Manoj K. Mahapatra

Easy-to-use mullite and spinel sols as bonding agents in a high-alumina based ultra low cement castable

This paper deals with the preparation of colloidal suspensions of mullite and magnesium-aluminate spinel via a cheaper precursor of alumina sol. Viscosity, pH, solid content, DTA, TGA and XRD studies at different temperatures were performed to characterize those two sols. These mullite and spinel sols were used separately as bonding agents in a high-alumina based ultra low cement castable composition prepared by simple tapping technique and their performances have been compared in terms of bulk density, apparent porosity, cold crushing strength, flexural strength, slag corrosion, thermal shock, XRD and SEM reports. The results confirm that the mullite sol excels while the spinel sol degrades the refractory castable quality.

Optical and electrochromic properties of sol-gel WO3 films on conducting glass

Abstract The precursor containing peroxotungstic acid (PTA) was prepared by the reaction of tungstic acid with H 2 O 2 (30%) solution in water–ethanol mixture. This was utilized for the deposition of WO 3 · n H 2 O film on conducting (F-doped SnO 2 coated) flat glass substrate by the dipping technique. The films were cured in the temperature range of 200–300 °C in air. The optimum thickness of the film (300–500 nm) was obtained by successive operations (3–5 numbers). Films of around 500 nm thickness exhibited 60–70% transmission in the visible region. Electrochromic properties (colouration↔bleaching) of the films were studied by cyclic voltammetry (CV) using a classical three-electrode potentiostatic cell system. The cell system consists of a WO 3 -coated sample as working electrode, a platinum rod as counter electrode, Ag/AgCl as reference electrode and 0.5 M LiClO 4 in propylene carbonate as an electrolyte. Several voltammograms were recorded within the voltage range of +1.5 to −1.8 V with a scan rate of 50 mV/s. A continuous curve was observed for the films at a certain voltage sweep where a random insertion of Li + occurred reversibly in a definite crystallographic site [WO 3 (colourless)+ n Li + + n e − ↔ Li n WO 3 (blue)]. A dark blue colouration (% T =20–30% in the visible region) was observed under a constant voltage of −1.8 V whereas bleaching occurred at +1.0 V (% T =60–70%), which was studied simultaneously along with the voltage sweep of CV. The colouration time ( T col ) and the bleaching time ( T bl ) were almost equal as revealed by the simultaneous study of the second signal (photomultiplier output coupled with the electrochemistry system) during colouration↔bleaching. Coatings of about 500 nm thickness exhibited more that 500 cycles (colouration↔bleaching). The reversibility of the cycle remained good but the intensity of the colouration decreased with the number of cycles. This was possibly due to the structural deformation of WO 3 films for its long time exposure to the electrolytic solution. The cathodic current ( I c ) and anodic current ( I a ) increased with increasing thickness.

Network structure and thermal stability study of high temperature seal glass

High temperature seal glass has stringent requirement on glass thermal stability, which is dictated by glass network structures. In this study, a SrO–La2O3–Al2O3–B2O3–SiO2 based glass system was studied using nuclear magnetic resonance, Raman spectroscopy, and x-ray diffraction for solid oxide cell application purpose. Glass structural unit neighboring environment and local ordering were evaluated. Glass network connectivity as well as silicon and boron glass former coordination were calculated for different B2O3:SiO2 ratios. Thermal stability of the borosilicate glasses was studied after thermal treatment at 850 °C. The study shows that high B2O3 content induces BO4 and SiO4 structural unit ordering, increases glass localized inhomogeneity, decreases glass network connectivity, and causes devitrification. Glass modifiers interact with either silicon- or boron-containing structural units and form different devitrified phases at different B2O3:SiO2 ratios. B2O3-free glass shows the best thermal stability a...

Hybrid Electrodes by In-Situ Integration of Graphene and Carbon-Nanotubes in Polypyrrole for Supercapacitors.

Supercapacitors also known as electrochemical capacitors, that store energy via either Faradaic or non-Faradaic processes, have recently grown popularity mainly because they complement, and can even replace, conventional energy storage systems in variety of applications. Supercapacitor performance can be improved significantly by developing new nanocomposite electrodes which utilizes both the energy storage processes simultaneously. Here we report, fabrication of the freestanding hybrid electrodes, by incorporating graphene and carbon nanotubes (CNT) in pyrrole monomer via its in-situ polymerization. At the scan rate of 5 mV s−1, the specific capacitance of the polypyrrole-CNT-graphene (PCG) electrode film was 453 F g−1 with ultrahigh energy and power density of 62.96 W h kg−1 and 566.66 W kg−1 respectively, as shown in the Ragone plot. A nanofibrous membrane was electrospun and effectively used as a separator in the supercapacitor. Four supercapacitors were assembled in series to demonstrate the device performance by lighting a 2.2 V LED.

Effects of moisture on (La, A)MnO3 (A = Ca, Sr, and Ba) solid oxide fuel cell cathodes: a first-principles and experimental study

One of the major challenges in developing clean, environmentally friendly energy technologies such as solid oxide fuel cells (SOFCs) is performance degradation at higher temperatures. Solid oxide fuel cell (SOFC) cathode degradation in the presence of moisture is one of the major concerns. Combining computational and experimental studies provides a comprehensive picture of the interaction between moisture and lanthanum manganite based SOFC cathodes. To better understand the surface chemistry, (La, A)MnO3 (A = Ca, Sr and Ba) (001) surfaces are explored using first-principles calculations. This computational study suggests that dissociative adsorption of water molecules is favored on (La, A)O-terminated (001) surfaces. The covalently unsaturated surface terminal O atom (via strong H-bond) attracts one of the H atoms of the water molecule, with a subsequent breakup of the water molecule into H+ and OH− groups. The surface should also be significantly enriched with A-site dopants under all realistic conditions, with all the three dopants driven to segregate to the surface over a wide range of T–pH2O conditions. Atomic force microscopy reveals just such a segregation of dopants to the surface of doped LaMnO3, enhanced in the presence of moisture. It is hypothesized that the interplay of the resulting oxygen vacancy defects and moisture from the operating environment further drives cationic surface segregation, ultimately degrading catalytic activity. In addition to providing insights into the surface chemistry, this combined experimental and computational investigation opens pathways for designing new materials with enhanced catalytic functionality.

Manganese induced modifications in yttria stabilized zirconia

We have investigated the role of manganese oxide on the crystallographic and morphological modifications of cubic 8 mol. % yttria stabilized zirconia (YSZ). X-ray diffraction studies indicate that manganese dissolution leads to partial transformation of cubic YSZ into the tetragonal polymorph along with contraction of the unit cell. Evolution of an undulated surface with 2–15 nm roughness has been observed using electron and atomic force microscopies.

Chapter 24 – Fuel Cells: Energy Conversion Technology

The drive for fuel cell technology research and development stems from cleanliness of the technology, high chemical to electrical conversion efficiency and versatile applications ranging from large-scale, stand-alone stationary power plant to modular distributed generation systems to advanced mobile auxiliary power units. Portable systems and those that can be carried are also currently being designed for civilian and military markets. Fuel cells are capable of generating electricity with virtually negligible to zero pollution (e.g. SOx, NOx, volatile organic compounds (VOC), particulate matters (PMs)). They also offer a reduced carbon footprint and have the potential to be engineered for ‘zero carbon’ systems. Despite the potential to meet the pressing needs for clean and efficient fuel cell–based power generation systems, high capital and maintenance cost remains a challenge for large-scale commercialisation and global market entry. Solid oxide fuel cell (SOFC) is one of the most promising fuel cell technologies as it offers significantly higher electrical efficiency as well as co-production of high-quality process heat. The system lifetime, its reliability and cost, however, remain a concern due to the performance degradation with time, commonly associated with the instability of materials in complex operating environment and high exposure temperature (650–1000)°C. New materials, systems design and operating conditions are being developed to increase the lifetime. Centralised and distributed SOFC power systems in the range of hundreds of kilowatt to megawatt are being considered for integration with advanced coal power plants, hybrid systems integrated with energy storage and carbon-capture technologies to fully exploit the commercial potential.

Alumina and Silica Sols as Binders in a Typical ULC Castable

Alumina and silica sols prepared from cheap precursors have been characterized with respect to viscosity, zeta potential and differential thermal analysis. It has been observed that silica sol possesses higher viscosity and zeta potential values than those of alumina sol. The effect of these sols on high alumina based ULC castables has been investigated by comparing their bulk density, apparent porosity, cold crushing strength, flexural strength, slag corrosion and thermal shock resistance properties. XRD and SEM studies have been carried out on fired samples to explain the effect of sols on the fired strength and homogeneity in structure.

Carbon Capture and Storage

Rising oil and gas prices, insecure energy supplies, and increased energy consumption in transition economies have boosted the use of coal—the most abundant fossil fuel and one that many countries have considerable reserves of. The United States, China, and some other countries are highly dependent on coal. In the United States, coal-powered plants generate more than half the electricity, and some observers expect that expanding the use of coal will help reduce U.S. reliance on foreign oil. But coal is the most carbon-intensive fossil fuel. Thus a new technology called carbon capture and storage (CCS) has recently gained considerable attention. CCS aims to capture carbon dioxide (CO2) from any large point source, liquefy it, and store it underground. Because of its high costs and complex infrastructure, CCS is by necessity suited primarily for centralized, large-scale power stations or big industrial facilities like cement plants and steelworks. With today’s technologies, there are three ways to capture CO2. Post-combustion capture, which involves capturing CO2 from flue gases in conventional power stations, is basically available today, but it has not yet been demonstrated at a commercial power station scale. In the longer term, this technology is unlikely to become widely established unless its energy consumption can be reduced significantly. A more efficient method is pre-combustion capture of CO2 in coal-fired power stations with integrated gasification combined cycle technology. These plants use heat to gasify coal that is then burned to generate electricity. During the gasification step, CO2 can be removed relatively easily. Apart from its higher efficiency levels, the prime advantage of this method lies in its flexibility in terms of both fuel (coal, biomass, and substitute fuels) and product (electricity, hydrogen, synthetic gas, and liquid fuel). Pre-combustion capture of CO2 has not yet been demonstrated on a large scale. The so-called oxyfuel process currently offers the best prospects for CO2 capture in terms of achievable overall process efficiency as well as costs because it is largely based on conventional power station components and technology. Combustion takes place in 95 percent pure oxygen rather than air, enabling efficient CO2 capture due to the concentrated flue gas. This process is still near the beginning of its demonstration phase. It is expected to capture 99.5 percent of the emissions directly at the stack, while the post-combustion and pre-combustion methods would reduce CO2 by 88–90 percent on average.1 Carbon Capture and Storage

Effects of Humidity on Solid Oxide Fuel Cell Cathodes

This report summarizes results from experimental studies performed by a team of researchers assembled on behalf of the Solid-state Energy Conversion Alliance (SECA) Core Technology Program. Team participants employed a variety of techniques to evaluate and mitigate the effects of humidity in solid oxide fuel cell (SOFC) cathode air streams on cathode chemistry, microstructure, and electrochemical performance.