Investigation into the Probable Cause of Failure of Economizer Tube of a Thermal Power Plant

In this investigation, we examined the probable cause of failure of a welded joint of a economizer tube of a 210 MW thermal power plant. X-ray radiography and chemical analysis along with detailed optical and scanning electron microscopic (SEM) examination of the economizer tube were carried out. It was concluded that severe blowholes, pipings, and porosity along with brittle fracture were responsible for the failure.     

Science and Technology of High Dielectric Constant Thin Films and Materials Integration for Application to High Frequency Devices

Thin films of Ba_1?x Sr _x Ti_1+y O_3+z (BST), were fabricated using both by RF-magnetron sputtering and MOCVD to demonstrate application to high frequency devices. Precise control of composition and microstructure is critical for the production of (Ba _x Sr_1?x )Ti_1+y O_3+z (BST) dielectric thin films with the large dependence of permittivity on electric field, low losses, and high electrical breakdown fields that are required for successful integration of BST into tunable high frequency devices. Here we review results on composition-microstructure-electrical property relationships of polycrystalline BST films produced by magnetron sputter deposition that are appropriate for microwave devices such as phase shifters. BST films with a multilayer structure were also developed with different Ti-elemental ratio in each layer to minimize losses and leakage current. Interfacial contamination from C and H species was studied and implications on electrical properties are highlighted. Finally, York's group at the University of California-Santa Barbara successfully integrated our BST films onto phase shifter arrays. The results show potential of BST films in such applications. Results from initial work on the integration of Cu-electrodes with BST films are also presented.     

Impact of Stone-Wales and lattice vacancy defects on the electro-thermal transport of the free standing structure of metallic ZGNR

We report the effect of topological as well as lattice vacancy defects on the electro-thermal transport properties of the metallic zigzag graphene nano ribbons at their ballistic limit. We employ the density function theory–Non equilibrium green’s function combination to calculate the transmission details. We then present an elaborated study considering the variation in the electrical current and the heat current transport with the change in temperature as well as the voltage gradient across the nano ribbons. The comparative analysis shows, that in the case of topological defects, such as the Stone-Wales defect, the electrical current transport is minimum. Besides, for the voltage gradient of 0.5 Volt and the temperature gradient of 300 K, the heat current transport reduces by \({\sim }62\,\%\) and \({\sim }50\,\%\) for the cases of Stones-Wales defect and lattice vacancy defect respectively, compared to that of the perfect one.     

Excimer laser ablation processed ferroelectric and antiferroelectric thin films

Abstract

The dielectric and electrical properties of excimer laser ablated processed paraelectric (Ba_0.5, Sr_0.5)TiO₃, ferroelectric Bi-layered SrBi₂(Ta_0.5Nb_0.5)₂O₉, and antiferroelectric (PbZrO₃) thin films have been investigated. The effect of processing parameters on the microstructure of the films and the functional properties has been presented in detail. Some of the recent studies of stress induced effects, dielectric, hysteresis and ac and dc electrical properties have been highlighted in conjunction with microstructures of the films.     

Experience with return voltage measurements for assessing insulation conditions in service-aged transformers

This paper describes the investigation of the insulation condition of a number of power and distribution type transformers of different manufacturing dates and with different operating histories. Return voltage measurements were conducted for these transformers. Effects of moisture and aging on the oil-paper insulation of these transformers were investigated and results are presented in this paper. Moisture in oil samples at known temperature was measured for these transformers. Previously accelerated aging experiments were performed on paper wrapped insulated conductors in different environments over a temperature range of 115 to 145/spl deg/C. Results from the measurements on transformers are compared with those of the accelerated aged samples and are described in this paper.     

Impact of channel length,gate insulator thickness,gate insulator material,and temperature on the performance of nanoscale FETs

Aggressive technology scaling as per Moore’s law has led to elevated power dissipation levels owing to an exponential increase in subthreshold leakage power. Short channel effects (SCEs) due to channel length reduction, gate insulator thickness change, application of high-k gate insulator, and temperature change in a double-gate metal–oxide–semiconductor field-effect transistor (DG MOSFET) and carbon nanotube field-effect transistor (CNTFET) were investigated in this work. Computational simulations were performed to investigate SCEs, viz. the threshold voltage (V_th) roll-off, subthreshold swing (SS), and I_on/I_off ratio, in the DG MOSFET and CNTFET while reducing the channel length. The CNTFET showed better performance than the DG MOSFET, including near-zero SCEs due to its pure ballistic transport mechanism. We also examined the threshold voltage (V_th), subthreshold swing (SS), and I_on/I_off ratio of the DG MOSFET and CNTFET with varying gate insulator thickness, gate insulator material, and temperature. Finally, we handpicked almost similar parameters for both the CNTFET and DG MOSFET and carried out performance analysis based on the simulation results. Comparative analysis of the results showed that the CNTFET provides 47.8 times more I_on/I_off ratio than the DG MOSFET. Its better control over the threshold voltage, near-zero SCEs, high on-current, low leakage power consumption, and ability to operate at high temperature make the CNTFET a viable option for use in enhanced switching applications and low-voltage digital applications in nanoelectronics.     

Poly dimethylsiloxane/carbon nanofiber nanocomposites: fabrication and characterization of electrical and thermal properties

This article presents the fabrication and characterization of poly dimethylsiloxane/carbon nanofiber (CNF)-based nanocomposites. Although silica and carbon nanoparticles have been traditionally used to reinforce mechanical properties in PDMS matrix nanocomposites, this article focuses on understanding their impacts on electrical and thermal properties. By adjusting both the silica and CNF concentrations, 12 different nanocomposite formulations were studied, and the thermal and electrical properties of these materials were experimentally characterized. The developed nanocomposites were prepared using a solvent-assisted method providing uniform dispersion of the CNFs in the polymer matrix. Scanning electron microscopy was employed to determine the dispersion of the CNFs at different length scales. The thermal properties, such as thermal stability and thermal diffusivity, of the developed nanocomposites were studied using thermogravimetirc and laser flash techniques. Furthermore, the electrical volume conductivity of each type of nanocomposite was tested using the four-probe method to eliminate the effects of contact electrical resistance during measurement. Experimental results showed that both CNFs and silica were able to impact on the overall properties of the synthesized PDMS/CNF nanocomposites. The developed nanocomposites have the potential to be applied to the development of new load sensors in the future.     

Nano fibrillated cellulose-based foam by Pickering emulsion: Preparation,characterizations, and application as dye adsorbent

An ecofriendly and biodegradable porous structure was prepared from drying aqueous foams based on nano fibrillated cellulose (NFC), extracted from softwood pulp by subcritical water/CO₂ treatment (SC-NFC). The primary aim of this work was to use the modified SC-NFC as stabilizer for a water-based Pickering emulsion which upon drying, yielded porous cellulosic materials, a good dye adsorbent. In order to exploit the carboxymethylated SC-NFC (CMSC-NFC, with a degree of substitution of 0.35 and a charge density of 649 μeqv/g) as a stabilizer for water-based Pickering emulsion in subsequent step, an optimized quantity of octyl amine (30 mg/g of SC-NFC) was added to make them partially hydrophobic. A series of dry foam structures were prepared by varying the concentrations of treated CMSC-NFCs and 4 wt% was found to be the optimum concentration to yield foam with high porosity (99%) and low density (0.038 g/cc) along with high compression strength (0.24 MPa), superior to the conventionally extracted NFC. The foams were applied to capture as high as 98% of methylene blue dyes, making them a potential green candidate for treating industrial effluent. In addition, the dye adsorption kinetics and isotherms were found to be well suited with second order kinetics and Langmuir isotherm models.     

Polydimethylsiloxane based polyurethane and its composite with layered double hydroxide: Synthesis and its thermal properties

This investigation reports the synthesis of a new class of polyurethane (PU) based on bis(hydroxyalkyl) polydimethylsiloxane (PDMS) as diol and isophorone diisocyanate as diisocyanate followed by the preparation of PU/layered double hydroxide (PU/LDH) nanocomposite via ex-situ technique. Nuclear magnetic resonance and Fourier-transform infrared spectroscopy studies confirm the formation of PU and incorporation of PDMS into the PU backbone. Thermogravimetry analysis revealed that thermal stability of the composite improves significantly with incorporation of LDH into the PU matrix. This may be accredited to the barrier effect rendered by the LDH layers. Differential scanning calorimetry study reveals that with the incorporation of LDH, glass transition temperature (T_g) of the composite increases for an optimum level of loading beyond which it remains constant.