Results of phase transformations, enthalpy released and specific heat of Ge22Se78–xBix(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, Tg, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of Tg (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of Tg, at a heating rate of 5 K min–1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol–1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference Tc–Tg and the enthalpy released during the crystallization process. Below Tg, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.
Authors:M. Doshi, G. Unnikrishnan, K. Gopukumar, N. Bhandari, and D. Krishnan
Some modifications of the stannous chloride reduction method for the estimation of inorganic phosphate reported by Berenblum-Chain are suggested. By this method, it is possible to measure 25 g l–1 of phosphorus /P/ as inorganic phosphate in the presence of macromolecules like deoxyribonucleic acid /100 g ml–1/, as compared to 200 g l–1 of P by the original method. If a larger sample volume /30 ml/ is used, even 5 g l–1 of P can be measured.
Authors:H. Chaudhuri, D. Ghose, R. Bhandari, P. Sen, and B. Sinha
Helium was first observed in the sun and subsequently much later on the earth. Starting from the early days of its discovery, helium continues to be entwined with the Indian scientific scenario in more ways than one. The element thus has a special charm and significance to the currently emerging situation where it is applied to solve problems in the exceptionally challenging field of tracing the formation of earthquakes and anticipating its occurrence. The present article delves into some of the broader aspects of the problem through a historical approach. The paper also deals with the statistical analysis of the pre-seismic geochemical (He and 222Rn) anomalies recorded at our existing field site laboratories ahead of some major earthquakes that occurred in and around India. A description of the experimentally recorded geochemical (He, F−, Cl−, SO
, and B) and geophysical (temperature, pH, conductivity) characteristics of some thermal springs of north and north-east India is included. A dedicated mass spectrometer analyzed intensities of 3He and 4He in air sample made in our laboratory and implication of the pre-seismic enhancement of 3He/4He ratios measured in thermal spring gases is briefly discussed.
Authors:N. Das, R. Bhandari, D. Ghose, P. Sen, and B. Sinha
Strong anomalies in the concentration of helium, radon and gamma were observed in gases at the geochemical monitoring station, Bakreswar, West Bengal, India, about two weeks before the 7.9 M earthquake at Sichuan, China. The distance between the epicenter of the earthquake and the monitoring site is about 1800 km. This long distance preseismic observation indicates that the radius of influence of large magnitude earthquakes may be substantially large and may cut across plate boundaries. This paper presents the observed geochemical anomalies for the Sichuan earthquake and discusses empirical postulates between earthquake magnitude and its radius of influence.