A calorimetric study of blends of poly(ethylene terephthalate-co-p-oxybenzoate), PET/PHB, with poly(butylene terephthalate),
PBT has been carried out in the form of as-spun and drawn fibres. DSC melting and crystallization results show that PBT is
compatible with LCP and the crystallization of PBT decreases by the addition of LCP in the matrix. The crystallization behaviour
of blend fibres is investigated as a function of temperature of crystallization. A detailed analysis of the crystallization
course has been made utilizing the Avrami expression. The isothermal calorimetric measurements provide evidence of decrease
of rate of crystallization of PBT on addition of the liquid crystalline component up to about 50% by weight. The values of
the Avrami exponents change in the temperature range from 200° to 215°C. Dimensionality changes in crystallization could be
due to LCP mesophase-transition.
The transformation of gibbsite have been studied under hydrothermal influence. Results of the X-ray diffraction analysis of the samples heated at different temperatures from 170°C to 265°C are also discussed in detail. The percentage of the boehmite phase formed, due to the transformation of the gibbsite, have been determined by comparing the intensity of the most strongest reflection of the boehmite phase with a fully transformed sample. The activation energy value calculated form X-ray diffractograms is almost comparable with the value calculated from main DTA endotherm of gibbsite.
Authors:S. K. Mehta, Ravneet Kaur, and Sukhjinder Singh
Thermal behavior of various synthesized transition metal surfactant complexes of the type [M(CH3COO)4]2−[C12H25NH3+]2 where M: Cu(II), Ni(II), Co(II) has been investigated using Thermogravimetric Analysis (TGA). It was found that pyrolytic decomposition occurs with melting in metal complexes, and that metal oxides remain as final products. The activation energy order obtained, ECu > ENi > ECo, could be explained on the basis of size of transition metal ion and metal ligand bond strength. In the course of our investigation on the decomposition of complexes, we carried out a comparative study of different measurement and calculation procedures for the thermal decomposition. A critical examination was made of the kinetic parameters of non-isothermal thermoanalytic rate measurement by means of several methods such as Coats–Redfern (CR), Horowitz–Metzger (HM), van Krevelen (vK), Madhusudanan–Krishnan–Ninan (MKN), and Wanjun–Yuwen–Hen–Cunxin (WYHC). The most appropriate method among these was determined for each decomposition step according to the least-squares linear regression. It was found that the results obtained using CR method differ considerably from HM method, as the former method involves a lot of approximations and is not much reliable. The application of thermoanalytic techniques to the investigation of rate processes has also been discussed.
Authors:R. Venkataramani, S. Mehta, M. Iyer, V. Natarajan, and M. Sastry
Accidental exposure dose assessment by electron spin resonance (ESR) technique from the free radicals generated in a cotton handkerchief has been attempted in this investigation. The cotton handkerchief, a common material carried by individuals, was taken as the medium for free radical estimation. About 55 mg of the irradiated piece of cloth was loaded into a quartz tube and the dose dependence of the ESR signal at g=2.0026 was measured at room temperature, using a Bruker ESP-300 ESR spectrometer in X-band (9.74 GHz). The intensity of this signal was found to be proportional to the dose in the range of 1–1000 Gy. The stability of the free radicals with time of storage was followed. Dependence of dose rate as well as the presence of water on the yield of free radicals were also investigated.
Authors:R. S. Tiwari, N. Mehta, R. K. Shukla, and A. Kumar
The present paper reports the Differential Scanning Calorimetric (DSC) study of some Ag doped Se-Te chalcogenide glasses.
DSC runs were taken at different heating rates. Well-defined endothermic and exothermic peaks were obtained at glass transition
and crystallization temperatures. The variation of glass transition temperature Tgwith Ag concentration has been studied. It has been found that Tgdecreases with increase in Ag concentration. The heating rate dependence of Tgis used to evaluate the activation energy of glass transition (DEt). The value ofDEthas been found to increase with increase in Ag concentration followed by nearly constant value at higher concentrations of
Authors:R. A. Sayanam, A. K. Kalsotra, S. K. Mehta, R. S. Singh, and G. Mandal
Clay from the Nagrotta area of Jammu (J & K State, India) was calcined at various temperatures. The products were analysed by X-ray diffraction. The mode of loss of hydroxyl group from the structure with respect to temperature is discussed. The results were supplemented by differential thermal analysis. The calcined products were subjected to lime reactivity tests and the data obtained were correlated with those of the above study to investigate the pozzolanic activity at various temperatures.