions in providing the thermal stability and tensile strength to the cross-linked biopolymer material. Type I collagen from rat tail tendon treated with oxalic acid at optimized concentrations provided a biopolymer material without changing the triple helical pattern of collagen (CD spectrum) and also with 6–7 fold increase in tensile strength than native collagen. FTIR spectral details demonstrate the ionic interactions between collagen and oxalic acid. Thermal stability analyses of oxalic acid cross-linked biopolymer revealed, high thermal stability compared to materials of glutaraldehyde cross-linked. The results of the study suggest oxalic acid as a suitable cross-linker for collagen and it cross-link with collagen through ionic interactions.
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.
Authors:H. Tan, S. Mitra, L. Wielopolski, A. Fallu-Labruyere, W. Hennig, Y. Chu, and W. Warburton
Neutron activation analysis (NAA) systems that use pulsed neutron generators (NGs) employ spectrum gating procedures to segregate
nuclear processes by acquiring gamma-ray spectra separately when the generator is on (HIGH gate) and off (LOW gate). Often,
the actual neutron burst lags the leading edge of the HIGH gate signal by a few μs. Thus, count rates vary not only between
the on and off states of the NG, but within them as well. Recent advances in digital gamma-ray spectrometers that allowed
the concurrent acquisition of data by sorting events into two separate spectra based on gate status suggested that a time-resolved
analysis that further subdivided the neutron pulse cycle could obtain further information to separate gamma-rays produced
by different nuclear reactions. In this paper we introduce a gating system for time-resolved NAA that is capable of concurrently
acquiring as many as 16 spectra from up to 8 user-defined time intervals during each of the HIGH gate and LOW gate periods,
each with all required timing and count rate information. We present the new gating system’s implementation, operation and
some first experimental test results.
Authors:D. Gupta, J. Chatterjee, R. Ghosh, A. Mitra, S. Roy, and M. Sarkar
Radish plant was collected along with root and soil from the nearby area of a Municipal Solid Waste dumping site of the metropolitan
city of Kolkata, West Bengal, India and analyzed for a wide range of elements using the EDXRF technique with a 109Cd point source and a Si(Li) detector. The samples comprized of the root-soil, root and leaves. For quality control purposes,
NIST standard reference material (SRM) 1648 Urban Particulate Matter had also been analyzed using the same procedure as for
the samples. Concentrations of elements with X-ray energies in the range of 3–20 keV in the soil around the root and their
uptake pattern by the root and the leaves have been estimated.