Search Results

You are looking at 1 - 10 of 36 items for :

  • Author or Editor: N. Kumar x
  • Chemistry and Chemical Engineering x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

The crystallization kinetics of a-Se80–xTe20Cdx (x=0, 5, 10, 15) and a-Se80–xTe20Gex (x=5, 15, 20) alloys has been studied by an isothermal method. For this purpose, conductivity measurements are done during isothermal annealing at various temperatures between the glass transition and crystallization temperatures. Avrami’s equation is used to calculate the activation energy of crystallization (E c) and order parameter (n). It is shown that Avrami’s theory of isothermal crystallization correctly describes the crystallization kinetics in the present alloys. The composition dependence of E c in these alloys has also been discussed.

Full access

Abstract  

The spin transitions in two new cationic complexes of iron, i. e., iron bipyridine formate, [Fe/bipy/3]/HCOO/2. 5/HCOOH/ and iron bipyridine tetrafluoro borate, [Fe/bipy/3]/BF4/2. 2H2O have been studied by using Mössbauer spectroscopy. From quadrupole splitting values, at different temperatures, it has been established that both the complexes show the coexistence of both the high spin state and the low spin state at 300 K while complete transformation to low spin state occurs at 77 K. Both compounds were prepared by electrochemical technique.

Full access

Abstract  

Different methods have been used by various workers to determine the activation energy of thermal crystallization (E c) in chalcogenide glasses using non-isothermal DSC data. In the present work, the crystallization kinetics of two important binary alloys Se80Te20 and Se80In20 is studied using non-isothermal DSC data. DSC scans of these alloys have been taken at five different heating rates. The values of activation energy of crystallization (E c) have been determined by four different methods, i.e., Kissinger's method, Matusita-Sakka method, Augis-Bennett's method and Ozawa's method, have been used to calculate E c. The results obtained have been compared with each other to see the effect of using different methods in the determination of E c.

Full access

Abstract

Calorimetric measurements have been performed in glassy Se90M10 (M=In, Te, Sb) alloys to study the effect of In, Te and Sb additives on the kinetics of glass transition and crystallization in glassy Se90M10 system. Kinetic parameters of glass transition and crystallization such as the activation energy of glass transition (E g), the activation energy of crystallization (M c), the order parameter (n), the rate constant (K), etc. have been determined using different non-isothermal methods. The composition dependence of the activation energies of glass transition and crystallization processes is also discussed.

Full access

Abstract

This work reports the effect of Ge, Sb, Sn additives on the thermally activated glass to crystal phase transition in binary Se90In10 alloy. Differential scanning calorimetry (DSC) technique is used for this purpose. Different kinetic parameters of glass/crystal transformation have been calculated. The results are explained using the chemical bond approach for the covalent network of such glasses.

Full access

Abstract  

Radiation dose-risk assessment was carried out for cereal species Brassica compestris var. dichotoma, Oryza sativa var. Shalum1, Zea mays, Lactuca indica, Cumunis sativum, and Clocasia esculanta due to naturally available radionuclides 40K, 238U and 232Th in Domiasiat area. The activity in biota and corresponding soil was measured by precipitation method using NaI(TI) detector. Transfer factor (TF) was for Oryza spp. (1.00E−01-40K, 8.76E−05-232Th, and 9.11E−05-238U), for Brassica spp. (5.39E−01-40K, 8.17E−04-232Th and 2.96E−04-238U) and for Zea spp. (3.41E−01-40K, 5.84E−05-232Th, 8.87E−05-238U) etc., respectively. A detailed physio-morphological study of the biota and extensive investigation of ecosystem was carried out for assessment. The data was modeled using FASSET for dose estimation and obtained total dose was 1.58E−04 
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\upmu \hbox{Gy}\,h^{-1}$$ \end{document}
in Oryza spp., 2.87E−04 
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\upmu \hbox{Gy}\,h^{-1}$$ \end{document}
Brassica spp. and 6.90E−03 
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\upmu \hbox{Gy}\,h^{-1}$$ \end{document}
in Zea spp. etc. The dose was compared with the UNSCEAR dataset for screening level dose for biota. Zea spp. was more susceptible for the chronic radiation exposure.
Full access

Thermal decomposition of mono pyridine N-oxide complexe; of cobalt(II), nickel(II) and copper(II) propionates and mono quinoline N-oxide complex of copper(II) ben zoate has been studied by TG and DTA techniques. These dimeric complexes are stable upto 350–380 K and decompose in two stages: (i) successive elimination of the two ligand molecules (mostly endothermic); and (ii) decomposition of the resulting anhydrous metal(II) carboxylates by an exothermic multistep process in air.

Full access

Abstract  

A radiation dose assessment exercise was carried out for the Ipomea batata, Allium sativum, Dacaus carota, and Solanum tuberosum due to naturally available radionuclide 40K, 238U and 232Th in the Domiasiat area of Meghalaya. The concentration of radionuclides in biota as well as corresponding soil was measured by precipitation method using NaI detector for continuous 12 months. Transfer factor was calculated and was, for 40K(3.96E−05, 3.40E−05, 3.40E−05, 2.70E−05), for 232Th(3.94E−05, 3.20E−05, 3.20E−054.93E−05), for 238U(3.60E−05, 3.89E−05, 3.85E−054.57E−05), respectively in each biota due to each radionuclide. The point source dose distribution (source ↔ target) hypotheses was applied for the consideration of absorbed fraction. The generated data were modeled using the FASSET method and obtained dose was 8.42E−03, 8.36E−03, 7.78E−03, 7.74E−03 μGy h−1, respectively and finally compared with the IAEA and UNSCEAR dataset for screening level dose for terrestrial biota.

Full access

Abstract  

The thermolysis of potassium hexa(carboxylato)ferrate(III) precursors, K3[Fe(L)6xH2O (L=formate, acetate, propionate, butyrate), has been carried out in flowing air atmosphere from ambient temperature to 900°C. Various physico-chemical techniques i.e. TG, DTG, DTA, XRD, IR, Mössbauer spectroscopy etc. have been employed to characterize the intermediates and end products. After dehydration, the anhydrous complexes undergo exothermic decomposition to yield various intermediates i.e. potassium carbonate/acetate/propionate/butyrate and α-Fe2O3. A subsequent decomposition of these intermediates leads to the formation of potassium ferrite (KFeO2) above 700°C. The same ferrite has also been prepared by the combustion method at a comparatively lower temperature (600°C) and in less time than that of conventional ceramic method.

Full access