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28 results on '"Senguttuvan, T.D."'

10. Three-Dimensional Physico-chemical Characterization 1 of Coarse Atmospheric Particles from Urban and Arid Environment of India: An Insight into Particle Optics

Author

Goel, Vikas, Mishra, Sumit K., Ahlawat, Ajit, Kumar, Prashant, Senguttuvan, T.D, Shrama, Chhemendra, and Reid, Jeffrey S.

Abstract

Aerosol particles scatter and absorb solar radiation and affects earth's radiation budget. The aerosol particles are usually non-spherical in shape and inhomogeneous in chemical composition. For simplicity, these particles are approximated as homogeneous spheres/spheroids in radiative models and in retrieval algorithms of the ground and spaceborne observations. The lack of information on particle morphology (especially shape), chemical composition (that govern their spectral refractive indices) and most importantly internal structure (three Dimensional, 3D spatial distribution of chemical species) lead to uncertainty in the numerical estimation of their optical and radiative properties. Here, we present a comprehensive assessment of the particles' volumetric composition. The particles were collected from typical arid and urban environments of India and subjected to Focused Ion-Beam (FIB) coupled with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscope (EDS). Particles from the arid environment were observed to be composed of Fe, Ca, C, Al, and Mg rich shell with Si and O rich core opposed to those from urban environment consisting Hg, Ag, C, S and N rich shell with Cu and S rich core. Based on the homogeneous sphere/spheroid assumption, conventional SEM-EDS and FIB-SEM-EDS results, different particle model shapes [single species homogeneous sphere (S1) and spheroid (SPH1); multiple species homogeneously mixed sphere (S2) and spheroid (SPH2); and core-shell (CS)] were considered for simulating their respective optical properties; SSA (Single Scattering Albedo) and g (Asymmetric parameter). The effect of internal structure on SSA was found to be prominent in particles having low value of the imaginary part of refractive index (k). While the same was observed to be low (nearly negligible) for the particle with the high value of “k”. The particles rich in copper are found to be highly absorbing in nature which causes positive radiative forcing.

Published
2020

24. Molecular Kinetic Based Dielectric Polarization in Sol-Gel Derived Nanocrystalline CaCu3Ti4O12

Author

Kumar, Ranjit, Zulfequar, M., and Senguttuvan, T.D.

Abstract

Nano-sized powders of dielectric CaCu3Ti4O12 was synthesized by sol-gel reaction route. The powders are calcined at 700 °C and sintered at 1000 °C. The calcined powders diameter is in the range of 50 - 150 nm. Structural studies were carried out using the XRD, HRTEM and SEM. Frequency dependent dielectric properties were studied within the range of 20 Hz to 5 MHz. Molecular kinetics associated with dielectric relaxations is analyzed by Havriliak Negami function. It is found that the grain dipoles obey the Debye type of dielectric relaxation, while grain boundary dipoles follow the Cole-Cole type of dielectric relaxation. The observed grain and grain boundary dipole relaxation time are 6.598E-08 sec and 5.755E-04 sec, respectively.

Published
2013
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26. Microwave sintering of dielectric CaCu3Ti4O12: An interfacial conductance and dipole relaxation effect

Author

Kumar, Ranjit, Zulfequar, M., Singh, V.N., Tawale, J.S., and Senguttuvan, T.D.

Subjects
*DIELECTRICS, *MICROWAVE sintering, *CALCIUM compounds, *RELAXATION phenomena, *MICROSTRUCTURE, *CERAMIC materials, *TEMPERATURE measurements
Abstract

Abstract: A correlation between the microstructure and dielectric properties of microwave sintered CaCu3Ti4O12 (CCTO) ceramic was studied as a function of sintering temperature, frequency and measurement temperature. CaCu3Ti4O12 dielectrics ceramic were prepared by solid-state reaction route. Pellets were sintered for 15min at 1000–1075°C at an interval of 25°C using microwave furnace operated at 2.45GHz frequency, 8.8kW power. XRD pattern revealed the formation of cubic perovskite CaCu3Ti4O12. The SEM micrographs show grain growth and reduction in porosity of the pellets on increasing the sintering temperature. The grains are cuboid shaped having well polished edges. Dielectric properties increase with increasing sintering temperature. The influence of conductivity across the barriers at grain and grain boundary are observed in the cole–cole plot. An improved conductivity or enhanced dielectric loss with respect to sintering temperature was observed at high frequencies. It is found that the grains dipole relaxation time increases, but the grain boundaries dipole relaxation time deceases with increasing sintering temperature. When the measurements were made at temperature greater than 40°C, relaxation peaks of grain and grain boundary merged into single relaxation peak. Such relaxation leads to the minimum dielectric loss. [Copyright &y& Elsevier]

Published
2012
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27. Highly sensitive and pulse-like response toward ethanol of Nb doped TiO2 nanorods based gas sensors

Author

Singh, Sujatha, Kaur, Harjeet, Singh, V.N., Jain, Kiran, and Senguttuvan, T.D.

Subjects
*TITANIUM dioxide, *ETHANOL, *GAS detectors, *NANOROD synthesis, *NIOBIUM, *HYDROLYSIS, *SURFACE active agents, *TEMPERATURE effect
Abstract

Abstract: Highly crystalline TiO2 and 3wt% Nb-doped TiO2 nanorods were synthesized by a low-temperature surfactant directed hydrolysis method followed by calcination at 600–900°C. The microstructure and the chemical composition of the thick films were characterized using XRD, SEM, EDX, TEM, XPS, and FTIR. The sensing behavior of TiO2 thick films toward reducing gases (H2, ethanol and LPG) in the temperature range 350–550°C was studied. Niobium doping retards the anatase to rutile transformation. It was observed that doped TiO2 thick films have an enhanced sensor response compared to the undoped ones. The increased sensor response may be because of presence of anatase phase and the smaller dimension of the nanorods. [Copyright &y& Elsevier]

Published
2012
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